Interaction of surfactants with vesicle membrane of dipalmitoylphosphatidylcholine: fluorescence depolarization study

The effect of surfactants on the "fluidity" of dipalmitoylphosphatidylcholine (DPPC) vesicle membrane was studied by means of the fluorescence depolarization technique with fatty acid fluorescent probes, in which the anthroyloxy group is introduced at different positions along the acyl chain. Three types of surfactants were examined; anionic sodium alkylsulfates, cationic alkyltrimethylammonium chlorides, and non-ionic alkanoyl-N-methylglucamides (MEGA-n). Perturbing effects of the surfactants depended on both the alkyl chain-length and the type of head group. Sodium alkylsulfates with octyl- and decyl-chain and alkyltrimethylammonium chlorides with octyl-, decyl- and dodecyl-chain did not affect the membrane fluidity when incorporated in the membrane, whereas sodium dodecylsulfate and tetradecyltrimethylammonium chloride decreased the membrane fluidity at both gel and liquid crystalline states of the membrane. All the MEGA series surfactants decreased the membrane fluidity, whose perturbing potency was in the order of MEGA-8 less than MEGA-9 approximately equal to MEGA-10. The perturbation at different depths in the membrane by sodium dodecylsulfate and MEGA-9 was also examined. No significant change in the fluidity gradient across the membrane was induced by the addition of these surfactants.