DIELECTRIC-RELAXATION AND MOLECULAR MOTIONS IN LECITHIN-C-14 WATER SYSTEMS

The dependence of the complex permittivity on the frequency has been measured between 105 and 6 × 1010 Hz for aqueous solutions of dimyristoylphosphatidylcholine at several temperatures around the crystalline/liquid-crystalline phase transition temperature of the samples. To the observed data is fitted a sum of Cole-Cole functions and also a model relaxation function to yield various relaxation parameters. The variation of these parameters with temperature is discussed. A noteworthy result is that there exists a pronounced cooperativity effect in the diffusive motions of the phosphorylcholine groups at the bilayer surface and that the mobility of the cationic trimethylammonium head group is dramatically smaller than with lysolecithin micelles in aqueous solutions. As another remarkable result the hydration water relaxation time appears to be distinctly smaller than the reorientation time of the molecules in the pure solvent at the same temperature. © 1979.