MOLECULAR PACKING IN STEROID-LECITHIN MONOLAYERS .2. MIXED FILMS OF CHOLESTEROL WITH DIPALMITOYLPHOSPHATIDYLCHOLINE AND TETRADECANOIC ACID

Mixed film studies of the systems cholesterol/tetradecanoic acid and cholesterol/dipalmitoylphosphatidylcholine have been carried out over the entire compositional range at 21°C. When compared on an acyl chain basis the condensing effects were found to be essentially independent of which host-lipid was utilized. The phase change of the host lipid was shifted to higher pressures, then broadened and eliminated. Maximal condensation occurred at just above 42 mol% for the cholesterol/DPPC system. In both systems the two components were initially found to be miscible at all proportions. The results are interpreted in terms of the molecular packing of cholesterol with acyl boundary layers, one significantly, one weakly affected. Maximum condensation is a result of packing that provides maximum cholesterol/acyl chain contact. Consideration is given to both long term stability of such mixed monolayers and the behaviour of the corresponding bilayer states. © 1979.