Components and fractions for differently bound water molecules of dipalmitoylphosphatidylcholine–water system as studied by DSC and 2H-NMR spectroscopy

Abstract

Differently bound water molecules of dipalmitoylphosphatidylcholine (DPPC)–H 2O system were investigated with differential scanning calorimetry (DSC). According to a method previously reported by us, the ice-melting DSC curves of the DPPC–H 2O samples of varying water contents were deconvoluted into multiple components, and the ice-melting enthalpies for the individual deconvoluted components were used to estimate average molar ice-melting enthalpies for freezable interlamellar and bulk waters, respectively. With these average molar ice-melting enthalpies, the numbers of differently bound water molecules of the DPPC–H 2O system were calculated at varying water contents and were used to construct a water distribution diagram of this system. Furthermore, to evaluate the reliability of the present DSC deconvolution method, 2H-NMR T 1 measurements of DPPC– 2H 2O system were carried out at 5 °C of the gel phase temperature, and components and fractions for differently bound water ( 2H 2O) molecules were estimated from the analysis of nonexponential magnetization recovery curves.