PHASE-BEHAVIOR OF A METHYL-BRANCHED PHOSPHATIDYLETHANOLAMINE IN 2-DIMENSIONAL AND 3-DIMENSIONAL SYSTEMS

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