HYDRATION OF PHOSPHATIDYLCHOLINE REVERSE MICELLES AND MULTILAYERS - AN INFRARED SPECTROSCOPIC STUDY

Effects of incremental hydration from 0 to 10 water molecules per lipid were observed on the indicating C = O and asOPO stretching bands in the spectra of chloroform dispersions and cast films of DMPC, DPPC and DSPC. Besides these usual indicators we introduced a new one, antisymmetric CH3 stretching of the quaternary ammonium, which yields very useful information. The results indicate that the first water molecules diminish the interaction between the phosphate and quaternary ammonium groups by binding to the phosphate oxygens. Concomitant conformational change of the choline chain is revealed by changes in C-N frequencies in the 904-930 cm-1 absorption. No evidence is found for early water binding to carbonyl groups. In discussing these results use is made of ab-initio calculations of model systems and of NMR hydration studies of micelles.