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Extended frequency range depolarized light scattering is a spectroscopic technique operating in the GHz-THz range that, applied to aqueous solutions of biomolecules, is able to disentangle the dynamics of the solute from that of water, and relaxation processes of bulk from those of hydration water. Experiments performed on aqueous solution of a variety of biological systems of different nature, such as small hydrophobic and hydrophilic molecules, amino acids, dipeptides, and proteins, have shown that a significant increase in the dynamical retardation and in the extent of the perturbation of water surrounding solute molecules occurs at increasing chemical complexity of the solute. The behavior of aqueous solutions of lysozyme is here analyzed in detail, as a function of solute concentration. Our results provide evidence of a dynamical perturbation extending over more than three water layers in diluted solutions. We find a strong reduction in the average hydration number at increasing solute concentration that cannot be explained by the random superposition of hydration layers among lysozyme molecules in close proximity. This behavior is consistent with the formation of clusters in solution. © 2014 Elsevier B.V.

We measure the dynamic structure factor of m-toluidine through inelastic X-ray scattering in the mesoscopic Q range between 1 and 10 nm(-1), where the static structure factor exhibits a prepeak resulting from a molecular spatial organization in nanometer size clusters, due to the formation of hydrogen bonds. We present experimental evidence of the square-root cusp in the temperature behavior of the non-ergodicity factor of in-toluidine which supports the view that the mode-coupling theory succeeds in describing the dynamics of supercooled molecular liquids, even for liquids with a local order, notwithstanding the cage formation is controlled by a mechanism different from the packing constraints typical of simple liquids. Moreover, we report on the behavior of the non-ergodicity factor in the low-temperature and wavevector regimes, finding a confirmation of the phenomenologic law proposed by Scopigno et al. [T. Scopigno, G. Ruocco, F. Sette; G. Monaco, Science 302 (2003) 849] which correlates the vibrational dynamics of the glass to the fragility of the supercooled liquid. (c) 2006 Published by Elsevier B.V.