Experimental Evidence of Fragile-to-Strong Dynamic Crossover in DNA Hydration Water

Abstract

We used high-resolution quasielastic neutron scattering spectroscopy to study the single-particle dynamics of water molecules on the surface of hydrated DNA samples. Both H2O and D2O hydrated samples were measured. The contribution of scattering from DNA is subtracted out by taking the difference of the signals between the two samples. The measurement was made at a series of temperatures from 270 K down to 185 K. The Relaxing-Cage Model was used to analyze the quasielastic spectra. This allowed us to extract a Q-independent average translational relaxation time of water molecules as a function of temperature. We observe clear evidence of a fragile-to-strong dynamic crossover (FSC) at TL = 222+-2 K by plotting log of average translational relaxation time vs. T. The coincidence of the dynamic transition temperature Tc of DNA, signaling the onset of anharmonic molecular motion, and the FSC temperature TL of the hydration water suggests that the change of mobility of the hydration water molecules across TL drives the dynamic transition in DNA.

4 pages (Latex), 5 figures (Postscript)

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• Pressure Dependence of Fragile-to-Strong Transition and a Possible Second Critical Point in Supercooled Confined Water
• Observation of Fragile-to-Strong Dynamic Crossover in Protein Hydration Water
• The High-Flux Backscattering Spectrometer at the NIST Center for Neutron Research
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• Dynamics from elastic neutron-scattering via direct measurement of the running time-integral of the van Hove distribution function
• Influence of Surface Hydrophilicity and Hydration on the Rotational Relaxation of Supercooled Water on Graphene Oxide Surfaces
• Dynamic Heterogeneity in Crossover Spin Facilitated Model of Supercooled Liquid and Fractional Stokes-Einstein Relation