text:
Edmond R. Tucci; E. Doody; Norman C. Li
Acid disscciation constants of uracil-5-carboxylic acid (isoorotic ; acid), 2-ethylthio-isoorotic acid, uracil-6carboxylic acid (orotic acid), 5-; nitroorotic acid, and adenosine-5' -monophosphate were determined at an ionic ; strength of 0.1, 25 deg . The formation constants of the Cu(II), Ni(II), Co(II), ; Zn(II), Mn(II), and Cd(II) complexes of some of these pyrimdine derivatives were ; determined using pH and ion-exchange
Investigation of the Composition and Formation Constant of Molecular Complexes
R. Sahai; G. L. Loper; S. H. Lin; H. Eyring
It has been the purpose of the present paper to investigate and explore the conditions under which the linear relation between Delta \\/CD{}0 and Delta in the Hanna-Ashbaugh-Foster-Fyfe equation for the evaluation of equilibrium constants holds, (CD{}0 is initial concentration of a donor and Delta is the observed chemical shift relative to the chemical shift of the acceptor) to obtain
Formation constants of ternary complexes of some heavy metal ions with N-(2-acetamido)iminodiacetic acid and aliphatic or aromatic acids
Hamed, M.M.A.; Mahmoud, M.R. (Assiut Univ. (Egypt). Dept. of Chemistry); Saleh, M.B.; Ahmed, I.T. (El-Minia Univ. (Egypt). Dept. of Chemistry)
N-(2-Acetamido)iminodiacetic acid (H[sub 2]ADA) is considered as one of the biologically important ligands. It is used as a complexing agent in the field of metal ion buffers working at the physiological pH range. Furthermore, it is widely used as an analytical chelating agent for the spectrophotometric determination of metal ions. Solution equilibria of the ternary systems involving La(III), Y(III), Ce(III), and UO[sub 2][sup 2+], N-(2-acetamido)iminodiacetic acid, and some aliphatic or aromatic acids have been investigated potentiometrically. The formation of 1:1:1 mixed ligand complexes is inferred from the potentiometric titration curves. Formation constants of the different binary and ternary complexes formed in such systems were determined at 25 [+-] 0.1 C and [mu] = 0.1 mol dm[sup [minus]3] (KNO[sub 3]). It is deduced that the mixed ligand complexes are more stable than the corresponding binary complexes containing the aliphatic or aromatic acidate moiety. The order of stability of the binary and ternary complexes is investigated and discussed in terms of the nature of both the metal ion and the secondary ligand (aliphatic or aromatic acid).
Navigating Software Architectures with Constant Visual Complexity
Navigating Software Architectures with Constant Visual Complexity Wanchun Li, Peter Eades, Seok complexity and visual complexity. This paper presents an approach for visualizing software architecture [3]. The visualization and navigation of software architectures faces the challenge of complexity
How the cosmological constant affects gravastar formation
Chan, R. [Coordenação de Astronomia e Astrofísica, Observatório Nacional, Rua General José Cristino, 77, São Cristóvão, CEP 20921-400, Rio de Janeiro, RJ (Brazil); Silva, M.F.A. da [Departamento de Física Teórica, Instituto de Física, Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier 524, Maracanã, CEP 20550-900, Rio de Janeiro - RJ (Brazil); Rocha, P., E-mail: email@example.com, E-mail: email@example.com, E-mail: firstname.lastname@example.com [Instituto de Física, Universidade Federal Fluminense, Av. Litorânea s/n, Boa Viagem, CEP 24210-340, Niterói, RJ (Brazil)
Here we generalized a previous model of gravastar consisted of an internal de Sitter spacetime, a dynamical infinitely thin shell with an equation of state, but now we consider an external de Sitter-Schwarzschild spacetime. We have shown explicitly that the final output can be a black hole, a ''bounded excursion'' stable gravastar, a stable gravastar, or a de Sitter spacetime, depending on the total mass of the system, the cosmological constants, the equation of state of the thin shell and the initial position of the dynamical shell. We have found that the exterior cosmological constant imposes a limit to the gravastar formation, i.e., the exterior cosmological constant must be smaller than the interior cosmological constant. Besides, we have also shown that, in the particular case where the Schwarzschild mass vanishes, no stable gravastar can be formed, but we still have formation of black hole.
Formation of interpolymer complexes
Eishun Tsuchida; Yoshihito Osada; Hiroyuki Ohno
Interpolymer complex formations of poly(methacrylic acid) (PMAA) or poly(acrylic acid) (PAA) with oligocations as well as poly(ethylene oxide) (PEO), and poly-(N-vinyl-2-pyrrolidone of various chain lengths were studied. For the case of complexation between PMAA and oligocations, the standard free energy change for the complexation ?G° was found to be linearly dependent on the number of interacting sites, n. The stability
Determination of the formation constant for the inclusion complex between Lanthanide ions and Dansyl chloride derivative by fluorescence spectroscopy: Theoretical and experimental investigation
NASA Astrophysics Data System (ADS)
Riahi, Siavash; Ganjali, Mohammad Reza; Hariri, Maryam; Abdolahzadeh, Shaghayegh; Norouzi, Parviz
In this paper, a sensitive, easy, efficient, and suitable method for the calculation of Kf values of complexation between one derivative of Dansyl chloride [5-(dimethylamino) naphthalene-1-sulfonyl 4-phenylsemicarbazide] (DMNP) and Lanthanide(III) (Ln) ions is proposed, using both spectrofluorometric and spectrophotometric methods. Determination of Kf showed that DMNP was mostly selective towards the erbium (III) ion. The validity of the method was also confirmed calculating the Stern-Volmer fluorescence quenching constants ( Ksv) that resulted in the same consequence, obtained by calculating the Kf of complexation values. In addition, the UV-vis spectroscopy was applied for the determination of Kf only for the Ln ions that had interactions with DMNP. Finally, the DFT studies were done on Er 3+ and the DMNP complex for distinguishing the active sites and estimating the pair wise interaction energy. It can be concluded that this derivative of Dansyl chloride with inherent high fluorescence intensity is a suitable reagent for the selective determination of the Er 3+ ion which can be used in constructing selective Er 3+ sensors.
Thiocyanato Chromium (III) Complexes: Separation by Paper Electrophoresis and Estimate of Stability Constants
ERIC Educational Resources Information Center
Larsen, Erik; Eriksen, J.
Describes an experiment wherein the student can demonstrate the existence of all the thiocyanato chromium complexes, estimate the stepwise formation constants, demonstrate the robustness of chromium III complexes, and show the principles of paper electrophoresis. (GS)
A 1H NMR titration study on the binding constants for D- and L-tryptophan inclusion complexes with 6-O-?-D-glucosyl-?-cyclodextrin. Formation of 1:1 and 2:1 (host:guest) complexes
NASA Astrophysics Data System (ADS)
Akita, Tomoki; Matsui, Yoshihisa; Yamamoto, Tatsuyuki
A 1H NMR titration study revealed that 6-O-?-D-glucosyl-?-cyclodextrin (G1-?-CD) forms 1:1 and 2:1 (host:guest) inclusion complexes with D- and L-tryptophan in alkaline D2O solutions (pD 11.0). The binding constants (K1's) for the 1:1 complexes of D-isomer at 298 K (59 mol-1 dm3) were virtually equal to that of L-isomer (54 mol-1 dm3). On the other hand, the K2 values for 2:1 complexes of D-isomer (42 mol-1 dm3) were larger than that of L-counterpart (12 mol-1 dm3). These facts suggest that the first CD molecule includes the indole ring moiety of tryptophan, followed by inclusion with the second CD molecule in the vicinity of chiral center, ?-carbon of the guest, to result in the difference in K2's for two enantiomers. Two-dimensional NMR measurement (Rotating-frame nuclear Overhauser Effect SpectroscopY, ROESY) supported this interpretation.
Density functional theory-based prediction of the formation constants of complexes of ammonia in aqueous solution: indications of the role of relativistic effects in the solution chemistry of gold(I).
Hancock, Robert D; Bartolotti, Libero J
A prediction of the formation constants (log K1) for complexes of metal ions with a single NH3 ligand in aqueous solution, using quantum mechanical calculations, is reported. DeltaG values at 298 K in the gas phase for eq 1 (DeltaG(DFT)) were calculated for 34 metal ions using density functional theory (DFT), with the expectation that these would correlate with the free energy of complex formation in aqueous solution (DeltaG(aq)). [M(H2O)6]n+(g) + NH(3)(g) = [M(H2O)5NH3]n+(g) + H2O(g) (eq 1). The DeltaG(aq) values include the effects of complex changes in solvation on complex formation, which are not included in eq 1. It was anticipated that such changes in solvation would be constant or vary systematically with changes in the log K(1) value for different metal ions; therefore, simple correlations between DeltaG(DFT) and DeltaG(aq) were sought. The bulk of the log K1(NH3) values used to calculate DeltaG(aq) were not experimental, but estimated previously (Hancock 1978, 1980) from a variety of empirical correlations. Separate linear correlations between DeltaG(DFT) and DeltaG(aq) for metal ions of different charges (M2+, M3+, and M4+) were found. In plots of DeltaG(DFT) versus DeltaG(aq), the slopes ranged from 2.201 for M2+ ions down to 1.076 for M4+ ions, with intercepts increasing from M2+ to M4+ ions. Two separate correlations occurred for the M3+ ions, which appeared to correspond to small metal ions with a coordination number (CN) of 6 and to large metal ions with a higher CN in the vicinity of 7-9. The good correlation coefficients (R) in the range of 0.97-0.99 for all these separate correlations suggest that the approach used here may be the basis for future predictions of aqueous phase chemistry that would otherwise be experimentally inaccessible. Thus, the log K1(NH3) value for the transuranic Lr3+, which has a half-life of 3.6 h in its most stable isotope, is predicted to be 1.46. These calculations should also lead to a greater insight into the factors governing complex formation in aqueous solution. All of the above DFT calculations involved corrections for scalar relativistic effects (RE). Au has been described (Koltsoyannis 1997) as a "relativistic element". The chief effect of RE for group 11 ions is to favor linear coordination geometry and greatly increase covalence in the M-L bond. The correlation for M+ ions (H+, Cu+, Ag+, Au+) involved the preferred linear coordination of the [M(H2O)2]+ complexes, so that the DFT calculations of DeltaG for the gas-phase reaction in eq 2 were carried out for M = H+, Cu+, Ag+, and Au+. [M(H2O)2]+(g) + NH3(g) = [M(H2O)NH3]+(g) + H2O(g) (eq 2). Additional DFT calculations for eq 2 were carried out omitting corrections for RE. These indicated, in the absence of RE, virtually no change in the log K1(NH3) value for H+, a small decrease for Cu+, and a larger decrease for Ag+. There would, however, be a very large decrease in the log K1(NH3) value for Au(I) from 9.8 (RE included) to 1.6 (RE omitted). These results suggest that much of "soft" acid behavior in aqueous solution in the hard and soft acid-base classification of Pearson may be the result of RE in the elements close to Au in the periodic table. PMID:16180881
Predicting stability constants for uranyl complexes using density functional theory.
Vukovic, Sinisa; Hay, Benjamin P; Bryantsev, Vyacheslav S
The ability to predict the equilibrium constants for the formation of 1:1 uranyl/ligand complexes (log K1 values) provides the essential foundation for the rational design of ligands with enhanced uranyl affinity and selectivity. We use density functional theory (B3LYP) and the integral equation formalism polarizable continuum model (IEF-PCM) to compute aqueous stability constants for UO2(2+) complexes with 18 donor ligands. Theoretical calculations permit reasonably good estimates of relative binding strengths, while the absolute log K1 values are significantly overestimated. Accurate predictions of the absolute log K1 values (root-mean-square deviation from experiment <1.0 for log K1 values ranging from 0 to 16.8) can be obtained by fitting the experimental data for two groups of mono- and divalent negative oxygen donor ligands. The utility of correlations is demonstrated for amidoxime and imide dioxime ligands, providing a useful means of screening for new ligands with strong chelating capability to uranyl. PMID:25835578
Reverse hydrotropy by complex formation.
Wojciechowski, Kamil; Gutberlet, Thomas; Raghuwanshi, Vikram Singh; Terry, Ann
Self-aggregation of three di-N-alkylated diaza-18-crown-6 ethers (ACEs) was studied in non-polar solvents. The three ACEs differed by the length of the alkyl chain: n-decyl (ACE-10), n-hexadecyl (ACE-16) and n-tetracosane (ACE-24). From the previously reported interfacial tension isotherms, the formation of reverse micelles was expected above ACE concentrations of ?10(-3) M. However, the water content analysis in conjunction with Dynamic Light Scattering (DLS), Fluorescence Correlation Spectroscopy (FCS) and (1)H NMR Diffusion Ordered Spectroscopy (DOSY) do not provide any clear proof of the existence of aggregates. Only the Small Angle Neutron Scattering (SANS) of concentrated toluene ACE solutions reveals the existence of small reverse micelles (probably ACE dimers forming small cages hosting 1-2 water molecules). On the other hand, spectrophotometric and fluorescence dye dissolution studies using eosin Y, tropaeolin OO and methyl orange suggest that ACEs can dissolve these dyes without requiring the formation of aggregates. This discrepancy was interpreted assuming the dye-ACE complexation as the driving force for dye solubilisation, providing a possible mechanism of reverse hydrotropy ("lipotropy") in non-polar solvents. This example shows that special care should be taken when dye solubilisation is used to probe self-aggregation of an amphiphile in non-polar solvents. The amphiphile-dye complex formation might be responsible for false positive results and the aggregate formation should always be confirmed with other methods. PMID:25415596
The formation constants of ionomycin with divalent cations in 80% methanol/water.
Stiles, M K; Craig, M E; Gunnell, S L; Pfeiffer, D R; Taylor, R W
The protonation constants and complex formation constants of ionomycin have been determined in 80% methanol/water (w/w) at 25.0 degrees C and mu = 0.050 (tetraethylammonium perchlorate). Potentiometric and spectrometric titration techniques give the following values for the mixed-mode protonation constants of ionomycin: log KH1 = 11.94 +/- 0.02 and log KH2 = 6.80 +/- 0.03. Comparison of these values with those for model compounds indicates that KH1 and KH2 refer to equilibria involving the beta-diketone and carboxylic acid moieties, respectively. Titrations of ionomycin with metal ion at fixed values of pH produced changes in the UV-visual absorbance spectra which were analyzed to give conditional complex formation constants, KMI'. The pH dependence of the values of KMI' indicated that 1:1 divalent metal ion-ionomycin (MI) complexes and protonated MHI+ complexes were formed in the pH range studied. The values of log KMI ranged from 5.30 +/- 0.11 for Sr2+ to 10.25 +/- 0.03 for Ni2+. The selectivity pattern and relative affinities (in parentheses) for the formation of the species MI are as follows: Ni2+ (2000) greater than Zn2+ (600) greater than CO2+ (440) greater than Mn2+ (47) greater than Mg2+ (1.00) greater than Ca2+ (0.21) greater than Sr2+ (0.022). Logarithmic values of KMHI, for the reaction MI + H+ in equilibrium MHI+, ranged from 5.9 (Ni2+) to 8.4 (Sr2+). Calculations using the values of the equilibrium constants determined indicate that an appreciable fraction of the complexed ionophore exists as the protonated complex, MHI+, in the pH range of 6.5-8.5. PMID:1850743
Thermodynamics and kinetics of aqueous ferric phosphate complex formation
Wilhelmy, R.B.; Patel, R.C.; Matijevic, E.
The equilibria and kinetics of complexation of iron(III) with phosphoric acid (at pH < 2) were studied at 25 and 50/sup 0/C at ionic strength ..mu.. = 2.5 M by using spectrophotometric and stopped-flow techniques. The results are consistent with the formation of two complexes, FeH/sub 2/PO/sub 4//sup 2 +/ and Fe(H/sub 2/PO/sub 4/)/sub 2//sup +/. The second species could only be detected by the analysis of kinetic data. The equilibrium constants, extinction coefficients, rate constants, and activation parameters for the formation of these complexes are given. A mechanism is proposed to account for the observed hydrogen ion dependency of the apparent forward rate constants. 35 references, 8 figures, 6 tables.
Spectrophotometric Determination of Iron(III)-Glycine Formation Constant in Aqueous Medium Using Competitive Ligand Binding
ERIC Educational Resources Information Center
Prasad, Rajendra; Prasad, Surendra
The formation constant of iron(III) complex with glycine (Gly) ligand in aqueous acidic medium (0.2 M HNO[subscript 3], I = 0.2 M at 28 plus or minus 1 degree C) was determined spectrophotometrically in which a competing color reaction between Fe(III) and SCN[superscript -] was used as an indicator reaction. Under the specified conditions Fe(III)…
Stereoregularity Drives Precipitation in Polyelectrolyte Complex Formation
NASA Astrophysics Data System (ADS)
Tirrell, Matthew; Perry, Sarah; Leon, Lorraine; Kade, Matthew; Priftis, Dimitris; Black, Katie; Hoffman, Kyle; Whitmer, Jonathan; Qin, Jian; de Pablo, Juan
This study investigates the effect of stereoregularity on the formation of polypeptide-based complex formation and assembly into micelles, hydrogels and ordered phases. We demonstrate that fluid complex coacervate formation (rather than solid complex precipitation) between oppositely charged polypeptides requires at least one racemic partner in order to disrupt backbone hydrogen bonding networks and prevent the hydrophobic collapse of the polymers into compact, fibrillar secondary structures. Computer simulations bear this out and enable visualization of the molecular structure of the complexes. The ability to choose between conditions of fluid phase formation and solid phase formation is a useful tool in developing new self-assembled materials based on polyelectrolyte complex formation. Support from the Argonne National Laboratory Laboratory Research and Development Program (2011-217) is gratefully acknowledged.
The formation of Pu(IV) complexes in phosphoric acid solutions and the ; dissociation constants of Pu(IV) phosphate complexes were studied by solubility ; methods. The Me: addend ratio of various Pu(IV) phosphate complexes and ; complexes of other investigated systems tends to shift, with the increase of ; complex forming agent concentration, toward the side of complexes with larger ;
Surface tension method for determining binding constants for cyclodextrin inclusion complexes of ionic surfactants
Dharmawardana, U.R.; Christian, S.D.; Tucker, E.E.; Taylor, R.W.; Scamehorn, J.F. (Univ. of Oklahoma, Norman, OK (United States))
A new method has been developed for determining binding constants of complexes of cyclodextrins with surface-active compounds, including water-soluble ionic surfactants. The technique requires measuring the change in surface tension caused by addition of a cyclodextrin (CD) to aqueous solutions of the surfactant; the experimental results lead directly to inferred values of the thermodynamic activity of the surfactant. Surface tension results are reported for three different surfactants sodium dodecyl sulfate (SDS), cetylpyridinium chloride (CPC), and cetyltrimethylammonium bromide (CTAB) in the presence and in the absence of added [beta]-CD. Data for CPC have been obtained at surfactant concentrations below and above the critical micelle concentration. Correlations between surface tension and surfactant activity are expressed by the Szyszkowski equation, which subsumes the Langmuir adsorption model and the Gibbs equation. It is observed that the surface tension increases monotonically as [beta]-cyclodextrin is added to ionic surfactant solutions. At concentrations of CD well in excess of the surfactant concentration, the surface tension approaches that of pure water, indicating that neither the surfactant-CD complexes nor CD itself are surface active. Binding constants are inferred from a model that incorporates the parameters of the Szyszkowski equation and mass action constants relating to the formation of micelles from monomers of the surfactant and the counterion. Evidence is given that two molecules of CD can complex the C-16 hydrocarbon chain of the cetyl surfactants. 30 refs., 5 figs., 1 tab.
Stoichiometry and Formation Constant Determination by Linear Sweep Voltammetry.
ERIC Educational Resources Information Center
Schultz, Franklin A.
In this paper an experiment is described in which the equilibrium constants necessary for determining the composition and distribution of lead (II)-oxalate species may be measured by linear sweep voltammetry. (Author/BB)
Determination of thermodynamic values of acidic dissociation constants and complexation constants of profens and their utilization for optimization of separation conditions by Simul 5 Complex.
Riesová, Martina; Svobodová, Jana; Ušelová, Kate?ina; Tošner, Zden?k; Zusková, Iva; Gaš, Bohuslav
In this paper we determine acid dissociation constants, limiting ionic mobilities, complexation constants with ?-cyclodextrin or heptakis(2,3,6-tri-O-methyl)-?-cyclodextrin, and mobilities of resulting complexes of profens, using capillary zone electrophoresis and affinity capillary electrophoresis. Complexation parameters are determined for both neutral and fully charged forms of profens and further corrected for actual ionic strength and variable viscosity in order to obtain thermodynamic values of complexation constants. The accuracy of obtained complexation parameters is verified by multidimensional nonlinear regression of affinity capillary electrophoretic data, which provides the acid dissociation and complexation parameters within one set of measurements, and by NMR technique. A good agreement among all discussed methods was obtained. Determined complexation parameters were used as input parameters for simulations of electrophoretic separation of profens by Simul 5 Complex. An excellent agreement of experimental and simulated results was achieved in terms of positions, shapes, and amplitudes of analyte peaks, confirming the applicability of Simul 5 Complex to complex systems, and accuracy of obtained physical-chemical constants. Simultaneously, we were able to demonstrate the influence of electromigration dispersion on the separation efficiency, which is not possible using the common theoretical approaches, and predict the electromigration order reversals of profen peaks. We have shown that determined acid dissociation and complexation parameters in combination with tool Simul 5 Complex software can be used for optimization of separation conditions in capillary electrophoresis. PMID:25213298
Complex organic molecules and star formation
NASA Astrophysics Data System (ADS)
Bacmann, A.; Faure, A.
Star forming regions are characterised by the presence of a wealth of chemical species. For the past two to three decades, ever more complex organic species have been detected in the hot cores of protostars. The evolution of these molecules in the course of the star forming process is still uncertain, but it is likely that they are partially incorporated into protoplanetary disks and then into planetesimals and the small bodies of planetary systems. The complex organic molecules seen in star forming regions are particularly interesting since they probably make up building blocks for prebiotic chemistry. Recently we showed that these species were also present in the cold gas in prestellar cores, which represent the very first stages of star formation. These detections question the models which were until now accepted to account for the presence of complex organic molecules in star forming regions. In this article, we shortly review our current understanding of complex organic molecule formation in the early stages of star formation, in hot and cold cores alike and present new results on the formation of their likely precursor radicals.
A metal complexing property of furosemide and bumetanide: determination of pK and stability constant.
Orita, Y; Ando, A; Urakabe, S; Abe, H
Furosemide and bumetanide have been found to have different pK values and undergo complex formation with several metal ions in dioxane-water solution. pK values of these diuretics were determined. Evidence for complex formation was provided by a drop in pH during complex formation, production of a characteristic color and precipitation. PMID:7275
Approximate Complex Polynomial Evaluation in Near Constant Work Per Point
John H. Reif
Given the n complex coefficients of a degreen 1 complex polynomial, we wish to evaluate the polynomial at a large number mn of points on the complex plane. This problem is required by many algebraic computations and so is considered in most basic algorithm texts (e.g., (A. V. Aho, J. E. Hopcroft, and J. D. Ullman, The Design and Analysis
Nonlinear Dynamics and Structure Formation in Complex Systems
Zonca, Fulvio
Nonlinear Dynamics and Structure Formation in Complex Systems F. Zonca - Complex behaviors ENEA, Frascati, Italy #12;Nonlinear Dynamics and Structure Formation in Complex Systems F. Zonca-heating) of charged fusion products balances power losses #12;Nonlinear Dynamics and Structure Formation in Complex
Computational complexity via programming languages: constant factors do matter
Amir M. Ben-amram; Neil D. Jones
. The purpose of this work is to promote a programming-language approach to studying computability and complexity, with an\\u000a emphasis on time complexity. The essence of the approach is: a programming language, with semantics and complexity measure,\\u000a can serve as a computational model that has several advantages over the currently popular models and in particular the Turing\\u000a machine. An obvious
Size effect of nano-copper films on complex optical constant and permittivity in infrared region
H. Du; S. W. Lee; J. Gong; C. Sun; L. S. Wen
Nano-copper films were prepared by DC magnetron sputtering. Their reflectivity and transmittivity to electromagnetic wave in infrared region were measured with Fourier Transformation Infrared Spectrometer (FTIR), by which their complex optical constant and permittivity were obtained. The results show that the complex optical constant and permittivity of nano-copper films depend upon the film thickness. This dependence is correlated with microstructure
Dielectric-constant-enhanced hall mobility in complex oxides.
Siemons, Wolter; McGuire, Michael A; Cooper, Valentino R; Biegalski, Michael D; Ivanov, Ilia N; Jellison, Gerald E; Boatner, Lynn A; Sales, Brian C; Christen, Hans M
The high dielectric constant of doped ferroelectric KTa(1-x)Nb(x)O(3) is shown to increase dielectric screening of electron scatterers, and thus to enhance the electronic mobility, overcoming one of the key limitations in the application of functional oxides. These observations are based on transport and optical measurements as well as band structure calculations. PMID:22718520
Dielectric-Constant-Enhanced Hall Mobility in Complex Oxides
Siemons, Wolter [ORNL; McGuire, Michael A [ORNL; Cooper, Valentino R [ORNL; Biegalski, Michael D [ORNL; Ivanov, Ilia N [ORNL; Jellison Jr, Gerald Earle [ORNL; Boatner, Lynn A [ORNL; Sales, Brian C [ORNL; Christen, Hans M [ORNL
The high dielectric constant of doped ferroelectric KTa{sub 1-x}Nb{sub x}O{sub 3} is shown to increase dielectric screening of electron scatterers, and thus to enhance the electronic mobility, overcoming one of the key limitations in the application of functional oxides. These observations are based on transport and optical measurements as well as band structure calculations.
Star Formation Across the W3 Complex
Román-Zúñiga, C G; Megias, G; Tapia, M; Lada, E A; Alves, J F
We present a multi-wavelength analysis of the history of star formation in the W3 complex. Using deep, near-infrared ground-based images, combined with images obtained with Spitzer and Chandra observatories, we identified and classified young embedded sources. We identified the principal clusters in the complex, and determined their structure and extension. We constructed extinction-limited samples for five principal clusters, and constructed K-band luminosity functions (KLF) that we compare with those of artificial clusters with varying ages. This analysis provided mean ages and possible age spreads for the clusters. We found that IC 1795, the centermost cluster of the complex, still hosts a large fraction of young sources with circumstellar disks. This indicates that star formation was active in IC 1795 as recently as 2 Myr ago, simultaneous to the star forming activity in the flanking embedded clusters, W3-Main and W3(OH). A comparison with carbon monoxide emission maps indicates strong velocity gradients ...
Complex formation of uranium(VI) with 4-hydroxy-3-methoxybenzoic acid and related compounds
D. Vulpius; G. Geipel; L. Baraniak; A. Rossberg; G. Bernhard
Summary The complex formation of uranium(VI) with 4-hydroxy-3-methoxybenzoic acid as well as with benzoic acid and 4-hydroxybenzoic\\u000a acid was studied. In aqueous solution weak carboxylic 1 : 1 complexes, are formed in which the carboxyl group is bidentately\\u000a coordinated to the metal atom. The logarithmic stability constants of these complexes regarding the reaction of the uranyl\\u000a ion with the single charged
Microchip-ESI-MS determination of dissociation constant of the lysozyme-NAG(3) complex.
Svobodová, Jaroslava; Mathur, Sonal; Muck, Alexander; Letzel, Thomas; Svatos, Ales
An on-line microfluidic system for determination of dissociation constants of enzyme/substrate weak interactions by nanoESI-MS is introduced. The microchip was designed to permit the enzyme and the substrate to mix by molecular diffusion in a pressure-driven laminar flow. Introduction of reagent solutions into the chip was an optimized combination of a micropump and an autosampler to enable automation of the measurements. The system performance was tested for monitoring of non-covalent interactions of hen egg white lysozyme with N-acetyl glucosamine oligomers. Dissociation constant (K(D)) of the hen egg white lysozyme-N-acetyl glucosamine oligomer complex was determined by non-linear regression analysis, and the range of K(D) values (39+/-6 x 10(-6) and 19.6+/-8 x 10(-6) M for manual and automated infusions, respectively) confirms the previously reported values. Such miniaturization of a continuous-flow enzyme assay system to a microfluidic format can maximize the capabilities of mass spectrometric detection, reduce the sample size and analysis time required, as well as the associated costs for on-line enzymatic kinetic studies. PMID:20665926
Electronic and Steric Effects on the Lewis Acidities of Transient Silylenes and Germylenes: Equilibrium Constants for Complexation
Leigh, William J.
: Equilibrium Constants for Complexation with Chalcogen and Pnictogen Donors Svetlana S. Kostina, Tishaan Singh homologues with chalcogen and pnictogen donors in solution. The equilibrium constants (KC) for complexation-1 . Equilibrium constants have been determined for complexation of SiMes2 and GeMes2 with all
Measuring Dissociation Rate Constants of Protein Complexes through Subunit Exchange: Experimental Design and Theoretical Modeling
Pan, Chongle [ORNL
Protein complexes are generally dynamic macromolecules that constantly disintegrate into, and simultaneously are assembled from, free subunits. Dissociation rate constants, koff, provide important structure and function information on protein complexes. However, because all existing methods for measuring koff require high-quality purification and specific modifications of protein complexes, dissociation kinetics has only been studied for a small set of model complexes. Here we propose a new method, called Metabolically-labeled Affinity-tagged Subunit Exchange (MASE) to measure koff using metabolic labeling, affinity purification and mass spectrometry. MASE is based on a subunit exchange process between an unlabeled affinity-tagged variant and a metabolically-labeled untagged variant of a complex. In this study, the subunit exchange process was modeled theoretically for a heterodimeric complex. The results showed that koff determines, and hence can be estimated from, the observed rate of subunit exchange. Future study will be needed to experimentally validate the new method.
Y. Xia; J.I. Friese; D.A. Moore; L. Rao
A solvent extraction method was used to determine the stability constants of Np(V) complexes with fluoride and sulfate in 1.0 M NaClO{sub 4} from 25 C to 60 C. The distribution ratio of Np(V) between the organic and aqueous phases was found to decrease as the concentrations of fluoride and sulfate were increased. Stability constants of the 1:1 Np(V)-fluoride complexes and the 1:1 Np(V)-sulfate and 1:2 Np(V)-sulfate complexes, dominant in the aqueous phase under the experimental conditions, were calculated from the effect of [F{sup -}] and [SO{sub 4}{sup 2-}] on the distribution ratio. The enthalpy and entropy of complexation were calculated from the stability constants at different temperatures by using the Van't Hoff equation.
A Simple Method for the Consecutive Determination of Protonation Constants through Evaluation of Formation Curves
ERIC Educational Resources Information Center
Hurek, Jozef; Nackiewicz, Joanna
A simple method is presented for the consecutive determination of protonation constants of polyprotic acids based on their formation curves. The procedure is based on generally known equations that describe dissociation equilibria. It has been demonstrated through simulation that the values obtained through the proposed method are sufficiently…
Stability constants important to the understanding of plutonium in environmental waters, hydroxy and carbonate complexation of PuO{sub 2}{sup +}
Bennett, D A [California Univ., Berkeley, CA (USA). Dept. of Chemistry
The formation constants for the reactions PuO{sub 2}{sup +} + H{sub 2}O = PuO{sub 2}(OH) + H{sup +} and PuO{sub 2}{sup +} + CO{sub 3}{sup 2} = PuO{sub 2}(CO{sub 3}){sup {minus}} were determined in aqueous sodium perchlorate solutions by laser-induced photoacoustic spectroscopy. The molar absorptivity of the PuO{sub 2}{sup +} band at 569 nm decreased with increasing hydroxide concentration. Similarly, spectral changes occurred between 540 and 580 nm as the carbonate concentration was increased. The absorption data were analyzed by the non-linear least-squares program SQUAD to yield complexation constants. Using the specific ion interaction theory, both complexation constants were extrapolated to zero ionic strength. These thermodynamic complexation constants were combined with the oxidation-reduction potentials of Pu to obtain Eh versus pH diagrams. 120 refs., 35 figs., 12 tabs.
Quasi-optical measurement of complex dielectric constant at 300 GHz
Bernd Stöckel
A two beam interferometer in the Martin-Puplett configuration is used to determine the complex dielectric constant at 300 GHz of teflon, TPX-plastics, SPECTRALON and paraffin waxes with melting temperatures of 48° C and 72° C, respectively. The design of the quasi-optical system leads to a constant beam diameter at the power detector independent of path delay and frequency. The power
Formation of complex films with water-soluble CTAB molecules
S. Biswas; S. A. Hussain; S. Deb; R. K. Nathb; D. Bhattacharjee
This communication reports the formation of complex Langmuir monolayer at the air–water interface with the water-soluble N-cetyl N,N,N-trimethyl ammonium bromide (CTAB) molecules when interacted with the stearic acid (SA) molecules. The reaction kinetics of the formation of the CTAB–SA complex was monitored by observing the surface pressure versus time graph. Multilayered LB films of this complex doped with Congo red
Formation of complex films with water-soluble CTAB molecules
Syed Arshad Hussain; S. Biswas; R. K. Nath; S. Deb; D. Bhattacharjee
This communication reports the formation of complex Langmuir monolayer at the air-water interface with the water-soluble -trimethyl ammonium bromide (CTAB) molecules when interacted with the stearic acid (SA) molecules. The reaction kinetics of the formation of the CTAB-SA complex was monitored by observing the surface pressure versus time graph. Multilayered LB films of this complex doped with congo red was
1 Introduction Our sensory systems are constantly bombarded with a complex array of information
Shams, Ladan B.
1 Introduction Our sensory systems are constantly bombarded with a complex array of information pertaining to our physical environment. Somehow, we are able to make sense of these inputs and structure our of the early sensory systems can be accounted for by the statistical regularities of the sensory environment
Determining conditional stability constants for Pb complexation by carboxymethyl-beta-cyclodextrin (CMCD).
Skold, Magnus E; Thyne, Geoffrey D; Drexler, John W; McCray, John E
Carboxymethyl-beta-cyclodextrin (CMCD) has been proposed for remediation of metal-contaminated sediments. This research presents stability constants for CMCD-lead complexes, and demonstrates a rigorous methodology for estimating stability constants for metal-complexing agents. The conditional stability constant for the lead-CMCD aqueous complex was determined to be 10(5.18) with the 95% confidence interval ranging from 10(5.14) to 10(5.22). The best fit for experimental data was made by assuming a reaction between divalent CMCD(2-) and Pb(2+) and using the WATEQ activity coefficient formulation. The optimized value was derived from experimental data with the geochemical model PHREEQC coupled to UCODE_2005, a parameter optimization program. Like FITEQL, UCODE has a built-in option to optimize parameter values by minimizing the weighted sum of squared residuals (WSSR). However, our approach not only allows rapid, automatic optimization of the stability constant, but also allows determination of uncertainties in estimated parameter values and statistical analysis to assess the appropriateness of the conceptual model. The automation of the process allows testing of multiple conceptual models and the final values produced are internally consistent with the PHREEQC database. In this case five different conceptual models to describe the metal complexation and protonation reactions of CMCD were considered. PMID:17412450
We determined the number and the dissociation rate constants of different complexes formed from arsenite and two peptides containing either one (RV AVGNDYASGYHYGV for peptide 20) or three cysteines (LE AWQGK VEGTEHLYSMK K for peptide 10) via radioactive 73As labeled arsenite and ...
Formation, structure, and reactivity of palladium superoxo complexes
Talsi, E.P.; Babenko, V.P.; Shubin, A.A.; Chinakov, V.D.; Nekipelov, V.M.; Zamaraev, K.I.
The mechanism of formation of palladium superoxo complexes, their structure, and their reactivity are discussed. The formation of the palladium superoxo complexes in the reaction of palladium(II) acetate, propionate, trifluororacetate, and bis(acetylacetonate) and palladium(0) tetrakis(triphenylphosphine) with hydrogen peroxide and potassium superoxide has been detected in solution by electron proton resonance. The oxidation of olefins and carbon monoxide by these complexes is considered. Reaction mechanisms and reaction kinetics for these oxidations are reported using the palladium superoxo complexes. 44 references, 8 figures, 2 tables.
Formation of complex films with water-soluble CTAB molecules
NASA Astrophysics Data System (ADS)
Biswas, S.; Hussain, S. A.; Deb, S.; Nath, R. K.; Bhattacharjee, D.
This communication reports the formation of complex Langmuir monolayer at the air-water interface with the water-soluble N-cetyl N, N, N-trimethyl ammonium bromide (CTAB) molecules when interacted with the stearic acid (SA) molecules. The reaction kinetics of the formation of the CTAB-SA complex was monitored by observing the surface pressure versus time graph. Multilayered LB films of this complex doped with Congo red was successfully formed onto a quartz substrate. UV-Vis absorption and steady-state fluorescence spectroscopic characteristics of this doped LB films confirms the successful incorporation of Congo red molecules in to the CTAB-SA complex films.
Formation of complex films with water-soluble CTAB molecules.
Biswas, S; Hussain, S A; Deb, S; Nath, R K; Bhattacharjee, D
This communication reports the formation of complex Langmuir monolayer at the air-water interface with the water-soluble N-cetyl N,N,N-trimethyl ammonium bromide (CTAB) molecules when interacted with the stearic acid (SA) molecules. The reaction kinetics of the formation of the CTAB-SA complex was monitored by observing the surface pressure versus time graph. Multilayered LB films of this complex doped with Congo red was successfully formed onto a quartz substrate. UV-Vis absorption and steady-state fluorescence spectroscopic characteristics of this doped LB films confirms the successful incorporation of Congo red molecules in to the CTAB-SA complex films. PMID:16549387
Analysis of association constant for ground state dye-electron acceptor complex of photoinitiator systems and the association constant effect on the kinetics of visible-light-induced polymerizations.
Kim, Dongkwan; Scranton, Alec B; Stansbury, Jeffrey W
We investigated the formation of ground state donor/acceptor complexes between xanthene dyes (rose Bengal (RB) and fluorescein (FL)) and a diphenyl iodonium salt (DPI) which is dissolved in 2-hydroxyethyl methacrylate (HEMA) monomer. To characterize the association constant of the complex, we have suggested a new analysis model based upon the Benesi-Hildebrand model. Because the assumption of the original Benesi-Hildebrand model is that the absorption bands are due only to the presence of the complex and that the absorption by the free component is negligible; the model cannot be applied to our systems, which is a dye-based initiator system. For each dye, the molar absorptivity of the ground state complex was evaluated as a function of wavelength and this analysis confirmed the validity of the modified Benesi-Hildebrand model. In addition, we observed the RB/DPI photoinitiator system failed to produce a perceptible polymerization rate but the FL/DPI photoinitiator system provided very high rates of polymerization. Based upon the association constant for these complexes, we concluded that the observed kinetic differences arise from the different association constant values of the ground state dye-acceptor complex, resulting in back electron transfer reaction. PMID:20161099
Structural determinants for the formation of sulfhemeprotein complexes
Elddie Román-Morales; Ruth Pietri; Brenda Ramos-Santana; Serge N. Vinogradov; Ariel Lewis-Ballester; Juan López-Garriga
Several hemoglobins were explored by UV–Vis and resonance Raman spectroscopy to define sulfheme complex formation. Evaluation of these proteins upon the reaction with H2O2 or O2 in the presence of H2S suggest: (a) the formation of the sulfheme derivate requires a HisE7 residue in the heme distal site with an adequate orientation to form an active ternary complex; (b) that
Dissociation of Bimolecular ?IIb ?3Fibrinogen Complex under a Constant Tensile Force
Rustem I. Litvinov; Valeri Barsegov; Andrew J. Schissler; Andrew R. Fisher; Joel S. Bennett; John W. Weisel; Henry Shuman
The regulated ability of integrin ?IIb?3 to bind fibrinogen plays a crucial role in platelet aggregation, adhesion, and hemostasis. Employing an optical-trap-based electronic force clamp, we studied the thermodynamics and kinetics of ?IIb?3-fibrinogen bond formation and dissociation under constant unbinding forces, mimicking the forces of physiologic blood shear on a thrombus. The distribution of bond lifetimes was bimodal, indicating that
Factors affecting the threading of axle molecules through macrocycles: Binding constants for semirotaxane formation
Clifford, Thomas; Abushamleh, Ahmad; Busch, Daryle H.
The threading of more or less linear axle molecules through macrocyclic molecules, a fundamental process relating to the formation of interlocked molecular structures, has been investigated through the study in acetone of the equilibrium constants for the formation of pseudorotaxanes by NMR methods. The 30 new axle molecules have in common a secondary ammonium group, present as the thiocyanate salt, and an anthracen-9-ylmethyl group, but are rendered unique by the second amine substituent. All rotaxanes involve the well known polyether macrocycle, benzo[24]crown-8. The constants for the binding of axles having linear groups ranging from 2 to 18 carbon atoms show little variation in binding constant but are divided into two groups by their equilibration rates. Those with less than five methylene groups react rapidly on the NMR timescale, whereas those having more than five methylene groups are slow. Branching inhibits binding, but the effect decreases as the branch is moved away from the amine. Phenyl groups weaken binding when close to the amine but strengthen binding when more remote. Some functional groups decrease pseudorotaxane stability (alcohol functions), whereas others increase binding (carboxylic acid groups). PMID:11959934
Formation of Phenylene Oligomers Using Platinum-Phosphine Complexes
Jones, William D.
Formation of Phenylene Oligomers Using Platinum-Phosphine Complexes Nira Simhai, Carl N. Iverson to the formation of two strong metal-aryl bonds. This is demonstrated by the reaction of biphenylene with (C5Me5)Rh, R. H.; Dion, R. P.; Gibboni, D. J.; McGrath, D. V.; Holt, E. M. J. Am. Chem. Soc. 1986, 108, 7222
Dynamics of Lane Formation in Driven Binary Complex Plasmas
Suetterlin, K. R.; Ivlev, A. V.; Raeth, C.; Thomas, H. M.; Rubin-Zuzic, M.; Morfill, G. E. [Max Planck Institute for Extraterrestrial Physics, 85741 Garching (Germany); Wysocki, A.; Loewen, H. [Heinrich-Heine-Universitaet Duesseldorf, 40225 Duesseldorf (Germany); Goedheer, W. J. [FOM-Institute for Plasma Physics Rijnhuizen, 3430 BE Nieuwegein (Netherlands); Fortov, V. E.; Lipaev, A. M.; Molotkov, V. I.; Petrov, O. F. [Joint Institute for High Temperatures, 125412 Moscow (Russian Federation)
The dynamical onset of lane formation is studied in experiments with binary complex plasmas under microgravity conditions. Small microparticles are driven and penetrate into a cloud of big particles, revealing a strong tendency towards lane formation. The observed time-resolved lane-formation process is in good agreement with computer simulations of a binary Yukawa model with Langevin dynamics. The laning is quantified in terms of the anisotropic scaling index, leading to a universal order parameter for driven systems.
Dynamics of lane formation in driven binary complex plasmas.
Sütterlin, K R; Wysocki, A; Ivlev, A V; Räth, C; Thomas, H M; Rubin-Zuzic, M; Goedheer, W J; Fortov, V E; Lipaev, A M; Molotkov, V I; Petrov, O F; Morfill, G E; Löwen, H
The dynamical onset of lane formation is studied in experiments with binary complex plasmas under microgravity conditions. Small microparticles are driven and penetrate into a cloud of big particles, revealing a strong tendency towards lane formation. The observed time-resolved lane-formation process is in good agreement with computer simulations of a binary Yukawa model with Langevin dynamics. The laning is quantified in terms of the anisotropic scaling index, leading to a universal order parameter for driven systems. PMID:19257747
Variation of stability constants of thorium and uranium oxalate complexes with ionic strength
Erten, H.N; Mohammed, A.K.; Choppin, G.R. [Florida State Univ., Tallahassee, FL (United States). Dept. of Chemistry
Extraction of Th(IV) and UO{sub 2}{sup 2+} by a solution of TTA and HDEHP, respectively, in toluene was used to obtain stability constants of their oxalate complexes in 1, 3, 5, 7 and 9 M ionic strength (NaClO{sub 2}) solutions. The complexes formed were the MOx, MHOx, MOx{sub 2} and M(HOx){sub 2} (M = Th, UO{sub 2}) species. The values were analyzed by the Specific Interaction Theory and agreed to I {le} 3 M but required an additional term for fitting at I > 3 M.
The Determination of Complex Dielectric Constants of Absorptive Liquids by Microwave Interferometry
Franklin H. Branin
This paper describes both a traveling-wave method and a standing-wave method for determining complex dielectric constants of liquids from measurements made at 10-cm wavelength with a traveling probe immersed in a dielectric-filled slotted line. An interferometric null technique was developed for improving the accuracy of the measurements, especially in highly absorptive media. In the traveling-wave method, absolute measurements of both
Complex dielectric constants for selected near-millimeter-wave materials at 245 GHz
NASA Technical Reports Server (NTRS)
Dutta, J. M.; Jones, C. R.; Dave, H.
A double-beam instrument developed in this laboratory has been used to measure the complex dielectric constant of selected materials at 245 GHz. It is reported here the results for crystalline quartz, fused silica (Spectrosil WF and Dynasil 4000), beryllia (iso-pressed), boron nitride (hot-pressed), and a nickel ferrite (Trans-Tech 2-111). Results are compared with the data obtained by other researchers.
Stability constants of chloro-complexes of cadmium(II) in sea-water medium.
Simoes, M L; Vaz, M C; da Silva, J J
Potentiometry with ion-selective electrodes and anodic stripping voltammetry were used to measure the stability constants for cadmium chloro-complexes at 20 +/- 0.1 degrees in synthetic sea-water and at an ionic strength of 0.700 (NaClO(4) + NaCl). The values of beta(ML) and beta(ML(2)) obtained by the two methods are in good agreement. PMID:18962906
Bow shock formation in a complex plasma.
Saitou, Y; Nakamura, Y; Kamimura, T; Ishihara, O
A bow shock is observed in a two-dimensional supersonic flow of charged microparticles in a complex plasma. A thin conducting needle is used to make a potential barrier as an obstacle for the particle flow in the complex plasma. The flow is generated and the flow velocity is controlled by changing a tilt angle of the device under the gravitational force. A void, microparticle-free region, is formed around the potential barrier surrounding the obstacle. The flow is bent around the leading edge of the void and forms an arcuate structure when the flow is supersonic. The structure is characterized by the bow shock as confirmed by a polytropic hydrodynamic theory as well as numerical simulation. PMID:22401079
Complex molecule formation around massive young stellar objects.
Oberg, Karin I; Fayolle, Edith C; Reiter, John B; Cyganowski, Claudia
Interstellar complex organic molecules were first identified in the hot inner regions of massive young stellar objects (MYSOs), but have more recently been found in many colder sources, indicating that complex molecules can form at a range of temperatures. However, individually these observations provide limited constraints on how complex molecules form, and whether the same formation pathways dominate in cold, warm and hot environments. To address these questions, we use spatially resolved observations from the Submillimeter Array of three MYSOs together with mostly unresolved literature data to explore how molecular ratios depend on environmental parameters, especially temperature. Towards the three MYSOs, we find multiple complex organic emission peaks characterized by different molecular compositions and temperatures. In particular, CH3CCH and CH3CN seem to always trace a lukewarm (T = 60 K) and a hot (T > 100 K) complex chemistry, respectively. These spatial trends are consistent with abundance-temperature correlations of four representative complex organics--CH3CCH, CH3CN, CH3OCH3 and CH3CHO--in a large sample of complex molecule hosts mined from the literature. Together, these results indicate a general chemical evolution with temperature, i.e. that new complex molecule formation pathways are activated as a MYSO heats up. This is qualitatively consistent with model predictions. Furthermore, these results suggest that ratios of complex molecules may be developed into a powerful probe of the evolutionary stage of a MYSO, and may provide information about its formation history. PMID:25302375
Direct electronic probing of biological complexes formation
NASA Astrophysics Data System (ADS)
Macchia, Eleonora; Magliulo, Maria; Manoli, Kyriaki; Giordano, Francesco; Palazzo, Gerardo; Torsi, Luisa
Functional bio-interlayer organic field - effect transistors (FBI-OFET), embedding streptavidin, avidin and neutravidin as bio-recognition element, have been studied to probe the electronic properties of protein complexes. The threshold voltage control has been achieved modifying the SiO2 gate diaelectric surface by means of the deposition of an interlayer of bio-recognition elements. A threshold voltage shift with respect to the unmodified dielectric surface toward more negative potential values has been found for the three different proteins, in agreement with their isoelectric points. The relative responses in terms of source - drain current, mobility and threshold voltage upon exposure to biotin of the FBI-OFET devices have been compared for the three bio-recognition elements.
Thermodynamics of cesium complexes formation with 18-crown-6 in ionic liquids
A. G. Vendilo; H. Rönkkömäki; M. Hannu-Kuure; M. Lajunen; J. Asikkala; V. G. Krasovsky; E. A. Chernikova; P. Oksman; L. H. J. Lajunen; T. Tuomi; K. I. Popov
Thermodynamic data for cesium complexes formation with 18-crown-6 (18C6, L) [Cs(18C6)]+ in N-butyl-4-methyl-pyridinium tetrafluoroborate ([BMPy][BF4], I), in 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4], II) and in 1-butyl-3-methylimidazolium dicyanamide ([BMIM][N(CN)2], III) were measured with NMR 133Cs technique at 23–50 °C. The stability of cesium complex in RTILs is estimated to be in the range between water and DMFA.\\u000a Stability constants for [Cs(18C6)]+ are found to
Equilibrium star formation in a constant Q disc: model optimization and initial tests
NASA Astrophysics Data System (ADS)
Zheng, Zheng; Meurer, Gerhardt R.; Heckman, Timothy M.; Thilker, David A.; Zwaan, Martin A.
We develop a model for the distribution of the interstellar medium (ISM) and star formation in galaxies based on recent studies that indicate that galactic discs stabilize to a constant stability parameter, which we combine with prescriptions of how the phases of the ISM are determined and for the star formation law (SFL). The model predicts the gas surface mass density and star formation intensity of a galaxy given its rotation curve, stellar surface mass density and the gas velocity dispersion. This model is tested on radial profiles of neutral and molecular ISM surface mass density and star formation intensity of 12 galaxies selected from the H I Nearby Galaxy Survey sample. Our tests focus on intermediate radii (0.3 to 1 times the optical radius) because there are insufficient data to test the outer discs and the fits are less accurate in detail in the centre. Nevertheless, the model produces reasonable agreement with the ISM mass and star formation rate integrated over the central region in all but one case. To optimize the model, we evaluate four recipes for the stability parameter, three recipes for apportioning the ISM into molecular and neutral components, and eight versions of the SFL. We find no clear-cut best prescription for the two-fluid (gas and stars) stability parameter Q2f and therefore for simplicity, we use the Wang and Silk approximation (QWS). We found that an empirical scaling between the molecular-to-neutral ISM ratio (Rmol) and the stellar surface mass density proposed by Leroy et al. works marginally better than the other two prescriptions for this ratio in predicting the ISM profiles, and noticeably better in predicting the star formation intensity from the ISM profiles produced by our model with the SFLs we tested. Thus, in the context of our modelled ISM profiles, the linear molecular SFL and the two-component SFL work better than the other prescriptions we tested. We incorporate these relations into our `constant Q disc' model.
Thermodynamics of cationic lipid-DNA complex formation as studied by isothermal titration calorimetry.
Pozharski, Edwin; MacDonald, Robert C
The detailed analysis of the cationic lipid-DNA complex formation by means of isothermal titration calorimetry is presented. Most experiments were done using 1,2-dioleyl-sn-glycero-3-ethylphosphocholine (EDOPC), but basic titrations were also done using DOTAP, DOTAP:DOPC, and DOTAP:DOPE mixtures. Complex formation was endothermic with less than 1 kcal absorbed per mole of lipid or DNA charge. This enthalpy change was attributed to DNA-DNA mutual repulsion within the lamellar complex. The exception was DOTAP:DOPE-containing lipoplex for which the enthalpy of formation was exothermic, presumably because of DOPE amine group protonation. Experimental conditions, namely, direction and titration increment as well as concentration of titrant, which dictate the structure of resulting lipoplex (whether lamellar complex or DNA-coated vesicle), were found to affect the apparent thermodynamics of complex formation. The structure, in turn, influences the biological properties of the lipoplex. If the titration of lipid into DNA was carried out in large increments, the DeltaH was larger than when the injection increments were smaller, a finding that is consistent with increased vesicle disruption under large increments and which is expected theoretically. Cationic lipid-DNA binding was weak in high ionic strength solutions, however, the effective binding constant is within micromolar range because of macromolecular nature of the interaction. PMID:12080142
Synthesis, characterization and thermodynamics of complex formation of some new Schiff base ligands with some transition metal ions and the adduct formation of zinc Schiff base complexes with some organotin chlorides
NASA Astrophysics Data System (ADS)
Asadi, Mozaffar; Asadi, Zahra; Torabi, Susan; Lotfi, Najmeh
Four new complexes, [M(Salpyr)] where Salpyr = N,N'-bis(Salicylidene)-2,3- and 3,4-diiminopyridine and M = Co, Cu, Mn, Ni and Zn were synthesized and characterized by 1H NMR, IR spectroscopy, elemental analysis and UV-vis spectrophotometry. UV-vis spectrophotometric study of the adduct formation of the zinc(II) complexes, [Zn(2,3-Salpyr)] and [Zn(3,4-Salpyr)], as donor with R2SnCl2 (R = methyl, phenyl, n-butyl), PhSnCl3 and Bu3SnCl as acceptors has been investigated in methanol, as solvent. The formation constants and the thermodynamic free energies were measured using UV-vis spectrophotometry. Titration of the organotin chlorides with Zn(II) complexes at various temperatures (T = 283-313 K) leads to 1:1 adduct formation. The results show that the formation constants were decreased by increasing the temperature. The trend of the reaction of RnSnCl4-n as acceptors toward given zinc complexes was as follows: PhSnCl3 > Me2SnCl2 > Ph2SnCl2 > Bu2SnCl2 > Bu3SnCl By considering the formation constants and the ?G° of the complex formation for the Schiff base as donor and the M(II) as acceptor, the following conclusion was drawn: the formation constant for a given Schiff base changes according to the following trend: Ni > Cu > Co > Zn > Mn
Spectrophotometric determination of the formation constant of triiodide ions in aqueous-organic solvent or polymer mixed media both in absence and presence of a surfactant.
Naorem, Homendra; Devi, Seram Dushila
The formation constant of triiodide ions from iodine-iodide equilibrium in aqueous-organic solvent or polymer mixed media have been determined spectrophotometrically at three different temperatures 20, 30 and 40°C. The organic solvents chosen for the study are ethylene glycol, 2-methoxy ethanol, and 2-ethoxy ethanol while the polymers include polyethylene glycol (PEG), hydroxypropyl cellulose (HPC) or polyethylene oxide (PEO). Effect of a surfactant on the formation of triiodide ions in the mixed media has also been investigated. Though presence of the organic solvents led to an increase in the triiodide formation except for 2-ethoxy ethanol mixed media at low percentage, the increase in presence of PEG or the other polymer mixed media even at very low percentage was much higher as compared to those in ethylene glycol or its homologues. The increase in the formation constant has been discussed in terms of changes in its solvation properties and the hydrophobic character of the mixed media besides the solvent dielectric effects. The sharp increase in triiodide formation in presence of the polymer under study suggests the possibility of iodine being present as triiodide or other higher polyiodides in the inclusion complexes of iodine with other polymers like starch or PVA. The decrease in the triiodide formation in presence of surfactant micelles may, however, be attributed to solubilization of iodine by the micelles. Iodine was found to be better solubilized in TX-100 micelles as compared to SDS micelles. PMID:23099162
Variation of lattice constant and cluster formation in GaAsBi
Puustinen, J.; Schramm, A.; Guina, M. [Optoelectronics Research Centre, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere (Finland)] [Optoelectronics Research Centre, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere (Finland); Wu, M.; Luna, E. [Paul-Drude Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)] [Paul-Drude Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany); Laukkanen, P. [Department of Physics and Astronomy, University of Turku, FI-20014 Turku (Finland)] [Department of Physics and Astronomy, University of Turku, FI-20014 Turku (Finland); Laitinen, M.; Sajavaara, T. [Department of Physics, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä (Finland)] [Department of Physics, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä (Finland)
We investigate the structural properties of GaAsBi layers grown by molecular beam epitaxy on GaAs at substrate temperatures between 220–315 °C. Irrespective of the growth temperature, the structures exhibited similar Bi compositions, and good overall crystal quality as deduced from X-Ray diffraction measurements. After thermal annealing at temperatures as low as 500 °C, the GaAsBi layers grown at the lowest temperatures exhibited a significant reduction of the lattice constant. The lattice variation was significantly larger for Bi-containing samples than for Bi-free low-temperature GaAs samples grown as a reference. Rutherford backscattering spectrometry gave no evidence of Bi diffusing out of the layer during annealing. However, dark-field and Z-contrast transmission electron microscopy analyses revealed the formation of GaAsBi clusters with a Bi content higher than in the surrounding matrix, as well as the presence of metallic As clusters. The apparent reduction of the lattice constant can be explained by a two-fold process: the diffusion of the excess As incorporated within As{sub Ga} antisites to As clusters, and the reduction of the Bi content in the GaAs matrix due to diffusion of Bi to GaAsBi clusters. Diffusion of both As and Bi are believed to be assisted by the native point defects, which are present in the low-temperature as-grown material.
Complex-anisotropy-induced pattern formation in bistable media.
He, Zhi Zhu; Liu, Jing
A construct of anisotropy in bistable media is adopted to characterize the effects of anisotropy on pattern formation by means of anisotropic line tension. A velocity curvature relation is further derived to account for the anisotropic wave propagations. Stability analysis of transverse perturbations indicates that a sufficiently strong complex anisotropy can induce dynamical instabilities and even lead to a breakup of the wave patterns. Numerical simulations show that complex anisotropy can induce rich spatiotemporal behaviors in bistable media. The results of analysis and simulations demonstrate that this method successfully incorporates complex anisotropy into the reaction diffusion model and has general significance. PMID:19391804
Effect of ternary complex formation on chromatographic selectivity using in situ complexation chromatography
O'Riordan, K.P.; Heneghan, G.; Wallace, G.G.
In situ complexation chromatography is a relatively novel form of reversed-phase chromatography. A method for controlling selectivity via ternary complex formation is discussed. This method is potentially useful, not only for controlling separations but also for enhancing detection of metal species. Limitations of the methods are discussed. 30 references, 5 figures, 4 tables.
Disulfide bond formation involves a quinhydrone-type chargetransfer complex
Bardwell, James
Disulfide bond formation involves a quinhydrone-type chargetransfer complex James Regeimbal, September 17, 2003 (received for review July 14, 2003) The chemistry of disulfide exchange in biological to form disulfide bonds in proteins is not clear. In prokaryotic organisms, it is known that DsbB delivers
Stability constants of copper(II) mixed complexes with some 4-quinolone antibiotics and (N-N) donors
Guillermo Mendoza-Díaz; Raul Perez-Alonso; Rafael Moreno-Esparza
Studies of complexation equilibria of the antibiotic anions nalidixate and cinoxacinate with [Cu(phen)]2+ and [Cu(bipy)]2+ are reported. These studies indicate that the stability of this type of complex is strongly related to the metal environment. A correlation between the stability constants, determined here, with the sigma donation character of the ligand is proposed. This study shows that the stability constant
Complexation of Arsenite with Dissolved Organic Matter: Conditional Distribution Coefficients and Apparent Stability Constants
Liu, Guangliang; Cai, Yong
The complexation of arsenic (As) with dissolved organic matter (DOM), although playing an important role in regulating As mobility and transformation, is poorly characterized, as evidenced by scarce reporting of fundamental parameters of As-DOM complexes. The complexation of arsenite (AsIII) with Aldrich humic acid (HA) at different pHs was characterized using a recently developed analytical technique to measure both free and DOM-bound As. Conditional distribution coefficient (KD), describing capacity of DOM in binding AsIII from the mass perspective, and apparent stability constant (Ks), describing stability of resulting AsIII-DOM complexes, were calculated to characterize AsIII-DOM complexation. Log KD of AsIII ranged from 3.7 to 2.2 (decreasing with increase of As/DOM ratio) at pH 5.2, from 3.6 to 2.6 at pH 7, and from 4.3 to 3.2 at pH = 9.3, respectively. Two-site ligand binding models can capture the heterogeneity of binding sites and be used to calculate Ks by classifying the binding sites into strong (S1) and weak (S2) groups. Log Ks for S1 sites are 7.0, 6.5, and 5.9 for pH 5.2, 7, and 9.3, respectively, which are approximately 1–2 orders of magnitude higher than for weak S2 sites. The results suggest that AsIII complexation with DOM increases with pH, as evidenced by significant spikes in concentrations of DOM-bound AsIII and in KD values at pH 9.3. In contrary to KD, log Ks decreased with pH, in particular for S1 sites, probably due to the presence of negatively charged H2AsO3? and the involvement of metal-bridged AsIII-DOM complexation at pH 9.3. PMID:20801484
Complex unconstrained three-dimensional hand movement and constant equi-affine speed.
Maoz, Uri; Berthoz, Alain; Flash, Tamar
One long-established simplifying principle behind the large repertoire and high versatility of human hand movements is the two-thirds power law-an empirical law stating a relationship between local geometry and kinematics of human hand trajectories during planar curved movements. It was further generalized not only to various types of human movements, but also to motion perception and prediction, although it was unsuccessful in explaining unconstrained three-dimensional (3D) movements. Recently, movement obeying the power law was proved to be equivalent to moving with constant planar equi-affine speed. Generalizing such motion to 3D space-i.e., to movement at constant spatial equi-affine speed-predicts the emergence of a new power law, whose utility for describing spatial scribbling movements we have previously demonstrated. In this empirical investigation of the new power law, subjects repetitively traced six different 3D geometrical shapes with their hand. We show that the 3D power law explains the data consistently better than both the two-thirds power law and an additional power law that was previously suggested for spatial hand movements. We also found small yet systematic modifications of the power-law's exponents across the various shapes, which further scrutiny suggested to be correlated with global geometric factors of the traced shape. Nevertheless, averaging over all subjects and shapes, the power-law exponents are generally in accordance with constant spatial equi-affine speed. Taken together, our findings provide evidence for the potential role of non-Euclidean geometry in motion planning and control. Moreover, these results seem to imply a relationship between geometry and kinematics that is more complex than the simple local one stipulated by the two-thirds power law and similar models. PMID:19073811
Complex formation of ionic liquid surfactant and ?-cyclodextrin
Na Li; Jie Liu; Xueyan Zhao; Yan'an Gao; Liqiang Zheng; Jin Zhang; Li Yu
An ionic liquid (IL) surfactant, 1-dodecyl-3-methylimidazolium hexafluorophosphate (C12mimPF6) can form the inclusion complexes (ICs) with ?-cyclodextrin (?-CD). The surface tension measurements revealed that there were two kinds of inclusion formations, 1:1 and 1:2 (?-CD\\/IL) stoichiometry for ?-CD-C12mimPF6 ICs. The inclusion complexation interaction was further confirmed by FT-IR spectra. The inclusion compound was also characterized by Powder X-ray diffraction (XRD), 13C
Measurements of the complex dielectric constant of sand and dust particles at 11 GHz
NASA Astrophysics Data System (ADS)
Al-Rizzo, Hussain M.; Al-Hafid, Hafid T.
Measurements are reported of the refractive index (Delta-n) and loss tangent (tan delta) of dust particles in a laboratory-simulated model of dust storms, carried out at 11 GHz utilizing a confocal microwave open-cavity resonator. Four samples were used namely, sandy, silty, clayey silt, and clayey, for concentrations varying from 10-4 to 4 x 10-3 g/cu cm. The particle-size distribution (PSD) of each sample was measured by seiving along with the hydrometer technique. Dielectric-constant measurements were also conducted at bulk concentrations using the standing-wave technique for the dry samples and as a function of volumetric moisture content for up to 0.5 cu cm/cu cm. The complex dielectric constant of the dust particle material was evaluated by two approaches. In one the data for permittivities obtained over the whole range of measured concentrations were extrapolated to the particle densities of the samples. In the other a mixing formula was utilized for the determination of epsilon(s) from permittivities measured at bulk concentrations.
Polarographic determination of lead hydroxide formation constants at low ionic strength
Lind, Carol J.
Values of formation constants for lead hydroxide at 25 ??C were calculated from normal pulse polarographic measurements of 10-6 M lead in 0.01 M sodium perchlorate. The low concentrations simulate those found in many freshwaters, permitting direct application of the values when considering distributions of lead species. The precise evaluation of species distribution in waters at other ionic strengths requires activity coefficient corrections. As opposed to much of the previously published work done at high ionic strength, the values reported here were obtained at low ionic strength, permitting use of smaller and better defined activity coefficient corrections. These values were further confirmed by differential-pulse polarography and differential-pulse anodic stripping voltammetry data. The logs of the values for ??1??? ??2???, and ??3??? were calculated to be 6.59, 10.80, and 13.63, respectively. When corrected to zero ionic strength these values were calculated to be 6.77, 11.07, and 13.89, respectively.
Formation of Complex and Unstable Chromosomal Translocations in Yeast
Schmidt, Kristina H.; Viebranz, Emilie; Doerfler, Lillian; Lester, Christina; Rubenstein, Aaron
Genome instability, associated with chromosome breakage syndromes and most human cancers, is still poorly understood. In the yeast Saccharomyces cerevisiae, numerous genes with roles in the preservation of genome integrity have been identified. DNA-damage-checkpoint-deficient yeast cells that lack Sgs1, a RecQ-like DNA helicase related to the human Bloom's-syndrome-associated helicase BLM, show an increased rate of genome instability, and we have previously shown that they accumulate recurring chromosomal translocations between three similar genes, CAN1, LYP1 and ALP1. Here, the chromosomal location, copy number and sequence similarity of the translocation targets ALP1 and LYP1 were altered to gain insight into the formation of complex translocations. Among 844 clones with chromosomal rearrangements, 93 with various types of simple and complex translocations involving CAN1, LYP1 and ALP1 were identified. Breakpoint sequencing and mapping showed that the formation of complex translocation types is strictly dependent on the location of the initiating DNA break and revealed that complex translocations arise via a combination of interchromosomal translocation and template-switching, as well as from unstable dicentric intermediates. Template-switching occurred between sequences on the same chromosome, but was inhibited if the genes were transferred to different chromosomes. Unstable dicentric translocations continuously gave rise to clones with multiple translocations in various combinations, reminiscent of intratumor heterogeneity in human cancers. Base substitutions and evidence of DNA slippage near rearrangement breakpoints revealed that translocation formation can be accompanied by point mutations, and their presence in different translocation types within the same clone provides evidence that some of the different translocation types are derived from each other rather than being formed de novo. These findings provide insight into eukaryotic genome instability, especially the formation of translocations and the sources of intraclonal heterogeneity, both of which are often associated with human cancers. PMID:20711256
The catalytic role of uranyl in formation of polycatechol complexes
To better understand the association of contaminant uranium with natural organic matter (NOM) and the fate of uranium in ground water, spectroscopic studies of uranium complexation with catechol were conducted. Catechol provides a model for ubiquitous functional groups present in NOM. Liquid samples were analyzed using Raman, FTIR, and UV-Vis spectroscopy. Catechol was found to polymerize in presence of uranyl ions. Polymerization in presence of uranyl was compared to reactions in the presence of molybdate, another oxyion, and self polymerization of catechol at high pH. The effect of time and dissolved oxygen were also studied. It was found that oxygen was required for self-polymerization at elevated pH. The potential formation of phenoxy radicals as well as quinones was monitored. The benzene ring was found to be intact after polymerization. No evidence for formation of ether bonds was found, suggesting polymerization was due to formation of C-C bonds between catechol ligands. Uranyl was found to form outer sphere complexes with catechol at initial stages but over time (six months) polycatechol complexes were formed and precipitated from solution (forming humic-like material) while uranyl ions remained in solution. Our studies show that uranyl acts as a catalyst in catechol-polymerization. PMID:21396112
Hierarchical structure formation of cylindrical brush polymer-surfactant complexes.
Cong, Yang; Gunari, Nikhil; Zhang, Bin; Janshoff, Andreas; Schmidt, Manfred
The complex formation of cylindrical brush polymers with poly(l-lysine) side chains (PLL) and sodium dodecyl sulfate (SDS) can induce a helical conformation of the cylindrical brush polymer in aqueous solution (Gunari, N.; Cong, Y.; Zhang, B.; Fischer, K.; Janshoff, A.; Schmidt, M. Macromol. Rapid Commun. 2008, 29, 821-825). Herein, we have systematically investigated the influence of surfactant, salt, and pH on the supramolecular structure formation. The cylindrical brush polymers and their complexes with surfactants were directly visualized by atomic force microscopy in air and in aqueous solution. The alkyl chain length (measured by the carbon number, n) of the surfactant plays a key role. While helical structures were formed with n=10, 11, and 12, no helices were observed with n<10 and n>13. Addition of salt destroys the helical structures as do pH conditions below 4 and above 6, most probably because the polymer-surfactant complexes start to disintegrate. Circular dichroism was utilized to monitor the PLL side chain conformation and clearly revealed that beta-sheet formation of the side chains induces the helical conformation of the atactic main chain. PMID:19326944
The Effect of Multiple Formats on Understanding Complex Visual Displays
NSDL National Science Digital Library
Holly Taylor
Students in introductory science courses frequently have difficulty comprehending complex graphics such as contour maps. Computer-assisted instruction (CAI), because of its ability to convey the same information in different formats, may help students gain necessary graphic interpretation skills. This article describes a research project in which students practiced reading two temperature maps in either a standard black and white contour or a color-enhanced contour format. They were then divided into groups and tested using only standard contour maps. The tests examined comprehension of the distribution of sea surface temperature, oceanographic phosphate concentration, and brain activation. Results suggest that having students practice with differently formatted maps of the same information improves later comprehension of standard contour maps.
Revised coordination model and stability constants of Cu(II) complexes of tris buffer.
Nagaj, Justyna; Stokowa-So?tys, Kamila; Kurowska, Ewa; Fr?czyk, Tomasz; Je?owska-Bojczuk, Ma?gorzata; Bal, Wojciech
2-Amino-2-hydroxymethyl-propane-1,3-diol, or tris(hydroxymethyl)aminomethane (Tris), is probably the most common biochemical buffer used alone or in combination with other buffers because it is stable, unreactive, and compatible with most proteins and other biomolecules. Being nontoxic, it has even found applications in medicine. Tris is known, however, to coordinate transition metal ions, Cu(II) among them. Although often ignored, this feature affects interactions of Cu(II) ions with biomolecules, as Tris is usually used in high molar excess. Therefore, it is important to have precise knowledge on the stoichiometry, stability, and reactivity of cupric Tris complexes. The literature data are incoherent in this respect. We reinvestigated the complex formation in the Tris-Cu(II) system by potentiometry, UV-vis, ESI-MS, and EPR at a broad range of concentrations and ratios. We found, contrary to several previous papers, that the maximum stoichiometry of Tris to Cu(II) is 2 and at neutral pH, dimeric complexes are formed. The apparent affinity of Tris buffer for Cu(II), determined by the competitivity index (CI) approach [Kr??el, A.; Wójcik, J.; Maciejczyk, M.; Bal, W. Chem. Commun. 2003, 6, 704-705] at pH 7.4 varies between 2 × 10(6) and 4 × 10(4) M(-1), depending on the Tris and Cu(II) concentrations and molar ratio. PMID:24304384
Discrete site surface complexation constants for lanthanide adsorption to bacteria as determined by experiments and linear free energy relationships.
Ngwenya, Bryne T; Magennis, Marisa; Olive, Valerie; Mosselmans, J Fred W; Ellam, Robert M
Bacteria are abundant in many natural and engineered environments where they are thought to exert important controls on the cycling, mobility, bioavailability, and toxicity of metal contaminants. In order to probe their role in moderating the behavior of lanthanides, pH-dependent adsorption edges of 13 individual lanthanides and yttrium to the Gram-negative bacterium Pantoea agglomerans were used to generate discrete site surface complexation constants. The calculated surface complexation constants were compared with stability constants estimated using linear free energy relationships based on a number of hydroxyl-containing ligands. The experimental data suggests that lanthanide adsorption edges below pH 6.5 are consistent with adsorption to phosphate groups for the light and some of the middle lanthanides (La to Gd), whereas some of the middle and heavy lanthanides appear to favor carboxyl co-ordination (Tb to Yb), although exceptions occur in each grouping. The experimentally derived surface complexation constants for carboxyl coordination were of similar magnitude to stability constants estimated from linear free energy correlations using fulvic acid stability constants. The implication is that the adsorption of lanthanides to bacterial surfaces could be modeled reasonably well using lanthanide stability constants for natural organic matter, except perhaps at low pH where phosphate binding dominates. PMID:20000843
Thermodynamic parameters and stability constants of some tervalent lanthanide complexes of 1-(3-aryl-5-hydroxy 4-isoxazolylazo) 4-sulphonic acids
Ch. Nagarjun Rao; K. C. Rajanna; Y. Uma Devi; V. Surender Rao; P. K. Saiprakash
The stability constants of some tervalent lanthanide chelates of 1-(3-aryl-5-hydroxy 4-isoxazolylazo) 4-sulphonic acid (PHI-4S)\\u000a and its substituents have been carried out by potentiometric and spectrophotometric methods. The results indicated the formation\\u000a of 1:1 and 1:2 complexes with an order: Yb(III) > Y(III) > Gd(III) > Dy(III) > Tb(III) > Sm(III) > Nd(III) > Pr(III) > La(III).\\u000a The stabilities increase with
Formation of polyelectrolyte complexes with diethylaminoethyl dextran: charge ratio and molar mass effect.
Le Cerf, Didier; Pepin, Anne Sophie; Niang, Pape Momar; Cristea, Mariana; Karakasyan-Dia, Carole; Picton, Luc
The formation of polyelectrolyte complexes (PECs) between carboxymethyl pullulan and DEAE Dextran, was investigated, in dilute solution, with emphasis on the effect of charge density (molar ratio or pH) and molar masses. Electrophoretic mobility measurements have evidenced that insoluble PECs (neutral electrophoretic mobility) occurs for charge ratio between 0.6 (excess of polycation) and 1 (stoichiometry usual value) according to the pH. This atypical result is explained by the inaccessibility of some permanent cationic charge when screened by pH dependant cationic ones (due to the Hoffman alkylation). Isothermal titration calorimetry (ITC) indicates an endothermic formation of PEC with a binding constant around 10(5) L mol(-1). Finally asymmetrical flow field flow fractionation coupled on line with static multi angle light scattering (AF4/MALS) evidences soluble PECs with very large average molar masses and size around 100 nm, in agreement with scrambled eggs multi-association between various polyelectrolyte chains. PMID:25256478
The ribosome-associated complex antagonizes prion formation in yeast.
