The Dynamics of Water Molecules

Nagy et investigated the effect of the external electric field on the dynamics of water molecules at the water/metal interface. They found... 

An important signature of the dynamics of water molecules is the reorientation of its dipole vector that can be probed by dielectric and NMR measurements. We have calculated the single molecule dipole-dipole time correlation function (TCF), defined as,... 

Section 2.2.1 summarizes the spectroscopic measurements that have been performed to examine the dynamics of water molecules in hydrate versus ice networks. Sections 2.2.2 and 2.2.3 provide a brief overview of the mechanical and thermal properties, respectively, of hydrates compared to ice. Characterization of these properties will aid in facilitating the accurate interpretation of data obtained from in situ detection measurements of natural hydrates. These natural hydrates occur in sediments in permafrost and marine environments. The hydrate mechanical and thermal properties are also important in the evaluation of the location and distribution of natural hydrates in sediments. (Further details are given in Chapter 7—Hydrates in the Earth.)... 

In order to characterize the hydration phenomena in more detail, it is worthwhile to obtain information on the dynamics of water molecules involved in the hydration shell. One of the useful techniques for such a purpose is 170-NMR spectroscopy. In the so-called two-state model, 170 nuclei in the aqueous solution are assumed to be distributed between the following two motional states the water in the hydration shell and the bulk water. Under this assumption, the analysis of concentration-dependent changes of the spin-lattice relaxation time of 170 nucleus gives the following important parameter known as the dynamic hydration number [17] ... 

Water is one of the most familiar material in our life and is indispensable to all living things. In contrast to its apparently simple molecular structure, water shows many anomalous properties from both macroscopic and microscopic points of view. However, the basic physical property of water, for example the dynamical structure of water, has not yet been fully clioified. To un rstand the dynamical aspect of water structure and its significant role in life, it is essential to clarify not only the dynamics of water molecules themselves but also the dynamics of water in the aqueous solutions. 

Water Sorbed on to Solids. Solid-state 3H NMR spectroscopy was used to determine the characteristics of H20 adsorbed on Ti02 photocatalytic systems.623,624 The dynamics of water molecules in the deuteriated analogue of H3PWi204o.nH20, where n = 5.5 or 0.1, were followed by solid-state 2H NMR spectra.625... 

Watanabe and Klein have reported MD simulations of the hexagonal mesophase of sodium octanoate in water with hexagonal symmetry. The singlet (i.e., one atom) probability distribution functions of the carbon atoms on the hydrocarbon chains show close similarity to those in the micelle. The dynamics of water molecules close to the head groups shows lower mean square displacements, and their orientational correlation function decays more slowly than those of waters farther from the head groups, as was seen in a recent bilayer simulation.6 ... 

THE DYNAMICS OF WATER MOLECULES ON YVO4 PHOTO-CATALYST SURFACE... 

The Dynamics of Water Molecules on YVO4 Photo-Catalyst Surface... 

Thermodynamic data mentioned in Fig. 2.1 refer to the properties of stable states and therefore give information pertaining to a time scale that also is effectively infinite with respect to the dynamics of water molecules. Besides this well-known fact, there are two important features of thermodynamic methods that set them apart from the other methods indicated in Fig. 2.1. First, since the sole objective of chemical thermodynamics is the... 

While considerable progress has been made in simulating the dynamics of water molecules around proteins and DNA, relatively less success has been achieved in the study of the biomolecules themselves as they move on much smaller timescales. Thus, the study of the detailed role of water in biological functions is stiU at its... 

The dynamics of water molecules near Ag+ ions (Armunanto et al. 2003) showed the hydration shells to be non-symmetric, irregular, and labile. The RMRTs noted cannot be compared with those listed above because the RMRT value near a water molecule was not reported and the minimal time t above which a molecule is deemed to have left its position was set to 1 or 2 ps rather than 0.5 ps used in the other studies quoted above. This was amended in a subsequent paper (Blauth et al. 2010), where the RMRT was reported as 80 %, hence considering the ion as a... 

In MD simulation, atoms and molecules are allowed to interact for a period of time by approximations of known physics in order to explore the physicochemical properties of solutions and structures such as interfacial phenomena and the dynamics of water molecules and ions, thus providing detailed information and fundamental understanding on relationships between molecular structure, movement, and function (Brossard et al. 2008 Du and Miller 2007a, 2007b Du et al. 2007a, 2007b Lazarevic et al. 2007 Miller et al. 2007 Nalaskowski, et al. 2007). With MD simulation, scientists are able to examine the motion of individual atoms and molecules in a way not possible in laboratory experiments. 

Recently, it was found that the surface layers of ice might be disordered by hydrocarbon contamination or HCl traces. " Molina first postulated the liquid-like ice surface of type II PSCs at stratospheric temperatures to explain HCl adsorption, which was supported experimentally by a zeroth-order rate dependence on HCl partial pressure. Further support comes from molecular dynamics simulations showing that the water molecules on the ice surface are substantially disordered even at 200 and the dynamics of water molecules in the uppermost bilayer of hexagonal ice is substantially faster than in the bulk leading to partial disorder. Therefore, small water clusters can be used to model the reactions occurring on type II PSCs. Both the nature of the type II PSCs and the detailed mechanisms of reactions within them have been the subjects of many studies. Whereas the reactions are reasonably well understood from a phenomenological point of view, there is still a vast amount of uncertainty in the microscopic view of the reaction mechanism. 

Many techniques have been used to characterize the state of water and the dynamics of water molecules in W/0 micro-emulsions. It is usual in that case to consider the molar concentration ratio Wo = [water]/[surfactant]. All the techniques used demonstrate that for low values of w , the water molecules are essentially bound to the counterions and to the surfactant polar heads. It is only when w exceeds a certain value (around 6-10 for AOT-based systems for instance) that free water can be detected. Properties such as the local microviscosity, or the local dielectric constant, are strongly affected by the state of water. 

Despite the limitations of the equations used for the calculation of the parameter a, these results can be interpreted on the basis that for these species there is no hydration shell for either cation or anion, and that the coalescence of these ions through the interactions resulting from their combination leads to the compaction of their hydration shells to some extent. This suggests that the solvation waters are only weakly boimd, and is consistent with the dynamics of water molecules in their primary hydration spheres and evocative of what is observed in electrostriction. °... 

S. Takahara, S. Kittaka, T. Mori, Y. Kuroda, T. Yamaguchi, K. Shibata, Neutron scattering study on the dynamics of water molecules adsorbed on Srp2 and ZnO surfaces, J. Phys. Chem. B 106 (2002)5689-5694. 

---