MOLECULAR PACKING IN STEROID-LECITHIN MONOLAYERS .3. MIXED FILMS OF 3-DOXYL CHOLESTANE AND 3-DOXYL-17-HYDROXYL-ANDROSTANE WITH DIPALMITOYLPHOSPHATIDYLCHOLINE

A comparison is made of the condensing capability of 3-doxyl cholestane and 3-doxyl-17-hydroxyl-androstane in mixed monomolecular film systems with dipalmitoyl phosphatidylcholine. 3-doxyl cholestane closely resembled cholesterol in its mixed film behavior while 3-doxyl-17-hydroxyl-androstane did not. This was taken to indicate that the ability of cholesterol to condense expanded host lipids results primarily from hydrophobic interactions and does not involve specific direct polar interactions. A general model is set up based on steroid tilt angle in the mixed film, which indicates that the greater the tilt angle, the more ineffective the condensing capability. A quantitative comparison is made of these properties for cholesterol, cholestanol, epicholesterol, cholestone, 3-doxyl cholestane and coprostanol. © 1979.