Kinetic investigation of the vesicle-micelle transition

Dissolution of surfactants into bilayer lipid membranes results in their destabilization so that, as a final result, mixed micelles containing both polar lipids and surfactants molecules are formed. It is to note that eventual transient aggregates, formed during the process, could be multilamellar vesicles. The equilibrium and the transient structures occurred in the transition, as well as kinetic of dissolution of the surfactant in the bilayer membrane are very important issues for the study of the stability of liposomes used in medical therapy and for the study of the interaction between detergent and living cells. In previous studies Almagren has related the structures and the equilibrium properties encountered in the transition to the phase behavior. However in his studies the kinetic of the process and details on the structural properties of the transient aggregates are missing. In this poster, we present a study on the dissolution kinetics of DOPC phospholipids due to presence of C10E8 surfactant molecules, at different concentrations at 25°C. Structural characterization performed by means of small angle neutron scattering and Electron Spin Resonance Spectroscopy allowed establishing a different behavior dependent on the surfactant amount. When the C10E8 concentration is below its cmc values, the DOPC unilamellar liposomes are progressively transformed in mixed giant multilamellar vesicles as shown by SANS measurements: the transition occurs in ~ 2 weeks after the insertion of the surfactant. When the C10E8 concentration is well above its cmc the liposome rupture is much faster (less than 12 hours) and results in the formation of small mixed micelles formed by the two solutes.