Polymorphism of phosphatidylcholines varied in the hydrophobic part

Abstract

Variations of the hydrophobic part of phosphatidylcholines (PCs) such as chain shortening, chain branching, and chain linkage lead to different homologous series in which, surprisingly, a uniform behavior of the phase transition parameters is observed, namely, the parameters pass through a minimum. The first member of the monobranched 1-ether-2-ester-lecithins with a methyl branching in the sn-2-chain was investigated in mixtures with excess water by DSC and x-ray diffraction. It shows a polymorphism, which more resembles that of the 1,2-di-ester-PC than that of an unbranched 1-ether-2-ester-PC. In the subgel phase a bilayer structure with tilted, orthorhombic packed chains were detected which are oppositely arranged. On heating, a gel phase with titled, hexagonal packed chains appears which becomes fluid above the main transition at 313.8 K. The idea of frustration is applied to gel phases to understand the drastic structural variations in PCs, in which only small chemical modifications in the hydrophobic part were created.