INTERACTION OF ANIONIC NONIONIC SURFACTANT MIXTURES WITH PHOSPHATIDYLCHOLINE LIPOSOMES/

The mechanisms governing the interaction of mixtures of sodium dodecyl sulfate (SDS) and nonylphenol oxyethylenated with 10 mol of ethylene oxide (NP(EO)(10)) with phosphatidylcholine liposomes were investigate d, Permeability alterations were detected as a change in 5(6)-carboxyf luorescein (CF) released from the interior of vesicles and bilayer sol ubilization as a decrease in the static light scattered by liposome su spensions. Three parameters were described as the effective surfactant /lipid molar ratios (Re) at which the surfactant system (a) resulted i n 50% of CF release (Re-50%CF), (b) saturated the liposomes (Re-SAT), and (c) led to a complete solubilization of these structures (Re-SOL). From these parameters the corresponding surfactant partition coeffici ents (K-50%CF), K-SAT, and K-SOL) were determined. Despite the fact th at Re increased as the mole fraction of the SDS rose (X(SDS)), the K p arameters showed maximum values at X(SDS) 0.6 and 0.2 for K-50%CF and K-SAT, respectively, the K-SOL reaching the highest value in the absen ce of SDS X(SDS) = 0). Thus, the higher the surfactant contribution in surfactant/lipid system, the lower the X(SDS) at which the maximum bi layer/water partitioning of mixed surfactant systems added took place. The free surfactant concentrations S-W were lower than the mixed surf actant CMCs at subsolubilizing level, whereas it remained similar to t hese values during saturation and solubilization of bilayers in all ca ses. (C) 1995 Academic Press,Inc.