CHANGES IN LIPOSOME PERMEABILITY DUE TO C-14 ALKYL BETAINE SODIUM DODECYL-SULFATE MIXED SYSTEMS

The alterations in the permeability of unilamellar liposomes caused by the presence of N-tetradecyl-N,N-dimethylbetaine (C-14-Bet) and sodium dodecyl sulphate (SDS) mixed systems have been investigated. Unilamellar liposomes were prepared from egg phosphatidylcholine and phosphatidic acid (9:1 molar ratio). The partition coefficients of these surfactant mixed systems between the aqueous phase and the lipid bilayers of the liposomes were determined for different mole fractions of the zwitterionic surfactant. The surfactant mixed systems were formed by mixtures of both surfactants in the presence of 20 mM piperazine-1,/1-bis (2-ethane sulphonic acid) (PIPES) buffer and 110 mM Na2SO4, at pH 7.20. The changes in the liposome permeability were determined by studying the half-maximal-release value of the fluorescent dye 5-(6)carboxyfluorescein. When the mole fraction of C-14-Bet/SDS was about 0.4, the CMC values of these mixed systems exhibited a minimum, whereas their partition coefficient between the aqueous medium and the lipid domain of the bilayers showed a maximum. The surfactant concentrations in the aqueous medium for these partition coefficients were always lower than the corresponding CMC values. There was a consistent correlation between the partition coefficient and the ability of the different surfactant mixed systems to modify the permeability of the liposomes.