Structures and phase transitions in aqueous dispersions of branched-chain glycerophosphoethanolamines

Glycerophosphoethanolamines with alpha-branched fatty acids were synthesized, varying the side-chain length. Differential scanning calorimetry and X-ray diffraction were applied to investigate the influence of the chemical alteration on the physico-chemical parameters and the structures formed in lipid-water dispersions. The results show that the introduction and stepwise elongation of side-chains decrease the transition temperature from gel to liquid-crystalline phases. The T-m values pass through a minimum and increase slightly on going to the triple-chain lipid. The change in the transition parameters is connected with a modified polymorphism. Short side-chains induce a tilt in the gel state and the elongation of the branch leads to interdigitated gel phases. With increasing side-chain length, non-lamellar liquid-crystalline phases are stabilized. For the long-branched derivative, an interdigitation of head-groups from adjacent bilayers is proposed.