We have simulated structure and dynamics of water in the grooves of a DNAduplex using moleculear dynamics simulations. We find signatures of a dynamicaltransition in both translational and orientational dynamics of water moleculesin both the major and the minor grooves of a DNA duplex. The transition occursat a slightly higher temperature ($T_{GL} \approx $ 255 K) than the temperature($T_L\approx$ 247 K) where the bulk water is conjectured to undergo a dynamicaltransition. Groove water, however, exhibits markedly different temperaturedependence of its properties from the bulk. Entropy calculations reveal thatthe minor groove water is ordered even at room temperature and the transitionat $T \approx$ 255 K can be characterized as a {\em strong-to-strong} dynamicaltransition. The low temperature water is characterized by pronouncedtetrahedral order, as manifested in the sharp rise near $109^{\circ}$ in theO-O-O angle distribution. We find that Adams-Gibbs relation betweenconfigurational entropy and translational diffusion holds quite well when thetwo quantities are plotted together in a master plot for different region ofaqueous DNA duplex (bulk, major and minor grooves) at different temperatures.The activation energy for the transfer of water molecules between differentregions of DNA is found to be independent of temperature.
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