Study on dynamics of hydrated water molecules by high-pressure NMR spectroscopy

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The spin-lattice relaxation rates(RィイD21ィエD2) of D andィイD117ィエD1O nuclei of a heavy water (DィイD22ィエD2O) molecule in alkali bromide (LiBr, NaBr, KBr and CsBr) aqueous solutions were measured in the range of 0-1.0 molkgィイD1-1ィエD1, 10-50℃ and 0.1-300 MPa by NMR spectroscopy. In these solution, the RィイD21ィエD2 value varies linearly with concentration under constant temperature and constant pressure. Even under high pressure, R1 can be expressed as a weighed sum of the limiting relaxation rates in infinite dilution based on two-state model. The activation volume is estimated from pressure dependence of the rotational correlation times (τ) for the DィイD22ィエD2O molecule coordinated to alkali metal ions. It decreases with increasing radius of alkali metal ion and with increasing pressure at each temperature. The activation energy is estimated from temperature dependence of τ. It decreases with increasing radius of alkali metal ion and with increasing temperature even under high pressure.