SOLUBILIZING EFFECTS CAUSED BY THE NONIONIC SURFACTANT OCTYL GLUCOSIDE IN PHOSPHATIDYLCHOLINE LIPOSOMES

The mechanisms governing the interaction of the nonionic surfactant oc tyl glucoside (OG) on phosphatidyl-choline (PC) liposomes were investi gated. Permeability alterations were detected as a change in 5(6)-carb oxyfluorescein (CF) released from the interior of vesicles, and bilaye r solubilization was determined as a decrease in the static light scat tered by liposome suspensions. A direct relationship was established i n the initial interaction steps (10-50% CF release) between the growth of vesicles, the leakage of entrapped CF, and the effective molar rat io 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 concentrat ions at subsolubilizing and solubilizing levels showed lower and simil ar, respectively, values than its critical micelle concentration (CMC) . These findings indicated that the alterations in bilayer permeabilit y were due to the action of surfactant monomers, whereas bilayer solub ilization was determined by the formation of mixed micelles. This find ing supports the generally accepted assumption that the concentration of free surfactant must reach the CMC for solubilization to occur.