α,α-trehalose-water solutions.: 3.: Vibrational dynamics studies by inelastic light scattering

Results of Raman Scattering measurements performed on aqueous solutions of alpha,alpha-trehalose, an effective bioprotector against dehydration and freezing, are reported. To acquire some insight into the effects of trehalose on the hydrogen-bond network of water, we investigate the intramolecular O-H and intermolecular OH ... O stretching and bending modes, which are particularly sensitive to environmental modifications. We will show that the shape of the O-H stretching band can be reproduced by a suitable superposition of the spectra of bulk and hydration water. The relative amount of the two contributions changes with concentration and temperature, furnishing information on the number of the water molecules bonded to trehalose. In addition, two different approaches are employed for the O-H stretching region analysis, namely a decomposition of the isotropic spectra into an "open" and a "closed" contribution and a spectral stripping procedure to extract the "collective" contribution from the polarized spectra. Both the procedures agree in suggesting that trehalose promotes a destructuring effect on the tetrahedral H-bond network of pure water. These conclusions are also supported by the analysis of the intermolecular spectral contributions. Considered together, these results make plausible the hypothesis that trehalose obstructs the crystallization process, reducing the amount of freezable water, namely destroying the network of water compatible with that of ice.