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Aggregation of 1-Palmitoyl-2-Oleoyl-Sn-Glycero-3-Phosphocholine in Nonaqueous Solutions Studied by Spectroscopic and Kinetic Probe Molecules and Dynamic Light Scattering

Abstract The aggregation behavior of 1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in the nonaqueous solvents formamide (FA) and 3-hydroxypropionitrile (HPN) has been studied. UV/Vis absorption maximum λmax and thermal cis → trans isomerization rate constant kiso of an azo dye, as well as fluorescence intensity ratios IM/IE of monomer and excimer, and the excimer lifetime τE of two dipyrenyl compounds as probe molecules have been determined. For comparison, aggregation of the amphiphile POPC molecules was followed “probe-free” by means of dynamic light scattering (DLS) measurements. Combining the results of probe molecule studies and DLS it turned out that the critical aggregation concentration of POPC in FA < 0.05mmol dm−3. At ≥ 0.2mmol dm−3, aggregates have hydrodynamic radii 30 < Rh < 80nm and high microviscosity in their hydrocarbon interior. A vesicle-like structure of the aggregates can therefore be assumed. Aggregation behavior of POPC in HPN is much less pronounced, essentially small aggregates with radii of a few nanometer have been detected which include solvent molecules.