Amor, Alvaro J; Castanzo, Dominic T; Delany, Sean P; Selechnik, Daniel M; van Ooy, Alex; Cameron, Dale M
The number of known fungal proteins capable of switching between alternative stable conformations is steadily increasing, suggesting that a prion-like mechanism may be broadly utilized as a means to propagate altered cellular states. To gain insight into the mechanisms by which cells regulate prion formation and toxicity we examined the role of the yeast ribosome-associated complex (RAC) in modulating both the formation of the [PSI(+)] prion - an alternative conformer of Sup35 protein - and the toxicity of aggregation-prone polypeptides. The Hsp40 RAC chaperone Zuo1 anchors the RAC to ribosomes and stimulates the ATPase activity of the Hsp70 chaperone Ssb. We found that cells lacking Zuo1 are sensitive to over-expression of some aggregation-prone proteins, including the Sup35 prion domain, suggesting that co-translational protein misfolding increases in ?zuo1 strains. Consistent with this finding, ?zuo1 cells exhibit higher frequencies of spontaneous and induced prion formation. Cells expressing mutant forms of Zuo1 lacking either a C-terminal charged region required for ribosome association, or the J-domain responsible for Ssb ATPase stimulation, exhibit similarly high frequencies of prion formation. Our findings are consistent with a role for the RAC in chaperoning nascent Sup35 to regulate folding of the N-terminal prion domain as it emerges from the ribosome. PMID:25739058
GABAergic complex basket formations in the human neocortex.
Blazquez-Llorca, Lidia; García-Marín, Virginia; DeFelipe, Javier
Certain GABAergic interneurons in the cerebral cortex, basket cells, establish multiple connections with cell bodies that typically outline the somata and proximal dendrites of pyramidal cells. During studies into the distribution of the vesicular GABA transporter (VGAT) in the human cerebral cortex, we were struck by the presence of a very dense, pericellular arrangement of multiple VGAT-immunoreactive (-ir) terminals in certain cortical areas. We called these terminals "Complex basket formations" (Cbk-formations) to distinguish them from the simpler and more typical pericellular GABAergic innervations of most cortical neurons. Here we examined the distribution of these VGAT-ir Cbk-formations in various cortical areas, including the somatosensory (area 3b), visual (areas 17 and 18), motor (area 4), associative frontal (dorsolateral areas 9, 10, 45, 46, and orbital areas 11, 12, 13, 14, 47), associative temporal (areas 20, 21, 22, and 38), and limbic cingulate areas (areas 24, 32). Furthermore, we used dual or triple staining techniques to study the chemical nature of the innervated cells. We found that VGAT-ir Cbk-formations were most frequently found in area 4 followed by areas 3b, 13, and 18. In addition, they were mostly observed in layer III, except in area 17, where they were most dense in layer IV. We also found that 70% of the innervated neurons were pyramidal cells, while the remaining 30% were multipolar cells. Most of these multipolar cells expressed the calcium-binding protein parvalbumin and the lectin Vicia villosa agglutinin. PMID:21031559
Factor Xa dimerization competes with prothrombinase complex formation on platelet-like membrane surfaces.
Koklic, Tilen; Chattopadhyay, Rima; Majumder, Rinku; Lentz, Barry R
Exposure of phosphatidylserine (PS) molecules on activated platelet membrane surface is a crucial event in blood coagulation. Binding of PS to specific sites on factor Xa (fXa) and factor Va (fVa) promotes their assembly into a complex that enhances proteolysis of prothrombin by approximately 10?. Recent studies demonstrate that both soluble PS and PS-containing model membranes promote formation of inactive fXa dimers at 5 mM Ca²?. In the present study, we show how competition between fXa dimerization and prothrombinase formation depends on Ca²? and lipid membrane concentrations. We used homo-FRET measurements between fluorescein-E-G-R-chloromethylketone (CK)-Xa [fXa irreversibly inactivated by alkylation of the active site histidine residue with FEGR (FEGR-fXa)] and prothrombinase activity measurements to reveal the balance between fXa dimer formation and fXa-fVa complex formation. Changes in FEGR-fXa dimer homo-FRET with addition of fVa to model-membrane-bound FEGR-fXa unambiguously demonstrated that formation of the FEGR-fXa-fVa complex dissociated the dimer. Quantitative global analysis according to a model for protein interaction equilibria on a surface provided an estimate of a surface constant for fXa dimer dissociation (K(fXa×fXa)(d, ?)) approximately 10-fold lower than K(fXa×fVa)(d,?) for fXa-fVa complex. Experiments performed using activated platelet-derived microparticles (MPs) showed that competition between fXa dimerization and fXa-fVa complex formation was even more prominent on MPs. In summary, at Ca²? concentrations found in the maturing platelet plug (2-5 mM), fVa can compete fXa off of inactive fXa dimers to significantly amplify thrombin production, both because it releases dimer inhibition and because of its well-known cofactor activity. This suggests a hitherto unanticipated mechanism by which PS-exposing platelet membranes can regulate amplification and propagation of blood coagulation. PMID:25572019
Ion wake formation with dust charge fluctuation in complex plasma
Bhattacharjee, Saurav; Das, Nilakshi [Department of Physics, Tezpur University, Tezpur, Assam, 784 028 (India)] [Department of Physics, Tezpur University, Tezpur, Assam, 784 028 (India)
In complex plasma, the interaction mechanism among dust grains near the plasma sheath is significantly influenced by the downward ion flow towards the sheath and dust charge fluctuation over grain surface. Asymmetric ion flow towards the sheath gives rise to well known attractive wake potential in addition to repulsive Yukawa type of potential. The present work shows that the charging dynamics play a significant role in modification of plasma dielectric response function and hence the interaction mechanism among test dust particulates. The effective Debye length is found to be a characteristic of dust size and background plasma response towards the grain along with ion flow speed. The potentials thus obtained show a damping in strength of interaction in the presence of dynamical charging of dust as compared to that of constant charge dust grains. The result also shows decrease in focal length of ion lensing with increase in grain size.
Microcalorimetric determination of thermodynamic parameters for ionophore-siderophore host-guest complex formation.
Trzaska, S M; Toone, E J; Crumbliss, A L
Thermodynamic parameters (delta H, delta S, and delta G) were determined by microcalorimetry in wet chloroform for host-guest assembly formation involving second-sphere complexation of the siderophore ferrioxamine B by crown ether (18-crown-6, cis-dicyclohexano-18-crown-6, benzo-18-crown-6) and cryptand (2.2.2 cryptand) hosts. Similar data were also collected for the same hosts with the pentylammonium ion guest, which corresponds to the pendant pentylamine side chain of ferroxamine B. Host-guest assembly formation constants (Ka) obtained from microcalorimetry agree with values obtained indirectly from chloroform/water extraction studies in those cases where comparable data are available. On the basis of a trend established by the pentylammonium guest, an enhanced stability relative to the crown ethers is observed for the assembly composed of ferrioxamine B and 2.2.2 cryptand that is due to entropic effects. Trends in delta H and delta S with changes in host and guest structure are discussed and attributed directly to host-guest complex formation, as solvation effects were determined to be insignificant (delta Cp = 0). PMID:12526393
Simulation of Titan haze formation using a photochemical flow reactor. The optical constants of the polymer
NASA Astrophysics Data System (ADS)
Tran, Buu N.; Joseph, Jeffrey C.; Ferris, James P.; Persans, Peter D.; Chera, John J.
Solar UV is the principal energy source impinging the atmosphere of Titan while the energy from the electrons in Saturn's magnetosphere is less than 0.5% of the UV light. Titan haze analogs were prepared by the photolysis of a mixture of gases that simulate the composition of its atmosphere (nitrogen, methane, hydrogen, acetylene, ethylene, and cyanoacetylene). The real (n) and imaginary (k) parts of the complex refractive index of haze analogs formed from four different gas mixtures were calculated from the spectral properties of the solid polymer in UV-visible, near infrared and infrared wavelength spectral regions. The value of n was constant at 1.6±0.1 throughout the 0.2-2.5 ?m region. The variation of k with wavelength for the values derived for Titan has a lower error than the absolute values of k so the more significant comparisons are with the slopes of the k( ?) plots in the UV-VIS region. Three of the photochemical Titan haze analogs had slopes comparable to those derived for Titan from the Voyager data (Rages and Pollack, 1980, Icarus 41, 119-130; McKay and Toon, 1992, in: Proceedings of the Symposium on Titan, in: ESA SP, Vol. 338, pp. 185-190). The slopes of the k( ?) plots for haze analogs prepared by spark discharge (Khare et al., 1984, Icarus 60, 127-137) and plasma discharge (Ramirez et al., 2002, Icarus 156, 515-529) were also comparable to Titan's. These finding show that the k( ?) plots do not differentiate between different laboratory simulations of atmospheric chemistry on Titan in the UV-VIS near IR region (0.2-2.5 microns). There is a large difference between the k( ?) in the infrared between the haze analogs prepared photochemically and analogs prepared using a plasma discharges (Khare et al., 1984, Icarus 60, 127-137; Coll et al., 1999, Planet. Space Sci. 47, 1331-1340; Khare et al., 2002, Icarus 160, 172-182). The C/N ratio in the haze analog prepared by discharges is in the 2-11 range while that of the photochemical analogs is in the 18-24 range. The use of discharges and UV light for initiating the chemistry in Titan's atmosphere is discussed.
Interference-mediated synaptonemal complex formation with embedded crossover designation
Zhang, Liangran; Espagne, Eric; de Muyt, Arnaud; Zickler, Denise; Kleckner, Nancy E.
Biological systems exhibit complex patterns at length scales ranging from the molecular to the organismic. Along chromosomes, events often occur stochastically at different positions in different nuclei but nonetheless tend to be relatively evenly spaced. Examples include replication origin firings, formation of chromatin loops along chromosome axes and, during meiosis, localization of crossover recombination sites ("crossover interference"). We present evidence in the fungus Sordaria macrospora that crossover interference is part of a broader pattern that includes synaptonemal complex (SC) nucleation. This pattern comprises relatively evenly spaced SC nucleation sites, among which a subset are crossover sites that show a classical interference distribution. This pattern ensures that SC forms regularly along the entire length of the chromosome as required for the maintenance of homolog pairing while concomitantly having crossover interactions locally embedded within the SC structure as required for both DNA recombination and structural events of chiasma formation. This pattern can be explained by a threshold-based designation and spreading interference process. This model can be generalized to give diverse types of related and/or partially overlapping patterns, in two or more dimensions, for any type of object. PMID:25380597
Incipient species formation in salamanders of the Ensatina?complex
Wake, David B.
The Ensatina eschscholtzii complex of plethodontid salamanders, a well-known "ring species," is thought to illustrate stages in the speciation process. Early research, based on morphology and coloration, has been extended by the incorporation of studies of protein variation and mitochondrial DNA sequences. The new data show that the complex includes a number of geographically and genetically distinct components that are at or near the species level. The complex is old and apparently has undergone instances of range contraction, isolation, differentiation, and then expansion and secondary contact. While the hypothesis that speciation is retarded by gene flow around the ring is not supported by molecular data, the general biogeographical hypothesis is supported. There is evidence of a north to south range expansion along two axes, with secondary contact and completion of the ring in southern California. Current research targets regions once thought to show primary intergradation, but which molecular markers reveal to be zones of secondary contact. Here emphasis is on the subspecies E. e. xanthoptica, which is involved in four distinct secondary contacts in central California. There is evidence of renewed genetic interactions upon recontact, with greater genetic differentiation within xanthoptica than between it and some of the interacting populations. The complex presents a full array of intermediate conditions between well-marked species and geographically variable populations. Geographically differentiated segments represent a diversity of depths of time of isolation and admixture, reflecting the complicated geomorphological history of California. Ensatina illustrates the continuing difficulty in making taxonomic assignments in complexes studied during species formation. PMID:9223261
Thermodynamic study of complex formation between Ce3+ and cryptand 222 in some binary mixed nonaqueous solvents
NASA Astrophysics Data System (ADS)
Rounaghi, G. H.; Dolatshahi, S.; Tarahomi, S.
The stoichiometry, stability and the thermodynamic parameters of complex formation between cerium(III) cation and cryptand 222 (4,7,13,16,21,24-hexaoxa-1,10-diazabycyclo[8.8.8]-hexacosane) were studied by conductometric titration method in some binary solvent mixtures of dimethylformamide (DMF), 1,2-dichloroethane (DCE), ethyl acetate (EtOAc) and methyl acetate (MeOAc) with methanol (MeOH), at 288, 298, 308, and 318 K. A model based on 1: 1 stoichiometry has been used to analyze the conductivity data. The data have been fitted according to a non-linear least-squares analysis that provide the stability constant, K f, for the cation-ligand inclusion complex. The results revealed that the stability order of [Ce(cryptand 222)]3+ complex changes with the nature and composition of the solvent system. A non-linear relationship was observed between the stability constant (log K f) of [Ce(cryptand 222)]3+ complex versus the composition of the binary mixed solvent. Standard thermodynamic values were obtained from temperature dependence of the stability constant of the complex, show that the studied complexation process is mainly entropy governed and are influenced by the nature and composition of the binary mixed solvent solutions.
Ion-Selective Electrodes with Unusual Response Functions: Simultaneous Formation of Ionophore–Primary Ion Complexes with Different Stoichiometries
Miyake, Masafumi; Chen, Li D.; Pozzi, Gianluca; Bühlmann, Philippe
It is well known that the selectivity of an ion-selective electrode (ISE) depends on the stoichiometry of the complexes between its ionophore and the target and interfering ions. It is all the more surprising that the possibility for the simultaneous occurrence of multiple target ion complexes with different complex stoichiometries was mostly ignored in the past. Here we report on the simultaneous formation of 1:1 and 1:2 complexes of a fluorophilic crown ether in fluorous ISE membranes, and how this results in what look like super-Nernstian responses. These increased response slopes are not caused by mass transfer limitations and can be readily explained with a phase boundary model, a finding that is supported by experimentally determined complex formation constants and excellent fits of response curves. Not only Cs+ but also the smaller ions Li+, Na+, K+, and NH4+ form 1:1 and 1:2 complexes with the fluorophilic crown ether, with cumulative formation constants of up to 1015.0 and 1021.0 for of the 1:1 and 1:2 complexes, respectively. Super-Nernstian responses of the type observed with these electrodes are probably not particularly rare, but lacking in the past an adequate discussion in the literature remained ignored or misinterpreted. Preliminary calculations also predict sub-Nernstian responses and potential dips of a similar origin. The proper understanding of such phenomena will facilitate the development of new ISEs based on ionophores that form complexes of higher stoichiometries. PMID:22128799
Estimation of the initial equilibrium constants in the formation of tetragonal lysozyme nuclei
NASA Technical Reports Server (NTRS)
Pusey, Marc L.
Results are presented from a study of the equilibria, kinetic rates, and the aggregation pathway which leads from a lysozyme monomer crystal to a tetragonal crystal, using dialyzed and recrystallized commercial hen eggwhite lysozyme. Relative light scattering intensity measurements were used to estimate the initial equilibrium constants for undersaturated lysozyme solutions in the tetragonal regime. The K1 value was estimated to be (1-3) x 10 exp 4 L/mol. Estimates of subsequent equilibrium constants depend on the crystal aggregation model chosen or determined. Experimental data suggest that tetragonal lysozyme crystal grows by addition of aggregates preformed in the bulk solution, rather than by monomer addition.
Micelle formation of coenzyme Q10 with dipotassium glycyrrhizate using inclusion complex of coenzyme Q10 with ?-cyclodextrin.
Uekaji, Yukiko; Onishi, Mayu; Nakata, Daisuke; Terao, Keiji; Paananen, Arja; Partanen, Riitta; Yoshii, Hidefumi
Micelles can be formed from coenzyme Q10 (CoQ10) and dipotassium glycyrrhizate (GZK2) by using an inclusion complex of CoQ10 with ?-cyclodextrin (?-CD). The mechanism of micelle formation was kinetically investigated. Adding GZK2 to a supersaturated solution of the CoQ10/?-CD inclusion complex led to a linear increase in the solubility of CoQ10 due to the formation of micelles of CoQ10 when the molar ratio of GZK2/?-CD increased to ?1.6, after which the concentration remained constant. The equilibrium constant K for micelle formation was 0.68 (-) and the ratio of GZK2 to CoQ10 was 1. These results suggest that the formation of CoQ10 micelles with GZK2 might proceed via the displacement of CoQ10 by GZK2 in the ?-CD cavity followed by the formation of CoQ10 micelles. PMID:25187379
Physical volcanology of the Gubisa Formation, Kone Volcanic Complex, Ethiopia
NASA Astrophysics Data System (ADS)
Rampey, Michael L.; Oppenheimer, Clive; Pyle, David M.; Yirgu, Gezahegn
Despite their significance for understanding the potential environmental factors involved in hominin evolution in Ethiopia, very few modern volcanologic studies have been carried out on the Quaternary calderas and associated silicic tephra deposits of the Ethiopian Rift. We present here the second of a set of papers reporting the findings of fieldwork and laboratory analyses of one of the largest of these structures, Kone Caldera, located within the Kone Volcanic Complex in the northern Main Ethiopian Rift. The most recent major episode of explosive eruptive activity at Kone Caldera was apparently associated with formation of part of the overall 8-km-diameter collapse area, and deposited a widely-dispersed alkali rhyolite tephra that reaches a thickness of up to 60 m in vent-proximal deposits. We report here the physical characteristics of this unit in order to constrain eruptive conditions. The pumice fall deposit suggests that an abrupt decrease in magma discharge rate occurred part way through the eruption.
Single Nucleoprotein Residue Modulates Arenavirus Replication Complex Formation
Knopp, Kristeene A.; Ngo, Tuan; Gershon, Paul D.
ABSTRACT The Arenaviridae are enveloped, negative-sense RNA viruses with several family members that cause hemorrhagic fevers. This work provides immunofluorescence evidence that, unlike those of New World arenaviruses, the replication and transcription complexes (RTC) of lymphocytic choriomeningitis virus (LCMV) colocalize with eukaryotic initiation factor 4E (eIF4E) and that eIF4E may participate in the translation of LCMV mRNA. Additionally, we identify two residues in the LCMV nucleoprotein (NP) that are conserved in every mammalian arenavirus and are required for recombinant LCMV recovery. One of these sites, Y125, was confirmed to be phosphorylated by using liquid chromatography-tandem mass spectrometry (LC-MS/MS). NP Y125 is located in the N-terminal region of NP that is disordered when RNA is bound. The other site, NP T206, was predicted to be a phosphorylation site. Immunofluorescence analysis demonstrated that NP T206 is required for the formation of the punctate RTC that are typically observed during LCMV infection. A minigenome reporter assay using NP mutants, as well as Northern blot analysis, demonstrated that although NP T206A does not form punctate RTC, it can transcribe and replicate a minigenome. However, in the presence of matrix protein (Z) and glycoprotein (GP), translation of the minigenome message with NP T206A was inhibited, suggesting that punctate RTC formation is required to regulate viral replication. Together, these results highlight a significant difference between New and Old World arenaviruses and demonstrate the importance of RTC formation and translation priming in RTC for Old World arenaviruses. PMID:25922393
Superoxide-mediated Fe(II) formation from organically complexed Fe(III) in coastal waters
NASA Astrophysics Data System (ADS)
Fujii, Manabu; Ito, Hiroaki; Rose, Andrew L.; Waite, T. David; Omura, Tatsuo
Fe(III) complexed by organic ligands (Fe(III)L) is the primary form of dissolved Fe in marine and coastal environments. Superoxide, typically produced in biological and photochemical processes, is one of the reducing agents that contributes to transformation of Fe(III)L to bioavailable, free dissolved Fe(II) (Fe(II)'). In this work, the kinetics of superoxide-mediated Fe(II)' formation from Fe(III)L in a simulated coastal water system were investigated and a comprehensive kinetic model was developed using citrate and fulvic acid as exemplar Fe-binding ligands. To simulate a coastal environment in laboratory experiments, Fe(III)L samples with various ligand/Fe ratios were incubated for 5 min to 1 week in seawater medium. At each ratio and incubation time, the rate of superoxide-mediated Fe(II)' formation was determined in the presence of the strong Fe(II) binding ligand ferrozine by spectrophotometrically measuring the ferrous-ferrozine complex generated at a constant concentration of superoxide. The Fe(II)' formation rate generally decreased with incubation time, as Fe(III)L gradually dissociated to form less reactive Fe(III) oxyhydroxide. However, when the ligand/Fe ratio was sufficiently high, the dissociation of Fe(III)L (and subsequent Fe precipitation) was suppressed and Fe(II)' was formed at a higher rate. The rate of Fe(II)' produced during the experiment was explained by the kinetic model. The model confirmed that both the ligand/Fe ratio and incubation time have a significant effect on the pathway via which Fe(II)' is formed from Fe(III)-fulvic acid complexes.
Viswanath's constant Mills' constant
Do, Norman
Viswanath's constant Mills' constant Conway's constant Constant Curiosity Norman Do Not all numbers Constant Curiosity #12;Viswanath's constant Mills' constant Conway's constant The Fibonacci sequence, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, . . . Norman Do Constant Curiosity #12;Viswanath
Modelling formation of complex topography by the seagrass Posidonia oceanica
NASA Astrophysics Data System (ADS)
Kendrick, Gary A.; Marbà, Núria; Duarte, Carlos M.
Posidonia oceanica is a slow growing seagrass species that extends via growing rhizomes that grow only centimetres both horizontally and vertically each year. Posidonia oceanica forms topographically complex biogenic reefs of dead rhizome and sediments that are up to 4 m in height that are called "matte". This study investigates the role of slow horizontal and vertical growth of rhizomes in the formation of topographic complexity in P. oceanica matte using agent-based modelling. The simulated infilling of landscapes by P. oceanica was run over 600 iterations (years) for 10 random starts of 150 agents each. Initial infilling rates were very slow and P. oceanica had limited cover after a century of growth. Growth accelerated after 100 years but plateaued after 400 years such that after 600 years only two-thirds of the landscape was occupied by P. oceanica. The pattern of spread of agents was initially random in direction but after larger patches were formed spread was radial from these patches. The seagrass landscape was initially highly fragmented with many small separate patches made up of a few agents each, with a Landscape Division index close to 1. Between 300 and 600 years Landscape Division declined sharply to 0.42, indicating patches had coalesced into larger more continuous meadows forming a less fragmented landscape. Perimeter to area ratio of seagrass patches declined exponentially from >1 to approximately 0.2 over 600 years of simulation. The matte developed from growth of patches and its greatest height occurred in more continuously occupied cells of the grid. The topography of the reef that occupied two-thirds of the landscape after six centuries of growth could be described as a pattern of channels between reef plateaus elevated 1-2 m above channels. These results demonstrate that development in P. oceanica meadows of three-dimensional structure, in the formation of biogenic reefs, can be explained by, and is an emergent property of, slow horizontal and vertical rhizome growth rates combined with the time it takes for the accumulation of rhizomes in any region of the landscape. As such, the model provides a parsimonious explanation for the development of complex matte topography.
Stability constants of copper(II) mixed complexes with some 4-quinolone antibiotics and (N-N) donors.
Mendoza-Díaz, G; Perez-Alonso, R; Moreno-Esparza, R
Studies of complexation equilibria of the antibiotic anions nalidixate and cinoxacinate with [Cu(phen)]2+ and [Cu(bipy)]2+ are reported. These studies indicate that the stability of this type of complex is strongly related to the metal environment. A correlation between the stability constants, determined here, with the sigma donation character of the ligand is proposed. This study shows that the stability constant for the reaction between the quinolones and the moiety [Cu(N-N)]2+ is dependent on the coordinate diamine to the metal ion. This is in agreement with previous studies where other physical properties as their electronic absorption spectra in the visible region, display similar behavior. These results suggest that inside the living cells, a possible interaction with some metal ion will be strongly controlled by the type of ligand bound to the cation. PMID:8893520
Silver(I) Complex formation with Cysteine, Penicillamine and Glutathione
Leung, Bonnie O.; Jalilehvand, Farideh; Mah, Vicky; Parvez, Masood; Wu, Qiao
The complex formation between silver(I) and cysteine (H2Cys), penicillamine (H2Pen) or glutathione (H3Glu) in alkaline aqueous solution was examined using extended X-ray absorption fine structure (EXAFS) and 109Ag NMR spectroscopic techniques. The complexes formed in 0.1 mol·dm?3 Ag(I) solutions with cysteine and penicillamine were investigated for ligand/Ag(I) (L/Ag) mole ratios increasing from 2.0 to 10.0. For the series of cysteine solutions (pH 10 - 11) a mean Ag-S bond distance 2.45 ± 0.02 Å consistently emerged, while for penicillamine (pH 9) the average Ag-S bond distance gradually increased from 2.40 to 2.44 ± 0.02 Å. EXAFS and 109Ag NMR spectra of a concentrated Ag(I)-cysteine solution (CAg(I) = 0.8 mol·dm?3, L/Ag = 2.2) showed the mean Ag-S bond distance 2.47 ± 0.02 Å and ?(109Ag) = 1103 ppm, consistent with prevailing, partially oligomeric AgS3 coordinated species, while for penicillamine (CAg(I) = 0.5 mol·dm?3, L/Ag = 2.0) the mean Ag-S bond distance 2.40 ± 0.02 Å and ?(109Ag) = 922 ppm indicate that mononuclear AgS2 coordinated complexes dominate. For Ag(I)-glutathione solutions (CAg(I) = 0.01 mol·dm?3, pH ~ 11), mononuclear AgS2 coordinated species with the mean Ag-S bond distance 2.36 ± 0.02 Å dominate for L/Ag mole ratios from 2.0 to 10.0. The crystal structure of the silver(I)-cysteine compound (NH4)Ag2(HCys)(Cys)·H2O (1) precipitating at pH ~ 10 was solved and showed a layer structure with both AgS3 and AgS3N coordination to the cysteinate ligands. A redetermination of the crystal structure of Ag(HPen)·H2O (2) confirmed the proposed digonal AgS2 coordination environment to bridging thiolate sulfur atoms in polymeric intertwining chains forming a double helix. A survey of Ag-S bond distances for crystalline Ag(I) complexes with S-donor ligands in different AgS2, AgS2(O/N) and AgS3 coordination environments was used, together with a survey of 109Ag NMR chemical shifts, to assist assignments of the Ag(I) coordination in solution. PMID:23556419
Dioxygen complexes of 3d transition-metal atoms: Formation reactions in the gas phase
Brown, C.E.; Mitchell, S.A.; Hackett, P.A. (National Research Council of Canada, Ottawa, Ontario (Canada))
Reactions of ground-state 3d transition-metal atoms including Ti, Mn, Co, Ni, and Cu with molecular oxygen in Ar buffer gas have been investigated in the pressure range 5-700 Torr at 296 K. Attention has been given to termolecular association reactions in which mono(dioxygen) complexes are formed. A pulsed laser photolysis-laser fluorescence technique is used where metal atoms are produced by visible multiphoton dissociation of a volatile organometallic precursor in a static pressure reaction cell, and reactions of metal atoms are monitored by resonance fluorescence excitation at variable time delay following the photolysis pulse. The present study completes a survey of the reactions of 3d transition-metal atoms with O{sub 2} under room temperature conditions, from which it emerges that reactivity with respect to complex formation is correlated with a d{sub n}s{sup 1} valence electron configuration of the metal atoms. Simplified RRKM calculations have been used to interpret termolecular rate constants for the association reactions in terms of a trend in the binding energies of the dioxygen complexes.
Formation of ZnO at zinc oxidation by near- and supercritical water under the constant electric field
NASA Astrophysics Data System (ADS)
Shishkin, A. V.; Sokol, M. Ya.; Shatrova, A. V.; Fedyaeva, O. N.; Vostrikov, A. A.
The work has detected an influence of a constant electric field (up to E = 300 kV/m) on the structure of a nanocrystalline layer of zinc oxide, formed on the surface of a planar zinc anode in water under supercritical (673 K and 23 MPa) and near-critical (673 K and 17. 5 MPa) conditions. The effect of an increase of zinc oxidation rate with an increase in E is observed under supercritical conditions and is absent at near-critical ones. Increase in the field strength leads to the formation of a looser structure in the inner part of the zinc oxide layer.
Absorption spectrometric study of charge transfer complex formation between 4-acetamidophenol (paracetamol) and a series of quinones including Vitamin K 3
NASA Astrophysics Data System (ADS)
Saha, Avijit; Mukherjee, Asok K.
The formation of charge transfer (CT) complexes of 4-acetamidophenol (commonly called 'paracetamol') and a series of quinones (including Vitamin K 3) has been studied spectrophotometrically in ethanol medium. The vertical ionisation potential of paracetamol and the degrees of charge transfer of the complexes in their ground state has been estimated from the trends in the charge transfer bands. The oscillator and transition dipole strengths of the complexes have been determined from the CT absorption spectra at 298 K. The complexes have been found by Job's method of continuous variation to have the uncommon 2:1 (paracetamol:quinone) stoichiometry in each case. The enthalpies and entropies of formation of the complexes have been obtained by determining their formation constants at five different temperatures.
Sub-THz complex dielectric constants of montmorillionite clay thin samples with Na$^{+}$/Ca$^{++}$-ions
Rezwanur Rahman; Douglas K. McCarty; Manika Prasad; John A. Scales
We implement a technique to characterize electromagnetic properties at frequencies 100 to 165 GHz (3 cm$^{-1}$ to 4.95 cm$^{-1}$) of oriented montmorillionite samples using an open cavity resonator connected to a sub-millimeter wave VNA (Vector Network Analyzer). We measured dielectric constants perpendicular to the bedding plane on oriented Na$^{+}$ and Ca$^{++}$-ion stabilized montmorillionite samples deposited on a glass slide at ambient laboratory conditions (room temperature and room light). The clay layer is much thinner ($\\sim$ 30 $\\mu$m) than the glass substrate ($\\sim$ 2.18 mm). The real part of dielectric constant,$\\epsilon_{re}$, is essentially constant over this frequency range but is larger in Na$^{+}$- than in Ca$^{++}$-ioned clay. The total electrical conductivity (associated with the imaginary part of dielectric constant, $\\epsilon_{im}$) of both samples increases monotonically at lower frequencies ($$ 110 GHz. The dispersion of the samples display a dependence on the ionic strength in the clay interlayers, i.e., $\\zeta$-potential in the Stern layers.
Measurements of the complex dielectric constant of volcanic ash from 4 to 19 GHz
Perger, Warren F.
requires a dielectric constant of a solid rock equivalent of a dilute vol- canic ash suspended in air (in of volcanic ash in a shorted waveg- uide. The standing wave which results will have its nulls shifted, which. The ratio of the maximum electric field to the minimum (the standing wave ratio) will decrease as a result
Integrin activation and focal complex formation in cardiac hypertrophy
NASA Technical Reports Server (NTRS)
Laser, M.; Willey, C. D.; Jiang, W.; Cooper, G. 4th; Menick, D. R.; Zile, M. R.; Kuppuswamy, D.
Cardiac hypertrophy is characterized by both remodeling of the extracellular matrix (ECM) and hypertrophic growth of the cardiocytes. Here we show increased expression and cytoskeletal association of the ECM proteins fibronectin and vitronectin in pressure-overloaded feline myocardium. These changes are accompanied by cytoskeletal binding and phosphorylation of focal adhesion kinase (FAK) at Tyr-397 and Tyr-925, c-Src at Tyr-416, recruitment of the adapter proteins p130(Cas), Shc, and Nck, and activation of the extracellular-regulated kinases ERK1/2. A synthetic peptide containing the Arg-Gly-Asp (RGD) motif of fibronectin and vitronectin was used to stimulate adult feline cardiomyocytes cultured on laminin or within a type-I collagen matrix. Whereas cardiocytes under both conditions showed RGD-stimulated ERK1/2 activation, only collagen-embedded cells exhibited cytoskeletal assembly of FAK, c-Src, Nck, and Shc. In RGD-stimulated collagen-embedded cells, FAK was phosphorylated only at Tyr-397 and c-Src association occurred without Tyr-416 phosphorylation and p130(Cas) association. Therefore, c-Src activation is not required for its cytoskeletal binding but may be important for additional phosphorylation of FAK. Overall, our study suggests that multiple signaling pathways originate in pressure-overloaded heart following integrin engagement with ECM proteins, including focal complex formation and ERK1/2 activation, and many of these pathways can be activated in cardiomyocytes via RGD-stimulated integrin activation.
Adhesion and formation of microbial biofilms in complex microfluidic devices
Kumar, Aloke [ORNL; Karig, David K [ORNL; Neethirajan, Suresh [University of Guelph; Suresh, Anil K [ORNL; Srijanto, Bernadeta R [ORNL; Mukherjee, Partha P [ORNL; Retterer, Scott T [ORNL; Doktycz, Mitchel John [ORNL
Shewanella oneidensis is a metal reducing bacterium, which is of interest for bioremediation and clean energy applications. S. oneidensis biofilms play a critical role in several situations such as in microbial energy harvesting devices. Here, we use a microfluidic device to quantify the effects of hydrodynamics on the biofilm morphology of S. oneidensis. For different rates of fluid flow through a complex microfluidic device, we studied the spatiotemporal dynamics of biofilms, and we quantified several morphological features such as spatial distribution, cluster formation and surface coverage. We found that hydrodynamics resulted in significant differences in biofilm dynamics. The baffles in the device created regions of low and high flow in the same device. At higher flow rates, a nonuniform biofilm develops, due to unequal advection in different regions of the microchannel. However, at lower flow rates, a more uniform biofilm evolved. This depicts competition between adhesion events, growth and fluid advection. Atomic force microscopy (AFM) revealed that higher production of extra-cellular polymeric substances (EPS) occurred at higher flow velocities.
In vivo analysis of synaptonemal complex formation during yeast meiosis.
White, Eric J; Cowan, Carrie; Cande, W Zacheus; Kaback, David B
During meiotic prophase a synaptonemal complex (SC) forms between each pair of homologous chromosomes and is believed to be involved in regulating recombination. Studies on SCs usually destroy nuclear architecture, making it impossible to examine the relationship of these structures to the rest of the nucleus. In Saccharomyces cerevisiae the meiosis-specific Zip1 protein is found throughout the entire length of each SC. To analyze the formation and structure of SCs in living cells, a functional ZIP1::GFP fusion was constructed and introduced into yeast. The ZIP1::GFP fusion produced fluorescent SCs and rescued the spore lethality phenotype of zip1 mutants. Optical sectioning and fluorescence deconvolution light microscopy revealed that, at zygotene, SC assembly was initiated at foci that appeared uniformly distributed throughout the nuclear volume. At early pachytene, the full-length SCs were more likely to be localized to the nuclear periphery while at later stages the SCs appeared to redistribute throughout the nuclear volume. These results suggest that SCs undergo dramatic rearrangements during meiotic prophase and that pachytene can be divided into two morphologically distinct substages: pachytene A, when SCs are perinuclear, and pachytene B, when SCs are uniformly distributed throughout the nucleus. ZIP1::GFP also facilitated the enrichment of fluorescent SC and the identification of meiosis-specific proteins by MALDI-TOF mass spectroscopy. PMID:15166136
Development of Improved Empirical Models for Estimating the Binding Constant of a ?-Cyclodextrin Inclusion Complex
Ravi Chari; Farooq Qureshi; John Moschera; Ralph Tarantino; Devendra Kalonia
Purpose To develop empirical models for predicting the binding between a drug and ?-cyclodextrin. Specifically, the logarithm of the\\u000a 1:1 binding constant is expressed as the function of various molecular descriptors of the drug. Many potential drugs exhibit\\u000a poor aqueous solubility. Also, the amount available for solubility studies is limited early in drug development. Thus, models\\u000a that show which excipients can
Seeking the constant in what is transient: Karl Ernst von Baer's vision of organic formation.
Vienne, Florence
A well-established narrative in the history of science has it that the years around 1800 saw the end of a purely descriptive, classificatory and static natural history. The emergence of a temporal understanding of nature and the new developmental-history approach, it is thought, permitted the formation of modern biology. This paper questions that historical narrative by closely analysing the concepts of development, history and time set out in Karl Ernst von Baer's study of the mammalian egg (1827). I show that Baer's research on embryogenesis aimed not simply to explain temporal changes, but to inscribe the formation of new individual organisms into a continuous, unending organic process. I confront Baer's views with other explanations of embryogenesis arising in the 1820s and 1830s, especially those of Jean-Baptiste Dumas and Jean-Louis Prévost and of Theodor Schwann. By highlighting divergences between these scientists, especially as to their view of the role of gender differences in reproduction, I argue that biology evolved not from a homogeneous concept of developmental history but out of various, even opposing, views and research programmes. Thus, the birth of biology did not imply the end of all natural history's thought models. PMID:26013434
Intramolecular excimer formation of oligostyrenes from dimer to tridecamer: The measurements of rate constants for excimer formation, singlet energy migration, and relaxation of internal rotation
NASA Astrophysics Data System (ADS)
Itagaki, Hideyuki; Horie, Kazuyuki; Mita, Itaru; Washio, Masakazu; Tagawa, Seiichi; Tabata, Yoneho
The emission properties of styrene oligomers from dimer to tridecamer have been investigated by picosecond pulse radiolysis at room temperature. The oligomers are precisely fractionated and are considered to be models of atactic polystyrene. The rate constant for excimer formation kDM of the order of 108 s-1, increases with increasing number of monomer units n for 2?n?8, then levels off at the value for polystyrene. The rate constant for singlet energy migration between adjacent chromophores in polystyrene was determined to be 3×1010 s-1 (˜30 ps). An average time of 7.2 ns was found to be necessary for two adjacent chromophores to assume the excimer conformation (g-t or tg- in a racemo dyad; tt in a meso dyad) from their initial equilibrium distribution of conformations. The present result is an indication that one may investigate the dynamics of internal rotation by photophysical techniques. Moreover, from a comparison of the results of photostationary measurements with those of transient methods, it is found that there is a discrepancy between them. This discrepancy is assumed to be caused by a molecular weight dependence either of the rate constant for the radiative deactivation from the excited monomer singlet kFM or of intramolecular self-quenching.
[Simple screening method for judging the complex formation between drug and aluminum (III)].
Miyachi, Kanako; Nakao, Masahiro; Kurokawa, Hisashi; Tomida, Mayu; Kamino, Shinichiro; Moriyama, Kenzo; Yamaguchi, Takako; Fujita, Yoshikazu
We examined a simple screening method for judging the complex formation between a drug and aluminum(III) on a spot plate. As few drug had color reaction by basing on the binary complex formation of drug-aluminum(III), the ternary complex formation of drug-aluminum(III)-dye was studied this time using 50 kinds of drugs. The dyes used were Chromazurol S and Erythrosin. As a result, in the drug that the complex formation with aluminum(III) was assumed, a remarkable coloration difference was recognized in comparison with the blank prepared under the same conditions. The proposed simple screening method should be very useful for judging instantly the complex formation between a drug and aluminum(III). PMID:19952536
Complex formation between chlorine dioxide and 2,2,6,6-tetramethylpiperidin-1-oxyl
I. M. Ganiev; V. V. Shereshovets; I. A. Grigor'ev; G. A. Tolstikov
The complex formation of ClO2 with 2,2,6,6-tetramethylpiperidin-1-oxyl (TMPO) in acetone, acetonitrile,n-heptane, diethyl ether, carbon tetrachloride, and toluene was studied spectrophotometrically at ?20 to +20 C. The thermodynamic\\u000a parameters of complex formation were determined at 20 C. The transformation of the complex into the oxoammonium salt TMPO+ClO\\u000a 2\\u000a ?\\u000a was found.
Inhibitory mechanism of pancreatic amyloid fibril formation: formation of the complex between tea catechins and the fragment of residues 22-27.
Kamihira-Ishijima, Miya; Nakazawa, Hiromi; Kira, Atsushi; Naito, Akira; Nakayama, Tsutomu
Islet amyloid polypeptide (IAPP) is a major component of pancreatic amyloid deposits associated with type 2 diabetes. Polyphenols contained in plant foods have been found to inhibit amyloid fibril formation of proteins and/or peptides. However, the inhibition mechanism is not clear for a variety of systems. Here the inhibition mechanism of green tea polyphenols, catechins, on amyloid fibril formation of the IAPP fragment (IAPP22-27), which is of sufficient length for formation of ?-sheet-containing amyloid fibrils, was investigated by means of kinetic analysis. A quartz crystal microbalance (QCM) determined that the association constants of gallate-type catechins [epicatechin 3-gallate (ECg) and epigallocatechin 3-gallate] for binding to IAPP22-27 immobilized on the gold plate in QCM were 1 order of magnitude larger than those of the free IAPP22-27 peptide, and also those of epicatechin and epigallocatechin. Kinetic analysis using a two-step autocatalytic reaction mechanism revealed that ECg significantly reduced the rate constants of the first nucleation step of amyloid fibril formation, while the rate of autocatalytic growth was less retarded. (1)H nuclear magnetic resonance studies clarified that a IAPP22-27/ECg complex clearly forms as viewed from the (1)H chemical shift changes and line broadening. Our study suggests that tea catechins specifically inhibit the early stages of amyloid fibril formation to form amyloid nuclei by interacting with the unstructured peptide and that this inhibition mechanism is of great therapeutic value because stabilization of the native state could delay the pathogenesis of amyloid diseases and also the toxicity of the small oligomer (protofibril) is reported to be greater than that of the mature fibril. PMID:23205879
The Effect of Complex Formation upon the Redox Potentials of Metallic Ions. Cyclic Voltammetry Experiments.
ERIC Educational Resources Information Center
Ibanez, Jorge G.; And Others
Describes experiments in which students prepare in situ soluble complexes of metal ions with different ligands and observe and estimate the change in formal potential that the ion undergoes upon complexation. Discusses student formation and analysis of soluble complexes of two different metal ions with the same ligand. (CW)
Dynamics of electrical double layer formation in room-temperature ionic liquids under constant-current charging conditions
Jiang, Xikai [ORNL; Huang, Jingsong [ORNL; Zhao, Hui [University of Nevada, Las Vegas; Sumpter, Bobby G [ORNL; Qiao, Rui [Clemson University
We report detailed simulation results on the formation dynamics of an electrical double layer (EDL) inside an electrochemical cell featuring room-temperature ionic liquids (RTILs) enclosed between two planar electrodes. Under relatively small charging currents, the evolution of cell potential during charging can be suitably predicted by the Landau-Ginzburg-type continuum model proposed recently (M. Z. Bazant, B. D. Storey, and A. A. Kornyshev, Phys. Rev. Lett., 106, 046102, 2011). Under very large charging currents, the cell potential shows pronounced oscillation during the initial stage of charging, a feature not captured by the continuum model. Such oscillation originates from the sequential growth of the ionic space charge layers near the electrode surface, allowing the evolution of EDLs in RTILs with time, an atomistic process difficult to visualize experimentally, to be studied by analyzing the cell potential under constant current charging conditions. While the continuum model cannot predict the potential oscillation under such far-from-equilibrium charging conditions, it can nevertheless qualitatively capture the growth of cell potential during the later stage of charging. Improving the continuum model by introducing frequency-dependent dielectric constant and density-dependent ion diffusion coefficients may help to further extend the applicability of the model. Keywords: ionic
Teasing out Simplicity from Complexity: the Law of Constant Bankfull Velocity in Alluvial Rivers
NASA Astrophysics Data System (ADS)
Parker, G.
Of interest here are single-tread alluvial channels (or mildly anastomosing reaches with a single dominant channel) which are self-formed within their own floodplain. The 232 reaches considered here cover nearly the entire range of such channels, with bankfull discharge varying from 3.3x10-1 m3/s to 2.6x105 m3/s, characteristic bed material size varying from 0.04 mm to 168 mm, bed slopes varying from 8x7x10-6 to 5.2x10-2 and bankfull depths varying from 2.2x10-1 m to 4.8x101 m. These channels show complexity at every scale, including the organization of bed grains, the existence or absence of bedforms such as dunes and bars, the state of eroding banks (e.g. fallen trees, rooted stumps, or slump blocks) and the species and density of floodplain vegetation. Scientific research can often be broadly classified into two types: a) research that shows that a system formerly thought to be relatively simple is instead much more complex, with an increase in the number of factors which must be considered to obtain understanding; and b) research which extracts general, broad-brush simplicity from complexity. Both approaches can contribute to the advancement of science. Here we consider the second approach. The problem in question pertains to an explanation of an observation from the time of Luna Leopold: the single bankfull parameter that appears to be invariant is bankfull flow velocity. Here we demonstrate this result empirically at first-order, obtaining the estimate of 1.5 m/s across scales. We then derive a single, universal dimensionless number that specifies bankfull velocity, again across scales. The result is independent of bed material grain size, suggesting that previously-ignored wash load plays a major, and perhaps the dominant role as floodplain material load in setting bankfull velocity.
The microwave properties of the jovian clouds: A new model for the complex dielectric constant of aqueous ammonia
NASA Astrophysics Data System (ADS)
Duong, Danny; Steffes, Paul G.; Noorizadeh, Sahand
A new model for the complex dielectric constant of aqueous ammonia (NH4OH) under conditions characteristic of the jovian clouds has been developed. The new model is based on laboratory measurements in the frequency range between 2 and 8.5 GHz for ammonia concentrations of 0-8.5% by volume and temperatures between 274 and 297 K. The new model is based on the Meissner and Wentz (Meissner, T., Wentz, F.J. [2004]. IEEE Trans. Geosci. Rem. Sens. 42, 1836-1849) model of the complex dielectric constant of pure water but contains corrections for dissolved ammonia. Assuming Raleigh scattering, these measurements are applied to a cloud attenuation model to calculate the range of opacity of the jovian aqueous ammonia clouds. These measurements will improve our understanding of the data collected by the Juno microwave radiometer (MWR) by better characterizing the absorption properties of the aqueous ammonia present in the jovian atmosphere. The new model has been validated for temperatures up to 313 K, and may be consistently used for the expected conditions for aqueous clouds in all of the outer planets. The model fits 60.26% of all laboratory measurements within 2-sigma uncertainty. Descriptions of the experimental setups, uncertainties associated with the laboratory measurements, the model fitting process, the new model, and its application to approximating jovian cloud opacity are provided.
Crystal structures of complexes of NAD{sup +}-dependent formate dehydrogenase from methylotrophic bacterium Pseudomonas sp. 101 with formate
Filippova, E. V., E-mail: firstname.lastname@example.com; Polyakov, K. M. [Russian Academy of Sciences, Engelhardt Institute of Molecular Biology (Russian Federation); Tikhonova, T. V.; Stekhanova, T. N.; Boiko, K. M.; Sadykhov, I. G. [Russian Academy of Sciences, Bach Institute of Biochemistry (Russian Federation); Tishkov, V. I. [Moscow State University (Russian Federation); Popov, V. O. [Russian Academy of Sciences, Bach Institute of Biochemistry (Russian Federation); Labru, N. [Agricultural University (Greece)
Formate dehydrogenase (FDH) from the methylotrophic bacterium Pseudomonas sp. 101 catalyzes oxidation of formate to NI{sub 2} with the coupled reduction of nicotinamide adenine dinucleotide (NAD{sup +}). The three-dimensional structures of the apo form (the free enzyme) and the holo form (the ternary FDH-NAD{sup +}-azide complex) of FDH have been established earlier. In the present study, the structures of FDH complexes with formate are solved at 2.19 and 2.28 A resolution by the molecular replacement method and refined to the R factors of 22.3 and 20.5%, respectively. Both crystal structures contain four protein molecules per asymmetric unit. These molecules form two dimers identical to the dimer of the apo form of FDH. Two possible formatebinding sites are found in the active site of the FDH structure. In the complexes the sulfur atom of residue Cys354 exists in the oxidized state.
Crystal structures of complexes of NAD+-dependent formate dehydrogenase from methylotrophic bacterium Pseudomonas sp. 101 with formate
NASA Astrophysics Data System (ADS)
Filippova, E. V.; Polyakov, K. M.; Tikhonova, T. V.; Stekhanova, T. N.; Boiko, K. M.; Sadykhov, I. G.; Tishkov, V. I.; Popov, V. O.; Labru, N.
Formate dehydrogenase (FDH) from the methylotrophic bacterium Pseudomonas sp. 101 catalyzes oxidation of formate to NI2 with the coupled reduction of nicotinamide adenine dinucleotide (NAD+). The three-dimensional structures of the apo form (the free enzyme) and the holo form (the ternary FDH-NAD+-azide complex) of FDH have been established earlier. In the present study, the structures of FDH complexes with formate are solved at 2.19 and 2.28 Å resolution by the molecular replacement method and refined to the R factors of 22.3 and 20.5%, respectively. Both crystal structures contain four protein molecules per asymmetric unit. These molecules form two dimers identical to the dimer of the apo form of FDH. Two possible formatebinding sites are found in the active site of the FDH structure. In the complexes the sulfur atom of residue Cys354 exists in the oxidized state.
Double layer formation at the interface of complex plasmas
Yaroshenko, V. V.; Thoma, M. H.; Thomas, H. M.; Morfill, G. E. [Max Planck Institute for Extraterrestrial Physics, 85741 Garching (Germany)
Necessary conditions are formulated for the generation of a double layer at the interface of a complex plasma and a particle-free electron-ion plasma in a weakly collisional discharge. Examples are calculated for realistic observed complex plasmas, and it is shown that situations of both ''smooth'' transitions and 'sharp' transitions can exist. The model can explain the abrupt boundaries observed.
Formation of categories for complex novel auditory stimuli
Daniel Mirman; Lori L. Holt; James L. McClelland
Categorization of complex sounds with multiple, imperfectly valid cues is fundamental to phonetic perception. To study the general perceptual and cognitive processes that support complex sound categories, a novel stimulus set was created that allows tight control of category structure and input distributions. Stimuli were created from 300-ms noise bursts by applying bandstop filters at varying center frequencies and manipulating
Incipient species formation in salamanders of the Ensatina complex
The Ensatina eschscholtzii complex of pleth- odontid salamanders, a well-known ''ring species,'' is thought to illustrate stages in the speciation process. Early research, based on morphology and coloration, has been extended by the incorporation of studies of protein variation and mitochon- drial DNA sequences. The new data show that the complex includes a number of geographically and genetically distinct components
Evaluation of photoinduced changes in stability constants for metal-ion complexes of crowned spirobenzopyran derivatives by electrospray ionization mass spectrometry
Makoto Nakamura; Kenta Takahashi; Takeshi Fujioka; Shinpei Kado; Hidefumi Sakamoto; Keiichi Kimura
The photoinduced changes of metal-ion complexing ability of crowned spirobenzopyran derivatives were studied by using electrospray\\u000a ionization mass spectrometry (ESI-MS). Stability constants for the complexation with various metal ions in methanol under\\u000a visible-irradiation conditions were determined for the first time by ESI-MS. It was found that the stability constants of\\u000a crowned bis(spirobenzopyran) derivatives with metal ions are decreased dramatically by
Rotational spectroscopic constants and structure of the mercury-hydrogen chloride van der Waals complex
NASA Astrophysics Data System (ADS)
Campbell, E. J.; Shea, J. A.
High resolution rotational spectra for nine isotopic species of a weakly bound 1:1 gas phase complex formed between mercury and hydrogen chloride have been measured using pulsed Fourier transform microwave spectroscopy carried out in a Fabry-Perot cavity. For 202Hg H35Cl we obtain: B¯0=998.006 4 (2), DJ=0.003 697 (1), and ?aa (35Cl=-40.350(94), and for 202Hg H37Cl: B¯0=953.046 9 (8), DJ=0.003 375 (6), and ?aa (37Cl=-31.894(400), in units of MHz. The proton is found to be between the two heavy atoms. The heavy atom separation in mercury-hydrogen chloride is 4.097 Å, giving a van der Waals radius for mercury of approximately 1.99 Å.
Cyclodextrin-mediated enantioseparation of phenylalanine amide derivatives and amino alcohols by capillary electrophoresis-role of complexation constants and complex mobilities.
Aranyi, Anita; Péter, Antal; Ilisz, István; Fülöp, Ferenc; Scriba, Gerhard K E
The separation of the enantiomers of phenylalanine amide and N-methyl derivatives as well as some amino alcohols was studied by CE in acidic BGEs using CDs as chiral selectors. The native CDs displayed only low chiral recognition ability at a concentration of 15 mg/mL in 20 mM sodium phosphate buffer, pH 2.5. In contrast, the analyte enantiomers were separated in the presence of randomly sulfated CDs under reversed polarity of the applied voltage. Sulfated ?-CD proved to be the most universal selector resulting in the enantioseparation of all analytes. Opposite enantiomer migration order depending on the size of the CD cavity was observed for phenylalanine amide and 2-amino-2-phenylethanol. The R-enantiomers migrated first in the presence of sulfated ?-CD and ?-CD while the S-enantiomers were detected first in the presence of sulfated ?-CD. The enantioseparations could be rationalized based on analyte complexation by the respective CDs except for 2-amino-2-phenylethanol and sulfated ?-CD where essentially equal complexation constants were derived for the enantiomers. In this case, the migration behavior could be attributed to the mobilities of the enantiomer-CD complexes adding another example to the CE-specific phenomenon of enantioseparations based primarily on complex mobilities. PMID:24890817
Ferric-transferrin and ferric-transferrin-anion complexes: formation and characterization.
Schlabach, Michael Ray
found to be nonsyn- ergistic. Dihydroxyacetone and glyceraldehyde were also ineffective in promoting ternary complex formation. Dicarboxylic acids were found 3+ to form stable Fe -transferrin ? anion complexes which were only slowly displaced...-TRANSFERRIN BINARY COMPLEXES EXPERIMENTAL PROCEDURES RESULTS AND INTERPRETATION FERRIC-TRANSFERRIN-ANION TERNARY COMPLEXES ~ ~ ~ ~ o ~ ~ EXPERIMENTAL PROCEDURES RESULTS AND INTERPRETATION DISCUSSION 21 21 25 47 VITA 56 viii LIST OF TABLES Table Page A...
Study of the formation equilibria of electron donor-acceptor complexes between [60]fullerene and methylbenzenes by absorption spectrometric method
NASA Astrophysics Data System (ADS)
Bhattacharya, Sumanta; Banerjee, Manas; Mukherjee, Asok K.
The electron donor-acceptor (EDA) interaction between [60]fullerene and three methylbenzenes, viz., durene, pentamethylbenzene and hexamethylbenzene has been studied in carbon tetrachloride medium at a number of temperatures. It has been found that these methylbenzenes form stable 1:1 EDA complexes with [60]fullerene. Charge transfer (CT) absorption bands of the complexes in the 410-460 nm region are more intense than the usual 420-700 nm absorption band of C60. The CT transition energies ( h?CT) of the complexes change systematically with change in the number and position of the methyl groups in the donor molecules (methylbenzenes) and also with the donor ionisation potentials. From an analysis of this variation the electron affinity of C60 has been found to be 2.30 eV and also an inductive effect Hückel parameter of the methyl group has been determined. Formation constants ( K) have been determined at three different temperatures from which the enthalpies and entropies of formation of the complexes have been determined.
Study of the formation equilibria of electron donor-acceptor complexes between [60]fullerene and methylbenzenes by absorption spectrometric method.
Bhattacharya, S; Banerjee, M; Mukherjee, A K
The electron donor-acceptor (EDA) interaction between [60]fullerene and three methylbenzenes, viz., durene, pentamethylbenzene and hexamethylbenzene has been studied in carbon tetrachloride medium at a number of temperatures. It has been found that these methylbenzenes form stable 1:1 EDA complexes with [60]fullerene. Charge transfer (CT) absorption bands of the complexes in the 410-460 nm region are more intense than the usual 420-700 nm absorption band of C60. The CT transition energies (hvCT) of the complexes change systematically with change in the number and position of the methyl groups in the donor molecules (methylbenzenes) and also with the donor ionisation potentials. From an analysis of this variation the electron affinity of C60 has been found to be 2.30 eV and also an inductive effect Hückel parameter of the methyl group has been determined. Formation constants (K) have been determined at three different temperatures from which the enthalpies and entropies of formation of the complexes have been determined. PMID:11446701
New Pathways for the Formation of Complex Organics and Prebiotic Synthesis in the Gas Phase
NASA Astrophysics Data System (ADS)
El-Shall, M. S.
We study the formation mechanisms of complex organics that are present in interstellar clouds. The reaction of acetylene ion with water produces vinyl alcohol while the reaction of benzene ion with acetylene produces naphthalene-type ion.
A simple scheme for universal linear optics quantum computing with constant experimental complexity using fiber-loops
Peter P. Rohde
Recently, Motes, Gilchrist, Dowling & Rohde [Phys. Rev. Lett. 113, 120501 (2014)] presented a scheme for photonic boson-sampling using a fiber-loop architecture. Here we show that the same architecture can be modified to implement full, universal linear optics quantum computing, in various incarnations. The scheme employs two embedded fiber-loops, a single push-button photon source, three dynamically controlled beamsplitters, and a single time-resolved photo-detector. The architecture has only a single point of interference, and thus may be significantly easier to align than other schemes. The experimental complexity of the scheme is constant, irrespective of the size of the computation, limited only by fiber lengths and their respective loss rates.
Sensory rhodopsin II\\/transducer complex formation in detergent and in lipid bilayers studied with FRET
J. Kriegsmann; M. Brehs; J. P. Klare; M. Engelhard; J. Fitter
The photophobic receptor from Natronomonas pharaonis (NpSRII) forms a photo-signalling complex with its cognate transducer (NpHtrII). In order to elucidate the complex formation in more detail, we have studied the intermolecular binding of both constituents (NpSRII and NpHtrII157; truncated at residue 157) in detergent buffers, and in lipid bilayers using FRET. The data for hetero-dimer formation of NpSRII\\/NpHtrII in detergent
Effect of torsional isomerization and inclusion complex formation with cucurbit[7]uril on the fluorescence of 6-methoxy-1-methylquinolinium.
Miskolczy, Zsombor; Harangozó, József G; Biczók, László; Wintgens, Véronique; Lorthioir, Cédric; Amiel, Catherine
Inclusion of 6-methoxy-1-methylquinolinium (C1MQ) in the cavity of cucurbit[7]uril (CB7) was studied by absorption, fluorescence, NMR and isothermal calorimetric methods in aqueous solution at 298 K. The free C1MQ exhibited dual-exponential fluorescence decay kinetics due to the two torsional isomers differing in the orientation of the methoxy moiety relative to the heterocyclic ring. The enthalpy-driven encapsulation of the heterocycle in CB7 led to a very stable 1?:?1 complex with a binding constant of (2.0 ± 0.4) × 10(6) M(-1). The rate of C1MQ-CB7 complex dissociation was found to be comparable to the NMR timescale. Because the methoxy moiety is oriented outward from the host, its s-cis-s-trans isomerization is slightly affected by the confinement. Inclusion complex formation significantly slowed down the photoinduced electron transfer from I(-) and N3(-) to the singlet-excited C1MQ, but did not preclude the reaction because long distance electron transfer occurred through the wall of the CB7 macrocycle. Due to the large difference in the quenching rate constant for free and encapsulated forms, C1MQ is an excellent probe for the study of the inclusion of nonfluorescent compounds in CB7 in the presence of Cl(-) or Br(-). PMID:24346633
Physicochemical Controls on the Formation of Polynuclear Metal Complexes at Clay Mineral Surfaces
Sparks, Donald L.
Physicochemical Controls on the Formation of Polynuclear Metal Complexes at Clay Mineral Surfaces R. G. Ford Metal sorption to clay minerals may lead to the formation of secondary precipitates, by enhanced dissolution of the clay mineral structure as indicated by enhanced levels of dissolved silica
Ligand exchange and complex formation kinetics studied by NMR exemplified on fac-[(CO) 3M(H 2O)] + (M = Mn, Tc, Re)
Lothar Helm
In this review ligand exchange and complex formation reactions on fac-[(CO)3M(H2O)3]+ (M=Mn, Tc, Re) and on fac-[(CO)2(NO)Re(H2O)3]2+ are presented. A variety of experimental NMR techniques are described and it is shown that sometimes combinations of techniques applied at variable temperature or variable pressure allowed to measure exchange rate constants and their activation parameters as well as thermodynamic parameters. Furthermore, the
Variation in DNA binding constants with a change in geometry of ternary copper(II) complexes with N2O donor Schiff base and cyanate or dicyanamide
NASA Astrophysics Data System (ADS)
Jana, Subrata; Santra, Ramesh Chandra; Das, Saurabh; Chattopadhyay, Shouvik
Two new copper(II) complexes, [Cu(L)(OCN)] (1) and [CuL(dca)]n (2), where HL = 2-(-(2-(diethylamino)ethylimino)methyl)naphthalen-1-ol, dca = N(CN)2-, have been synthesized and characterized by elemental analysis, IR, UV-VIS spectroscopy and single crystal X-ray diffraction studies. Complex 1 has square planar and complex 2 square pyramidal geometries in solid state around metal centre. Interactions of the complexes with calf thymus DNA (CT DNA) were studied by UV-VIS spectroscopy. Binding constant and site size of interaction were determined. Binding site size and intrinsic binding constant K revealed complex 1 interacted with calf thymus DNA better than complex 2.
Rhodopsin-phospholipid complexes in apolar solvents: Formation and properties
A. Darszon; M. Philipp; J. Zarco; M. Montal
Summary The extraction of rhodopsin-phospholipid complexes into lipid solvents is described. Two general procedures were developed: (i) the extraction of detergent-solubilized rhodopsin which involved: (a) solubilization of rhodopsin from bovine retinal rod disc membranes in detergent solutions; (b) partial removal of detergent from solubilized rhodopsin; (c) recombination with a defined lipid mixture by sonication of lipid and protein in salt
Interferogram formation in the presence of complex and large deformation
's caldera subsided about 5.4 meters. Three hours prior to the onset of the eruption, an earthquake (Mw 5.4) occurred, near the caldera. Because of the large and complex phase gradient due to the huge subsidence and the earthquake, it is difficult to form an interferogram inside the caldera that spans the eruption
Base Flipping in Open Complex Formation at Bacterial Promoters
Karpen, Mary E.; deHaseth, Pieter L.
In the process of transcription initiation, the bacterial RNA polymerase binds double-stranded (ds) promoter DNA and subsequently effects strand separation of 12 to 14 base pairs (bp), including the start site of transcription, to form the so-called "open complex" (also referred to as RPo). This complex is competent to initiate RNA synthesis. Here we will review the role of ?70 and its homologs in the strand separation process, and evidence that strand separation is initiated at the ?11A (the A of the non-template strand that is 11 bp upstream from the transcription start site) of the promoter. By using the fluorescent adenine analog, 2-aminopurine, it was demonstrated that the ?11A on the non-template strand flips out of the DNA helix and into a hydrophobic pocket where it stacks with tyrosine 430 of ?70. Open complexes are remarkably stable, even though in vivo, and under most experimental conditions in vitro, dsDNA is much more stable than its strand-separated form. Subsequent structural studies of other researchers have confirmed that in the open complex the ?11A has flipped into a hydrophobic pocket of ?70. It was also revealed that RPo was stabilized by three additional bases of the non-template strand being flipped out of the helix and into hydrophobic pockets, further preventing re-annealing of the two complementary DNA strands. PMID:25927327
Formation of Vacancy-Impurity Complexes by Kinetic Processes in Highly As-Doped Si
V. Ranki; J. Nissilä; K. Saarinen
Positron annihilation experiments have been applied to verify the formation mechanism of electrically inactive vacancy-impurity clusters in highly n-type Si. We show that the migration of V-As pairs at 450 K leads to the formation of V-As2 complexes, which in turn convert to stable V-As3 defects at 700 K. These processes manifest the formation of V-As3 as the dominant vacancy-impurity
Determination of Binding Constants by Flow Injection Gradient Technique
Reid, Scott A.
of inclusion complex formation between -cyclodextrin ( -CD) and phenolphthalein and of the incorporation for the determination of binding constants of substrates with cyclodextrins or micelles. The concentration gradient Complex formations through noncovalent interactions are known to play an essential role in processes
Functional cooperation between FACT and MCM is coordinated with cell cycle and differential complex formation
Bertrand Chin-Ming Tan; Hsuan Liu; Chih-Li Lin; Sheng-Chung Lee
BACKGROUND: Functional cooperation between FACT and the MCM helicase complex constitutes an integral step during DNA replication initiation. However, mode of regulation that underlies the proper functional interaction of FACT and MCM is poorly understood. METHODS & RESULTS: Here we present evidence indicating that such interaction is coordinated with cell cycle progression and differential complex formation. We first demonstrate the
Molecular factors affecting the complex formation between deferiprone (L1) and Cu(II). Possible implications on efficacy and toxicity.
Pashalidis, I; Kontoghiorghes, G J
Deferiprone (1,2-dimethyl-3-hydroxypyrid-4-one, L1, CAS 30652-11-0) is a new chelating drug used worldwide for the treatment of iron overloading conditions. Spectrophotometric and potentiometric measurements were carried out to investigate the interaction of L1 with Cu(II) ions under different conditions. The complexation of Cu(II) ions with L1 in aqueous solution leads predominantly to the formation of the Cu(L1)2 species at a pH range of 4-9. The experimental results indicate that L1 has high affinity for Cu(II) with stability constants log beta 11 = 10.3 +/- 0.9 and log beta 12 = 19.2 +/- 0.6. The effect of Cu(II) ions on the affinity of L1 for Fe(III) ions by competition reactions in vitro indicate displacement of Fe(III) in a concentration dependent manner by Cu(II). Similarly, the presence of different buffers at various pH values resulted in the formation of different stoichiometry L1 complexes with Cu(II) and of mixed complexes with buffer anions. The strong interaction of L1 with Cu(II) may have implications on the therapeutic and toxicological properties of this chelating drug. In particular, L1 may be used in the treatment of copper overloading conditions, such as Wilson's disease or other conditions where copper toxicity is implicated. PMID:11799848
Real-time Live Imaging of T-cell Signaling Complex Formation
Barda-Saad, Mira
Protection against infectious diseases is mediated by the immune system 1,2. T lymphocytes are the master coordinators of the immune system, regulating the activation and responses of multiple immune cells 3,4. T-cell activation is dependent on the recognition of specific antigens displayed by antigen presenting cells (APCs). The T-cell antigen receptor (TCR) is specific to each T-cell clone and determines antigen specificity 5. The binding of the TCR to the antigen induces the phosphorylation of components of the TCR complex. In order to promote T-cell activation, this signal must be transduced from the membrane to the cytoplasm and the nucleus, initiating various crucial responses such as recruitment of signaling proteins to the TCR;APC site (the immune synapse), their molecular activation, cytoskeletal rearrangement, elevation of intracellular calcium concentration, and changes in gene expression 6,7. The correct initiation and termination of activating signals is crucial for appropriate T-cell responses. The activity of signaling proteins is dependent on the formation and termination of protein-protein interactions, post translational modifications such as protein phosphorylation, formation of protein complexes, protein ubiquitylation and the recruitment of proteins to various cellular sites 8. Understanding the inner workings of the T-cell activation process is crucial for both immunological research and clinical applications. Various assays have been developed in order to investigate protein-protein interactions; however, biochemical assays, such as the widely used co-immunoprecipitation method, do not allow protein location to be discerned, thus precluding the observation of valuable insights into the dynamics of cellular mechanisms. Additionally, these bulk assays usually combine proteins from many different cells that might be at different stages of the investigated cellular process. This can have a detrimental effect on temporal resolution. The use of real-time imaging of live cells allows both the spatial tracking of proteins and the ability to temporally distinguish between signaling events, thus shedding light on the dynamics of the process 9,10. We present a method of real-time imaging of signaling-complex formation during T-cell activation. Primary T-cells or T-cell lines, such as Jurkat, are transfected with plasmids encoding for proteins of interest fused to monomeric fluorescent proteins, preventing non-physiological oligomerization 11. Live T cells are dropped over a coverslip pre-coated with T-cell activating antibody 8,9, which binds to the CD3/TCR complex, inducing T-cell activation while overcoming the need for specific activating antigens. Activated cells are constantly imaged with the use of confocal microscopy. Imaging data are analyzed to yield quantitative results, such as the colocalization coefficient of the signaling proteins. PMID:23851483
Formation of ruthenium thiolates via complexes of molecular hydrogen
Field, L.D.; Hambley, T.W.; Yau, B.C.K. (Univ. of Sydney, Sydney (Australia))
RuH[sub 2](DMPE)[sub 2][DMPE = 1,2-bis(dimethylphosphino)ethane] was synthesized by reduction of trans-RuCl[sub 2](DMPE)[sub 2] with sodium/2-propanol. Protonation of RuH[sub 2](DMPE)[sub 2] with weak organic acids such as methanol, ethanol, and thiols affords the molecular hydrogen complex trans-[RuH([eta][sup 2]-H[sub 2])(DMPE)[sub 2
Disulphide bond formation by glutathione via the glutathione-trimethylamine- N-oxide complex
NASA Astrophysics Data System (ADS)
Brzezinski, Bogumil; Labowski, M.; Zundel, Georg
Glutathione and its diethyl ester complexes (1 : 1) with trimethylamine N-oxide (TMAO) were studied by FTIR and 1H NMR spectrocopy. Immediately after mixing, complexes with strong SH⋯ON ? S -⋯H +ON hydrogen bonds are formed. They show large proton polarizability due to the fluctuation of the proton within these bonds. These complexes are, however, not stable since disulphide bonds are formed. Thus, TMAO regulates the disulphide bond formation in glutathione systems.
The formation and study of titanium, zirconium, and hafnium complexes
NASA Technical Reports Server (NTRS)
Wilson, Bobby; Sarin, Sam; Smith, Laverne; Wilson, Melanie
Research involves the preparation and characterization of a series of Ti, Zr, Hf, TiO, and HfO complexes using the poly(pyrazole) borates as ligands. The study will provide increased understanding of the decomposition of these coordination compounds which may lead to the production of molecular oxygen on the Moon from lunar materials such as ilmenite and rutile. The model compounds are investigated under reducing conditions of molecular hydrogen by use of a high temperature/pressure stainless steel autoclave reactor and by thermogravimetric analysis.
Ganymede and Callisto - Complex crater formation and planetary crusts
NASA Technical Reports Server (NTRS)
Schenk, Paul M.
Results are presented on measurements of crater depths and other morphological parameters (such as central peak and terrace frequency) of fresh craters on Ganymede and Callisto, two geophysically very similar but geologically divergent large icy satellites of Jupiter. These data were used to investigate the crater mechanics on icy satellites and the intersatellite crater scaling and crustal properties. The morphological transition diameters of and complex crater depths on Ganymede and Callisto were found to be similar, indicating that the crusts of both satellites are dominated by water ice with only a minor rocky component.
Complex experience promotes capillary formation in young rat visual cortex.
Black, J E; Sirevaag, A M; Greenough, W T
The metabolic support of neural plasticity was examined by comparing cerebral vasculature of weanling rats reared in complex environments (EC) to littermates reared individually (IC) or socially in pairs (SC). EC rats have a thicker occipital cortex, more synaptic contacts per neuron and larger dendritic arbors compared to SC or IC rats, potentially increasing local metabolic demands on microvasculature. Capillaries of EC rats were closer together than those of SC or IC rats and potentially filled a greater fraction of cortex with blood. The closer capillary spacing in young EC rats suggests compensatory angiogenesis in response to increased metabolic demand. PMID:2450317
Anglesite (PbSO 4) solubility in acetate solutions: The determination of stability constants for lead acetate complexes to 85°C
NASA Astrophysics Data System (ADS)
Giordano, Thomas H.
Anglesite solubilities were determined at 25, 40, 55, 70, and 85°C in solutions with equal molal concentrations of acetic acid and sodium acetate (each ranging from 0.001 to 0.25 m) and at pH values near 4.6. Experiments were conducted using 1000 ml, externally heated glass reaction vessels, and lead concentrations were measured using atomic absorption spectrophotometry. For run conditions with free acetate concentrations less than about 0.01 m, measured a anglesite solubilities are less than or equal to 100 mg/l. Above free acetate concentrations of 0.01 m, measured anglesite solubilities rise sharply to concentrations near 1000 mg/l. Extracted from these solubility data, by a numerical successive linear extrapolation method, were stoichiometries and thermodynamic stability constants (ionic strength = 0) for the complexes Pb(CH 3COO) + and Pb(CH 3COO) 2. Log K1 and log K2 values for the formation reactions Pb + + CH 3COO - = PbCH 3COO + and Pb 2+ + 2CH 3COO - = Pb(CH 3COO) 2 respectively are log K1: (2.4±0.1, 25°C), (2.4±0.1, 40°C), (2.5±0.1, 55°C), (2.6±0.1, 70°C), (2.7±0.2, 85°C) and log K2: (3.4±0.4, 25°C), (3.6±0.2, 40°C), (3.8 ±0.2, 55°C), (4.0±0.2, 70°C), (4.3±0.2, 85°C). Lead hydrolysis was found to be significant in those experiments conducted at 70 and 85°C. However, hydrolyzed lead was not detected at 25, 40, and 55°C. PbOH + as percent of total observed lead ranged from 0.2 to 24% and 2 to 86% in those experiments at 70 and 85°C, respectively. Calculations of lead speciation in acetate solutions show that the equivalence point for PbCH 3COO + and Pb(CH 3COO) 2 shifts to lower acetate concentrations from 25 to 85°C. These speciation calculations also suggest that lead acetate complexes could be significant in high acetate formation waters. These waters typically contain at least 1,000 ppm acetate (0.017 molal as acetic acid). Furthermore, if these waters are not too acid and if concentrations of competing ligands are low, lead acetate complexes should be the dominant lead species.
Effect of nonionic surfactant micelles on the formation of beryllium complexes with Chromazurol S and Chromazurol B and their use in the spectrophotometric determination of beryllium
Hayashi, K.; Sasaki, Y.; Tagashira, S.; Kosaka, E.
The triphenylmethane dyes, Chromazurol S (CAS) and Chromazurol B (CAB), react with beryllium to form the dye-rich complexes Be(CAS)/sub 2/ and Be(CAB)/sub 2/ in nonionic micellar solutions. The partition equilibria of the dyes and the complexes were spectrophotometrically studied, and the partition coefficients between the micellar and water phases were evaluated in Triton X-100, Emulgen 120, and Brij 58 micellar systems. The micellar effects, i.e., a local increase in the dye concentration in the micelles, contribute to the formation of the dye-rich complexes. Formation constants of the beryllium-CAS complex are ..beta../sub 1/ = 10/sup 4.79/ and ..beta../sub 2/ = 10/sup 7.19/. At a low CAS concentration, the formation of Be(CAS)/sub 2/ is negligible in aqueous solutions. The molar absorptivities of the dye-rich complexes are about 4 times larger than those of the 1:1 complexes. The spectrophotometric determination of beryllium using the high molar absorptivities of these complexes was performed in the Triton X-100 micellar system.
