Anomalous behaviour of supercooled water and its implication for protein dymamics

Book chapter, 2008

Water is the foundation of life, and without it life as we know it would not exist. An organism consists to a large extent of water and, apart from a few larger reservoirs, almost all water in a living organism is closely associated with surfaces of biomolecules of different kinds. This so-called biological water is known to affect the dynamics of biomaterials such as proteins, which. in turn is crucial for its functions. However, how and why the surrounding environment affects the dynamics of proteins and other biomolecules is still not fully understood. Recently, it was suggested [Fenimore et al. PNAS 2004, 101 14408] that local and more global protein motions are slaved (or driven) by the local beta-relaxation and the more large-scale cooperative a-relaxation in the surrounding solvent, respectively. In this chapter we present results from dielectric measurements on myoglobin in water-glycerol mixtures that support this slaving idea. Moreover, we show how confined supercooled water changes its dynamical behaviour from a low temperature Arrhenius behaviour to a high temperature non-Arrhenius behaviour at a certain temperature (around 200 K), and then we discuss likely explanations for the crossover and its consequence for protein dynamics.