Glassy character of DNA hydration water.

The coherent excitations of DNA hydration water at 100 K have been investigated by neutron scattering spectroscopy to extract the excess signal of D(2)O-hydrated DNA with respect to dry DNA samples. A structural characterization of the sample, through the analysis of the static structure factor, has suggested that DNA hydration water is largely in an amorphous state up to high hydration degree, with only a small contribution coming from slightly deformed crystalline ice. To describe the inelastic spectra of DNA hydration water, we exploited a phenomenological model already applied in similar disordered systems, such as bulk water (Sacchetti et al.

Collective density fluctuations of DNA hydration water in the time-window below 1 ps.

The coherent density fluctuations propagating through DNA hydration water were studied by neutron scattering spectroscopy. Two collective modes were found to be sustained by the aqueous solvent: a propagating excitation, characterised by a speed of about 3500 m/s, and another one placed at about 6 meV. These results globally agree with those previously found for the coherent excitations in bulk water, although in DNA hydration water the speed of propagating modes is definitely higher than that of the pure solvent.

Picosecond-time-scale fluctuations of proteins in glassy matrices: the role of viscosity.

Through elastic neutron scattering we investigated the fast dynamics of lysozyme in hydrated powder form or embedded in glycerol-water and glucose-water matrices. We calculated the relaxational contribution to the mean square displacements of protein hydrogen atoms. We found that the inverse of this quantity is linearly proportional to the logarithm of the viscosity of the solvent glassy matrix.

Molecular-beam study of the water-helium system: features of the isotropic component of the intermolecular interaction and a critical test for the available potential-energy surfaces.

We report molecular-beam measurements of the total integral cross sections for the scattering of water molecules by helium atoms. A combined analysis of the new experimental data together with available differential cross section results has allowed an accurate determination of the isotropic component of the interaction potential for this prototypical system. The potential well shows a depth of 0.