CONFORMATIONAL-ANALYSES OF THE POLYMORPHISM OF TRIGLYCERIDES

Triglycerides, the major components of neutral lipids, are important b iomaterials, as they take part in the edification of membranes. In thi s perspective, the consideration of biological membranes at a molecula r level requires detailed knowledge of the preferred conformations of the triglycerides in their various polymorphic forms. In this context, we adapted a molecular modeling approach, which allows the simulation the three-dimensional structure of the different polymorphic forms (a lpha, beta', and beta) valid for any triglyceride. Their conformationa l analysis is based on molecular mechanics calculations, as follows: F irst, a large number of isolated molecular structures were generated i n asystematic structure-tree analysis. For their generation, atomic ch arges within the Mulliken scheme, calculated at the ab initio RHF-LCAO -MO-SCF level (6-31G), were considered. The lowest-energy conformers w ere, next, correlated with experimental data (NMR, powder X-ray diffra ction) in order to select alpha, beta', or beta structures. Then, in a second step, these selected conformers were assembled, in head-to-tai l dimers in order to form a monolayer. For this step, the use of poten tial-derived atomic charges is known to be more suitable. In this stud y, we consider triglycerides derived from the predominant fatty acids, i.e., stearic, elaidic, and oleic acids. (C) 1994 John Wiley & Sons, Inc.