Solubilizing effects caused by the nonionic surfactant octyl glucoside in phosphatidylcholine liposomes

The mechanisms governing the interaction of the nonionic surfactant octyl glucoside (OG) on phosphatidyl-choline (PC) liposomes were investigated. Permeability alterations were detected as a change in 5(6)-carboxyfluorescein (CF) released from the interior of vesicles, and bilayer solubilization was determined as a decrease in the static light scattered by liposome suspensions. A direct relationship was established in the initial interaction steps (10-50% CF release) between the growth of vesicles, the leakage of entrapped CF, and the effective molar ratio of surfactant to phospholipid in bilayers (Re). This dependence was also detected during the solubilization range of Re values between 1.3 and 3.0, where the decrease in the surfactant-PC aggregate size and in the light scattering of the system depended on the Re parameter and, hence on the composition of these aggregates, The free OC concentrations at subsolubilizing and solubilizing levels showed lower and similar, respectively, values than its critical micelle concentration (CMC). These findings indicated that the alterations in bilayer permeability were due to the action of surfactant monomers, whereas bilayer solubilization was determined by the formation of mixed micelles. This finding supports the generally accepted assumption that the concentration of free surfactant must reach the CMC for solubilization to occur.