PULSED NMR-STUDY OF LIPIDS, BOUND WATER AND SODIUM-IONS IN MACROSCOPICALLY-ORIENTED LECITHIN-WATER LYOTROPIC LIQUID-CRYSTAL MODEL MEMBRANE SYSTEMS

The temperature and orientation dependence of pulsed NMR 'free induction decay' signals have been studied in detail for lipid bilayers macroscopically-oriented between glass slides. Results for the lipid molecules (1H, 31P), bound water (2H2O) and ions dissolved in the aqueous phase (23Na) are presented. Bilayers of egg-lecithin, dimyristoyl lecithin and potassium oleate have been investigated. In the liquid crystal phase all the signals, including those from bound water and ions exhibit a |3 cos2φ{symbol} - 1| dependence on orientation of the bilayer normal to the magnetic field. In the case of DML samples, some orientation dependence of both 1H and 2H signals persists in the gel phase, indicating that the lipid molecules retain a degree of reorientational freedom about their long axes in this phase. At the gel-liquid crystal transition the 2H quadrupole spittings undergo a discontinuous change. Results are interpreted in terms of a model in which water molecules are bound to individual lipid head groups and reorient with them, while sodium ions are located in the aqueous channel between bilayers. © 1979.