Estimation of Differently Bound Water Molecules for the Gel Phase of Dimyristoylphosphatidylethanolamine-Water System as Studied by DSC and (2)H-NMR Spectroscopy.

A measurement of (2)H spin-lattice relaxation time, T(1), forD(2)O was performed with a high resolution liquid NMR apparatus fortwo samples of dimyristoylphosphatidylethanolamine (DMPE)-D(2)Osystem in a full hydration at varying temperatures of -20, -10, and 5 (°)C, and both components and compositions of differently boundfreezable water molecules were estimated from a best-fitted curve toexperimental inversion recovery data. A choice of the best-fitted curve wasbased on a distribution of weighted residuals for the experimental data. Asingle component was found for a temperature of -20 (°)C. At 5 (°)C, where all the freezable water exists in the liquid state, threecomponents were observed to be characterized by T(1) values ofapproximately 20, 100, and 200 ms, respectively. By comparingcompositions of these individual components with those obtained in ourprevious DSC study, it was revealed that the first and secondarycomponents are members of freezable interlamellar water and the last oneis comparable to bulk water.