Landscape complexity influences route-memory formation in navigating pigeons
Mann, Richard P.; Armstrong, Chris; Meade, Jessica; Freeman, Robin; Biro, Dora; Guilford, Tim
Observations of the flight paths of pigeons navigating from familiar locations have shown that these birds are able to learn and subsequently follow habitual routes home. It has been suggested that navigation along these routes is based on the recognition of memorized visual landmarks. Previous research has identified the effect of landmarks on flight path structure, and thus the locations of potentially salient sites. Pigeons have also been observed to be particularly attracted to strong linear features in the landscape, such as roads and rivers. However, a more general understanding of the specific characteristics of the landscape that facilitate route learning has remained out of reach. In this study, we identify landscape complexity as a key predictor of the fidelity to the habitual route, and thus conclude that pigeons form route memories most strongly in regions where the landscape complexity is neither too great nor too low. Our results imply that pigeons process their visual environment on a characteristic spatial scale while navigating and can explain the different degrees of success in reproducing route learning in different geographical locations. PMID:24451267
Formation of Au and tetrapyridyl porphyrin complexes in superfluid helium.
Feng, Cheng; Latimer, Elspeth; Spence, Daniel; Al Hindawi, Aula M A A; Bullen, Shem; Boatwright, Adrian; Ellis, Andrew M; Yang, Shengfu
Binary clusters containing a large organic molecule and metal atoms have been formed by the co-addition of 5,10,15,20-tetra(4-pyridyl)porphyrin (H2TPyP) molecules and gold atoms to superfluid helium nanodroplets, and the resulting complexes were then investigated by electron impact mass spectrometry. In addition to the parent ion H2TPyP yields fragments mainly from pyrrole, pyridine and methylpyridine ions because of the stability of their ring structures. When Au is co-added to the droplets the mass spectra are dominated by H2TPyP fragment ions with one or more Au atoms attached. We also show that by switching the order in which Au and H2TPyP are added to the helium droplets, different types of H2TPyP-Au complexes are clearly evident from the mass spectra. This study suggests a new route for the control over the growth of metal-organic compounds inside superfluid helium nanodroplets. PMID:26059415
SEPALLATA3: the 'glue' for MADS box transcription factor complex formation
Immink, Richard GH; Tonaco, Isabella AN; de Folter, Stefan; Shchennikova, Anna; van Dijk, Aalt DJ; Busscher-Lange, Jacqueline; Borst, Jan W; Angenent, Gerco C
Background Plant MADS box proteins play important roles in a plethora of developmental processes. In order to regulate specific sets of target genes, MADS box proteins dimerize and are thought to assemble into multimeric complexes. In this study a large-scale yeast three-hybrid screen is utilized to provide insight into the higher-order complex formation capacity of the Arabidopsis MADS box family. SEPALLATA3 (SEP3) has been shown to mediate complex formation and, therefore, special attention is paid to this factor in this study. Results In total, 106 multimeric complexes were identified; in more than half of these at least one SEP protein was present. Besides the known complexes involved in determining floral organ identity, various complexes consisting of combinations of proteins known to play a role in floral organ identity specification, and flowering time determination were discovered. The capacity to form this latter type of complex suggests that homeotic factors play essential roles in down-regulation of the MADS box genes involved in floral timing in the flower via negative auto-regulatory loops. Furthermore, various novel complexes were identified that may be important for the direct regulation of the floral transition process. A subsequent detailed analysis of the APETALA3, PISTILLATA, and SEP3 proteins in living plant cells suggests the formation of a multimeric complex in vivo. Conclusions Overall, these results provide strong indications that higher-order complex formation is a general and essential molecular mechanism for plant MADS box protein functioning and attribute a pivotal role to the SEP3 'glue' protein in mediating multimerization. PMID:19243611
Investigation of the solid-state conductivity and the potentiometric stability constant relationships of new amino acid-Schiff bases and their complexes
Nur?en Sarì; Perihan Gürkan
CuII, NiII and CoII complexes of new tridentate amino acid-Schiff bases derived from furfural and DL-alanine, DL-valine and DL-phenylalanine were prepared and characterized by analytical, spectroscopic, (i.r., u.v.–vis., 1H-n.m.r and 13C-n.m.r) techniques, molar conductivity, magnetic and thermal measurements. Protonation constants of the Schiff bases and stability constants of the complexes have been determined potentiometrically in water. Solid-state conductivities of the
Cleavage and formation of molecular dinitrogen in a single system assisted by molybdenum complexes bearing ferrocenyldiphosphine.
Miyazaki, Takamasa; Tanaka, Hiromasa; Tanabe, Yoshiaki; Yuki, Masahiro; Nakajima, Kazunari; Yoshizawa, Kazunari; Nishibayashi, Yoshiaki
The N?N bond of molecular dinitrogen bridging two molybdenum atoms in the pentamethylcyclopentadienyl molybdenum complexes that bear ferrocenyldiphosphine as an auxiliary ligand is homolytically cleaved under visible light irradiation at room temperature to afford two molar molybdenum nitride complexes. Conversely, the bridging molecular dinitrogen is reformed by the oxidation of the molybdenum nitride complex at room temperature. This result provides a successful example of the cleavage and formation of molecular dinitrogen induced by a pair of two different external stimuli using a single system assisted by molybdenum complexes bearing ferrocenyldiphosphine under ambient conditions. PMID:25214300
Reactions of sulfur-nitrosyl iron complexes of "g=2.03" family with hemoglobin (Hb): kinetics of Hb-NO formation in aqueous solutions.
Sanina, N A; Syrtsova, L A; Shkondina, N I; Rudneva, T N; Malkova, E S; Bazanov, T A; Kotel'nikov, A I; Aldoshin, S M
NO-donating ability of nitrosyl [Fe-S] complexes, namely, mononuclear dinitrosyl complexes of anionic type [Fe(S2O3)2(NO)2]-(I) and neutral [Fe2(SL1)2(NO)2] with L1=1H-1,2,4-triazole-3-yl (II); tetranitrosyl binuclear neutral complexes [Fe2(SL2)2(NO)4] with L2=5-amino-1,2,4-triazole-3-yl (III); 1-methyl-1H-tetrazole-5-yl (IV); imidazole-2-yl (V) and 1-methyl-imidazole-2-yl (VI) has been studied. In addition, Roussin's "red salt" Na2[Fe2S2(NO)4] x 8H2O (VII) and Na2[Fe(CN)5NO] x H2O (VIII) have been investigated. The method for research has been based on the formation of Hb-NO adduct upon the interaction of hemoglobin with NO generated by complexes I-VIII in aqueous solutions. Kinetics of NO formation was studied by registration of absorption spectra of the reaction systems containing Hb and the complex under study. For determination of HbNO concentration, the experimental absorption spectra were processed during the reaction using standard program MATHCAD to determine the contribution of individual Hb and HbNO spectra in each spectrum. The reaction rate constants were obtained by analyzing kinetic dependence of Hb interaction with NO donors under study. All kinetic dependences for complexes I-VI were shown to be described well in the frame of formalism of pseudo first-order reactions. The effective first-order rate constants for the studied reactions have been determined. As follows from the values of rate constants, the rate of interaction of sulfur-nitrosyl iron complexes (I-VI) with Hb is limited by the stage of NO release in the solution. PMID:17140821
Oxidative peptide /and amide/ formation from Schiff base complexes
NASA Technical Reports Server (NTRS)
Strehler, B. L.; Li, M. P.; Martin, K.; Fliss, H.; Schmid, P.
One hypothesis of the origin of pre-modern forms of life is that the original replicating molecules were specific polypeptides which acted as templates for the assembly of poly-Schiff bases complementary to the template, and that these polymers were then oxidized to peptide linkages, probably by photo-produced oxidants. A double cycle of such anti-parallel complementary replication would yield the original peptide polymer. If this model were valid, the Schiff base between an N-acyl alpha mino aldehyde and an amino acid should yield a dipeptide in aqueous solution in the presence of an appropriate oxidant. In the present study it is shown that the substituted dipeptide, N-acetyl-tyrosyl-tyrosine, is produced in high yield in aqueous solution at pH 9 through the action of H2O2 on the Schiff-base complex between N-acetyl-tyrosinal and tyrosine and that a great variety of N-acyl amino acids are formed from amino acids and aliphatic aldehydes under similar conditions.
Interferogram formation in the presence of complex and large deformation
Yun, S.-H.; Zebker, H.; Segall, P.; Hooper, A.; Poland, M.
Sierra Negra volcano in Isabela island, Gala??pagos, erupted from October 22 to October 30 in 2005. During the 8 days of eruption, the center of Sierra Negra's caldera subsided about 5.4 meters. Three hours prior to the onset of the eruption, an earthquake (Mw 5.4) occurred, near the caldera. Because of the large and complex phase gradient due to the huge subsidence and the earthquake, it is difficult to form an interferogram inside the caldera that spans the eruption. The deformation is so large and spatially variable that the approximations used in existing InSAR software (ROI, ROI_PAC, DORIS, GAMMA) cannot properly coregister SAR image pairs spanning the eruption. We have developed here a two-step algorithm that can form intra-caldera interferograms from these data. The first step involves a "rubber-sheeting" SAR image coregistration. In the second step we use range offset estimates to mitigate the steep phase gradient. Using this new algorithm, we retrieve an interferogram with the best coverage to date inside the caldera of Sierra Negra. Copyright 2007 by the American Geophysical Union.
An illustration of the complexity of continent formation
NASA Technical Reports Server (NTRS)
Burke, Kevin
It was pointed out that a consensus may be emerging in crustal growth models, considering the clustering of most growth curves and their uncertainties. Curves most distant from this clustering represent models involving extensive recycling of continental material back into the mantle, but the author wondered if geochemical signatures for this would be recognizable considering the lack of evidence from seismic tomography for discrete mantle reservoirs, and the likelihood of core-mantle interaction based on recent high pressure experiments. Unreactivated Archean rocks represent only 2 percent of present continental area, and the author was uncomfortable about basing inferences on what the early Earth was like on such a small amount of information. He feels that the hypothesis of continental assembly that needs testing is that of banging together of island arcs, such as in Indonesia today. As an example of how complex this process can be, the author described the geology of the Caribbean arc system, which shows evidence for reversals of subduction polarity, numerous collisional events, and substantial strike-slip movements. It seemed unlikely to the author that Archean examples would have been less complicated.
Thermodynamics of the formation of copper(II) complexes with L-histidine in aqueous solution
NASA Astrophysics Data System (ADS)
Gorboletova, G. G.; Metlin, A. A.
The heat effects from the reaction between L-histidine solutions and Cu(NO3)2 solutions at 298.15 K in the 0.2 to 1.0 (KNO3) range of ionic strength are measured by means of direct calorimetry. The experimental data is treated with allowance for the simultaneous proceeding of several processes. The heat effects of the formation of complexes Cu(His)+, Cu(His)2, CuHHis2+, CuH(His){2/+} and CuH2(His){2/2+} are calculated from calorimetric measurements. The standard enthalpies of formation for complexes of L-histidine with Cu2+ ions are obtained via extrapolation to zero ionic strength. The relationship between the thermodynamic characteristics of the formation of complexes of copper(II) with L-histidine and their structure is determined.
Complex Formation and Functional Versatility of Mre11 of Budding Yeast in Recombination
Takehiko Usui; Tsutomu Ohta; Hiroyuki Oshiumi; Jun-ichi Tomizawa; Hideyuki Ogawa; Tomoko Ogawa
Meiotic recombination of S. cerevisiae contains two temporally coupled processes, formation and processing of double-strand breaks (DSBs). Mre11 forms a complex with Rad50 and Xrs2, acting as the binding core, and participates in DSB processing. Although these proteins are also involved in DSB formation, Mre11 is not necessarily holding them. The C-terminal region of Mre11 is required only for DSB
Human RNase P ribonucleoprotein is required for formation of initiation complexes of RNA polymerase III.
Serruya, Raphael; Orlovetskie, Natalie; Reiner, Robert; Dehtiar-Zilber, Yana; Wesolowski, Donna; Altman, Sidney; Jarrous, Nayef
Human RNase P is implicated in transcription of small non-coding RNA genes by RNA polymerase III (Pol III), but the precise role of this ribonucleoprotein therein remains unknown. We here show that targeted destruction of HeLa nuclear RNase P inhibits transcription of 5S rRNA genes in whole cell extracts, if this precedes the stage of initiation complex formation. Biochemical purification analyses further reveal that this ribonucleoprotein is recruited to 5S rRNA genes as a part of proficient initiation complexes and the activity persists at reinitiation. Knockdown of RNase P abolishes the assembly of initiation complexes by preventing the formation of the initiation sub-complex of Pol III. Our results demonstrate that the structural intactness, but not the endoribonucleolytic activity per se, of RNase P is critical for the function of Pol III in cells and in extracts. PMID:25953854
Human RNase P ribonucleoprotein is required for formation of initiation complexes of RNA polymerase III
Serruya, Raphael; Orlovetskie, Natalie; Reiner, Robert; Dehtiar-Zilber, Yana; Wesolowski, Donna; Altman, Sidney; Jarrous, Nayef
Human RNase P is implicated in transcription of small non-coding RNA genes by RNA polymerase III (Pol III), but the precise role of this ribonucleoprotein therein remains unknown. We here show that targeted destruction of HeLa nuclear RNase P inhibits transcription of 5S rRNA genes in whole cell extracts, if this precedes the stage of initiation complex formation. Biochemical purification analyses further reveal that this ribonucleoprotein is recruited to 5S rRNA genes as a part of proficient initiation complexes and the activity persists at reinitiation. Knockdown of RNase P abolishes the assembly of initiation complexes by preventing the formation of the initiation sub-complex of Pol III. Our results demonstrate that the structural intactness, but not the endoribonucleolytic activity per se, of RNase P is critical for the function of Pol III in cells and in extracts. PMID:25953854
Conductometric study of cationic and anionic complexes in propylene carbonate
Mark Salomon
Conductivity data are used to determine thermodynamic complex formation constants for cases in which both the initial electrolyte and the complexed electrolyte form ion pairs. Using the method described in the text, the complex formation constants of Li+, Na+ and K+ with the crown ether 18-crown-6 and of Li+ with the ligand triphenylphosphine oxide in propylene carbonate have been evaluated
SEPALLATA3: the 'glue' for MADS box transcription factor complex formation
Isabella AN Tonaco; Stefan de Folter; Anna Shchennikova; Aalt DJ van Dijk; Jacqueline Busscher-Lange; Jan W Borst; Gerco C Angenent
BACKGROUND: Plant MADS box proteins play important roles in a plethora of developmental processes. In order to regulate specific sets of target genes, MADS box proteins dimerize and are thought to assemble into multimeric complexes. In this study a large-scale yeast three-hybrid screen is utilized to provide insight into the higher-order complex formation capacity of the Arabidopsis MADS box family.
A permeability transition in liposomes induced by the formation of Ca 2+\\/palmitic acid complexes
Alexey Agafonov; Elena Gritsenko; Konstantin Belosludtsev; Alexandr Kovalev; Odile Gateau-Roesch; Nils-Erik L. Saris; Galina D. Mironova
Formation of palmitic acid\\/Ca2+ (PA\\/Ca2+) complexes was suggested to play a key role in the non-classical permeability transition in mitochondria (NCPT), which seems to be involved in the PA-induced apoptosis of cardiomyocytes. Our previous studies of complexation of free fatty acids (FFA) with Ca2+ showed that long-chain (C:16–C:22) saturated FFA had an affinity to Ca2+, which was much higher than
Formation of Stable Cationic Lipid/DNA Complexes for Gene Transfer
NASA Astrophysics Data System (ADS)
Hofland, Hans E. J.; Shephard, Lee; Sullivan, Sean M.
Stable cationic lipid/DNA complexes were formed by solubilizing cationic liposomes with 1% octylglucoside and complexing a DNA plasmid with the lipid in the presence of detergent. Removal of the detergent by dialysis yielded a lipid/DNA suspension that was able to transfect tissue culture cells up to 90 days after formation with no loss in activity. Similar levels of gene transfer were obtained by mixing the cationic lipid in a liposome form with DNA just prior to cell addition. However, expression was completely lost 24 hr after mixing. The transfection efficiency of the stable complex in 15% fetal calf serum was 30% of that obtained in the absence of serum, whereas the transient complex was completely inactivated with 2% fetal calf serum. A 90-day stability study comparing various storage conditions showed that the stable complex could be stored frozen or as a suspension at 4 degrees C with no loss in transfection efficiency. Centrifugation of the stable complex produced a pellet that contained approximately 90% of the DNA and 10% of the lipid. Transfection of cells with the resuspended pellet and the supernatant showed that the majority of the transfection activity was in the pellet and all the toxicity was in the supernatant. Formation of a stable cationic lipid/DNA complex has produced a transfection vehicle that can be stored indefinitely, can be concentrated with no loss in transfection efficiency, and the toxicity levels can be greatly reduced when the active complex is isolated from the uncomplexed lipid.
Formation of Vacancy-Impurity Complexes by Kinetic Processes in Highly As-Doped Si
NASA Astrophysics Data System (ADS)
Ranki, V.; Nissilä, J.; Saarinen, K.
Positron annihilation experiments have been applied to verify the formation mechanism of electrically inactive vacancy-impurity clusters in highly n-type Si. We show that the migration of V-As pairs at 450 K leads to the formation of V-As2 complexes, which in turn convert to stable V-As3 defects at 700 K. These processes manifest the formation of V-As3 as the dominant vacancy-impurity cluster in highly n-type Si. They further explain the electrical deactivation and clustering of As in epitaxial or ion-implanted Si during postgrowth heat treatment at 700 K.
Cation-induced formation of a macro-glucan synthase complex
Delmer, D.; Solomon, M.; Andrawis, A.; Amor, Y. (Hebrew Univ., Jerusalem (Israel))
Incubation of Chaps or digitonin-solubilized membrane proteins from cotton fiber with Ca{sup 2+} in combination with Mg{sup 2+}, leads to formation of a complex which can be sedimented within 15 min at 15,000 g. The complex is enriched >10-fold in callose synthase activity and possesses a characteristic pattern of enriched polypeptides when analyzed by SDS-PAGE. Although cation dependent, formation of the complex is not dependent upon the presence of the callose synthase substrate, UDP-glc, indicating that complex formation is not due to entrapment of the enzyme by association with glucan product. The enriched polypeptides include: >200, 50, and 46 kD, all of which have been shown by direct photo-labeling to interact with {sup 92}P-UDP-glc in a Ca{sup 2+} or beta-glucoside dependent reaction are considered likely subunits of callose synthase; a 60-62 kD doublet which is recognized by our MAb 2-1 which can form an immune complex with callose synthase; 74 and 34 kD polypeptides which also interact with UDP-glc, but do not associate with callose synthase in the presence of EDTA. A similar phenomenon is also observed with solubilized membrane proteins from mung beans. Possible functions of each of the enriched polypeptides, the catalytic properties, and ultra-structure of this macro-glucan synthase complex are currently under investigation.
Spectroscopic studies on the formation of molecular complexes of sulfamethoxazole with novel 2,3,5-trichloro-6-alkoxy-1,4-benzoquinones
NASA Astrophysics Data System (ADS)
Ganesh, K.; Balraj, C.; Satheshkumar, A.; Elango, K. P.
UV-Vis, 1H NMR, FT-IR, LC-MS and fluorescence spectral techniques were employed to investigate the mechanism of interaction of sulfamethoxazole with alkoxy substituted 2,3,5-trichloro-1,4-benzoquinones and to characterize the reaction products. The interactions of these quinones with sulfamethoxazole (SULF) were found to proceed through the formation of donor-acceptor complex, containing radical anion and its conversion to the product. Fluorescence quenching studies indicated that the interaction between the donor and the acceptors are spontaneous. Correlation of association constants of the CT complexes with Taft's polar and steric constants indicated that polar factor plays a significant role in governing the reactivity. The results indicated that the electronic effects of the substituents play significant role in governing the reactivity of the quinones when compared to steric factor.
Nup155 regulates nuclear envelope and nuclear pore complex formation in nematodes and vertebrates
Franz, Cerstin; Askjaer, Peter; Antonin, Wolfram; Iglesias, Carmen López; Haselmann, Uta; Schelder, Malgorzata; de Marco, Ario; Wilm, Matthias; Antony, Claude; Mattaj, Iain W
Nuclear envelope (NE) formation during cell division in multicellular organisms is a central yet poorly understood biological process. We report that the conserved nucleoporin Nup155 has an essential function in NE formation in Caenorhabditis elegans embryos and in Xenopus laevis egg extracts. In vivo depletion of Nup155 led to failure of nuclear lamina formation and defects in chromosome segregation at anaphase. Nup155 depletion inhibited accumulation of nucleoporins at the nuclear periphery, including those recruited to chromatin early in NE formation. Electron microscopy analysis revealed that Nup155 is also required for the formation of a continuous nuclear membrane in vivo and in vitro. Time-course experiments indicated that Nup155 is recruited to chromatin at the time of NE sealing, suggesting that nuclear pore complex assembly has to progress to a relatively late stage before NE membrane assembly occurs. PMID:16193066
Validated Stability indicating Spectrophotometric Method for the Determination of Acetazolamide in Dosage Forms through Complex Formation with Palladium (II)
Walash, M. I.; El-Brashy, A.; El-Enany, N.; Wahba, M. E. K.
A simple and sensitive spectrophotometric method was developed for the determination of acetazolamide (ACM) in pure form and pharmaceutical preparations. The proposed method is based on the complex formation of acetazolamide with Palladium (II) chloride in acetate buffer pH5.4 and measuring the absorbance at 308 nm. The absorbance- concentration plot was rectilinear over the concentration range of 5-70 ?g/ml with a minimum detection limit (LOD) of 0.98 ?g/ml, limit of quantification (LOQ) of 2.96 ?g/ml, and a molar absorptivity ?=2.7 × 103 L/mol.cm. The factors affecting the absorbance of the formed complex were carefully studied and optimized. The composition of the complex as well as its stability constant was also investigated. The proposed method was applied for the determination of acetazolamide in its tablets and the results obtained were favorably compared with those obtained using the official method. A proposal of the reaction pathway was postulated. PMID:23675188
Structural, electronic properties and heat of formation of Mg2FeH6 complex hydride: an ab initio study
NASA Astrophysics Data System (ADS)
Zareii, S. M.; Sarhaddi, R.
In this work, the structural, energetic and electronic properties of Mg2FeH6 complex hydride have been studied using two different methods based on the density functional theory (DFT): the full potential linearized augmented plane wave plus local orbitals (FP-LAPW + lo) and the pseudo-potentials plane waves (PP-PW) methods. Based on the calculated results, the ground state of Mg2FeH6 is found to be paramagnetic (PM), which is in agreement with experimental results, and also, the optimized structural parameters including lattice constants and atomic positions are very close to the experimental and other theoretical works. For a detailed study, electronic structure calculations including those of the energy band, density of states (DOS) and charge density distribution have been performed. It is found that Mg2FeH6 hydride is a semiconductor with a direct energy gap at the X-point of about 1.87 and 2.25 eV for the FP-LAPW + lo and PW-PP methods, respectively, and the Mg atom acts as a donor to form a cation ion and the negatively charged FeH6 complex results in a mainly ionic bonding between the Mg and FeH6 complex. Other physical and energetic properties such as bulk modulus, cohesive energy and formation enthalpy of Mg2FeH6 are in good agreement with the theoretically and experimentally determined values.
Complex formation of Zn-, Ni-, and Pd-derivatives of purpurin-18 with serum albumin
NASA Astrophysics Data System (ADS)
Golovina, G. V.; Novikov, F. N.; Ol'shevskaya, V. A.; Kalinin, V. N.; Shtil, A. A.; Kuzmin, V. A.
We analyzed the spectral characteristics of the complexes of Zn2+, Ni2+, and Pd2+ derivatives of purpurin-18 with human serum albumin (HSA) in aqueous buffer at pH 7.0. Pd2+ in the coordination sphere of purpurin-18 decreased the affinity to HSA compared to the respective complexes of zinc and nickel derivatives. Since the formation of complexes with HSA is an important parameter of photodynamic activity of tetrapyrrolic compounds, the differential affinity of metal derivatives of purpurin-18 to this protein should be considered for the optimization of photosensitizers.
Salting Constants of Small Organic Molecules in Aerosol-Relevant Salts and Application to Aerosol Formation in the Southeastern United States
NASA Astrophysics Data System (ADS)
Waxman, E.; Carlton, A. M. G.; Ziemann, P. J.; Volkamer, R. M.
Secondary organic aerosol (SOA) formation from small water-soluble molecules such as glyoxal and methyl glyoxal is a topic of emerging interest. Results from recent field campaigns, e.g. Waxman et al. (2013, GRL) and Knote et al. (2014, ACP), show that these molecules can form significant SOA mass as a result of 'salting-in'. Salting-in happens when a molecule's solubility increases with salt concentration and salting-out is the reverse. Salting effects modify the solubility exponentially with increasing salt concentration, and thus the effective Henry's law constant can strongly modify partitioning, and multiphase chemical reaction rates in aerosol water. Moreover, the solubility in aerosol water cannot easily inferred based on the solubility in cloud water, as the salting effects could change the solubility by a factor of 104 or more. In this work, we have devised and applied a novel experimental setup to measure salting constants using an ion trap mass spectrometer. We focus on small, water soluble molecules like methyl glyoxal and similar compounds and measure salting constants for aerosol-relevant salts including ammonium sulfate, ammonium nitrate, and sodium chloride. The Setschenow salting-constant values are then used to parameterize the effects of salting in CMAQ. We present a series of sensitivity studies of the effects that inorganic aerosols have on the SOA formation from small soluble molecules in the southeastern United States.
Phosphonato complexes of platinum(II): kinetics of formation and phosphorus-31 NMR characterization studies.
Slavin, L L; Bose, R N
Reactions of cis-diamminedichloroplatinum(II) with phosphonoformic acid (PFA), phosphonoacetic acid (PAA), and methylenediphosphonic acid (MDP) yield various phosphonatoplatinum(II) chelates which were characterized by phosphorus-31 NMR spectroscopy. The P-31 resonances for the chelates appear at 6-12 ppm downfield as compared to the uncomplexed ligands. All complexes exhibit monoprotic acidic behavior in the pH range 2-10. The chemical shift-pH profiles yielded acidity constants, 1.0 x 10(-4), 1.5 x 10(-4), and 1.3 x 10(-6) M-1, for the PFA, PAA, and MDP chelates. In addition to the monomeric chelate, MDP formed a bridged diplatinum(II,II) complex when it reacted with cis-Pt (NH3)2(H2O)2(2)+. The P-31 resonance for this binuclear complex appears at 22 ppm downfield from the unreacted ligand. Rate data for the complexation reactions of the phosphonate ligands with the dichloroplatinum complex are consistent with a mechanism in which a monodentate complex is formed initially through rate-limiting aquation process of the platinum complex, followed by a rapid chelation. For the PFA and PAA complexes, initial binding sites are the carboxylato oxygens. Implications of the various binding modes of the phosphonates in relationship to their antiviral activities are discussed. PMID:2150856
Phosphonato complexes of platinum(II): kinetics of formation and phosphorus-31 NMR characterization studies
Slavin, L.L.; Bose, R.N. (Chemistry Department, Kent State University, OH (USA))
Reactions of cis-diamminedichloroplatinum(II) with phosphonoformic acid (PFA), phosphonoacetic acid (PAA), and methylenediphosphonic acid (MDP) yield various phosphonatoplatinum(II) chelates which were characterized by phosphorus-31 NMR spectroscopy. The P-31 resonances for the chelates appear at 6-12 ppm downfield as compared to the uncomplexed ligands. All complexes exhibit monoprotic acidic behavior in the pH range 2-10. The chemical shift-pH profiles yielded acidity constants, 1.0 x 10(-4), 1.5 x 10(-4), and 1.3 x 10(-6) M-1, for the PFA, PAA, and MDP chelates. In addition to the monomeric chelate, MDP formed a bridged diplatinum(II,II) complex when it reacted with cis-Pt (NH3)2(H2O)2(2)+. The P-31 resonance for this binuclear complex appears at 22 ppm downfield from the unreacted ligand. Rate data for the complexation reactions of the phosphonate ligands with the dichloroplatinum complex are consistent with a mechanism in which a monodentate complex is formed initially through rate-limiting aquation process of the platinum complex, followed by a rapid chelation. For the PFA and PAA complexes, initial binding sites are the carboxylato oxygens. Implications of the various binding modes of the phosphonates in relationship to their antiviral activities are discussed.
Phosphonato complexes of platinum(II): kinetics of formation and phosphorus-31 NMR characterization studies
L. L. Slavin; R. N. Bose
Reactions of cis-diamminedichloroplatinum(II) with phosphonoformic acid (PFA), phosphonoacetic acid (PAA), and methylenediphosphonic acid (MDP) yield various phosphonatoplatinum(II) chelates which were characterized by phosphorus-31 NMR spectroscopy. The P-31 resonances for the chelates appear at 6-12 ppm downfield as compared to the uncomplexed ligands. All complexes exhibit monoprotic acidic behavior in the pH range 2-10. The chemical shift-pH profiles yielded acidity constants,
Intense phosphorescence triggered by alcohols upon formation of a cyclodextrin ternary complex
Adrian Ponce; Peter A. Wong; Daniel G. Nocera
Intense phosphorescence is observed when alcohols (ROH) are introduced to aqueous solutions containing 1 -bromonaphthalene (1 -BrNp) and a glucosyl-modified cyclodextrin (G@-CD). Steady- state and time-resolved luminescence measurements and equilibrium constant data are consistent with phosphorescence arising from l-BrNp as part of a l-BrNpG@-CD*ROH ternary complex. The association of the l-BrNp to Gj3-CD is increased in the presence of the
Transcription by RNA polymerase II: initiator-directed formation of transcription-competent complexes
Studies of transcription by RNA polymer- ase II have revealed two promoter elements, the TATA motif and the initiator (Inr), capable of directing specific transcription initiation. Although binding to the TATA motif by one of the components of the transcription machinery has been shown to be the initial recognition step in transcription complex formation, many promoters that lack a traditional
Monte Carlo simulations of complex formation between a mixed fluid vesicle and a charged colloid
Iglic, Ales
Monte Carlo simulations of complex formation between a mixed fluid vesicle and a charged colloid fluidlike vesicle to adhere to and encapsulate an oppositely charged spherical colloidal particle. The vesicle contains mobile charges that interact with the colloid and among themselves through a screened
The effect of an ?-globulin preparation and of polyribonuclease complexes on humoral antibody formation
Pullar, Diane M.; James, K.; Naysmith, J. D.
The effects of bovine ?-globulin (BAG), bovine-ribonuclease serum albumin (BSA-RNase) and polyribonuclease (poly-RNase) complexes on the primary response of rodents to sheep erythrocytes have been investigated. These preparations frequently failed to cause marked suppression of humoral antibody formation. PMID:4173925
To clarify the photochemical smog formation mechanisms under conditions of complex flow, the SAI Urban Airshed Model was evaluated using a 1981 field observed data base. In the Tokyo Metropolitan Area higher O3 concentrations are usually observed near the shore in the morning. As...
Dynamics of cadherin\\/catenin complex formation: novel protein interactions and pathways of complex assembly
Lindsay Hinck; Inke S. Ntithke; Jackie Papkoff; W. James Nelson
Calcium-dependent cell-cell adhesion is mediated by the cadherin family of cell adhesion pro- teins. Transduction of cadherin adhesion into cellular reorganization is regulated by cytosolic proteins, termed ct-, ~-, and qc-catenin (plakoglobin), that bind to the cytoplasmic domain of cadherins and link them to the cytoskeleton. Previous studies of cadherin\\/cate- nin complex assembly and organization relied on the coimmunoprecipitation of
Complexes of dextran sulfate and anthocyanins from Vaccinium myrtillus: Formation and stability.
Klimaviciute, Rima; Navikaite, Vesta; Jakstas, Valdas; Ivanauskas, Liudas
To improve the stability and antioxidant activity of anthocyanins (ATC), complexes of dextran sulfate (DESU) and ATC extracted from Vaccinium myrtillus were formed during electrostatic interaction between sulfo groups of DESU and cationic moieties of ATC. At the optimal weight ratio DESU/ATC=0.4g/g, the amount of ATC introduced into a complex depended on the total concentration of the reagents. About 1.7g of ATC per g of DESU could be incorporated into a complex. The formation of DESU/ATC complexes was confirmed by HPLC and FT-IR spectroscopy. According to HPLC analysis, the amount of individual ATC incorporated into a complex varied from 73.7% in the case of malvidin-3-O-glucoside to 90.8% in the case of delphinidin-3-arabinoside. PMID:26050890
Mechanism of acyl-enzyme complex formation from the Henry-Michaelis complex of class C ?-lactamases with ?-lactam antibiotics.
Tripathi, Ravi; Nair, Nisanth N
Bacteria that cause most of the hospital-acquired infections make use of class C ?-lactamase (CBL) among other enzymes to resist a wide spectrum of modern antibiotics and pose a major public health concern. Other than the general features, details of the defensive mechanism by CBL, leading to the hydrolysis of drug molecules, remain a matter of debate, in particular the identification of the general base and role of the active site residues and substrate. In an attempt to unravel the detailed molecular mechanism, we carried out extensive hybrid quantum mechanical/molecular mechanical Car-Parrinello molecular dynamics simulation of the reaction with the aid of the metadynamics technique. On this basis, we report here the mechanism of the formation of the acyl-enzyme complex from the Henry-Michaelis complex formed by ?-lactam antibiotics and CBL. We considered two ?-lactam antibiotics, namely, cephalothin and aztreonam, belonging to two different subfamilies. A general mechanism for the formation of a ?-lactam antibiotic-CBL acyl-enzyme complex is elicited, and the individual roles of the active site residues and substrate are probed. The general base in the acylation step has been identified as Lys67, while Tyr150 aids the protonation of the ?-lactam nitrogen through either the substrate carboxylate group or a water molecule. PMID:24010547
Lethal synergism between organic and inorganic wood preservatives via formation of an unusual lipophilic ternary complex
Sheng, Zhi-Guo; Li, Yan; Fan, Rui-Mei; Chao, Xi-Juan [State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, Beijing 100085 (China)] [State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, Beijing 100085 (China); Zhu, Ben-Zhan, E-mail: email@example.com [State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, Beijing 100085 (China) [State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, Beijing 100085 (China); Linus Pauling Institute, Oregon State University, Corvallis, OR 97331 (United States)
We have shown previously that exposing bacteria to wood preservatives pentachlorophenol (PCP) and copper-containing compounds together causes synergistic toxicity. However, it is not clear whether these findings also hold true in mammalian cells; and if so, what is the underlying molecular mechanism? Here we show that PCP and a model copper complex bis-(1,10-phenanthroline) cupric (Cu(OP){sub 2}), could also induce synergistic cytotoxicity in human liver cells. By the single crystal X-ray diffraction and atomic absorption spectroscopy assay, the synergism was found to be mainly due to the formation of a lipophilic ternary complex with unusual structural and composition characteristics and subsequent enhanced cellular copper uptake, which markedly promoted cellular reactive oxygen species (ROS) production, leading to apoptosis by decreasing mitochondrial membrane potential, increasing pro-apoptotic protein expression, releasing cytochrome c from mitochondria and activating caspase-3, and -9. Analogous results were observed with other polychlorinated phenols (PCPs) and Cu(OP){sub 2}. Synergistic cytotoxicity could be induced by PCP/Cu(OP){sub 2} via formation of an unusual lipophilic complex in HepG2 cells. The formation of ternary complexes with similar lipophilic character could be of relevance as a general mechanism of toxicity, which should be taken into consideration especially when evaluating the toxicity of environmental pollutants found at currently-considered non- or sub-toxic concentrations. -- Highlights: ? The combination of PCP/Cu(OP){sub 2} induces synergistic cytotoxicity in HepG2 cells. ? The synergism is mainly due to forming a lipophilic ternary complex between them. ? The formation of lipophilic ternary complex enhances cellular copper uptake. ? PCP/Cu(OP){sub 2} stimulates the cellular ROS production. ? The ROS promoted by PCP/Cu(OP){sub 2} induces mitochondria-dependent apoptosis.
More efficient iterative uses of tricarbonyliron complexes are possible by diastereoselective formation of ? 5-cyclohexadienyl complexes
Christopher E. Anson; Michael R. Attwood; Tony M. Raynham; Donald G. Smyth; R. Richard Stephenson
Diastereoselective addition of nucleophiles to 1-(RCO)-substituted tricarbony?4-cyclohexadiene)iron(0) complexes, and a diastereoselective acid-induced rearrangement to form 1-(branched alkyl)-substituted tricarbonyl(?5-cyclohexadienyl)iron(1+) salts, are described. Stereocontrol in the rearrangement has been studied, and HPF6, Ac2O has been shown to be the most suitable acid to promote diastereoselectivity. The product was reacted with LiCH(SO2Ph)2, completing one turn of an iterative cycle which formed a chiral
Effect of citrate on the local Fe coordination in ferrihydrite, arsenate binding, and ternary arsenate complex formation
NASA Astrophysics Data System (ADS)
Mikutta, Christian; Frommer, Jakob; Voegelin, Andreas; Kaegi, Ralf; Kretzschmar, Ruben
In oxic environments contaminated with arsenate (As(V)), small polyhydroxycarboxylates such as citrate may impact the structure of precipitating ferrihydrite (Fh) and thus the surface speciation of As(V). In this study, '2-line' Fh was precipitated from ferric nitrate solutions that were neutralized to pH 6.5 in the presence of increasing citrate concentrations and in the absence or presence of As(V). The initial citrate/Fe and As/Fe ratios were 0-50 mol% and 5 mol%, respectively. The reaction products, enriched with up to 0.32 mol citrate per mole Fe, were characterized by X-ray diffraction, transmission electron microscopy, and Fe and As K-edge X-ray absorption spectroscopy. Citrate decreased the particle size of Fh by impairing the polymerization of Fe(O,OH) 6 octahedra via edge and corner linkages. In the presence of citrate and As(V), coordination numbers of Fe decreased by up to 28% relative to pure Fh. Citrate significantly reduced the static disorder of Fe-O bonds, implying a decreased octahedral distortion in Fh. Mean bond distances in Fh were not affected by citrate and remained constant within error at 1.98 Å for Fe-O, 3.03 Å for Fe-Fe1, and 3.45 Å for Fe-Fe2. Likewise, citrate had no effect on the As-Fe (3.31 Å) bond distance in As(V) coprecipitated with Fh. The As K-edge EXAFS data comply with the formation of (i) only monodentate binuclear ( 2C) As(V) surface complexes and (ii) combinations of 2C, monodentate mononuclear ( 1V), and outersphere As(V) surface complexes. Our results suggest that increasing citrate concentrations led to a decreasing 1V/ 2C ratio and/or that citrate increasingly impaired the formation of outersphere As(V) complexes. Moreover, citrate stabilized colloidal suspensions of Fh (pH 4.3-6.6, I ˜0.45 M) and reduced Fh formation at the expense of soluble Fe(III)-citrate complexes. At initial citrate/Fe ratios ?25 mol%, between 8% and 41% of total Fe was bound in Fe(III)-citrate complexes after Fh formation. Polynuclear Fe(III)-citrate species were found to bind As(V) via surface complexes indistinguishable by EXAFS from those of As(V) adsorbed to or coprecipitated with Fh. Our study implies that low molecular weight polyhydroxycarboxylates may enhance the mobility of As(V) in aqueous systems of high ionic strength (e.g., neutralizing acid mine drainage) by colloidal stabilization of suspended Fh particles and the formation of ternary As(V) complexes.
Formation and Reactivity of a Persistent Radical in a Dinuclear Molybdenum Complex
Appel, Aaron M.; Lee, Suh-Jane; Franz, James A.; DuBois, Daniel L.; Rakowski DuBois, Mary; Birnbaum, Jerome C.; Twamley, Brendan
The reactivity of the S-H bond in Cp*Mo(? S)2(? SMe)(? SH)MoCp* has been explored by hydrogen atom abstraction to form the radical Cp*Mo(? S)3(? SMe)MoCp*, as well as hydrogen addition to the radical to reform the S-H complex. The rate expression for abstraction of hydrogen atom by benzyl radical has been determined, giving log(kabs/M 1 s 1) = (2.41 ? 0.37)/(2.303RT) + (7.88 ? 0.25) with kabs = 1.3 x 106 M 1 s 1 at 25?C. The radical termination product of the Mo2S4 core was found to be the benzyl cross-termination product, Cp*Mo(? S)2(? SMe)(? SBz)MoCp*. Structures are presented for this complex as well as the cationic Cp*Mo(? S2)(? S)(? SMe)MoCp*(OTf), a precursor of the radical and the alkylated derivatives. The radical undergoes reversible dimerization to form the tetranuclear complex (Cp*Mo(? S)2(? SMe)MoCp*)2(? S2), as shown by the solid state structure. In solution, the radical and the dimer are in equilibrium, and the equilibrium constant for dimerization has been estimated from magnetic susceptibility and EPR data. The rate of dissociation of the dimer has been determined to be 640 s-1 at 25?C, based on variable temperature 1H NMR data. The rate constant for dimerization of the radical has been estimated to be ?1x107 M-1 s-1, based on the dimer dissociation rate constant and the lower limit of the equilibrium constant for dimerization.
Topoisomerase II? promotes activation of RNA polymerase I transcription by facilitating pre-initiation complex formation
Ray, Swagat; Panova, Tatiana; Miller, Gail; Volkov, Arsen; Porter, Andrew C. G.; Russell, Jackie; Panov, Konstantin I.; Zomerdijk, Joost C. B. M.
Type II DNA topoisomerases catalyse DNA double-strand cleavage, passage and re-ligation to effect topological changes. There is considerable interest in elucidating topoisomerase II roles, particularly as these proteins are targets for anti-cancer drugs. Here we uncover a role for topoisomerase II? in RNA polymerase I-directed ribosomal RNA gene transcription, which drives cell growth and proliferation and is upregulated in cancer cells. Our data suggest that topoisomerase II? is a component of the initiation-competent RNA polymerase I? complex and interacts directly with RNA polymerase I-associated transcription factor RRN3, which targets the polymerase to promoter-bound SL1 in pre-initiation complex formation. In cells, activation of rDNA transcription is reduced by inhibition or depletion of topoisomerase II, and this is accompanied by reduced transient double-strand DNA cleavage in the rDNA-promoter region and reduced pre-initiation complex formation. We propose that topoisomerase II? functions in RNA polymerase I transcription to produce topological changes at the rDNA promoter that facilitate efficient de novo pre-initiation complex formation. PMID:23511463
Sensory rhodopsin II/transducer complex formation in detergent and in lipid bilayers studied with FRET.
Kriegsmann, J; Brehs, M; Klare, J P; Engelhard, M; Fitter, J
The photophobic receptor from Natronomonas pharaonis (NpSRII) forms a photo-signalling complex with its cognate transducer (NpHtrII). In order to elucidate the complex formation in more detail, we have studied the intermolecular binding of both constituents (NpSRII and NpHtrII157; truncated at residue 157) in detergent buffers, and in lipid bilayers using FRET. The data for hetero-dimer formation of NpSRII/NpHtrII in detergent agrees well with KD values (approximately 200 nM) described in the literature. In lipid bilayers, the binding affinity between proteins in the NpSRII/NpHtrII complex is at least one order of magnitude stronger. In detergent the strength of binding is similar for both homo-dimers (NpSRII/NpSRII and NpHtrII/NpHtrII) but significantly weaker (KD approximately 16 microM) when compared to the hetero-dimer. The intermolecular binding is again considerably stronger in lipid bilayers; however, it is not as strong as that observed for the hetero-dimer. At a molar transducer/lipid ratio of 1:2000, which is still well above physiological concentrations, only 40% homo-dimers are formed. Apparently, in cell membranes the formation of the assumed functionally active oligomeric 2:2 complex depends on the full-length transducer including the helical cytoplasmic part, which is thought to tighten the transducer-dimer association. PMID:19094962
Formation of complexes between PAMAM-NH2 G4 dendrimer and L-?-tryptophan and L-?-tyrosine in water.
Buczkowski, Adam; Urbaniak, Pawel; Belica, Sylwia; Sekowski, Szymon; Bryszewska, Maria; Palecz, Bartlomiej
Interactions between electromagnetic radiation and the side substituents of aromatic amino acids are widely used in the biochemical studies on proteins and their interactions with ligand molecules. That is why the aim of our study was to characterize the formation of complexes between PAMAM-NH2 G4 dendrimer and L-?-tryptophan and L-?-tyrosine in water. The number of L-?-tryptophan and L-?-tyrosine molecules attached to the macromolecule of PAMAM-NH2 G4 dendrimer and the formation constants of the supramolecular complexes formed have been determined. The macromolecule of PAMAM-NH2 G4 can reversibly attach about 25 L-?-tryptophan molecules with equilibrium constant K equal to 130±30 and 24±6 L-?-tyrosine molecules. This characterization was deduced on the basis of the solubility measurements of the amino acids in aqueous dendrimer solutions, the (1)H NMR and 2D-NOESY measurements of the dendrimer solutions with the amino acids, the equilibrium dialysis and the circular dichroism measurements of the dendrimer aqueous solutions with L-?-tryptophan. Our date confirmed the interactions of L-?-tryptophan and L-?-tyrosine with the dendrimer in aqueous solution and indicated a reversible character of the formed complexes. PMID:24704481
Improved complexation of paraquat derivatives by the formation of crown ether-based cryptands.
Zhang, Mingming; Zhu, Kelong; Huang, Feihe
Self-assembly allows the construction of advanced molecular or supramolecular systems from small building blocks. Host-guest recognition, for its self-selectivity, environmental responsiveness and convenient application to complex molecular devices, plays a significant role in self-assembled systems. During this process, the association constant between the host and guest is an important standard to identify the properties of the systems. In order to prepare mechanically interlocked structures and large supramolecular systems efficiently from small molecules based on a host-guest recognition motif, it is necessary to increase host-guest association constants. Crown ether-based cryptands have been designed and prepared to improve the binding of paraquat derivatives. This feature article aims to describe the design and syntheses of crown ether-based cryptand hosts for paraquat derivatives and the application of the cryptand/paraquat recognition motif in the fabrication of threaded structures, molecular switches and supramolecular polymers. PMID:20830438
Formation equilibria of nickel complexes with glycyl-histidyl-lysine and two synthetic analogues.
Conato, Chiara; Koz?owski, Henryk; Swiatek-Koz?owska, Jolanta; M?ynarz, Piotr; Remelli, Maurizio; Silvestri, Sergio
Complex-formation equilibria between the Ni(II) ion and the natural tripeptide glycyl-L-histidyl-L-lysine have been investigated. Two synthetic analogues, where the histidine residue has been substituted with L-4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylic acid (L-Spinacine) and L-1,2,3,4-tetrahydro-isoquinolin-3-carboxylic acid (Tic), respectively, have been considered, as well. Different experimental techniques have been employed: potentiometry, calorimetry, visible spectrophotometry and CD spectroscopy. Structural hypotheses on the main complex species are suggested. Evidences on the formation of tetrameric species with the first ligand are shown. No involvement of the side-chain amino group of lysine residue in metal ion coordination was found. PMID:14659644
Improved production of 3-hydroxypropionaldehyde by complex formation with bisulfite during biotransformation of glycerol.
Sardari, Roya R R; Dishisha, Tarek; Pyo, Sang-Hyun; Hatti-Kaul, Rajni
3-Hydroxypropionaldehyde (3HPA) is an important specialty chemical which can be produced from glycerol using resting cells of Lactobacillus reuteri. This biocatalytic route, however, suffers from substrate- and product-mediated loss of enzyme activity within 2 h of biotransformation. In order to overcome the inhibitory effects of 3HPA, complex formation with sodium bisulfite was investigated, optimized and applied for in situ capture of the aldehyde during biotransformation of glycerol in a fed-batch process. As a result, the activity of the cells was maintained for at least 18 h. The 3HPA produced per gram cell dry weight was increased 5.7 times compared to the batch production process, and 2.2 times compared to fed-batch process without in situ complex formation. This approach may have potential for production and in situ removal of 3HPA after further process development. PMID:23172314
A rapid and quantitative coat protein complex II vesicle formation assay using luciferase reporters.
Fromme, J Chris; Kim, Jinoh
The majority of protein export from the endoplasmic reticulum (ER) is facilitated by coat protein complex II (COPII). The COPII proteins deform the ER membrane into vesicles at the ER exit sites. During the vesicle formation step, the COPII proteins load cargo molecules into the vesicles. Formation of COPII vesicles has been reconstituted in vitro in yeast and in mammalian systems. These in vitro COPII vesicle formation assays involve incubation of microsomal membranes and purified COPII proteins with nucleotides. COPII vesicles are separated from the microsomes by differential centrifugation. Interestingly, the efficiency of the COPII vesicle formation with purified recombinant mammalian COPII proteins is lower than that with cytosol, suggesting that an additional cytosolic factor(s) is involved in this process. Indeed, other studies have also implicated additional factors. To facilitate biochemical identification of such regulators, a rapid and quantitative COPII vesicle formation assay is necessary because the current assay is lengthy. To expedite this assay, we generated luciferase reporter constructs. The reporter proteins were packaged into COPII vesicles and yielded quantifiable luminescent signals, resulting in a rapid and quantitative COPII vesicle formation assay. PMID:22244805
Formation of 1:1 and 2:1 host-guest inclusion complexes of ?-cyclodextrin with cycloalkanols: A 1H and 13C NMR spectroscopic study
NASA Astrophysics Data System (ADS)
Akita, Tomoki; Yoshikiyo, Keisuke; Yamamoto, Tatsuyuki
Binding constants (Ka's) for the formation of inclusion complexes of ?-cyclodextrin (?-CD) with cycloalkanols (c-CnOH; n = 4-8) were determined by means of 1H and 13C NMR titration, under two different conditions: (i) only 1:1 host-guest inclusion complexes are formed when the guest is in excess; (ii) the formation of 2:1 inclusion complexes occurs only after that of 1:1 inclusion complexes, when the host is in excess. The results of this work showed that ?-CD can include c-C4OH or c-C5OH only when the molar ratio is 1:1; larger ring-sized cycloalkanols such as c-C6OH, c-C7OH or c-C8OH can be included only when the molar ratio is 2:1. These findings, together with those obtained for the four derivatives of ?-CD, per-6-O-methyl-?-CD, per-2-O-methyl-?-CD, per-3-O-methyl-?-CD, and per-2,6-di-O-methyl-?-CD, suggested that ?-CD forms 2:1 inclusion complexes with c-C6OH, c-C7OH or c-C8OH in a tail-to-tail manner, in which the secondary hydroxy sides of the two CD molecules face each other. Two-dimensional ROESY measurements confirmed our results.
Experimental and calculated complex formation curves for a labile metal-ligand system a differential pulse polarographic study of the Pb(II)-( N, N, N?, N?-tetramethylethylenediamine-OH system at fixed ligand to metal ratio and varied pH
Ignacy Cukrowski; Michael Adsetts
Experimental and calculated complex formation curves (ECFC and CCFC) for a labile metal-ligand system are defined and used for the speciation study by differential pulse polarography (DPP) at fixed total ligand (LT) to total metal (MT) concentration ratio and varied pH. The CCFC is used for the modeling of species formed in a solution and optimization of formation constants for
How important is polyelectrolyte complex formation in biomimetic mineralisation? Manipulation via alcohol addition.
Munro, Natasha H; McGrath, Kathryn M
Understanding the formation of biominerals like nacre can lead to the fabrication of more advanced biomimetic materials. Several factors are known to influence the final form of both native nacre and biomimetic synthetic variants. Two important components in calcium carbonate biominerals such as nacre are the organic scaffold and the acidic proteins. Interactions between these two components may also influence final composite characteristics. In this investigation chitosan hydrogels were prepared from acidic aqueous solution using four alcohols as cosolvents. The addition of alcohol enables direct modification of the network of the chitosan hydrogel (and thereby the nanometre and micrometre length-scale structure of the hydrogel). Both alcohol-modified chitosan and subsequently reacetylated chitin scaffolds were then mineralised with a combined soaking mineralisation method in the presence of poly(acrylic acid), the latter of which mimics the role of the acidic proteins in the native system. The effects of these structural variations of the hydrogel, induced by the presence of alcohol during fabrication, on (1) the formation of a polyelectrolyte complex between the chitosan or chitin and the poly(acrylic acid) and (2) the subsequent polymorph and morphology of calcium carbonate crystals mineralised within the hydrogel scaffold were investigated. Increasing the amount of the alcohols 1,2-propanediol or 1,3-propanediol led to increased disruption of the hydrogen bonding of the hydrogel scaffold and significant changes to, or reduced formation of, the polyelectrolyte complex formed between the scaffold carbohydrate and the poly(acrylic acid). The disruption of the polyelectrolyte complex in turn led to a loss of control over which polymorph of calcium carbonate is nucleated. These results show that the physical form of the polymer scaffold in these organic/inorganic composites, and the formation of the polyelectrolyte complex play a crucial role in determining the final composite structure and the calcium carbonate polymorphs and morphologies. PMID:23595573
Aluminum ion complex formation with 3-hydroxyflavone in Langmuir and Langmuir–Blodgett films
J. P Santos; M. E. D Zaniquelli; W. F De Giovani; S. E Galembeck
The flavonoid 3-hydroxyflavone (3HF) is insoluble in water at room temperature and it presents a poor spreading behavior at the air–water interface. The strategy used in this work for preparation of liquid monolayers was to spread pure 3HF and 3HF\\/hexadecanol mixtures on aluminum aqueous solution. The flavonoid is spontaneously spread at the air–liquid interface by its complex formation with aluminum
Anthrax Lethal Toxin Triggers the Formation of a Membrane-Associated Inflammasome Complex in Murine Macrophages
Adel M. Nour; Laura Santambrogio; Eric D. Boyden; E. Richard Stanley; Jurgen Brojatsch
Multiple microbial components trigger the formation of an inflammasome complex that contains pathogen- specific nucleotide oligomerization and binding domain (NOD)-like receptors (NLRs), caspase-1, and in some cases the scaffolding protein ASC. The NLR protein Nalp1b has been linked to anthrax lethal toxin (LT)- mediated cytolysis of murine macrophages. Here we demonstrate that in unstimulated J774A.1 macrophages, caspase-1 and Nalp1b are
An Efficient Format for Nearly Constant-Time Access to Arbitrary Time Intervals in Large Trace Files
Chan, Anthony; Gropp, William; Lusk, Ewing
A powerful method to aid in understanding the performance of parallel applications uses log or trace files containing time-stamped events and states (pairs of events). These trace files can be very large, often hundreds or even thousands of megabytes. Because of the cost of accessing and displaying such files, other methods are often used that reduce the size of the tracefiles at the cost of sacrificing detail or other information. This paper describes a hierarchical trace file format that provides for display of an arbitrary time window in a time independent of the total size of the file and roughlymore »proportional to the number of events within the time window. This format eliminates the need to sacrifice data to achieve a smaller trace file size (since storage is inexpensive, it is necessary only to make efficient use of bandwidth to that storage). The format can be used to organize a trace file or to create a separate file ofannotationsthat may be used with conventional trace files. We present an analysis of the time to access all of the events relevant to an interval of time and we describe experiments demonstrating the performance of this file format.« less
A histone H3 lysine-27 methyltransferase complex represses lateral root formation in Arabidopsis thaliana.
Gu, Xiaofeng; Xu, Tongda; He, Yuehui
Root branching or lateral root formation is crucial to maximize a root system acquiring nutrients and water from soil. A lateral root (LR) arises from asymmetric cell division of founder cells (FCs) in a pre-branch site of the primary root, and FC establishment is essential for lateral root formation. FCs are known to be specified from xylem pole pericycle cells, but the molecular genetic mechanisms underlying FC establishment are unclear. Here, we report that, in Arabidopsis thaliana, a PRC2 (for Polycomb repressive complex 2) histone H3 lysine-27 (H3K27) methyltransferase complex, functions to inhibit FC establishment during LR initiation. We found that functional loss of the PRC2 subunits EMF2 (for EMBRYONIC FLOWER 2) or CLF (for CURLY LEAF) leads to a great increase in the number of LRs formed in the primary root. The CLF H3K27 methyltransferase binds to chromatin of the auxin efflux carrier gene PIN FORMED 1 (PIN1), deposits the repressive mark H3K27me3 to repress its expression, and functions to down-regulate auxin maxima in root tissues and inhibit FC establishment. Our findings collectively suggest that EMF2-CLF PRC2 acts to down-regulate root auxin maxima and show that this complex represses LR formation in Arabidopsis. PMID:24711289
True boundary for the formation of homoleptic transition-metal hydride complexes.
Takagi, Shigeyuki; Iijima, Yuki; Sato, Toyoto; Saitoh, Hiroyuki; Ikeda, Kazutaka; Otomo, Toshiya; Miwa, Kazutoshi; Ikeshoji, Tamio; Aoki, Katsutoshi; Orimo, Shin-Ichi
Despite many exploratory studies over the past several decades, the presently known transition metals that form homoleptic transition-metal hydride complexes are limited to the Groups?7-12. Here we present evidence for the formation of Mg3 CrH8 , containing the first Group?6 hydride complex [CrH7 ](5-) . Our theoretical calculations reveal that pentagonal-bipyramidal H coordination allows the formation of ?-bonds between H and Cr. The results are strongly supported by neutron diffraction and IR spectroscopic measurements. Given that the Group?3-5 elements favor ionic/metallic bonding with H, along with the current results, the true boundary for the formation of homoleptic transition-metal hydride complexes should be between Group?5 and 6. As the H coordination number generally tends to increase with decreasing atomic number of transition metals, the revised boundary suggests high potential for further discovery of hydrogen-rich materials that are of both technological and fundamental interest. PMID:25773066
Rapid formation of cell-particle complexes via dielectrophoretic manipulation for the detection of surface antigens.
Horii, Takuma; Yamamoto, Masashi; Yasukawa, Tomoyuki; Mizutani, Fumio
A rapid and simple method for the fabrication of the island patterns with particles and cells was applied to detect the presence of specific antigens on the cell surface. An upper interdigitated microband array (IDA) electrode was mounted on a lower substrate with the same design to fabricate a microfluidic-channel device for dielectrophoretic manipulation. The electrode grid structure was fabricated by rotating the upper template IDA by 90° relative to the lower IDA. A suspension of anti-CD33 modified particles and HL-60 cells was introduced into the channel. An AC electrical signal (typically 20 V peak-to-peak, 100 kHz) was then applied to the bands of the upper and lower IDAs, resulting in the formation of island patterns at the intersections with low electric fields. Immunoreactions between the antibodies immobilized on the accumulated particles and the CD33 present on the surface of the cells led to the formation of complexes comprising corresponding antigen-antibody pairs. Non-specific pairs accumulated at the intersection, which did not form complexes, were then dispersed after removal of the applied field. The time required for the detection of the formation/dispersion of the complexes is as short as 6 min in the present procedure. Furthermore, this novel cell binding assay does not require pretreatment such as target labeling or washing of the unbound cells. PMID:24892783
Display format and highlight validity effects on search performance using complex visual displays
NASA Technical Reports Server (NTRS)
Donner, Kimberly A.; Mckay, Tim; O'Brien, Kevin M.; Rudisill, Marianne
Display format and highlight validity were shown to affect visual display search performance; however, these studies were conducted on small, artificial displays of alphanumeric stimuli. A study manipulating these variables was conducted using realistic, complex Space Shuttle information displays. A 2x2x3 within-subjects analysis of variance found that search times were faster for items in reformatted displays than for current displays. The significant format by highlight validity interaction showed that there was little difference in response time to both current and reformatted displays when the highlight validity was applied; however, under the non or invalid highlight conditions, search times were faster with reformatted displays. Benefits of highlighting and reformatting displays to enhance search and the necessity to consider highlight validity and format characteristics in tandem for predicting search performance are discussed.
The Toca-1-N-WASP complex links filopodial formation to endocytosis.
Bu, Wenyu; Chou, Ai Mei; Lim, Kim Buay; Sudhaharan, Thankiah; Ahmed, Sohail
The transducer of Cdc42-dependent actin assembly (Toca-1)-N-WASP complex was isolated as an essential cofactor for Cdc42-driven actin polymerization in vitro. Toca-1 consists of an N-terminal F-BAR domain, followed by a Cdc42 binding site (HR1 domain) and an SH3 domain, (the N-WASP interacting site). N-WASP is an activator of actin nucleation through the Arp2/3 complex. The aim of the present study was to investigate the cellular function of the Toca-1-N-WASP complex. We report that Toca-1 induces filopodia and neurites as does N-WASP in N1E115 neuroblastoma cells. Toca-1 requires the F-BAR domain, Cdc42 binding site, and SH3 domain to induce filopodia. Toca-1 and N-WASP both require each other to induce filopodia. The expression of Toca-1 and N-WASP affects the distribution, size, and number of Rab5 positive membranes. Toca-1 interacts directly with N-WASP in filopodia and Rab5 membrane as seen by Forster resonance energy transfer. Thus the Toca-1-N-WASP complex localizes to and induces the formation of filopodia and endocytic vesicles. Last, three inhibitors of endocytosis, Dynamin-K44A, Eps15Delta95/295, and clathrin heavy chain RNA interference, block Toca-1-induced filopodial formation. Taken together, these data suggest that the Toca-1-N-WASP complex can link filopodial formation to endocytosis. PMID:19213734
Thermodynamics of formation for the 18-crown-6-triglycine molecular complex in water-dimethylsulfoxide solvents
NASA Astrophysics Data System (ADS)
Usacheva, T. R.; Lan, Pham Thi; Sharnin, V. A.
The effect of a water-dimethylsulfoxide (DMSO) solvent on the formation of a molecular complex of 18-crown-6 (18C6) with triglycine (diglycylglycine, 3Gly) is studied via calorimetric titration. It is found that switching from water to an H2O-DMSO mixture with DMSO mole fraction of 0.30 is accompanied by a monotonic increase in the stability of [3Gly18C6] complex, from log K ? = 1.10 to log K ? = 2.44, and an increase in the exothermicity of the reaction of its formation, from -5.9 to -16.9 kJ/mol. It is shown that the [3Gly18C6] complex exhibits enthalpy stabilization with negative values of enthalpy and entropy over the investigated range of H2O-DMSO solvents. Analysis of the reagents' solvation characteristics reveals that the increase in the reaction's exothermicity of transfer is due to differences in the solvation of [3Gly18C6] and 18C6 with a small solvation contribution from 3Gly. It is concluded that the change in the Gibbs energy of the reaction 3Glysolv + 18C6solv ? [3Gly18C6]solv is due to differences in the change in the solvation state of the complex and the peptide (?tr G ?([3Gly18C6])-?tr G ?(3Gly)).
Chemical and Enzymatic Footprint Analyses of R-Loop Formation by Cascade-crRNA Complex.
Pul, Ümit
Cascade-crRNA complexes mediate the identification of the invading foreign DNA and initiate its neutralization by formation of an R-loop (RNA-induced DNA-loop) at the crRNA-complementary sequence (protospacer). After initial unspecific binding to the double-stranded DNA, Cascade-crRNA complex slides along the DNA to find the protospacer. Once the target site is detected, the crRNA hybridizes to the complementary strand with subsequent displacement of the non-complementary strand to form an R-loop structure. Here, we describe how Cascade-DNA complexes and the Cascade-induced strand separation can be characterized in detail by combining chemical and enzymatic footprint analyses. Selective modification of unpaired thymines by permanganate (KMnO4) and the specific cleavage of single-stranded DNA by Nuclease P1 can be used to probe an R-loop formation by Cascade. Localization of the Cascade-crRNA complex on the DNA can be achieved by an Exonuclease III protection assay. PMID:25981481
Formation of palladium(II) hydroxychloride complexes and precipitates in sodium chloride solutions and seawater
NASA Astrophysics Data System (ADS)
Byrne, Robert H.; Yao, Wensheng
Spectrophotometric measurements of Pd(II) in 0.5 M NaCl indicate that the PdCl3OH2- formation constant at 25°C is ClK?1 = [PdCl3OH2-][H+][Cl-][PdCl42-]-1 = 10-8.98. This constant is more than two orders of magnitude smaller than previous results derived through solubility analysis. Kinetic experiments indicate that equilibration between PdCl42- and PdCl3OH2- is complete in less than one second. The discrepancy between depictions of Pd(II) speciation obtained by using spectrophotometric and solubility analysis is apparently caused by the formation of mixed hydroxychloride solid phases (PdClaOH2-a), rather than pure Pd(OH)2(s), when Pd(OH)2(s) is equilibrated in concentrated chloride solutions at high pH. In Pd(II) solubility analysis, and solubility analyses of other strongly hydrolyzed metals in seawater, the composition of the solid phase must be carefully examined for appropriate deconvolution of data.
Actomyosin-dependent formation of the mechanosensitive talin-vinculin complex reinforces actin anchoring.
Ciobanasu, Corina; Faivre, Bruno; Le Clainche, Christophe
The force generated by the actomyosin cytoskeleton controls focal adhesion dynamics during cell migration. This process is thought to involve the mechanical unfolding of talin to expose cryptic vinculin-binding sites. However, the ability of the actomyosin cytoskeleton to directly control the formation of a talin-vinculin complex and the resulting activity of the complex are not known. Here we develop a microscopy assay with pure proteins in which the self-assembly of actomyosin cables controls the association of vinculin to a talin-micropatterned surface in a reversible manner. Quantifications indicate that talin refolding is limited by vinculin dissociation and modulated by the actomyosin network stability. Finally, we show that the activation of vinculin by stretched talin induces a positive feedback that reinforces the actin-talin-vinculin association. This in vitro reconstitution reveals the mechanism by which a key molecular switch senses and controls the connection between adhesion complexes and the actomyosin cytoskeleton. PMID:24452080
cAMP prevents TNF-induced apoptosis through inhibiting DISC complex formation in rat hepatocytes
Bhattacharjee, Rajesh [Department of Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA 15213 (United States)] [Department of Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA 15213 (United States); Xiang, Wenpei [Department of Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA 15213 (United States) [Department of Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA 15213 (United States); Family Planning Research Institute, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, People's Republic of China (China); Wang, Yinna [Vascular Medicine Institute, University of Pittsburgh School of Medicine, 10051-5A BST 3, 3501 Fifth Avenue, Pittsburgh, PA 15261 (United States)] [Vascular Medicine Institute, University of Pittsburgh School of Medicine, 10051-5A BST 3, 3501 Fifth Avenue, Pittsburgh, PA 15261 (United States); Zhang, Xiaoying [Department of Medicine/Endocrinology Division, University of Pittsburgh Medical Center, 200 Lothrop St., Pittsburgh, PA 15213 (United States)] [Department of Medicine/Endocrinology Division, University of Pittsburgh Medical Center, 200 Lothrop St., Pittsburgh, PA 15213 (United States); Billiar, Timothy R., E-mail: email@example.com [Department of Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA 15213 (United States)
Highlights: Black-Right-Pointing-Pointer cAMP blocks cell death induced by TNF and actinomycin D in cultured hepatocytes. Black-Right-Pointing-Pointer cAMP blocks NF-{kappa}B activation induced by TNF and actinomycin D. Black-Right-Pointing-Pointer cAMP blocks DISC formation following TNF and actinomycin D exposure. Black-Right-Pointing-Pointer cAMP blocks TNF signaling at a proximal step. -- Abstract: Tumor necrosis factor {alpha} (TNF) is a pleiotropic proinflammatory cytokine that plays a role in immunity and the control of cell proliferation, cell differentiation, and apoptosis. The pleiotropic nature of TNF is due to the formation of different signaling complexes upon the binding of TNF to its receptor, TNF receptor type 1 (TNFR1). TNF induces apoptosis in various mammalian cells when the cells are co-treated with a transcription inhibitor like actinomycin D (ActD). When TNFR1 is activated, it recruits an adaptor protein, TNF receptor-associated protein with death domain (TRADD), through its cytoplasmic death effector domain (DED). TRADD, in turn, recruits other signaling proteins, including TNF receptor-associated protein 2 (TRAF2) and receptor-associated protein kinase (RIPK) 1, to form a complex. Subsequently, this complex combines with FADD and procaspase-8, converts into a death-inducing signaling complex (DISC) to induce apoptosis. Cyclic AMP (cAMP) is a second messenger that regulates various cellular processes such as cell proliferation, gene expression, and apoptosis. cAMP analogues are reported to act as anti-apoptotic agents in various cell types, including hepatocytes. We found that a cAMP analogue, dibutyryl cAMP (db-cAMP), inhibits TNF + ActD-induced apoptosis in rat hepatocytes. The protein kinase A (PKA) inhibitor KT-5720 reverses this inhibitory effect of cAMP on apoptosis. Cytoprotection by cAMP involves down-regulation of various apoptotic signal regulators like TRADD and FADD and inhibition of caspase-8 and caspase-3 cleavage. We also found that cAMP exerts its affect at the proximal level of TNF signaling by inhibiting the formation of the DISC complex upon the binding of TNF to TNFR1. In conclusion, our study shows that cAMP prevents TNF + ActD-induced apoptosis in rat hepatocytes by inhibiting DISC complex formation.
Complex formation equilibria of Cu(II) and Zn(II) with triethylenetetramine and its mono- and di-acetyl metabolites.
Nurchi, Valeria M; Crisponi, Guido; Crespo-Alonso, Miriam; Lachowicz, Joanna I; Szewczuk, Zbigniew; Cooper, Garth J S
Triethylenetetramine (TETA) dihydrochloride, or trientine, is a therapeutic molecule that has long been used as a copper-chelating agent for the second-line treatment of patients with Wilson's disease. More recently, it has also been employed as an experimental therapeutic molecule in diabetes where it improves cardiac structure in patients with diabetic cardiomyopathy and left-ventricular hypertrophy. TETA is metabolized by acetylation, which leads to the formation of two main metabolites in humans and other mammals, monoacetyl-TETA (MAT) and diacetyl-TETA (DAT). These metabolites have been identified in the plasma and urine of healthy and diabetic subjects treated with TETA, and could themselves play a role in TETA-mediated copper chelation and restoration of physiological copper regulation in diabetes. In this regard, a potentiometric and spectrophotometric study of Cu(II)-complex formation equilibria of TETA, MAT and DAT is presented here, to provide a comprehensive evaluation of the stoichiometries of the complexes formed and of their relative stability constants. A potentiometric study has also been conducted on the corresponding Zn(II) complexes, to evaluate any possible interference with TETA-mediated Cu(II) binding by this second physiological transition-metal ion, which is present in similar concentrations in human plasma and which also binds to TETA. An ESI-MS study of these systems has both confirmed the complex formation mechanisms established from the potentiometric and spectrophotometric results, and in addition provided direct information on the stoichiometry of the complexes formed in solution. These data when taken together show that the 1 : 1 complexes formed with Cu(II) and Zn(II) have different degrees of protonation. The stability of the Cu(II) and Zn(II) complexes with the three ligands, evaluated by the parameters pCu and pZn, decreases with the introduction of the acetyl groups. Nevertheless the stability of Cu(II) complexes with MAT is sufficiently high to enable its participation in copper scavenging from the patient. A speciation study of the behavior of TETA and MAT with Cu(II) in the presence of Zn(II) at peri-physiological plasma concentrations is also presented. While Zn(II) did not hinder copper binding, the possibility is raised that prolonged TETA treatment could possibly alter the homeostatic regulation of this essential metal ion. The lack of reliable literature stability constants concerning the Cu(II) and Zn(II) interaction with the major transport proteins in plasma is also briefly considered. PMID:23202417
Studies on the weak interactions and CT complex formations between chloranilic acid, 2,3-dichloro-5,6-dicyano-p-benzoquinone, tetracyanoethylene and papaverine in acetonitrile and their thermodynamic properties, theoretically, spectrophotometrically aided by FTIR
NASA Astrophysics Data System (ADS)
Datta, Asim Sagar; (Chattaraj), Seema Bagchi; Chakrabortty, Ashutosh; Lahiri, Sujit Chandra
Spectrophotometric, FTIR and theoretical studies of the charge-transfer complexes between mild narcotic drug papaverine and the acceptors chloranilic acid (Cl-A), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and tetracyanoethylene (TCNE) in acetonitrile, their association constants, thermodynamic (?G0, ?H0 and ?S0) and other related properties had been described. Papaverine was found to form colored charge-transfer complexes with Cl-A, DDQ and TCNE in acetonitrile. The absorption maxima of the complexes were 518.5, 584.0 and 464.0 nm for Cl-A complex, DDQ complex, and TCNE complex respectively. The compositions of the papaverine complexes were determined to be 1:1 from Job's method of continuous variation. Solid complexes formed between papaverine and the acceptors were isolated. Comparison of the FTIR spectra of the solid complexes between papaverine and the acceptors and their constituents showed considerable shift in absorption peaks, changes in intensities of the peaks and formation of the new bands on complexation. However, no attempt has been made to purify the complexes and study the detailed spectra both theoretically and experimentally. The energies h?CT of the charge-transfer complexes were compared with the theoretical values of h?CT of the complexes obtained from HOMO and LUMO of the donor and the acceptors. The reasons for the differences in h?CT values were explained. Density function theory was used for calculation. h?CT (experimental) values of the transition energies of the complexes in acetonitrile differed from h?CT (theoretical) values. IDV value of papaverine was calculated. Charge-transfer complexes were assumed to be partial electrovalent compounds with organic dative ions D+ and A- (in the excited state) and attempts had been made to correlate the energy changes for the formation of the complexes with the energy changes for the formation of electrovalent compounds between M+ and X- ions.
