Bilayers at the air—water interface?

Abstract

FILMS of octadecanol and the corresponding C₁₈ acid (stearic acid) appear to occupy 10° A² per molecule at the air–water interface when spread from ethanol or acetone, as opposed to 20 A°² per molecule when spread from a (non-polar) solvent such as hexane or benzene. Ries¹ has proposed that in a polar or non-polar spreading solvent the amphipathic molecules adopt a bimolecular configuration with the hydrophilic groups pointing, respectively, outward and inward. It was further postulated that when spread at an air–water interface, only the latter could be ‘unzippered’ by the substrate to form a monolayer. Spreading from a polar solvent would thus result in bilayer formation and explain the apparent loss of half the film molecules. In view of the upsurge of interest in membrane and model membrane systems, the possibility of forming a lipid bilayer at the air–water interface was certainly exciting and clearly warranted further investigation.