The interactions of trace amounts of ionic surfactants with mixed 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)/Cholesterol membranes

Abstract

The influence of dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB), hexadecyltrimethylamonium bromide (CTAB) and sodium dodecylsulfate (SDS) on the properties of mixed DPPC/cholesterol layers with 30% of cholesterol was investigated. The studies proved that even a tiny amount of surfactant (below 10 µM) alters the zeta potential of the cholesterol containing liposomes significantly, to the greater extent for the anionic surfactant. Moreover, the surfactant effect increases with the increasing concentration. In the case of the cationic surfactants the effect increases with the carbon chain length. In order to confirm the observed findings the experiment was extended to the study of the corresponding Langmuir monolayers. The discussion based on the π-A isotherms, penetration tests and Brewster angle microscopy provided additional evidence of the surfactants interactions with the membrane lipids. It was also found that the penetration of DTAB and SDS surfactants was favoured by the presence of cholesterol molecules in the DPPC layers.