Dihexadecyl phosphate vesicles: Permeability to cationic components in solar photolysis systems

Abstract

Aqueous dihexadecyl phosphate (dhp) vesicles prepared at pH 5.6-6.3, and maintained at room temperature, retained ruthenium trisbipyridyl (Ru(bpy)₃²⁺) and methylviologen (mv²⁺) cations when these species were entrapped during vesicle formation or by penetration of the vesicle bilayer from aqueous solution. Increases in pH, or heating to above 35ºC, caused leakage of both Ru(bpy)₃²⁺ and mv²⁺ from vesicles. Ry(bpy)₃²⁺ penetrated the vesicles at room temperature and pH 6.3 when the external (non-adsorbed) Ru(bpy)₃²⁺ concentration was greater 10^-4than mol dm^-3. Penetration of Ru(bpy)₃²⁺ occurred at lower concentrations if the pH was increased and/or the vesicles were heated. The pH and heating conditions required to cause bilayer permeability towards mv²⁺ were more severe than for Ru(bpy)₃²⁺ It is concluded that the bilayer is more able to accommodate Ru(bpy)₃²⁺ and to permit its passage between the interior and exterior aqueous environments.