Abstract
The partitioning of a series of amphoteric alkylbetaine surfactants (alkyl chain lengths C-10, C-12 and C-14) between the aqueous phase and the lipid bilayers of liposomes that model the stratum corneum lipid compositions was investigated. Liposomes were formed from a lipid mixture containing 40% ceramides, 25% cholesterol, 25% palmitic acid and 10% of cholesteryl sulfate. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous phase partition coefficients (K) were determined at two sublytic levels by monitoring the increase in the fluorescence intensity of liposomes due to 5(6)-carboxyfluorescein (CF) release from the interior of the vesicles. Given that the free surfactant concentrations were always lower than their critical micelle concentrations, we may assume that the stratum corneum (SC) liposomes-surfactant sublytic interactions were mainly determined by the action of surfactant monomers. At the two interaction levels studied (50% and 100% of CF release) tetradecylbetaine showed the highest ability to alter the release of the CF trapped into bilayers (lowest Re values) and the highest degree of partitioning into liposomes or affinity with these structures (highest K values), whereas decylbetaine showed the opposite tendencies. Different trends in the evolution of Re and K were observed when comparing the results obtained with those reported for the interaction of the same surfactants with phosphatidylcholine (PC) liposomes. Thus, whereas SC liposomes appeared to be more resistant to the action of alkylbetaines, the degree of partitioning of these surfactants into the SC bilayers was always greater than that reported for PC bilayers.
Published Version
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