Influence of dominant HIV-1 epitopes on HLA-A3/peptide complex formation
Racape, Judith; Connan, Francine; Hoebeke, Johan; Choppin, Jeannine; Guillet, Jean-Gérard
The binding of peptides to MHC class I molecules induces MHC/peptide complexes that have specific conformational features. Little is known about the molecular and structural bases required for an optimal MHC/peptide association able to induce a dominant T cell response. We sought to characterize the interaction between purified HLA-A3 molecules and four well known CD8 epitopes from HIV-1 proteins. To define the characteristics of HLA–peptide complex formation and to identify potential structural changes, we used biochemical assays that detect well formed complexes. We tested the amplitude, stability, and kinetic parameters of the interaction between HLA-A3, peptides, and anti-HLA mAbs. Our results show that the four epitopes Nef73–82, Pol325–333, Env37–46, and Gag20–28 bind strongly to HLA-A3 molecules and form very stable complexes that are detected with differential patterns of mAb reactivity. The most striking result is the nonrecognition of the HLA-A3/Gag20–28 complex by the A11.1M mAb specific to HLA-A3/-A11 alleles. To explain this observation, from the data published on HLA-A11 crystallographic structure, we propose molecular models of the HLA-A3 molecule complexed with Nef73–82, Pol325–333, and Gag20–28 epitopes. In the HLA-A3/Gag20–28 complex, we suggest that Arg at position P1 of the peptide may push the ?2 helix residue Trp-167 of HLA-A3 and affect mAb recognition. Such observations may have great implications for T cell antigen receptor recognition and the immunogenicity of HLA/peptide complexes. PMID:17116886
Charge-transfer complex formation in gelation: the role of solvent molecules with different electron-donating capacities.
Basak, Shibaji; Bhattacharya, Sumantra; Datta, Ayan; Banerjee, Arindam
A naphthalenediimide (NDI)-based synthetic peptide molecule forms gels in a particular solvent mixture (chloroform/aromatic hydrocarbon, 4:1) through charge-transfer (CT) complex formation; this is evident from the corresponding absorbance and fluorescence spectra at room temperature. Various aromatic hydrocarbon based solvents, including benzene, toluene, xylene (ortho, meta and para) and mesitylene, have been used for the formation of the CT complex. The role of different solvent molecules with varying electron-donation capacities in the formation of CT complexes has been established through spectroscopic and computational studies. PMID:24677404
Mechanism of NH2 + CO2 formation in OH+HNCO reaction: Rate constant evaluation via ab initio calculations and statistical theory
NASA Astrophysics Data System (ADS)
Sengupta, Debasis; Nguyen, Minh Tho
Portions of the [CH2NO2] potential energy surface related to the OH+HNCO reaction were calculated by means of ab initio molecular orbital theory at the QCISD(T)/6-311++G(d,p) level based on UMP2/6-31G(d,p) optimized geometries. Of all possible three channels considered, the hydrogen abstraction turns out to be the dominant reaction channel. The addition to C atom requires activation energy slightly larger than that of the abstraction but smaller than that of the N addition, in contrast to the H+HNCO reaction. The structural and energetic parameters for the channels thus characterized were further utilized for the calculation of rate constants in the framework of a quantum statistical theory (QRRK). The contributions of the individual reaction channel towards the total rate constant have been examined. Although the OH+HNCO?NH2+CO2 reaction is more exothermic than the hydrogen abstraction OH+HNCO?H2+NCO, it is confirmed that rate constant for CO2 loss is much lower than that of H2O-elimination. The standard heat of formation of the adduct HNC(OH)O is estimated to be ?Hf298=-41.1±3 kcal/mol.
Direct measurements of the total rate constant of the reaction NCN + H and implications for the product branching ratio and the enthalpy of formation of NCN.
Fassheber, Nancy; Dammeier, Johannes; Friedrichs, Gernot
The overall rate constant of the reaction (2), NCN + H, which plays a key role in prompt-NO formation in flames, has been directly measured at temperatures 962 K < T < 2425 K behind shock waves. NCN radicals and H atoms were generated by the thermal decomposition of NCN3 and C2H5I, respectively. NCN concentration-time profiles were measured by sensitive narrow-line-width laser absorption at a wavelength of ? = 329.1302 nm. The obtained rate constants are best represented by the combination of two Arrhenius expressions, k2/(cm(3) mol(-1) s(-1)) = 3.49 × 10(14) exp(-33.3 kJ mol(-1)/RT) + 1.07 × 10(13) exp(+10.0 kJ mol(-1)/RT), with a small uncertainty of ±20% at T = 1600 K and ±30% at the upper and lower experimental temperature limits.The two Arrhenius terms basically can be attributed to the contributions of reaction channel (2a) yielding CH + N2 and channel (2b) yielding HCN + N as the products. A more refined analysis taking into account experimental and theoretical literature data provided a consistent rate constant set for k2a, its reverse reaction k1a (CH + N2 ? NCN + H), k2b as well as a value for the controversial enthalpy of formation of NCN, ?fH = 450 kJ mol(-1). The analysis verifies the expected strong temperature dependence of the branching fraction ? = k2b/k2 with reaction channel (2b) dominating at the experimental high-temperature limit. In contrast, reaction (2a) dominates at the low-temperature limit with a possible minor contribution of the HNCN forming recombination channel (2d) at T < 1150 K. PMID:24807121
Coordination chemistry of microbial iron transport compounds. IX. Stability constants for catechol models of enterobactin
Alex Avdeef; Stephen R. Sofen; Thomas L. Bregante; Kenneth N. Raymond
The stability constants of ferric complexes with several substituted catechol (1,2-dihydroxybenzene) ligands in aqueous solutions of low ionic strength have been determined at 27°C in the pH range 2 to 11. Enterobactin, the principal siderophore of enteric bacteria, is a tricatechol and, from the formation constants reported here, is estimated to have a formation constant with ferric ion which is
Structural and Thermodynamic Characterization of Cadherin·?-Catenin·?-Catenin Complex Formation*
Pokutta, Sabine; Choi, Hee-Jung; Ahlsen, Goran; Hansen, Scott D.; Weis, William I.
The classical cadherin·?-catenin·?-catenin complex mediates homophilic cell-cell adhesion and mechanically couples the actin cytoskeletons of adjacent cells. Although ?-catenin binds to ?-catenin and to F-actin, ?-catenin significantly weakens the affinity of ?-catenin for F-actin. Moreover, ?-catenin self-associates into homodimers that block ?-catenin binding. We investigated quantitatively and structurally ?E- and ?N-catenin dimer formation, their interaction with ?-catenin and the cadherin·?-catenin complex, and the effect of the ?-catenin actin-binding domain on ?-catenin association. The two ?-catenin variants differ in their self-association properties: at physiological temperatures, ?E-catenin homodimerizes 10× more weakly than does ?N-catenin but is kinetically trapped in its oligomeric state. Both ?E- and ?N-catenin bind to ?-catenin with a Kd of 20 nm, and this affinity is increased by an order of magnitude when cadherin is bound to ?-catenin. We describe the crystal structure of a complex representing the full ?-catenin·?N-catenin interface. A three-dimensional model of the cadherin·?-catenin·?-catenin complex based on these new structural data suggests mechanisms for the enhanced stability of the ternary complex. The C-terminal actin-binding domain of ?-catenin has no influence on the interactions with ?-catenin, arguing against models in which ?-catenin weakens actin binding by stabilizing inhibitory intramolecular interactions between the actin-binding domain and the rest of ?-catenin. PMID:24692547
Presenilin and nicastrin regulate each other and determine amyloid ?-peptide production via complex formation
Edbauer, Dieter; Winkler, Edith; Haass, Christian; Steiner, Harald
Amyloid ?-peptide (A?) is generated by the consecutive cuts of two membrane-bound proteases. ?-Secretase cuts at the N terminus of the A? domain, whereas ?-secretase mediates the C-terminal cut. Recent evidence suggests that the presenilin (PS) proteins, PS1 and PS2, may be ?-secretases. Because PSs principally exist as high molecular weight protein complexes, biologically active ?-secretases likely require other cofactors such as nicastrin (Nct) for their activities. Here we show that preferentially mature Nct forms a stable complex with PSs. Furthermore, we have down-regulated Nct levels by using a highly specific and efficient RNA interference approach. Very similar to a loss of PS function, down-regulation of Nct levels leads to a massive accumulation of the C-terminal fragments of the ?-amyloid precursor protein. In addition, A? production was markedly reduced. Strikingly, down-regulation of Nct destabilized PS and strongly lowered levels of the high molecular weight PS1 complex. Interestingly, absence of the PS1 complex in PS1?/? cells was associated with a strong down-regulation of the levels of mature Nct, suggesting that binding to PS is required for trafficking of Nct through the secretory pathway. Based on these findings we conclude that Nct and PS regulate each other and determine ?-secretase function via complex formation. PMID:12048259
Inhibition of human amylin fibril formation by insulin-mimetic vanadium complexes.
He, Lei; Wang, Xuesong; Zhao, Cong; Zhu, Dengsen; Du, Weihong
The toxicity of amyloid-forming proteins can be linked to many degenerative and systemic diseases. Human islet amyloid polypeptide (hIAPP, amylin) has been associated with type II diabetes. Methods for efficient inhibition of amyloid fibril formation are highly clinically important. This study demonstrated the significant inhibitory effects of six vanadium complexes on hIAPP aggregation. Vanadium complexes, such as bis(maltolato)-oxovanadium (BMOV), have been used as insulin-mimetic agents for the treatment of diabetes for many years. Different biophysical methods were applied to investigate the interaction between V complexes and hIAPP. The results indicated that the selected compounds affected the peptide aggregation by different action modes and protected the cells from the cytotoxicity induced by hIAPP. Both the high binding affinity and the ligand spatial effect on inhibiting hIAPP aggregation are significant. Although some of these compounds undergo biotransformation under the conditions of the experiments, and the active species are not identified, it is understood that the effect results from a particular compound and its conversion products. Importantly, our work provided information on the effects of the selected V complexes on hIAPP and demonstrated multiple levels of effects of V complexes against amyloid-related diseases. PMID:24714786
Young stellar population and ongoing star formation in the H II complex Sh2-252
NASA Astrophysics Data System (ADS)
Jose, Jessy; Pandey, A. K.; Samal, M. R.; Ojha, D. K.; Ogura, K.; Kim, J. S.; Kobayashi, N.; Goyal, A.; Chauhan, N.; Eswaraiah, C.
In this paper, an extensive survey of the star-forming complex Sh2-252 has been undertaken with an aim to explore its hidden young stellar population as well as to understand the structure and star formation history for the first time. This complex is composed of five prominent embedded clusters associated with the subregions A, C, E, NGC 2175s and Teu 136. We used Two Micron All Sky Survey-near-infrared and Spitzer-Infrared Array Camera, Multiband Imaging Photometer for Spitzer photometry to identify and classify the young stellar objects (YSOs) by their infrared (IR) excess emission. Using the IR colour-colour criteria, we identified 577 YSOs, of which, 163 are Class I, 400 are Class II and 14 are transition disc YSOs, suggesting a moderately rich number of YSOs in this complex. Spatial distribution of the candidate YSOs shows that they are mostly clustered around the subregions in the western half of the complex, suggesting enhanced star formation activity towards its west. Using the spectral energy distribution and optical colour-magnitude diagram-based age analyses, we derived probable evolutionary status of the subregions of Sh2-252. Our analysis shows that the region A is the youngest (˜0.5 Myr), the regions B, C and E are of similar evolutionary stage (˜1-2 Myr) and the clusters NGC 2175s and Teu 136 are slightly evolved (˜2-3 Myr). Morphology of the region in the 1.1 mm map shows a semicircular shaped molecular shell composed of several clumps and YSOs bordering the western ionization front of Sh2-252. Our analyses suggest that next generation star formation is currently under way along this border and that possibly fragmentation of the matter collected during the expansion of the H II region as one of the major processes is responsible for such stars. We observed the densest concentration of YSOs (mostly Class I, ˜0.5 Myr) at the western outskirts of the complex, within a molecular clump associated with water and methanol masers and we suggest that it is indeed a site of cluster formation at a very early evolutionary stage, sandwiched between the two relatively evolved CH II regions A and B.
Arp2/3 Complex Is Important for Filopodia Formation, Growth Cone Motility, and Neuritogenesis in Neuronal Cells
Korobova, Farida
A role of Arp2/3 complex in lamellipodia is well established, whereas its roles in filopodia formation remain obscure. We addressed this question in neuronal cells, in which motility is heavily based on filopodia, and we found that Arp2/3 complex is involved in generation of both lamellipodia and filopodia in growth cones, and in neuritogenesis, the processes thought to occur largely in Arp2/3 complex-independent manner. Depletion of Arp2/3 complex in primary neurons and neuroblastoma cells by small interfering RNA significantly decreased the F-actin contents and inhibited lamellipodial protrusion and retrograde flow in growth cones, but also initiation and dynamics of filopodia. Using electron microscopy, immunochemistry, and gene expression, we demonstrated the presence of the Arp2/3 complex-dependent dendritic network of actin filaments in growth cones, and we showed that individual actin filaments in filopodia originated at Arp2/3 complex-dependent branch points in lamellipodia, thus providing a mechanistic explanation of Arp2/3 complex functions during filopodia formation. Additionally, Arp2/3 complex depletion led to formation of multiple neurites, erratic pattern of neurite extension, and excessive formation of stress fibers and focal adhesions. Consistent with this phenotype, RhoA activity was increased in Arp2/3 complex-depleted cells, indicating that besides nucleating actin filaments, Arp2/3 complex may influence cell motility by altering Rho GTPase signaling. PMID:18256280
Molybdenum Hydride and Dihydride Complexes Bearing Diphosphine Ligands with a Pendant Amine: Formation of Complexes with Bound Amines.
Zhang, Shaoguang; Bullock, R Morris
CpMo(CO)(PNP)H complexes (PNP = (R2PCH2)2NMe, R = Et or Ph) were synthesized by displacement of two CO ligands of CpMo(CO)3H by the PNP ligand; these complexes were characterized by IR and variable temperature (1)H and (31)P NMR spectroscopy. CpMo(CO)(PNP)H complexes are formed as mixture of cis- and trans-isomers. The structures of both cis-CpMo(CO)(P(Et)N(Me)P(Et))H and trans-CpMo(CO)(P(Ph)N(Me)P(Ph))H were determined by single crystal X-ray diffraction. Electrochemical oxidation of CpMo(CO)(P(Et)N(Me)P(Et))H and CpMo(CO)(P(Ph)N(Me)P(Ph))H in CH3CN are both irreversible at slow scan rates and quasireversible at higher scan rates, with E1/2 = -0.36 V (vs Cp2Fe(+/0)) for CpMo(CO)(P(Et)N(Me)P(Et))H and E1/2 = -0.18 V for CpMo(CO)(P(Ph)N(Me)P(Ph))H. Hydride abstraction from CpMo(CO)(PNP)H with [Ph3C](+)[A](-) (A = B(C6F5)4 or BAr(F)4; [Ar(F) = 3,5-bis(trifluoromethyl)phenyl]) afforded "tuck-in" [CpMo(CO)(?(3)-PNP)](+) complexes that feature the amine bound to the metal. Displacement of the ?(3) Mo-N bond by CD3CN gives [CpMo(CO)(PNP)(CD3CN)](+). The kinetics of this reaction were studied by (31)P{(1)H} NMR spectroscopy for [CpMo(CO)(?(3)-P(Et)N(Me)P(Et))](+), providing the activation parameters ?H(?) = 21.6 ± 2.8 kcal/mol, ?S(?) = -0.3 ± 9.8 cal/(mol K), Ea = 22.1 ± 2.8 kcal/mol. Protonation of CpMo(CO)(P(Et)N(Me)P(Et))H affords the Mo dihydride complex [CpMo(CO)(?(2)-P(Et)N(Me)P(Et))(H)2](+), which loses H2 to generate [CpMo(CO)(?(3)-P(Et)N(Me)P(Et))](+) at room temperature. Our results show that the pendant amine has a strong driving force to form stable "tuck-in" [CpMo(CO)(?(3)-PNP)](+) complexes, and also promotes hydrogen elimination from [CpMo(CO)(PNP)(H)2](+) complexes by formation of a Mo-N dative bond. CpMo(CO)(dppp)H (dppp = 1,3-bis(diphenylphosphino)propane) was studied as a Mo diphosphine analogue without a pendant amine, and the product of protonation of this complex gives [CpMo(CO)(dppp)(H)2](+). PMID:26054002
Isolation and Characterization of FORMATE/NI(CYCLAM)^{2+} Complexes with Cryogenic Ion Vibrational Predissociation
NASA Astrophysics Data System (ADS)
Wolk, Arron B.; Fournier, Joseph A.; Wolke, Conrad T.; Johnson, Mark A.
Transition metal-based organometallic catalysts are a promising means of converting CO_{2} to transportable fuels. Ni(cyclam)^{2+}(cyclam = 1,4,8,11-tetraazacyclotetradecane), a Ni^{II} complex ligated by four nitrogen centers, has shown promise as a catalyst selective for CO_{2} reduction in aqueous solutions. The cyclam ligand has four NH hydrogen bond donors that can adopt five conformations, each offering distinct binding motifs for coordination of CO_{2} close to the metal center. To probe the ligand conformation and the role of hydrogen bonding in adduct binding, we extract Ni(cyclam)^{2+} complexes with the formate anion and some of its analogs from solution using electrospray ionization, and characterize their structures using cryogenic ion vibrational predissociation spectroscopy. Using the signature vibrational features of the embedded carboxylate anion and the NH groups as reporters, we compare the binding motifs of oxalate, benzoate, and formate anions to the Ni(cyclam)^{2+} framework. Finally, we comment on possible routes to generate the singly charged Ni(cyclam)^{+} complex, a key intermediate that has been invoked in the catalytic CO_{2} reduction cycle, but has never been isolated through ion processing techniques.
Complex conductivity response to microbial growth and biofilm formation on phenanthrene spiked medium
NASA Astrophysics Data System (ADS)
Albrecht, Remy; Gourry, Jean Christophe; Simonnot, Marie-Odile; Leyval, Corinne
Several laboratory studies have recently demonstrated the utility of geophysical methods for the investigation of microbial-induced changes over contaminated sites. However, it remains difficult to distinguish the effects due to the new physical properties imparted by microbial processes, to bacterial growth, or to the development of bacterial biofilm. We chose to study the influence of biofilm formation on geophysical response using complex conductivity measurements (0.1-1000 Hz) in phenanthrene-contaminated media. Biotic assays were conducted with two phenanthrene (PHE) degrading bacterial strains: Burkholderia sp (NAH1), which produced biofilm and Stenophomonas maltophilia (MATE10), which did not, and an abiotic control. Results showed that bacterial densities for NAH1 and MATE10 strains continuously increased at the same rate during the experiment. However, the complex conductivity signature showed noticeable differences between the two bacteria, with a phase shift of 50 mrad at 4 Hz for NAH1, which produced biofilm. Biofilm volume was quantified by Scanning Confocal Laser Microscopy (SCLM). Significant correlations were established between phase shift decrease and biofilm volume for NAH1 assays. Results suggest that complex conductivity measurements, specifically phase shift, can be a useful indicator of biofilm formation inside the overall signal of microbial activity on contaminated sites.
Gas phase uranyl activation: formation of a uranium nitrosyl complex from uranyl azide.
Gong, Yu; de Jong, Wibe A; Gibson, John K
Activation of the oxo bond of uranyl, UO2(2+), was achieved by collision induced dissociation (CID) of UO2(N3)Cl2(-) in a quadrupole ion trap mass spectrometer. The gas phase complex UO2(N3)Cl2(-) was produced by electrospray ionization of solutions of UO2Cl2 and NaN3. CID of UO2(N3)Cl2(-) resulted in the loss of N2 to form UO(NO)Cl2(-), in which the "inert" uranyl oxo bond has been activated. Formation of UO2Cl2(-) via N3 loss was also observed. Density functional theory computations predict that the UO(NO)Cl2(-) complex has nonplanar Cs symmetry and a singlet ground state. Analysis of the bonding of the UO(NO)Cl2(-) complex shows that the side-on bonded NO moiety can be considered as NO(3-), suggesting a formal oxidation state of U(VI). Activation of the uranyl oxo bond in UO2(N3)Cl2(-) to form UO(NO)Cl2(-) and N2 was computed to be endothermic by 169 kJ/mol, which is energetically more favorable than formation of NUOCl2(-) and UO2Cl2(-). The observation of UO2Cl2(-) during CID is most likely due to the absence of an energy barrier for neutral ligand loss. PMID:25906363
Spitzer Analysis of HII Region Complexes in the Magellanic Clouds: Determining a Suitable Monochromatic Obscured Star Formation Indicator
Lawton, Brandon; Babler, Brian; Block, Miwa; Bolatto, Alberto D; Bracker, Steve; Carlson, Lynn R; Engelbracht, Charles W; Hora, Joseph L; Indebetouw, Remy; Madden, Suzanne C; Meade, Marilyn; Meixner, Margaret; Misselt, Karl; Oey, M S; Oliveira, Joana M; Robitaille, Thomas; Sewilo, Marta; Shiao, Bernie; Vijh, Uma P; Whitney, Barbara
HII regions are the birth places of stars, and as such they provide the best measure of current star formation rates (SFRs) in galaxies. The close proximity of the Magellanic Clouds allows us to probe the nature of these star forming regions at small spatial scales. We aim to determine the monochromatic IR band that most accurately traces the bolometric IR flux (TIR), which can then be used to estimate an obscured SFR. We present the spatial analysis, via aperture/annulus photometry, of 16 LMC and 16 SMC HII region complexes using the Spitzer IRAC and MIPS bands. UV rocket data and SHASSA H-alpha data are also included. We find that nearly all of the LMC and SMC HII region SEDs peak around 70um, from ~10 to ~400 pc from the central sources. As a result, the sizes of HII regions as probed by 70um is approximately equal to the sizes as probed by TIR (about 70 pc in radius); the radial profile of the 70um flux, normalized by TIR, is constant at all radii (70um ~ 0.45 TIR); the 1-sigma standard deviation of the 7...
Smog chamber experiments to investigate Henry's law constants of glyoxal using different seed aerosols as well as imidazole formation in the presence of ammonia
NASA Astrophysics Data System (ADS)
Jakob, Ronit
Aerosols play an important role in the chemistry and physics of the atmosphere. Hence, they have a direct as well as an indirect impact on the earth's climate. Depending on their formation, one distinguishes between primary and secondary aerosols[1]. Important groups within the secondary aerosols are the secondary organic aerosols (SOAs). In order to improve predictions about these impacts on the earth's climate the existing models need to be optimized, because they still underestimate SOA formation[2]. Glyoxal, the smallest ?-dicarbonyl, not only acts as a tracer for SOA formation but also as a direct contributor to SOA. Because glyoxal has such a high vapour pressure, it was common knowledge that it does not take part in gas-particle partitioning and therefore has no impact on direct SOA formation. However, the Henry's law constant for glyoxal is surprisingly high. This has been explained by the hydration of the aldehyde groups, which means that a species with a lower vapour pressure is produced. Therefore the distribution of glyoxal between gas- and particle phase is atmospherically relevant and the direct contribution of glyoxal to SOA can no longer be neglected[3]. Besides this particulate glyoxal is able to undergo heterogeneous chemistry with gaseous ammonia to form imidazoles. This plays an important role for regions with aerosols exhibiting alkaline pH values for example from lifestock or soil dust because imidazoles as nitrogen containing compounds change the optical properties of aerosols[4]. A high salt concentration present in chamber seed aerosols leads to an enhanced glyoxal uptake into the particle. This effect is called "salting-in". The salting effect depends on the composition of the seed aerosol as well as the soluble compound. For very polar compounds, like glyoxal, a "salting-in" is observed[3]. Glyoxal particle formation during a smog chamber campaign at Paul-Scherrer-Institut (PSI) in Switzerland was examined using different seed aerosols such as ammonium sulfate, sodium chloride and sodium nitrate. The aim of this campaign was to investigate Henry's law constants for different seed aerosols. Additionally imidazole formation was studied. During the campaign filter samples were taken to investigate the amount of glyoxal and imidazole in the particle phase. After filter extraction and derivatisation of glyoxal, the compounds were measured using UHPLC-ESI-HR-MS. Additionally, gas-phase glyoxal has been analysed during the campaign. The results will be used to calculate the Henry's law constants. In this work, results of the glyoxal study as well as imidazole formation are presented. [1] J. Schnelle-Kreis, M. Sklorz, H. Herrmann, R. Zimmermann, Chem. Unserer Zeit, 2007, 41, 220-230 [2] M. M. Galloway, P. S. Chhabra, A. W. H. Chan, J. D. Surratt, R. C. Flagan, J. H. Seinfeld, F. N. Keutsch, Atmos. Chem. Phys, 9, 3331-3345, 2009 [3] C. J. Kampf, E. M. Waxman, J. G. Slowik, J. Dommen, L. Pfaffenberger, A. P. Praplan, A. S. H. Prévôt, U. Baltensperger, T. Hoffmann, R. Volkamer, Environ. Sci. Technol., 2013, 47, 4236-4244 [4] C. J. Kampf, R. Jakob, T. Hoffmann, Atmos. Chem. Phys., 12, 6323-6333, 2012
Two quorum sensing systems control biofilm formation and virulence in members of the Burkholderia cepacia complex.
Suppiger, Angela; Schmid, Nadine; Aguilar, Claudio; Pessi, Gabriella; Eberl, Leo
The Burkholderia cepacia complex (Bcc) consists of 17 closely related species that are problematic opportunistic bacterial pathogens for cystic fibrosis patients and immunocompromised individuals. These bacteria are capable of utilizing two different chemical languages: N-acyl homoserine lactones (AHLs) and cis-2-unsaturated fatty acids. Here we summarize the current knowledge of the underlying molecular architectures of these communication systems, showing how they are interlinked and discussing how they regulate overlapping as well as specific sets of genes. A particular focus is laid on the role of these signaling systems in the formation of biofilms, which are believed to be highly important for chronic infections. We review genes that have been implicated in the sessile lifestyle of this group of bacteria. The new emerging role of the intracellular second messenger cyclic dimeric guanosine monophosphate (c-di-GMP) as a downstream regulator of the fatty acid signaling cascade and as a key factor in biofilm formation is also discussed. PMID:23799665
Struvite crystal growth inhibition by trisodium citrate and the formation of chemical complexes in growth solution
NASA Astrophysics Data System (ADS)
Prywer, Jolanta; Mielniczek-Brzóska, Ewa; Olszynski, Marcin
Effect of trisodium citrate on the crystallization of struvite was studied. To evaluate such an effect an experiment of struvite growth from artificial urine was performed. The investigations are related to infectious urinary stones formation. The crystallization process was induced by the addition of aqueous ammonia solution to mimic the bacterial activity. The spectrophotometric results demonstrate that trisodium citrate increases induction time with respect to struvite formation and decreases the growth efficiency of struvite. The inhibitory effect of trisodium citrate on the nucleation and growth of struvite is explained in base of chemical speciation analysis. Such an analysis demonstrates that the inhibitory effect is related with the fact that trisodium citrate binds NH4 + and Mg2+ ions in the range of pH from 7 to 9.5 characteristic for struvite precipitation. The most important is the MgCit- complex whose concentration strongly depends on an increase in pH rather than on an increase in citrate concentrations.
Free Radical Formation in Novel Carotenoid Metal Ion Complexes of Astaxanthin
Polyakov, Nikolay E.; Focsan, A. Ligia; Bowman, Michael K.; Kispert, Lowell D.
The carotenoid astaxanthin forms novel metal ion complexes with Ca2+, Zn2+ and Fe2+. MS and NMR measurements indicate that the two oxygen atoms on the terminal cyclohexene ring of astaxanthin chelate the metal to form 1:1 complexes with Ca2+ and Zn2+ at low salt concentrations < 0.2 mM. The stability constants of these complexes increased by a factor of 85 upon changing the solvent from acetonitrile to ethanol for Ca2+ and by a factor of 7 for Zn2+ as a consequence of acetonitrile being a part of the complex. Optical studies showed that at high concentrations (> 0.2 mM) of salt 2:1 metal:astaxanthin complexes were formed in ethanol. In the presence of Ca2+ and Zn2+ salts the lifetime of the radical cation and dication formed electrochemically decreased relative to that of the carotenoid neutral radical. DFT calculations showed that the deprotonation of the radical cation at the carbon C3 position resulted in the lowest energy neutral radical while proton loss at the C5, C9 or C13 methyl groups was less favorable. Pulsed EPR measurements were carried out on UV-produced radicals of astaxanthin supported on silica-alumina, MCM-41 or Ti-MCM-41. The pulsed EPR measurements detected the radical cation and neutral radicals formed by proton loss at 77 K from the C3, C5, C9, and C13-methyl groups and a radical anion formed by deprotonation of the neutral radical at C3. There was more than an order of magnitude increase in the concentration of radicals on Ti-MCM-41 relative to MCM-41, and the radical cation concentration exceeded that of the neutral radicals. PMID:21114306
Pancreatic beta-cell granule peptides form heteromolecular complexes which inhibit islet amyloid polypeptide fibril formation.
Jaikaran, Emma T A S; Nilsson, Melanie R; Clark, Anne
Islet amyloid polypeptide (IAPP), or 'amylin', is co-stored with insulin in secretory granules of pancreatic islet beta-cells. In Type 2 diabetes, IAPP converts into a beta-sheet conformation and oligomerizes to form amyloid fibrils and islet deposits. Granule components, including insulin, inhibit spontaneous IAPP fibril formation in vitro. To determine the mechanism of this inhibition, molecular interactions of insulin with human IAPP (hIAPP), rat IAPP (rIAPP) and other peptides were examined using surface plasmon resonance (BIAcore), CD and transmission electron microscopy (EM). hIAPP and rIAPP complexed with insulin, and this reaction was concentration-dependent. rIAPP and insulin, but not pro-insulin, bound to hIAPP. Insulin with a truncated B-chain, to prevent dimerization, also bound hIAPP. In the presence of insulin, hIAPP did not spontaneously develop beta-sheet secondary structure or form fibrils. Insulin interacted with pre-formed IAPP fibrils in a regular repeating pattern, as demonstrated by immunoEM, suggesting that the binding sites for insulin remain exposed in hIAPP fibrils. Since rIAPP and hIAPP form complexes with insulin (and each other), this could explain the lack of amyloid fibrils in transgenic mice expressing hIAPP. It is likely that IAPP fibrillogenesis is inhibited in secretory granules (where the hIAPP concentration is in the millimolar range) by heteromolecular complex formation with insulin. Alterations in the proportions of insulin and IAPP in granules could disrupt the stability of the peptide. The increase in the proportion of unprocessed pro-insulin produced in Type 2 diabetes could be a major factor in destabilization of hIAPP and induction of fibril formation. PMID:14565847
Analysis of Complexity and Power Consumption in DSP-Based Optical Modulation Formats
Wei, J. L.; Cheng, Q.; Penty, R. V.; White, I. H.
Analysis of Complexity and Power Consumption in DSP-Based Optical Modulation Formats J. L. Wei, Q. Cheng, R. V. Penty, and I. H. White Centre for Photonic Systems, Electrical Engineering Division, Department of Engineering, University... of Cambridge, 9 J J Thomson Avenue, Cambridge CB3 0FA, UK. E-mail: email@example.com D. G. Cunningham Avago Technologies, Framlingham Technology Centre, Station Road, Framlingham, Suffolk, IP13 9EZ, UK. Abstract: Analysis shows that 400 GbE links using DSP...
Formation of complex two-dimensional dissipative solitons via spontaneous symmetry breaking
NASA Astrophysics Data System (ADS)
Skarka, V.; Aleksi?, N. B.; Leki?, M.; Aleksi?, B. N.; Malomed, B. A.; Mihalache, D.; Leblond, H.
We propose a complex Ginzburg-Landau equation (CGLE) with localized linear gain as a two-dimensional model for pattern formation proceeding via spontaneous breaking of the axial symmetry. Starting from steady-state solutions produced by an extended variational approximation, simulations of the CGLE generate a vast class of robust solitary structures. These are varieties of asymmetric rotating vortices carrying the topological charge (TC), and four- to ten-pointed revolving stars, whose angular momentum is decoupled from the TC. The four- and five-pointed stars feature a cyclic change of their structure in the course of the rotation.
Protein Kinase C and Differentially Regulate Death-Inducing Signaling Complex Formation in Cigarette Smoke Extract-Induced Apoptosis1
Jeong-Woong Park; Hong Pyo Kim; Seon-Jin Lee; Xue Wang; Yong Wang; Emeka Ifedigbo; Simon C. Watkins; Motoi Ohba; Stefan W. Ryter; Yatin M. Vyas; Augustine M. K. Choi
Cigarette smoke, a major risk factor in emphysema, causes cell death by incompletely understood mechanisms. Death-inducing signaling complex (DISC) formation is an initial event in Fas-mediated apoptosis. We demonstrate that cigarette smoke extract (CSE) induces DISC formation in human lung fibroblasts (MRC-5) and promotes DISC trafficking from the Golgi complex to membrane lipid rafts. We demonstrate a novel role of
Effects of the Preparation Method on the Formation of True Nimodipine SBE-?-CD/HP-?-CD Inclusion Complexes and Their Dissolution Rates Enhancement.
Semcheddine, Farouk; Guissi, Nida El Islem; Liu, XueYin; Wu, ZuoMin; Wang, Bo
The aims of this study were to enhance the solubility and dissolution rate of nimodipine (ND) by preparing the inclusion complexes of ND with sulfobutylether-b-cyclodextrin (SBE-?-CD) and 2-hydroxypropyl-b-cyclodextrin (HP-?-CD) and to study the effect of the preparation method on the in vitro dissolution profile in different media (0.1 N HCl pH 1.2, phosphate buffer pH 7.4, and distilled water). Thus, the inclusion complexes were prepared by kneading, coprecipitation, and freeze-drying methods. Phase solubility studies were conducted to characterize the complexes in the liquid state. The inclusion complexes in the solid state were investigated with differential scanning calorimetry (DSC), X-ray diffractometry (X-RD), and Fourier transform infrared spectroscopy (FT-IR). Stable complexes of ND/SBE-?-CD and ND/HP-?-CD were formed in distilled water in a 1:1 stoichiometric inclusion complex as indicated by an AL-type diagram. The apparent stability constants (Ks) were 1334.4 and 464.1 M(-1) for ND/SBE-?-CD and ND/HP-?-CD, respectively. The water-solubility of ND was significantly increased in an average of 22- and 8-fold for SBE-?-CD and HP-?-CD, respectively. DSC results showed the formation of true inclusion complexes between the drug and both SBE-?-CD and HP-?-CD prepared by the kneading method. In contrast, crystalline drug was detectable in all other products. The dissolution studies showed that all the products exhibited higher dissolution rate than those of the physical mixtures and ND alone, in all mediums. However, the kneading complexes displayed the maximum dissolution rate in comparison with drug and other complexes, confirming the influence of the preparation method on the physicochemical properties of the products. PMID:25511809
Fluids circulations during the formation of the Naxos Metamorphic Core Complex (Greece)
NASA Astrophysics Data System (ADS)
Vanderhaeghe, Olivier; Boiron, Marie-Christine; Siebenaller, Luc
The island of Naxos, in the central part of the Cycladic Metamorphic Core Complex (Greece) represents a perfect example to address the evolution of fluid circulations during collapse of an orogenic belt. It displays a complex detachment system characterized by mylonites, cataclasites and high-angle normal faults which geometric relationships reflect rheological layering of the orogenic crust and its evolution during collapse. The chemistry of fluid inclusions determined by microthermometry, RAMAN spectroscopy, LA-ICPMS, and crush-leach combined with C and H isotopic signatures point to three distinct types of fluids, namely (i) a H2O-dominated fluid, (ii) a composite H2O-CO2 fluid, and (iii) a NaCl-rich fluid concentrated in metals. These different types of fluids are interpreted to reflect mixtures to various degrees among fluids generated by (i) condensation of clouds (meteoric aqueous fluid), (ii) dehydration and decarbonatation of metasedimentary rocks during metamorphism (metamorphic aqueous-carbonic fluid), and (iii) crystallization of granitic magmas (magmatic saline fluid with high metal contents). The distribution of fluids with respect to microstructures evidences the close link between deformation and fluid circulations at the mineral scale from intracristalline deformation to fracturing. The orientation of fluid inclusion planes, veins and alteration zones allows to identify the scale and geometry of the reservoir into which fluids are circulating and their evolution during the formation of the Metamorphic Core Complex. These data indicate that the orogenic crust is subdivided in two reservoirs separated by the ductile/fragile transition. Meteoric fluids circulate in the upper crust affected by brittle deformation whereas metamorphic and magmatic fluids circulate in relation to intracristalline ductile deformation affecting the lower crust. The geometry of these reservoirs evolves during the formation of the Naxos Metamorphic Core Complex as the orogenic crust is extended and cooled. In particular, the exhumation of metamorphic rocks and their transfer from the ductile to the fragile reservoir is marked by a transition from a lithostatic to an hydrostatic pressure associated with a drastic decrease of the geothermal gradient from 60-100°C/km to 35-60°C/km. This implies that fluid circulations during the formation of a Metamorphic Core Complex are intimately related to the rheologic layering of the orogenic crust and its evolution during collapse. Accordingly, the ductile/fragile transition, in addition to represent a fundamental rheologic boundary, also corresponds to a thermal and hydrologic crustal-scale transition zone.
Hormad1 Mutation Disrupts Synaptonemal Complex Formation, Recombination, and Chromosome Segregation in Mammalian Meiosis
Erdin, Serpil Uckac; Yatsenko, Svetlana A.; Kloc, Malgorzata; Yang, Fang; Wang, P. Jeremy; Meistrich, Marvin L.; Rajkovic, Aleksandar
Meiosis is unique to germ cells and essential for reproduction. During the first meiotic division, homologous chromosomes pair, recombine, and form chiasmata. The homologues connect via axial elements and numerous transverse filaments to form the synaptonemal complex. The synaptonemal complex is a critical component for chromosome pairing, segregation, and recombination. We previously identified a novel germ cell–specific HORMA domain encoding gene, Hormad1, a member of the synaptonemal complex and a mammalian counterpart to the yeast meiotic HORMA domain protein Hop1. Hormad1 is essential for mammalian gametogenesis as knockout male and female mice are infertile. Hormad1 deficient (Hormad1?/?) testes exhibit meiotic arrest in the early pachytene stage, and synaptonemal complexes cannot be visualized by electron microscopy. Hormad1 deficiency does not affect localization of other synaptonemal complex proteins, SYCP2 and SYCP3, but disrupts homologous chromosome pairing. Double stranded break formation and early recombination events are disrupted in Hormad1?/? testes and ovaries as shown by the drastic decrease in the ?H2AX, DMC1, RAD51, and RPA foci. HORMAD1 co-localizes with ?H2AX to the sex body during pachytene. BRCA1, ATR, and ?H2AX co-localize to the sex body and participate in meiotic sex chromosome inactivation and transcriptional silencing. Hormad1 deficiency abolishes ?H2AX, ATR, and BRCA1 localization to the sex chromosomes and causes transcriptional de-repression on the X chromosome. Unlike testes, Hormad1?/? ovaries have seemingly normal ovarian folliculogenesis after puberty. However, embryos generated from Hormad1?/? oocytes are hyper- and hypodiploid at the 2 cell and 8 cell stage, and they arrest at the blastocyst stage. HORMAD1 is therefore a critical component of the synaptonemal complex that affects synapsis, recombination, and meiotic sex chromosome inactivation and transcriptional silencing. PMID:21079677
Metal-organic-frameworks-derived general formation of hollow structures with high complexity.
Zhang, Lei; Wu, Hao Bin; Lou, Xiong Wen David
Increasing the complexity of hollow structures, in terms of chemical composition and shell architecture, is highly desirable for both fundamental studies and realization of various functionalities. Starting with metal-organic frameworks (MOFs), we demonstrate a general approach toward the large-scale and facile synthesis of complex hollow microboxes via manipulation of the template-engaged reactions between the Prussian blue (PB) template and different alkaline substances. The reaction between PB microcubes with NaOH solution leads to the formation of Fe(OH)3 microboxes with controllable multishelled structure. In addition, PB microcubes will react with the conjugate bases of metal oxide based weak acids, generating multicompositional microboxes (Fe2O3/SnO2, Fe2O3/SiO2, Fe2O3/GeO2, Fe2O3/Al2O3, and Fe2O3/B2O3), which consist of uniformly dispersed oxides/hydroxides of iron and another designed element. Such complex hollow structures and atomically integrated multiple compositions might bring the usual physiochemical properties. As an example, we demonstrate that these complex hollow microboxes, especially the Fe2O3/SnO2 composite microboxes, exhibit remarkable electrochemical performance as anode materials for lithium ion batteries. PMID:23805894
Formation of iron(II)-nitrosoalkane complexes: a new activity of microperoxidase 8.
Ricoux, R; Boucher, J L; Mansuy, D; Mahy, J P
Microperoxidase 8 (MP8) is a heme octapeptide, obtained by enzymatic hydrolysis of heart cytochrome c, in which a histidine is axially coordinated to the heme iron, and acts as its fifth ligand. It exhibits two kinds of activities: a peroxidase-like activity and a cytochrome P450-like activity. We here show that MP8 is not only able to oxidize various aliphatic and aromatic hydroxylamines with the formation of MP8-Fe(II)-nitrosoalkane or -arene complexes absorbing around 414 nm, but also that these complexes can be obtained by reduction of nitroalkanes. This is the first example of fully characterized iron(II)-metabolite complexes of MP8. Such complexes constitute good models for those obtained upon oxidation of amphetamine or macrolids by cytochromes P450. In addition, this is a new catalytic activity of MP8, which validates the use of this mini-enzyme as a convenient model for hemoproteins of interest in toxicology and pharmacology such as cytochromes P450 and peroxidases. PMID:11071875
Zeaxanthin Radical Cation Formation in Minor Light-Harvesting Complexes of Higher Plant Antenna
Avenson, Thomas H.; Ahn, Tae Kyu; Zigmantas, Donatas; Niyogi, Krishna K.; Li, Zhirong; Ballottari, Matteo; Bassi, Roberto; Fleming, Graham R.
Previous work on intact thylakoid membranes showed that transient formation of a zeaxanthin radical cation was correlated with regulation of photosynthetic light-harvesting via energy-dependent quenching. A molecular mechanism for such quenching was proposed to involve charge transfer within a chlorophyll-zeaxanthin heterodimer. Using near infrared (880-1100 nm) transient absorption spectroscopy, we demonstrate that carotenoid (mainly zeaxanthin) radical cation generation occurs solely in isolated minor light-harvesting complexes that bind zeaxanthin, consistent with the engagement of charge transfer quenching therein. We estimated that less than 0.5percent of the isolated minor complexes undergo charge transfer quenching in vitro, whereas the fraction of minor complexes estimated to be engaged in charge transfer quenching in isolated thylakoids was more than 80 times higher. We conclude that minor complexes which bind zeaxanthin are sites of charge transfer quenching in vivo and that they can assume Non-quenching and Quenching conformations, the equilibrium LHC(N)<--> LHC(Q) of which is modulated by the transthylakoid pH gradient, the PsbS protein, and protein-protein interactions.
The Inhibition of Calcium Phosphate Precipitation by Fetuin Is Accompanied by the Formation of a Fetuin-Mineral Complex*
Price, Paul A.
The Inhibition of Calcium Phosphate Precipitation by Fetuin Is Accompanied by the Formation- apatite from supersaturated solutions of calcium and phosphate in vitro is accompanied by the formation of the fetuin-mineral complex, a high molecular mass com- plex of calcium phosphate mineral and the proteins fe
Ternary complex formation by vaccinia virus RNA polymerase at an early viral promoter: analysis by native gel electrophoresis.
Hagler, J; Shuman, S
We have resolved, by native gel electrophoresis, two intermediates in the transcription of a vaccinia virus early gene by the virus-encoded RNA polymerase. Polymerase holoenzyme containing the vaccinia virus early transcription factor (VETF) forms a complex of VETF bound to the promoter as the first step in a pathway leading to establishment of a committed ternary elongation complex. Formation of the VETF-DNA complex is stimulated by magnesium but is uninfluenced by nucleoside triphosphates. A stable binary complex of RNA polymerase bound to DNA is not detected. Assembly of a gel-stable polymerase-DNA complex depends on conditions permissive for RNA synthesis. Nucleotide omission experiments suggest that at least a tetrameric RNA must be made before a ternary complex is stabilized. RNA analysis indicates that complexes containing nascent transcripts 20 nucleotides long are stable and active. Ternary complex formation requires hydrolyzable ATP. This is consistent with an essential role for the ATPase activity of VETF at a step subsequent to DNA binding, as proposed by Broyles (S. S. Broyles, J. Biol. Chem. 266:15545-15548, 1991). The ternary complex, once formed, is resistant to dissociation by competitor DNA, as well as by salt, Sarkosyl, and heparin. The effects of these inhibitory agents on transcription complex formation suggest that they target different steps in the assembly pathway. Images PMID:1373199
Electrostatic and hydrophobic interactions during complex formation and electron transfer in the ferredoxin/ferredoxin: NADP{sup +} reductase system from Anabaena
Hurley, J.K.; Tollin, G. [Univ. of Arizona, Tucson, AZ (United States)] [Univ. of Arizona, Tucson, AZ (United States); Fillat, M.F.; Gomez-Moreno, C. [Universidad de Zaragoza (Spain)] [Universidad de Zaragoza (Spain)
Transient kinetics and protein-protein binding measurements over a wide range of ionic strength (I) have been used to characterize the interactions occurring during complex formation and electron transfer (et) between recombinant ferredoxin (Fd) and both native and recombinant ferredoxin: NADP{sup +} reductase (FNR) from the cyanobacterium Anabaena. Between I = 12 mM and I = 100 mM, the dissociation constant (K{sub d}) for the complex formed between oxidized Fd and oxidized native FNR increases from 4.5 to 8.1 {mu}M, whereas K{sub d} for the Fd complex with recombinant FNR increases from 0.3 to 3.3 {mu}M. For both pairs of proteins, the ionic strength dependence of k{sub obs} for the et reaction is biphasic. Electrostatic analysis of the kinetic data above I = 100 mM allows a prediction of the ionic strength dependence of the K{sub d} values, if electrostatic interactions are the only determinant of complex stability. The predicted dependence is dramatically larger than the observed one, indicating that hydrophobic interactions make an important contribution to complex stability. The differences in binding between native and recombinant FNR are ascribed to proteolytic cleavage at the N-terminus, which occurs during preparation of the native enzyme and which removes two positively charged residues, thereby decreasing the electrostatic interactions with Fd. 39 refs., 4 figs., 1 tab.
Effect of Solvent Dielectric Constant and Acidity on the OH Vibration Frequency in Hydrogen-Bonded Complexes of Fluorinated Ethanols.
Pines, Dina; Keinan, Sharon; Kiefer, Philip M; Hynes, James T; Pines, Ehud
Infrared spectroscopy measurements were used to characterize the OH stretching vibrations in a series of similarly structured fluoroethanols, RCH2OH (R = CH3, CH2F, CHF2, CF3), a series which exhibits a systematic increase in the molecule acidity with increasing number of F atoms. This study, which expands our earlier efforts, was carried out in non-hydrogen-bonding solvents comprising molecules with and without a permanent dipole moment, with the former solvents being classified as polar solvents and the latter designated as nonpolar. The hydrogen bond interaction in donor-acceptor complexes formed in solution between the fluorinated ethanol H-donors and the H-acceptor base DMSO was investigated in relation to the solvent dielectric and to the differences ?PA of the gas phase proton affinities (PAs) of the conjugate base of the fluorinated alcohols and DMSO. We have observed that ?OH decreases as the acidity of the alcohol increases (?PA decreases) and that ?OH varies inversely with ?, exhibiting different slopes for nonpolar and polar solvents. These 1/? slopes tend to vary linearly with ?PA, increasing with increasing acidity. These experimental findings, including the ?PA trends, are described with our recently published two-state Valence Bond-based theory for acid-base H-bonded complexes. Lastly, the correlation of the alcohol's conjugate base PAs with Taft ?* values of the fluorinated ethyl groups CHnF3-nCH2- provides a connection of the inductive effects for these groups with the acidity parameter ?PA associated with the H-bonded complexes. PMID:25420059
Probing formation of cargo/importin-? transport complexes in plant cells using a pathogen effector.
Wirthmueller, Lennart; Roth, Charlotte; Fabro, Georgina; Caillaud, Marie-Cécile; Rallapalli, Ghanasyam; Asai, Shuta; Sklenar, Jan; Jones, Alexandra M E; Wiermer, Marcel; Jones, Jonathan D G; Banfield, Mark J
Importin-?s are essential adapter proteins that recruit cytoplasmic proteins destined for active nuclear import to the nuclear transport machinery. Cargo proteins interact with the importin-? armadillo repeat domain via nuclear localization sequences (NLSs), short amino acids motifs enriched in Lys and Arg residues. Plant genomes typically encode several importin-? paralogs that can have both specific and partially redundant functions. Although some cargos are preferentially imported by a distinct importin-? it remains unknown how this specificity is generated and to what extent cargos compete for binding to nuclear transport receptors. Here we report that the effector protein HaRxL106 from the oomycete pathogen Hyaloperonospora arabidopsidis co-opts the host cell's nuclear import machinery. We use HaRxL106 as a probe to determine redundant and specific functions of importin-? paralogs from Arabidopsis thaliana. A crystal structure of the importin-?3/MOS6 armadillo repeat domain suggests that five of the six Arabidopsis importin-?s expressed in rosette leaves have an almost identical NLS-binding site. Comparison of the importin-? binding affinities of HaRxL106 and other cargos in vitro and in plant cells suggests that relatively small affinity differences in vitro affect the rate of transport complex formation in vivo. Our results suggest that cargo affinity for importin-?, sequence variation at the importin-? NLS-binding sites and tissue-specific expression levels of importin-?s determine formation of cargo/importin-? transport complexes in plant cells. PMID:25284001
Frataxin Accelerates [2Fe-2S] Cluster Formation on the Human Fe-S Assembly Complex.
Fox, Nicholas G; Das, Deepika; Chakrabarti, Mrinmoy; Lindahl, Paul A; Barondeau, David P
Iron-sulfur (Fe-S) clusters function as protein cofactors for a wide variety of critical cellular reactions. In human mitochondria, a core Fe-S assembly complex [called SDUF and composed of NFS1, ISD11, ISCU2, and frataxin (FXN) proteins] synthesizes Fe-S clusters from iron, cysteine sulfur, and reducing equivalents and then transfers these intact clusters to target proteins. In vitro assays have relied on reducing the complexity of this complicated Fe-S assembly process by using surrogate electron donor molecules and monitoring simplified reactions. Recent studies have concluded that FXN promotes the synthesis of [4Fe-4S] clusters on the mammalian Fe-S assembly complex. Here the kinetics of Fe-S synthesis reactions were determined using different electron donation systems and by monitoring the products with circular dichroism and absorbance spectroscopies. We discovered that common surrogate electron donor molecules intercepted Fe-S cluster intermediates and formed high-molecular weight species (HMWS). The HMWS are associated with iron, sulfide, and thiol-containing proteins and have properties of a heterogeneous solubilized mineral with spectroscopic properties remarkably reminiscent of those of [4Fe-4S] clusters. In contrast, reactions using physiological reagents revealed that FXN accelerates the formation of [2Fe-2S] clusters rather than [4Fe-4S] clusters as previously reported. In the preceding paper [Fox, N. G., et al. (2015) Biochemistry 54, DOI: 10.1021/bi5014485], [2Fe-2S] intermediates on the SDUF complex were shown to readily transfer to uncomplexed ISCU2 or apo acceptor proteins, depending on the reaction conditions. Our results indicate that FXN accelerates a rate-limiting sulfur transfer step in the synthesis of [2Fe-2S] clusters on the human Fe-S assembly complex. PMID:26016518
Formation of complex organic molecules in cold objects: the role of gas-phase reactions
NASA Astrophysics Data System (ADS)
Balucani, Nadia; Ceccarelli, Cecilia; Taquet, Vianney
While astrochemical models are successful in reproducing many of the observed interstellar species, they have been struggling to explain the observed abundances of complex organic molecules. Current models tend to privilege grain surface over gas-phase chemistry in their formation. One key assumption of those models is that radicals trapped in the grain mantles gain mobility and react on lukewarm ( ? 30 K) dust grains. Thus, the recent detections of methyl formate (MF) and dimethyl ether (DME) in cold objects represent a challenge and may clarify the respective role of grain-surface and gas-phase chemistry. We propose here a new model to form DME and MF with gas-phase reactions in cold environments, where DME is the precursor of MF via an efficient reaction overlooked by previous models. Furthermore, methoxy, a precursor of DME, is also synthesized in the gas phase from methanol, which is desorbed by a non-thermal process from the ices. Our new model reproduces fairly well the observations towards L1544. It also explains, in a natural way, the observed correlation between DME and MF. We conclude that gas-phase reactions are major actors in the formation of MF, DME and methoxy in cold gas. This challenges the exclusive role of grain-surface chemistry and favours a combined grain-gas chemistry.
Multicomponent complex formation between vinpocetine, cyclodextrins, tartaric acid and water-soluble polymers monitored by NMR and solubility studies
Laura Ribeiro; Rui A. Carvalho; Domingos C. Ferreira; Francisco J. B. Veiga
This work deals with multicomponent complex formation of vinpocetine (VP) with ?-cyclodextrin (?CD), sulfobutyl ether ?-cyclodextrin (SBE?CD) and tartaric acid (TA), in the presence or absence of water-soluble polymers, in aqueous solution. Complexation was monitored by phase-solubility and proton nuclear magnetic resonance (1H NMR) studies. TA demonstrated a synergistic effect on VP solubility, and in the complexation efficiency of ?CD
Increasing of the solubility of the AgI nuclei in rain drops induced by the complex formation with dominant ions
NASA Astrophysics Data System (ADS)
Reutova, T. V.; Zhinzhakova, L. Z.; Chernyak, M. M.
Rainwater has a complex chemical composition. Investigations showed that such cations as Ca 2+, Mg 2+, K +, NH 4+ and anions SO 42-, NO 2-, Cl -, and HCO 3- are constantly present in rainwater. Among them Cl - and NH 4+ form the stable complex compounds with Ag + -ions and thus can increase the solubility of AgI. The I --ions having the property of complex formation to Ag + are introduced into the cloud media by crystallizing agents at seeding. The simple calculations of AgI solubility, taking into account the property of Ag + to form the complex compound with Cl -, I - and NH 4+ at same concentrations as in rainwater, showed that the solubility increase did not exceed 50% and in average was of 13%. Particularly, the solubility in one third of the samples increased from 2 to 5%, in the other two third of the samples it increased from 5 to 25%. And only in two cases the solubility increased by 36% and 46%, respectively, was observed. The increase of solubility was due to the presence of NH 4+-ions. Just this ion was one of the main impurities of the rainwater in the studied region. The contribution of halogen-ions was very negligible in spite of the high values of the stability constants of their complexes. The more the solubility the less the lifetime of AgI particles in raindrops. According to our calculations the particles with diameters of 0.03-0.1 ?m which can serve as the ice-forming nuclei may exist not less than 10 minutes in the rainwater containing the ligands.
BAG3 regulates formation of the SNARE complex and insulin secretion
Iorio, V; Festa, M; Rosati, A; Hahne, M; Tiberti, C; Capunzo, M; De Laurenzi, V; Turco, M C
Insulin release in response to glucose stimulation requires exocytosis of insulin-containing granules. Glucose stimulation of beta cells leads to focal adhesion kinase (FAK) phosphorylation, which acts on the Rho family proteins (Rho, Rac and Cdc42) that direct F-actin remodeling. This process requires docking and fusion of secretory vesicles to the release sites at the plasma membrane and is a complex mechanism that is mediated by SNAREs. This transiently disrupts the F-actin barrier and allows the redistribution of the insulin-containing granules to more peripheral regions of the ? cell, hence facilitating insulin secretion. In this manuscript, we show for the first time that BAG3 plays an important role in this process. We show that BAG3 downregulation results in increased insulin secretion in response to glucose stimulation and in disruption of the F-actin network. Moreover, we show that BAG3 binds to SNAP-25 and syntaxin-1, two components of the t-SNARE complex preventing the interaction between SNAP-25 and syntaxin-1. Upon glucose stimulation BAG3 is phosphorylated by FAK and dissociates from SNAP-25 allowing the formation of the SNARE complex, destabilization of the F-actin network and insulin release. PMID:25766323
Substrate-Na{sup +} complex formation: Coupling mechanism for {gamma}-aminobutyrate symporters
Pallo, Anna; Simon, Agnes [Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences (Hungary)] [Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences (Hungary); Bencsura, Akos [Department of Theoretical Chemistry, Institute of Structural Chemistry, Chemical Research Center, Hungarian Academy of Sciences, Budapest (Hungary)] [Department of Theoretical Chemistry, Institute of Structural Chemistry, Chemical Research Center, Hungarian Academy of Sciences, Budapest (Hungary); Heja, Laszlo [Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences (Hungary)] [Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences (Hungary); Kardos, Julianna, E-mail: email@example.com [Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences (Hungary)] [Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences (Hungary)
Crystal structures of transmembrane transport proteins belonging to the important families of neurotransmitter-sodium symporters reveal how they transport neurotransmitters across membranes. Substrate-induced structural conformations of gated neurotransmitter-sodium symporters have been in the focus of research, however, a key question concerning the mechanism of Na{sup +} ion coupling remained unanswered. Homology models of human glial transporter subtypes of the major inhibitory neurotransmitter {gamma}-aminobutyric acid were built. In accordance with selectivity data for subtype 2 vs. 3, docking and molecular dynamics calculations suggest similar orthosteric substrate (inhibitor) conformations and binding crevices but distinguishable allosteric Zn{sup 2+} ion binding motifs. Considering the occluded conformational states of glial human {gamma}-aminobutyric acid transporter subtypes, we found major semi-extended and minor ring-like conformations of zwitterionic {gamma}-aminobutyric acid in complex with Na{sup +} ion. The existence of the minor ring-like conformation of {gamma}-aminobutyric acid in complex with Na{sup +} ion may be attributed to the strengthening of the intramolecular H-bond by the electrostatic effect of Na{sup +} ion. Coupling substrate uptake into cells with the thermodynamically favorable Na{sup +} ion movement through substrate-Na{sup +} ion complex formation may be a mechanistic principle featuring transmembrane neurotransmitter-sodium symporter proteins.
Solventless Formation of G-Quartet Complexes Based on Alkali and Alkaline Earth Salts on Au(111).
Zhang, Chi; Wang, Likun; Xie, Lei; Kong, Huihui; Tan, Qinggang; Cai, Liangliang; Sun, Qiang; Xu, Wei
Template cations have been extensively employed in the formation, stabilization and regulation of structural polymorphism of G-quadruplex structures in vitro. However, the direct addition of salts onto solid surfaces, especially under ultra-high-vacuum (UHV) conditions, to explore the feasibility and universality of the formation of G-quartet complexes in a solventless environment has not been reported. By combining UHV-STM imaging and DFT calculations, we have shown that three different G-quartet-M (M: Na/K/Ca) complexes can be obtained on Au(111) using alkali and alkaline earth salts as reactants. We have also identified the driving forces (intra-quartet hydrogen bonding and electrostatic ionic bonding) for the formation of these complexes and quantified the interactions involved. Our results demonstrate a novel route to fabricate G-quartet-related complexes on solid surfaces, providing an alternative feasible way to bring metal elements to surfaces for constructing metal-organic systems. PMID:25917128
Determination of equilibrium constant of amino carbamate adduct formation in sisomicin by a high pH based high performance liquid chromatography.
Wlasichuk, Kenneth B; Tan, Li; Guo, Yushen; Hildebrandt, Darin J; Zhang, Hao; Karr, Dane E; Schmidt, Donald E
Amino carbamate adduct formation from the amino group of an aminoglycoside and carbon dioxide has been postulated as a mechanism for reducing nephrotoxicity in the aminoglycoside class compounds. In this study, sisomicin was used as a model compound for amino carbamate analysis. A high pH based reversed-phase high performance liquid chromatography (RP-HPLC) method is used to separate the amino carbamate from sisomicin. The carbamate is stable as the breakdown is inhibited at high pH and any reactive carbon dioxide is removed as the carbonate. The amino carbamate was quantified and the molar fraction of amine as the carbamate of sisomicin was obtained from the HPLC peak areas. The equilibrium constant of carbamate formation, Kc, was determined to be 3.3×10(-6) and it was used to predict the fraction of carbamate over the pH range in a typical biological systems. Based on these results, the fraction of amino carbamate at physiological pH values is less than 13%, and the postulated mechanism for nephrotoxicity protection is not valid. The same methodology is applicable for other aminoglycosides. PMID:25880243
Ojha, D. K.; Ghosh, S. K. [Tata Institute of Fundamental Research, Mumbai (Bombay) 400 005 (India); Samal, M. R.; Pandey, A. K.; Sharma, Saurabh [Aryabhatta Research Institute of Observational Sciences, Nainital 263 129 (India); Bhatt, B. C. [Indian Institute of Astrophysics, Koramangala, Bangalore 560 034 (India); Tamura, M. [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Mohan, V. [Inter-University Centre for Astronomy and Astrophysics, Pune 411 007 (India); Zinchenko, I., E-mail: email@example.com [Institute of Applied Physics of the Russian Academy of Sciences, Ulyanova 46, 603950 Nizhny Novgorod (Russian Federation)
We present results on the star formation activity of an optically obscured region containing an embedded cluster (S255-IR) and molecular gas between two evolved H II regions, S255 and S257. We have studied the complex using optical and near-infrared (NIR) imaging, optical spectroscopy, and radio continuum mapping at 15 GHz, along with Spitzer-IRAC results. We found that the main exciting sources of the evolved H II regions S255 and S257 and the compact H II regions associated with S255-IR are of O9.5-B3 V nature, consistent with previous observations. Our NIR observations reveal 109 likely young stellar object (YSO) candidates in an area of {approx}4.'9 x 4.'9 centered on S255-IR, which include 69 new YSO candidates. To see the global star formation, we constructed the V - I/V diagram for 51 optically identified IRAC YSOs in an area of {approx}13' x 13' centered on S255-IR. We suggest that these YSOs have an approximate age between 0.1 and 4 Myr, indicating a non-coeval star formation. Using spectral energy distribution models, we constrained physical properties and evolutionary status of 31 and 16 YSO candidates outside and inside the gas ridge, respectively. The models suggest that the sources associated with the gas ridge are younger (mean age {approx}1.2 Myr) than the sources outside the gas ridge (mean age {approx}2.5 Myr). The positions of the young sources inside the gas ridge at the interface of the H II regions S255 and S257 favor a site of induced star formation.
The formation of glycine and other complex organic molecules in exploding ice mantles.
Rawlings, J M C; Williams, D A; Viti, S; Cecchi-Pestellini, C; Duley, W W
Complex Organic Molecules (COMs), such as propylene (CH3CHCH2) and the isomers of C2H4O2 are detected in cold molecular clouds (such as TMC-1) with high fractional abundances (Marcelino et al., Astrophys. J., 2007, 665, L127). The formation mechanism for these species is the subject of intense speculation, as is the possibility of the formation of simple amino acids such as glycine (NH2CH2COOH). At typical dark cloud densities, normal interstellar gas-phase chemistries are inefficient, whilst surface chemistry is at best ill defined and does not easily reproduce the abundance ratios observed in the gas phase. Whatever mechanism(s) is/are operating, it/they must be both efficient at converting a significant fraction of the available carbon budget into COMs, and capable of efficiently returning the COMs to the gas phase. In our previous studies we proposed a complementary, alternative mechanism, in which medium- and large-sized molecules are formed by three-body gas kinetic reactions in the warm high density gas phase. This environment exists, for a very short period of time, after the total sublimation of grain ice mantles in transient co-desorption events. In order to drive the process, rapid and efficient mantle sublimation is required and we have proposed that ice mantle 'explosions' can be driven by the catastrophic recombination of trapped hydrogen atoms, and other radicals, in the ice. Repeated cycles of freeze-out and explosion can thus lead to a cumulative molecular enrichment of the interstellar medium. Using existing studies we based our chemical network on simple radical addition, subject to enthalpy and valency restrictions. In this work we have extended the chemistry to include the formation pathways of glycine and other large molecular species that are detected in molecular clouds. We find that the mechanism is capable of explaining the observed molecular abundances and complexity in these sources. We find that the proposed mechanism is easily capable of explaining the large abundances of all three isomers of C2H4O2 that are observationally inferred for star-forming regions. However, the model currently does not provide an obvious explanation for the predominance of methyl formate, suggesting that some refinement to our (very simplistic) chemistry is necessary. The model also predicts the production of glycine at a (lower) abundance level, that is consistent with its marginal detection in astrophysical sources. PMID:25302390
The development of folds and cleavages in slate belts by underplating in accretionary complexes: A comparison of the Kodiak Formation, Alaska and the Calaveras Complex, California
NASA Astrophysics Data System (ADS)
Paterson, Scott R.; Sample, James C.
The development of folds and cleavages in slate and graywacke belts is commonly attributed to arc-continent or continent-continent collisions. However, the Kodiak Formation of southern Alaska and the Calaveras Complex of the western Sierra Nevada, California, are two slate and graywacke belts in which folds and slaty cleavages developed during simple underthrusting and underplating within accretionary wedges. The Maastrichtian Kodiak Formation is composed dominantly of coherent turbidites but includes lesser pebbly mudstone, minor conglomerate, and rare chert. The Kodiak Formation is part of a large accretionary complex that youngs in age seaward, but bedding tops generally show landward younging. A progression of structures has been determined by crosscutting relationships and includes (1) syndeformational depositional features; (2) broken formation; (3) slaty cleavage, folds, and thrust faults; (4) crenulations and crenulation cleavage; (5) late brittle thrust faults; and (6) right-lateral strike-slip faults. Broken formation, slaty cleavage, thrust faults, and folds developed during underthrusting and underplating within an accretionary wedge. Crenulations and brittle thrust faults are related to subsequent intrawedge shortening. Based on peak metamorphism in the uppermost zeolite to prehnite-pumpellyite facies, underplating occurred at a minimum depth of 10 km. The Calaveras Complex is composed of argillite, chert, graywacke, pebbly mudstone, limestone, and volcanic rocks. Its age of deposition has a maximum range from Permian to Early Jurassic. Overall, the unit appears to young westward, but local facing indicators show eastward younging of individual blocks. The sequence of structures developed in the Calaveras Complex is (1) syn-depositional olistostromes; (2) broken formation; (3) slaty cleavage, folds, and thrust faults; and (4) younger Jura-Triassic folds and crenulation cleavages. Broken formation and slaty cleavage developed during underthrusting and underplating in an accretionary wedge, in an analogous fashion to the Kodiak Formation. Greenschist facies metemorphism during underplating suggests that the Calaveras Complex was accreted at deeper levels, or in a wedge with a higher geothermal gradient, than the Kodiak Formation. Some other probable examples of slate/graywacke belts that became folded and well-foliated during underplating include part of the Dunnage Zone (Newfoundland), the Southern Uplands complex (Scotland), the Torlesse terrane (New Zealand), part of the Hamburg klippe (Pennsylvania), and the Taconic allochthons (New York). Peak metamorphism in these belts indicates that they were accreted in accretionary wedges with geothermal gradients higher than usually assumed for such tectonic settings; such wedges may have been fairly common features at convergent margins.
The application of the constants of motion to nonlinear stationary waves in complex plasmas: a unified fluid dynamic viewpoint
NASA Astrophysics Data System (ADS)
McKenzie, J. F.; Dubinin, E.; Sauer, K.; Doyle, T. B.
Perturbation reductive procedures, as used to analyse various weakly nonlinear plasma waves (solitons and periodic waves), normally lead to the dynamical system being described by KdV, Burgers' or a nonlinear Schrödinger-type equation, with properties that can be deduced from an array of mathematical techniques. Here we develop a fully nonlinear theory of one-dimensional stationary plasma waves, which elucidates the common nature of various diverse wave phenomena. This is accomplished by adopting an essentially fluid dynamic viewpoint. In this unified treatment the constants of the motion (for mass, momentum and energy) lead naturally to the construction of the wave structure equations. It is shown, for example, that electrostatic, Hall magnetohydrodynamic and ion cyclotron acoustic nonlinear waves all obey first-order differential equations of the same generic type for the longitudinal flow field of the wave. The equilibrium points, which define the soliton amplitude, are given by the compressive and/or rarefactive roots of a total plasma 'energy' or 'momentum' function characterizing the wave type. This energy function, which is an algebraic combination of the Bernoulli momentum and energy functions for the longitudinal flow field, is the fluid dynamic counterpart of the pseudo-potentials, which are characteristic of system structure equations formulated in other than fluid variables. Another general feature of the structure equation is the phenomenon of choked flow, which occurs when the flow speed becomes sonic. It is this trans-sonic property that limits the soliton amplitudes and defines the critical collective Mach numbers of the waves. These features are also obtained in multi-component plasmas where, for example, in a bi-ion plasma, momentum exchanges between protons and heavier ions are mediated by the Maxwell magnetic stresses. With a suitable generalization of the concept of a sonic point in a bi-ion system and the corresponding choked flow feature, the wave structures, although now more complicated, can also be understood within this overall fluid framework. Particularly useful tools in this context are the momentum hodograph (an algebraic relation between the bi-ion speeds and the electron speed, or magnetic field, which follows from the conservation of mass, momentum and charge-neutrality) and a generalized Bernoulli energy density for each species. Analysis shows that the bi-ion solitons are essentially compressive, but contain the remarkable feature of the presence of a proton rarefactive core. A new type of soliton, called an 'oscilliton' because embedded spatial oscillations are superimposed on the classical soliton, is also described and discussed. A necessary condition for the existence of this type of wave is that the linear phase velocity must exhibit an extremum where the phase speed matches the group speed. The remarkable properties of this wave are illustrated for the case of both whistler waves and bi-ion waves where, for the latter, the requisite condition is met near the cross-over frequencies. In the case of the whistler oscilliton, which propagates at speeds in excess of one half of the Alfvén speed (based on the electrons), an analytic solution has been constructed through a phase-portrait integral of the system in which the proton and electron dynamics must be placed on the same footing. The relevance of the different wave structures to diverse space environments is briefly discussed in relation to recently available high-time and spatial resolution data from satellite observations.
Spontaneous formation of complex structures made from elastic membranes in an aluminum-hydroxide-carbonate system.
Kiehl, Micah; Kaminker, Vitaliy; Pantaleone, James; Nowak, Piotr; Dyonizy, Agnieszka; Maselko, Jerzy
A popular playground for studying chemo-hydrodynamic patterns and instabilities is chemical gardens, also known as silicate gardens. In these systems, complex structures spontaneously form, driven by buoyant forces and either osmotic or mechanical pumps. Here, we report on systems that differ somewhat from classical chemical gardens in that the membranes are much more deformable and soluble. These properties lead to structures that self-construct and evolve in new ways. For example, they exhibit the formation of chemical balloons, a new growth mechanism for tubes, and also the homologous shrinking of these tubes. The stretching mechanism for the membranes is probably different than for other systems by involving membrane "self-healing." Other unusual properties are osmosis that sometimes occurs out of the structure and also small plumes that flow away from the structure, sometimes upwards, and sometimes downwards. Mathematical models are given that explain some of the observed phenomena. PMID:26117121
Spontaneous formation of complex structures made from elastic membranes in an aluminum-hydroxide-carbonate system
NASA Astrophysics Data System (ADS)
Kiehl, Micah; Kaminker, Vitaliy; Pantaleone, James; Nowak, Piotr; Dyonizy, Agnieszka; Maselko, Jerzy
A popular playground for studying chemo-hydrodynamic patterns and instabilities is chemical gardens, also known as silicate gardens. In these systems, complex structures spontaneously form, driven by buoyant forces and either osmotic or mechanical pumps. Here, we report on systems that differ somewhat from classical chemical gardens in that the membranes are much more deformable and soluble. These properties lead to structures that self-construct and evolve in new ways. For example, they exhibit the formation of chemical balloons, a new growth mechanism for tubes, and also the homologous shrinking of these tubes. The stretching mechanism for the membranes is probably different than for other systems by involving membrane "self-healing." Other unusual properties are osmosis that sometimes occurs out of the structure and also small plumes that flow away from the structure, sometimes upwards, and sometimes downwards. Mathematical models are given that explain some of the observed phenomena.
A study of multi-ligand beta-lactoglobulin complex formation.
Zhang, Jie; Liu, Xiaoming; Subirade, Muriel; Zhou, Peng; Liang, Li
Beta-lactoglobulin (?-LG), the principal whey protein, possesses multiple sites for binding ligands. Most studies of ?-LG-ligand interactions have focused on the formation and dissociation of protein complexes with single ligands, such as ?-tocopherol, resveratrol or folic acid. In this study, the possibility of a plurality of bioactive compounds binding simultaneously to ?-LG was analysed using protein intrinsic fluorescence quenching. It was found that ?-LG could bind two or three ligands simultaneously, although the sequence in which the ligands were added affected binding affinity. The impact of binding to ?-LG on physicochemical properties of these three ligands is discussed in view of fluorescence spectroscopy and high performance liquid chromatography results. The data obtained in this study suggest the feasibility of developing ?-LG-based carriers of a plurality of active compounds. PMID:25038674
Metformin activates AMP-activated protein kinase by promoting formation of the ??? heterotrimeric complex.
Meng, Shumei; Cao, Jia; He, Qiyi; Xiong, Lishou; Chang, Evan; Radovick, Sally; Wondisford, Fredric E; He, Ling
Metformin is the most widely prescribed oral anti-diabetic agent. Recently, we have shown that low metformin concentrations found in the portal vein suppress glucose production in hepatocytes through activation of AMPK. Moreover, low concentrations of metformin were found to activate AMPK by increasing the phosphorylation of AMPK? at Thr-172. However, the mechanism underlying the increase in AMPK? phosphorylation at Thr-172 and activation by metformin remains unknown. In the current study, we find that low concentrations of metformin promote the formation of the AMPK ??? complex, resulting in an increase in net phosphorylation of the AMPK ? catalytic subunit at Thr-172 by augmenting phosphorylation by LKB1 and antagonizing dephosphorylation by PP2C. PMID:25538235
Hydration of the sulfuric acid-methylamine complex and implications for aerosol formation.
Bustos, Danielle J; Temelso, Berhane; Shields, George C
The binary H2SO4-H2O nucleation is one of the most important pathways by which aerosols form in the atmosphere, and the presence of ternary species like amines increases aerosol formation rates. In this study, we focus on the hydration of a ternary system of sulfuric acid (H2SO4), methylamine (NH2CH3), and up to six waters to evaluate its implications for aerosol formation. By combining molecular dynamics (MD) sampling with high-level ab initio calculations, we determine the thermodynamics of forming H2SO4(NH2CH3)(H2O)n, where n = 0-6. Because it is a strong acid-base system, H2SO4-NH2CH3 quickly forms a tightly bound HSO4(-)-NH3CH3(+) complex that condenses water more readily than H2SO4 alone. The electronic binding energy of H2SO4-NH2CH3 is -21.8 kcal mol(-1) compared with -16.8 kcal mol(-1) for H2SO4-NH3 and -12.8 kcal mol(-1) for H2SO4-H2O. Adding one to two water molecules to the H2SO4-NH2CH3 complex is more favorable than adding to H2SO4 alone, yet there is no systematic difference for n ? 3. However, the average number of water molecules around H2SO4-NH2CH3 is consistently higher than that of H2SO4, and it is fairly independent of temperature and relative humidity. PMID:24730699
When Does E = Mc2? Conditions Under Which Extension Leads To Metamorphic Core Complex Formation
NASA Astrophysics Data System (ADS)
Wijns, C.; Gessner, K.; Weinberg, R.; Moresi, L.
