Reorientation of hydration water during the thermotropic main phase transition of 1-palmitoyl-2-oleolyl-sn-glycero-3-phosphocholine (POPC) bilayers at low degrees of hydration

Calorimetric scans of a number of low-hydrated phospholipids provide quite complex heat capacity profiles during the thermotropic main phase transition. This short study proposes some explanations that are based on experimental data obtained from four different methods (DSC, 31P-NMR, 2H-NMR, X-ray diffraction). eliminary results show for POPC in which way DSC data are related to the melting of the hydrocarbon chains. Furthermore, the quadrupolar splitting data obtained from the 2H-NMR spectra of hydration water reveal how the water reorientation might contribute to the main phase transition of phospholipids.