The dynamics of water molecules in ionic solution. I. the application of quasi-elastic neutron scattering to the study of translational diffusive proton motion (original) (raw)
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Influence of Ions on Water Diffusion—A Neutron Scattering Study
The Journal of Physical Chemistry B, 2013
Using quasielastic neutron scattering spectroscopy, we measured the averaged translational diffusion of water in solutions of biologically relevant salts, NaCl, a kosmotrope, and KCl, a chaotrope. The analysis revealed the striking difference in the influence of these ions on water dynamics. While the averaged water diffusion slows down in the presence of the structure making (kosmotrope) Na + ion, the diffusion becomes faster in the presence of the structure breaking (chaotrope) K + ion. The latter means that, despite strong Coulombic interactions introduced by the K + ions, their disruption of the hydrogenbonding network is so significant that it leads to faster diffusion of the water molecules.
Journal of the American Chemical Society, 1991
The method of high-resolution incoherent quasi-elastic neutron scattering (IQENS) is applied to investigate the translational diffusive motion of water protons and the cation to water proton binding time in concentrated Cia3+, AI3+, Fe3+, and Dy3+ aqueous solutions. The IQENS data for the Ga3+, AI3+, and Fe3+ solutions are consistent with the model for slow exchange wherein the dynamic hydration number nh = 6. This gives a limit of T , 2 5 X s for the binding time of protons in the hexa-aquo metal ion species. The IQENS data for the Dy3+ aqueous solution show that the water protons are in intermediate or slow exchange, which sets a lower limit of T ] > s. The second-shell water protons in the Cia3+, AI3+, and Fe3+ solutions are not observed to be in slow exchange with the cation which gives a binding time for these protons of T , (~) C 5 X s.
Journal of the American Chemical Society, 1991
The method of high-resolution incoherent quasi-elastic neutron scattering (IQENS) is applied to investigate the translational diffusive motion of water protons and the cation to water proton binding time in concentrated Cia3+, AI3+, Fe3+, and Dy3+ aqueous solutions. The IQENS data for the Ga3+, AI3+, and Fe3+ solutions are consistent with the model for slow exchange wherein the dynamic hydration number nh = 6. This gives a limit of T , 2 5 X s for the binding time of protons in the hexa-aquo metal ion species. The IQENS data for the Dy3+ aqueous solution show that the water protons are in intermediate or slow exchange, which sets a lower limit of T ] > s. The second-shell water protons in the Cia3+, AI3+, and Fe3+ solutions are not observed to be in slow exchange with the cation which gives a binding time for these protons of T , (~) C 5 X s.
The ion to water-proton binding time in aqueous ionic solution
Physica B: Condensed Matter, 1992
A summary is given of the information which is made available, on the ion to water-proton binding time in aqueous ionic solution, by using the method of high energy-resolution incoherent quasi-elastic neutron scattering (IQENS). A full account is presented of the physical significance of the dynamic hydration number, n h, which is measured by the method. Results are given for the cation to water-proton binding time, r,, in several solutions (Cu e, Zn:*, Nd :'~ ) for which it has proved difficult or impossible to measure the water exchange rate by using more conventional nuclear magnetic resonance techniques. By investigating the sensitivity of the method to the value of n,, in certain trivalent metal ion solutions (AIm+, Ga ~', Cr~,Fe ~ ) it has proved possible to place limits on the binding time of second-shell water-protons to the cation and also to gain information on hydrolysis effects.
Molecular Physics, 1989
After some preliminary considerations on the abnormally high proton mobility in acidic solutions, quasielastic neutron scattering results on concentrated sulphuric and nitric solutions are presented. The mean proton translational and rotational diffusive motions are first characterized and compared to those of pure water. Then, the observation of an additional component due to a faster dynamical process is discussed. As this component is also present in concentrated salt solutions, it is concluded that its origin is more related to the peculiar vibrational density of states of electrolyte solutions than to fast proton diffusivity.
Journal of Molecular Liquids, 2014
Neutron scattering is an excellent tool to study the dynamics of hydrogen-rich materials. In the present work we subsume our results on pyridinium-based ionic liquids. We have performed inelastic, quasielastic and elastic. Neutron scattering is an excellent tool to study the dynamics of hydrogen-rich materials. In the present work we subsume our work on pyridinium-based ionic liquids. We have performed inelastic, quasielastic and elastic neutron scattering experiments aiming to understand the different dynamical processes that occur at different temperatures in ionic liquids. Using quasielastic scattering we obtained data that can be described as a superposition of localized dynamical processes and long range diffusion. The localized processes, which originate from the alkyl chain and the pyridinium ring of the cation, have been modelled in terms of the so-called Gaussian model. The influence of the length of the alkyl chain, attached to the cation, on the dynamical processes is discussed in detail. Furthermore we show neutron backscattering data, obtained on partially deuterated samples, that clearly demonstrate the melting of the alkyl chain and the activation of methyl end-group rotations at low temperatures. Finally, the power of deuterium labelling is evidenced for inelastic neutron scattering data.
The Journal of Chemical Physics, 1996
A detailed study of the single-particle dynamics of liquid water in normal and supercooled regime has been carried out by comparing molecular dynamics ͑MD͒ simulation results with now available high resolution quasielastic neutron scattering ͑QENS͒ data. Simulation runs have been performed at 264, 280, 292, and 305 K, using the extended simple point charge model, well suited for reproducing single-particle properties of H 2 O. The microscopic dynamics has been probed over a wide range of times and distances. The MD results indicate that a substantial coupling between translational and rotational dynamics exists already at about 1 ps. The decay of the translational dynamic correlations has been phenomenologically analyzed in terms of three exponential components, and the agreement between the parameters thus obtained from experimental and simulation derived datasets is quite satisfactory. Both QENS and MD data can not be described with sufficient accuracy by simple diffusion models over the entire range of examined wave vectors.
The Journal of Chemical Physics, 2006
Quasi-elastic neutron scattering (QENS) measurements have been performed to investigate the surface selfdiffusion of hydrogen molecules. A monolayer of molecular hydrogen was adsorbed on a carbon material commonly used in polymer electrolyte membrane fuel cells, called XC-72. QENS spectra were recorded at the time-of-flight spectrometer IN5 at Institut Laue-Langevin (ILL) in Grenoble at 40, 50, 60, and 70 K. By using the Chudley & Elliott model for jump diffusion, we found the diffusion coefficient at each temperature. The logarithm of the diffusion coefficient was plotted versus the inverse of the temperature to give the coefficient in the Arrhenius equation. From this, we can estimate the diffusion at higher temperatures as well. Our observed diffusion follows the same trend as that found for hydrogen molecules on the surface of singlewalled carbon nanotubes and Grafoil.
Dynamics of water studied by coherent and incoherent inelastic neutron scattering
Journal of Molecular Structure, 1991
This paper reviews the more recent results obtained on the dynamics of water by neutron scattering and shows that some information can be obtained by this technique at the microscopic level of the hydrogen bond. It also accounts for some very recent results obtained with the hydrated protein C-phycocyanin.