Preparation of asymmetric bilayer-vesicles with inner and outer monolayers composed of different amphiphilic molecules

Asymmetric vesicles were prepared layer by layer from reverse micelles. The aqueous solution was first entrapped into reverse micelles prepared from lipid, then these reverse micelles penetrated the monolayer formed by another kind of amphiphilic agent at organic solvent/water interface by centrifugation and were assembled spontaneously by the second layer to form asymmetric vesicles. In general, the diameters of the vesicles ranged from 30 to 100 nm. A fluorescein quenching experiment showed that asymmetric vesicles with the inner layer being lipid and the outer layer being single-chain amphiphilic molecules, [(bpy)₂ Ru(diazafluorenone) (CH₂)₁₅CH₃](PF₆)₂, were successfully prepared. The half-life of flip–flop of the amphiphilic molecules between inner and outer layers was estimated to be about 17 days.