  High-resolution quasi-elastic neutron scattering spectroscopy was used to
measure H2O and D2O hydrated RNA samples. The contribution of scattering from
RNA was subtracted out by taking the difference of the signals between the two
samples. The measurements were made at a series of temperatures from 270 K down
to 180 K. The Relaxing-Cage Model was used to analyze the difference
quasi-elastic spectra. We observed clear evidence of a fragile-to-strong
dynamic crossover (FSC) at TL = 220 K in RNA hydration water. We further show
that the mean-square displacement of the hydrogen atoms in both RNA and its
hydration water exhibit a sharp change in slope at approximately the same
temperature 220 K. This latter fact suggests that the dynamic transition (or
the glass transition) in RNA is triggered by the abrupt change of mobility of
the hydration water at its FSC temperature TL.
