Effects of tumbling and lateral diffusion on phosphatidylcholine model membrane 31P-NMR lineshapes

Two factors determining the isotropic motional averaging of NMR spectra obtained from lipids in model and biological membranes systems are particle tumbling and lateral diffusion. The influence of these motions (of which the magnitudes are detemined by the medium viscosity and temperature) on the 31P-NMR spectra arising from unilamellar dioleoyl phosphatidylcholine vesicles of a defined size are examined. It is shown that the lineshapes obtained are in good agreement with those predicted by the theory of motional narrowing. These results are discussed with regard to order parameter determinations and polymorphic phase identifications as obtained by NMR techniques.