The glassy state of water: A 'stop and go' device for biological processes

Abstract

What is unique about the properties of intracellular water that prevent its replacement by another compound? We tackle this question by combining experimental techniques as diverse as Electron Spin Resonance, Thermally Stimulated Depolarization Current, broadband dielectric spectroscopy, and neutron diffraction to a set of samples, namely a globular enzyme, intact plant seeds, and porous silica glasses, largely differing in terms of composition and complexity. Results indicate that interfacial and intracellular water is directly involved in the formation of amorphous matrices, with glass-like structural and dynamical properties. We propose that this glassiness of water, geometrically confined by the presence of solid intracellular surfaces, is a key characteristic that has been exploited by Nature in setting up a mechanism able to match the quite different time scales of protein and solvent dynamics, namely to slow down fast solvent dynamics to make it overlap with the much slower protein turnover times in order to sustain biological functions. Additionally and equally important, the same mechanism can be used to completely stop or slow down biological processes, as a protection against extreme conditions such as low temperature or dehydration © 2006 Springer.