Incoherent quasielastic neutron scattering from H2O and aqueous ZnCl2 solutions

A study of the diffusive motions of the protons in pure water and ZnCl₂ aqueous solutions has been performed, using incoherent quasielastic neutron scattering. It is shown that it is essential to take into account the rotational motion of the water molecules. The translational linewidth is conveniently fitted over the whole Q-range, using the Random Jump Diffusion model for which the jump length turns out to be roughly the same for pure H₂O and the saturated solution, fairly close to the distance between protons in the water molecule.     

Small angle neutron scattering and structural properties in electrolytic solutions

A new direct indication concerning the structural properties of liquid systems is obtained for the first time. Small angle neutron scattering (SANS) measurements have been performed on solutions of ZnCl₂, NiCl₂, CuBr₂ in D₂O and in non aqueous solvent (EtOAc). The spectra, taken at room temperature, as a function of concentration, in the range $\text{0.019 ? K ? 0.25 (}\text{A}\text{?}{}^{\mathrm{?1}}\text{)}$ show in aqueous solvent an “abnormal” k-dependent small angle coherent cross section. This anomalous contribution clearly indicates the existence in the systems of correlated regions (～ 30 Å) perhaps connected through a preferred distance of ～ 50 Å. Also in pure water the results seem to indicate the existence of correlated regions of finite size.     

Structure of supercooled and glassy water under pressure

We use molecular-dynamics simulations to study the effect of temperature and pressure on the local structure of liquid water in parallel with neutron-scattering experiments. We find, in agreement with experimental results, that the simulated liquid structure at high pressure is nearly independent of temperature, and remarkably similar to the known structure of the high-density amorphous ice. Further, at low pressure, the liquid structure appears to approach the experimentally measured structure of low-density amorphous ice as temperature decreases. These results are consistent with the postulated continuity between the liquid and glassy phases of H2O.     

Hydration water in dynamics of a hydrated beta-lactoglobulin

Incoherent spin-echo signals of a hydrated β-lactoglobulin protein were investigated, at 275 and 293 K. The intermediate scattering functions I(Q,t) were divided in two contributions from surface water and protein, respectively. On one hand, the dynamics of the surface water follows a KWW stretched exponential function (the exponent is ~0.5), on the other hand, that of the protein follows a single exponential. The present results are consistent with our previous results of hydrated C-phycocyanin combining elastic and quasielastic neutron scattering and by molecular dynamics simulation.     

Phase transitions of interfacial water at 165 and 240 K. Connections to bulk water physics and protein dynamics

We are considering water adsorbed as a monolayer on Vycor, a porous silica glass. The interfacial water molecules interact with the substrate through hydrogen bonding with the numerous silanol (Si-OH) groups present all over the surface. This special form of water exhibits peculiar dynamical properties. A combined calorimetric, diffraction, high resolution quasi-elastic and inelastic neutron scattering study shows that interfacial water experiences a glass transition at 165 K and a liquid-liquid transition at 240 K from a low-density to a high density-liquid. We show that this unusual behaviour, compared to the bulk, is due to a strong weakening of the hydrogen-bond strength, possibly due to the reduced number of hydrogen-bonds engaged by water molecules when they are in an interfacial two dimensional situation. The connections of these findings to the physics of bulk water and protein dynamics are discussed.