Diversity in the fatty-acid conformation and chain packing of cis-unsaturated lipids.

Recent X-ray diffraction and Fourier transform IR spectroscopic studies have unveiled a great diversity in the molecular conformation and chain packing of lipid molecules containing cis-unsaturated fatty-acid chains. Specifically, a dramatic diversity in the olefinic conformation, subcell packing and chain-chain interactions has been clearly revealed by crystal structures of principal cis-monounsaturated fatty acids. The structural diversity is most manifest in oleic acid crystals. These findings were applied to analyses of the complicated structural transformation of diacylglycerols and triacylglycerols containing oleic acid and saturated acid moieties, in which the stabilization of the oleic acid causes the complexity of the transformation and mixing behavior. Although this knowledge has been obtained in the crystalline state, one may assume that the structural diversity of these unsaturated molecules plays a similar role in the lipids of biomembranes, lipoproteins and lipid deposits in which aliphatic chain packing is a critical problem, since most lipid domains can undergo liquid to solid or solid to liquid alterations.