Dihexadecyl phosphate vesicles: Permeability to cationic components in solar photolysis systems
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 35�C, 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.