Autori: M. Rovere and P. Gallo

During the last decade there has been a great progress in statistical mechanical methods applied to the study of fluids confined in disordered porous materials. This is a vast and important field which is connected from on one side to fundamental problems like phase transitions in confined space and on the other side with the study of biological problems like water-protein interaction. While the study of the former aspects requires to account for the interconnected network of pores usually present in the disordered confining system, the calculations relevant for biochemical applications must include a detailed modeling of the pore surface in contact with the fluid.

We will concentrate mainly on this second type of approach, where computer simulation plays an important role. Emphasis will be put in particular on the recent studies of water confined close to proteins and porous glasses. Understanding how the dynamics of liquid water is perturbed by the interaction with hydrophilic or hydrophobic substrates at various levels of hydration is fundamental for both biological and technological problems. Many experimental studies on confined and interfacial water showed evidence of a substantial degree of slowing down of water in the proximity of a polar surface. We will present some results of the dynamics simulation of water confined in a vitreous silica cell modeled to represent the pores of Vycor glass. The latter has been intensively studied by experimentalists as a representative of mesoscale confining systems with strong hydrophilic interaction.

At all hydration levels we observe a distortion of the H-bond tetrahedral network of water molecules in the regions close to the substrate. At lower hydrations we observe the onset of a slow dynamics probably due to the cage effect. The conventional picture of the stochastic single-particle diffusion looses therefore its validity already at room temperature for confined water.

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