Behavior of specific natural lecithins and cholesterol at the air water-interface

Individual molecular species of lecithins were mixed with cholesterol and their pressure-area curves were measured at the air-water interface at 22±1°. The lecithins investigated were: L-16:0-16:0-, D-16:0-16:0-, L-16:0-18:3-, L-18:0-18:3-, L-16:0-20:4-, L-18:0-20:4- and L-18:0-18:0-lecithins. All of these except the D-16:0-16:0- and L-18:0-18:0-lecithins have been found in nature. Considerable condensation of monolayers with cholesterol was observed in all cases except that of 18:0-18:0-lecithin, in which there was little condensation. The naturally-occurring structure of lecithins, that is, 1-saturated-2-unsaturated, leads to large condensations in mixed monolayers. This geometrical fit between cholesterol and lecithins may be of importance in enzyme reactions involving cholesterol or lecithins.