Magnetic resonance studies on membrane and model membrane systems: III. Fatty acid motions in aqueous lecithin dispersions

Magnetic resonance spectra and relaxation rates of sonicated and unsonicated vesicles of egg yolk lecithin are reviewed and compared. The NMR relaxation rates differ by about two orders of magnitude while the ESR order parameters show no such variation. The apparent contradiction may be removed by proposing that the ESR data reflect the order of segments of the fatty acids while the NMR relaxation rates reflect positional fluctuations. Macroscopic vesicular tumbling contributes insignificantly to the relaxation rates. Resonance and non-resonance data converge on a dynamic model in which the fatty acid molecules are configurationally mobile yet relatively ordered.