Metamorphic core complexes (MC2) form during continental extension when stretch- ing is strongly localised onto relatively few normal fault systems, each accomodating large displacements, and resulting in exhumation of the lower crust. Extending litho- sphere is assumed to be mechanically stratified with a "weak" ductile lower crust overlain by a "strong" brittle upper crust. Our work shows that the formation of an MC2 may be a direct consequence of the localising nature of the rheological layering, rather than depending upon lateral rheological contrasts. In the absence of lateral het- erogeneities, the ratio of upper to lower crustal strength determines whether the upper crust is completely dissected (MC2 mode), or whether densely spaced faults occur, with limited slip on each fault, and no exposure of lower crustal rocks. We use a two-dimensional Lagrangian Integration Point finite element code to explore the different behaviours of the crust during extension. This particle-in-cell approach allows simulations to develop very large strains comparable to those found in analogue models, while still tracking strain history accurately for the constitutive laws. We con- sider viscoplastic materials with strain and/or strain-rate weakening behaviour, which gives rise to the localisation of deformation and necking of layers. Lateral hetero- geneities in intrinsic rock strength or in heat flow may be included, acting as nuclei for the formation of large-scale detachment faults. The Central Menderes metamorphic core complex in Turkey is the field example against which we match results of our simulations. We compare temperature-time paths and pressure-temperature paths with field data from apatite fission-track ther- mochronology in order to assess the numerical models.
Effects of Electric Double Layer and Space Charge Polarization by Plural Kinds of Ions on Complex Dielectric Constant of Liquid Crystal Materials
NASA Astrophysics Data System (ADS)
Sawada, Atsushi; Tarumi, Kazuaki; Naemura, Shohei
The complex dielectric constant of a liquid crystal material, 4-cyano-4?-alkyl-biphenyl (5CB), was measured in low-frequency regions below 1000 Hz. The anomalous increasing behavior was analyzed using an equivalent circuit which takes two kinds of contributions into account: one is from the electric double layer and the other is from the space charge polarization. It was found by numerical calculations that these two effects exhibit different dependences of dielectric dispersion on the thickness of a specimen, and both effects were successfully distinguished in the experimental results. In the analysis of the space charge polarization, the experimental results were best fitted by the calculated results with five kinds of ions in terms of the diffusion coefficient. These measurements can be applied to a precise determination of the attributes of plural kinds of ions, such as the diffusion coefficient and the number density.
Formation of complex organic molecules in cold objects: the role of gas phase reactions
Balucani, Nadia; Taquet, Vianney
While astrochemical models are successful in reproducing many of the observed interstellar species, they have been struggling to explain the observed abundances of complex organic molecules. Current models tend to privilege grain surface over gas phase chemistry in their formation. One key assumption of those models is that radicals trapped in the grain mantles gain mobility and react on lukewarm (>30 K) dust grains. Thus, the recent detections of methyl formate (MF) and dimethyl ether (DME) in cold objects represent a challenge and may clarify the respective role of grain surface and gas phase chemistry. We propose here a new model to form DME and MF with gas phase reactions in cold environments, where DME is the precursor of MF via an efficient reaction overlooked by previous models. Furthermore, methoxy, a precursor of DME, is also synthetized in the gas phase from methanol, which is desorbed by a non-thermal process from the ices. Our new model reproduces fairy well the observations towards L1544. It also...
Spitzer Analysis of H II Region Complexes in the Magellanic Clouds: Determining a Suitable Monochromatic Obscured Star Formation Indicator
NASA Astrophysics Data System (ADS)
Lawton, B.; Gordon, K. D.; Babler, B.; Block, M.; Bolatto, A. D.; Bracker, S.; Carlson, L. R.; Engelbracht, C. W.; Hora, J. L.; Indebetouw, R.; Madden, S. C.; Meade, M.; Meixner, M.; Misselt, K.; Oey, M. S.; Oliveira, J. M.; Robitaille, T.; Sewilo, M.; Shiao, B.; Vijh, U. P.; Whitney, B.
H II regions are the birth places of stars, and as such they provide the best measure of current star formation rates (SFRs) in galaxies. The close proximity of the Magellanic Clouds allows us to probe the nature of these star forming regions at small spatial scales. To study the H II regions, we compute the bolometric infrared flux, or total infrared (TIR), by integrating the flux from 8 to 500 ?m. The TIR provides a measure of the obscured star formation because the UV photons from hot young stars are absorbed by dust and re-emitted across the mid-to-far-infrared (IR) spectrum. We aim to determine the monochromatic IR band that most accurately traces the TIR and produces an accurate obscured SFR over large spatial scales. We present the spatial analysis, via aperture/annulus photometry, of 16 Large Magellanic Cloud (LMC) and 16 Small Magellanic Cloud (SMC) H II region complexes using the Spitzer Space Telescope's IRAC (3.6, 4.5, 8 ?m) and MIPS (24, 70, 160 ?m) bands. Ultraviolet rocket data (1500 and 1900 Å) and SHASSA H? data are also included. All data are convolved to the MIPS 160 ?m resolution (40 arcsec full width at half-maximum), and apertures have a minimum radius of 35''. The IRAC, MIPS, UV, and H? spatial analysis are compared with the spatial analysis of the TIR. We find that nearly all of the LMC and SMC H II region spectral energy distributions (SEDs) peak around 70 ?m at all radii, from ~10 to ~400 pc from the central ionizing sources. As a result, we find the following: the sizes of H II regions as probed by 70 ?m are approximately equal to the sizes as probed by TIR (?70 pc in radius); the radial profile of the 70 ?m flux, normalized by TIR, is constant at all radii (70 ?m ~ 0.45TIR); the 1? standard deviation of the 70 ?m fluxes, normalized by TIR, is a lower fraction of the mean (0.05-0.12 out to ~220 pc) than the normalized 8, 24, and 160 ?m normalized fluxes (0.12-0.52); and these results are the same for the LMC and the SMC. From these results, we argue that 70 ?m is the most suitable IR band to use as a monochromatic obscured star formation indicator because it most accurately reproduces the TIR of H II regions in the LMC and SMC and over large spatial scales. We also explore the general trends of the 8, 24, 70, and 160 ?m bands in the LMC and SMC H II region SEDs, radial surface brightness profiles, sizes, and normalized (by TIR) radial flux profiles. We derive an obscured SFR equation that is modified from the literature to use 70 ?m luminosity, SFR(M sun yr-1) = 9.7(0.7) × 10-44 L 70(ergs s-1), which is applicable from 10 to 300 pc distance from the center of an H II region. We include an analysis of the spatial variations around H II regions between the obscured star formation indicators given by the IR and the unobscured star formation indicators given by UV and H?. We compute obscured and unobscured SFRs using equations from the literature and examine the spatial variations of the SFRs around H II regions.
UXT-V1 protects cells against TNF-induced apoptosis through modulating complex II formation
Huang, Yuefeng; Chen, Liang; Zhou, Yi; Liu, Heng; Yang, Jueqing; Liu, Zhenggang; Wang, Chen
Proteins that directly regulate tumor necrosis factor (TNF) signaling have critical roles in determining cell death and survival. Previously we characterized ubiquitously expressed transcript (UXT)-V2 as a novel transcriptional cofactor to regulate nuclear factor-?B in the nucleus. Here we report that another splicing isoform of UXT, UXT-V1, localizes in cytoplasm and regulates TNF-induced apoptosis. UXT-V1 knockdown cells are hypersensitive to TNF-induced apoptosis. We demonstrated that UXT-V1 is a new component of TNF receptor signaling complex. We found that UXT-V1 binds to TNF receptor-associated factor 2 and prevents TNF receptor–associated death domain protein from recruiting Fas-associated protein with death domain. More importantly, UXT-V1 is a short-half-life protein, the degradation of which facilitates the formation of the apoptotic receptor complex II in response to TNF treatment. This study demonstrates that UXT-V1 is a novel regulator of TNF-induced apoptosis and sheds new light on the underlying molecular mechanism of this process. PMID:21307340
UXT-V1 protects cells against TNF-induced apoptosis through modulating complex II formation.
Huang, Yuefeng; Chen, Liang; Zhou, Yi; Liu, Heng; Yang, Jueqing; Liu, Zhenggang; Wang, Chen
Proteins that directly regulate tumor necrosis factor (TNF) signaling have critical roles in determining cell death and survival. Previously we characterized ubiquitously expressed transcript (UXT)-V2 as a novel transcriptional cofactor to regulate nuclear factor-?B in the nucleus. Here we report that another splicing isoform of UXT, UXT-V1, localizes in cytoplasm and regulates TNF-induced apoptosis. UXT-V1 knockdown cells are hypersensitive to TNF-induced apoptosis. We demonstrated that UXT-V1 is a new component of TNF receptor signaling complex. We found that UXT-V1 binds to TNF receptor-associated factor 2 and prevents TNF receptor-associated death domain protein from recruiting Fas-associated protein with death domain. More importantly, UXT-V1 is a short-half-life protein, the degradation of which facilitates the formation of the apoptotic receptor complex II in response to TNF treatment. This study demonstrates that UXT-V1 is a novel regulator of TNF-induced apoptosis and sheds new light on the underlying molecular mechanism of this process. PMID:21307340
Beerer, I. M. [Department of Astronomy, University of California, Berkeley, CA (United States); Koenig, X. P.; Hora, J. L.; Keto, E.; Smith, H. A.; Fazio, G. G. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA (United States); Gutermuth, R. A. [Smith College, Northampton, MA (United States); Bontemps, S.; Schneider, N. [Observatoire de Bordeaux, BP 89, 33270 Floirac (France); Megeath, S. T. [Department of Physics and Astronomy, University of Toledo, Toledo, OH (United States); Motte, F. [AIM/SAp, CEA-Saclay, 91191 Gif Sur Yvette Cedex (France); Carey, S. [Spitzer Science Center, Pasadena, CA (United States); Simon, R. [I. Physik. Institut, Universitaet zu Koeln, 50937 Koeln (Germany); Allen, L. E. [NOAO, 950 North Cherry Avenue, Tucson, AZ (United States); Kraemer, K. E.; Price, S. [Air Force Research Laboratory, Hanscom AFB, MA (United States); Mizuno, D. [Institute for Scientific Research, Boston College, Boston, MA (United States); Adams, J. D. [Cornell University, Department of Radiophysics Space Research, Ithaca, NY (United States); Hernandez, J. [Centro de Investigaciones de AstronomIa, Apdo. Postal 264, Merida 5101-A (Venezuela, Bolivarian Republic of); Lucas, P. W. [Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield (United Kingdom)
We present new images and photometry of the massive star-forming complex Cygnus X obtained with the Infrared Array Camera (IRAC) and the Multiband Imaging Photometer for Spitzer (MIPS) on board the Spitzer Space Telescope. A combination of IRAC, MIPS, UKIRT Deep Infrared Sky Survey, and Two Micron All Sky Survey data are used to identify and classify young stellar objects (YSOs). Of the 8231 sources detected exhibiting infrared excess in Cygnus X North, 670 are classified as class I and 7249 are classified as class II. Using spectra from the FAST Spectrograph at the Fred L. Whipple Observatory and Hectospec on the MMT, we spectrally typed 536 sources in the Cygnus X complex to identify the massive stars. We find that YSOs tend to be grouped in the neighborhoods of massive B stars (spectral types B0 to B9). We present a minimal spanning tree analysis of clusters in two regions in Cygnus X North. The fraction of infrared excess sources that belong to clusters with {>=}10 members is found to be 50%-70%. Most class II objects lie in dense clusters within blown out H II regions, while class I sources tend to reside in more filamentary structures along the bright-rimmed clouds, indicating possible triggered star formation.
Determination of Binding Constants of Cyclodextrins in Room-Temperature Ionic Liquids
Reid, Scott A.
Determination of Binding Constants of Cyclodextrins in Room-Temperature Ionic Liquids by Near to determine association binding constants between phe- nol and r-, - and -cyclodextrin (CD) in [butylmethyl interaction between phenol and CDs may not be inclusion complex formation but rather external adsorption
Amphiphilic Residues 29-44 of DREAM N-Termini Mediate Calmodulin:DREAM Complex Formation.
Gonzalez, Walter G; Arango, Andres S; Miksovska, Jaroslava
DREAM (downstream regulatory element antagonist modulator) is a neuronal calcium sensor that has been shown to modulate gene expression as well as to be involved in numerous neuronal processes. In this report, we show that association of calcium-bound calmodulin (CaM) with DREAM is mediated by a short amphipathic amino acid sequence located between residues 29 and 44 on DREAM. The association of CaM with a peptide analogous to DREAM(29-44) or to full-length DREAM protein is calcium-dependent with a dissociation constant of 136 nM or 3.4 ?M, respectively. Thermodynamic and kinetic studies show that the observed decrease in affinity for the native protein is due to electrostatic interactions between the basic N-terminus and an electronegative surface on DREAM. These results are further supported by circular dichroism, binding studies, and molecular dynamics simulations. Additionally, fluorescence anisotropy decay measurements show a rotational correlation time of 10.8 ns for a complex of CaM with a DREAM(29-44) peptide, supporting a wraparound semispherical model with 1:1 stoichiometry. Furthermore, the interaction between an IEDANS-labeled CaM construct with DREAM is best modeled as a heterotetramer that adopts an elongated conformation with a correlation time of 45 ns in the presence of Ca(2+). We also demonstrate that association of CaM with DREAM eliminates the nonspecific interaction of DREAM with the DRE double-stranded DNA sequence of the human prodynorphin gene. This work provides molecular insight into the CaM:DREAM complex and its potential role in modulation of gene expression. PMID:26108881
Features of the ESI mechanism that affect the observation of multiply charged noncovalent protein complexes and the determination of the association constant by the titration method.
Peschke, Michael; Verkerk, Udo H; Kebarle, Paul
Several factors, attributable to the ESIMS mechanism, that can affect the assumptions of the titration method are examined: (1) The assumption that the concentrations in solution of the protein P, the ligand L, and the complex PL are proportional to the respective ion intensities observed with ESIMS, is examined with experiments in which ion intensities of two non-interacting proteins are compared with the respective concentrations. The intensities are found to be approximately proportional to the concentrations. The proportionality factors are found to increase as the mass of the protein is decreased. Very small proteins have much higher intensities. The results suggest that it is preferable to use only the intensity ratio of PL and P, whose masses are very close to each other when L is small, to determine the association constant KA in solution. (2) From the charge residue model (CRM) one expects that the solution will experience a very large increase of concentration due to evaporation of the precursor droplets, before the proteins P and PL are produced in the gas phase. This can shift the equilibrium in the droplets: P + L = PL, towards PL. Analysis of the droplet evaporation history shows that such a shift is not likely, because the time of droplet evolution is very short, only several micros, and the equilibrium relaxation time is much longer. (3) The droplet history shows that unreacted P and L can be often present together in the same droplet. On complete evaporation of such droplets L will land on P leading to PL and this effect will lead to values of KA that are too high. However, it is argued that mostly accidental, weakly bonded, complexes will form and these will dissociate in the clean up stages (heated transfer capillary and CAD region). Thus only very small errors are expected due to this cause. (4) Some PL complexes may have bonding that is too weak in the gas phase even though they have KA values in solution that predict high solution PL yields. In this case the PL complexes may decompose in the clean up stages and not be observed with sufficient intensity in the mass spectrum. This will lead to KA values that are too low. The effect is expected for complexes that involve significant hydrophobic interaction that leads to high stability of the complex in solution but low stability in the gas phase. The titration method is not suited for such systems. PMID:15465355
The earliest phases of high-mass star formation: the NGC 6334-NGC 6357 complex
NASA Astrophysics Data System (ADS)
Russeil, D.; Zavagno, A.; Motte, F.; Schneider, N.; Bontemps, S.; Walsh, A. J.
Context. Our knowledge of high-mass star formation has been mainly based on follow-up studies of bright sources found by IRAS, and has thus been incomplete for its earliest phases, which are inconspicuous at infrared wavelengths. With a new generation of powerful bolometer arrays, unbiased large-scale surveys of nearby high-mass star-forming complexes now search for the high-mass analog of low-mass cores and class 0 protostars. Aims: Following the pioneering study of Cygnus X, we investigate the star-forming region NGC 6334-NGC 6357 (~1.7 kpc). Methods: We study the complex NGC 6334-NGC 6357 in an homogeneous way following the previous work of Motte and collaborators. We used the same method to extract the densest cores which are the most likely sites for high-mass star formation. We analyzed the SIMBA/SEST 1.2 mm data presented in Munoz and coworkers, which covers all high-column density areas (A v ? 15 mag) of the NGC 6334-NGC 6357 complex and extracted dense cores following the method used for Cygnus X. We constrain the properties of the most massive dense cores (M > 100 M_?) using new molecular line observations (as SiO, N2H+,H13CO+, HCO+ (1-0) and CH3CN) with Mopra and a complete cross-correlation with infrared databases (MSX, GLIMPSE, MIPSGAL) and literature. Results: We extracted 163 massive dense cores of which 16 are more massive than 200 M_?. These high-mass dense cores have a typical FWHM size of 0.37 pc, an average mass of M ~ 600 M_?, and a volume-averaged density of ~ 1.5 × 105 cm-3. Among these massive dense cores, 6 are good candidates for hosting high-mass infrared-quiet protostars, 9 cores are classified as high-luminosity infrared protostars, and we find only one high-mass starless clump (~0.3 pc, ~ 4 × 104 cm-3) that is gravitationally bound. Conclusions: Since our sample is derived from a single molecular complex and covers every embedded phase of high-mass star formation, it provides a statistical estimate of the lifetime of massive stars. In contrast to what is found for low-mass class 0 and class I phases, the infrared-quiet protostellar phase of high-mass stars may last as long as their more well known high-luminosity infrared phase. As in Cygnus X, the statistical lifetime of high-mass protostars is shorter than found for nearby, low-mass star-forming regions which implies that high-mass pre-stellar and protostellar cores are in a dynamic state, as expected in a molecular cloud where turbulent and/or dynamical processes dominate. Based on observations made with Mopra telescope. The Mopra telescope is part of the Australia Telescope which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO.Table 1 and Appendix are only available in electronic form at http://www.aanda.orgProfiles as FITS files are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/515/A55
Assessment of the CCSD and CCSD(T) Coupled-Cluster Methods in Calculating Heats of Formation for Zn Complexes
Weaver, Michael N.; Yang, Yue
Heats of formation were calculated using coupled-cluster methods for a series of zinc complexes. The calculated values were evaluated against previously conducted computational studies using density functional methods as well as experimental values. Heats of formation for nine neutral ZnXn complexes [X = -Zn, -H, -O, -F2, -S, -Cl, -Cl2, -CH3, (-CH3)2] were determined at the CCSD and CCSD(T) levels using the 6–31G** and TZVP basis sets, as well as the LANL2DZ-6–31G** (LACVP**) and LANL2DZ-TZVP hybrid basis sets. The CCSD(T)/6–31G** level of theory was found to predict the heat of formation for the non-alkyl Zn complexes most accurately. The alkyl Zn species were problematic in that none of the methods that were tested accurately predicted the heat of formation for these complexes. For the seven non-alkyl species, the CCSD(T)/6–31G** level of theory was shown to predict the most accurate heat of formation values. In instances where experimental geometric parameters were available, these were most accurately predicted by the CCSD/6–31G** level of theory; going to CCSD(T) did not improve agreement with the experimental values. PMID:19691272
Colorimetric determination of sildenafil citrate (Viagra) through ion-associate complex formation.
Amin, Alaa S; Moustafa, Moustafa E; El-Dosoky, Reham
A simple, quick, accurate, and sensitive colorimetric method is described for the determination of sildenafil citrate (SLD). The method is based on the reaction of SLD with Congo Red, Sudan II, and Gentian Violet in buffered aqueous solutions at pH 2.5, 6.5, and 11.0, respectively, to give highly colored soluble ion-associate complex species; the colored products are quantitated colorimetrically at 523, 554, and 569 nm, respectively. The various experimental conditions were optimized. The stoichiometric ratio was found to be 1:1 for all ion associates; the calculated logarithmic stability constants were 8.51, 7.79, and 5.58, respectively. Beer's law was obeyed over the concentration range of 0.2-7.0 microg/mL, whereas the Ringbom optimum concentration range was 0.4-6.5 microg/mL. Values for molar absorptivity, Sandell sensitivity, and detection and quantification limits were also calculated. The proposed method was successfully applied to the determination of SLD in Viagra tablets and in serum samples by using the technique of standard additions with mean accuracy values of 100.06 +/- 1.14, 99.87 +/- 0.70, and 99.86 +/- 0.97% for Viagra tablets and 99.88 +/- 0.60, 99.90 +/- 0.90, and 100.24 +/- 0.80% for serum samples, respectively. PMID:19382569
GlnK effects complex formation between NifA and NifL in Klebsiella pneumoniae
Jessica Stips; Robert Thummer; Melanie Neumann; Ruth A. Schmitz
In Klebsiella pneumoniae, the nif specific transcriptional activator NifA is inhibited by NifL in response to molecular oxygen and ammonium. Here, we demonstrate complex formation between NifL and NifA (approximately 1 : 1 ratio), when synthesized in the presence of oxygen and\\/or ammonium. Under simultaneous oxygen- and nitrogen- limitation, significant but fewer NifL-NifA complexes (approximately 1%) were formed in the
Polymorphism of 4- tert-butylcalix[4]arene upon the formation and thermal destruction of its complex with acetonitrile
NASA Astrophysics Data System (ADS)
Surov, O. V.; Voronova, M. I.; Smirnov, P. R.; Trostin, V. N.; Mamardashvili, N. Zh.
It is demonstrated that combined analysis of powder X-ray diagrams and differential scanning calorimetry allows us to reveal complex polymorphic transformations of 4- tert-butylcalix[4]arene upon the formation and thermal destruction of its complex with acetonitrile. The stability of 4- tert-butylcalix[4]arene polymorph containing no solvent molecules in the crystal lattice after the removal of acetonitrile is assumed.
Analysis of the Enhanced Stability of R(+)-Alpha Lipoic Acid by the Complex Formation with Cyclodextrins
Ikuta, Naoko; Sugiyama, Hironori; Shimosegawa, Hiroshi; Nakane, Rie; Ishida, Yoshiyuki; Uekaji, Yukiko; Nakata, Daisuke; Pallauf, Kathrin; Rimbach, Gerald; Terao, Keiji; Matsugo, Seiichi
R(+)-alpha lipoic acid (RALA) is one of the cofactors for mitochondrial enzymes and, therefore, plays a central role in energy metabolism. RALA is unstable when exposed to low pH or heat, and therefore, it is difficult to use enantiopure RALA as a pharma- and nutra-ceutical. In this study, we have aimed to stabilize RALA through complex formation with cyclodextrins (CDs). ?-CD, ?-CD and ?-CD were used for the formation of these RALA-CD complexes. We confirmed the complex formation using differential scanning calorimetry and showed by using HPLC analysis that complexed RALA is more stable than free RALA when subjected to humidity and high temperature or acidic pH conditions. Scanning electron microscopy studies showed that the particle size and shape differed depending on the cyclodextrin used for complexation. Further, the complexes of CD and RALA showed a different particle size distribution pattern compared with that of CD itself or that of the physical mixture of RALA and CD. PMID:23434662
A peroxynitrite complex of copper: formation from a copper–nitrosyl complex, transformation to nitrite and exogenous phenol oxidative coupling or nitration
Park, Ga Young; Deepalatha, Subramanian; Puiu, Simona C.; Lee, Dong-Heon; Mondal, Biplab; Sarjeant, Amy A. Narducci; del Rio, Diego; Pau, Monita Y. M.; Solomon, Edward I.; Karlin, Kenneth D.
Reaction of nitrogen monoxide with a copper(I) complex possessing a tridentate alkylamine ligand gives a Cu(I)–(·NO) adduct, which when exposed to dioxygen generates a peroxynitrite (O=NOO?)–Cu(II) species. This undergoes thermal transformation to produce a copper(II) nitrito (NO2?) complex and 0.5 mol equiv O2. In the presence of a substituted phenol, the peroxynitrite complex effects oxidative coupling, whereas addition of chloride ion to dissociate the peroxynitrite moiety instead leads to phenol ortho nitration. Discussions include the structures (including electronic description) of the copper–nitrosyl and copper–peroxynitrite complexes and the formation of the latter, based on density functional theory calculations and accompanying spectroscopic data. PMID:19662443
Enantioseparation of mandelic acid derivatives by high performance liquid chromatography with substituted ?-cyclodextrin as chiral mobile phase additive and evaluation of inclusion complex formation
Tong, Shengqiang; Zhang, Hu; Shen, Mangmang
The enantioseparation of ten mandelic acid derivatives was performed by reverse phase high performance liquid chromatography with hydroxypropyl-?-cyclodextrin (HP-?-CD) or sulfobutyl ether-?-cyclodextrin (SBE-?-CD) as chiral mobile phase additives, in which inclusion complex formations between cyclodextrins and enantiomers were evaluated. The effects of various factors such as the composition of mobile phase, concentration of cyclodextrins and column temperature on retention and enantioselectivity were studied. The peak resolutions and retention time of the enantiomers were strongly affected by the pH, the organic modifier and the type of ?-cyclodextrin in the mobile phase, while the concentration of buffer solution and temperature had a relatively low effect on resolutions. Enantioseparations were successfully achieved on a Shimpack CLC-ODS column (150×4.6 mm i.d., 5 ?m). The mobile phase was a mixture of acetonitrile and 0.10 mol L-1 of phosphate buffer at pH 2.68 containing 20 mmol L-1 of HP-?-CD or SBE-?-CD. Semi-preparative enantioseparation of about 10 mg of ?-cyclohexylmandelic acid and ?-cyclopentylmandelic acid were established individually. Cyclodextrin-enantiomer complex stoichiometries as well as binding constants were investigated. Results showed that stoichiomertries for all the inclusion complex of cyclodextrin-enantiomers were 1:1. PMID:24893270
Enantioseparation of mandelic acid derivatives by high performance liquid chromatography with substituted ?-cyclodextrin as chiral mobile phase additive and evaluation of inclusion complex formation.
Tong, Shengqiang; Zhang, Hu; Shen, Mangmang; Ito, Yoichiro; Yan, Jizhong
The enantioseparation of ten mandelic acid derivatives was performed by reverse phase high performance liquid chromatography with hydroxypropyl-?-cyclodextrin (HP-?-CD) or sulfobutyl ether-?-cyclodextrin (SBE-?-CD) as chiral mobile phase additives, in which inclusion complex formations between cyclodextrins and enantiomers were evaluated. The effects of various factors such as the composition of mobile phase, concentration of cyclodextrins and column temperature on retention and enantioselectivity were studied. The peak resolutions and retention time of the enantiomers were strongly affected by the pH, the organic modifier and the type of ?-cyclodextrin in the mobile phase, while the concentration of buffer solution and temperature had a relatively low effect on resolutions. Enantioseparations were successfully achieved on a Shimpack CLC-ODS column (150×4.6mm i.d., 5?m). The mobile phase was a mixture of acetonitrile and 0.10molL(-1) of phosphate buffer at pH 2.68 containing 20mmolL(-1) of HP-?-CD or SBE-?-CD. Semi-preparative enantioseparation of about 10mg of ?-cyclohexylmandelic acid and ?-cyclopentylmandelic acid were established individually. Cyclodextrin-enantiomer complex stoichiometries as well as binding constants were investigated. Results showed that stoichiometries for all the inclusion complex of cyclodextrin-enantiomers were 1:1. PMID:24893270
Swarming and complex pattern formation in Paenibacillus vortex studied by imaging and tracking cells
Ingham, Colin J; Jacob, Eshel Ben
Background Swarming motility allows microorganisms to move rapidly over surfaces. The Gram-positive bacterium Paenibacillus vortex exhibits advanced cooperative motility on agar plates resulting in intricate colonial patterns with geometries that are highly sensitive to the environment. The cellular mechanisms that underpin the complex multicellular organization of such a simple organism are not well understood. Results Swarming by P. vortex was studied by real-time light microscopy, by in situ scanning electron microscopy and by tracking the spread of antibiotic-resistant cells within antibiotic-sensitive colonies. When swarming, P. vortex was found to be peritrichously flagellated. Swarming by the curved cells of P. vortex occurred on an extremely wide range of media and agar concentrations (0.3 to 2.2% w/v). At high agar concentrations (> 1% w/v) rotating colonies formed that could be detached from the main mass of cells by withdrawal of cells into the latter. On lower percentage agars, cells moved in an extended network composed of interconnected "snakes" with short-term collision avoidance and sensitivity to extracts from swarming cells. P. vortex formed single Petri dish-wide "supercolonies" with a colony-wide exchange of motile cells. Swarming cells were coupled by rapidly forming, reversible and non-rigid connections to form a loose raft, apparently connected via flagella. Inhibitors of swarming (p-Nitrophenylglycerol and Congo Red) were identified. Mitomycin C was used to trigger filamentation without inhibiting growth or swarming; this facilitated dissection of the detail of swarming. Mitomycin C treatment resulted in malcoordinated swarming and abortive side branch formation and a strong tendency by a subpopulation of the cells to form minimal rotating aggregates of only a few cells. Conclusion P. vortex creates complex macroscopic colonies within which there is considerable reflux and movement and interaction of cells. Cell shape, flagellation, the aversion of cell masses to fuse and temporary connections between proximate cells to form rafts were all features of the swarming and rotation of cell aggregates. Vigorous vortex formation was social, i.e. required > 1 cell. This is the first detailed examination of the swarming behaviour of this bacterium at the cellular level. PMID:18298829
Inclusion complex of [gamma]-cyclodextrin-C[sub 60]. Formation, characterization, and photophysical properties in aqueous solutions
Priyadarsini, K.I.; Mohan, H.; Tyagi, A.K.; Mittal, J.P. (Bhabha Atomic Research Centre, Bombay (India))
A simple method of preparing water-soluble C[sub 60] at room temperature has been developed by complexing it with [gamma]-cyclodextrin. By this method concentrations as high as 1.0 x 10[sup [minus]4] mol dm[sup [minus]3] of C[sub 60] can be solubilized in water. The complex is characterized by thermogravimetric, optical absorption, and powder X-ray diffraction analysis. The optical absorption spectrum, extinction coefficient, and equilibrium constant for a 2:1 (CD:C[sub 60]) complex of C[sub 60] with [gamma]-cyclodextrin are reported. With the help of picosecond and nanosecond laser photolysis techniques, the triplet characteristics of the CD-C[sub 60] complex are determined. 21 refs., 5 figs., 1 tab.
Inclusion complex formation of ternary system: Fluoroscein-p-sulfonato calix[4]arene-Cu(2+) by cooperative binding.
Gawhale, Sharadchandra; Jadhav, Ankita; Rathod, Nilesh; Malkhede, Dipalee; Chaudhari, Gajanan
The aqueous solution of fluorescein-para sulfonato calix[4]arene-metal ion complex has been studied based on absorption, fluorescence, (1)H NMR and FTIR spectroscopic results. It was found that the fluorescence intensity quenched regularly upon addition of pSCX4 and metal ion. The quenching constants and binding constants were determined for pSCX4-FL and pSCX4-FL-Cu(2+) systems. 1:1 stoichiometry is obtained for pSCX4-Cu(2+) system by continuous variation method. The NMR and IR results indicates the interaction among FL, pSCX4 and Cu(2+). The combined results demonstrate the cooperative binding to design the complex for ternary system. The life time for binary and ternary system has been studied. PMID:25919326
EPR demonstration of iron-nitrosyl complex formation by cytotoxic activated macrophages
Lancaster, J.R. Jr.; Hibbs, J.B. Jr. (Utah State Univ., Logan (USA))
Activated macrophage cytotoxicity is characterized by loss of intracellular iron and inhibition of certain enzymes that have catalytically active nonheme-iron coordinated to sulfur. This phenomenon involves the oxidation of one of the terminal guanidino nitrogen atoms of L-arginine, which results in the production of citrulline and inorganic nitrogen oxides (NO2-, NO3-, and NO). We report here the results of an electron paramagnetic resonance spectroscopic study performed on cytotoxic activated macrophage (CAM) effector cells, which develop the same pattern of metabolic inhibition as their targets. Examination of activated macrophages from mice infected with Mycobacterium bovis (strain bacillus Calmette-Guerin) that were cultured in medium with lipopolysaccharide and L-arginine showed the presence of an axial signal at g = 2.039, which is similar to previously described iron-nitrosyl complexes formed from the destruction of iron-sulfur centers by nitric oxide (NO). Inhibition of the L-arginine-dependent pathway by addition of NG-monomethyl-L-arginine (methyl group on a terminal guanidino nitrogen) inhibits the production of nitrite, nitrate, citrulline, and the g = 2.039 signal. Comparison of the hyperfine structure of the signal from cells treated with L-arginine with terminal guanidino nitrogen atoms of natural abundance N14 atoms or labeled with N15 atoms showed that the nitrosyl group in this paramagnetic species arises from one of these two atoms. These results show that loss of iron-containing enzyme function in CAM is a result of the formation of iron-nitrosyl complexes induced by the synthesis of nitric oxide from the oxidation of a terminal guanidino nitrogen atom of L-arginine.
The formation of host-guest complexes between surfactants and cyclodextrins.
Valente, Artur J M; Söderman, Olle
Cyclodextrins are able to act as host molecules in supramolecular chemistry with applications ranging from pharmaceutics to detergency. Among guest molecules surfactants play an important role with both fundamental and practical applications. The formation of cyclodextrin/surfactant host-guest compounds leads to an increase in the critical micelle concentration and in the solubility of surfactants. The possibility of changing the balance between several intermolecular forces, and thus allowing the study of, e.g., dehydration and steric hindrance effects upon association, makes surfactants ideal guest molecules for fundamental studies. Therefore, these systems allow for obtaining a deep insight into the host-guest association mechanism. In this paper, we review the influence on the thermodynamic properties of CD-surfactant association by highlighting the effect of different surfactant architectures (single tail, double-tailed, gemini and bolaform), with special emphasis on cationic surfactants. This is complemented with an assessment of the most common analytical techniques used to follow the association process. The applied methods for computation of the association stoichiometry and stability constants are also reviewed and discussed; this is an important point since there are significant discrepancies and scattered data for similar systems in the literature. In general, the surfactant-cyclodextrin association is treated without reference to the kinetics of the process. However, there are several examples where the kinetics of the process can be investigated, in particular those where volumes of the CD cavity and surfactant (either the tail or in special cases the head group) are similar in magnitude. This will also be critically reviewed. PMID:24011696
Complexity, segregation, and pattern formation in rotating-drum flows Max Planck Institute for Dynamics and Self-Organization,
Thomas, Peter J.
Complexity, segregation, and pattern formation in rotating-drum flows G. Seiden* Max Planck 17 November 2011) Rotating-drum flows span a variety of research areas, ranging from physics. The existing literature related to rotating-drum flows is reviewed, highlighting similarities and differences
Identifying Complex Fluvial Sandstone Reservoirs Using Core, Well Log, and 3D Seismic Data: Cretaceous Cedar Mountain and Dakota Formations,
Seamons, Kent E.
i Identifying Complex Fluvial Sandstone Reservoirs Using Core, Well Log, and 3D Seismic Data Log, and 3D Seismic Data: Cretaceous Cedar Mountain and Dakota Formations, Southern Uinta Basin, Utah core, well-log, and 3D seismic data. The detailed stratigraphy and sedimentology of the interval were
Impact of cosolvents on formation and properties of biopolymer nanoparticles formed by heat treatment of ?-lactoglobulin–Pectin complexes
Wanlop Chanasattru; Owen Griffith Jones; Eric A. Decker; David Julian McClements
The purpose of this study was to determine the influence of neutral cosolvents on the formation and properties of biopolymer nanoparticles formed by thermal treatment of protein–polysaccharide electrostatic complexes. Biopolymer particles were formed by heating (85 °C, 20 min) an aqueous solution containing a globular protein (?-lactoglobulin) and an anionic polysaccharide (beet pectin) above the thermal denaturation temperature (Tm) of the protein
A Developmental Framework for Complex Plasmodesmata Formation Revealed by Large-Scale Imaging of the Arabidopsis Leaf Epidermis[W
Fitzgibbon, Jessica; Beck, Martina; Zhou, Ji; Faulkner, Christine; Robatzek, Silke; Oparka, Karl
Plasmodesmata (PD) form tubular connections that function as intercellular communication channels. They are essential for transporting nutrients and for coordinating development. During cytokinesis, simple PDs are inserted into the developing cell plate, while during wall extension, more complex (branched) forms of PD are laid down. We show that complex PDs are derived from existing simple PDs in a pattern that is accelerated when leaves undergo the sink–source transition. Complex PDs are inserted initially at the three-way junctions between epidermal cells but develop most rapidly in the anisocytic complexes around stomata. For a quantitative analysis of complex PD formation, we established a high-throughput imaging platform and constructed PDQUANT, a custom algorithm that detected cell boundaries and PD numbers in different wall faces. For anticlinal walls, the number of complex PDs increased with increasing cell size, while for periclinal walls, the number of PDs decreased. Complex PD insertion was accelerated by up to threefold in response to salicylic acid treatment and challenges with mannitol. In a single 30-min run, we could derive data for up to 11k PDs from 3k epidermal cells. This facile approach opens the door to a large-scale analysis of the endogenous and exogenous factors that influence PD formation. PMID:23371949
Monitoring the formation of carbide crystal phases during the thermal decomposition of 3d transition metal dicarboxylate complexes.
Huba, Zachary J; Carpenter, Everett E
Single molecule precursors can help to simplify the synthesis of complex alloys by minimizing the amount of necessary starting reagents. However, single molecule precursors are time consuming to prepare with very few being commercially available. In this study, a simple precipitation method is used to prepare Fe, Co, and Ni fumarate and succinate complexes. These complexes were then thermally decomposed in an inert atmosphere to test their efficiency as single molecule precursors for the formation of metal carbide phases. Elevated temperature X-ray diffraction was used to identify the crystal phases produced upon decomposition of the metal dicarboxylate complexes. Thermogravimetric analysis coupled with an infrared detector was used to identify the developed gaseous decomposition products. All complexes tested showed a reduction from the starting M(2+) oxidation state to the M(0) oxidation state, upon decomposition. Also, each complex tested showed CO2 and H2O as gaseous decomposition products. Nickel succinate, iron succinate, and iron fumarate complexes were found to form carbide phases upon decomposition. This proves that transition metal dicarboxylate salts can be employed as efficient single molecule precursors for the formation of metal carbide crystal phases. PMID:24905401
Substitution effects on the formation of T-shaped palladium carbene and thioketone complexes from Li/Cl carbenoids.
Molitor, Sebastian; Feichtner, Kai-Stephan; Kupper, Claudia; Gessner, Viktoria H
The preparation of palladium thioketone and T-shaped carbene complexes by treatment of thiophosphoryl substituted Li/Cl carbenoids with a Pd(0) precursor is reported. Depending on the steric demand, the anion-stabilizing ability of the silyl moiety (by negative hyperconjugation effects) and the remaining negative charge at the carbenic carbon atom, isolation of a three-coordinate, T-shaped palladium carbene complex is possible. In contrast, insufficient charge stabilization results in the transfer of the sulfur of the thiophosphoryl moiety and thus in the formation of a thioketone complex. While the thioketones are stable compounds the carbene complexes are revealed to be highly reactive and decompose under elimination of Pd metal. Computational studies revealed that both complexes are formed by a substitution mechanism. While the ketone turned out to be the thermodynamically favored product, the carbene is kinetically favored and thus preferentially formed at low reaction temperatures. PMID:24664573
Formation of the asymmetric pineal complex in zebrafish requires two independently acting transcription factors.
Snelson, Corey D; Burkart, Jarred T; Gamse, Joshua T
The pineal complex of zebrafish consists of a pineal organ and a left-sided parapineal organ. Mutation of the floating head (flh) gene, which encodes a homeodomain protein, causes premature termination of pineal cell division without affecting specification or asymmetric placement of the parapineal. The from beyond (fby) mutation, a premature stop codon in the T-domain-containing protein Tbx2b, disrupts formation of the parapineal while leaving the pineal largely intact. However, flh is reported as being required for tbx2b transcription. To resolve the paradox that flhand tbx2b mutants have opposite phenotypes but have been placed in the same genetic pathway, we have examined transcriptional cross-regulation in single flh or fby mutants and genetic epistasis in double mutants. Careful analysis shows that flh is not required for tbx2b transcription and double mutants exhibit an additive phenotype. We conclude that Flh and Tbx2b regulate separate programs of pineal and parapineal development. PMID:18629869
Floatation-spectrophotometric Determination of Thorium, Using Complex Formation with Eriochrome Cyanine R
Shiri, Sabah; Delpisheh, Ali; Haeri, Ali; Poornajaf, Abdolhossein; Khezeli, Tahereh; Badkiu, Nadie
A novel and sensitive floatation-spectrophotometric method is presented for determination of trace amounts of thorium in water samples. The method is based on the ion-associated formation between thorium, Eriochrome cyanine R and Brij-35 at pH = 4 media. The complex was floated in the interface of the aqueous phase and n-hexane by vigorous shaking. After removing the aqueous phase the floated particles were dissolved in methanol and the absorbance was measured at 607 nm. The influence of different important parameters such as Eriochrome cyanine R and surfactants concentration, pH, volume of n-hexane, standing time and interfering ions were evaluated. Under optimized conditions the calibration graph was linear in the range of 6–230 ng mL?1 of thorium with a correlation coefficient of 0.9985. The limit of detections (LOD), based on signal to noise ratio (S/N) of 3 was 1.7 ng mL?1. The relative standard deviations for determination of 150 and 30 ng ml?1 of thorium were 3.26 and 4.41%, respectively (n = 10). The method showed a good linearity, recoveries, as well as some advantages such as sensitivity, simplicity, affordability and a high feasibility. The method was successfully applied to determine thorium in different water and urine samples. PMID:21340019
Formation of BaSO4 fibres with morphological complexity in aqueous polymer solutions.
Qi, L; Cölfen, H; Antonietti, M; Li, M; Hopwood, J D; Ashley, A J; Mann, S
BaSO4 fibres with morphological complexity were formed in aqueous solution with polyacrylate and partially monophosphonated poly(ethyleneoxide)-block-poly(methacrylic acid) additives by a simple precipitation reaction. For polyacrylate, formation of the fibrous deposits was strongly dependent on the level of supersaturation (S) and Ba2+:polymer molar ratio (R). At S = 60 to 80, and R = 3 to 14, highly anisotropic crystalline fibres consisting of bundles of BaSO4 nanofilaments were formed after several weeks, although the yield was low. The nanofilaments were also organized into cone-shaped aggregates at S = 80, and at lower R values these formed higher-order structures that consisted of multiple cone-on-cone assemblies with remarkable self-similarity. Increasing the supersaturation produced ovoid or cross-shaped dendritic particles for the range of molar ratios studied. In contrast, BaSO4 crystallisation in the presence of a partially phosphonated block copolymer gave a high yield of BaSO4 fibres up to 100 microm in length, and consisting of co-aligned bundles of 30 nm-diameter defect-free single-crystal nanofilaments with a uniform growth tip. A model for the defect-free growth of BaSO4 nanofilaments in aqueous polymer solutions based on amorphous precursor particles, vectorially directing forces and van der Waals attraction is proposed. PMID:11560323
Endocytic Rab proteins are required for hepatitis C virus replication complex formation
Manna, David; Aligo, Jason; Xu, Chenjia; Park, Wei Sun; Koc, Hasan; Do Heo, Won; Konan, Kouacou V.
During infection, hepatitis C virus (HCV) NS4B protein remodels host membranes to form HCV replication complexes (RC) which appear as foci under fluorescence microscopy (FM). To understand the role of Rab proteins in forming NS4B foci, cells expressing the HCV replicon were examined biochemically and via FM. First, we show that an isolated NS4B-bound subcellular fraction is competent for HCV RNA synthesis. Further, this fraction is differentially enriched in Rab1, 2, 5, 6 & 7. However, when examined via FM, NS4B foci appear to be selectively associated with Rab5 & Rab7 proteins. Additionally, dominant negative (DN) Rab6 expression impairs Rab5 recruitment into NS4B foci. Further, silencing of Rab5 or Rab7 resulted in a significant decrease in HCV genome replication. Finally, expression of DN Rab5 or Rab7 led to a reticular NS4B subcellular distribution, suggesting that endocytic proteins Rab5 and Rab7, but not Rab11, may facilitate NS4B foci formation. PMID:20005553
Decamethylytterbocene Complexes of Bipyridines and Diazabutadienes: Multiconfigurational Ground States and Open-Shell Singlet Formation
Booth, Corwin H.; Walter, Marc D.; Kazhdan, Daniel; Hu, Yung-Jin; Lukens, Wayne W.; Bauer, Eric D.; Maron, Laurent; Eisenstein, Odile; Andersen, Richard A.
Partial ytterbium f-orbital occupancy (i.e., intermediate valence) and open-shell singlet formation are established for a variety of bipyridine and diazabutadiene adducts with decamethylytterbocene, (C5Me5)2Yb, abbreviated as Cp*2Yb. Data used to support this claim include ytterbium valence measurements using Yb LIII-edge X-ray absorption near-edge structure spectroscopy, magnetic susceptibility, and complete active space self-consistent field (CASSCF) multiconfigurational calculations, as well as structural measurements compared to density functional theory calculations. The CASSCF calculations indicate that the intermediate valence is the result of a multiconfigurational ground-state wave function that has both an open-shell singlet f13(?*)1, where pi* is the lowest unoccupied molecular orbital of the bipyridine or dpiazabutadiene ligands, and a closed-shell singlet f14 component. A number of other competing theories for the unusual magnetism in these materials are ruled out by the lack of temperature dependence of the measured intermediate valence. These results have implications for understanding chemical bonding not only in organolanthanide complexes but also for f-element chemistry in general, as well as understanding magnetic interactions in nanoparticles and devices.
Decamethylytterbocene complexes of bipyridines and diazabutadines: multiconfigurational ground states and open-shell singlet formation
Bauer, Eric D [Los Alamos National Laboratory; Booth, C H [LBNL; Walter, M D [LBNL; Kazhdan, D [LBNL; Hu, Y - J [LBNL; Lukens, Wayne [LBNL; Maron, Laurent [INSA TOULOUSE; Eisentein, Odile [UNIV MONTPELLIER 2; Anderson, Richard [LBNL
Partial ytterbium f-orbital occupancy (i.e. intermediate valence) and open-shell singlet Draft 12/formation are established for a variety of bipyridine and diazabutadiene adducts to decamethylytterbocene, (C{sub 5}Me{sub 5}){sub 2}Yb or Cp*{sub 2}Yb. Data used to support this claim includes ytterbium valence measurements using Yb Lm-edge x-ray absorption near-edge structure (XANES) spectroscopy, magnetic susceptibility and Complete Active Space Self-Consistent Field (CASSCF) multi configurational calculations, as well as structural measurements compared to density-functional theory (DFT) calculations. The CASSCF calculations indicate that the intermediate valence is the result of a multiconfigurational ground state wave function that has both an open-shell singlet f{sup 13} and a closed-shell singlet f{sup 14} component. A number of other competing theories for the unusual magnetism in these materials are ruled out by the presence of intermediate valence and its lack of any significant temperature dependence. These results have implications for understanding chemical bonding not only in organolanthanide complexes, but also for organometallic chemistry in general, as well as understanding magnetic interactions in nanopartic1es and devices.
Formation and Identification of Unresolved Complex Mixtures in Lacustrine Biodegraded Oil from Nanxiang Basin, China
Guo, Pengfei; He, Sheng; Zhu, Shukui; Chai, Derong; Yin, Shiyan; Dai, Wei; Zhang, Wanfeng
A comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GC × GC/TOFMS) method has been developed for the formation and identification of unresolved complex mixtures (UCMs) in lacustrine biodegraded oils that with the same source rock, similar maturity, and increasing degradation rank from Nanxiang Basin, China. Normal alkanes, light hydrocarbons, isoprenoids, steranes, and terpanes are degraded gradually from oil B330 to oil G574. The compounds in biodegraded oil (oil G574) have fewer types, the polarity difference of compounds in different types is minor, and the relative content of individual compounds is similar. All the features make the compounds in biodegraded oil coelute in GC analysis and form the raised "baseline hump" named UCMs. By injecting standard materials and analyzing mass spectrums of target compounds, it is shown that cyclic alkanes with one to five rings are the major components of UCMs. Furthermore, UCMs were divided into six classes. Classes I and II, composed of alkyl-cyclohexanes, alkyl-naphthanes, and their isomers, are originated from the enrichment of hydrocarbons resistant to degradation in normal oils. Classes III ~ VI, composed of sesquiterpenoids, tricyclic terpanes, low molecular steranes, diasteranes, norhopanes, and their isomers, are probably from some newly formed compounds during the microbial transformation of oil. PMID:25177711
Hemolymph Melanization in the Silkmoth Bombyx mori Involves Formation of a High Molecular Mass Complex That Metabolizes Tyrosine*
Clark, Kevin D.; Strand, Michael R.
The phenoloxidase (PO) cascade regulates the melanization of blood (hemolymph) in insects and other arthropods. Most studies indicate that microbial elicitors activate the PO cascade, which results in processing of the zymogen PPO to PO. PO is then thought to oxidize tyrosine and o-diphenols to quinones, which leads to melanin. However, different lines of investigation raise questions as to whether these views are fully correct. Here we report that hemolymph from the silkmoth, Bombyx mori, rapidly melanizes after collection from a wound site. Prior studies indicated that in vitro activated PPO hydroxylates Tyr inefficiently. Measurement of in vivo substrate titers, however, suggested that Tyr was the only PO substrate initially present in B. mori plasma and that it is rapidly metabolized by PO. Fractionation of plasma by gel filtration chromatography followed by bioassays indicated that melanization activity was primarily associated with a high mass complex (?670 kDa) that contained PO. The prophenoloxidase-activating protease inhibitor Egf1.0 blocked formation of this complex and Tyr metabolism, but the addition of phenylthiourea to plasma before fractionation enhanced complex formation and Tyr metabolism. Mass spectrometry analysis indicated that the complex contained PO plus other proteins. Taken together, our results indicate that wounding alone activates the PO cascade in B. mori. They also suggest that complex formation is required for efficient use of Tyr as a substrate. PMID:23553628
He-ThO(1?+) interactions at low temperatures: elastic and inelastic collisions, transport properties, and complex formation in cold 4He gas.
Tscherbul, T V; Sayfutyarova, E R; Buchachenko, A A; Dalgarno, A
We present an ab initio study of cold (4)He + ThO((1)?(+)) collisions based on an accurate potential energy surface (PES) evaluated by the coupled cluster method with single, double, and noniterative triple excitations using an extended basis set augmented by bond functions. Variational calculations of rovibrational energy levels show that the (4)He-ThO van der Waals complex has a binding energy of 10.9 cm(-1) in its ground J = 0 rotational state. The calculated energy levels are used to obtain the temperature dependence of the chemical equilibrium constant for the formation of the He-ThO complex. We find that complex formation is thermodynamically favored at temperatures below 1 K and predict the maximum abundance of free ground-state ThO(v = 0, j = 0) molecules between 2 and 3 K. The calculated cross sections for momentum transfer in elastic He + ThO collisions display a rich resonance structure below 5 cm(-1) and decline monotonically above this collision energy. The cross sections for rotational relaxation accompanied by momentum transfer decline abruptly to zero at low collision energies (<0.1 cm(-1)). We find that Stark relaxation in He + ThO collisions can be enhanced by applying an external dc electric field of less than 100 kV?cm. Finally, we present calculations of thermally averaged diffusion cross sections for ThO in He gas, and find these to be insensitive to small variations of the PES at temperatures above 1 K. PMID:21495749
Are Fundamental Constants Really Constant?
ERIC Educational Resources Information Center
Swetman, T. P.
Dirac's classical conclusions, that the values of e2, M and m are constants and the quantity of G decreases with time. Evoked considerable interest among researchers and traces historical development by which further experimental evidence points out that both e and G are constant values. (PS)
Quenching rate constants for metastable argon, krypton, and xenon atoms by fluorine containing molecules and branching ratios for metastable XeF and KrF formation
J. E. Velazco; J. H. Kolts; D. W. Setser
Total quenching rate constants and branching ratios for reactions of fluorine-containing molecules with metastable Xe and Kr are reported along with rate constants for metastable Ar reactions with fluorine- and other halogen-containing molecules. The rate constants were determined by the flowing-afterglow technique, and the branching ratios were measured by comparing total integrated excimer emission intensities from a given reaction with
Structure Formation of Ultrathin PEO Films at Solid Interfaces—Complex Pattern Formation by Dewetting and Crystallization
Braun, Hans-Georg; Meyer, Evelyn
The direct contact of ultrathin polymer films with a solid substrate may result in thin film rupture caused by dewetting. With crystallisable polymers such as polyethyleneoxide (PEO), molecular self-assembly into partial ordered lamella structures is studied as an additional source of pattern formation. Morphological features in ultrathin PEO films (thickness < 10 nm) result from an interplay between dewetting patterns and diffusion limited growth pattern of ordered lamella growing within the dewetting areas. Besides structure formation of hydrophilic PEO molecules, n-alkylterminated (hydrophobic) PEO oligomers are investigated with respect to self-organization in ultrathin films. Morphological features characteristic for pure PEO are not changed by the presence of the n-alkylgroups. PMID:23385233
NMR diffusion measurements in complex mixtures using constant-time-HSQC-IDOSY and computer-optimized spectral aliasing for high resolution in the carbon dimension.
Vitorge, Bruno; Jeannerat, Damien; Jeanneat, Damien
A new 3D pulse sequence for NMR diffusion measurements in complex mixtures is presented. It is based on the constant-time (CT) HSQC experiment and combines diffusion delay with the carbon evolution time. This combination has great potential to obtain high resolution in the carbon dimension. When using classical sampling of the carbon dimension, maximal resolution would require a large number of time increments, leading to unrealistically long acquisition times. The application of computer-optimized spectral aliasing allows one to reduce the number of time increments and the total acquisition time by 1-2 orders of magnitude by taking advantage of the information content of 1D carbon spectra, HSQC experiments, or both. With the new CT-HSQC-IDOSY experiment, the diffusion rates of the six anomers present in a 0.1 M D2O solution of glucose, maltose, and maltotriose could be obtained at natural abundance in 8 h with standard deviations below 5%. PMID:16878902
Premelting base pair opening probability and drug binding constant of a daunomycin-poly d(GCAT).poly d(ATGC) complex.
Chen, Y Z; Prohofsky, E W
We calculate room temperature thermal fluctuational base pair opening probability of a daunomycin-poly d(GCAT).poly d(ATGC) complex. This system is constructed at an atomic level of detail based on x-ray analysis of a crystal structure. The base pair opening probabilities are calculated from a modified self-consistent phonon approach of anharmonic lattice dynamics theory. We find that daunomycin binding substantially enhances the thermal stability of one of the base pairs adjacent the drug because of strong hydrogen bonding between the drug and the base. The possible effect of this enhanced stability on the drug inhibition of DNA transcription and replication is discussed. We also calculate the probability of drug dissociation from the helix based on the selfconsistent calculation of the probability of the disruption of drug-base H-bonds and the unstacking probability of the drug. The calculations can be used to determine the equilibrium drug binding constant which is found to be in good agreement with observations on similar daunomycin-DNA systems. PMID:8011914
Human platelet-initiated formation and uptake of the C5-9 complex of human complement.
Zimmerman, T S; Kolb, W P
We have studied the interaction of radiolabeled complement components with normal human platelets, platelets from a patient with paroxysmal nocturnal hemoglobinuria, and rabbit platelets in the absence of known complement activators or in the presence of cobra venom factor (CVF). When unwashed platelets in platelet-rich plasma, or washed platelets suspended in serum or autologous plasma, were incubated for 30 min, C3 and terminal components (C5, C8, and C9) were found to bind to them. The terminal components were shown to be bound as the C5-9 complex, rather than as individual proteins, by eluting them from the platelet membrane and examining their behavior on ultracentrifugation. They cosedimented at a rate characteristic of the stable C5-9 complex (22S). As many as 370-1,380 C5-9 complexes/platelet were calculated to have been bound during the incubation period. The complex so formed did not differ by ultracentrifugational criteria from that binding to rabbit platelets after CVF activation of complement. Though C3 was not included in the complex, it did not appear to be bound by nonspecific absorption. It could not be removed by washing but rather was eluted by the freeze-thaw technique used to elute the C5-9 complex. Incubation of radiolabeled components in platelet-free plasma did not result in C5-9 complex formation, indicating an initiating role for platelets in this reaction. In contrast to platelets, erythrocytes incubated in analogous plasma did not induce detectable C5-9 formation. Neither EDTA, phenylmethylsulfonylfluoride, nor epsilon-amino-N-caproic acid prevented platelet-initiated formation of C5-9, suggesting that the reaction may involve mechanisms of complement activation not previously described. Images PMID:812888
Inclusion complex formation of ionic liquids with 4-sulfonatocalixarenes studied by competitive binding of berberine alkaloid fluorescent probe
NASA Astrophysics Data System (ADS)
Miskolczy, Zsombor; Biczók, László
A clinically important natural isoquinoline alkaloid, berberine, was used as a fluorescent probe to study the encapsulation of 1-alkyl-3-methylimidazolium (C nMIm +) type ionic liquids in 4-sulfonato-substituted calix[4]arene (SCX4) and calix[6]arene (SCX6) at pH 2. Addition of ionic liquids to the aqueous solution of berberine-SCXn inclusion complexes brought about considerable fluorescence intensity diminution due to the extrusion of berberine from the macrocycle into the aqueous phase by the competitive inclusion of C nMIm + cation. The lengthening of the aliphatic side chain of the imidazolium moiety diminished the equilibrium constant of complexation with SCX4, but enhanced the stability of SCX6 complexes. Larger binding strength was found for SCX4.
Linking megathrust earthquakes to faulting and mineral vein formation in a fossil accretionary complex
NASA Astrophysics Data System (ADS)
Dielforder, Armin; Herwegh, Marco; Berger, Alfons
Geodetic and seismological data recorded at active subduction zones suggest that megathrust earthquakes induce transient stress changes in the upper plate, which shift the wedge into an unstable state and trigger >Mw 6 aftershocks. These stress changes have, however, never been linked to geological structures that are preserved within fossil accretionary wedges, although plate interface of palaeo-subduction zones has been studied. The conditions under which accretionary wedges fail have therefore remained controversial. Here we show that faulting and associated vein formation in the palaeo-accretionary complex of the European Alps record stress changes generated by the subduction earthquake cycle. Our data integrate wedge deformation over millions of years but still demonstrate the dominance of specific fracture modes at different depths within the wedge. We trace the subduction of sediments by means of the 87Sr/86Sr isotope-systematics of mineral veins, which became more radiogenic at deeper levels. By combining our field observations and geochemical data with a dynamic Mohr-Coulomb wedge analysis, we show that early veins were formed in shallow levels by bedding-parallel shear during coseismic compression of the outer wedge. In contrast, later veins originated at deeper levels during normal faulting and extensional fracturing recording coseismic extension of the inner wedge. Our study shows how mineral veins can be used to reveal the dynamics of outer and inner wedges, which response in opposite ways to megathrust earthquakes by compressional and extensional faulting, respectively. We emphasise, that coseismic fracturing implicates an increase in permeability within the hanging wall of megathrusts. Understanding how fractures are generated throughout the subduction earthquake cycle is therefore essential to better contstrain the nature of postseismic fluid flow and to assess the seismic hazard of hydraulically driven aftershocks.
Protection of Metal Artifacts with the Formation of Metal–Oxalates Complexes by Beauveria bassiana
Joseph, Edith; Cario, Sylvie; Simon, Anaële; Wörle, Marie; Mazzeo, Rocco; Junier, Pilar; Job, Daniel
Several fungi present high tolerance to toxic metals and some are able to transform metals into metal–oxalate complexes. In this study, the ability of Beauveria bassiana to produce copper oxalates was evaluated. Growth performance was tested on various copper-containing media. B. bassiana proved highly resistant to copper, tolerating concentrations of up to 20?g?L?1, and precipitating copper oxalates on all media tested. Chromatographic analyses showed that this species produced oxalic acid as sole metal chelator. The production of metal–oxalates can be used in the restoration and conservation of archeological and modern metal artifacts. The production of copper oxalates was confirmed directly using metallic pieces (both archeological and modern). The conversion of corrosion products into copper oxalates was demonstrated as well. In order to assess whether the capability of B. bassiana to produce metal–oxalates could be applied to other metals, iron and silver were tested as well. Iron appears to be directly sequestered in the wall of the fungal hyphae forming oxalates. However, the formation of a homogeneous layer on the object is not yet optimal. On silver, a co-precipitation of copper and silver oxalates occurred. As this greenish patina would not be acceptable on silver objects, silver reduction was explored as a tarnishing remediation. First experiments showed the transformation of silver nitrate into nanoparticles of elemental silver by an unknown extracellular mechanism. The production of copper oxalates is immediately applicable for the conservation of copper-based artifacts. For iron and silver this is not yet the case. However, the vast ability of B. bassiana to transform toxic metals using different immobilization mechanisms seems to offer considerable possibilities for industrial applications, such as the bioremediation of contaminated soils or the green synthesis of chemicals. PMID:22291684
Processing of a cellular polypeptide by 3CD proteinase is required for poliovirus ribonucleoprotein complex formation.
Roehl, H H; Parsley, T B; Ho, T V; Semler, B L
Poliovirus interactions with host cells were investigated by studying the formation of ribonucleoprotein complexes at the 3' end of poliovirus negative-strand RNA which are presumed to be involved in viral RNA synthesis. It was previously shown that two host cell proteins with molecular masses of 36 and 38 kDa bind to the 3' end of viral negative-strand RNA at approximately 3 to 4 h after infection. We tested the hypothesis that preexisting cellular proteins are modified during the course of infection and are subsequently recruited to play a role in viral replication. It was demonstrated that the 38-kDa protein, either directly or indirectly, is the product of processing by poliovirus 3CD/3C proteinase. Only the modified 38-kDa protein, not its precursor protein, has a high affinity for binding to the 3' end of viral negative-strand RNA. This modification depends on proteolytically active proteinase, and a direct correlation between the levels of 3CD proteinase and the 38-kDa protein was demonstrated in infected tissue culture cells. The nucleotide (nt) 5-10 region (positive-strand numbers) of poliovirus negative-strand RNA is important for binding of the 38-kDa protein. Deletion of the nt 5-10 region in full-length, positive-strand RNA renders the RNA noninfectious in transfection experiments. These results suggest that poliovirus 3CD/3C proteinase processes a cellular protein which then plays an essential role during the viral life cycle. PMID:8985386
Petrological and geochemical constraints on granitoid formation: The Waldoboro Pluton Complex, Maine
Barton, M. (Ohio State Univ., Columbus, OH (United States). Dept. of Geological Science); Sidle, W.S. (Oak Ridge National Lab., TN (United States))
The Waldoboro Pluton Complex (WPC) comprises seven units ranging from qtz-diorite to aplite. The country rocks are biotite-rich metagraywackes with minor shales mostly belonging to the Proterozoic Z-Ordovician Bucksport Formation. Field evidence strongly suggests that the WPC formed in-situ: contacts with the country rock are cryptic, transitional and concordant; restitic minerals in the granitoids are identical to those in the country rocks; prolific metasedimentary enclaves in the WPC are locally derived. Major and trace element data for country rock and the most voluminous units of the WPC define consistent linear trends suggesting limited melt segregation and retention of a high proportion of restite. Mixing models and partial melting models require 54--76% melting for generation of the gneissic granites and two-mica granites. Garnet-biotite geothermometry and garnet-Al[sub 2]SiO[sub 5]-SiO[sub 2]-plagioclase geobarometry indicate that the WPC formed at T = 740--780 C and P = 0.4--0.7 GPa. Published experimental data show that < 50% melting is likely under these conditions if melting is controlled by dehydration reactions. Bucksport lithologies contain < 20% biotite, suggesting that the maximum amount of melt that could have formed by dehydration melting is < 20%, even if all biotite was consumed during melting. It seems probable that a free fluid phase was required to generate the WPC. Migmatization is apparent in all lithologies (including amphibolites) in the vicinity of the WPC, consistent with fluid-present melting. Fluid may have ingressed along the St. George thrust, but the source of the fluid is unknown.
The tiger formation: Paleogene fluvial sediments deposited adjacent to a deforming Cordilleran metamorphic core complex, northeastern Washington
NASA Astrophysics Data System (ADS)
Gager, Barry R.
The Eocene to Oligocene(?) Tiger Formation and associated upper-plate rocks of northeastern Washington are juxtaposed along low-angle fault zones with structurally lower, or "lower-plate", rocks of the Spokane dome, a metamorphic core complex. Strata of the Tiger Formation that were derived solely from upper-plate rock are termed intraplate strata and those that include clasts of lower-plate rock are termed extraplate strata. The Cliff Ridge and Ione regions are situated on opposite sides of an arch of typical lower-plate rock. The Tiger Formation here consists of predominantly conglomeratic intraplate strata that were deposited by braided streams on both valley fills and alluvial fans. These strata were derived from a tectonically active source terrane where lower-plate rock now exists. Intraplate strata of the Cusick region consist of conglomeratic, sandstone, and siltstone facies. Alluvial fans and a sandy braided-alluvial plain graded downstream to a floodplain-dominated environment. Intraplate strata exposed in the Cliff Ridge, Ione and Cusick regions record deposition in response to differential uplift of the core complex in the subsurface. Extraplate conglomeratic strata deposited in alluvial-fan and braided alluvial-plain environments conformably and unconformably overlie the intraplate sandstone and siltstone facies of the Cusick region. These extraplate conglomerates were derived from the area now occupied solely by the core complex and record the erosion of intraplate Tiger strata and other upper-plate rocks, exposure of the fault zone at the paleosurface, and erosion of the core complex. The Tiger Formation provides valuable insight to the spatial and temporal distribution of deformation that accompanies the development of a Cordilleran metamorphic core complex.
Three-color single molecule imaging shows WASP detachment from Arp2/3 complex triggers actin filament branch formation
Smith, Benjamin A; Padrick, Shae B; Doolittle, Lynda K; Daugherty-Clarke, Karen; Corrêa, Ivan R; Xu, Ming-Qun; Goode, Bruce L; Rosen, Michael K; Gelles, Jeff
During cell locomotion and endocytosis, membrane-tethered WASP proteins stimulate actin filament nucleation by the Arp2/3 complex. This process generates highly branched arrays of filaments that grow toward the membrane to which they are tethered, a conflict that seemingly would restrict filament growth. Using three-color single-molecule imaging in vitro we revealed how the dynamic associations of Arp2/3 complex with mother filament and WASP are temporally coordinated with initiation of daughter filament growth. We found that WASP proteins dissociated from filament-bound Arp2/3 complex prior to new filament growth. Further, mutations that accelerated release of WASP from filament-bound Arp2/3 complex proportionally accelerated branch formation. These data suggest that while WASP promotes formation of pre-nucleation complexes, filament growth cannot occur until it is triggered by WASP release. This provides a mechanism by which membrane-bound WASP proteins can stimulate network growth without restraining it. DOI: http://dx.doi.org/10.7554/eLife.01008.001 PMID:24015360
Complex formation between a nanoparticle and a weak polyelectrolyte chain: Monte Carlo simulations
Serge Ulrich; Abohachem Laguecir; Serge Stoll
Understanding the complexation processes between nanoparticles and polyelectrolytes is an essential aspect in many branches of nanotechnology, nanoscience, chemistry, and biology to describe processes such as nanoparticle stabilization\\/destabilization and dispersion, water treatment, microencapsulation, complexation with biomolecules for example, and evolution of the interface of many natural and synthetic systems. In view of the complexity of such processes, applications are often
Role of biologically active inorganic anions Cl- and Br- in inclusion complex formation of ?-cyclodextrin with some aromatic carboxylic acids
NASA Astrophysics Data System (ADS)
Terekhova, Irina; Chibunova, Ekaterina; Kumeev, Roman; Alper, Gennady
1H NMR spectroscopy was used to evaluate the effects of biologically active anions Cl- and Br- in inclusion complex formation of ?-cyclodextrin with some aromatic carboxylic acids. It was demonstrated that presence of Br- anions induces the decrease in ?-cyclodextrin binding affinity to carboxylic acids, while Cl- has no a noticeable effect. The observed difference was discussed in terms of selective interactions of ?-cyclodextrin with Br- and Cl-. Only Br- anions are able to penetrate into ?-cyclodextrin cavity and compete with carboxylic acid molecule for the macrocyclic cavity. This competition shifts the ?-cyclodextrin/acid equilibrium in the direction of complex dissociation.
Study of the dynamic complex formation of pentanoic acid with ?-cyclodextrin by using an ultrasonic relaxation method
NASA Astrophysics Data System (ADS)
Bae, Jong-Rim
This study examined the effects of pentanoic acid as a guest molecule on the inclusion complex formation with ?-cyclodextrin ( ?-CD). Ultrasonic absorption measurements were carried out for ?-CD solutions with pentanoic acid over the frequency range from 0.2 to 45 MHz. A single relaxational absorption resulting from the perturbation of chemical equilibrium was observed for the inclusion of pentanoic acid into the ?-CD cavity. The undissociated form of pentanoic acid produced a more stable complex with ?-CD than its dissociated form. An ultrasonic relaxation associated with a protontransfer reaction was also observed when no additive was present in the solution.
Direct Measurements of the Dissociation-Rate Constant for Inhibitor-Enzyme Complexes via the T1? and T2 (CPMG) Methods
NASA Astrophysics Data System (ADS)
Davis, D. G.; Perlman, M. E.; London, R. E.
The unimolecular dissociation rate constant, k-1, for the inhibitor-enzyme complex tubercidin- Escherichia coli purine nucleoside phosphorylase (PNPase) has been determined directly via two related 1H NMR methods for studying exchange-mediated transverse relaxation. One method involves measurements of the decay rate, 1/ T1?, of spin-locked magnetization in the rotating frame as a function of the strength of the spin-locking field, ? SL The second method involves measurements of the Carr-Purcell-Meiboom-Gill (CPMG) spin-echo decay rate, 1/ TCPMG2 as a function of the repetition rate, 1/ tcp, of the refocusing pulses. Expressions describing the dependence of TCPMG2 as a function of 1/ tcp and k-1 have been previously derived with sufficient generality to include the two-site inhibitor-enzyme exchange case. Existing expressions for T1? as a function of kex and ? SL, however, had to be reformulated to take into account differences between Tb2 and Tb1 for the bound form of the inhibitor as well as offset corrections important at low values of ? SL A new expression for exchange-mediated T1? has been derived to take these factors into account and is shown to provide a more accurate description of observed T1? data than previous models. Numerical analysis of relaxation rates, measured independently by either the rotating-frame or the spin-echo method for the H 1' and H 2 protons of tubercidin at different inhibitor:enzyme ratios, yields comparable values for k-1 of 2400 (±350) and 900 (±80) s -1 at 20 and 10°C, respectively. The merits of both methods are compared and suggestions for optimizing the experiments are discussed.
Crossover\\/Noncrossover Differentiation, Synaptonemal Complex Formation, and Regulatory Surveillance at the Leptotene\\/Zygotene Transition of Meiosis
G. Valentin Börner; Nancy Kleckner; Neil Hunter
Yeast mutants lacking meiotic proteins Zip1, Zip2, Zip3, Mer3, and\\/or Msh5 (ZMMs) were analyzed for recombination, synaptonemal complex (SC), and meiotic progression. At 33°C, recombination-initiating double-strand breaks (DSBs) and noncrossover products (NCRs) form normally while formation of single-end invasion strand exchange intermediates (SEIs), double Holliday junctions, crossover products (CRs), and SC are coordinately defective. Thus, during wild-type meiosis, recombinational interactions
Cobalamin reduction by dithionite. Evidence for the formation of a six-coordinate cobalamin(II) complex.
