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 sodiu m dodecyl sulphate (SDS) mixed systems have been investigated. Unilame llar liposomes were prepared from egg phosphatidylcholine and phosphat idic acid (9:1 molar ratio). The partition coefficients of these surfa ctant mixed systems between the aqueous phase and the lipid bilayers o f the liposomes were determined for different mole fractions of the zw itterionic surfactant. The surfactant mixed systems were formed by mix tures 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 7.2 0. The changes in the liposome permeability were determined by studyin g the half-maximal-release value of the fluorescent dye 5-(6)carboxyfl uorescein. When the mole fraction of C-14-Bet/SDS was about 0.4, the C MC values of these mixed systems exhibited a minimum, whereas their pa rtition coefficient between the aqueous medium and the lipid domain of the bilayers showed a maximum. The surfactant concentrations in the a queous medium for these partition coefficients were always lower than the corresponding CMC values. There was a consistent correlation betwe en the partition coefficient and the ability of the different surfacta nt mixed systems to modify the permeability of the liposomes.