Reaction Kinetic Effects of Liposomes on the Alkaline Fading of Crystal Violet

Investigating the alkaline fading of crystal violet in 0.01 N NaOH as a model reaction, micelles as well as liposomes were shown toaffect the kinetics of bimolecular reactions between apolar water-soluble compounds and ions. Since liposomes, despite their negative electrophoretic mobility, catalyzed this reaction under certain conditions, it was concluded that theobserved phenomenon could not be solely explained by the surface charge. The much faster fading in methanol as compared to the reaction in aqueous media indicated that the more apolar molecular environment of solubilized crystal violet increased the reaction rate in the liposomal pseudo-phase. As a further consequence, the reaction kinetic effect was not only determined by the charge of the polar head group of the phospholipids, but also by the fatty acid composition. Besides, added surfactants highly influenced the reaction, even at concentrations below their critical micelle concentration: adding dodecyl trimethylammonium bromide to liposomes consisting of soybean lecithin, which had a marked reaction-inhibiting effect, the alkaline fading of crystal violet was strongly catalyzed. On the other hand, the particle size of the liposomes, the phospholipid concentration and the electrolyte composition of the liposomal dispersion influenced the reaction kinetics only to a very small extent.