Ab initio studies of phospholipid headgroups

Li, Wen (1995) Ab initio studies of phospholipid headgroups. Masters thesis, Memorial University of Newfoundland.

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Abstract

The thesis consists of two distinct but closely related parts. In the first part we present a systematic conformational study of the stable headgroup structures for phospholipid single molecule using five model compounds: CH₃PO₋₄CH₃, CH₃CH₂PO₋₄CH₂CH₃, CH₃CH₂PO₋₄CH₂CH₂NH₊₃ (phosphorylethanolamine, PE, with methyl end group), glycerophosphorylethanolamine (GPE) and glycerophosphorylcholine (GPC). The potential energy scans and the fully geometry optimized structures were obtained using the molecular orbital program Gaussian 92. The changes in geometrical parameters and conformational energy differences due to the usage of different basis sets (STO-3G, 3-21G*, 6-31G* and 6-31+G*) were investigated. Since 3-21G* and 6-31G* basis sets gave similar results, 3-21G* basis set was chosen for our calculations. The comparison was made between the phospholipid structural parameters (such as molecular area, thickness of the polar region, thickness of the headgroup and dipole) obtained for the model compounds. In the second part of the thesis, the hydrated PE and GPE are investigated. The results show that the structures of PE and GPE are strongly dependent upon the hydration force. We also investigated the effect of hydration on other model compounds. We have studied the following (hydrated) model systems: PE + 4H₂O, GPE + 6H₂O and 2PE + 4H₂O. Direct comparisons of the calculated geometry parameters of compounds in the presence of water with the crystallographic results has been also presented. The geometrical parameters for hydrated molecules are closer to the crystallographic experimental data than those obtained for isolated molecules.

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