Salnikov, Denis S; Silaghi-Dumitrescu, Radu; Makarov, Sergei V; van Eldik, Rudi; Boss, Gerry R
Evidence for the formation of a unique, six-coordinate cobalamin(II) complex with the anion-radical SO(2)(-) during the reduction of aquacobalamin(III) by sodium dithionite, was obtained from spectrophotometric and EPR measurements. The pK(a) value of the weakly coordinated dimethylbenzimidazole group was found to be 4.8 ± 0.1 at 25 °C. PMID:21879074
The formation of carbon surface oxygen complexes by oxygen and ozone. The effect of transition metal oxides
G. Mul; J. P. A. Neeft; F. Kapteijn; J. A. Moulijn
Various surface oxygen complexes (SOCs) have been identified by DRIFT spectroscopy on the surface of carbon black (Printex-U) after partial non-catalytic conversion in 10% O2 in Ar and ozone. An in situ DRIFT analysis of the oxidation of fullerene C60 showed the formation of similar functionalities and validated the use of C60 as a carbon black model compound for DRIFT
Formation of colloidal silver nanoparticles stabilized by Na +–poly(?-glutamic acid)–silver nitrate complex via chemical reduction process
Da-Guang Yu
Macromolecular and polyanionic Na+–poly(?-glutamic acid) (PGA) silver nitrate complex acted as both a metal ion provider and a particle protector to fabricate nanosized silver colloids under chemical reduction by dextrose. The formation and size of particles have been characterized from transmission electron microscopy (TEM), dynamic light scattering analysis and UV–vis spectrophotometer. The results showed that the average particle size was
Epithelial junction formation requires confinement of Cdc42 activity by a novel SH3BP1 complex
Elbediwy, Ahmed; Zihni, Ceniz; Terry, Stephen J.; Clark, Peter
Epithelial cell–cell adhesion and morphogenesis require dynamic control of actin-driven membrane remodeling. The Rho guanosine triphosphatase (GTPase) Cdc42 regulates sequential molecular processes during cell–cell junction formation; hence, mechanisms must exist that inactivate Cdc42 in a temporally and spatially controlled manner. In this paper, we identify SH3BP1, a GTPase-activating protein for Cdc42 and Rac, as a regulator of junction assembly and epithelial morphogenesis using a functional small interfering ribonucleic acid screen. Depletion of SH3BP1 resulted in loss of spatial control of Cdc42 activity, stalled membrane remodeling, and enhanced growth of filopodia. SH3BP1 formed a complex with JACOP/paracingulin, a junctional adaptor, and CD2AP, a scaffolding protein; both were required for normal Cdc42 signaling and junction formation. The filamentous actin–capping protein CapZ also associated with the SH3BP1 complex and was required for control of actin remodeling. Epithelial junction formation and morphogenesis thus require a dual activity complex, containing SH3BP1 and CapZ, that is recruited to sites of active membrane remodeling to guide Cdc42 signaling and cytoskeletal dynamics. PMID:22891260
Insulin-like Growth Factor (IGF) Signaling Requires ?v?3-IGF1-IGF Type 1 Receptor (IGF1R) Ternary Complex Formation in Anchorage Independence, and the Complex Formation Does Not Require IGF1R and Src Activation
Fujita, Masaaki; Takada, Yoko K.; Takada, Yoshikazu
Integrin ?v?3 plays a role in insulin-like growth factor 1 (IGF1) signaling (integrin-IGF1 receptor (IGF1R) cross-talk) in non-transformed cells in anchorage-dependent conditions. We reported previously that IGF1 directly binds to ?v?3 and induces ?v?3-IGF1-IGF1R ternary complex formation in these conditions. The integrin-binding defective IGF1 mutant (R36E/R37E) is defective in inducing ternary complex formation and IGF signaling, whereas it still binds to IGF1R. We studied if IGF1 can induce signaling in anchorage-independent conditions in transformed Chinese hamster ovary cells that express ?v?3 (?3-CHO) cells. Here we describe that IGF1 signals were more clearly detectable in anchorage-independent conditions (polyHEMA-coated plates) than in anchorage-dependent conditions. This suggests that IGF signaling is masked by signals from cell-matrix interaction in anchorage-dependent conditions. IGF signaling required ?v?3 expression, and R36E/R37E was defective in inducing signals in polyHEMA-coated plates. These results suggest that ?v?3-IGF1 interaction, not ?v?3-extracellular matrix interaction, is essential for IGF signaling. Inhibitors of IGF1R, Src, AKT, and ERK1/2 did not suppress ?v?3-IGF-IGF1R ternary complex formation, suggesting that activation of these kinases are not required for ternary complex formation. Also, mutations of the ?3 cytoplasmic tail (Y747F and Y759F) that block ?3 tyrosine phosphorylation did not affect IGF1R phosphorylation or AKT activation. We propose a model in which IGF1 binding to IGF1R induces recruitment of integrin ?v?3 to the IGF-IGF1R complex and then ?3 and IGF1R are phosphorylated. It is likely that ?v?3 should be together with the IGF1-IGF1R complex for triggering IGF signaling. PMID:23243309
Assessment of oxidative DNA damage formation by organic complex mixtures from airborne particles PM(10).
Gábelová, Alena; Valovicová, Zuzana; Lábaj, Juraj; Bacová, Gabriela; Binková, Blanka; Farmer, Peter B
The free radical generating activity of airborne particulate matter (PM(10)) has been proposed as a primary mechanism in biological activity of ambient air pollution. In an effort to determine the impact of the complex mixtures of extractable organic matter (EOM) from airborne particles on oxidative damage to DNA, the level of 8-oxo-2'-deoxyguanosine (8-oxodG), the most prevalent and stable oxidative lesion, was measured in the human metabolically competent cell line Hep G2. Cultured cells were exposed to equivalent EOM concentrations (5-150microg/ml) and oxidative DNA damage was analyzed using a modified single cell gel electrophoresis (SCGE), which involves the incubation of whole cell DNA with repair specific DNA endonuclease, which cleaves oxidized DNA at the sites of 8-oxodG. EOMs were extracted from PM(10) collected daily (24h intervals) in three European cities: Prague (Czech Republic, two monitoring sites, Libus and Smíchov), Kosice (Slovak Republic) and Sofia (Bulgaria) during 3-month sampling periods in the winter and summer seasons. No substantial time- and dose-dependent increase of oxidative DNA lesions was detected in EOM-treated cells with the exception of the EOM collected at the monitoring site Kosice, summer sampling. In this case, 2h cell exposure to EOM resulted in a slight but significant increase of oxidative DNA damage at three from total of six concentrations. The mean 8-oxodG values at these concentrations ranged from 15.3 to 26.1 per 10(6) nucleotides with a value 3.5 per 10(6) nucleotides in untreated cells. B[a]P, the positive control, induced a variable but insignificant increase of oxidative DNA damage in Hep G2 cell (approximately 1.6-fold increase over control value). Based on these data we believe that EOM samples extracted from airborne particle PM(10) play probably only a marginal role in oxidative stress generation and oxidative lesion formation to DNA. However, adsorbed organic compounds can undergo various interactions (additive or synergistic) with other PM components or physical factors (UV-A radiation) and in this way they might enhance/multiply the adverse health effects of air pollution. PMID:17403525
Complex formation of myrosinase isoenzymes in oilseed rape seeds are dependent on the presence of myrosinase-binding proteins.
Eriksson, Susanna; Andréasson, Erik; Ekbom, Barbara; Granér, Georg; Pontoppidan, Bo; Taipalensuu, Jan; Zhang, Jiaming; Rask, Lars; Meijer, Johan
The enzyme myrosinase (EC 22.214.171.124) degrades the secondary compounds glucosinolates upon wounding and serves as a defense to generalist pests in Capparales. Certain myrosinases are present in complexes together with other proteins such as myrosinase-binding proteins (MBP) in extracts of oilseed rape (Brassica napus) seeds. Immunhistochemical analysis of wild-type seeds showed that MBPs were present in most cells but not in the myrosin cells, indicating that the complex formation observed in extracts is initiated upon tissue disruption. To study the role of MBP in complex formation and defense, oilseed rape antisense plants lacking the seed MBPs were produced. Western blotting and immunohistochemical staining confirmed depletion of MBP in the transgenic seeds. The exclusive expression of myrosinase in idioblasts (myrosin cells) of the seed was not affected by the down-regulation of MBP. Using size-exclusion chromatography, we have shown that myrosinases with subunit molecular masses of 62 to 70 kD were present as free dimers from the antisense seed extract, whereas in the wild type, they formed complexes. In accordance with this, MBPs are necessary for myrosinase complex formation of the 62- to 70-kD myrosinases. The product formed from sinalbin hydrolysis by myrosinase was the same whether MBP was present or not. The performance of a common beetle generalist (Tenebrio molitor) fed with seeds, herbivory by flea beetles (Phyllotreta undulata) on cotyledons, or growth rate of the Brassica fungal pathogens Alternaria brassicae or Lepthosphaeria maculans in the presence of seed extracts were not affected by the down-regulation of MBP, leaving the physiological function of this protein family open. PMID:12177471
Significant enhancement of XeCl(B, C) and XeF(B, C) formation rate constants in reactions of Xe(5p/sup 5/6p) atoms with halogen donors
Ku, J.K.; Setser, D.W.
The quenching rate constants for Xe(6p) atoms by several halogens and halogen-containing molecules have been measured and they are substantially larger than for reactions of Xe(6s) metastable atoms. The effect is largest for molecules with small Xe(6s /sup 3/P/sub 2/) quenching rate constants and the Xe(6p) rate constants for NF/sub 3/ are 5--20 times larger. Moreover, the branching fractions for XeCl(B, C) and XeF(B, C) formation are also larger for Xe(6p) atoms than for Xe(6s /sup 3/P/sub 2/) atoms; the branching fractions for HCl are enhanced by more than an order of magnitude. These findings may have important implications for the operation and modeling of rare gas halide lasers and other gas discharge devices.
Spectrographic method for the investigation of complex formation equilibria for the whole series of rare earth elements and several other elements
T. V. Ternovaya
A spectrographic method has previously been developed for the investigationof complex formation equilibria which is mainly suitable for neodymium complexes and, to a lesser degree, for europium and erbium complexes [i]. The method is based on the energy levels of the above mentioned ions which are not split by the ligand field where a single absorption band corresponds to each
Multicomponent complex formation between vinpocetine, cyclodextrins, tartaric acid and water-soluble polymers monitored by NMR and solubility studies.
Ribeiro, Laura; Carvalho, Rui A; Ferreira, Domingos C; Veiga, Francisco J B
This work deals with multicomponent complex formation of vinpocetine (VP) with beta-cyclodextrin (betaCD), sulfobutyl ether beta-cyclodextrin (SBEbetaCD) and tartaric acid (TA), in the presence or absence of water-soluble polymers, in aqueous solution. Complexation was monitored by phase-solubility and proton nuclear magnetic resonance ((1)H NMR) studies. TA demonstrated a synergistic effect on VP solubility, and in the complexation efficiency of betaCD and SBEbetaCD. Additionally, water-soluble polymers increased even more the complexation efficiency of the CDs that was reflected by a 2.1-2.5 increase on K(C) values for VP-CD-TA-polymer multicomponent complexes. SBEbetaCD was more effective in VP solubilization, as K(C) values of VP-SBEbetaCD-TA multicomponent complexes were notably higher than in corresponding betaCD complexes. The large chemical shift displacements from protons located in the interior of the hydrophobic CD cavities (i.e., H-3 and H-5) coupled with significant chemical shift displacements of VP aromatic protons suggested that this moiety was included in the cavity of both betaCD and SBEbetaCD. Two-dimensional rotating frame nuclear Overhauser effect spectroscopy (ROESY) experiments were carried out in order to obtain information about the multicomponent complex geometry in solution. Inspection of ROESY spectra allowed the establishment of spatial proximities between all aromatic protons of VP and the internal protons of the CDs, confirming that the aromatic moiety of VP is included in CD cavities being deeply inserted in SBEbetaCD multicomponent complexes, since additional interactions with the sulfobutyl side chains were evidenced. PMID:15626573
Reactivity of Cys4 Zinc Finger Domains with Gold(III) Complexes: Insights into the Formation of "Gold Fingers".
Jacques, Aurélie; Lebrun, Colette; Casini, Angela; Kieffer, Isabelle; Proux, Olivier; Latour, Jean-Marc; Sénèque, Olivier
Gold(I) complexes such as auranofin or aurothiomalate have been used as therapeutic agents for the treatment of rheumatoid arthritis for several decades. Several gold(I) and gold(III) complexes have also shown in vitro anticancer properties against human cancer cell lines, including cell lines resistant to cisplatin. Because of the thiophilicity of gold, cysteine-containing proteins appear as likely targets for gold complexes. Among them, zinc finger proteins have attracted attention and, recently, gold(I) and gold(III) complexes have been shown to inhibit poly(adenosine diphosphate ribose)polymerase-1 (PARP-1), which is an essential protein involved in DNA repair and in cancer resistance to chemotherapies. In this Article, we characterize the reactivity of the gold(III) complex [Au(III)(terpy)Cl]Cl2 (Auterpy) with a model of Zn(Cys)4 "zinc ribbon" zinc finger by a combination of absorption spectroscopy, circular dichroism, mass spectrometry, high-performance liquid chromatography analysis, and X-ray absorption spectroscopy. We show that the Zn(Cys)4 site of Zn·LZR is rapidly oxidized by Auterpy to form a disulfide bond. The Zn(2+) ion is released, and the two remaining cysteines coordinate the Au(+) ion that is produced during the redox reaction. Subsequent oxidation of these cysteines can take place in conditions of excess gold(III) complex. In the presence of excess free thiols mimicking the presence of glutathione in cells, mixing of the zinc finger model and gold(III) complex yields a different product: complex (Au(I))2·LZR with two Au(+) ions bound to cysteines is formed. Thus, on the basis of detailed speciation and kinetic measurements, we demonstrate herein that the destruction of Zn(Cys)4 zinc fingers by gold(III) complexes to achieve the formation of "gold fingers" is worth consideration, either directly or mediated by reducing agents. PMID:25839236
On the formation of aliphatic polycarbonates from epoxides with chromium(III) and aluminum(III) metal-salen complexes.
Luinstra, Gerrit A; Haas, Gerhard R; Molnar, Ferenc; Bernhart, Volker; Eberhardt, Robert; Rieger, Bernhard
A DFT-based description is given of the CO2/epoxide copolymerization with a catalyst system consisting of metal (chromium, iron, titanium, aluminum)-salen complexes (salen = N,N'-bis(3,5-di-tert-butylsalicyliden-1,6-diaminophenyl) in combination with either chloride, acetate, or dimethylamino pyridine (DMAP) as external nucleophile. Calculations indicate that initiation proceeds through nucleophilic attack at a metal-coordinated epoxide, and the most likely propagation reaction is a bimolecular process in which a metal-bound nucleophile attacks a metal-bound epoxide. Carbon dioxide insertion occurs at a single metal center and is most likely the rate-determining step at low pressure. The prevalent chain terminating/degradation-the so-called backbiting, a reaction leading to formation of cyclic carbonate from the polymer chain-would involve attack of a carbonate nucleophile rather than an alkoxide at the last unit of the growing chain. The backbiting of a free carbonato chain end is particularly efficient. Anion dissociation from six-coordinate aluminum is appreciably easier than from chromium-salen complexes, indicating the reason why in the former case cyclic carbonate is the sole product. Experimental data were gathered for a series of chromium-, aluminum-, iron-, and zinc-salen complexes, which were used in combination with external nucleophiles like DMAP and mainly (tetraalkyl ammonium) chloride/acetate. Aluminum complexes transform PO (propylene oxide) and CO2 to give exclusively propylene carbonate. This is explained by rapid carbonate anion dissociation from a six-coordinate complex and cyclic formation. CO2 insertion or nucleophilic attack of an external nucleophile at a coordinated epoxide (at higher CO2 pressure) are the rate-determining steps. Catalysis with [Cr(salen)(acetate/chloride)] complexes leads to the formation of both cyclic carbonate and polypropylene carbonate with various quantities of ether linkages. The dependence of the activity and selectivity on the CO2 pressure, added nucleophile, reaction temperature, and catalyst concentration is complex. A mechanistic description for the chromium-salen catalysis is proposed comprising a multistep and multicenter reaction cycle. PO and CO2 were also treated with mixtures of aluminum- and chromium-salen complexes to yield unexpected ratios of polypropylene carbonate and cyclic propylene carbonate. PMID:16106457
Terminal Axonal Arborization and Synaptic Bouton Formation Critically Rely on Abp1 and the Arp2/3 Complex
Koch, Nicole; Kobler, Oliver; Thomas, Ulrich; Qualmann, Britta; Kessels, Michael M.
Neuronal network formation depends on properly timed and localized generation of presynaptic as well as postsynaptic structures. Although of utmost importance for understanding development and plasticity of the nervous system and neurodegenerative diseases, the molecular mechanisms that ensure the fine-control needed for coordinated establishment of pre- and postsynapses are still largely unknown. We show that the F-actin-binding protein Abp1 is prominently expressed in the Drosophila nervous system and reveal that Abp1 is an important regulator in shaping glutamatergic neuromuscular junctions (NMJs) of flies. STED microscopy shows that Abp1 accumulations can be found in close proximity of synaptic vesicles and at the cell cortex in nerve terminals. Abp1 knock-out larvae have locomotion defects and underdeveloped NMJs that are characterized by a reduced number of both type Ib synaptic boutons and branches of motornerve terminals. Abp1 is able to indirectly trigger Arp2/3 complex-mediated actin nucleation and interacts with both WASP and Scar. Consistently, Arp2 and Arp3 loss-of-function also resulted in impairments of bouton formation and arborization at NMJs, i.e. fully phenocopied abp1 knock-out. Interestingly, neuron- and muscle-specific rescue experiments revealed that synaptic bouton formation critically depends on presynaptic Abp1, whereas the NMJ branching defects can be compensated for by restoring Abp1 functions at either side. In line with this presynaptic importance of Abp1, also presynaptic Arp2 and Arp3 are crucial for the formation of type Ib synaptic boutons. Interestingly, presynaptic Abp1 functions in NMJ formation were fully dependent on the Arp2/3 complex, as revealed by suppression of Abp1-induced synaptic bouton formation and branching of axon terminals upon presynaptic Arp2 RNAi. These data reveal that Abp1 and Arp2/3 complex-mediated actin cytoskeletal dynamics drive both synaptic bouton formation and NMJ branching. Our data furthermore shed light on an intense bidirectional functional crosstalk between pre- and postsynapses during the development of synaptic contacts. PMID:24841972
Vasyunin, A. I. [Department of Chemistry, University of Virginia, Charlottesville, VA (United States); Herbst, Eric, E-mail: email@example.com, E-mail: firstname.lastname@example.com [Departments of Chemistry, Astronomy, and Physics, University of Virginia, Charlottesville, VA (United States)
The recent discovery of terrestrial-type organic species such as methyl formate and dimethyl ether in the cold interstellar gas has proved that the formation of organic matter in the Galaxy begins at a much earlier stage of star formation than was previously thought. This discovery represents a challenge for astrochemical modelers. The abundances of these molecules cannot be explained by the previously developed ''warm-up'' scenario, in which organic molecules are formed via diffusive chemistry on surfaces of interstellar grains starting at 30 K, and then released to the gas at higher temperatures during later stages of star formation. In this article, we investigate an alternative scenario in which complex organic species are formed via a sequence of gas-phase reactions between precursor species formed on grain surfaces and then ejected into the gas via efficient reactive desorption, a process in which non-thermal desorption occurs as a result of conversion of the exothermicity of chemical reactions into the ejection of products from the surface. The proposed scenario leads to reasonable if somewhat mixed results at temperatures as low as 10 K and may be considered as a step toward the explanation of abundances of terrestrial-like organic species observed during the earliest stages of star formation.
Metal extraction in water\\/micelle systems: Complex formation, stripping and recovery of Cd(II)
Lisa Ghezzi; Gabriele Monteleone; Brian Robinson; Fernando Secco; Maria Rosaria Tiné; Marcella Venturini
The extraction and recovery of cadmium from aqueous solutions has been performed by a method which avoids the use of organic solvents. The method makes use of surfactant micelles in combination with metal complexing agents. The complexed metals are concentrated on the micelle surface and then treated by a ligand-modified micellar enhanced ultrafiltration process (LM-MEUF). Subsequently the metal ions are
Reaction of aromatic diazonium salts with carrier-free radioiodine and astatine, evidence for complex formation
G. J. Meyer; K. Roessler; G. Stoecklin
Systematic studies of the astatodiazoniation reaction and a comparison with iododediazoniation under comparable conditions are reported. The yields for all astatohalobenzenes and -toluenes were nearly constant and unaffected by the nature of the diazonium compound, its isomeric form, and the number of isomers used at the same time. Only astatofluorobenzenes were obtained at higher yields. An electron-transfer mechanism is proposed
Evidence of complex formation between FADD and c-FLIP death effector domains for the death inducing signaling complex
Hwang, Eun Young; Jeong, Mi Suk; Park, So Young; Jang, Se Bok
Adaptor protein FADD forms the death inducing signaling complex (DISC) by recruiting the initiating caspases-8 and -10 through homotypic death effector domain (DED) interactions. Cellular FLICE-inhibitory protein (c-FLIP) is an inhibitor of death ligand-induced apoptosis downstream of death receptors, and FADD competes with procaspase-8/10 for recruitment for DISC. However, the mechanism of action of FADD and c-FLIP proteins remain poorly understood at the molecular level. In this study, we provide evidence indicating that the death effector domain (DED) of FADD interacts directly with the death effector domain of human c-FLIP. In addition, we use homology modeling to develop a molecular docking model of FADD and c-FLIP proteins. We also find that four structure-based mutants (E80A, L84A, K169A and Y171A) of c-FLIP DEDs disturb the interaction with FADD DED, and that these mutations lower the stability of the c-FLIP DED. [BMB Reports 2014; 47(9): 488-493] PMID:24355299
Shatter Complex Formation in the Twin Craters Lava Flow, Zuni-Bandera Field, New Mexico
NASA Astrophysics Data System (ADS)
von Meerscheidt, H. C.; Bleacher, J. E.; Brand, B. D.; deWet, A.; Samuels, R.; Hamilton, C.; Garry, W. B.; Bandfield, J. L.
Lava channels, tubes and sheets are transport structures that deliver flowing lava to a flow front. The type of structure can vary within a flow field and evolve throughout an eruption. The 18.0 × 1.0 ka Twin Craters lava flow in the Zuni-Bandera lava field provides a unique opportunity to study morphological changes of a lava flow partly attributable to interaction with a topographic obstacle. Facies mapping and airborne image analysis were performed on an area of the Twin Craters flow that includes a network of channels, lava tubes, shatter features, and disrupted pahoehoe flows surrounding a 45 m tall limestone bluff. The bluff is 1000 m long (oriented perpendicular to flow.) The general flow characteristics upstream from the bluff include smooth, lobate pahoehoe flows and a >2.5 km long lava tube (see Samuels et al., this meeting.) Emplacement characteristics change abruptly where the flow encountered the bluff, to include many localized areas of disrupted pahoehoe and several pahoehoe-floored depressions. Each depression is fully or partly surrounded by a raised rim of blocky material up to 4 m higher than the surrounding terrain. The rim is composed of 0.05 - 4 m diameter blocks, some of which form a breccia that is welded by lava, and some of which exhibit original flow textures. The rim-depression features are interpreted as shatter rings based on morphological similarity to those described by Orr (2011.Bul Volcanol.73.335-346) in Hawai';i. Orr suggests that shatter rings develop when fluctuations in the lava supply rate over-pressurize the tube, causing the tube roof to repeatedly uplift and subside. A rim of shattered blocks and breccias remains surrounding the sunken tube roof after the final lava withdraws from the system. One of these depressions in the Twin Craters flow is 240 m wide and includes six mounds of shattered material equal in height to the surrounding undisturbed terrain. Several mounds have depressed centers floored with rubbly pahoehoe. Prominent ';a';a channels travel around the bluff, leaving a 'wake' of uncovered ground on the downstream side. We interpret this shatter area to have been a branching tube network within an active sheet. The limestone bluff acted as an obstacle that caused a backup of lava within the tubes, driving episodes of shattering. The mounds likely represent earlier solidified sections between active, possibly braided, tube branches, which remained as mounds within the shatter area after the adjacent crust subsided. When lava broke out from the pressurized sheet-like lobe, it formed the ';a';a channels. This section of the flow field is interpreted using inferences from shatter ring formation, but is perhaps better termed a shatter sheet or shatter complex. This study has implications for understanding lava flow dynamics at constriction points, as well as the evolution and morphology of shatter rings.
Evaluation of CO2 migration and formation storage capacity in the Dalders formations, Baltic Sea - Preliminary analysis by means of models of increasing complexity
NASA Astrophysics Data System (ADS)
Niemi, Auli; Yang, Zhibing; Tian, Liang; Jung, Byeongju; Fagerlund, Fritjof; Joodaki, Saba; Pasquali, Riccardo; O'Neill, Nick; Vernon, Richard
We present preliminary data analysis and modeling of CO2 injection into selected parts of the Dalders Monocline and Dalders Structure, formations situated under the Baltic Sea and of potential interest for CO2 geological storage. The approach taken is to use models of increasing complexity successively, thereby increasing the confidence and reliability of the predictions. The objective is to get order-of-magnitude estimates of the behavior of the formations during potential industrial scale CO2 injection and subsequent storage periods. The focus has been in regions with best cap-rock characteristics, according to the present knowledge. Data has been compiled from various sources available, such as boreholes within the region. As the first approximation we use analytical solutions, in order to get an initial estimate the CO2 injection rates that can be used without causing unacceptable pressure increases. These preliminary values are then used as basis for more detailed numerical analyses with TOUGH2/TOUGH2-MP (e.g. Zhang et al, 2008) simulator and vertical equilibrium based (e.g. Gasda et al, 2009) models. With the numerical models the variations in material properties, formation thickness etc., as well as more processes such as CO2 dissolution can also be taken into account. The presentation discusses results from these preliminary analyses in terms of estimated storage capacity, CO2 and pressure plume extent caused by various injection scenarios, as well as CO2 travel time after the end of the injection. The effect of factors such as number of injection wells and the positioning of these, the effect of formation properties and the boundary conditions are discussed as are the benefits and disadvantages of the various modeling approaches used. References: Gasda S.E. et al, 2009. Computational Geosciences 13, 469-481. Zhang et al, 2008. Report LBNL-315E, Lawrence Berkeley National Laboratory.
An Easy and Fast Experiment for the Determination of the Equilibrium Constants of an AcidBase Pair, Free and Complexed with a Molecular Receptor
Elena Junquera; Emilio Aicart
This paper shows a pH-potentiometric technique, an experimental procedure, and a mathematical model, easily affordable in the laboratory, for the simultaneous and fast determination of all the equilibrium constants involved in the competitive association of an acid-base pair substrate with a molecular receptor in aqueous solution. From the dependence of these association constants on temperature (van't Hoff analysis), the change
Autophosphorylation is crucial for CDK-activating kinase (Ee;CDKF;1) activity and complex formation in leafy spurge.
Jia, Ying; Anderson, James V; Chao, Wun S
Ee;CDKF;1 protein is a leafy spurge (Euphorbia esula) CDK-activating kinase that is involved in a phosphorylation cascade linked to early stages of cell cycle progression. Yeast two-hybrid screening performed using Ee;CDKF;1 as a bait indicated that one of the interacting proteins was Ee;CDKF;1. Protein-protein interaction of Ee;CDKF;1 was further confirmed by yeast two-hybrid interaction and in vitro pull-down assays. Gel exclusion chromatography and/or native PAGE showed that GST-CDKF;1, MBP-CDKF;1, GST-CDKF;1 devoid of GST, and endogenous Ee;CDKF;1 were capable of forming homo protein complexes which are in dimer, trimer, and/or higher molecular-mass complex in its native state. In addition, Ee;CDKF;1 complexes were autophosphorylated and able to phosphorylate CDK. Moreover, mutant forms of Ee;CDKF;1 (106G/A, 166K/A), which lost autophosphorylation capability completely, were unable to form homo protein complexes in their native state. The result thus demonstrated that autophosphorylation of Ee;CDKF;1 is crucial for both kinase activity and complex formation. PMID:21421369
Uranium(III)-mediated C-C-coupling of terminal alkynes: formation of dinuclear uranium(IV) vinyl complexes.
Kosog, Boris; Kefalidis, Christos E; Heinemann, Frank W; Maron, Laurent; Meyer, Karsten
The previously reported uranium(III) complex [(((Ad)ArO)(3)N)U(III)(DME)] (1; Ad = adamantane, DME = 1,2-dimethoxyethane) reacts with the terminal bis-alkynes 1,7-octadiyne or 1,6-heptadiyne in C-C-coupling reactions to form the uranium(IV) vinyl complexes [{(((Ad)ArO)(3)N)U(IV)}(2)(?-?(2):?(1)-1,2-(CH)(2)-cyclohexane)] (2) and [{(((Ad)ArO)(3)N)U(IV)}(2)(?-?(2):?(2)-1,2-(CH)(2)-cyclopentane)] (3). With the monoalkynes 1-hexyne or 4-(t)butyl-phenylacetylene, the complexes [{(((Ad)ArO)(3)N)U(IV)}(2)(?-?(2)(C1):?(1)(C4)-2-(n)Bu-1,3-octadiene)] (4) and [{(((Ad)ArO)(3)N)U(IV)}(2)(?-?(2)(C4):?(1)(C1)-1,3-di-(p-(t)Bu-phenyl)butadiene))] (5), are formed. These are the first four examples of uranium vinyl complexes that are reported and crystallographically characterized. In addition, detailed DFT calculations are presented to establish a possible mechanism for their formation and explain the differences found for the coordination of the hydrocarbon fragments. In contrast to a previously proposed monometallic pathway for catalytic hydroamination of alkynes and alkyne dimerization involving a uranium vinyl intermediate at uranium(III) complexes, the calculations clearly support a bimetallic mechanism, since its transition states are energetically the most favored. PMID:22738030
Direct observation of R-loop formation by single RNA-guided Cas9 and Cascade effector complexes.
Szczelkun, Mark D; Tikhomirova, Maria S; Sinkunas, Tomas; Gasiunas, Giedrius; Karvelis, Tautvydas; Pschera, Patrizia; Siksnys, Virginijus; Seidel, Ralf
Clustered, regularly interspaced, short palindromic repeats (CRISPR)/CRISPR-associated (Cas) systems protect bacteria and archaea from infection by viruses and plasmids. Central to this defense is a ribonucleoprotein complex that produces RNA-guided cleavage of foreign nucleic acids. In DNA-targeting CRISPR-Cas systems, the RNA component of the complex encodes target recognition by forming a site-specific hybrid (R-loop) with its complement (protospacer) on an invading DNA while displacing the noncomplementary strand. Subsequently, the R-loop structure triggers DNA degradation. Although these reactions have been reconstituted, the exact mechanism of R-loop formation has not been fully resolved. Here, we use single-molecule DNA supercoiling to directly observe and quantify the dynamics of torque-dependent R-loop formation and dissociation for both Cascade- and Cas9-based CRISPR-Cas systems. We find that the protospacer adjacent motif (PAM) affects primarily the R-loop association rates, whereas protospacer elements distal to the PAM affect primarily R-loop stability. Furthermore, Cascade has higher torque stability than Cas9 by using a conformational locking step. Our data provide direct evidence for directional R-loop formation, starting from PAM recognition and expanding toward the distal protospacer end. Moreover, we introduce DNA supercoiling as a quantitative tool to explore the sequence requirements and promiscuities of orthogonal CRISPR-Cas systems in rapidly emerging gene-targeting applications. PMID:24912165
NSDL National Science Digital Library
Kristen Chandler
This complete lesson plan requires students to measure the length and width of a rectangle using both standard and non-standard units of measure, such as pennies, beads, etc. As students graph the ordered pairs, they discover that the ratio of length to width of a rectangle is constant, in spite of the units. This leads to the definition of a linear function and to the rule that relates the dimensions of this rectangle. An activity sheet and questions for class discussion are included.
Catalytic C-N and C-F bond formation by organometallic group 11 complexes
Akana, Jennifer Anne
This thesis presents a study of the reaction between an (NHC)gold(I) fluoride complex (NHC = N-heterocyclic carbene) and alkynes (Chapter 1). Gold(I) and fluoride add trans across the triple bond of 3-hexyne and ...
The Non-canonical Tetratricopeptide Repeat (TPR) Domain of Fluorescent (FLU) Mediates Complex Formation with Glutamyl-tRNA Reductase.
Zhang, Min; Zhang, Feilong; Fang, Ying; Chen, Xuemin; Chen, Yuhong; Zhang, Wenxia; Dai, Huai-En; Lin, Rongcheng; Liu, Lin
The tetratricopeptide repeat (TPR)-containing protein FLU is a negative regulator of chlorophyll biosynthesis in plants. It directly interacts through its TPR domain with glutamyl-tRNA reductase (GluTR), the rate-limiting enzyme in the formation of ?-aminolevulinic acid (ALA). Delineation of how FLU binds to GluTR is important for understanding the molecular basis for FLU-mediated repression of synthesis of ALA, the universal tetrapyrrole precursor. Here, we characterize the FLU-GluTR interaction by solving the crystal structures of the uncomplexed TPR domain of FLU (FLU(TPR)) at 1.45-Å resolution and the complex of the dimeric domain of GluTR bound to FLU(TPR) at 2.4-Å resolution. Three non-canonical TPR motifs of each FLU(TPR) form a concave surface and clamp the helix bundle in the C-terminal dimeric domain of GluTR. We demonstrate that a 2:2 FLU(TPR)-GluTR complex is the functional unit for FLU-mediated GluTR regulation and suggest that the formation of the FLU-GluTR complex prevents glutamyl-tRNA, the GluTR substrate, from binding with this enzyme. These results also provide insights into the spatial regulation of ALA synthesis by the membrane-located FLU protein. PMID:26037924
Excessive formation of hydroxyl radicals and aldehydic lipid peroxidation products in cultured skin fibroblasts from patients with complex I deficiency.
Luo, X; Pitkänen, S; Kassovska-Bratinova, S; Robinson, B H; Lehotay, D C
Previous studies suggest oxygen free radicals' involvement in the etiology of cardiomyopathy with cataracts. To investigate the role of free radicals in the pathogenesis of the cardiomyopathy with cataracts and complex I deficiency, fibroblasts from patients were assessed for hydroxyl radical formation and aldehydic lipid peroxidation products with and without redox active agents that increase free radicals. The rate of hydroxyl radical formation in patient cells was increased over 2-10-fold under basal conditions, and up to 20-fold after menadione or doxorubicin treatment compared with normal cells. We also found an overproduction of aldehydes in patient cells both under basal conditions and after treatment. Both hydroxyl radicals and toxic aldehydes such as hexanal, 4-hydroxynon-2-enal, and malondialdehyde were elevated in cells from patients with three types of complex I deficiency. In contrast, acyloins, the less toxic conjugated products of pyruvate and saturated aldehydes, were lower in the patient cells. Our data provide direct evidence for the first time that complex I deficiency is associated with excessive production of hydroxyl radicals and lipid peroxidation. The resultant damage may contribute to the early onset of cardiomyopathy and cataracts and death in early infancy in affected patients with this disease. PMID:9185510
DNA Polymerase ? Subunit Residues and Interactions Required for Efficient Initiation Complex Formation Identified by a Genetic Selection.
Lindow, Janet C; Dohrmann, Paul R; McHenry, Charles S
Biophysical and structural studies have defined many of the interactions that occur between individual components or subassemblies of the bacterial replicase, DNA polymerase III holoenzyme (Pol III HE). Here, we extended our knowledge of residues and interactions that are important for the first step of the replicase reaction: the ATP-dependent formation of an initiation complex between the Pol III HE and primed DNA. We exploited a genetic selection using a dominant negative variant of the polymerase catalytic subunit that can effectively compete with wild-type Pol III ? and form initiation complexes, but cannot elongate. Suppression of the dominant negative phenotype was achieved by secondary mutations that were ineffective in initiation complex formation. The corresponding proteins were purified and characterized. One class of mutant mapped to the PHP domain of Pol III ?, ablating interaction with the ? proofreading subunit and distorting the polymerase active site in the adjacent polymerase domain. Another class of mutation, found near the C terminus, interfered with ? binding. A third class mapped within the known ?-binding domain, decreasing interaction with the ?2 processivity factor. Surprisingly, mutations within the ? binding domain also ablated interaction with ?, suggesting a larger ? binding site than previously recognized. PMID:25987558
Reinforcing the LINC complex connection to actin filaments: the role of FHOD1 in TAN line formation and nuclear movement.
Antoku, Susumu; Zhu, Ruijun; Kutscheidt, Stefan; Fackler, Oliver T; Gundersen, Gregg G
Positioning the nucleus is critical for many cellular processes including cell division, migration and differentiation. The linker of nucleoskeleton and cytoskeleton (LINC) complex spans the inner and outer nuclear membranes and has emerged as a major factor in connecting the nucleus to the cytoskeleton for movement and positioning. Recently, we discovered that the diaphanous formin family member FHOD1 interacts with the LINC complex component nesprin-2 giant (nesprin-2G) and that this interaction plays essential roles in the formation of transmembrane actin-dependent nuclear (TAN) lines and nuclear movement during cell polarization in fibroblasts. We found that FHOD1 strengthens the connection between nesprin-2G and rearward moving dorsal actin cables by providing a second site of interaction between nesprin-2G and the actin cable. These results indicate that the LINC complex connection to the actin cytoskeleton can be enhanced by cytoplasmic factors and suggest a new model for TAN line formation. We discuss how the nesprin-2G-FHOD1 interaction may be regulated and its possible functional significance for development and disease. PMID:26083340
Inhibition of interferon-inducible gene expression by adenovirus E1A proteins: Block in transcriptional complex formation
Kalvakolanu, D.V.R.; Bandyopadhyay, S.K.; Harter, M.L.; Sen, G.C. (Cleveland Clinic Foundation, OH (United States))
Infection with wild-type adenovirus 5, but not with a mutant lacking the E1A gene, prevented the induction by interferon (IFN) {alpha} of chloramphenicol acetyltransferase (CAT) activity in HeLaM cell lines that had been permanently transfected with chimeric CAT reporter genes driven by the transcriptional regulatory regions of the IFN-inducible CAT activity was observed in cells that were cotransfected with the same reporter genes and plasmids expressing either the E1A 289- or 243-amino acid protein. These proteins also prevented the induction of CAT activity by IFN-{gamma} from a cotransfected HLA-DR{alpha}-CAT gene. Experiments with E1A mutants mapped the inhibitory activity to amino acid residues 38-65 of these proteins. In a HeLa cell line permanently expressing the E1A 289-amino acid protein, the replication of vesicular stomatitis virus and encephalomyocarditis virus was not inhibited by IFN-{alpha}, suggesting a global blockade of IFN responses. The observed transcriptional inhibition could be attributed to the lack of formation of the crucial IFN-stimulated gene factor 3 (ISGF3) transcriptional complex. As shown by mobility shift assays, this complex was not formed in the nuclear extracts of IFN-treated adenovirus-infected cells or IFN-treated E1A-producing cells. These nuclear extracts were deficient in both ISGF3{alpha} and ISGF3{gamma} subunits. However, they did not block the formation of ISGF3 complex from exogenously added components.
Factors influencing the formation of complexes between oxidized lipids and proteins
K. A. Narayan; F. A. Kummerow
Complexes were formed between egg albumin and oxidized lipids, such as thermally oxidized corn oil and autoxidized linoleic\\u000a acid, under a standardized set of conditions. No complex could be obtained under these conditions when lysine, glycine, bactopeptone,\\u000a gelatin or sodium caseinate were substituted for egg albumin. Lactalbumin was equally as reactive, casein much less and fresh\\u000a egg white superior to
Association of phycoerythrin and phycocyanin: in vitro formation of a functional energy transferring phycobilisome complex of Porphyridium sordidum
Lipschultz, C.A.; Gantt, E.
Functional in vitro association and dissociation of a phycobiliprotein complex, isolated from phycobilisomes of the red alga Porphyridium sordidum, were studied. The complex contained large bangiophyceaen phycoerythrin and cyanophytan phycocyanin in an equimolar ratio and had absorption maxima at 625, 567, and 550 nm and a shoulder at 495 nm. Emission at 655 nm (with excitation at 545 nm) from phycocyanin indicated functional coupling. The complex was stable over a wide buffer concentration range, and, notably, it was maximally stable in low phosphate, <0.01 M, unlike the phycobilisomes, which dissociate at this concentration. Its molecular weight was estimated to be ca. 510 000, and by electron microscopy it was seen to consist of two units of similar size. The complex in 0.1 M phosphate was separated on a sucrose gradient into a homogeneous phycoerythrin band and a spectrally heterogeneous phycocyanin band. In vitro association of phycoerythrin and phycocyanin resulted in a complex with the same absorbance, emission, sedimentation, and molar pigment ratio as those of the native complex. The spectrally heterogeneous phycocyanin fractions from the dissociation gradient varied in the degree of association with phycoerythrin. Phycocyanin fractions absorbing from 622 to 633 nm exhibited high associability (>70%), whereas those with maxima at 617-620 nm had low associability (<30%). The presence of a 30 000 molecular weight polypeptide accompanied high associability, where it was ca. 2-fold more prominent. It is suggested that this polypeptide is involved in complex formation and could serve either in the stabilization of the conformational state of cyanophytan phycocyanin or as a direct linker between phycobiliproteins.
Stability constant estimator user`s guide
Hay, B.P.; Castleton, K.J.; Rustad, J.R.
The purpose of the Stability Constant Estimator (SCE) program is to estimate aqueous stability constants for 1:1 complexes of metal ions with ligands by using trends in existing stability constant data. Such estimates are useful to fill gaps in existing thermodynamic databases and to corroborate the accuracy of reported stability constant values.
Diffusion NMR study of complex formation in membrane-associated peptides
Suliman Barhoum; Valerie Booth; Anand Yethiraj
Pulsed-field-gradient nuclear magnetic resonance (PFG-NMR) is used to obtain the true hydrodynamic size of complexes of peptides with sodium dodecyl sulfate SDS micelles. The peptide used in this study is a 19-residue antimicrobial peptide, GAD-2. Two smaller dipeptides, alanine-glycine (Ala-Gly) and tyrosine-leucine (Tyr-Leu), are used for comparison. We use PFG-NMR to simultaneously measure diffusion coefficients of both peptide and surfactant. These two inputs, as a function of SDS concentration, are then fit to a simple two species model that neglects hydrodynamic interactions between complexes. From this we obtain the fraction of free SDS, and the hydrodynamic size of complexes in a GAD-2--SDS system as a function of SDS concentration. These results are compared to those for smaller dipeptides and for peptide-free solutions. At low SDS concentrations ([SDS] $\\leq$ 25 mM), the results self-consistently point to a GAD-2--SDS complex of fixed hydrodynamic size R =(5.5 $\\pm$ 0.3) nm. At intermediate SDS concentrations (25 mM $peptide ratio within a complex, most likely implying an increase in the number of peptides in a complex. For peptide-free solutions, the self-diffusion coefficients of SDS with and without buffer are significantly different at low SDS concentrations but merge above [SDS]=60 mM. We find that in order to obtain unambiguous information about the hydrodynamic size of a peptide-surfactant complex from diffusion measurements, experiments must be carried out at or below [SDS] = 25 mM.
Engineering Hydrogen Gas Production from Formate in a Hyperthermophile by Heterologous Production of an 18-Subunit Membrane-bound Complex*
Lipscomb, Gina L.; Schut, Gerrit J.; Thorgersen, Michael P.; Nixon, William J.; Kelly, Robert M.; Adams, Michael W. W.
Biohydrogen gas has enormous potential as a source of reductant for the microbial production of biofuels, but its low solubility and poor gas mass transfer rates are limiting factors. These limitations could be circumvented by engineering biofuel production in microorganisms that are also capable of generating H2 from highly soluble chemicals such as formate, which can function as an electron donor. Herein, the model hyperthermophile, Pyrococcus furiosus, which grows optimally near 100 °C by fermenting sugars to produce H2, has been engineered to also efficiently convert formate to H2. Using a bacterial artificial chromosome vector, the 16.9-kb 18-gene cluster encoding the membrane-bound, respiratory formate hydrogen lyase complex of Thermococcus onnurineus was inserted into the P. furiosus chromosome and expressed as a functional unit. This enabled P. furiosus to utilize formate as well as sugars as an H2 source and to do so at both 80° and 95 °C, near the optimum growth temperature of the donor (T. onnurineus) and engineered host (P. furiosus), respectively. This accomplishment also demonstrates the versatility of P. furiosus for metabolic engineering applications. PMID:24318960
A molecular loop with interstitial channels in a chiral environment and study of formation of metal-metal bonds in dinickel, dipalladium and dititanium complexes
Ibragimov, Sergey
This dissertation consists of two independent topics: (1) a molecular loop with interstitial channels in a chiral environment; (2) study of formation of metal-metal bonds in dinickel, dipalladium and dititanium complexes On ...
Tetrapeptide-coumarin conjugate 3D networks based on hydrogen-bonded charge transfer complexes: gel formation and dye release.
Guo, Zongxia; Gong, Ruiying; Jiang, Yi; Wan, Xiaobo
Oligopeptide-based derivatives are important synthons for bio-based functional materials. In this article, a Gly-(l-Val)-Gly-(l-Val)-coumarin (GVGV-Cou) conjugate was synthesized, which forms 3D networks in ethanol. The gel nanostructures were characterized by UV-vis spectroscopy, FT-IR spectroscopy, X-ray diffraction (XRD), SEM and TEM. It is suggested that the formation of charge transfer (CT) complexes between the coumarin moieties is the main driving force for the gel formation. The capability of the gel to encapsulate and release dyes was explored. Both Congo Red (CR) and Methylene Blue (MB) can be trapped in the CT gel matrix and released over time. The present gel might be used as a functional soft material for guest encapsulation and release. PMID:26138931
Redistribution of material and formation of polygenic mélanges in the External Ligurian accretionary complex (Northern Apennines, Italy)
NASA Astrophysics Data System (ADS)
Codegone, G.; Festa, A.; Dilek, Y.; Pini, G.
Tectonic, sedimentary and diapiric processes may strongly control the dynamics of the shallower part of subduction-accretionary complexes, and formation of polygenic mélanges at different scales. In modern accretionary complexes, drill cores and seismic images provide in-situ samples and measurements about large-scale features, and crucial informations on the structural processes that control their dynamics. However, minor-scale geological features and processes that are responsible for their formation are still difficult to decipher based on these techniques alone. On-land, exhumed accretionary complexes, on the other hand, can provide essential informations at all scales about (i) 3D features and structural architecture of mélanges, (ii) the role and interplay of different processes of mélange formation, and (iii) the redistribution of material in shallower parts of accretionary complexes (Festa et al., 2010). Detailed structural-stratigraphic observations in the exhumed Ligurian accretionary complex in the westernmost Northern Apennines show that a larger part of it (i.e., the Argille varicolori Formation) represents a composite chaotic unit consisting of diverse scale mélange types formed by tectonic, sedimentary and diapiric processes and their mutual superposition. Here, the spatial and temporal relationships between these mélange types resulted from two main episodes of deformation: (i) late Cretaceous-middle Eocene accretion, producing tectonic deformation of sediments at the wedge-front and formation of tectonically disrupted bodies through layer-parallel extension and contraction. Episodes of dynamic instability of the wedge-front alternating with steady-state accretion caused the removal of material locally and the subsequent emplacement of gravity-driven chaotic bodies within the tectonically disrupted bodies; (ii) late Oligocene-middle Miocene out-of-sequence thrusting, overprinting the previously formed chaotic bodies and producing a new and polygenic type of tectonically disrupted bodies through shearing close to the main thrusts. This deformation event also led to the emplacement of large (regional-scale) olistostromes at the wedge-front. The rapid burial due to the emplacement of these olistostromes and/or the tectonic shaking of unconsolidated sediments might have triggered the focused mobilization of overpressured fluids forming diapiric mélanges. We conclude that superposition of tectonic, sedimentary and diapiric processes resulted in the occurrence at different scales of different types of mélanges and polygenic mélanges in the Ligurian accretionary complex. Our recognition of these polygenic mélanges in the rock record is highly important for better understanding the dynamics, crustal architecture, and structural evolution of other ancient subduction-accretionary complexes around the world. Festa A., Pini G.A., Dilek Y. and Codegone G. (2010) - Mélanges and mélange-forming processes: a historical overview and new concepts. International Geology Review, v. 52, n. 10-12, p. 1040-1105.
Chloroplast SRP54 Was Recruited for Posttranslational Protein Transport via Complex Formation with Chloroplast SRP43 during Land Plant Evolution.
Dünschede, Beatrix; Träger, Chantal; Schröder, Christine Vera; Ziehe, Dominik; Walter, Björn; Funke, Silke; Hofmann, Eckhard; Schünemann, Danja
In bacteria, membrane proteins are targeted cotranslationally via a signal recognition particle (SRP). During the evolution of higher plant chloroplasts from cyanobacteria, the SRP pathway underwent striking adaptations that enable the posttranslational transport of the abundant light-harvesting chlorophyll-a/b-binding proteins (LHCPs). The conserved 54-kDa SRP subunit in higher plant chloroplasts (cpSRP54) is not bound to an SRP RNA, an essential SRP component in bacteria, but forms a stable heterodimer with the chloroplast-specific cpSRP43. This heterodimeric cpSRP recognizes LHCP and delivers it to the thylakoid membrane whereby cpSRP43 plays a central role. This study shows that the cpSRP system in the green alga Chlamydomonas reinhardtii differs significantly from that of higher plants as cpSRP43 is not complexed to cpSRP54 in Chlamydomonas and cpSRP54 is not involved in LHCP recognition. This divergence is attributed to altered residues within the cpSRP54 tail and the second chromodomain of cpSRP43 that are crucial for the formation of the binding interface in Arabidopsis. These changes are highly conserved among chlorophytes, whereas all land plants contain cpSRP proteins with typical interaction motifs. These data demonstrate that the coevolution of LHCPs and cpSRP43 occurred independently of complex formation with cpSRP54 and that the interaction between cpSRP54 and cpSRP43 evolved later during the transition from chlorophytes to land plants. Furthermore, our data show that in higher plants a heterodimeric form of cpSRP is required for the formation of a low molecular weight transit complex with LHCP. PMID:25833951
The G305 star-forming complex: embedded massive star formation discovered by Herschel Hi-GAL
NASA Astrophysics Data System (ADS)
Faimali, A.; Thompson, M. A.; Hindson, L.; Urquhart, J. S.; Pestalozzi, M.; Carey, S.; Shenoy, S.; Veneziani, M.; Molinari, S.; Clark, J. S.
We present a Herschel far-infrared study towards the rich massive star-forming complex G305, utilizing PACS 70, 160 ?m and SPIRE 250, 350, and 500 ?m observations from the Hi-GAL survey of the Galactic plane. The focus of this study is to identify the embedded massive star-forming population within G305, by combining far-infrared data with radio continuum, H2O maser, methanol maser, MIPS and Red MSX Source survey data available from previous studies. By applying a frequentist technique we are able to identify a sample of the most likely associations within our multiwavelength data set, which can then be identified from the derived properties obtained from fitted spectral energy distributions (SEDs). By SED modelling using both a simple modified blackbody and fitting to a comprehensive grid of model SEDs, some 16 candidate associations are identified as embedded massive star-forming regions. We derive a two-selection colour criterion from this sample of log (F70/F500) ? 1 and log (F160/F350) ? 1.6 to identify an additional 31 embedded massive star candidates with no associated star formation tracers. Using this result we can build a picture of the present-day star formation of the complex, and by extrapolating an initial mass function, suggest a current population of ?2 × 104 young stellar objects (YSOs) present, corresponding to a star formation rate (SFR) of 0.01-0.02 M? yr-1. Comparing this resolved SFR, to extragalactic SFR tracers (based on the Kennicutt-Schmidt relation), we find that the star formation activity is underestimated by a factor of ?2 in comparison to the SFR derived from the YSO population. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Unified Format for Information Sharing among Libraries at the Los Banos Complex.
ERIC Educational Resources Information Center
Anday, V. G.
This paper discusses the resources, current operations, and various bibliographic formats and standards used in the University of the Philippines at Los Banos (UPLB) libraries, where the information systems have been independently developed and tailored to their particular needs. Such a situation has resulted in data incompatibility leading to…
A complex microbiota from snowball Earth times: Microfossils from the Neoproterozoic Kingston Peak Formation, Death Valley, USA
Corsetti, Frank A.; Awramik, Stanley M.; Pierce, David
A thin carbonate unit associated with a Sturtian-age (?750–700 million years ago) glaciogenic diamictite of the Neoproterozoic Kingston Peak Formation, eastern California, contains microfossil evidence of a once-thriving prokaryotic and eukaryotic microbial community (preserved in chert and carbonate). Stratiform stromatolites, oncoids, and rare columnar stromatolites also occur. The microbial fossils, which include putative autotrophic and heterotrophic eukaryotes, are similar to those found in chert in the underlying preglacial units. They indicate that microbial life adapted to shallow-water carbonate environments did not suffer the significant extinction postulated for this phase of low-latitude glaciation and that trophic complexity survived through snowball Earth times. PMID:12682298
Weak bases and formation of a less soluble lauryl sulfate salt/complex in sodium lauryl sulfate (SLS) containing media.
Bhattachar, Shobha N; Risley, Donald S; Werawatganone, Pornpen; Aburub, Aktham
This work reports on the solubility of two weakly basic model compounds in media containing sodium lauryl sulfate (SLS). Results clearly show that the presence of SLS in the media (e.g. simulated gastric fluid or dissolution media) can result in an underestimation of solubility of some weak bases. We systematically study this phenomenon and provide evidence (chromatography and pXRD) for the first time that the decrease in solubility is likely due to formation of a less soluble salt/complex between the protonated form of the weak base and lauryl sulfate anion. PMID:21527324
Assembly of the functional membrane attack complex of human complement: formation of disulfide-linked C9 dimers.
Ware, C F; Kolb, W P
The 158,000 Mr protein, previously designated C5c, present in fully assembled complement (C) membrane attack complexes (MC5b-9) has been identified as a disulfide-bonded dimer of C9. This conclusion was based on the observations that: (i) a portion of the 125I-radiolabeled precursor C9 incorporated into MC5b-9 complexes comigrated with the 158,000 Mr protein band in NaDodSO4/polyacrylamide slab gels; (ii) monospecific antisera produced against native C9 and the 158,000 Mr protein immunologically crossreacted with monomeric native C9 by double immunodiffusion and with monomeric C9 and the 158,000 Mr protein on immunoreplication procedures; and (iii) two-dimensional NaDodSO4/polyacrylamide slab gel electrophoresis, in which the second dimension was conducted under reducing conditions, revealed that the 158,000 Mr protein contained two identical 71,000 Mr subunits which comigrated with monomeric C9. Molar ratio estimates indicated that 1 mol of C5b, C9 dimer, C6, C7, and C8 and 3-4 mol of C9 monomer were present per MC5b-9 complex. Each fully assembled membrane-bound MC5b-9 complex would therefore have a calculated Mr of 982,000. The presence of C9 dimers in the hemolytically active 29S dimeric form of the MC5b-9 complex and the absence of C9 dimers in the hemolytically inactive 23S monomeric form of the fluid phase SC5b-9 complex strongly suggest an important role for C9 dimer formation in MC5b-9 complex structure and function. The most probable function of C9 dimers would be the formation of intercomplex disulfide crosslinks which would provide a mechanism to stabilize the assembly of MC5b-9 into aggregates of increasing size on the target membrane surface which would thus be responsible for the observed pore size heterogeneity of functional C lesions. Images PMID:6796960
Micellar effect on the sensitivity of spectrophotometric Mo(VI) determination based on the formation of gallic acid complex providing evidence for the polyoxoanion structure of molybdate ions
Senay Ta?c?o?lu; Olcay ?endil; ?ivekar Beyreli
In this study effects of anionic (sodium dodecyl sulfate, SDS), cationic (cetyltrimethylammonium bromide, CTAB) and nonionic (Triton X-100, TX100) micelles on the sensitivity of spectrophotometric molybdenum(VI) (Mo) determination based on the formation of a binary complex with gallic acid (GA) were investigated.Micellar CTAB was found to enhance the formation of Mo–GA complex. SDS micelles exerted an inhibitory effect while TX100
Use of spectroscopic technique to develop a reagent for Mo(VI) utilizing micellar effects on complex formation
NASA Astrophysics Data System (ADS)
Ta?cio?lu, Sülin; Kaki, E.; Ta?cio?lu, Senay
Ultraviolet and visible spectral properties of aqueous solutions of molybdenum(VI) (Mo), gallic acid (GA), Lalanine (Ala), and L-Phenylalanine (Phe), and of their binary and ternary solutions were investigated in the absence and presence of anionic, cationic, and nonionic surfactant micelles. Evaluation of the spectra in a comparative way revealed that both Ala and Phe form ternary complexes with Mo and GA. The formation of a quaternary complex between Mo, GA, Phe, and cetyltrimethylammonium bromide at pH 4.5 provided a reagent system with a strikingly high sensitivity (1.2•106 l/(mol•cm)) for use in the spectrophotometric determination of Mo. A mechanism of micellar effects was discussed in terms of the substrate molecular charge and hydrophobicity, and rationalized on the basis of the spectral data obtained above and below the isoelectric pH of the amino acids.
Development of an aquacatalytic system based on the formation of vesicles of an amphiphilic palladium NNC-pincer complex.
Sakurai, Fumie; Hamasaka, Go; Uozumi, Yasuhiro
Two amphiphilic palladium NNC-pincer complexes bearing hydrophilic tri(ethylene glycol) chains and hydrophobic dodecyl chains were designed and prepared for the development of a new aquacatalytic system. In water, these amphiphilic complexes self-assembled to form vesicles, the structures which were established by means of a range of physical techniques. When the catalytic activities of the vesicles were investigated in the arylation of terminal alkynes in water, they were found to catalyze the reaction of aryl iodides with terminal alkynes to give good yields of the corresponding internal alkynes. The formation of a vesicular structure was shown to be essential for efficient promotion of this reaction in water. PMID:25820251
Study of complex formation of 5,5'-(2 E, 2' E)-2,2'-(ethane-1,2-diylidene)bis(hydrazine-1-yl-2-ylidene)bis(4-amino-4H-1,2,4-triazole-3-thiol) (HYT) macrocyclic ligand with Cd2+ cation in non-aqueous solution by spectroscopic and conductometric methods
NASA Astrophysics Data System (ADS)
Mallaekeh, Hassan; Shams, Alireza; Shaker, Mohammad; Bahramzadeh, Ehsan; Arefi, Donya
In this paper the complexation reaction of the 5,5'-(2 E,2' E)-2,2'-(ethane-1,2-diylidene)bis(hydrazine-1-yl-2-ylidene)bis(4-amino-4H-1,2,4-triazole-3-thiol) ligand (HYT) with Cd2+ education was studied in some binary mixtures of methanol (MeOH), n-propanol (PrOH) and dimethyl-formamide (DMF) at different temperatures using the conductometry and spectrophotometry. The stability constants of the complex was determined using a GENPLOT computer program. The conductance data and absorbance-mole ratio plots show that in all solvent systems, the stoichiometry of the complex formed between (HYT) and Cd2+ cation is 1: 1. The obtained results show that the stability of (HYT)-Cd complex is sensitive to the mixed solvents composition. The values of thermodynamic parameters (? G ?, ? H ?, and ? S ?) for formation of (HYT)-Cd complex were obtained from temperature dependence of the stability constant using the van't Hoff plots. The results show that in most cases, the complex are enthalpy destabilized but entropy stabilized and the complex formation is affected by pH, time, temperature and the nature of the solvent.
Coupling of mitochondrial translation with the formation of respiratory complexes in yeast mitochondria.
Chaci?ska, A; Boguta, M
In contrast to most other eukaryotic organisms, yeast can survive without respiration. This ability has been exploited to investigate nuclear genes required for expression of mitochondrial DNA. Availability of complete Saccharomyces cerevisiae genomic sequence has provided additional help in detailed molecular analysis. Seven of the eight major products encoded by mitochondrial DNA are hydrophobic subunits of respiratory complexes in the inner membrane. Localization of the translation process in the same cellular compartment ensures synthesis of mitochondrially encoded proteins near sites of their assembly into multimeric respiratory complexes. Association of mitochondrial ribosomes with the membrane is mediated by mRNA-specific translational activators, that are involved in the recognition of initiation codon. The newly synthesized mitochondrial proteins are transferred to membrane by a specific export system. This review discusses the role of membrane-localized factors responsible for quality control and turnover of mitochondrially synthesized subunits as well as for assembly of respiratory complexes. PMID:11996120
Controlled formation of silica structures using siloxane/block copolymer complexes prepared in various solvent mixtures.
Kataoka, Sho; Takeuchi, Yasutaka; Kawai, Akiko; Yamada, Mitsuhiko; Kamimura, Yoshihiro; Endo, Akira
Block copolymers exhibit regularly patterned structures induced by microphase separation. Here we present a method for preparing various particulate silica (SiO2) nanostructures by controlling the microphase separation of block copolymers. In this method, siloxane, a SiO2 precursor, is adsorbed onto poly(4-vinylpyridine) blocks of polystyrene-block-poly(4-vinylpyridine) in solvent mixtures. After siloxane/polymer complexes are coprecipitated via further siloxane polycondensation, the resulting precipitates are heated to remove the polymer. The results of scanning electron microscopy revealed that SiO2 formed various structures including cylindrical, spherical, and lamellar. Different SiO2 nanostructures formed via the microphase separation of siloxane/polymer complexes are prepared simply by varying solvent mixtures without changing the polymer chain. The structural change is interpreted in terms of polymer-solvent interactions and volume fractions in siloxane/polymer complexes. PMID:24093890
CK1? restrains lipin-1 induction, lipid droplet formation and cell proliferation under hypoxia by reducing HIF-1?/ARNT complex formation
Kourti, Maria; Ikonomou, Georgia; Giakoumakis, Nikolaos-Nikiforos; Rapsomaniki, Maria Anna; Landegren, Ulf; Siniossoglou, Symeon; Lygerou, Zoi; Simos, George; Mylonis, Ilias
Proliferation of cells under hypoxia is facilitated by metabolic adaptation, mediated by the transcriptional activator Hypoxia Inducible Factor-1 (HIF-1). HIF-1?, the inducible subunit of HIF-1 is regulated by oxygen as well as by oxygen-independent mechanisms involving phosphorylation. We have previously shown that CK1? phosphorylates HIF-1? in its N-terminus and reduces its affinity for its heterodimerization partner ARNT. To investigate the importance of this mechanism for cell proliferation under hypoxia, we visually monitored HIF-1? interactions within the cell nucleus using the in situ proximity ligation assay (PLA) and fluorescence recovery after photobleaching (FRAP). Both methods show that CK1?-dependent modification of HIF-1? impairs the formation of a chromatin binding HIF-1 complex. This is confirmed by analyzing expression of lipin-1, a direct target of HIF-1 that mediates hypoxic neutral lipid accumulation. Inhibition of CK1? increases lipid droplet formation and proliferation of both cancer and normal cells specifically under hypoxia and in an HIF-1?- and lipin-1-dependent manner. These data reveal a novel role for CK1? in regulating lipid metabolism and, through it, cell adaptation to low oxygen conditions. PMID:25744540
Considerable fluorescence enhancement upon supramolecular complex formation between berberine and p-sulfonated calixarenes
NASA Astrophysics Data System (ADS)
Megyesi, Mónika; Biczók, László
Remarkably strong binding of berberine to 4-sulfonatocalix[8]arene was found in aqueous solution, which led to fluorescence quantum yield increase of a factor about 40 at pH 2. The hypsochromic shift of the fluorescence maximum implied that berberine sensed less polar microenvironment when confined to SCX8. The stability of the supramolecular complex significantly diminished when sulfocalixarenes of smaller ring size served as host compounds but the pH affected the association strength to a much lesser extent. All berberine complexes proved to be barely fluorescent at pH 12.2 because of excited state quenching by the hosts via electron transfer.
Variant PRC1 Complex-Dependent H2A Ubiquitylation Drives PRC2 Recruitment and Polycomb Domain Formation
Blackledge, Neil P.; Farcas, Anca M.; Kondo, Takashi; King, Hamish W.; McGouran, Joanna F.; Hanssen, Lars L.P.; Ito, Shinsuke; Cooper, Sarah; Kondo, Kaori; Koseki, Yoko; Ishikura, Tomoyuki; Long, Hannah K.; Sheahan, Thomas W.; Brockdorff, Neil; Kessler, Benedikt M.; Koseki, Haruhiko; Klose, Robert J.
Summary Chromatin modifying activities inherent to polycomb repressive complexes PRC1 and PRC2 play an essential role in gene regulation, cellular differentiation, and development. However, the mechanisms by which these complexes recognize their target sites and function together to form repressive chromatin domains remain poorly understood. Recruitment of PRC1 to target sites has been proposed to occur through a hierarchical process, dependent on prior nucleation of PRC2 and placement of H3K27me3. Here, using a de novo targeting assay in mouse embryonic stem cells we unexpectedly discover that PRC1-dependent H2AK119ub1 leads to recruitment of PRC2 and H3K27me3 to effectively initiate a polycomb domain. This activity is restricted to variant PRC1 complexes, and genetic ablation experiments reveal that targeting of the variant PCGF1/PRC1 complex by KDM2B to CpG islands is required for normal polycomb domain formation and mouse development. These observations provide a surprising PRC1-dependent logic for PRC2 occupancy at target sites in vivo. PMID:24856970
WRAP53 is essential for Cajal body formation and for targeting the survival of motor neuron complex to Cajal bodies.
Mahmoudi, Salah; Henriksson, Sofia; Weibrecht, Irene; Smith, Stephen; Söderberg, Ola; Strömblad, Staffan; Wiman, Klas G; Farnebo, Marianne
The WRAP53 gene gives rise to a p53 antisense transcript that regulates p53. This gene also encodes a protein that directs small Cajal body-specific RNAs to Cajal bodies. Cajal bodies are nuclear organelles involved in diverse functions such as processing ribonucleoproteins important for splicing. Here we identify the WRAP53 protein as an essential factor for Cajal body maintenance and for directing the survival of motor neuron (SMN) complex to Cajal bodies. By RNA interference and immunofluorescence we show that Cajal bodies collapse without WRAP53 and that new Cajal bodies cannot be formed. By immunoprecipitation we find that WRAP53 associates with the Cajal body marker coilin, the splicing regulatory protein SMN, and the nuclear import receptor importin?, and that WRAP53 is essential for complex formation between SMN-coilin and SMN-importin?. Furthermore, depletion of WRAP53 leads to accumulation of SMN in the cytoplasm and prevents the SMN complex from reaching Cajal bodies. Thus, WRAP53 mediates the interaction between SMN and associated proteins, which is important for nuclear targeting of SMN and the subsequent localization of the SMN complex to Cajal bodies. Moreover, we detect reduced WRAP53-SMN binding in patients with spinal muscular atrophy, which is the leading genetic cause of infant mortality worldwide, caused by mutations in SMN1. This suggests that loss of WRAP53-mediated SMN trafficking contributes to spinal muscular atrophy. PMID:21072240
Competition between Decapping Complex Formation and Ubiquitin-Mediated Proteasomal Degradation Controls Human Dcp2 Decapping Activity.
Erickson, Stacy L; Corpuz, Elizabeth O; Maloy, Jeffrey P; Fillman, Christy; Webb, Kristofer; Bennett, Eric J; Lykke-Andersen, Jens
mRNA decapping is a central step in eukaryotic mRNA decay that simultaneously shuts down translation initiation and activates mRNA degradation. A major complex responsible for decapping consists of the decapping enzyme Dcp2 in association with decapping enhancers. An important question is how the activity and accumulation of Dcp2 are regulated at the cellular level to ensure the specificity and fidelity of the Dcp2 decapping complex. Here, we show that human Dcp2 levels and activity are controlled by a competition between decapping complex assembly and Dcp2 degradation. This is mediated by a regulatory domain in the Dcp2 C terminus, which, on the one hand, promotes Dcp2 activation via decapping complex formation mediated by the decapping enhancer Hedls and, on the other hand, targets Dcp2 for ubiquitin-mediated proteasomal degradation in the absence of Hedls association. This competition between Dcp2 activation and degradation restricts the accumulation and activity of uncomplexed Dcp2, which may be important for preventing uncontrolled decapping or for regulating Dcp2 levels and activity according to cellular needs. PMID:25870104
Centers of discharge of the Vendian-Motian complex of the Angara-Lena artesian basin and their role in the formation of oil and gas deposits
A. M. Ovchinnikov; G. Ya. Bogdanov
Theories for formation of and classification of centers of discharge of subsurface waters and brines under pressure are reviewed. The geological formations of the Vendian-Motian complex which occurs over the whole area of the Angara-Lena artesian basin are discussed. Both open and closed centers of discharge of salt waters and brines in the basin have been reported. The two types
Formation of Neoproterozoic metamorphic core complexes during oblique convergence (Eastern Desert, Egypt)
Major portions of the Pan-African Orogen in the Eastern Desert of Egypt were formed by island-arc accretion in the Neoproterozoic. These areas are characterized by their lack of major crustal thickening. Metamorphic core complexes occur parallel to the strike of the Eastern Desert Orogen. These domes exhibit polyphase metamorphism and deformation in contrast to the structurally overlying nappes which include
Report on the Formation of a New Entity in the Areas of Complex
de Weck, Olivier L.
& anchored& in& the& cross;disciplinary& fields& of& statistics,& information& and& decision& sciences,&and&human&and&institutional&behavior) mathematical,) behavioral) and) empirical) sciences) and) its) impact) on) complex) societal)problems.)The)new)Entity)will)have)an)impact)on)research)and)educ, Information and Decision Systems, and Statistics Munther!Dahleh!!!!EECS,!ESD,!LIDS! ! ! #12;! 2! Table
Diffusion NMR study of complex formation in membrane-associated peptides
Barhoum, Suliman; Yethiraj, Anand
Pulsed-field-gradient nuclear magnetic resonance (PFG-NMR) is used to obtain the true hydrodynamic size of complexes of peptides with sodium dodecyl sulfate SDS micelles. The peptide used in this study is a 19-residue antimicrobial peptide, GAD-2. Two smaller dipeptides, alanine-glycine (Ala-Gly) and tyrosine-leucine (Tyr-Leu), are used for comparison. We use PFG-NMR to simultaneously measure diffusion coefficients of both peptide and surfactant. These two inputs, as a function of SDS concentration, are then fit to a simple two species model that neglects hydrodynamic interactions between complexes. From this we obtain the fraction of free SDS, and the hydrodynamic size of complexes in a GAD-2--SDS system as a function of SDS concentration. These results are compared to those for smaller dipeptides and for peptide-free solutions. At low SDS concentrations ([SDS] $\\leq$ 25 mM), the results self-consistently point to a GAD-2--SDS complex of fixed hydrodynamic size R =(5.5 $\\pm$ 0.3) nm. At intermediate SDS conc...
Percentages: The Effect of Problem Structure, Number Complexity and Calculation Format
ERIC Educational Resources Information Center
Baratta, Wendy; Price, Beth; Stacey, Kaye; Steinle, Vicki; Gvozdenko, Eugene
This study reports how the difficulty of simple worded percentage problems is affected by the problem structure and the complexity of the numbers involved. We also investigate which methods students know. Results from 677 Year 8 and 9 students are reported. Overall the results indicate that more attention needs to be given to this important topic.…
Separation of drug stereoisomers by the formation of. beta. -cyclodextrin inclusion complexes
D. W. Armstrong; T. J. Ward; R. D. Armstrong; T. E. Beesley
For many drugs, only racemic mixtures are available for clinical use. Because different stereoisomers of drugs often cause different physiological responses, the use of pure isomers could elicit more exact therapeutic effects. Differential complexation of a variety of drug stereoisomers by immobilized ..beta..-cyclodextrin was investigated. Chiral recognition and racemic resolution were observed with a number of compounds from such clinically
Sarcomere Formation Occurs by the Assembly of Multiple Latent Protein Complexes
Perrimon, Norbert
of muscle organization that is critical to its function. Although most components that constitute the basic. To gain insights into this process, we investigated the functional relationships of sarcomeric protein complexes. Specifically, we systematically analyzed, using either RNAi in primary muscle cells or available
Isotopic evidence for complex microbial ecosystems in the phosphate-rich interval of the Miocene Monterey Formation
NASA Astrophysics Data System (ADS)
Theiling, B. P.; Coleman, M. L.
The middle Miocene Monterey Formation has long been debated as a crucial global sink for organic carbon that led to global cooling. We evaluate proxies for the microbial ecosystem to investigate organic carbon burial within the phosphate-rich interval of the Monterey Formation at Naples Beach, California by combining mineralogical evidence with ?34S analyses of carbonate associated sulfate (CAS). All ?34S are below Miocene seawater values (~22‰, VCDT) and range from +12.2‰ to +18.5‰. ?34SCAS < ?34Sseawater sulfate is typical of microbial environments at or near the interface between oxic and suboxic waters. Low pyrite concentrations characteristic of the Monterey Formation indicate that the system is iron-limited; iron reducing bacteria consume all ferric iron, producing a small amount of pyrite. Sulfate reducing bacteria then consume the excess, residual sulfate, generating free H2S in the absence of available iron. H2S diffuses upward towards the sediment-water interface (an oxic-suboxic mixing zone) where H2S is oxidized to 34S-depleted sulfate either aerobically or coupled to nitrate reduction, and lowers seawater pH. The high phosphate content and low carbonate content of this interval of the Monterey Formation supports a model of precipitation in lower pH waters. Assuming a -40‰ fractionation of ?34S due to microbial sulfate reduction, we estimate at least a 10%-20% contribution of sulfate from sulfide oxidation to marine porewater sulfate. These results suggest that the phosphate-rich interval of the Monterey Formation housed a complex suite of iron and sulfate reducing bacteria as well as sulfide oxidizing bacteria, suggesting that significant organic carbon was consumed during early diagenesis and may account for low organic carbon content described in previous studies.
Initial formation of an indigenous crop complex in eastern North America at 3800 B.P.
Smith, Bruce D; Yarnell, Richard A
Although geneticists and archaeologists continue to make progress world-wide in documenting the time and place of the initial domestication of a growing number of plants and animals, far less is known regarding the critically important context of coalescence of various species into distinctive sets or complexes of domesticates in each of the world's 10 or more independent centers of agricultural origin. In this article, the initial emergence of a crop complex is described for one of the best-documented of these independent centers, eastern North America (ENA). Before 4000 B.P. there is no indication of a crop complex in ENA, only isolated evidence for single indigenous domesticate species. By 3800 B.P., however, at least 5 domesticated seed-bearing plants formed a coherent complex in the river valley corridors of ENA. Accelerator mass spectrometer radiocarbon dates and reanalysis of archaeobotanical assemblages from a short occupation of the Riverton Site in Illinois documents the contemporary cultivation at 3800 B.P. of domesticated bottle gourd (Lagenaria siceraria), marshelder (Iva annua var. macrocarpa), sunflower (Helianthus annuus var. macrocarpus), and 2 cultivated varieties of chenopod (Chenopodium berlandieri), as well as the possible cultivation of Cucurbita pepo squash and little barley (Hordeum pusillum). Rather than marking either an abrupt developmental break or a necessary response to population-packing or compressed resource catchments, the coalescence of an initial crop complex in ENA appears to reflect an integrated expansion and enhancement of preexisting hunting and gathering economies that took place within a context of stable long-term adaptation to resource-rich river valley settings. PMID:19366669
We report the use of a pH-dependent continuous multiligand distribution model to determine the stability constant between Cu(II) and dissolved humic material. luorescence quenching of the humic material by Cu(II) is used to produce spectral titration curves. he values form the ti...
First evidence for the formation of technetium oxosulfide complexes: synthesis, structure and characterization.
Ferrier, Maryline; Weck, Philippe F; Poineau, Frederic; Kim, Eunja; Stebbins, Alan; Ma, Longzhou; Sattelberger, Alfred P; Czerwinski, Kenneth R
The reaction of tetrabutylammonium pertechnetate with bis(trimethylsilyl) sulfide in solution was studied by UV-Visible spectroscopy and mass spectrometry. Experimental results and density functional calculations provide the first evidence for the formation of a TcO(3)S(-) precursor. Larger scale synthesis afforded a solid that was characterized by EDX and XANES spectroscopy. XANES showed the presence of technetium in tetravalent state. EDX indicated the solid contained technetium, sulfur and oxygen. PMID:22495730
Melatonin stimulates dendrite formation and complexity in the hilar zone of the rat hippocampus: participation of the Ca++/Calmodulin complex.
