Structural requirements of sterols for the interaction with lecithin at the air-water interface

1. 1. The force area characteristics of monolayers of 3β-, 3α-hydroxysterols and ketosteroids have been studied. 2. 2. The 3β-hydroxysterols cholesterol, cholestanol, lathosterol, 7-dehydrocholesterol, and B-norcholesterol are perpendicularly oriented at the air-water interface and show high collapse pressures. Ergosterol, stigmasterol, and androstan-3β-ol demonstrate a similar behavior at high pressures, but the collapse pressure is reduced. The cis-structured coprostanol shows an increased area per molecule. 3α-Hydroxysterols (epicholesterol and androstan-3α-ol) reveal strongly reduced collapse pressures when compared with the respective 3β-hydroxysterols. All ketosteroids show high areas per molecule. 3. 3. The force-area curves show little temperature effect. 4. 4. The interaction of 18:1/18:0 lecithin with sterols is dependent on: (a) planar sterol nucleus, (b) 3β-hydroxy group, (c) intact side chain. 5. 5. Besides 3β-hydroxysterols, 3α-hydroxysterols and ketosteroids can also show some condensation effect. However, minimal area per molecule can be achieved only with 3β-hydroxysterols. 6. 6. The interaction of lecithin and sterol in monolayers is governed by a number of factors including van der Waal's interactions, but also hydrogen bonding between the 3β-hydroxy group and environment is considered to be important