AN FT-IR STUDY OF WATER HYDRATING DIPALMITOYLPHOSPHATIDYLCHOLINE MULTIBILAYERS AND REVERSED MICELLES

Infrared spectra of H2O and HDO (5% D2O in H2O) in the stretching and bending regions are presented and discussed with respect to location and energy of bonding of the first water molecules hydrating the polar heads of the title systems. Spectral features of water in the higher hydrated bilayers are compared to those of ordinary water. The nu1,3 and nu2 bands of water at low hydration are only slightly sensitive to low temperatures. As an indication that these water molecules do not freeze, we take the absence of any major effects of cooling as the main evidence for the origin of the bandwidth. We propose that the nu1,3 band broadening is of a statistical character, i.e. it is caused by various binding topologies of the water molecules, and not by homogeneous broadening mechanisms. With highly hydrated bilayers, the formation of amorphous ice is observed. Differences are noted between some spectral features of water inside the reverse micelles and water hydrating the bilayers, particularly at subzero temperatures.