Domínguez-Alonso, Aline; Valdés-Tovar, Marcela; Solís-Chagoyán, Héctor; Benítez-King, Gloria
Melatonin (MEL), the main product synthesized by the pineal gland, stimulates early and late stages of neurodevelopment in the adult brain. MEL increases dendrite length, thickness and complexity in the hilar and mossy neurons of hippocampus. Dendrite formation involves activation of Ca2+/Calmodulin (CaM)-dependent kinase II (CaMKII) by CaM. Previous work showed that MEL increased the synthesis and translocation of CaM, suggesting that MEL activates CaM-dependent enzymes by this pathway. In this work we investigated whether MEL stimulates dendrite formation by CaMKII activation in organotypic cultures from adult rat hippocampus. We found that the CaMKII inhibitor, KN-62, abolished the MEL stimulatory effects on dendritogenesis and that MEL increased the relative amount of CaM in the soluble fraction of hippocampal slices. Also, PKC inhibition abolished dendritogenesis, while luzindole, an antagonist of MEL receptors (MT1/2), partially blocked the effects of MEL. Moreover, autophosphorylation of CaMKII and PKC was increased in presence of MEL, as well as phosphorylation of ERK1/2. Our results indicate that MEL stimulates dendrite formation through CaMKII and the translocation of CaM to the soluble fraction. Dendritogenesis elicited by MEL also required PKC activation, and signaling through MT1/2 receptors was partially involved. Data strongly suggest that MEL could repair the loss of hippocampal dendrites that occur in neuropsychiatric disorders by increasing CaM levels and activation of CaMKII. PMID:25603176
Polymorphic conversions of 4- tert-butylcalix[4]arene upon the formation and thermal destruction of a complex with n-hexane
NASA Astrophysics Data System (ADS)
Surov, O. V.; Voronova, M. I.; Smirnov, P. R.; Trostin, V. N.; Mamardashvili, N. Zh.; Zakharov, A. G.
Complex polymorphic conversions of 4- tert-butylcalix[4]arene upon the formation and thermal destruction of a complex with n-hexane were revealed by combined analysis of powder X-ray pictures and data obtained by differential scanning calorimetry.
Intermediates in reactions of copper(I) complexes with N-oxides: from the formation of stable adducts to oxo transfer.
Hong, Sungjun; Gupta, Aalo K; Tolman, William B
Reactions of copper(I) complexes of bidentate N-donor supporting ligands with pyridine- and trimethylamine-N-oxides or PhIO were explored. Key results include the identification of novel copper(I) N-oxide adducts, aryl substituent hydroxylation, and bis(mu-oxo)dicopper complex formation via a route involving oxo transfer. PMID:19425587
A Mild C-O Bond Formation Catalyzed by a Rhenium-Oxo Complex Benjamin D. Sherry, Alexander T. Radosevich, and F. Dean Toste*
Toste, Dean
A Mild C-O Bond Formation Catalyzed by a Rhenium-Oxo Complex Benjamin D. Sherry, Alexander T to terminal propargyl alcohols.5b Herein, we describe the development and application of a rhenium hindered. A rhenium(V)-oxo complex bearing a bidentate phosphine ligand (dppm ) diphenylphosphinomethane
Formation of a G-quartet-Fe complex and modulation of electronic and magnetic properties of the Fe center.
Wang, Likun; Kong, Huihui; Zhang, Chi; Sun, Qiang; Cai, Liangliang; Tan, Qinggang; Besenbacher, Flemming; Xu, Wei
Although the G-quartet structure has been extensively investigated due to its biological importance, the formation mechanism, in particular, the necessity of metal centers, of an isolated G-quartet on solid surfaces remains ambiguous. Here, by using scanning tunneling microscopy under well-controlled ultra-high-vacuum conditions and density functional theory calculations we have been able to clarify that besides the intraquartet hydrogen bonding a metal center is mandatory for the formation of an isolated G-quartet. Furthermore, by subtly perturbing the local coordination bonding schemes within the formed G-quartet complex via local nanoscale scanning tunneling microscopy manipulations, we succeed in modulating the d orbitals and the accompanying magnetic properties of the metal center. Our results demonstrate the feasibility of forming an isolated G-quartet complex on a solid surface and that the strategy of modulating electronic and magnetic properties of the metal center can be extended to other related systems such as molecular spintronics. PMID:25347538
Complex formation of human T-cell leukemia virus type I p40tax transactivator with cellular polypeptides.
Nagata, K; Ide, Y; Takagi, T; Ohtani, K; Aoshima, M; Tozawa, H; Nakamura, M; Sugamura, K
We examined cellular components which associate with p40tax, the viral transactivation molecule of human T-cell leukemia virus type I. Such molecules were searched by immunoprecipitation with polyclonal and monoclonal antibodies specific for p40tax. Two cellular proteins with molecular masses of 95 kDa (p95) and 60 kDa (p60) were specifically coprecipitated with p40tax from extracts of all p40tax-producing cell lines but not from p40tax-negative cell lines. The p60 component was also shown to associate with p40tax in vitro, by using radiolabel-chase experiments. Rabbit antisera specific for p60 and p95 were prepared by immunization with electrophoretically purified molecules. While anti-p95 antiserum coprecipitated p40tax, no p40tax could be identified in immunoprecipitates by using a polyclonal anti-p60 antiserum. The partial amino acid sequence of p60 demonstrated that p60 is identical to the human 60-kDa heat shock protein (a member of the chaperonin family of proteins). Although the biological significance of the complex formation of p40tax with p95 and p60 has yet to be determined, it may be that the complex formation is one of the mechanisms by which the biological activity of p40tax can be regulated. Images PMID:1731090
In vitro platelet activation, aggregation and platelet-granulocyte complex formation induced by surface modified single-walled carbon nanotubes.
Fent, János; Bihari, Péter; Vippola, Minnamari; Sarlin, Essi; Lakatos, Susan
Surface modification of single-walled carbon nanotubes (SWCNTs) such as carboxylation, amidation, hydroxylation and pegylation is used to reduce the nanotube toxicity and render them more suitable for biomedical applications than their pristine counterparts. Toxicity can be manifested in platelet activation as it has been shown for SWCNTs. However, the effect of various surface modifications on the platelet activating potential of SWCNTs has not been tested yet. In vitro platelet activation (CD62P) as well as the platelet-granulocyte complex formation (CD15/CD41 double positivity) in human whole blood were measured by flow cytometry in the presence of 0.1mg/ml of pristine or various surface modified SWCNTs. The effect of various SWCNTs was tested by whole blood impedance aggregometry, too. All tested SWCNTs but the hydroxylated ones activate platelets and promote platelet-granulocyte complex formation in vitro. Carboxylated, pegylated and pristine SWCNTs induce whole blood aggregation as well. Although pegylation is preferred from biomedical point of view, among the samples tested by us pegylated SWCNTs induced far the most prominent activation and a well detectable aggregation of platelets in whole blood. PMID:25956790
Spectroscopic behavior on the formation complex of three double-armed calix[4]arene derivatives with lanthanoid nitrates in acetonitrile
NASA Astrophysics Data System (ADS)
Liu, Yu; Zhang, Ning; Zhao, Bang Tun; Zhang, Heng Yi
The complexation spectroscopic behavior of three p- tert-butylcalix[4]arene Schiff bases i.e. 5,11,17,23-tetra- tert-butyl-25,27-bis[2-[ N-(3-nitrobenzylidene)amino]ethoxy]-26,28-dihydroxycalix[4]arene ( 1), 5,11,17,23-tetra- tert-butyl-25,27-bis[2-[ N-(2-hydroxybenzylidene)amino]ethoxy]-26,28-dihydroxycalix[4]arene ( 2), and 5,11,17,23-tetra- tert-butyl-25,27-bis[2-[ N-(2-hydroxy-3-methoxybenzylidene)amino]ethoxy]-26,28-dihydroxycalix[4]arene ( 3) with lanthanoid nitrates (Tb 3+ and Eu 3+) has been investigated in anhydrous acetonitrile at 25 °C by using UV-vis and FT-IR as well as fluorescence spectra. The results obtained indicated that the spectroscopic behavior of compounds 1- 2 upon complexation with lanthanoid ions did not show any significant larger difference in comparison with free compounds 1 and 2, which may be contributed to the poor binding ability. Contrary to compounds 1 and 2, the lower rim functional groups in compound 3 can form two large ? electron conjugate system with lanthanide ion and encapsulate lanthanide ions tightly, displaying the novel spectroscopic behavior upon complexation with lanthanide ions. As compared with compound 3, the formation complexes of compound 3 with Tb 3+ and Eu 3+ showed new broad intense absorption at 398 nm, respectively, and IR spectra showed that O?H stretching vibration at 3413.40 cm -1 displayed a large drop. It is interestingly noted that the narrow emission line spectra were observed only for 3 complex with Tb 3+, but did not for 3-Eu 3+complex. In the 3-Eu 3+ complex, the broad-band emission at ?max=534 nm was obtained at the excitation of 398 nm. The spectroscopic behavior of three calix[4]arene derivatives upon complexation with lanthanoids was discussed from the relationship between the host structure and the properties of guest lanthanide ions.
Tectonic evolution of the Priest River complex, northern Idaho and Washington: A reappraisal of the Newport fault with new insights on metamorphic core complex formation
NASA Astrophysics Data System (ADS)
Doughty, P. Ted; Price, Raymond A.
New geologic mapping, 40Ar/39Ar thermochronometry, and geobarometry in the Middle Eocene Priest River metamorphic core complex provide the basis for unraveling the role of en echelon fault systems in core complex formation and for determining the scale of crustal fragments that form during continental extension. Four faults occur in the Priest River complex. The east verging Purcell Trench fault zone on the eastern side consists of two distinct en echelon fault segments separated by an unfaulted homocline. The U-shaped Newport fault system on the northwestern side is a conjugate normal fault set. The west verging eastern Newport fault terminates within the Silver Point Wrencoe pluton, which was intruded syntectonically into the fault zone. The east verging western Newport fault merges with the east verging Spokane dome mylonite zone in the underlying infrastructure. New geobarometric data show that this midcrustal shear zone, which evidently forms part of the regional basal décollement of the Cordilleran fold and thrust belt, also records significant Eocene extensional shearing. Rocks that formed beneath the mylonite zone at a depth of 30-35 km are juxtaposed against rocks that formed at a depth of 10 km above the zone. Eocene 40Ar/39Ar chrontours in the southern part of the infrastructure record progressive exhumation and quenching that becomes younger eastward. In the northern fragment of the infrastructure, alternating domains of progressive westward exhumation/quenching and progressive eastward exhumation/quenching occur beneath the eastern Newport fault and the northern Purcell Trench fault, respectively. These relationships form the basis for a new model of the evolution of the Priest River complex. The southern part of the infrastructure was exhumed by a major east verging detachment system comprising the western Newport fault and the reactivated eastern part of the Spokane dome mylonite zone, into which the western Newport fault merges. This master detachment fault, which roots in the southern Purcell Trench on the east side of the core complex, plunges beneath the northern part of the infrastructure (the Selkirk Crest block). Below the detachment, the infrastructure appears to be intact; above the detachment, the crust extended along a set of relaying conjugate detachment faults. These faults are the eastern Newport fault and the north and south Purcell Trench faults. Kinematic analysis shows that the Selkirk Crest block is a crustal-scale extensional horse that was stranded as continued extension moved the underlying metamorphic infrastructure out from beneath it and toward the west along the master detachment. This study shows that large tracts of midcrustal rocks can be translated and stranded as allochthonous fragments during continental crustal extension.
McIntosh, Scott W. [High Altitude Observatory, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307 (United States); Leamon, Robert J., E-mail: email@example.com [Department of Physics, Montana State University, Bozeman, MT 59717 (United States)
Recent work has revealed a phenomenological picture of the how the ?11 yr sunspot cycle of the Sun arises. The production and destruction of sunspots is a consequence of the latitudinal-temporal overlap and interaction of the toroidal magnetic flux systems that belong to the 22 yr magnetic activity cycle and are rooted deep in the Sun's convective interior. We present a conceptually simple extension of this work, presenting a hypothesis on how complex active regions can form as a direct consequence of the intra- and extra-hemispheric interaction taking place in the solar interior. Furthermore, during specific portions of the sunspot cycle, we anticipate that those complex active regions may be particularly susceptible to profoundly catastrophic breakdown, producing flares and coronal mass ejections of the most severe magnitude.
Analysis of De Novo Golgi Complex Formation after Enzyme-based Inactivation
Jollivet, Florence; Raposo, Graça; Dimitrov, Ariane; Sougrat, Rachid; Goud, Bruno
The Golgi complex is characterized by its unique morphology of closely apposed flattened cisternae that persists despite the large quantity of lipids and proteins that transit bidirectionally. Whether such a structure is maintained through endoplasmic reticulum (ER)-based recycling and auto-organization or whether it depends on a permanent Golgi structure is strongly debated. To further study Golgi maintenance in interphase cells, we developed a method allowing for a drug-free inactivation of Golgi dynamics and function in living cells. After Golgi inactivation, a new Golgi-like structure, containing only certain Golgi markers and newly synthesized cargos, was produced. However, this structure did not acquire a normal Golgi architecture and was unable to ensure a normal trafficking activity. This suggests an integrative model for Golgi maintenance in interphase where the ER is able to autonomously produce Golgi-like structures that need pre-existing Golgi complexes to be organized as morphologically normal and active Golgi elements. PMID:17855505
Formation and alteration of complex amino acid precursors in cosmic dusts and their relevance to origins of life
NASA Astrophysics Data System (ADS)
Kobayashi, Kensei; Kaneko, Takeo; Mita, Hajime; Obayashi, Yumiko; Kawamoto, Yukinori; Kanda, Kazuhiro; Takayama, Ken; Shibata, Hiromi
A wide variety of organic compounds including many kinds of amino acids have been detected in carbonaceous chondrites. It has been known that comets also bring complex organic compounds. The relevance of extraterrestrial organics to the origin of life is extensively discussed. There have been many scenarios of the origin of amino acids found in meteorites or comets, including the Strecker synthesis in the parent bodies of meteorites, the Fischer-Tropsch type reaction in the solar nebula and reactions in cosmic dusts. We examined possible formation of amino acids or their precursors in interstellar dust environments. When possible interstellar media (a mixture of carbon monoxide, ammonia and water) was irradiated with high energy protons, complex organic compounds whose molecular weights are thousands were formed [1], which gave amino acids after acid hydrolysis: Hereafter we will refer them simulated interstellar organics. It was suggested that complex amino acid precursors could be formed in ice mantles of interstellar dust particles in prior to the formation of the solar system. We are planning to irradiate simulated interstellar ices with high-energy heavy ions from the Digital Accelerator (KEK) to confirm the scenario. The simulated interstellar oraganics were so hydrophilic that they were easy to dissolve in water. Complex organics found in meteorites are generally so hydrophobic and are insoluble to water. Organics found in cometary dusts sampled by the Stardust Mission contains organics with various hydrophobicity. We irradiated the simulated interstellar organics with UV and/or soft X-rays. Soft X-rays irradiation of the simulated interstellar organics resulted in the formation of more hydrophobic compounds as seen in some of cometary dusts. It was suggested that organics of interstellar origin on dusts were altered when the solar system was being formed with soft X-rays from the young Sun in prior to the incorporation to planetesimals or comets. Dusts have another important role: Delivery of extraterrestrial organics to the primitive Earth. We are planning a novel astrobiology mission named Tanpopo by utilizing the Exposed Facility of Japan Experimental Module (JEM/EF) of the International Space Station (ISS). We will collect cosmic dusts by using ultra-low density silica gel (aerogel), and will analyze them after returning them to the Earth. Details will be presented in the other session of COSPAR 2014 [2]. [1] Y. Takano et al., Appl. Phys. Lett., 84 (2004) 1410-1412. [2] K. Kobayashi et al., COSPAR 2014, Session F31, #14256, Moscow, Russia.
Cobalt(II) Chloride Complex Formation in Acetamide–Calcium Nitrate Tetrahydrate Melts
Jelena Savovi?; Ružica Nikoli?; Dragan Veselinovi?
The absorption spectra of Co(II) chloride complexes, containing variable concentrations of chloride ligand, in a molten mixture of 80 mol% acetamide–20 mol% calcium nitrate tetrahydrate, were studied at 313, 333, 353, and 363 K, in the wavelength range 400-800 nm. The melt contains three possible ligands (CH3CONH2, H2O, and NO3-) for competition with added chloride ligand. Addition of chloride caused
Stable complex formation of CENP-B with the CENP-A nucleosome.
Fujita, Risa; Otake, Koichiro; Arimura, Yasuhiro; Horikoshi, Naoki; Miya, Yuta; Shiga, Tatsuya; Osakabe, Akihisa; Tachiwana, Hiroaki; Ohzeki, Jun-Ichirou; Larionov, Vladimir; Masumoto, Hiroshi; Kurumizaka, Hitoshi
CENP-A and CENP-B are major components of centromeric chromatin. CENP-A is the histone H3 variant, which forms the centromere-specific nucleosome. CENP-B specifically binds to the CENP-B box DNA sequence on the centromere-specific repetitive DNA. In the present study, we found that the CENP-A nucleosome more stably retains human CENP-B than the H3.1 nucleosome in vitro. Specifically, CENP-B forms a stable complex with the CENP-A nucleosome, when the CENP-B box sequence is located at the proximal edge of the nucleosome. Surprisingly, the CENP-B binding was weaker when the CENP-B box sequence was located in the distal linker region of the nucleosome. This difference in CENP-B binding, depending on the CENP-B box location, was not observed with the H3.1 nucleosome. Consistently, we found that the DNA-binding domain of CENP-B specifically interacted with the CENP-A-H4 complex, but not with the H3.1-H4 complex, in vitro. These results suggested that CENP-B forms a more stable complex with the CENP-A nucleosome through specific interactions with CENP-A, if the CENP-B box is located proximal to the CENP-A nucleosome. Our in vivo assay also revealed that CENP-B binding in the vicinity of the CENP-A nucleosome substantially stabilizes the CENP-A nucleosome on alphoid DNA in human cells. PMID:25916850
Stable complex formation of CENP-B with the CENP-A nucleosome
Fujita, Risa; Otake, Koichiro; Arimura, Yasuhiro; Horikoshi, Naoki; Miya, Yuta; Shiga, Tatsuya; Osakabe, Akihisa; Tachiwana, Hiroaki; Ohzeki, Jun-ichirou; Larionov, Vladimir; Masumoto, Hiroshi; Kurumizaka, Hitoshi
CENP-A and CENP-B are major components of centromeric chromatin. CENP-A is the histone H3 variant, which forms the centromere-specific nucleosome. CENP-B specifically binds to the CENP-B box DNA sequence on the centromere-specific repetitive DNA. In the present study, we found that the CENP-A nucleosome more stably retains human CENP-B than the H3.1 nucleosome in vitro. Specifically, CENP-B forms a stable complex with the CENP-A nucleosome, when the CENP-B box sequence is located at the proximal edge of the nucleosome. Surprisingly, the CENP-B binding was weaker when the CENP-B box sequence was located in the distal linker region of the nucleosome. This difference in CENP-B binding, depending on the CENP-B box location, was not observed with the H3.1 nucleosome. Consistently, we found that the DNA-binding domain of CENP-B specifically interacted with the CENP-A-H4 complex, but not with the H3.1-H4 complex, in vitro. These results suggested that CENP-B forms a more stable complex with the CENP-A nucleosome through specific interactions with CENP-A, if the CENP-B box is located proximal to the CENP-A nucleosome. Our in vivo assay also revealed that CENP-B binding in the vicinity of the CENP-A nucleosome substantially stabilizes the CENP-A nucleosome on alphoid DNA in human cells. PMID:25916850
Regulation of insulin-like growth factor-binding protein-3 ternary complex formation in pregnancy
M S Lewitt; F P Scott; N M Clarke; T Wu; M J Sinosich; R C Baxter
The IGFs are believed to be important in pregnancy and are implicated in the pathophysiology of pre-eclampsia. In adults the IGFs circulate primarily with IGF-binding protein-3 (IGFBP-3) and an acid-labile glycoprotein (ALS) in a 140 kDa complex which limits IGF bioavail- ability. Less than 10% of IGFBP-3 is in lower molecular weight forms. We have investigated the developmental regulation of
Formation of ion-conducting channels by the membrane attack complex proteins of complement.
Shiver, J W; Dankert, J R; Esser, A F
The effects of sequential additions of purified human complement proteins C5b-6, C7, C8, and C9 to assemble the C5b-9 membrane attack complex (MAC) of complement on electrical properties of planar lipid bilayers have been analyzed. The high resistance state of such membranes was impaired after assembly of large numbers of C5b-8 complexes as indicated by the appearance of rapidly fluctuating membrane currents. The C5b-8 induced conductance was voltage dependent and rectifying at higher voltages. Addition of C9 to membranes with very few C5b-8 complexes caused appearance of few discrete single channels of low conductance (5-25 pS) but after some time very large (greater than 0.5 nS) jumps in conductance could be monitored. This high macroscopic conductance state was dominated by 125-pS channels having a lifetime of approximately 1 s. The high conductance state was not stable and declined again after a period of 1-3 h. Incorporation of MAC extracted from complement-lysed erythrocytes into liposomes and subsequent transformation of such complexes into planar bilayers via an intermediate monolayer state resulted in channels with characteristics similar to the ones produced by sequential assembly of C5b-9. Comparison of the high-conductance C5b-9 channel characteristics (lifetime, ion preference, ionic-strength dependence) with those produced by poly(C9) (the circular or tubular aggregation product of C9) as published by Young, J.D.-E., Z.A. Cohn, and E.R. Podack. (1986. Science [Wash. DC]. 233:184-190.) indicates that the two are significantly different. PMID:1720679
Donor–acceptor complex formation in evaporated small molecular organic photovoltaic cells
Diana K. Susarova; Pavel A. Troshin; Doris Höglinger; Robert Koeppe; Sergey D. Babenko; Rimma N. Lyubovskaya; Vladimir F. Razumov; N. Serdar Sariciftci
Novel perylene diimide Py-PDI and naphthalene diimide Py-NDI possessing chelating pyridyl groups have been synthesized. The materials are comparatively investigated as electron acceptors in small molecular photovoltaic cells comprising zinc phthalocyanine ZnPc as an electron donor component. It was shown that these compounds form self-assembled coordination complexes with ZnPc in solution and co-evaporated solid blends. Py-PDI and Py-NDI used as
Gas-phase formation of large neutral alkaline-earth metal tryptophan complexes
Markus Marksteiner; Philipp Haslinger; Hendrik Ulbricht; Michele Sclafani; Harald Oberhofer; Christoph Dellago; Markus Arndt
We report on the first observation of isolated large neutral metal amino acid complexes such as Trp\\u000a n\\u000a Me\\u000a k\\u000a , with Me = Ca, Ba, Sr, cluster combinations covering n = 1–33, k = 0..2 and masses beyond 6500 u. The cluster beam is generated using UV laser desorption from a mixed powder of alkaline-earth\\u000a metal salts and tryptophan
Ammonia formation by a thiolate-bridged diiron amide complex as a nitrogenase mimic
NASA Astrophysics Data System (ADS)
Li, Yang; Li, Ying; Wang, Baomin; Luo, Yi; Yang, Dawei; Tong, Peng; Zhao, Jinfeng; Luo, Lun; Zhou, Yuhan; Chen, Si; Cheng, Fang; Qu, Jingping
Although nitrogenase enzymes routinely convert molecular nitrogen into ammonia under ambient temperature and pressure, this reaction is currently carried out industrially using the Haber-Bosch process, which requires extreme temperatures and pressures to activate dinitrogen. Biological fixation occurs through dinitrogen and reduced NxHy species at multi-iron centres of compounds bearing sulfur ligands, but it is difficult to elucidate the mechanistic details and to obtain stable model intermediate complexes for further investigation. Metal-based synthetic models have been applied to reveal partial details, although most models involve a mononuclear system. Here, we report a diiron complex bridged by a bidentate thiolate ligand that can accommodate HN=NH. Following reductions and protonations, HN=NH is converted to NH3 through pivotal intermediate complexes bridged by N2H3- and NH2- species. Notably, the final ammonia release was effected with water as the proton source. Density functional theory calculations were carried out, and a pathway of biological nitrogen fixation is proposed.
Metamorphic core complex formation by density inversion and lower-crust extrusion.
Martinez, F; Goodliffe, A M; Taylor, B
Metamorphic core complexes are domal uplifts of metamorphic and plutonic rocks bounded by shear zones that separate them from unmetamorphosed cover rocks. Interpretations of how these features form are varied and controversial, and include models involving extension on low-angle normal faults, plutonic intrusions and flexural rotation of initially high-angle normal faults. The D'Entrecasteaux islands of Papua New Guinea are actively forming metamorphic core complexes located within a continental rift that laterally evolves to sea-floor spreading. The continental rifting is recent (since approximately 6 Myr ago), seismogenic and occurring at a rapid rate ( approximately 25 mm yr-1). Here we present evidence-based on isostatic modelling, geological data and heat-flow measurements-that the D'Entrecasteaux core complexes accommodate extension through the vertical extrusion of ductile lower-crust material, driven by a crustal density inversion. Although buoyant extrusion is accentuated in this region by the geological structure present-which consists of dense ophiolite overlaying less-dense continental crust-this mechanism may be generally applicable to regions where thermal expansion lowers crustal density with depth. PMID:11418853
Complex formation with layered double hydroxides for the remediation of hygroscopicity.
Hayashi, Aki; Kubota, Mai; Okamura, Miki; Nakayama, Hirokazu
Layered double hydroxides (LDHs) have been used commercially as antacids, to stabilize drugs, to allow the controlled release of incorporated drugs, and to act as drug carriers to reduce drug accumulation within the body. Several types of LDH were investigated: nitrate type (LDH-NO3); chloride type (LDH-Cl); and carbonate type (LDH-CO3). Each type was added to an aqueous or methanol (MeOH) solution containing a drug (pravastatin or nateglinide). With pravastatin sodium, the interlayer distance expanded after reaction with LDH-NO3 and LDH-Cl in aqueous solution. In contrast, the interlayer distance of LDH-CO3 increased in methanol with nateglinide. Each drug was intercalated into the interlayer space of LDH by ion exchange. The hygroscopicity of the drug substances, complexes, and physical mixtures were determined at 70% relative humidity. Increases in weight (%) of the complexes were less than those of the physical mixtures, which demonstrates that hygroscopicity was reduced upon complexation with LDH due to the layer of LDH over the drugs. PMID:25743189
Plasmodium falciparum Hop: detailed analysis on complex formation with Hsp70 and Hsp90.
Hatherley, Rowan; Clitheroe, Crystal-Leigh; Faya, Ngonidzashe; Tastan Bishop, Özlem
The heat shock organizing protein (Hop) is important in modulating the activity and co-interaction of two chaperones: heat shock protein 70 and 90 (Hsp70 and Hsp90). Recent research suggested that Plasmodium falciparum Hop (PfHop), PfHsp70 and PfHsp90 form a complex in the trophozoite infective stage. However, there has been little computational research on the malarial Hop protein in complex with other malarial Hsps. Using in silico characterization of the protein, this work showed that individual domains of Hop are evolving at different rates within the protein. Differences between human Hop (HsHop) and PfHop were identified by motif analysis. Homology modeling of PfHop and HsHop in complex with their own cytosolic Hsp90 and Hsp70 C-terminal peptide partners indicated excellent conservation of the Hop concave TPR sites bound to the C-terminal motifs of partner proteins. Further, we analyzed additional binding sites between Hop and Hsp90, and showed, for the first time, that they are distinctly less conserved between human and malaria parasite. These sites are located on the convex surface of Hop TPR2, and involved in interactions with the Hsp90 middle domain. Since the convex sites are less conserved than the concave sites, it makes their potential for malarial inhibitor design extremely attractive (as opposed to the concave sites which have been the focus of previous efforts). PMID:25482441
Ammonia formation by a thiolate-bridged diiron amide complex as a nitrogenase mimic.
Li, Yang; Li, Ying; Wang, Baomin; Luo, Yi; Yang, Dawei; Tong, Peng; Zhao, Jinfeng; Luo, Lun; Zhou, Yuhan; Chen, Si; Cheng, Fang; Qu, Jingping
Although nitrogenase enzymes routinely convert molecular nitrogen into ammonia under ambient temperature and pressure, this reaction is currently carried out industrially using the Haber-Bosch process, which requires extreme temperatures and pressures to activate dinitrogen. Biological fixation occurs through dinitrogen and reduced NxHy species at multi-iron centres of compounds bearing sulfur ligands, but it is difficult to elucidate the mechanistic details and to obtain stable model intermediate complexes for further investigation. Metal-based synthetic models have been applied to reveal partial details, although most models involve a mononuclear system. Here, we report a diiron complex bridged by a bidentate thiolate ligand that can accommodate HN=NH. Following reductions and protonations, HN=NH is converted to NH3 through pivotal intermediate complexes bridged by N2H3(-) and NH2(-) species. Notably, the final ammonia release was effected with water as the proton source. Density functional theory calculations were carried out, and a pathway of biological nitrogen fixation is proposed. PMID:23511421
Ultrahigh-resolution imaging reveals formation of neuronal SNARE/Munc18 complexes in situ
Pertsinidis, Alexandros; Mukherjee, Konark; Sharma, Manu; Pang, Zhiping P.; Park, Sang Ryul; Zhang, Yunxiang; Brunger, Axel T.; Südhof, Thomas C.; Chu, Steven
Membrane fusion is mediated by complexes formed by SNAP-receptor (SNARE) and Secretory 1 (Sec1)/mammalian uncoordinated-18 (Munc18)-like (SM) proteins, but it is unclear when and how these complexes assemble. Here we describe an improved two-color fluorescence nanoscopy technique that can achieve effective resolutions of up to 7.5-nm full width at half maximum (3.2-nm localization precision), limited only by stochastic photon emission from single molecules. We use this technique to dissect the spatial relationships between the neuronal SM protein Munc18-1 and SNARE proteins syntaxin-1 and SNAP-25 (25 kDa synaptosome-associated protein). Strikingly, we observed nanoscale clusters consisting of syntaxin-1 and SNAP-25 that contained associated Munc18-1. Rescue experiments with syntaxin-1 mutants revealed that Munc18-1 recruitment to the plasma membrane depends on the Munc18-1 binding to the N-terminal peptide of syntaxin-1. Our results suggest that in a primary neuron, SNARE/SM protein complexes containing syntaxin-1, SNAP-25, and Munc18-1 are preassembled in microdomains on the presynaptic plasma membrane. Our superresolution imaging method provides a framework for investigating interactions between the synaptic vesicle fusion machinery and other subcellular systems in situ. PMID:23821748
Discovery of multi-seeded multi-mode formation of embedded clusters in the Rosette Molecular Complex
J. Z. Li; M. D. Smith
An investigation based on data from the spatially complete 2MASS Survey reveals that a remarkable burst of clustered star formation is taking place throughout the south-east quadrant of the Rosette Molecular Cloud. Compact clusters are forming in a multi-seeded mode, in parallel and at various places. In addition, sparse aggregates of embedded young stars are extensively distributed. In this study, we report the primary results and implications for high-mass and clustered star formation in giant molecular clouds. In particular, we incorporate for the first time the birth of medium to low-mass stars into the scenario of sequential formation of OB clusters. Following the emergence of the young OB cluster NGC 2244, a variety of manifestations of forming clusters of medium to high mass appear in the vicinity of the swept-up layer of the H{\\small II} region as well as further into the molecular cloud. The embedded clusters appear to form in a structured manner, which suggests they follow tracks laid out by the decay of macroturbulence. We address the possible origins of the turbulence. This leads us to propose a tree model to interpret the neat spatial distribution of clusters within a large section of the Rosette complex. Prominent new generation OB clusters are identified at the root of the tree pattern.
A Gip1p–Glc7p phosphatase complex regulates septin organization and spore wall formation
Tachikawa, Hiroyuki; Bloecher, Andrew; Tatchell, Kelly; Neiman, Aaron M.
Sporulation of Saccharomyces cerevisiae is a developmental process in which a single cell is converted into four haploid spores. GIP1, encoding a developmentally regulated protein phosphatase 1 interacting protein, is required for spore formation. Here we show that GIP1 and the protein phosphatase 1 encoded by GLC7 play essential roles in spore development. The gip1? mutant undergoes meiosis and prospore membrane formation normally, but is specifically defective in spore wall synthesis. We demonstrate that in wild-type cells, distinct layers of the spore wall are deposited in a specific temporal order, and that gip1? cells display a discrete arrest at the onset of spore wall deposition. Localization studies revealed that Gip1p and Glc7p colocalize with the septins in structures underlying the growing prospore membranes. Interestingly, in the gip1? mutant, not only is Glc7p localization altered, but septins are also delocalized. Similar phenotypes were observed in a glc7–136 mutant, which expresses a Glc7p defective in interacting with Gip1p. These results indicate that a Gip1p–Glc7p phosphatase complex is required for proper septin organization and initiation of spore wall formation during sporulation. PMID:11724821
A Novel High Throughput Biochemical Assay to Evaluate the HuR Protein-RNA Complex Formation
D'Agostino, Vito G.; Adami, Valentina; Provenzani, Alessandro
The RNA binding protein HuR/ELAVL1 binds to AU-rich elements (AREs) promoting the stabilization and translation of a number of mRNAs into the cytoplasm, dictating their fate. We applied the AlphaScreen technology using purified human HuR protein, expressed in a mammalian cell-based system, to characterize in vitro its binding performance towards a ssRNA probe whose sequence corresponds to the are present in TNF? 3' untranslated region. We optimized the method to titrate ligands and analyzed the kinetic in saturation binding and time course experiments, including competition assays. The method revealed to be a successful tool for determination of HuR binding kinetic parameters in the nanomolar range, with calculated Kd of 2.5±0.60 nM, kon of 2.76±0.56*106 M-1 min-1, and koff of 0.007±0.005 min-1. We also tested the HuR-RNA complex formation by fluorescent probe-based RNA-EMSA. Moreover, in a 384-well plate format we obtained a Z-factor of 0.84 and an averaged coefficient of variation between controls of 8%, indicating that this biochemical assay fulfills criteria of robustness for a targeted screening approach. After a screening with 2000 small molecules and secondary verification with RNA-EMSA we identified mitoxantrone as an interfering compound with rHuR and TNF? probe complex formation. Notably, this tool has a large versatility and could be applied to other RNA Binding Proteins recognizing different RNA, DNA, or protein species. In addition, it opens new perspectives in the identification of small-molecule modulators of RNA binding proteins activity. PMID:23951323
Major kinetic features of the formation of the. pi. -complex of cobalt hydrocarbonyl with olefin and its conversion to R'Co(CO)/sub 4/
Kardashina, L.F.; Sapunov, V.N.
The major kinetic features were studied for the formation of the ..pi..-complex of cobalt hydrocarbonyl with 1-hexene and its conversion to R'Co(CO)/sub 4/. The composition of the catalytically active ..pi..-complex with the olefin was established. The slow steps of the hydroformylation reaction were determined. A procedure was proposed for the preparation of solutions of cobalt hydrocarbonyl containing a ..pi..-complex with an olefin or R'Co(CO)/sub 4/.
Diniobium inverted sandwich complexes with ?-?6:?6-arene ligands: synthesis, kinetics of formation, and electronic structure.
Gianetti, Thomas L; Nocton, Grégory; Minasian, Stefan G; Tomson, Neil C; Kilcoyne, A L David; Kozimor, Stosh A; Shuh, David K; Tyliszczak, Tolek; Bergman, Robert G; Arnold, John
Monometallic niobium arene complexes [Nb(BDI)(N(t)Bu)(R-C(6)H(5))] (2a: R = H and 2b: R = Me, BDI = N,N'-diisopropylbenzene-?-diketiminate) were synthesized and found to undergo slow conversion into the diniobium inverted arene sandwich complexes [[(BDI)Nb(N(t)Bu)](2)(?-RC(6)H(5))] (7a: R = H and 7b: R = Me) in solution. The kinetics of this reaction were followed by (1)H NMR spectroscopy and are in agreement with a dissociative mechanism. Compounds 7a-b showed a lack of reactivity toward small molecules, even at elevated temperatures, which is unusual in the chemistry of inverted sandwich complexes. However, protonation of the BDI ligands occurred readily on treatment with [H(OEt(2))][B(C(6)F(5))(4)], resulting in the monoprotonated cationic inverted sandwich complex 8 [[(BDI(#))Nb(N(t)Bu)][(BDI)Nb(N(t)Bu)](?-C(6)H(5))][B(C(6)F(5))(4)] and the dicationic complex 9 [[(BDI(#))Nb(N(t)Bu)](2)(?-RC(6)H(5))][B(C(6)F(5))(4)](2) (BDI(#) = (ArNC(Me))(2)CH(2)). NMR, UV-vis, and X-ray absorption near-edge structure (XANES) spectroscopies were used to characterize this unique series of diamagnetic molecules as a means of determining how best to describe the Nb-arene interactions. The X-ray crystal structures, UV-vis spectra, arene (1)H NMR chemical shifts, and large J(CH) coupling constants provide evidence for donation of electron density from the Nb d-orbitals into the antibonding ? system of the arene ligands. However, Nb L(3,2)-edge XANES spectra and the lack of sp(3) hybridization of the arene carbons indicate that the Nb ? arene donation is not accompanied by an increase in Nb formal oxidation state and suggests that 4d(2) electronic configurations are appropriate to describe the Nb atoms in all four complexes. PMID:23343247
Synergistic evaluation of a complex conglomerate reservoir for EOR, Barrancas formation, Argentina
Simlote, V.N.; Ebanks, W.J.; Eslinger, E.V.; Harpole, K.J.
An engineering/geological study of the Top Red Conglomerate (TRC) section of the Barrancas formation, Mendoza area, Argentina, was conducted (1) to evaluate historical waterflood performance and recovery efficiency and (2) to develop a reservoir description and predictive model for later use in evaluation of reservoir response to EOR process applications. Original oil in place (OOIP) in the TRC reservoir was about 400 million STB (63.6 x 10/sup 6/ stock-tank m/sup 3/). The field had produced about 154 million STB (24.5 x 10/sup 6/ stock-tank m/sup 3/) or 38.5% OOIP through 1980 and is under consideration for application of a caustic flooding EOR process. The TRC shows extremely large variations in permeability, both areally and vertically, owing to its origin as the uppermost part of a thick, alluvial fan, braided channel sequence of sediments. Porosity and permeability development in these rocks is governed primarily by the abundance of detrital clays. Reservoir quality also is reduced somewhat in localized areas by the presence of calcite and zeolite cements and by authigenic clays. An abundance of chemically reactive minerals in the formation poses a significant potential for formation damage and/or adverse reactions with injected EOR chemicals. A geological description of layering and areal variability in the reservoir was developed and used to guide the application of a black oil simulator to two cross-sectional models. Simulation of waterflood performance indicated good vertical sweep efficiency near injection wells, with less efficient sweep farther away owing to gravity segregation and an adverse mobility ratio. A preliminary screening and feasibility study evaluated several EOR processes for recovering the oil left after waterflooding. Caustic flooding appeared to be the most feasible EOR process for application in this reservoir.
Formation of vacancy-impurity complexes in highly As- and P-doped Si
NASA Astrophysics Data System (ADS)
Ranki, V.; Saarinen, K.
Positron lifetime and coincidence Doppler broadening measurements have been conducted to identify the defects formed during the annealing of electron irradiated highly As- and P-doped Si. We show that the vacancy-donor pairs (V-D1) formed during the electron irradiation migrate to form V-D2 at 450 K which in turn transform to V-D3 at 700 K. We furthermore show that the V-As3 defects anneal at 1100 K and that the formation and annealing of the V-D3 defects can explain the electrical compensation observed in highly doped Si.
Duri, Simon; Tran, Chieu D.
We have successfully developed a simple and one step method to prepare high performance supramolecular polysaccharide composites from cellulose (CEL), chitosan (CS) and (2,3,6-tri-O-acetyl)-?-, ?- and ?-cyclodextrin (?-, ?- and ?-TCD). In this method, [BMIm+Cl?], an ionic liquid (IL), was used as a solvent to dissolve and prepare the composites. Since majority (>88%) of the IL used was recovered for reuse, the method is recyclable. XRD, FT-IR, NIR and SEM were used to monitor the dissolution process and to confirm that the polysaccharides were regenerated without any chemical modifications. It was found that unique properties of each component including superior mechanical properties (from CEL), excellent adsorbent for pollutants and toxins (from CS) and size/structure selectivity through inclusion complex formation (from TCDs) remain intact in the composites. Specifically, results from kinetics and adsorption isotherms show that while CS-based composites can effectively adsorb the endocrine disruptors (polychlrophenols, bisphenol-A), its adsorption is independent on the size and structure of the analytes. Conversely, the adsorption by ?-TCD-based composites exhibits strong dependency on size and structure of the analytes. For example, while all three TCD-based composites (i.e., ?-, ?- and ?-TCD) can effectively adsorb 2-, 3- and 4-chlorophenol, only ?-TCD-based composite can adsorb analytes with bulky groups including 3,4-dichloro- and 2,4,5-trichlorophenol. Furthermore, equilibrium sorption capacities for the analytes with bulky groups by ?-TCD-based composite are much higher than those by CS-based composites. Together, these results indicate that ?-TCD-based composite with its relatively larger cavity size can readily form inclusion complexes with analytes with bulky groups, and through inclusion complex formation, it can strongly adsorb much more analytes and with size/structure selectivity compared to CS-based composites which can adsorb the analyte only by surface adsorption. PMID:23517477
Undergraduate Analytical Chemistry Experiment: The Determination of Formation Constants for Acetate and Mono-and Dichloroacetate Salts of Primary, Secondary, and Tertiary Methyl-and Ethylamines
ERIC Educational Resources Information Center
D'Amelia, Ronald P.; Chiang, Stephanie; Pollut, Stephanie; Nirode, William F.
The formation and the hydrolysis of organic salts produced by the titration of a 0.1 M solution of the following amines: methyl-, dimethyl-, trimethyl-, ethyl-, diethyl-, and triethylamine with a 0.1 M solution of acetic, chloroacetic, and dichloracetic acids are studied. The pK[subscript b] of the amine and the pH at the end point were determined…
Beiu, V.
In this paper the authors discuss several complexity aspects pertaining to neural networks, commonly known as the curse of dimensionality. The focus will be on: (1) size complexity and depth-size tradeoffs; (2) complexity of learning; and (3) precision and limited interconnectivity. Results have been obtained for each of these problems when dealt with separately, but few things are known as to the links among them. They start by presenting known results and try to establish connections between them. These show that they are facing very difficult problems--exponential growth in either space (i.e. precision and size) and/or time (i.e., learning and depth)--when resorting to neural networks for solving general problems. The paper will present a solution for lowering some constants, by playing on the depth-size tradeoff.
Ising-based model of opinion formation in a complex network of interpersonal interactions
NASA Astrophysics Data System (ADS)
Grabowski, A.; Kosi?ski, R. A.
In our work the process of opinion formation in the human population, treated as a scale-free network, is modeled and investigated numerically. The individuals (nodes of the network) are characterized by their authorities, which influence the interpersonal interactions in the population. Hierarchical, two-level structures of interpersonal interactions and spatial localization of individuals are taken into account. The effect of the mass media, modeled as an external stimulation acting on the social network, on the process of opinion formation is investigated. It was found that in the time evolution of opinions of individuals critical phenomena occur. The first one is observed in the critical temperature of the system TC and is connected with the situation in the community, which may be described by such quantifiers as the economic status of people, unemployment or crime wave. Another critical phenomenon is connected with the influence of mass media on the population. As results from our computations, under certain circumstances the mass media can provoke critical rebuilding of opinions in the population.
Synergistic evaluation of a complex conglomerate reservoir for enhanced oil recovery, Barrancas Formation, Argentina
Simlote, V.N.; Ebanks, W.J.; Eslinger, E.V.
An Engineering-geological study of the Top Red Conglomerate (TRC) portions of the Barrancas formation, Mendoza area, Argentina, was conducted to evaluate waterflood performance and develop a predictive model for use in evaluating reservoir response to caustic flooding. Initial oil in place of the TRC reservoir was approximately 400 million STB. The field has produced 154 million STB through 1980, and it is being considered for enhanced recovery processes. The TRC has large variations in permeability, owing to its origin as the uppermost part of a thick alluvial fan-braided channel sequence of sediments. Porosity and permeability development in these rocks are governed mainly by the abundance of detrital clay, and are reduced somewhat by calcite and zeolite cements and authigenic clays. Chemically reactive components are potential causes of formation damage by reactions with injected chemicals. A geological model of layering and areal variability in the reservoir was used to guide the application of a black oil simulator to two cross-sections. This simulation of waterflooded performance indicated good vertical sweep efficiency near injection wells but less efficient sweep farther away because of gravity segregation. The relative merits of several enhanced recovery processes were evaluated for recovering the oil left after waterflooding. Caustic flooding appears to be the most feasible; therefore, the chemical reactivity of representative core samples were evaluated. The mineralogy and cation exchange capacity (CEC) results are presented. CEC values were compared with short term caustic consumption measurements.
The complex interplay of iron, biofilm formation, and mucoidy affecting antimicrobial resistance of Pseudomonas aeruginosa.
Oglesby-Sherrouse, Amanda G; Djapgne, Louise; Nguyen, Angela T; Vasil, Adriana I; Vasil, Michael L
Pseudomonas aeruginosa is a Gram-negative opportunistic bacterial pathogen that is refractory to a variety of current antimicrobial therapeutic regimens. Complicating treatment for such infections is the ability of P. aeruginosa to form biofilms, as well as several innate and acquired resistance mechanisms. Previous studies suggest iron plays a role in resistance to antimicrobial therapy, including the efficacy of an FDA-approved iron chelator, deferasirox (DSX), or Gallium, an iron analog, in potentiating antibiotic-dependent killing of P. aeruginosa biofilms. Here, we show that iron-replete conditions enhance resistance of P. aeruginosa nonbiofilm growth against tobramycin and tigecycline. Interestingly, the mechanism of iron-enhanced resistance to each of these antibiotics is distinct. Whereas pyoverdine-mediated iron uptake is important for optimal resistance to tigecycline, it does not enhance tobramycin resistance. In contrast, heme supplementation results in increased tobramycin resistance, while having no significant effect on tigecycline resistance. Thus, nonsiderophore bound iron plays an important role in resistance to tobramycin, while pyoverdine increases the ability of P. aeruginosa to resist tigecycline treatment. Lastly, we show that iron increases the minimal concentration of tobramycin, but not tigecycline, required to eradicate P. aeruginosa biofilms. Moreover, iron depletion blocks the previous observed induction of biofilm formation by subinhibitory concentrations of tobramycin, suggesting iron and tobramycin signal through overlapping regulatory pathways to affect biofilm formation. These data further support the role of iron in P. aeruginosa antibiotic resistance, providing yet another compelling case for targeting iron acquisition for future antimicrobial drug development. PMID:24436170
3-Pyridylmethanol vs. N,N?-diethylnicotinamide in copper(II) complex formation - A comparative EPR study
NASA Astrophysics Data System (ADS)
Husáriková, L.; Repická, Z.; Valigura, D.; Valko, M.; Mazúr, M.
Copper(II) complexes, formed from 4-chlorosalicylic acid anion A (A = 4-Clsal-), different copper(II) salts (Cu(ac)2 or CuSO4) and different N-donor ligands B (B = 3-pyridylmethanol (ron) or N,N'-diethylnicotinamide (denia)) with varying N-donor ligand-to-metal ratio (x), were studied by EPR spectroscopy in the frozen water/methanol (1:3 v/v) solutions. The number of ligand B molecules coordinated to Cu(II) central ion was determined from the nitrogen perpendicular and parallel superhyperfine splitting multiplets of Cu(II) EPR spectra. It was found for both N-donor ligands: (i) At lower ligand B concentrations (x = 1, 2), [CuB] and/or [CuB2] species having one and/or two molecules of ligands B in equatorial position were dominant. The dominant ternary complex particles were [CuA2B2] species. (ii) At higher ligand B concentrations (x ? 4) the formation of [CuB3] and/or [CuB4] species having three and/or four molecules of ligands B in equatorial position was confirmed. Such information is not possible to get from Cu(II) EPR spectra of powdered samples of given copper(II) complexes.
DNA-directed control of enzyme-inhibitor complex formation: a modular approach to reversibly switch enzyme activity.
Janssen, Brian M G; Engelen, Wouter; Merkx, Maarten
DNA-templated reversible assembly of an enzyme-inhibitor complex is presented as a new and highly modular approach to control enzyme activity. TEM1-?-lactamase and its inhibitor protein BLIP were conjugated to different oligonucleotides, resulting in enzyme inhibition in the presence of template strand. Formation of a rigid dsDNA linker upon addition of a complementary target strand disrupts the enzyme-inhibitor complex and results in the restoration of enzyme activity, enabling detection of as little as 2 fmol DNA. The noncovalent assembly of the complex allows easy tuning of target and template strands without changing the oligonucleotide-functionalized enzyme and inhibitor domains. Using a panel of eight different template sequences, restoration of enzyme activity was only observed in the presence of the target viral DNA sequence. The use of stable, well-characterized protein domains and the intrinsic modularity of our system should allow easy integration with DNA/RNA-based logic circuits for applications in biomedicine and molecular diagnostics. PMID:25216042
Determination of second-order association constants by global analysis of 1H and 13C NMR chemical shifts. Application to the complexation of sodium fusidate and potassium helvolate by beta- and gamma-cyclodextrin.
Al-Soufi, Wajih; Cabrer, Pedro Ramos; Jover, Aida; Budal, Rosane M; Tato, José Vázquez
The host-guest interaction between the steroid antibiotics sodium fusidate and potassium helvolate as guests and the hosts beta- and gamma-cyclodextrin was studied by 13C and 1H NMR techniques. The analysis of chemical shifts of individual nuclei leads to inconsistent values of the association constants and fails generally in the case of mixtures of 1:1 and 1:2 stoichiometries. The problem of parameter correlation is identified and the global analysis of two or more nuclei is proposed as a very effective method for the detection of complexes of higher stoichiometries and for the precise determination of the involved association constants. A matrix formulation of global analysis and the determination of confidence intervals is described. An analytical solution of the cubic equation, necessary for the description of higher order complexes, is presented in detail and its use together with commercial fitting software is compared with dedicated implementations. gamma-Cyclodextrin forms with both studied steroids, sodium fusidate and potassium helvolate, 1:1 complexes with high values of the association constants, K(1)=(60+/-24)x10(3)lmol(-1), and K(2)=(22+/-9)x10(3)lmol(-1), respectively. To the contrary, beta-cyclodextrin forms 1:1 and 1:2 (guest:host) complexes with both steroids, with moderate K(1) and low K(2) values (K(1)=(0.74+/-0.13)x10(3)lmol(-1), K(2)=(0.210+/-0.075)x10(3)lmol(-1)), and (K(1)=(2.42+/-0.87)x10(3)lmol(-1), K(2)=(0.06+/-0.09)x10(3)lmol(-1)), respectively. PMID:12475722
A Submillimetre Study of Massive Star Formation Within the W51 Complex and Infrared Dark Clouds
NASA Astrophysics Data System (ADS)
Parsons, Harriet Alice Louise
Despite its importance the fundamental question of how massive stars form remains unanswered, with improvements to both models and observations having crucial roles to play. To quote Bate et al. (2003) computational models of star formation are limited because "conditions in molecular clouds are not sufficiently well understood to be able to select a representative sample of cloud cores for the initial conditions". It is this notion that motivates the study of the environments within Giant Molecular Clouds (GMCs) and Infrared Dark Clouds (IRDCs), known sites of massive star formation, at the clump and core level. By studying large populations of these objects, it is possible to make conclusions based on global properties. With this in mind I study the dense molecular clumps within one of the most massive GMCs in the Galaxy: the W51 GMC. New observations of the W51 GMC in the 12CO, 13CO and C18O (3-2) transitions using the HARP instrument on the JCMT are presented. With the help of the clump finding algorithm CLUMPFIND a total of 1575 dense clumps are identified of which 1130 are associated with the W51 GMC, yielding a dense mass reservoir of 1.5 × 10^5 M contained within these clumps. Of these clumps only 1% by number are found to be super-critical, yielding a super-critical clump formation efficiency of 0.5%, below current SFE estimates of the region. This indicates star formation within the W51 GMC will diminish over time although evidence from the first search for molecular outflows presents the W51 GMC in an active light with a lower limit of 14 outflows. The distribution of the outflows within the region searched found them concentrated towards the W51A region. Having much smaller sizes and masses, obtaining global properties of clumps and cores within IRDCs required studying a large sample of these objects. To do this pre-existing data from the SCUBA Legacy Catalogue was utilised to study IRDCs within a catalogues based on 8 ?m data. This data identified 154 IRDC cores that are detected at 850 ?m and 51 cores that were not. This work suggests that cores not detected at 850 ?m are low mass, low column density and low temperature cores that are below the sensitivity limit of SCUBA at 850 ?m Utilising observations at 24 ?m from the Spitzer space telescope, allows for an investigation of current star formation by looking for warm embedded objects within the cores. This work reveals 69% of the IRDC cores have 24 ?m embedded objects. IRDC cores without associated 24 ?m emission ("starless" IRDC cores) may have yet to form stars, or may contain low mass YSOs below the detection limit. If it is assumed that cores without 24 ?m embedded sources are at an earlier evolutionary stage to cores with embedded objects a statistical lifetime for the quiescent phase of a few 10^3 - 10^4 years is derived.
Spectrophotometric determination of benzydamine HCl, levamisole HCl and mebeverine HCl through ion-pair complex formation with methyl orange
NASA Astrophysics Data System (ADS)
El-Didamony, Akram M.
A simple, rapid and sensitive spectrophotometric method has been proposed for the assay of benzydamine HCl (BENZ), levamisole HCl (LEV) and mebeverine HCl (MBV) in bulk and pharmaceutical formulations. The method based on the reaction of the selected drugs with methyl orange (MO) in buffered aqueous solution at pH 3.6. The formed yellow ion-pair complexes were extracted with dichloromethane and measured quantitatively with maximum absorption at 422 nm. The analytical parameters and their effects on the reported systems are investigated. The extracts are intensely colored and very stable at room temperature. The calibration graphs were linear over the concentration range of 2-10 ?g ml -1 for BENZ, 6-24 ?g ml -1 for LEV and 4-14 ?g ml -1 for MBV. The stoichiometry of the reaction was found to be 1:1 in all cases and the conditional stability constant ( Kf) of the complexes have been calculated. The proposed method was successfully extended to pharmaceutical preparations-tablets. Excipients used as additive in commercial formulations did not interfere in the analysis. The proposed method can be recommended for quality control and routine analysis where time, cost effectiveness and high specificity of analytical technique are of great importance.
Spectrophotometric determination of benzydamine HCl, levamisole HCl and mebeverine HCl through ion-pair complex formation with methyl orange.
El-Didamony, Akram M
A simple, rapid and sensitive spectrophotometric method has been proposed for the assay of benzydamine HCl (BENZ), levamisole HCl (LEV) and mebeverine HCl (MBV) in bulk and pharmaceutical formulations. The method based on the reaction of the selected drugs with methyl orange (MO) in buffered aqueous solution at pH 3.6. The formed yellow ion-pair complexes were extracted with dichloromethane and measured quantitatively with maximum absorption at 422 nm. The analytical parameters and their effects on the reported systems are investigated. The extracts are intensely colored and very stable at room temperature. The calibration graphs were linear over the concentration range of 2-10 microg ml(-1) for BENZ, 6-24 microg ml(-1) for LEV and 4-14 microg ml(-1) for MBV. The stoichiometry of the reaction was found to be 1:1 in all cases and the conditional stability constant (K(f)) of the complexes have been calculated. The proposed method was successfully extended to pharmaceutical preparations-tablets. Excipients used as additive in commercial formulations did not interfere in the analysis. The proposed method can be recommended for quality control and routine analysis where time, cost effectiveness and high specificity of analytical technique are of great importance. PMID:17625955
Mechanical Loading in Osteocytes Induces Formation of a Src/Pyk2/MBD2 Complex That Suppresses Anabolic Gene Expression
Hum, Julia M.; Day, Richard N.; Bidwell, Joseph P.; Wang, Yingxiao; Pavalko, Fredrick M.
Mechanical stimulation of the skeleton promotes bone gain and suppresses bone loss, ultimately resulting in improved bone strength and fracture resistance. The molecular mechanisms directing anabolic and/or anti-catabolic actions on the skeleton during loading are not fully understood. Identifying molecular mechanisms of mechanotransduction (MTD) signaling cascades could identify new therapeutic targets. Most research into MTD mechanisms is typically focused on understanding the signaling pathways that stimulate new bone formation in response to load. However, we investigated the structural, signaling and transcriptional molecules that suppress the stimulatory effects of loading. The high bone mass phenotype of mice with global deletion of either Pyk2 or Src suggests a role for these tyrosine kinases in repression of bone formation. We used fluid shear stress as a MTD stimulus to identify a novel Pyk2/Src-mediated MTD pathway that represses mechanically-induced bone formation. Our results suggest Pyk2 and Src function as molecular switches that inhibit MTD in our mechanically stimulated osteocyte culture experiments. Once activated by oscillatory fluid shear stress (OFSS), Pyk2 and Src translocate to and accumulate in the nucleus, where they associate with a protein involved in DNA methylation and the interpretation of DNA methylation patterns –methyl-CpG-binding domain protein 2 (MBD2). OFSS-induced Cox-2 and osteopontin expression was enhanced in Pyk2 KO osteoblasts, while inhibition of Src enhanced osteocalcin expression in response to OFSS. We found that Src kinase activity increased in the nucleus of osteocytes in response to OFSS and an interaction activated between Src (Y418) and Pyk2 (Y402) increased in response to OFSS. Thus, as a mechanism to prevent an over-reaction to physical stimulation, mechanical loading may induce the formation of a Src/Pyk2/MBD2 complex in the nucleus that functions to suppress anabolic gene expression. PMID:24841674
Vanadium(IV) complexes inhibit adhesion, migration and colony formation of UMR106 osteosarcoma cells.
Molinuevo, María S; Cortizo, Ana M; Etcheverry, Susana B
Vanadium is a trace element widely distributed in the environment. In vertebrates it is mainly stored in bone tissue. The unique cellular environment in the bone and the variety of interactions that mediate cancer metastasis determine that certain types of cancer, such as breast and prostate cancer, preferentially metastize in the skeleton. Since this effect usually signifies serious morbidity and grave prognosis there is an increasing interest in the development of new treatments for this pathology. The present work shows that vanadium complexes can inhibit some parameters related to cancer metastasis such as cell adhesion, migration and clonogenicity. We have also investigated the role of protein kinase A in these processes. PMID:17576559
Lead(II) complex formation with L-cysteine in aqueous solution.
Jalilehvand, Farideh; Sisombath, Natalie S; Schell, Adam C; Facey, Glenn A
The lead(II) complexes formed with the multidentate chelator L-cysteine (H2Cys) in an alkaline aqueous solution were studied using (207)Pb, (13)C, and (1)H NMR, Pb LIII-edge X-ray absorption, and UV-vis spectroscopic techniques, complemented by electrospray ion mass spectrometry (ESI-MS). The H2Cys/Pb(II) mole ratios were varied from 2.1 to 10.0 for two sets of solutions with CPb(II) = 0.01 and 0.1 M, respectively, prepared at pH values (9.1-10.4) for which precipitates of lead(II) cysteine dissolved. At low H2Cys/Pb(II) mole ratios (2.1-3.0), a mixture of the dithiolate [Pb(S,N-Cys)2](2-) and [Pb(S,N,O-Cys)(S-HCys)](-) complexes with average Pb-(N/O) and Pb-S distances of 2.42 ± 0.04 and 2.64 ± 0.04 Å, respectively, was found to dominate. At high concentration of free cysteinate (>0.7 M), a significant amount converts to the trithiolate [Pb(S,N-Cys)(S-HCys)2](2-), including a minor amount of a PbS3-coordinated [Pb(S-HCys)3](-) complex. The coordination mode was evaluated by fitting linear combinations of EXAFS oscillations to the experimental spectra and by examining the (207)Pb NMR signals in the chemical shift range ?Pb = 2006-2507 ppm, which became increasingly deshielded with increasing free cysteinate concentration. One-pulse magic-angle-spinning (MAS) (207)Pb NMR spectra of crystalline Pb(aet)2 (Haet = 2-aminoethanethiol or cysteamine) with PbS2N2 coordination were measured for comparison (?iso = 2105 ppm). The UV-vis spectra displayed absorption maxima at 298-300 nm (S(-) ? Pb(II) charge transfer) for the dithiolate PbS2N(N/O) species; with increasing ligand excess, a shoulder appeared at ?330 nm for the trithiolate PbS3N and PbS3 (minor) complexes. The results provide spectroscopic fingerprints for structural models for lead(II) coordination modes to proteins and enzymes. PMID:25695880
Surfactant induced complex formation and their effects on the interfacial properties of seawater.
Guzmán, Eduardo; Santini, Eva; Benedetti, Alessandro; Ravera, Francesca; Ferrari, Michele; Liggieri, Libero
The effect of a cationic surfactant, hexadecyltrimethylammonium bromide (CTAB), on the interfacial properties of seawater has been studied by dynamic and equilibrium surface tension and by dilational rheology essays. Important modifications of the surface tension and dilational rheology response have been observed already at the very low CTAB concentrations, where the effects due to the high ionic strength are negligible. The comparison with the effects of CTAB in different seawater models, or in natural seawater fractions, points out the establishment of strong interactions between the surfactant molecules and the lipophilic fraction of organic material dispersed/dissolved in seawater, affecting the interfacial activity of the molecules. Considering the biochemical richness of seawater, these results can be explained assuming interaction mechanisms and adsorption schemes similar to those speculated for protein and other macromolecules in the presence of surfactants, which in fact show similar features. Thus already at the low concentrations the surfactant molecules form highly surface-active complexes with part of the organic fraction of seawater. At the larger surfactant concentrations these complexes compete for adsorption with an excess of free CTAB molecules which, according to the thermodynamic conditions, are most favoured to occupy the liquid interface. The results of this study underline the important role of the sea organic content in enhancing the surface-activity of surfactants, which is relevant for a deeper understand of the direct and indirect effects of these types of pollutants on the physico-chemical environment in the sea coastal areas and develop mitigation strategies. PMID:25456992
Formation and decay of the arrestin·rhodopsin complex in native disc membranes.
Beyrière, Florent; Sommer, Martha E; Szczepek, Michal; Bartl, Franz J; Hofmann, Klaus Peter; Heck, Martin; Ritter, Eglof
In the G protein-coupled receptor rhodopsin, light-induced cis/trans isomerization of the retinal ligand triggers a series of distinct receptor states culminating in the active Metarhodopsin II (Meta II) state, which binds and activates the G protein transducin (Gt). Long before Meta II decays into the aporeceptor opsin and free all-trans-retinal, its signaling is quenched by receptor phosphorylation and binding of the protein arrestin-1, which blocks further access of Gt to Meta II. Although recent crystal structures of arrestin indicate how it might look in a precomplex with the phosphorylated receptor, the transition into the high affinity complex is not understood. Here we applied Fourier transform infrared spectroscopy to monitor the interaction of arrestin-1 and phosphorylated rhodopsin in native disc membranes. By isolating the unique infrared signature of arrestin binding, we directly observed the structural alterations in both reaction partners. In the high affinity complex, rhodopsin adopts a structure similar to Gt-bound Meta II. In arrestin, a modest loss of ?-sheet structure indicates an increase in flexibility but is inconsistent with a large scale structural change. During Meta II decay, the arrestin-rhodopsin stoichiometry shifts from 1:1 to 1:2. Arrestin stabilizes half of the receptor population in a specific Meta II protein conformation, whereas the other half decays to inactive opsin. Altogether these results illustrate the distinct binding modes used by arrestin to interact with different functional forms of the receptor. PMID:25847250
Formation and reactivity of surface-bound high oxidation state Ruthenium-oxo complexes.
Hornstein, B. J. (Brooks J.); Dattelbaum, D. M. (Dana M.); Schoonover, J. R. (Jon R.); Meyer, T. J. (Thomas J.)
Ruthenium polypyridyl oxalate complexes are precursors to high oxidation state species that can catalyze the oxidation of a variety of substrates. Covalent attachment of these reactive species to surfaces such at ZrO{sub 2} or TiO{sub 2} inhibit catalyst deactivation and provide supports from which to build electrocatalytic and photoelectrocatalytic devices. Unfortunately, few details of the effects of surface binding on reactivity are available in the literature. To this end, precursors such as, Ru(H{sub 2}O{sub 3}Ptpy)(C{sub 2}O{sub 4})(H{sub 2}O) and (C{sub 2}O{sub 4})(H{sub 2}O{sub 3}Ptpy)Ru-O-Ru(H{sub 2}O{sub 3}Ptpy)(C{sub 2}O{sub 4}) (tpy is terpyridine) have been synthesized and attached to TiO{sub 2}. Quantitative surface binding studies were carried out and acid catalyzed solvolysis was used to form the aqua species. The complexes were oxidized with Ce(IV) to their high-valent analogs and their reactivity toward selected substrates was tested. These studies not only provide information about the effects of surface binding on the reactivity of metal oxides but also have implications for the development of light-driven catalysts.
CD81 gene defect in humans disrupts CD19 complex formation and leads to antibody deficiency
van Zelm, Menno C.; Smet, Julie; Adams, Brigitte; Mascart, Françoise; Schandené, Liliane; Janssen, Françoise; Ferster, Alina; Kuo, Chiung-Chi; Levy, Shoshana; van Dongen, Jacques J.M.; van der Burg, Mirjam
Antibody deficiencies constitute the largest group of symptomatic primary immunodeficiency diseases. In several patients, mutations in CD19 have been found to underlie disease, demonstrating the critical role for the protein encoded by this gene in antibody responses; CD19 functions in a complex with CD21, CD81, and CD225 to signal with the B cell receptor upon antigen recognition. We report here a patient with severe nephropathy and profound hypogammaglobulinemia. The immunodeficiency was characterized by decreased memory B cell numbers, impaired specific antibody responses, and an absence of CD19 expression on B cells. The patient had normal CD19 alleles but carried a homozygous CD81 mutation resulting in a complete lack of CD81 expression on blood leukocytes. Retroviral transduction and glycosylation experiments on EBV-transformed B cells from the patient revealed that CD19 membrane expression critically depended on CD81. Similar to CD19-deficient patients, CD81-deficient patients had B cells that showed impaired activation upon stimulation via the B cell antigen receptor but no overt T cell subset or function defects. In this study, we present what we believe to be the first antibody deficiency syndrome caused by a mutation in the CD81 gene and consequent disruption of the CD19 complex on B cells. These findings may contribute to unraveling the genetic basis of antibody deficiency syndromes and the nonredundant functions of CD81 in humans. PMID:20237408
On-Surface Observation of the Formation of Organometallic Complex in a Supramolecular Network
Li, Yibao; Cheng, Linxiu; Liu, Chunhua; Liu, Wei; Fan, Yulan; Fan, Xiaolin; Zeng, Qingdao
The on-surface formation of organometallic monomers or oligomers, especially in supramolecular network, attracts an extensive interest for chemists and material scientist. In this work, we have investigated metal coordination between zinc (II) phthalocyanine (ZnPc) and 1, 3-di (4-pyridyl) propane (dipy-pra) in the 2, 6, 11-tricarboxydecyloxy-3, 7, 10-triundecyloxy triphenylene (asym-TTT) supramolecular template by means of scanning tunneling microscopy (STM) on highly oriented pyrolytic graphite (HOPG) substrate under ambient conditions. The experimental results demonstrate that every two ZnPc molecules in one nano-reactor connect with each other through one dipy-pra molecule by metal-coordination interaction. In this coordinating process, the template of asym-TTT supramolecular networks plays a significant role. PMID:26061532
On-Surface Observation of the Formation of Organometallic Complex in a Supramolecular Network.
Li, Yibao; Cheng, Linxiu; Liu, Chunhua; Liu, Wei; Fan, Yulan; Fan, Xiaolin; Zeng, Qingdao
The on-surface formation of organometallic monomers or oligomers, especially in supramolecular network, attracts an extensive interest for chemists and material scientist. In this work, we have investigated metal coordination between zinc (II) phthalocyanine (ZnPc) and 1, 3-di (4-pyridyl) propane (dipy-pra) in the 2, 6, 11-tricarboxydecyloxy-3, 7, 10-triundecyloxy triphenylene (asym-TTT) supramolecular template by means of scanning tunneling microscopy (STM) on highly oriented pyrolytic graphite (HOPG) substrate under ambient conditions. The experimental results demonstrate that every two ZnPc molecules in one nano-reactor connect with each other through one dipy-pra molecule by metal-coordination interaction. In this coordinating process, the template of asym-TTT supramolecular networks plays a significant role. PMID:26061532
A Strategy for Complex Dimer Formation When Biomimicry Fails: Total Synthesis of Ten Coccinellid Alkaloids
Although dimeric natural products can often be synthesized in the laboratory by directly merging advanced monomers, these approaches sometimes fail, leading instead to non-natural architectures via incorrect unions. Such a situation arose during our studies of the coccinellid alkaloids, when attempts to directly dimerize Nature's presumed monomeric precursors in a putative biomimetic sequence afforded only a non-natural analogue through improper regiocontrol. Herein, we outline a unique strategy for dimer formation that obviates these difficulties, one which rapidly constructs the coccinellid dimers psylloborine A and isopsylloborine A through a terminating sequence of two reaction cascades that generate five bonds, five rings, and four stereocenters. In addition, a common synthetic intermediate is identified which allows for the rapid, asymmetric formal or complete total syntheses of eight monomeric members of the class. PMID:24959981
The complex interplay of iron, biofilm formation, and mucoidy affecting antimicrobial resistance of Pseudomonas aeruginosa
Oglesby-Sherrouse, Amanda G.; Djapgne, Louise; Nguyen, Angela T.; Vasil, Adriana I.; Vasil, Michael L.
Pseudomonas aeruginosa is a Gram-negative opportunistic bacterial pathogen that is refractory to a variety of current antimicrobial therapeutic regimens. Complicating treatment of such infections is the ability of P. aeruginosa to form biofilms, as well as several innate and acquired resistance mechanisms. Previous studies suggest iron plays a role in resistance to antimicrobial therapy, including the efficacy of an FDA-approved iron chelator, deferasirox (DSX), or Gallium, an iron analog, in potentiating antibiotic-dependent killing of P. aeruginosa biofilms. Here we show that iron-replete conditions enhance resistance of P. aeruginosa nonbiofilm growth against tobramycin and tigecycline. Interestingly, the mechanism of iron-enhanced resistance to each of these antibiotics is distinct. Whereas pyoverdine-mediated iron uptake is important for optimal resistance to tigecycline, it does not enhance tobramycin resistance. In contrast, heme supplementation results in increased tobramycin resistance, while having no significant effect on tigecycline resistance. Thus, non-siderophore bound iron plays an important role in resistance to tobramycin, while pyoverdine increases the ability of P. aeruginosa to resist tigecycline treatment. Lastly, we show that iron increases the minimal concentration of tobramycin, but not tigecycline, required to eradicate P. aeruginosa biofilms. Moreover, iron depletion blocks the previous observed induction of biofilm formation by sub-inhibitory concentrations of tobramycin, suggesting iron and tobramycin signal through overlapping regulatory pathways to affect biofilm formation. These data further support the role of iron in P. aeruginosa antibiotic resistance, providing yet another compelling case for targeting iron acquisition for future antimicrobial drug development. PMID:24436170
Visible Light Driven Nanosecond Bromide Oxidation by a Ru Complex with Subsequent Br-Br Bond Formation.
Li, Guocan; Ward, William M; Meyer, Gerald J
Visible light excitation of [Ru(deeb)(bpz)2](2+) (deeb = 4,4'-diethylester-2,2'-bipyridine; bpz = 2,2'-bipyrazine), in Br(-) acetone solutions, led to the formation of Br-Br bonds in the form of dibromide, Br2(•-). This light reactivity stores ?1.65 eV of free energy for milliseconds. Combined (1)H NMR, UV-vis and photoluminescence measurements revealed two distinct mechanisms. The first involves diffusional quenching of the excited state by Br(-) with a rate constant of (8.1 ± 0.1) × 10(10) M(-1) s(-1). At high Br(-) concentrations, an inner-sphere pathway is dominant that involves the association of Br(-), most likely with the 3,3'-H atoms of a bpz ligand, before electron transfer from Br(-) to the excited state, ket = (2.5 ± 0.3) × 10(7) s(-1). In both mechanisms, the direct photoproduct Br(•) subsequently reacts with Br(-) to yield dibromide, Br(•) + Br(-) ? Br2(•-). Under pseudo-first-order conditions, this occurs with a rate constant of (1.1 ± 0.4) × 10(10) M(-1) s(-1) that was, within experimental error, the same as that measured when Br(•) were generated with ultraviolet light. Application of Marcus theory to the sensitized reaction provided an estimate of the Br(•) formal reduction potential E(Br(•)/Br(-)) = 1.22 V vs SCE in acetone, which is about 460 mV less positive than the accepted value in H2O. The results demonstrate that Br(-) oxidation by molecular excited states can be rapid and useful for solar energy conversion. PMID:26085129
Angiopoietin-like protein 4 inhibition of lipoprotein lipase: evidence for reversible complex formation.
Lafferty, Michael J; Bradford, Kira C; Erie, Dorothy A; Neher, Saskia B
Elevated triglycerides are associated with an increased risk of cardiovascular disease, and lipoprotein lipase (LPL) is the rate-limiting enzyme for the hydrolysis of triglycerides from circulating lipoproteins. The N-terminal domain of angiopoietin-like protein 4 (ANGPTL4) inhibits LPL activity. ANGPTL4 was previously described as an unfolding molecular chaperone of LPL that catalytically converts active LPL dimers into inactive monomers. Our studies show that ANGPTL4 is more accurately described as a reversible, noncompetitive inhibitor of LPL. We find that inhibited LPL is in a complex with ANGPTL4, and upon dissociation, LPL regains lipase activity. Furthermore, we have generated a variant of ANGPTL4 that is dependent on divalent cations for its ability to inhibit LPL. We show that LPL inactivation by this regulatable variant of ANGPTL4 is fully reversible after treatment with a chelator. PMID:23960078
Preparation and spectral investigation on inclusion complex of ?-cyclodextrin with rutin
NASA Astrophysics Data System (ADS)
Haiyun, Ding; Jianbin, Chao; Guomei, Zhang; Shaomin, Shuang; Jinhao, Pan
Solid inclusion complex of rutin with ?-cyclodextrin (?-CD) was prepared by coprecipitate method. The formation of inclusion complex was confirmed by differential scanning calorimetry (DSC) and X-ray diffraction. The formation constant was obtained by steady-state fluorescence measurements and the result suggested the complex preferred 1:1 (rutin:CD) stoichiometry. Furthermore, the spatial configuration of the complex has been proposed based on NMR and molecular modeling.
