INVESTIGATION OF PHOSPHATIDYLETHANOLAMINE BILAYERS BY DEUTERIUM AND P-31 NUCLEAR MAGNETIC-RESONANCE

The motion of the ethanolamine head group in unsonicated lipid bilayers above and below the phase transition is studied by deuterium and P magnetic resonance. For this purpose, dipalmitoyl-3-sn-phosphatidylethanolamine is selectively deuterated at the 2 ethanolamine C atoms. The deuterium quadrupole splittings of the corresponding bilayer phases are measured at pH 5.5 as a function of temperature. The 31P chemical shift anisotropies of planar-oriented and randomly dispersed samples of dipalmitoyl-3-sn-phosphatidylethanolamine are measured at pH 5.5 and 11 by applying a proton-decoupling field. The knowledge of the static chemical shift tensor (Kohler and Klein, 1976) provides the basis for a quantitative analysis of the head-group motion. The NMR data are consistent with a model in which the ethanolamine group is rotating flat on the surface of the bilayer with rapid transitions occurring between 2 enantiomeric conformations.