Molecular motions in compressed liquid heavy water at low temperatures

Abstract

The NMR deuteron spin–lattice relaxation times T1, self-diffusion coefficients D, and shear viscosities η have been measured as a function of pressure in the temperature interval −15 to 10°C. The low-pressure extreme of the measurements is Ice I, whereas Ice V represents the high-pressure boundary of the experiments. In analogy with anomalous motional behavior in compressed liquid water, the initial compression of liquid D2O in the temperature interval studied results in higher motional freedom of D2O molecules so that T1 and D dependences with pressure exhibit a maximum and shear viscosity shows a minimum. This is a result of distortion and weakening of the hydrogen bond network owing to compression. Further compression hinders molecular motions as a result of increased repulsive interactions due to higher packing. This study also enables us to test the applicability of hydrodynamic equations at the molecular level for liquid heavy water. Analysis of the relaxation and shear viscosity data show that the Debye equation fails to describe the density effects on reorientation of D2O molecules. It appears that the success of the Debye equation to describe temperature effects on reorientation of H2O and D2O molecules at 1 bar is accidental. However, the data show that the deuteron relaxation rate (1/T1)D is proportional to η/T under isochoric conditions. The fact that the slope of the (1/T1)D vs η/T plot diminishes with increasing density indicates that compression leads to diminished coupling between rotational and translational motions of water molecules. The shear viscosity and self-diffusion data show that the Stokes–Einstein equation does not represent the relationship between D and η in liquid heavy water. A brief discussion of the isotope effects on shear viscosity in liquid D2O and H2O is presented.

Cold Denaturation of Proteins

“…Several studies of dielectric (33,34) and NMR relaxation (35)(36)(37) in liquid H 2 0 and D 2 0 indicated that the Debye equation describes well the temperature dependence of the reorientation of water molecules at atmospheric pressure. However, the results of high-pressure studies (29,30,38) show convincingly that the Debye equation fails to account for the density effects on reorientation of water molecules. One has to conclude that the success of the Debye equation for reorientation of water at 1 bar is accidental.…”

“…In several studies (29,30) we took advantage of the phase diagram of water and heavy water and measured various transport properties of these liquids down to temperatures of -15°C. Nuclear magnetic resonance spin-lattice relaxation time Ti, self-diffusion coefficients, and shear viscosities were measured as a function of pressure in the temperature interval -15°C to 30°C.…”

Cold and thermal neutron scattering in liquid water—II: Scattering laws and group constants for HO and DO

“…ðTÞ is assumed to obey an Arrhenius behavior like liquid H 2 O and have a magnitude determined by the fitting of the experimental results [28][29][30]: …”

Pressure and Temperature Dependence of the Longitudinal Deuterium Relaxation Times in Supercooled Heavy Water to 300 MPa and 188 K

“…should lower to 204 kHz which is close to our value. Different authors have claimed the CDQc to be independent of temperature [9,18] and only slightly decreasing with increasing density [8,9,35,36]. We therefore assume a constant value of the CDQC over the range of temperatures and pressures measured.…”