title: Orientation and flexibility of the choline head group in phosphatidylcholine bilayers.
abstract: The average orientation and flexibility of the phosphorylcholine group are deduced from deuterium and phosphorus-31 nuclear magnetic resonance measurements of unsonicated phosphatidylcholine bilayers in the liquid crystalline state. The experimental data are consistent with a model in which the polar head group exhibits a restricted flexibility characterized by rapid transitions between two enantiomeric conformations. A completely flexible or a completely rigid head group structure can be excluded. The phosphorylcholine residue is found to be bent at the position of the phosphate group, due to a gauche-gauche conformation of the phosphodiester linkage. The choline dipole is aligned parallel to the plane of the membrane, which is in agreement with X-ray and neutron diffraction studies. The average orientation of the phosphorylcholine group is therfore the same as that of the phosphorylethanolamine head group.
mesh_terms: D002794:Choline; D003460:Crystallization; D005997:Glycerylphosphorylcholine; D009682:Magnetic Resonance Spectroscopy; D008567:Membranes, Artificial; D008956:Models, Chemical; D008968:Molecular Conformation; D010713:Phosphatidylcholines
chemical_list: D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D005997:Glycerylphosphorylcholine; D002794:Choline