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INVESTIGATION OF INTERACTION BETWEEN L-HISTIDINE AND HETEROCYCLIC SUBSTANCES IN AQUEOUS SOLUTIONS BY UV SPECTROSCOPY

Drug – macromolecular interactions are an important phenomenon in multicomponents physiological media, such as blood, membranes, intra- and extracellular fluids, etc. The investigation of the mechanisms and driving forces for the molecular processes of the complexes formation, drug transport, and their delivery to target-cells is one of the priority tasks of chemistry, biology and pharmacology. It is imperative that one first investigate the properties of model compounds of macromolecules in an aqueous medium before beginning studies of the more complex systems. The features of their behavior essentially determine the biological activity of macromolecules. One of the well recognized approaches to the study of molecular interactions in fluids is the use of spectroscopic methods. As part of the longer term objective to investigate different aspects of interaction processes between model substances of protein and drug precursor, we report the results of spectroscopic investigation of aqueous solutions containing heterocyclic compounds – L-hystidine, nicotinic acid and uracil at fixed pH value. The electronic absorption spectrums of L-histidine were obtained for aqueous solutions with nicotinic acid and uracil at pH = 7.3 and T=296 K by UV spectroscopy. The spectral characteristics of the interaction between L-histidine and nicotinic acid or uracil were determined. The binding constants and the stoichiometry of the complexes were calculated on the basis of the saturation curves. The calculation of the equilibrium mixture of ionic forms of the studied amino acid as a function of the pH of the medium was carried out according to the computer program RRSU. The forms of reagents existence in an aqueous solution with pH = 7.3 have been determined. The specific features of the interactions of histidine with nicotinic acid and uracil were founded. It was shown that the interaction of histidine with uracil leads to the somewhat more stable complex formation than one with nicotinic acid.