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

摘要

We used high-resolution quasielastic neutron scattering spectroscopy to studythe single-particle dynamics of water molecules on the surface of hydrated DNAsamples. Both H2O and D2O hydrated samples were measured. The contribution ofscattering from DNA is subtracted out by taking the difference of the signalsbetween the two samples. The measurement was made at a series of temperaturesfrom 270 K down to 185 K. The Relaxing-Cage Model was used to analyze thequasielastic spectra. This allowed us to extract a Q-independent averagetranslational 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. Thecoincidence of the dynamic transition temperature Tc of DNA, signaling theonset of anharmonic molecular motion, and the FSC temperature TL of thehydration water suggests that the change of mobility of the hydration watermolecules across TL drives the dynamic transition in DNA.