Effect of cholesterol on structural and dynamic properties of tripalmitoyl glyceride. A high-pressure infrared spectroscopic study.

The infrared spectra of tripalmitoyl glyceride confirm the tuning fork configuration previously attributed to trilauroyl glyceride (Small, D. M. 1986. Handbook of Lipid Research. Vol. 4). The acyl chains in solid tripalmitoyl glycerol, either within each molecule or between neighboring molecules, are oriented parallel to each other with the sn-3 acyl chains extended toward the opposite direction of the sn-1 and sn-2 chains. The presence of cholesterol increases the orientational disorder of the tripalmitoyl glyceride molecules in terms of increased reorientational fluctuations and twisting/torsion motions of the acyl chains. In the solid mixture, cholesterol is embedded in the tripalmitoyl glyceride lattice which results in a reorientation of the acyl chains within each molecule from a parallel packing to a nonparallel packing. No evidence was found for hydrogen bond formation between the OH group of cholesterol and any of the three C = O groups of tripalmitoyl glyceride.