Vesicle Diameter Effect on Solubilization of Aromatic Compounds by Aqueous Solutions of Didodecyldimethylammonium Bromide Vesicles

Examination was made of the solubilization of aromatic compounds possessing hydrophilic groups using didodecyldimethylammonium bromide (DDAB) vesicles with different diameters in the equilibrium dialysis method, fluorescence probe method and dynamic-light scattering method. The solubilization equilibrium constants (K0) of benzoic acid (BA) and 3-phenylpropionic acid (HCA) were found to increase with vesicle diameter while K0 of phenol and 2-phenylethanol (PEA) to remain essentially unchanged. In the case of smaller vesicles, the electrostatic adsorption of BA and HCA molecules on DDAB head groups becomes more difficult since the hydration layer of the vesicles is more tightly bound to the vesicle surface. Phenol and PEA molecules may possibly bind more weakly to water in the hydrophilic region of vesicles.