Relaxation Processes in Supercooled Confined Water and Implications for Protein Dynamics

Abstract

We show that the viscosity-related main (alpha) relaxation of confined water vanishes at a temperature where the volume required for the cooperative alpha relaxation becomes larger than the size of the geometrically confined water cluster. This occurs typically around 200 K, implying that above this temperature we observe a merged alpha-beta relaxation, whereas below it only a local (beta) relaxation remains. This also means that such confined supercooled water does not exhibit any true glass transition, in contrast to other liquids in similar confinements. Furthermore, it implies that deeply supercooled water in biological systems, such as membranes and proteins, generally shows only a local beta relaxation, a finding of importance for low temperature properties of biological materials.