Lipid Interactions in Aqueous Surfaces, Membranes and Micellar Systems

Abstract

A variety of lipid molecules are involved in the structure of biological membranes. The study of the forces between lipid molecules is important for an understanding of the properties of these membranes. The results of a series of studies on pure model lipid systems were reported. These studies were on lipids at aqueous interfaces (examined by surface pressure [1], surface potential [2], and surface polarization [3] techniques) and on paraffinic colloidal electrolytes in aqueous solutions and micelles (examined by NMR [4] and Raman spectroscopy [5]). Theoretical calculations on the electrostatic and van der Waals interactions of lipids in membrane-like structures were also discussed [6]. These various lines of evidence suggest that phospholipid zwitterions are somewhat polarized normal to the membrane by applied electric fields of the magnitude of action potentials. The van der Waals interaction of the chains is also important but does not appear to obey the interaction law proposed by Salem [7]. Evidence of phase changes in lipid films was also presented in support of some of the schematic membrane changes discussed by Kavanau [8]. The importance of water as an essential component of membrane structures was illustrated by reference to spectroscopic data on chain-water interactions at the surface of micelles and in sub-micellar solutions of soap-like molecules. These data very strongly support the general view of water-chain interactions discussed by Nemeth y and Scheraga [9] and show that water is stabilized by the interaction. The paraffin chain is free to rotate internally, contrary to the view of Aranow and Witten [10] that the water chain interaction leads to a hindering of the chain rotation.