Influence of sucrose on surrounding water by extended frequency range depolarized light scattering

The role of disaccharides as bioprotectors is intimately connected with their interaction with hydration water. To investigate this issue, depolarized light scattering spectra of aqueous solutions of sucrose have been recorded in the range 0.3 GHz - 30 THz by combining the use of a double monochromator and a multipass Fabry-Perot interferometer. The spectra give us information on both the rotational diffusion of a single sucrose molecule and the effect induced by this solute on the picosecond dynamics of water. In particular, two distinct relaxation processes have been identified, and assigned to hydration and bulk water molecules. The mobility of water localized within the sugar hydration shell is found to be lower than the mobility of water in bulk. The number of molecules involved in the slower dynamics and the extent of retardation are quantified and discussed in comparison with the results recently obtained for other mono and disaccharide solutions.