Cholesterol binding to the alkyl chains of an intercalated surfactant bilayer

Abstract

Alkyl-chain bilayers can be formed within the galleries of layered inorganic solids by intercalation of long-chain amphiphilic surfactant molecules. It is shown here that cholesterol, normally found in lipid bilayers of biomembranes, can bind to the intercalated bilayer, thereby providing a novel route for the insertion of cholesterol in inorganic solids. The new hybrid material is held together by purely noncovalent, nonionic dispersive forces and is a novel example of supramolecular architecture in the solid state. Additionally, it provides a simple system to understand the nature of cholesterol - hydrocarbon interactions at a molecular level. The rigid sterol ring of the cholesterol is located within the intercalated bilayer and is oriented parallel to the alkyl chains. Its presence affects the conformation of neighboring alkyl chains. An analysis of the methylene progression bands in the infrared spectrum of the intercalated bilayer, with and without cholesterol, indicates that these chains are forced to adopt a rigid, all-trans, planar conformation. Conformational freedom of alkyl chains once-removed appear unaffected.