Anomalies of Bulk , Nanoconfined and Protein - Hydration Water

Anomalous behavior of water has been a long standing problem in physical and chemical sciences. The seeming divergence of response functions such as specific heat, compressibility, and coefficient of thermal expansion at low temperatures T , have been interpreted by some authors as the evidences for the liquid-gas spinodal retracing back to positive pressures P at low temperatures. Other authors have interpreted these anomalies as the result of a hypothesized first order liquid-liquid (LL) phase transition line separating high density liquid (HDL) at high temperatures and a low density liquid (LDL) at low temperatures which ends in a critical point. Finally, some authors have interpreted these anomalies as not requiring a singularity. A clue to test the validity of these scenarios comes from recent neutron scattering experiments on water in nanoscale confinement, where crystallization is suppressed. Such nanoscale confined water displays a crossover in the dynamics from non-Arrhenius at high T to Arrhenius at low T . To test if the LL critical point scenario is consistent with the dynamic crossover observed in the experiments, the dynamics of nanoconfined and bulk water is studied extensively by performing computer simulations of different water and water-like models which exhibit a liquid-liquid phase transition at low temperatures. It it found that the presence of a liquid-liquid critical point leads to a dynamic crossover. The locus of the temperature of crossover in the (T, P ) plane coincides with the locus of specific