Phase behaviour of a methyl branched phosphatidylethanolamine in two and three-dimensional systems

The influence of a methyl branching on the phase behaviour of a glycerophosphoethanolamine (PE) both in monolayers at the air-water interface and in multilayers in the lipid-water dispersions has been studied using grazing incidence X-ray diffraction (GIXD) and simultaneous small and wide-angle X-ray diffraction measurements, respectively. The methyl branch in 1-(alpha-methylstearoyl)-2-O-hexadecyl-PE (1) induces in centred rectangular phases of monolayers a change in the tilt direction towards NNN and suppresses the transition to a hexagonal phase with upright oriented chains, known from unbranched DPPE. In the lipid/water dispersions a phase sequence L-beta' --> L-alpha --> H-II was observed with increasing temperature. The introduction of the methyl branch results in the stabilisation of non-lamellar phases. Our investigations have shown that slight chemical changes in the hydrophobic region of PEs affect the phase behaviour drastically both in mono- and multilayers. (C) 1998 Elsevier Science B.V. All rights reserved.