Preparation of monodisperse vesicles with variable size by dilution of mixed micellar solutions of bile salt and phosphatidylcholine.

We have investigated by means of quasi-elastic light scattering the aggregative behavior of aqueous mixed micellar solutions of glycocholate and phosphatidylcholine. Upon dilution with buffer the micellar size and the polydispersity increases dramatically, and, as the system is diluted beyond the mixed micellar phase boundary, a spontaneous transition from polydisperse micelles to monodisperse vesicles occurs. The radius of the vesicles formed upon dilution depends strongly upon the final composition of the solution and can be varied between 120 and 550 A. In contrast to the thermodynamically stable mixed micelles these vesicle solutions can be brought into a metastable state in which it is possible to remove by dialysis the bile salt molecules from the mixed vesicles without changing their radius by more then 10%. The combination of dilution and dialysis thus represents a method for the preparation of unilamellar, monodisperse and detergent-free vesicles with a desired radius that can be chosen between 120 and 500 A.