ALTERATIONS IN PHOSPHOLIPID-BILAYERS CAUSED BY SODIUM DODECYL-SULFATETRITON X-100 MIXED SYSTEMS

The mechanisms governing the subsolubilizing and solubilizing interact ion of sodium dodecyl sulphate (SDS)/Triton X-100 mixtures and phospha tidylcholine liposomes were investigated. Permeability alterations wer e detected as a change in 5(6)-carboxy-fluorescein (CF) released from the interior of vesicles and bilayer solubilization as a decrease in t he static light-scattered by liposome suspensions. Three parameters we re described as the effective surfactant/lipid lipid molar ratios (Re) at which the surfactant system a) resulted in 50% of CF release (Re-5 0%CF); b) saturated the liposomes (Re-SAT); c) led to a complete solub ilization of these structures (Re-SOL). From these parameters the corr esponding surfactant partition coefficients K-50%CF, K-SAT and K-SOL w ere determined. The free surfactant concentrations S-W were lower than the mixed surfactant CMCs at subsolubilizing level, whereas they rema ined similar to these values during saturation and solubilization of b ilayers in all cases. Although the Re increased as the mole fraction o f the SDS rose (X(SDS)), the K parameters showed a maximum at X(SDS) v alues of about 0.6, 0.4 and 0.2 for K-50%CF, K-SAT and K-SOL respectiv ely. Thus, the higher the surfactant contribution in surfactant/lipid system, the lower the X(SDS) at which a maximum bilayer/water partitio ning of mixed surfactant systems added took place and, consequently, t he lower the influence of the SDS in this maximum bilayer/water partit ioning.