Alterations in phospholipid bilayers caused by sodium dodecyl sulphate/triton X-100 mixed systems

Abstract

The mechanisms governing the subsolubilizing and solubilizing interaction of sodium dodecyl sulphate (SDS)/Triton X-100 mixtures and phosphatidylcholine liposomes were investigated. Permeability alterations were detected as a change in 5(6)-carboxy-fluorescein (CF) released from the interior of vesicles and bilayer solubilization as a decrease in the static light-scattered by liposome suspensions. Three parameters were described as the effective surfactant/lipid molar ratios (Re) at which the surfactant system a) resulted in 50% of CF release (Re50%CF); b) saturated the liposomes (ReSAT;c) led to a complete solubilization of these structures (ReSOL). From these parameters the corresponding surfactant partition coefficientsK50%CF,KSAT andKSOL were determined. The free surfactant concentrationsSW were lower than the mixed surfactant CMCs at subsolubilizing level, whereas they remained similar to these values during saturation and solubilization of bilayers in all cases. Although theRe increased as the mole fraction of the SDS rose (XSDS), theK parameters showed a maximum atXSDS values of about 0.6, 0.4 and 0.2 forK50%CF,KSAT andKSOL respectively. Thus, the higher the surfactant contribution in surfactant/lipid system, the lower theXSDS at which a maximum bilayer/water partitioning of mixed surfactant systems added took place and, consequently, the lower the influence of the SDS in this maximum bilayer/water partitioning.