Temperature-dependent molecular motions of cholesterol esters: a carbon-13 nuclear magnetic resonance study
- 1 December 1982
- journal article
- research article
- Published by American Chemical Society (ACS) in Biochemistry
- Vol. 21 (26), 6857-6867
- https://doi.org/10.1021/bi00269a036
Abstract
13C NMR spectroscopy at 50.3 MHz was used to study 4 long-chain cholesterol esters with a double bond in the .omega.-9 position: cholesteryl oleate, C18:1, .omega.-9; cholesteryl linoleate, C18:2, .omega.-6,9; cholesteryl erucate, C22:1, .omega.-9; cholesteryl nervonate, C24:1, .omega.-9. The linoleate and oleate esters exhibit 2 metastable liquid-crystalline phases (cholesteric and smectic), whereas the longer chain esters form a stable smectic phase but no cholesteric phase. Line widths (.nu.1/2), spin-lattice relaxation times (T1), and nuclear Overhauser enhancements (NOE) were measured for all well-resolved resonances from ring and fatty acyl (FA) carbons at different temperatures in the isotropic liquid of each ester. T1 and NOE values of FA resonances were constant between the FA-2 carbon and olefinic region of each acyl chain and increased markedly for carbons near the chain terminus. FA carbon motions are thus restricted and/or highly correlated in the region between the ring and the olefinic carbons, suggesting that strong interactions occur between cholesterol ester molecules in this region of the FA chain. The FA chains are probably approximately extended in the isotropic liquid. Steroid ring methine C-6 and C-3 .nu.1/2 increased differentially on cooling to the liquid .fwdarw. liquid crystal transition temperature (Tm) of each ester, indicative of increasingly anisotropic ring rotations. The rotational anisotropy was quantitated by using a prolate ellipsoid model for the cholesterol ester molecule for which 2 correlation times (corresponding to rotations about the long and short molecular axes) were calculated from the C-3 and C-6 .nu.1/2 values. The C-3/C-6 .nu.1/2 ratio was directly proportional to the anisotropy of the ring motions as measured by the ratio of the 2 correlation times. At any given temperature relative to Tm, the C-3 and C-6 .nu.1/2 and the C-3/C-6 .nu.1/2 ratios were larger for cholesterol esters which have a cholesteric phase than for esters which have no cholesteric phase, showing that steroid ring motions were more restricted and more anisotropic prior to the formation of a cholesteric phase. Cholesteryl erucate and cholesteryl nervonate have longer regions of FA chain interactions which result in greater chain cooperativity, apparently preventing the preordering of steroid rings to the degree necessary for formation of a cholesteric phase. Thus, these esters form the smectic phase directly from the isotropic liquid. These results are applied to the cholesterol ester transition in plasma low-density lipoproteins.This publication has 12 references indexed in Scilit:
- Physical properties of cholesteryl esters having 20 carbons or moreBiochimica et Biophysica Acta (BBA) - Lipids and Lipid Metabolism, 1981
- Carbon-13 nuclear magnetic resonance studies of short-chain lecithins. Motional and conformational characteristics of micellar and monomeric phospholipidBiochemistry, 1980
- Lipid dynamics in human low density lipoproteins and human aortic tissue with fibrous plaques. A study by high field 13C NMR spectroscopy.Journal of Biological Chemistry, 1979
- The crystal structure of cholesteryl oleateChemistry and Physics of Lipids, 1979
- Studies on the Structure of Low Density Lipoproteins Isolated from Macaca Fascicularis Fed an Atherogenic DietJCI Insight, 1978
- Carbon-13 nuclear magnetic resonance studies of cholesteryl esters and cholesteryl ester/triglyceride mixtures.Journal of Biological Chemistry, 1977
- Structure of human plasma low-density lipoproteins: molecular organization of the central core.Proceedings of the National Academy of Sciences of the United States of America, 1977
- Structure and interactions of lipids in human plasma low density lipoproteins.Journal of Biological Chemistry, 1977
- Fatty acids. Part 50. 13C nuclear magnetic resonance studies of olefinic fatty acids and estersChemistry and Physics of Lipids, 1977
- Temperature-dependent carbon-13 nuclear magnetic resonance studies of human serum low density lipoproteinsBiochemistry, 1976