Interaction between lecithins and cholesterol at the air-water and oil-water interfaces

Spread mixed monolayers at the air—water of cholesterol and phospholipids (dipalmitoyl lecithin and stearoyl-oleoyl lecithin) were investigated using the Goodrich method. It was found that a weak interaction occurred between cholesterol and dipalmitoyl lecithin, on the contrary a large interaction was observed for the system cholesterol, stearoyl-oleoyl lecithin. Recently a theory was developed concerning the ideal behaviour of mixed adsorbed films. Since at the oil—water interface mixed adsorbed monolayers of cholesterol and the above mentioned phospholipids show an ideal behaviour, the conclusion was drawn that the interaction at the air—water interface is mainly due to Van der Waals—London attraction forces