RAMAN-SPECTRA OF HYDRATED PHOSPHOLIPID-BILAYERS .2. WATER AND HEADGROUP INTERACTIONS

Raman spectroscopy was used to study the effects of dehydration on vibrational spectra of lipid and water in multilamellar dispersions of DMPC1 over a relative humidity (RH) range of 99% RH to 0% RH. The Raman spectra indicated that at 30 and 40-degrees-C, removal of water induced at least two phase changes in the lipid. Integrated intensities of the OH stretching band were used to estimate the amount of water in the dispersion and confirmed that there was water present even at 0% RH. Relative changes in the profiles of the 3420- and 3240-cm-1 regions of the OH stretching band suggest that water molecules form stronger hydrogen bonds at low levels of hydration than water-water hydrogen bonds in fully hydrated lipid dispersions. The intensity and frequency of the symmetric C-N stretching band were found to be sensitive to the concentration of water in the lipid dispersion which provides evidence that head-group structure is influenced by the degree of hydration.