| Summary: | 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 ( 1 H, 31 P), bound water ( 2 H 2 O) and ions dissolved in the aqueous phase ( 23 Na) 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 cos 2 φ{symbol} - 1| dependence on orientation of the bilayer normal to the magnetic field. In the case of DML samples, some orientation dependence of both 1 H and 2 H 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 2 H 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.
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