Neutron Scattering Studies of Dynamic Crossover Phenomena in a Coupled System of Biopolymer and Its Hydration Water

We have observed a Fragile-to-Strong Dynamic Crossover (FSC) phenomenon of the α-relaxation time and self-diffusion constant in hydration water of three biopolymers: lysozyme, B-DNA and RNA. The mean squared displacement (MSD) of hydrogen atoms is measured by Elastic Neutron Scattering (ENS) experiments. The α-relaxation time is measured by Quasi-Elastic Neutron Scattering (QENS) experiments and the self-diffusion constant by Nuclear Magnetic Resonance (NMR) experiments. We discuss the active role of the FSC of the hydration water in initiating the dynamic crossover phenomenon (so-called glass transition) in the biopolymer. The latter transition controls the flexibility of the biopolymer and sets the low temperature limit of its biofunctionality. Finally, we show an MD simulation of a realistic hydrated powder model of lysozyme and demonstrate the agreement of the MD simulation with the experimental data on the FSC phenomenon in the plot of logarithm of the α-relaxation time vs. 1/T.