Preparation and spectral investigation on inclusion complex of beta-cyclodextrin with rutin.
Haiyun, Ding; Jianbin, Chao; Guomei, Zhang; Shaomin, Shuang; Jinhao, Pan
Solid inclusion complex of rutin with beta-cyclodextrin (beta-CD) was prepared by coprecipitate method. The formation of inclusion complex was confirmed by differential scanning calorimetry (DSC) and X-ray diffraction. The formation constant was obtained by steady-state fluorescence measurements and the result suggested the complex preferred 1:1 (rutin:CD) stoichiometry. Furthermore, the spatial configuration of the complex has been proposed based on NMR and molecular modeling. PMID:14607238
Formation of palladium nanofilms using electrochemical atomic layer deposition (E-ALD) with chloride complexation.
Sheridan, Leah B; Gebregziabiher, Daniel K; Stickney, John L; Robinson, David B
Pd thin films were formed by electrochemical atomic layer deposition (E-ALD) using surface-limited redox replacement (SLRR) of Cu underpotential deposits (UPD) on polycrystalline Au substrates. An automated electrochemical flow deposition system was used to deposit Pd atomic layers using a sequence of steps referred to as a cycle. The initial step was Cu UPD, followed by its exchange for Pd ions at open circuit, and finishing with a blank rinse to complete the cycle. Deposits were formed with up to 75 cycles and displayed proportional deposit thicknesses. Previous reports by this group indicated excess Pd deposition at the flow cell ingress, from electron probe microanalysis (EPMA). Those results suggested that the SLRR mechanism did not involve direct transfer between a Cu(UPD) atom and a Pd(2+) ion that would take its position. Instead, it was proposed that electrons are transferred through the metallic surface to reduce Pd(2+) ions near the surface where their activity is highest. It was proposed that if the cell was filled completely before a significant fraction of the Cu(UPD) atoms had been oxidized then the deposit would be homogeneous. Previous work with EDTA indicated that the hypothesis had merit, but it proved to be very sensitive to the EDTA concentration. In the present study, chloride was used to complex Pd(2+) ions, forming PdCl(4)(2-), to slow the exchange rate. Both complexing agents led to a decrease in the rate of replacement, producing more homogeneous films. Although the use of EDTA improved the homogeneity, it also decreased the deposit thickness by a factor of 3 compared to the thickness obtained via the use of chloride. PMID:23228276
Modeling Networks and Dynamics in Complex Systems: from Nano-Composites to Opinion Formation
NASA Astrophysics Data System (ADS)
Shi, Feng
Complex networks are ubiquitous in systems of physical, biological, social or technological origin. Components in those systems range from as large as cities in power grids, to as small as molecules in metabolic networks. Since the dawn of network science, significant attention has focused on the implications of dynamics in establishing network structure and the impact of structural properties on dynamics on those networks. The first part of the thesis follows this direction, studying the network formed by conductive nanorods in nano-materials, and focuses on the electrical response of the composite to the structure change of the network. New scaling laws for the shear-induced anisotropic percolation are introduced and a robust exponential tail of the current distribution across the network is identified. These results are relevant especially to "active" composite materials where materials are exposed to mechanical loading and strain deformations. However, in many real-world networks the evolution of the network topology is tied to the states of the vertices and vice versa. Networks that exhibit such a feedback are called adaptive or coevolutionary networks. The second part of the thesis examines two closely related variants of a simple, abstract model for coevolution of a network and the opinions of its members. As a representative model for adaptive networks, it displays the feature of self-organization of the system into a stable configuration due to the interplay between the network topology and the dynamics on the network. This simple model yields interesting dynamics and the slight change in the rewiring strategy results in qualitatively different behaviors of the system. In conclusion, the dissertation aims to develop new network models and tools which enable insights into the structure and dynamics of various systems, and seeks to advance network algorithms which provide approaches to coherently articulated questions in real-world complex systems such as social networks and composite materials.
Formation and dissociation of the BSS1 protein complex regulates plant development via brassinosteroid signaling.
Shimada, Setsuko; Komatsu, Tomoyuki; Yamagami, Ayumi; Nakazawa, Miki; Matsui, Minami; Kawaide, Hiroshi; Natsume, Masahiro; Osada, Hiroyuki; Asami, Tadao; Nakano, Takeshi
Brassinosteroids (BRs) play important roles in plant development and the response to environmental cues. BIL1/BZR1 is a master transcription factor in BR signaling, but the mechanisms that lead to the finely tuned targeting of BIL1/BZR1 by BRs are unknown. Here, we identified BRZ-SENSITIVE-SHORT HYPOCOTYL1 (BSS1) as a negative regulator of BR signaling in a chemical-biological analysis involving brassinazole (Brz), a specific BR biosynthesis inhibitor. The bss1-1D mutant, which overexpresses BSS1, exhibited a Brz-hypersensitive phenotype in hypocotyl elongation. BSS1 encodes a BTB-POZ domain protein with ankyrin repeats, known as BLADE ON PETIOLE1 (BOP1), which is an important regulator of leaf morphogenesis. The bss1-1D mutant exhibited an increased accumulation of phosphorylated BIL1/BZR1 and a negative regulation of BR-responsive genes. The number of fluorescent BSS1/BOP1-GFP puncta increased in response to Brz treatment, and the puncta were diffused by BR treatment in the root and hypocotyl. We show that BSS1/BOP1 directly interacts with BIL1/BZR1 or BES1. The large protein complex formed between BSS1/BOP1 and BIL1/BZR1 was only detected in the cytosol. The nuclear BIL1/BZR1 increased in the BSS1/BOP1-deficient background and decreased in the BSS1/BOP1-overexpressing background. Our study suggests that the BSS1/BOP1 protein complex inhibits the transport of BIL1/BZR1 to the nucleus from the cytosol and negatively regulates BR signaling. PMID:25663622
Assessment of drug-lipid complex formation by a high-throughput Langmuir-balance and correlation to phospholipidosis.
Vitovic, Pavol; Alakoskela, Juha-Matti; Kinnunen, Paavo K J
Phospholipidosis, the accumulation of phospholipids in cells, is a relatively frequent side effect of cationic amphiphilic drugs. In response to the industry need, several methods have been recently published for the prediction of the phospholipidosis-inducing potential of drug candidates. We describe here a high-throughput physicochemical approach, which is based on the measurement of drug-phospholipid complex formation observed by their effect on the critical micelle concentration (CMC) of a short-chain acidic phospholipid. The relative change due to the drug, CMC(DL)/CMC(L) provides a direct measure of the energy of the drug-phospholipid association, irrespective of the nature of the interaction. Comparison of results for 53 drugs to human data, animal testing, cell culture assays, and other screening methods reveals very good correlation to their phospholipidosis-inducing potential. The method is well suited for screening already in early phases of drug discovery. PMID:18318464
Transcriptional regulation of ATG9 by the Pho23-Rpd3 complex modulates the frequency of autophagosome formation.
Jin, Meiyan; Klionsky, Daniel J
Studies of the physiological and pathological roles of autophagy have revealed that too little or too much autophagy can be detrimental, and therefore autophagy activity needs to be tightly regulated. Altered transcription of autophagy-related (ATG) genes has been reported in many diseases, and ATG genes can be the most direct targets for the treatment of autophagy-associated diseases. Thus, it is important to understand how the amounts of different Atg proteins affect autophagy, and how the expression of their corresponding genes is regulated. Using budding yeast as the model, we showed that Pho23, a component of the Rpd3 large (Rpd3L) complex, represses the transcription of several ATG genes including ATG9, the expression of which regulates the frequency of autophagosome formation. More autophagosomes are formed in PHO23 null cells or in those overexpressing Atg9; conversely, there are fewer autophagosomes seen in cells with reduced Atg9 expression. PMID:25046109
Synthesis, DNA binding and complex formation reactions of 3-amino-5,6-dimethyl-1,2,4-triazine with Pd(II) and some selected biorelevant ligands
NASA Astrophysics Data System (ADS)
Shoukry, Azza A.; Alghanmi, Reem M.
With the purpose of studying the binding behavior of Pd(II) complexes with DNA as the main biological target, and their ability to penetrate reasonably into tumour cells and destroy their replication ability, Pd(ADT)Cl2 complex was synthesized and characterized, where ADT is 3-amino-5,6-dimethyl-1,2,4-triazine. Stoichiometry and stability constants of the complexes formed between various biologically relevant ligands (amino acids, amides, DNA constituents, and dicarboxylic acids) and [Pd(ADT)(H2O)2]2+ were investigated at 25 °C and at constant 0.1 mol dm-3 ionic strength. The concentration distribution diagrams of the various species formed are evaluated. Further investigation of the binding properties of the diaqua complex [Pd(ADT)(H2O)2]2+ with calf thymus DNA (CT-DNA) was investigated by UV-vis spectroscopy. The intrinsic binding constants (Kb) calculated from UV-vis absorption studies was calculated to be 2.00 × 103 mol dm-3. The calculated (Kb) value was found to be of lower magnitude than that of the classical intercalator EB (Ethidium bromide) (Kb = 1.23(±0.07) × 105 mol dm-3) suggesting an electrostatic and/or groove binding mode for the interaction with CT-DNA. Thermal denaturation has been systematically studied by spectrophotometric method and the calculated ?Tm was nearly 5 °C, supporting the electrostatic and/or groove binding mode for the interaction between the complex and CT-DNA
Formation of complex precursors of amino acids by irradiation of simulated interstellar media with heavy ions
NASA Astrophysics Data System (ADS)
Kobayashi, K.; Suzuki, N.; Taniuchi, T.; Kaneko, T.; Yoshida, S.
A wide variety of organic compounds have been detected in such extraterrestrial bodies as meteorites and comets Amino acids were identified in the extracts from Murchison meteorite and other carbonaceous chondrites It is hypothesized that these compounds are originally formed in ice mantles of interstellar dusts ISDs in molecular clouds by cosmic rays and ultraviolet light UV Formation of amino acid precursors by high energy protons or UV irradiation of simulated ISDs was reported by several groups The amino acid precursors were however not well-characterized We irradiated a frozen mixture of methanol ammonia and water with heavy ions to study possible organic compounds abiotically formed in molecular clouds by cosmic rays A mixture of methanol ammonia and water was irradiated with carbon beams 290 MeV u from a heavy ion accelerator HIMAC of National Institute of Radiological Sciences Japan Irradiation was performed either at room temperature liquid phase or at 77 K solid phase The products were characterized by gel filtration chromatography GFC FT-IR pyrolysis PY -GC MS etc Amino acids were analyzed by HPLC and GC MS after acid hydrolysis or the products Amino acids such as glycine and alanine were identified in the products in both the cases of liquid phase and solid phase irradiation Energy yields G-values of glycine were 0 014 liquid phase and 0 007 solid phase respectively Average molecular weights of the products were estimated as to 2300 in both the case Aromatic hydrocarbons N-containing heterocyclic
Electrospraying in a complex electrical field: jet formation and characteristics of final product
NASA Astrophysics Data System (ADS)
Khodadadi, Sheila; Rovers, Kirsten; Meesters, Gabriel; TUDelft-Delft project managment Team
The electrohydrodynamic atomization (EDHA) of liquid solutions is a technique developed to produce micro and nanometer size droplets. It consists of breaking a liquid jet by applying electrical forces. EHDA is one of the most suitable techniques for drug delivery and bio-nanotechnology, when precise (nm- ?m) particle size and narrow size distribution is needed. However there are some challenges facing application of this technique such as limitation in flow rate, characteristics of liquids (surface tension, conductivity,...), and the possible droplet size reduction due to evaporation of the liquid and Coulomb fission. To tackle these challenges in an EHDA-based inhalation device, we explored different possibilities to reach a stable mode in terms of jet formations, droplet-particle size and size distribution. In this contribution, we demonstrate how device configuration and operational conditions influence the electrosprayed liquid and final product. We will also discuss how our approach can be used to tailor morphological properties of nanostructured materials with identical chemical compositions.
[Formation/stabilization of the water oxidizing complex: Polypeptide/secondary donor requirement]. Progress report
Not Available
We have previously reported EPR analyses and optical spectrophotometric analyses of P{sub 680}{sup +} of NH{sub 2}OH-PSII following various durations of weak light photoinhibition. These analyses led to partial identification of the sites of damage responsible for the observed kinetic components of loss of electron transport. These analyses led us to conclude that the order of susceptibility of components of NH{sub 2}OH-PSII to weak light photodamage is Chl/Car>Y{sub Z} of D{sub 1}>Y{sub D}, of D{sub 2} {much_gt} = P{sub 680}, Pheo, Q{sub A}. These photodamages were significantly prevented by addition of an exogenous PSII electron donor (1 mM Mn{sup 2+}) to the NH{sub 2}OH-PSII prior to illumination suggesting that the damages were caused directly by P{sub 680} {sup +} or Chl{sup +}. During the last year, rather extensive efforts were made to understand the earliest event of photoinhibition of NH{sub 2}OH-PSII, the reaction mechanism causing inhibition of P{sub 680}{sup +} reduction by Y{sub Z} with accompanying formations of Chl{sup +}/Car{sup +}/quencher of Chla variable fluorescence, loss of photoactivation capability, and decrease of the quantum yield of photooxidation of Mn{sup 2+} via its high affinity binding site.
[Formation/stabilization of the water oxidizing complex: Polypeptide/secondary donor requirement
Not Available
We have previously reported EPR analyses and optical spectrophotometric analyses of P[sub 680][sup +] of NH[sub 2]OH-PSII following various durations of weak light photoinhibition. These analyses led to partial identification of the sites of damage responsible for the observed kinetic components of loss of electron transport. These analyses led us to conclude that the order of susceptibility of components of NH[sub 2]OH-PSII to weak light photodamage is Chl/Car>Y[sub Z] of D[sub 1]>Y[sub D], of D[sub 2] [much gt] = P[sub 680], Pheo, Q[sub A]. These photodamages were significantly prevented by addition of an exogenous PSII electron donor (1 mM Mn[sup 2+]) to the NH[sub 2]OH-PSII prior to illumination suggesting that the damages were caused directly by P[sub 680] [sup +] or Chl[sup +]. During the last year, rather extensive efforts were made to understand the earliest event of photoinhibition of NH[sub 2]OH-PSII, the reaction mechanism causing inhibition of P[sub 680][sup +] reduction by Y[sub Z] with accompanying formations of Chl[sup +]/Car[sup +]/quencher of Chla variable fluorescence, loss of photoactivation capability, and decrease of the quantum yield of photooxidation of Mn[sup 2+] via its high affinity binding site.
Complex igneous processes and the formation of the primitive lunar crustal rocks
NASA Technical Reports Server (NTRS)
Longhi, J.; Boudreau, A. E.
Crystallization of a magma ocean with initial chondritic Ca/Al and REE ratios such as proposed by Taylor and Bence (TB, 1975), is capable of producing the suite of primitive crustal rocks if the magma ocean underwent locally extensive assimilation and mixing in its upper layers as preliminary steps in formation of an anorthositic crust. Lunar anorthosites were the earliest permanent crustal rocks to form the result of multiple cycles of suspension and assimilation of plagioclase in liquids fractionating olivine and pyroxene. There may be two series of Mg-rich cumulate rocks: one which developed as a result of the equilibration of anorthositic crust with the magma ocean; the other which formed in the later stages of the magma ocean during an epoch of magma mixing and ilmenite crystallization. This second series may be related to KREEP genesis. It is noted that crystallization of the magma ocean had two components: a low pressure component which produced a highly fractionated and heterogeneous crust growing downward and a high pressure component which filled in the ocean from the bottom up, mostly with olivine and low-Ca pyroxene.
Kinetics of the ATP and dATP-mediated formation of a functionally-active RecA-ssDNA complex.
Nayak, Sunil; Bryant, Floyd R
The kinetics of the ATP and dATP-mediated formation of a functionally-active RecA-ssDNA complex were examined by stopped-flow fluorescence spectroscopy, using a modified version of the RecA protein that contains a fluorescent reporter group in the ssDNA binding site. The results indicated that: i) an active RecA-ssDNA complex was formed more rapidly on dT200 than on dT50 when either ATP or dATP was provided as the nucleotide cofactor, and ii) active complex formation occurred more rapidly with dATP than with ATP on either dT50 or dT200. The dependence on both the identity of the nucleotide cofactor and the length of the ssDNA effector indicated that active complex formation occurs by a cooperative mechanism and that dATP is more effective than ATP in mediating the interactions between RecA monomers that drive this process. Interestingly, the time courses of dATP-mediated active complex formation were closely similar to those that were obtained with ATP?S, an effectively non-hydrolyzable ATP analog that strongly stabilizes the active conformation of the RecA-ssDNA complex. These results provide mechanistic insight into the enhanced ssDNA binding and DNA strand exchange activities that are observed when dATP is provided in place of ATP in RecA biochemical assays. PMID:26100204
Structure-property relationships based on Hammett constants in cyclometalated iridium(III) complexes: their application to the design of a fluorine-free FIrPic-like emitter.
Frey, Julien; Curchod, Basile F E; Scopelliti, Rosario; Tavernelli, Ivano; Rothlisberger, Ursula; Nazeeruddin, Mohammad K; Baranoff, Etienne
While phosphorescent cyclometalated iridium(iii) complexes have been widely studied, only correlations between oxidation potential EOX and Hammett constant ?, and between the redox gap (?EREDOX = EOX-ERED) and emission or absorption wavelength (?abs, ?em) have been reported. We present now a quantitative model based on Hammett parameters that rationalizes the effect of the substituents on the properties of cyclometalated iridium(iii) complexes. This simple model allows predicting the apparent redox potentials as well as the electrochemical gap of homoleptic complexes based on phenylpyridine ligands with good accuracy. In particular, the model accounts for the unequal effect of the substituents on both the HOMO and the LUMO energy levels. Consequently, the model is used to anticipate the emission maxima of the corresponding complexes with improved reliability. We demonstrate in a series of phenylpyridine emitters that electron-donating groups can effectively replace electron-withdrawing substituents on the orthometallated phenyl to induce a blue shift of the emission. This result is in contrast with the common approach that uses fluorine to blue shift the emission maximum. Finally, as a proof of concept, we used electron-donating substituents to design a new fluorine-free complex, referred to as EB343, matching the various properties, namely oxidation and reduction potentials, electrochemical gap and emission profile, of the standard sky-blue emitter FIrPic. PMID:24345847
Breccia Formation at a Complex Impact Crater: Slate Islands, Lake Superior, Ontario, Canada
NASA Technical Reports Server (NTRS)
Dressler, B. O.; Sharpton, V. L.
The Slate Islands impact structure is the eroded remnant of a approximately 30-32 km-diameter complex impact structure located in northern Lake Superior, Ontario, Canada. Target rocks are Archean supracrustal and igneous rocks and Proterozoic metavolcanics, metasediments, and diabase. A wide variety of breccias occurs on the islands, many of which contain fragments exhibiting shock metamorphic features. Aphanitic, narrow and inclusion-poor pseudotachylite veins, commonly with more or less parallel boundaries and apophyses branching off them, represent the earliest breccias formed during the compression stage of the impact process. Coarse-grained, polymictic elastic matrix breccias form small to very large, inclusion-rich dikes and irregularly shaped bodies that may contain altered glass fragments. These breccias have sharp contacts with their host rocks and include a wide range of fragment types some of which were transported over minimum distances of approximately 2 km away from the center of the structure. They cut across pseudotachylite veins and contain inclusions of them. Field and petrographic evidence indicate that these polymictic breccias formed predominantly during the excavation and central uplift stages of the impact process. Monomictic breccias, characterized by angular fragments and transitional contacts with their host rocks, occur in parautochthonous target rocks, mainly on the outlying islands of the Slate Islands archipelago. A few contain fragmented and disrupted, coarse-grained, polymictic clastic matrix breccia dikes. This is an indication that at least some of these monomictic breccias formed late in the impact process and that they are probably related to a late crater modification stage. A small number of relatively large occurrences of glass-poor, suevitic breccias occur at the flanks of the central uplift and along the inner flank of the outer ring of the Slate Islands complex crater. A coarse, glass-free, allogenic breccia, containing shatter-coned fragments derived from Proterozoic target rocks (upper target strata), observed at two locations may be analogous to the 'Bunt Breccia' of the Ries crater in Germany. At one of these locations this breccia lies close to a crater suevite deposit. At the other, it overlies parautochthonous, monomictic breccia. The State Islands impact breccias are superbly exposed, much better than breccias in most other terrestrial impact structures. Observations, including those indicative of multiple and and sequential processes, provide insight on how impact breccias form and how they relate to the various phases of the impact process. Eventually they will lead to an improved understanding of planetary impact processes.
Autocatalytic formation of an iron(IV)-oxo complex via scandium ion-promoted radical chain autoxidation of an iron(II) complex with dioxygen and tetraphenylborate.
Nishida, Yusuke; Lee, Yong-Min; Nam, Wonwoo; Fukuzumi, Shunichi
A non-heme iron(IV)-oxo complex, [(TMC)Fe(IV)(O)](2+) (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), was formed by oxidation of an iron(II) complex ([(TMC)Fe(II)](2+)) with dioxygen (O2) and tetraphenylborate (BPh4(-)) in the presence of scandium triflate (Sc(OTf)3) in acetonitrile at 298 K via autocatalytic radical chain reactions rather than by a direct O2 activation pathway. The autocatalytic radical chain reaction is initiated by scandium ion-promoted electron transfer from BPh4(-) to [(TMC)Fe(IV)(O)](2+) to produce phenyl radical (Ph(•)). The chain propagation step is composed of the addition of O2 to Ph(•) and the reduction of the resulting phenylperoxyl radical (PhOO(•)) by scandium ion-promoted electron transfer from BPh4(-) to PhOO(•) to produce phenyl hydroperoxide (PhOOH), accompanied by regeneration of phenyl radical. PhOOH reacts with [(TMC)Fe(II)](2+) to yield phenol (PhOH) and [(TMC)Fe(IV)(O)](2+). Biphenyl (Ph-Ph) was formed via the radical chain autoxidation of BPh3 by O2. The induction period of the autocatalytic radical chain reactions was shortened by addition of a catalytic amount of [(TMC)Fe(IV)(O)](2+), whereas addition of a catalytic amount of ferrocene that can reduce [(TMC)Fe(IV)(O)](2+) resulted in elongation of the induction period. Radical chain autoxidation of BPh4(-) by O2 also occurred in the presence of Sc(OTf)3 without [(TMC)Fe(IV)(O)](2+), initiating the autocatalytic oxidation of [(TMC)Fe(II)](2+) with O2 and BPh4(-) to yield [(TMC)Fe(IV)(O)](2+). Thus, the general view for formation of non-heme iron(IV)-oxo complexes via O2-binding iron species (e.g., Fe(III)(O2(•-))) without contribution of autocatalytic radical chain reactions should be viewed with caution. PMID:24809677
Diagenesis of Metals Chemically Complexed to Bacteria: Laboratory Formation of Metal Phosphates, Sulfides, and Organic Condensates in Artificial Sediments
Beveridge, T. J.; Meloche, J. D.; Fyfe, W. S.; Murray, R. G. E.
Cells of Bacillus subtilis, when suspended in a 5mM metal solution, bind metals tenaciously to their cell walls. These metal-loaded cells, when mixed with a synthetic sediment and put under laboratory conditions to simulate low-temperature sediment diagenesis, nucleate the formation of a mixed assemblage of crystalline metal phosphates, metal sulfides, and polymeric, metal-complexed, organic residues. The sequential series of diagenetic events leading to the formation of authigenic mineral phases was followed by transmission electron microscopy and energy-dispersive X-ray analysis. The minerals quartz (SiO2) and calcite (CaCO3) were employed in the synthetic sediment. Crystalline magnetite (Fe2O3) and elemental sulfur were added as redox buffering agents to ensure anoxic conditions. Quartz and magnetite appeared unreactive throughout the experimental conditions. Elemental sulfur interacted with the metal-loaded cells, affected both the eventual chemistry and crystal habit of the metal phosphates, and formed a variety of crystalline metal sulfides. Calcite raised the pH of the fluid phase of the sediment, which influenced phosphate mineralization and inhibited metal sulfide genesis. Images PMID:16346230
Cone sheet formation and intrusive growth of an oceanic island—The Miocene Tejeda complex on Gran Canaria (Canary Islands)
NASA Astrophysics Data System (ADS)
Schirnick, Carsten; van den Bogaard, Paul; Schmincke, Hans-Ulrich
More than 500 trachytic to phonolitic cone sheet dikes, hypabyssal syenite stocks, and subordinate radial dikes form a 20-km-diameter intrusive complex in the volcaniclastic fill of the Miocene Tejeda caldera (20 × 35 km) on Gran Canaria (Canary Islands). The dikes intruded concentrically around a central axis of radial symmetry and dip uniformly an average of ˜41° toward the center. Single-crystal 40Ar/39Ar ages of dikes and syenite stocks ranging from 12.3 ± 0.1 to 7.32 ± 0.05 Ma suggest more or less continuous intrusive activity during both volcanically active and inactive phases. Intrusions were emplaced at average intervals of ˜5 10 k.y., while explosive eruptions took place at >50 k.y. intervals. The estimated aggregate volume of evolved cone sheet magma added at shallow level (<2000 m below sea level) amounts to ˜250 km3 compared to ?500 km3 of evolved extrusive volcanics erupted during the same period. Formation of the Tejeda cone sheets most likely resulted from deformation processes due to resurgent doming, initiated by the recurrent replenishment of a flat, laccolith-like shallow magma chamber. Magma supply exceeding the volume that could be compensated for by updoming of the overlying caldera fill resulted in the formation of cone-shaped fractures.
Eukaryotic DNA polymerases require an iron-sulfur cluster for the formation of active complexes
Netz, Daili J. A.; Stith, Carrie M.; Stümpfig, Martin; Köpf, Gabriele; Vogel, Daniel; Genau, Heide M.; Stodola, Joseph L.; Lill, Roland; Burgers, Peter M. J.; Pierik, Antonio J.
The eukaryotic replicative DNA polymerases (Pol ?, ?, and ?), and the major DNA mutagenesis enzyme Pol ? contain two conserved cysteine-rich metal-binding motifs (CysA and CysB) in the C-terminal domain (CTD) of their catalytic subunits. Here, we demonstrate by in vivo and in vitro approaches the presence of an essential [4Fe-4S] cluster in the CysB motif of all four yeast B-family DNA polymerases. Loss of the [4Fe-4S] cofactor by cysteine ligand mutagenesis in Pol3 destabilized the CTD and abrogated interaction with the Pol31-Pol32 subunits. Reciprocally, overexpression of accessory subunits increased the amount of CTD-bound Fe-S cluster. This implies an important physiological role of the Fe-S cluster in polymerase complex stabilization. Further, we demonstrate that the Zn-binding CysA motif is required for PCNA-mediated Pol ? processivity. Together, our findings show that the function of eukaryotic replicative DNA polymerases crucially depends on different metallocenters for accessory subunit recruitment and for replisome stability. PMID:22119860
[Role of polymer complexes in the formation of biofilms by corrosive bacteria on steel surfaces].
Purish, L M; Asaulenko, L G; Abdulina, D R; Vasil'ev, V N; Iutinskaia, G A
The composition of exopolymer complexes (EPCs), synthesized by the monocultures Desulfovibrio sp. 10, Bacillus subtilis 36, and Pseudomonas aeruginosa 27 and by microbial associations involved in the corrosion of metal surfaces has been studied. An analysis of the monosaccharide composition of carbohydrate components, as well as the fatty acid composition of the lipid part of EPCs, was carried out by gas-liquid chromatography (GLC). It was found that bacteria in biofilms synthesized polymers; this process was dominated by glucose, while the growth of bacteria in a suspension was marked by a high rhamnose content. Hexouronic acids and hexosamine have been revealed as a part of B. subtilis 36 and P. aeruginosa 27 EPCs. Qualitative differences were revealed in the fatty acid composition ofexopolymers in biofilms and in a bacterial suspension. It was shown that the transition to a biofilm form of growth led to an increase in the unsaturation degree of fatty acids in the exopolymers of associative cultures. The results can be used to develop methods to control microbial corrosion of metal surfaces. PMID:22834300
Formation of complex natural flavours by biotransformation of apple pomace with basidiomycetes.
Bosse, Andrea K; Fraatz, Marco A; Zorn, Holger
Altogether 30 different basidiomycetes were grown submerged in liquid culture media using seven different by-products of the food industry as the only carbon source. Seven fungus/substrate combinations revealed interesting flavour profiles. Culture supernatants of Tyromyces chioneus grown on apple pomace were extracted, and the aroma compounds were analysed by gas chromatography-olfactometry (GC-O). Potent odorants were identified by aroma extract dilution analysis (AEDA), calculation of the odour activity values (OAV), and proven by confection of an aroma model. 3-Phenylpropanal, 3-phenyl-1-propanol, and benzyl alcohol were identified as potent aroma biotransformation products. Headspace solid-phase microextraction gas chromatography mass spectrometry (HS-SPME-GC-MS) experiments showed that 3-phenylpropanal, 3-phenyl-1-propanol, benzyl alcohol, methyl 3-phenylpropionate, methyl 2-phenylacetate, cinnamaldehyde and methyl cinnamate were produced during the cultivation period of eight days. By means of labelling experiments, (E)-cinnamic acid was identified as the precursor of 3-phenylpropanal and 3-phenyl-1-propanol. Basidiomycetes were able to biotransform food by-products to pleasant complex flavour mixtures. PMID:23871045
Ternary uranyl-citrate-surface complex formation on geothite gibbsite, and phylosilicate minerals
Redden, G.D.; Li, J.; Leckie, J.O. [Stanford Univ., CA (United States)
Liquid radioactive wastes that contain transuranic elements are often associated with complexing organic co-contaminants. Prediction of radionuclide transpose in contaminated groundwater will require accounting for the effect of both organic co-solutes and naturally occurring compounds. A study has been conducted on the adsorption of uranyl ion (UO{sub 2}{sup 2+}) on goethite, gibbsite, and phylosilicate minerals in the presence of varying concentrations of citric acid. Adsorption of either solute separately as functions of pH yield sorption curves that are generally typical for cations and anions with differences in features reflecting differences in properties of the surface functional groups. At equimolar concentrations of uranyl and citrate little effect on the sorption of either solute is observed. However, at higher citrate concentrations uranyl sorption dramatically increases with nearly complete uranyl sorption even at relatively low pH values. A stable bridging structure involving uranyl and citrate is implied. These results have significant relevance to radionuclide transport modeling where soluble chelators may increase rather than decrease sorption of uranyl.
Soft matter strategies for controlling food texture: formation of hydrogel particles by biopolymer complex coacervation
NASA Astrophysics Data System (ADS)
Wu, Bi-cheng; Degner, Brian; McClements, David Julian
Soft matter physics principles can be used to address important problems in the food industry. Starch granules are widely used in foods to create desirable textural attributes, but high levels of digestible starch may pose a risk of diabetes. Consequently, there is a need to find healthier replacements for starch granules. The objective of this research was to create hydrogel particles from protein and dietary fiber with similar dimensions and functional attributes as starch granules. Hydrogel particles were formed by mixing gelatin (0.5?wt%) with pectin (0 to 0.2?wt%) at pH values above the isoelectric point of the gelatin (pH 9, 30?°C). When the pH was adjusted to pH 5, the biopolymer mixture spontaneously formed micron-sized particles due to electrostatic attraction of cationic gelatin with anionic pectin through complex coacervation. Differential interference contrast (DIC) microscopy showed that the hydrogel particles were translucent and spheroid, and that their dimensions were determined by pectin concentration. At 0.01?wt% pectin, hydrogel particles with similar dimensions to swollen starch granules (D3,2 ? 23?µm) were formed. The resulting hydrogel suspensions had similar appearances to starch pastes and could be made to have similar textural attributes (yield stress and shear viscosity) by adjusting the effective hydrogel particle concentration. These hydrogel particles may therefore be used to improve the texture of reduced-calorie foods and thereby help tackle obesity and diabetes.
Spectrophotometric determination of ?-adrenergic antagonists drugs via ion-pair complex formation using MO and EBT
NASA Astrophysics Data System (ADS)
El-Didamony, A. M.; Shehata, A. M.
Two simple, rapid and sensitive spectrophotometric methods have been proposed for the assay of bisoprolol fumarate (BSF), propranolol hydrochloride (PRH), and timolol maleate (TIM) either in bulk or in pharmaceutical formulations. The methods are based on the reaction of the selected drugs with methyl orange (MO) and eriochrome black T in acidic buffers, after extracting in dichloromethane and measured quantitatively with maximum absorption at 428 and 518 nm for MO and EBT, respectively. The analytical parameters and their effects on the reported systems are investigated. The extracts are intensely colored and very stable at room temperature. The calibration graphs were linear over the concentration range of 0.8-6.4, 0.4-3.6, 0.8-5.6 ?g/mL for BSF, PRH, and TIM, respectively, with MO and 0.8-6.4, 0.4-3.2, and 0.8-8.0 ?g/mL for BSF, PRH, and TIM, respectively, with EBT. The stoichiometry of the complexes was found to be 1 : 1 in all cases. The proposed methods were successfully extended to pharmaceutical preparations. Excipients used as additive in commercial formulations did not interfere in the analysis. The proposed methods can be recommended for quality control and routine analysis where time, cost effectiveness and high specificity of analytical technique are of great importance.
Formation of rhyolite at the Okataina Volcanic Complex, New Zealand: New insights from analysis of quartz clusters in plutonic lithics
NASA Astrophysics Data System (ADS)
Graeter, K.; Beane, R. J.; Deering, C. D.; Gravley, D. M.; Bachmann, O.
Granitoid lithic clasts from the 0.7 ka Kaharoa eruption at the Tarawera volcano (Okataina Volcanic Complex, Taupo Volcanic Zone, New Zealand) - the world's most productive region where rhyolite volcanism is currently active - give insight into the processes of rhyolite formation. The plutonic lithic clasts of the Kaharoa eruption consist of (1) quartz phenocrysts, which are often grouped into clusters of two to eight quartz grains, (2) plagioclase phenocrysts with anorthitic cores and albitic rims, and (3) interstitial potassium feldspar. Quartz orientations obtained through electron backscatter diffraction (EBSD) methods show that 78% of the 82 analyzed clusters have at least one pair of quartz grains with matched dipyramidal faces that are in either parallel or Esterel twin orientation. Variations in cathodoluminescence (CL) zoning patterns of the quartz suggest that quartz clusters in the plutonic lithics formed after initial crystal growth and that many quartz crystals were subject to one or more resorption events. Thus, individual quartz crystals with different magmatic histories came together into preferred orientations to form clusters; this process is indicative of oriented quartz synneusis and suggests a history of crystal accumulation. The quartz clusters are interpreted to have formed as part of a crystal cumulate mush within a shallow magma chamber where quartz crystals rotated into contact along their dipyramidal faces during hindered settling and/or compaction. Therefore, the preservation of oriented quartz clusters from the Kaharoa plutonic lithics provides direct evidence for synchronous, shallow pluton formation from a cumulate mush during active volcanism. This result is consistent with a model whereby melt-rich, high-silica rhyolite formation occurs via interstitial melt extraction from a low-silica rhyolite mush in the shallow crust.
Characterisation of sub-micron particle number concentrations and formation events in the western Bushveld Igeneous Complex, South Africa
NASA Astrophysics Data System (ADS)
Hirsikko, A.; Vakkari, V.; Tiitta, P.; Manninen, H. E.; Gagné, S.; Laakso, H.; Kulmala, M.; Mirme, A.; Mirme, S.; Mabaso, D.; Beukes, J. P.; Laakso, L.
South Africa holds significant mineral resources, with a substantial fraction of these reserves occurring in a large geological structure termed the Bushveld Igeneous Complex (BIC). The majority of the world's platinum group metals (PGMs) and chromium originate from the BIC. Considering the importance of PGMs in the manufacturing of automotive catalytic converters, as well as the relatively poor current state of air quality and the general lack of atmospheric research in the BIC, atmospheric related research in this geographical area is of local (South African) and of international interest. The western limb of the BIC is the most exploited, with at least eleven pyrometallurgical smelters occurring within a 55 km radius. Due to the lure of employment in the industrialised BIC, the area is populated by informal, semi-formal and formal residential developments. In order to investigate the characteristics and processes affecting sub-micron particle number concentrations and formation events, air ion and aerosol particle size distribution and concentration measurements were conducted for over two years at Marikana in the heart of the western BIC. Our results indicated that high amounts of Aitken and accumulation mode particles originated from domestic burning for heating and cooking in the morning and evening, while during daytime SO2-based nucleation (from industrial emissions) was the most probable source for large number concentrations of nucleation and Aitken mode particles. Nucleation event day frequency was extremely high, i.e. 86% of the analysed days, which to the knowledge of the authors is the highest frequency ever reported. Secondary particle formation was influenced both by local pollution sources and regional ambient conditions. Therefore, our observation of the annual cycle and magnitude of the particle formation and growth rates during nucleation events were similar to the results from a semi-clean savannah site in South Africa.
Early diagenesis of a phylloid algal-mound complex, Laborcita Formation, southeastern New Mexico
Ward, W.B.; Meyers, W.J.; Goldstein, R.
Marine carbonate cementation was the initial stage in the paragenesis of phylloid algal mounds in the Laborcita Formation (Wolfcampian), Sacramento Mountains, New Mexico, and the cements are almost identical to those in Holocene coral reefs of Belize. These cements include relics of botryoids and crusts of needle crystals, in part defined by inclusion patterns and luminescent ghosts in mosaic calcite. Individual needle crystals are pseudohexagonal in cross section and range from less than 1 to 30 ..mu..m wide. These nonluminescent early cements line cavity walls, coat phylloid-algal blades and stromatolites, and are interlayered with marine sediment. Early cements also include bladed, fibrous, and rare radiaxial fibrous calcites, which are microdolomite-rich. They have a proximal nonluminescent zone, a central bright-luminescent zone, and a distal blotchy, moderate-luminescent zone. The bright zone may be time equivalent to bright-luminescent micritic coatings on botryoids and grains. Botryoids are encrusted by isopachous bladed cement, some of which has prismatic overgrowths containing an early inclusion-rich zone. This initial cementation was followed closely by: (1) dissolution of algal blades and mollusks, (2) in-situ brecciation, and (3) cementation by blocky calcite. Botryoidal and acicular cements are interpreted as originally marine aragonite precipitates, based on morphology, occurrence, susceptibility to diagenesis, and similarity to Holocene reef cements. The same criteria, plus the microdolomite inclusions, indicate that the bladed, fibrous, and radiaxial cements had a marine Mg-calcite precursor. This assemblage followed by prismatic overgrowths, dissolution, and blocky-calcite cementation indicates an evolution from marine to freshwater diagenesis.
Cdc42-dependent formation of the ZO-1/MRCK? complex at the leading edge controls cell migration
Huo, Lin; Wen, Wenyu; Wang, Rui; Kam, Chuen; Xia, Jun; Feng, Wei; Zhang, Mingjie
Zonula occludens (ZO)-1 is a multi-domain scaffold protein known to have critical roles in the establishment of cell–cell adhesions and the maintenance of stable tissue structures through the targeting, anchoring, and clustering of transmembrane adhesion molecules and cytoskeletal proteins. Here, we report that ZO-1 directly binds to MRCK?, a Cdc42 effector kinase that modulates cell protrusion and migration, at the leading edge of migrating cells. Structural studies reveal that the binding of a ? hairpin from GRINL1A converts ZO-1 ZU5 into a complete ZU5-fold. A similar interaction mode is likely to occur between ZO-1 ZU5 and MRCK?. The interaction between ZO-1 and MRCK? requires the kinase to be primed by Cdc42 due to the closed conformation of the kinase. Formation of the ZO-1/MRCK? complex enriches the kinase at the lamellae of migrating cells. Disruption of the ZO-1/MRCK? complex inhibits MRCK?-mediated cell migration. These results demonstrate that ZO-1, a classical scaffold protein with accepted roles in maintaining cell–cell adhesions in stable tissues, also has an active role in cell migration during processes such as tissue development and remodelling. PMID:21240187
Nucleoprotein of influenza B virus binds to its type A counterpart and disrupts influenza A viral polymerase complex formation
Jaru-ampornpan, Peera, E-mail: email@example.com; Narkpuk, Jaraspim; Wanitchang, Asawin; Jongkaewwattana, Anan, E-mail: email@example.com
Highlights: •FluB nucleoprotein (BNP) can bind to FluA nucleoprotein (ANP). •BNP–ANP interaction inhibits FluA polymerase activity. •BNP binding prevents ANP from forming a functional FluA polymerase complex. •Nuclear localization of BNP is necessary for FluA polymerase inhibition. •Viral RNA is not required for the BNP–ANP interaction. -- Abstract: Upon co-infection with influenza B virus (FluB), influenza A virus (FluA) replication is substantially impaired. Previously, we have shown that the nucleoprotein of FluB (BNP) can inhibit FluA polymerase machinery, retarding the growth of FluA. However, the molecular mechanism underlying this inhibitory action awaited further investigation. Here, we provide evidence that BNP hinders the proper formation of FluA polymerase complex by competitively binding to the nucleoprotein of FluA. To exert this inhibitory effect, BNP must be localized in the nucleus. The interaction does not require the presence of the viral RNA but needs an intact BNP RNA-binding motif. The results highlight the novel role of BNP as an anti-influenza A viral agent and provide insights into the mechanism of intertypic interference.
A Loss-Of-Function Analysis Reveals That Endogenous Rem2 Promotes Functional Glutamatergic Synapse Formation and Restricts Dendritic Complexity
Moore, Anna R.; Ghiretti, Amy E.; Paradis, Suzanne
Rem2 is a member of the RGK family of small Ras-like GTPases whose expression and function is regulated by neuronal activity in the brain. A number of questions still remain as to the endogenous functions of Rem2 in neurons. RNAi-mediated Rem2 knockdown leads to an increase in dendritic complexity and a decrease in functional excitatory synapses, though a recent report challenged the specificity of Rem2-targeted RNAi reagents. In addition, overexpression in a number of cell types has shown that Rem2 can inhibit voltage-gated calcium channel (VGCC) function, while studies employing RNAi-mediated knockdown of Rem2 have failed to observe a corresponding enhancement of VGCC function. To further investigate these discrepancies and determine the endogenous function of Rem2, we took a comprehensive, loss-of-function approach utilizing two independent, validated Rem2-targeted shRNAs to analyze Rem2 function. We sought to investigate the consequence of endogenous Rem2 knockdown by focusing on the three reported functions of Rem2 in neurons: regulation of synapse formation, dendritic morphology, and voltage-gated calcium channels. We conclude that endogenous Rem2 is a positive regulator of functional, excitatory synapse development and a negative regulator of dendritic complexity. In addition, while we are unable to reach a definitive conclusion as to whether the regulation of VGCCs is an endogenous function of Rem2, our study reports important data regarding RNAi reagents for use in future investigation of this issue. PMID:23991227
Nice to know you: Positive emotions, self–other overlap, and complex understanding in the formation of a new relationship
Based on Fredrickson's ((1998). What good are positive emotions? Review of General Psychology, 2, 300–319.; (2001). The role of positive emotions in positive psychology: The broaden-and-build theory of positive emotions. American Psychologist, 56, 218–226) broaden-and-build theory and Aron and Aron's ((1986). Love as expansion of the self: Understanding attraction and satisfaction. New York: Hemisphere) self-expansion theory, it was hypothesized that positive emotions broaden people's feelings of self–other overlap in the beginning of a new relationship. In a prospective study of first-year college students, we found that, after 1 week in college, positive emotions predicted increased self–other overlap with new roommates, which in turn predicted a more complex understanding of the roommate. In addition, participants who experienced a high ratio of positive to negative emotions throughout the first month of college reported a greater increase in self–other overlap and complex understanding than participants with a low positivity ratio. Implications for the role of positive emotions in the formation of new relationships are discussed. PMID:21691460
High glucose levels induce inhibition of Na,K-ATPase via stimulation of aldose reductase, formation of microtubules and formation of an acetylated tubulin/Na,K-ATPase complex.
Rivelli, Juan F; Amaiden, Marina R; Monesterolo, Noelia E; Previtali, Gabriela; Santander, Verónica S; Fernandez, Adriana; Arce, Carlos A; Casale, Cesar H
Our previous studies demonstrated that acetylated tubulin forms a complex with Na(+),K(+)-ATPase and thereby inhibits its enzyme activity in cultured COS and CAD cells. The enzyme activity was restored by treatment of cells with l-glutamate, which caused dissociation of the acetylated tubulin/Na(+),K(+)-ATPase complex. Addition of glucose, but not elimination of glutamate, led to re-formation of the complex and inhibition of the Na(+),K(+)-ATPase activity. The purpose of the present study was to elucidate the mechanism underlying this effect of glucose. We found that exposure of cells to high glucose concentrations induced: (a) microtubule formation; (b) activation of aldose reductase by the microtubules; (c) association of tubulin with membrane; (d) formation of the acetylated tubulin/Na(+),K(+)-ATPase complex and consequent inhibition of enzyme activity. Exposure of cells to sorbitol caused similar effects. Studies on erythrocytes from diabetic patients and on tissues containing insulin-insensitive glucose transporters gave similar results. Na(+),K(+)-ATPase activity was >50% lower and membrane-associated tubulin content was >200% higher in erythrocyte membranes from diabetic patients as compared with normal subjects. Immunoprecipitation analysis showed that acetylated tubulin was a constituent of a complex with Na(+),K(+)-ATPase in erythrocyte membranes from diabetic patients. Based on these findings, we propose a mechanism whereby glucose triggers a synergistic effect of tubulin and sorbitol, leading to activation of aldose reductase, microtubule formation, and consequent Na(+),K(+)-ATPase inhibition. PMID:22565168
Reaction of dimethyl ether with hydroxyl radicals: kinetic isotope effect and prereactive complex formation.
Bänsch, Cornelie; Kiecherer, Johannes; Szöri, Milan; Olzmann, Matthias
The kinetic isotope effect of the reactions OH + CH3OCH3 (DME) and OH + CD3OCD3 (DME-d6) was experimentally and theoretically studied. Experiments were carried out in a slow-flow reactor at pressures between 5 and 21 bar (helium as bath gas) with production of OH by laser flash photolysis of HNO3 and time-resolved detection of OH by laser-induced fluorescence. The temperature dependences of the rate coefficients obtained can be described by the following modified Arrhenius expressions: k(OH+DME) = (4.5 ± 1.3) × 10(-16) (T/K)(1.48) exp(66.6 K/T) cm(3) s(-1) (T = 292-650 K, P = 5.9-20.9 bar) and k(OH+DME-d6) = (7.3 ± 2.2) × 10(-23) (T/K)(3.57) exp(759.8 K/T) cm(3) s(-1) (T = 387-554 K, P = 13.0-20.4 bar). A pressure dependence of the rate coefficients was not observed. The agreement of our experimental results for k(OH+DME) with values from other authors is very good, and from a fit to all available literature data, we derived the following modified Arrhenius expression, which reproduces the values obtained in the temperature range T = 230-1500 K at pressures between 30 mbar and 21 bar to better than within ±20%: k(OH+DME) = 8.45 × 10(-18) (T/K)(2.07) exp(262.2 K/T) cm(3) s(-1). For k(OH+DME-d6), to the best of our knowledge, this is the first experimental study. For the analysis of the reaction pathway and the kinetic isotope effect, potential energy diagrams were calculated by using three different quantum chemical methods: (I) CCSD(T)/cc-pV(T,Q)Z//MP2/6-311G(d,p), (II) CCSD(T)/cc-pV(T,Q)Z//CCSD/cc-pVDZ, and (III) CBS-QB3. In all three cases, the reaction is predicted to proceed via a prereaction OH-ether complex with subsequent intramolecular hydrogen abstraction and dissociation to give the methoxymethyl radical and water. Overall rate coefficients were calculated by assuming a thermal equilibrium between the reactants and the prereaction complex and by calculating the rate coefficients of the hydrogen abstraction step from canonical transition state theory. The results based on the molecular data from methods (I) and (II) showed a satisfactory agreement with the experimental values, which indicates that the pre-equilibrium assumption is reasonable under our conditions. In the case of method (III), the isotope effect was significantly underpredicted. The reason for this discrepancy was identified in a fundamentally differing reaction coordinate. Obviously, the B3LYP functional applied in method (III) for geometry and frequency calculations is inadequate to describe such systems, which is in line with earlier findings of other authors. PMID:23914942
Streptococcus pneumoniae phosphoglycerate kinase is a novel complement inhibitor affecting the membrane attack complex formation.
Blom, Anna M; Bergmann, Simone; Fulde, Marcus; Riesbeck, Kristian; Agarwal, Vaibhav
The Gram-positive bacterium Streptococcus pneumoniae is a major human pathogen that causes infections ranging from acute otitis media to life-threatening invasive disease. Pneumococci have evolved several strategies to circumvent the host immune response, in particular the complement attack. The pneumococcal glycolytic enzyme phosphoglycerate kinase (PGK) is both secreted and bound to the bacterial surface and simultaneously binds plasminogen and its tissue plasminogen activator tPA. In the present study we demonstrate that PGK has an additional role in modulating the complement attack. PGK interacted with the membrane attack complex (MAC) components C5, C7, and C9, thereby blocking the assembly and membrane insertion of MAC resulting in significant inhibition of the hemolytic activity of human serum. Recombinant PGK interacted in a dose-dependent manner with these terminal pathway proteins, and the interactions were ionic in nature. In addition, PGK inhibited C9 polymerization both in the fluid phase and on the surface of sheep erythrocytes. Interestingly, PGK bound several MAC proteins simultaneously. Although C5 and C7 had partially overlapping binding sites on PGK, C9 did not compete with either one for PGK binding. Moreover, PGK significantly inhibited MAC deposition via both the classical and alternative pathway at the pneumococcal surface. Additionally, upon activation plasmin(ogen) bound to PGK cleaved the central complement protein C3b thereby further modifying the complement attack. In conclusion, our data demonstrate for the first time to our knowledge a novel pneumococcal inhibitor of the terminal complement cascade aiding complement evasion by this important pathogen. PMID:25281746
Eco-Materials Processing of Magnesium Hydroxide Recovered from Seawater for Protein Complex Formation
NASA Astrophysics Data System (ADS)
Yoon, H.; Yoon, C.; Chung, K.
The recovery of valuable elements from seawater and their application had garnered considerable attention as a sustainable resources and a maintainable green technology not only for scientific interest but for economic purposes. Now days along with U, Li, B, Sr, and Mg earth elements also has gains great attention for their safe supplies through mining or recycling process. We have been developed recovery process of Mg from seawater and seawater bitterns for many years. The separation processes applied for recovery of magnesium were precipitation and separation with using CaOH, NaOH as those for the precipitation inducing chemicals. For each step the resulting precipitates were carefully examined by x-ray diffraction method along with chemical analysis for Ca, K, Na, and Mg contents along with other minor impurities including toxic elements like Hg, As and U. We achieved high purity in magnesium hydroxide precipitate even higher than 99.9%. Impurity controlled precipitation, and removing elements of harming was accomplished by the application of ion exchange columns along with cartridge for removing cations. Testing the reliability and the analytical techniques achieved had become a major interest and achieving low-level detection limits is requested before launching the commercial pilot plant. The resulting high purity magnesium hydroxide was tested for forming magnesium protein complexes for the eco-materials processing. In order to overcome low reaction yield, temperature controlled vessel was used throughout. Final product of magnesium and protein was examined by ICP-AES and ICP-MS for the trace and major ions analysis. Acknowledgements: This research was supported by a grant from the Development of Technology for Extraction of Resources Dissolved in Sea Water Program funded by Ministry of Land Transport and Maritime Affairs in Korean Government (2009).
Reversible formation of binuclear complexes between pyridine-2-carboxylato(tetraethylenepentamine)cobalt(III) and nickel(II)\\/cobalt(II) in aqueous solution. Anomalous behaviour in the dissociation of binuclear complexes
Nigamananda Das
The kinetics of the reversible formation of binuclear species between M(OH2)62+ (M = NiII and CoII) and oxygen-bonded (tetren)Co(pycH)3+ (tetren = tetraethylenepentamine, pycH = N-protonated pyridine-2-carboxylate) have been investigated by stopped-flow spectrophotometry at 25°C, I = 0.3 mol dm-3. Both the protonated (pyridine-N) and deprotonated forms of the CoIII complex were involved in the formation of the binuclear complex (tetren)Co(pyc)Co4+,
Modeling Exsolution (and Perthite Formation) as an Example of Complex-System Behavior
NSDL National Science Digital Library
David Mogk
Show Caption Hide This diagram shows the relationship of Gibbs Free Energy to composition. In this diagram there are two minima represented for free energy which is achieved by unmixing of two distinct phases each with definite composition. The dashed line, which is tangential to the two minima in the free energy curves, gives the composition of the coexisting minerals at a specific temperature. From: Klein, C., and Dutrow, B., Manual of Mineral Science, 23rd ed., J. Wiley and Sons. Used with permission. The phenomenon of solid solution is common in many rock-forming minerals. At high temperatures, thermal vibrations permit accomodation of ions with size differences on the order of 15-30%. However, as physical conditions change, ions no longer fit into similar sites which creates internal (lattice) strain energy. Consequently, the mineral composition must adjust to relieve this strain energy and minimize the Gibbs Free Energy of the system. One possible response of the system is for elements in a crystal to move from one chemical site to another via intracrystalline diffusion. This results in segregated domains that are enriched in one element or another--this is a process called exsolution. A good example of this process can be seen in the alkali feldspar mineral group. At high temperature the mineral anorthoclase (K,Na)AlSi3O8 shows complete solid solution, i.e. there is a random distribution of K and Na in the alkali sites of the crystal. Upon cooling, Na and K segregate into more ordered domains creating areas that are rich in albite NaAl Si3O8 and microcline KAlSi3O8(see Figure 1). The purpose of this exercise is to provide a number of activities to demonstrate how exsolution works and to demonstrate complex-system behavior in this relatively common natural phenomenon. Part I: Images of naturally occurring perthite. The following images show minerals that have undergone exsolution at different scales. The image on the top left shows exsolution as viewed with a Transmission Electron Microscope (TEM; field of view is 10 microns). The image on the top right is a photomicrograph of exsolution in microcline as seen in thin section (cross-polarized light, field of view is 2 mm). The picture on the bottom left is a hand sample of perthitic microcline as seen in hand sample (field of view is 10 cm). The picture on the bottom right is a picture of plagioclase feldspar showing the "schiller" effect. This is caused by sub-microscopic unmixing of two distinct plagioclase phases in the compositional range of labradorite (An50 - An70) which results in the beautiful play of colors seen in this photo; (field of view of 20 centimeters). This series of pictures is a good example of scale invariance of this physical phenomenon. Examine perthite textures from hand samples and thin sections from your own mineralogy collection. We can easily envision unmixing of two immiscible fluids--for example oil and vinegar salad dressing. The same thing happens when we unmix (i.e. exsolve) solid phases--the process just takes a bit longer as atoms have to migrate in the crystal lattice by intracrystalline diffusion! How can such a common feature as perthite be understood in terms of complex-system behavior? Exsolution observed on a sub-microscopic scale in this TEM picture; this microstructure shows unmixing of labradorite in very fine essentially parallel lamellae. From Champness, P.E., and G.W Lorimer, 1976. Exsolution in silicates. Chapter 4.1 in Electron Microscopy in Mineralogy. H.R. Wenk, ed. Springer-Verlag, New York. Field of view is 10 microns. Perthite observed in thin section. Field of view is 2 mm. Perthite observed in hand sample. Field of View is 10 cm. Unmixing of parallel lamellae, as observed in a hand specimen of labradorite from Madagascar. These lamellae act as diffraction grating for white light, producing spectral colors known as labradorescence or the "schiller effect"; the field of view is 20 cm. Photo by B. Dutrow; used by permission.] Part II: Exsolution Puzzle Exercise. This exercise is done in groups of 2-3 students. Coi
On the formation and structure of rare-earth element complexes in aqueous solutions under hydrothermal conditions with new data on gadolinium aqua and chloro complexes
Mayanovic, Robert A.; Anderson, Alan J.; Bassett, William A.; Chou, I-Ming (SMSU); (Cornell); (SFX); (USGS)
Synchrotron X-ray spectroscopy experiments were made on the Gd(III) aqua and chloro complexes in low pH aqueous solutions at temperatures ranging from 25 to 500 C and at pressures up to 480 MPa using a hydrothermal diamond anvil cell. Analysis of fluorescence Gd L{sub 3}-edge X-ray absorption fine structure (XAFS) spectra measured from a 0.006m Gd/0.16m HNO{sub 3} aqueous solution at temperatures up to 500 C and at pressures up to 260 MPa shows that the Gd-O distance of the Gd{sup 3+} aqua ion decreases steadily at a rate of {approx} 0.007 {angstrom}/100 C whereas the number of coordinated H{sub 2}O molecules decreases from 9.0 {+-} 0.5 to 7.0 {+-} 0.4. The loss of water molecules in the Gd{sup 3+} aqua ion inner hydration shell over this temperature range (a 22% reduction) is smaller than exhibited by the Yb{sup 3+} aqua ion (42% reduction) indicating that the former is significantly more stable than the later. We conjecture that the anomalous enrichment of Gd reported from measurement of REE concentrations in ocean waters may be attributed to the enhanced stability of the Gd{sup 3+} aqua ion relative to other REEs. Gd L{sub 3}-edge XAFS measurements of 0.006m and 0.1m GdCl{sub 3} aqueous solutions at temperatures up to 500 C and pressures up to 480 MPa reveal that the onset of significant Gd{sup 3+}-Cl{sup -} association occurs around 300 C. Partially-hydrated stepwise inner-sphere complexes most likely of the type Gd(H{sub 2}O){sub {delta}-n}Cl{sub n}{sup +3-n} occur in the chloride solutions at higher temperatures, where {delta} {approx} 8 at 300 C decreasing slightly to an intermediate value between 7 and 8 upon approaching 500 C. This is the first direct evidence for the occurrence of partially-hydrated REE Gd (this study) and Yb [Mayanovic, R.A., Jayanetti, S., Anderson, A.J., Bassett, W.A., Chou, I-M., 2002a. The structure of Yb{sup 3+} aquo ion and chloro complexes in aqueous solutions at up to 500 C and 270 MPa. J. Phys. Chem. A 106, 6591-6599.] chloro complexes in hydrothermal solutions. The number of chlorides (n) of the partially-hydrated Gd(III) chloro complexes increases steadily with temperature from 0.4 {+-} 0.2 to 1.7 {+-} 0.3 in the 0.006m chloride solution and from 0.9 {+-} 0.7 to 1.8 {+-} 0.7 in the 0.1m GdCl3 aqueous solution in the 300-500 C range. Conversely, the number of H{sub 2}O ligands of Gd(H{sub 2}O){sub {delta}-n}Cl{sub n}{sup +3-n} complexes decreases steadily from 8.9 {+-} 0.4 to 5.8 {+-} 0.7 in the 0.006m GdCl{sub 3} aqueous solution and from 9.0 {+-} 0.5 to 5.3 {+-} 1.0 in the 0.1m GdCl{sub 3} aqueous solution at temperatures from 25 to 500 C. Analysis of our results shows that the chloride ions partially displace the inner-shell water molecules during Gd(III) complex formation under hydrothermal conditions. The Gd-OH{sub 2} bond of the partially-hydrated Gd(III) chloro complexes exhibits slightly smaller rates of length contraction ({approx} 0.005 {angstrom}/100 C) for both solutions. The structural aspects of chloride speciation of Gd(III) as measured from this study and of Yb(III) as measured from our previous experiments are consistent with the solubility of these and other REE in deep-sea hydrothermal fluids.
Ni-Catalyzed C-H Functionalization in the Formation of a Complex Heterocycle: Synthesis of the Potent JAK2 Inhibitor BMS-911543.
Fitzgerald, Monica A; Soltani, Omid; Wei, Carolyn; Skliar, Dimitri; Zheng, Bin; Li, Jun; Albrecht, Jacob; Schmidt, Michael; Mahoney, Michelle; Fox, Richard J; Tran, Kristy; Zhu, Keming; Eastgate, Martin D
BMS-911543 is a complex pyrrolopyridine investigated as a potential treatment for myeloproliferative disorders. The development of a short and efficient synthesis of this molecule is described. During the course of our studies, a Ni-mediated C-N bond formation was invented, which enabled the rapid construction of the highly substituted 2-aminopyridine core. The synthesis of this complex, nitrogen-rich heterocycle was accomplished in only eight steps starting from readily available materials. PMID:25848821
Complexity gradients in the Yilgarn Craton: Fundamental controls on crustal-scale fluid flow and the formation of world-class orogenic-gold deposits
P. F. Hodkiewicz; R. F. Weinberg; S. J. Gardoll; D. I. Groves
Fractal-dimension analysis is an effective means of quantifying complex map patterns of structures and lithological contacts, which are conduits for hydrothermal fluid flow during the formation of orogenic-gold deposits. In this study, fractal dimensions, calculated on a 10 km grid across a geologic map of the Yilgarn Craton of uniform data quality, highlight relationships between geologic complexity and the location and
Discovery of a strongly-interrelated gene network in corals under constant darkness by correlation analysis after wavelet transform on complex network model.
Liu, Longlong; Qu, Jieqiong; Zhou, Xilong; Liu, Xuefeng; Zhang, Zhaobao; Wang, Xumin; Liu, Tao; Liu, Guiming
Coral reefs occupy a relatively small portion of sea area, yet serve as a crucial source of biodiversity by establishing harmonious ecosystems with marine plants and animals. Previous researches mainly focused on screening several key genes induced by stress. Here we proposed a novel method--correlation analysis after wavelet transform of complex network model, to explore the effect of light on gene expression in the coral Acropora millepora based on microarray data. In this method, wavelet transform and the conception of complex network were adopted, and 50 key genes with large differences were finally captured, including both annotated genes and novel genes without accurate annotation. These results shed light on our understanding of coral's response toward light changes and the genome-wide interaction among genes under the control of biorhythm, and hence help us to better protect the coral reef ecosystems. Further studies are needed to explore how functional connections are related to structural connections, and how connectivity arises from the interactions within and between different systems. The method introduced in this study for analyzing microarray data will allow researchers to explore genome-wide interaction network with their own dataset and understand the relevant biological processes. PMID:24651851
Gauge-Dependent Cosmological "Constant"
Bahram Mashhoon; Paul S. Wesson
When the cosmological constant of spacetime is derived from the 5D induced-matter theory of gravity, we show that a simple gauge transformation changes it to a variable measure of the vacuum which is infinite at the big bang and decays to an astrophysically-acceptable value at late epochs. We outline implications of this for cosmology and galaxy formation.
Effects of cell culture media on the dynamic formation of protein-nanoparticle complexes and influence on the cellular response.
Maiorano, Gabriele; Sabella, Stefania; Sorce, Barbara; Brunetti, Virgilio; Malvindi, Maria Ada; Cingolani, Roberto; Pompa, Pier Paolo
The development of appropriate in vitro protocols to assess the potential toxicity of the ever expanding range of nanoparticles represents a challenging issue, because of the rapid changes of their intrinsic physicochemical properties (size, shape, reactivity, surface area, etc.) upon dispersion in biological fluids. Dynamic formation of protein coating around nanoparticles is a key molecular event, which may strongly impact the biological response in nanotoxicological tests. In this work, by using citrate-capped gold nanoparticles (AuNPs) of different sizes as a model, we show, by several spectroscopic techniques (dynamic light scattering, UV-visible, plasmon resonance light scattering), that proteins-NP interactions are differently mediated by two widely used cellular media (i.e., Dulbecco Modified Eagle's medium (DMEM) and Roswell Park Memorial Institute medium (RPMI), supplemented with fetal bovine serum). We found that, while DMEM elicits the formation of a large time-dependent protein corona, RPMI shows different dynamics with reduced protein coating. Characterization of these nanobioentities was also performed by sodium dodecyl sulfate polyacrylamide gel electrophoresis and mass spectroscopy, revealing that the average composition of protein corona does not reflect the relative abundance of serum proteins. To evaluate the biological impact of such hybrid bionanostructures, several comparative viability assays onto two cell lines (HeLa and U937) were carried out in the two media, in the presence of 15 nm AuNPs. We observed that proteins/NP complexes formed in RPMI are more abundantly internalized in cells as compared to DMEM, overall exerting higher cytotoxic effects. These results show that, beyond an in-depth NPs characterization before cellular experiments, a detailed understanding of the effects elicited by cell culture media on NPs is crucial for standardized nanotoxicology tests. PMID:21082814
Fixation of atmospheric carbon dioxide by ruthenium complexes bearing an NHC-based pincer ligand: formation of a methylcarbonato complex and its methylation.
Arikawa, Yasuhiro; Nakamura, Takuo; Ogushi, Shinji; Eguchi, Kazushige; Umakoshi, Keisuke
A methylcarbonato ruthenium complex was prepared by capture of CO2 from air using the (CNC)(bpy)Ru scaffold. The methylcarbonato complex was relatively inert to decarboxylation. Treatments with methylating reagents released dimethylcarbonate. PMID:25711491
Reversible carbon-carbon bond formation induced by oxidation and reduction at a redox-active cobalt complex.
Atienza, Crisita Carmen Hojilla; Milsmann, Carsten; Semproni, Scott P; Turner, Zoë R; Chirik, Paul J
The electronic structure of the diamagnetic pyridine imine enamide cobalt dinitrogen complex, ((iPr)PIEA)CoN2 ((iPr)PIEA = 2-(2,6-(i)Pr2-C6H3N?CMe)-6-(2,6-(i)Pr2-C6H3NC?CH2)C5H3N), was determined and is best described as a low-spin cobalt(II) complex antiferromagnetically coupled to an imine radical anion. Addition of potential radical sources such as NO, PhSSPh, or Ph3Cl resulted in C-C coupling at the enamide positions to form bimetallic cobalt compounds. Treatment with the smaller halocarbon, PhCH2Cl, again induced C-C coupling to form a bimetallic bis(imino)pyridine cobalt chloride product but also yielded a monomeric cobalt chloride product where the benzyl group added to the enamide carbon. Similar cooperative metal-ligand addition was observed upon treatment of ((iPr)PIEA)CoN2 with CH2?CHCH2Br, which resulted in allylation of the enamide carbon. Reduction of Coupled-((iPr)PDI)CoCl (Coupled-((iPr)PDI)CoCl = [2-(2,6-(i)Pr2-C6H3N?CMe)-C5H3N-6-(2,6-(i)Pr2-C6H3N?CCH2-)CoCl]2) with NaBEt3H led to quantitative formation of ((iPr)PIEA)CoN2, demonstrating the reversibility of the C-C bond forming reactions. The electronic structures of each of the bimetallic cobalt products were also elucidated by a combination of experimental and computational methods. PMID:23594241
Eocene and Miocene extension, meteoric fluid infiltration, and core complex formation in the Great Basin (Raft River Mountains, Utah)
NASA Astrophysics Data System (ADS)
Methner, Katharina; Mulch, Andreas; Teyssier, Christian; Wells, Michael L.; Cosca, Michael A.; Gottardi, Raphaël.; Gébelin, Aude; Chamberlain, C. Page
Metamorphic core complexes (MCCs) in the North American Cordillera reflect the effects of lithospheric extension and contribute to crustal adjustments both during and after a protracted subduction history along the Pacific plate margin. While the Miocene-to-recent history of most MCCs in the Great Basin, including the Raft River-Albion-Grouse Creek MCC, is well documented, early Cenozoic tectonic fabrics are commonly severely overprinted. We present stable isotope, geochronological (40Ar/39Ar), and microstructural data from the Raft River detachment shear zone. Hydrogen isotope ratios of syntectonic white mica (?2Hms) from mylonitic quartzite within the shear zone are very low (-90‰ to -154‰, Vienna SMOW) and result from multiphase synkinematic interaction with surface-derived fluids. 40Ar/39Ar geochronology reveals Eocene (re)crystallization of white mica with ?2Hms ? -154‰ in quartzite mylonite of the western segment of the detachment system. These ?2Hms values are distinctively lower than in localities farther east (?2Hms ? -125‰), where 40Ar/39Ar geochronological data indicate Miocene (18-15 Ma) extensional shearing and mylonitic fabric formation. These data indicate that very low ?2H surface-derived fluids penetrated the brittle-ductile transition as early as the mid-Eocene during a first phase of exhumation along a detachment rooted to the east. In the eastern part of the core complex, prominent top-to-the-east ductile shearing, mid-Miocene 40Ar/39Ar ages, and higher ?2H values of recrystallized white mica, indicate Miocene structural and isotopic overprinting of Eocene fabrics.
TGF-{beta} signals the formation of a unique NF1/Smad4-dependent transcription repressor-complex in human diploid fibroblasts
Luciakova, Katarina, E-mail: email@example.com [Cancer Research Institute, Slovak Academy of Sciences, Bratislava, Vlarska 7, 833 91 Bratislava (Slovakia)] [Cancer Research Institute, Slovak Academy of Sciences, Bratislava, Vlarska 7, 833 91 Bratislava (Slovakia); Kollarovic, Gabriel; Kretova, Miroslava; Sabova, Ludmila [Cancer Research Institute, Slovak Academy of Sciences, Bratislava, Vlarska 7, 833 91 Bratislava (Slovakia)] [Cancer Research Institute, Slovak Academy of Sciences, Bratislava, Vlarska 7, 833 91 Bratislava (Slovakia); Nelson, B. Dean [Department of Biochemistry and Biophysics, Arrhenius Laboratories, Stockholm University, S-106 91 Stockholm (Sweden)] [Department of Biochemistry and Biophysics, Arrhenius Laboratories, Stockholm University, S-106 91 Stockholm (Sweden)
Highlights: {yields} TGF-{beta} induces the formation of unique nuclear NF1/Smad4 complexes that repress expression of the ANT-2 gene. {yields} Repression is mediated through an NF1-dependent repressor element in the promoter. {yields} The formation of NF1/Smad4 complexes and the repression of ANT2 are prevented by inhibitors of p38 kinase and TGF-{beta} RI. {yields} NF1/Smad complexes implicate novel role for NF1 and Smad proteins in the regulation of growth. -- Abstract: We earlier reported the formation of a unique nuclear NF1/Smad complex in serum-restricted fibroblasts that acts as an NF1-dependent repressor of the human adenine nucleotide translocase-2 gene (ANT2) [K. Luciakova, G. Kollarovic, P. Barath, B.D. Nelson, Growth-dependent repression of human adenine nucleotide translocator-2 (ANT2) transcription: evidence for the participation of Smad and Sp family proteins in the NF1-dependent repressor complex, Biochem. J. 412 (2008) 123-130]. In the present study, we show that TGF-{beta}, like serum-restriction: (a) induces the formation of NF1/Smad repressor complexes, (b) increases binding of the complexes to the repressor elements (Go elements) in the ANT2 promoter, and (c) inhibits ANT2 expression. Repression of ANT2 by TGF-{beta} is eliminated by mutating the NF1 binding sites in the Go repressor elements. All of the above responses to TGF-{beta} are prevented by inhibitors of TGF-{beta} RI and MAPK p38. These inhibitors also prevent NF1/Smad4 repressor complex formation and repression of ANT2 expression in serum-restricted cells, suggesting that similar signaling pathways are initiated by TGF-{beta} and serum-restriction. The present finding that NF1/Smad4 repressor complexes are formed through TGF-{beta} signaling pathways suggests a new, but much broader, role for these complexes in the initiation or maintenance of the growth-inhibited state.
Complex Pattern Formation in the Polyacrylamide-Methylene Blue-Oxygen Reaction Oliver Steinbock,*, Eric Kasper, and Stefan C. Mu1ller
Steinbock, Oliver
-MBO) reaction shows self-organization that gives rise to various patterns such as hexagons, stripes, and zigzagComplex Pattern Formation in the Polyacrylamide-Methylene Blue-Oxygen Reaction Oliver Steinbock from either white-eye patterns or hexagons. This transition occurs rapidly along propagating fronts
Nd isotopes demonstrate the role of contamination in the formation of coexisting quartz and nepheline syenites at the Abu Khruq Complex, Egypt
J. D. Landoll; K. A. Foland; C. M. B. Henderson
The petrogenesis of Abu Khruq, an 89 Ma alkaline ring complex of eastern Egypt which is composed of alkali gabbros and both silica over- and undersaturated syenites, has been investigated. Major and trace element relationships and Nd and Sr isotope data are consistent with formation of the gabbros from an alkaline mafic magma that experienced extensive fractionation, and all syenites
Non-covalent interactions of nitrous oxide with aromatic compounds: Spectroscopic and computational evidence for the formation of 1:1 complexes
NASA Astrophysics Data System (ADS)
Cao, Qian; Gor, Gennady Y.; Krogh-Jespersen, Karsten; Khriachtchev, Leonid
We present the first study of intermolecular interactions between nitrous oxide (N2O) and three representative aromatic compounds (ACs): phenol, cresol, and toluene. The infrared spectroscopic experiments were performed in a Ne matrix and were supported by high-level quantum chemical calculations. Comparisons of the calculated and experimental vibrational spectra provide direct identification and characterization of the 1:1 N2O-AC complexes. Our results show that N2O is capable of forming non-covalently bonded complexes with ACs. Complex formation is dominated by dispersion forces, and the interaction energies are relatively low (about -3 kcal mol-1); however, the complexes are clearly detected by frequency shifts of the characteristic bands. These results suggest that N2O can be bound to the amino-acid residues tyrosine or phenylalanine in the form of ? complexes.
Self-templated formation of uniform NiCo2O4 hollow spheres with complex interior structures for lithium-ion batteries and supercapacitors.
Shen, Laifa; Yu, Le; Yu, Xin-Yao; Zhang, Xiaogang; Lou, Xiong Wen David
Despite the significant advancement in preparing metal oxide hollow structures, most approaches rely on template-based multistep procedures for tailoring the interior structure. In this work, we develop a new generally applicable strategy toward the synthesis of mixed-metal-oxide complex hollow spheres. Starting with metal glycerate solid spheres, we show that subsequent thermal annealing in air leads to the formation of complex hollow spheres of the resulting metal oxide. We demonstrate the concept by synthesizing highly uniform NiCo2O4 hollow spheres with a complex interior structure. With the small primary building nanoparticles, high structural integrity, complex interior architectures, and enlarged surface area, these unique NiCo2O4 hollow spheres exhibit superior electrochemical performances as advanced electrode materials for both lithium-ion batteries and supercapacitors. This approach can be an efficient self-templated strategy for the preparation of mixed-metal-oxide hollow spheres with complex interior structures and functionalities. PMID:25522266