title: Monolayers of sterols and phosphatidylcholines containing a 20-carbon chain.
abstract: Pressure-area curves of monolayer films were measured for phosphatidylcholines (PC) in which the 1-position was occupied by palmitic acid and the 2-positions were occupied respectively by: 20 : 0,20 : 1n9, 20 : 2n6, 20 : 3n3, 20 :3n6, 20 :3n9, 20 :4n6 or 20 : 5n3 fatty acids. The interactions of these PC with cholesterol or desmosterol were studied. Fully saturated PC (16 : 0--20 : 0) displayed a relatively small molecular area. The presence of one double bond greatly increased the molecular area, but a second double bond resulted in only a small additional increase in area. A third double bond caused a further large expansion in area, but the presence of a fourth or fifth double bond had little additional effect. Condensation of molecular area was observed with all sterol/PC mixed films. Approximately equimolar mixtures of sterols and unsaturated PC condensed maximally, but 16 : 0--20 : 0 PC condensed most in mixtures containing 20--30 mol% of either sterol. The extent of condensation varied with surface pressure. The pressure at which maximum condensation occurred depended upon the structure of the PC and was always 20 dyn/cm or lower. The pressure at which maximum condensation with cholesterol occurred increased with increasing unsaturation of the PC.
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003897:Desmosterol; D005231:Fatty Acids, Unsaturated; D008567:Membranes, Artificial; D008954:Models, Biological; D010713:Phosphatidylcholines; D013261:Sterols; D013329:Structure-Activity Relationship; D013499:Surface Properties
chemical_list: D005231:Fatty Acids, Unsaturated; D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D013261:Sterols; D003897:Desmosterol