Formation of “Black” Lipid Membranes by Oxidation Products of Cholesterol

THE so-called bimolecular lipid leaflet1, postulated as a basic structural component of natural membranes, has only recently become available for direct experimental investigation2. The formation and properties of bilayer lipid and proteolipid membranes, separating two aqueous phases, have been investigated3–7. The thickness of these membranes in aqueous solution is of the order of 70 Å, and they appear “black” when viewed by reflected light8. For this reason they are called “black” lipid membranes (or films) to distinguish them from the well known black soap films in air9.