hide
Free keywords:
-
Abstract:
The artificial phospholipid Pad-PC-Pad was analyzed in 2D (monolayers at the air/water interface) and 3D (aqueous lipid dispersions) systems. In the gel phase, the two leaflets of a Pad-PC-Pad bilayer interdigitate completely and the the hydrophobic bilayer region has a thickness comparable to the length of a single phospholipid acyl chain. This leads to a stiff membrane with no spontaneous curvature. Forced into a vesicular structure, Pad-PC-Pad shows a faceted geometry and in its extreme form, tetrahedral vesicles were found as predicted a decade ago. Above the main-transition temperature, a non-interdigitated Lα phase with fluid chains has been observed. The addition of cholesterol leads to a slight decrease of the main-transition temperature and a gradual decrease of the transition enthalpy until the transition vanishes at 40 mol% cholesterol in the mixture. Additionally, cholesterol pulls the chains apart and a non-interdigitated gel phase is observed. In monolayers, cholesterol has an ordering effect on liquid-expanded phases and disorders condensed phases. The wavenumbers of the methylene stretching vibration indicate the formation of a liquid-ordered raft phase in mixtures with 40 mol% cholesterol.