Cooperative Micelle Binding and Matrix Effect in Oleate Vesicle Formation

Abstract

Kinetics and particle size distributions in the spontaneous micelle−vesicle transformation of oleate vesicles are investigated by dynamic light scattering and optical density measurements. It is shown that, depending upon the conditions, there are two different kinetic processes for vesicles formation, a cooperative and a uncooperative one. In particular, the time progress of vesicle formation follows a sigmoid behavior and it is accelerated by the presence of preformed vesicles, confirming that a cooperative micelle−vesicle interaction takes place. This effect is investigated by adding fresh oleate surfactant to preformed, extruded (50 and 100 nm) oleate vesicles as well as to 50 and 100 nm extruded POPC (POPC is 1-palmitoyil-2-oleyl-sn-glycero-3-phosphocholine) liposomes. It is shown that both in the case of oleate and POPC the rate process of vesicle formation is remarkably accelerated with respect to the control (no preformed vesicles); and the final size distribution is very close to the narrowly dis...