Comparison of global-minimum-energy conformations of phospholipids

Abstract

The Monte Carlo technique in combination with the procedure of “slow cooling” of a configurational ensemble has been used to establish the conformations of the global energy minima of phosphatidylcholine and phosphatidylethanolamine molecules with saturated and unsaturated fatty acid residues. Substituents of the ammonium group in saturated phospholipids have been shown to affect the head group only. In the case of 1-stearoyl-2-arachidonyl glycerol the type of the head group dramatically affects the geometry of the nearest region of the first fatty acid residue and leaves the second fatty acid residue practically intact. This fact is accounted for by electrostatic bonding between the ammonium group and the keto oxygen atom of the first fatty acid residue in an unsaturated lipid. It is the electrostatic force field that stipulates the specificity of head groups in lipids. It is shown that the minimum energy conformations of saturated fatty acid residues in double-chain lipids contain a large number of gauche-type defects.