Translational mobility of water

Nmr methods have unrivalled potential to explore interfaces, as this account has striven to show. We have been able to determine the mobility of hydrated sodium cations at the interface of the Ecca Gum BP montmorillonite, as 8.2 ns. We have been able to measure the translational mobility of water molecules at the interface, their diffusion coefficient is 1.6 10 15 m2.s. We have been able to determine also the rotational mobility of these water adsorbate molecules, it is associated to a reorientational correlation time of 1.6 ns. Furthermore, we could show the switch in preferred reorientation with the nature of the interlayer counterions, these water molecules at the interface tumbling about either the hydrogen bond to the anionic surface or around the electrostatic bond to the metallic cation they bear on their back. And we have been able to achieve the orientation of the Ecca Gum BP tactoids in the strong magnetic field of the nmr spectometer. 

Translational mobility of water on the surface of a flexible lysozyme is noticeably higher than on the surface of a rigid lysozjmie. This difference is about a factor of two at low hydrations, and it progressively vanishes at higher hydration levels. Considerable enhancement of water translational motion at low hydrations is obviously caused by the motions of the surface groups of a flexible lysozyme molecule. This effect diminishes at higher hydrations when the role of water-water interactions in translational motion of water molecules becomes more important. 

The reaction of water with low-loaded [Ru(bpy)3] + entrapped in zeolite Y has been reported [152]. Since translational mobility of the Ru molecules cannot occur in the zeolite, the multimolecular degradation step observed in solution is no longer possible. Instead, O2 was found to be formed from the reaction of [Ru(bpy)3] with water. It was possible to examine the evolution of this reaction at various pHs by spectroscopic methods, such as EPR, diffuse reflectance and Raman spectroscopy. Figure 30 shows the evolution of the diffuse reflectance spectra after exposure of Ru(bpy)3 +-zeolite Y to water at pH 7 [152]. Trace e is the spectrum of the... 

Water molecules are constantly in motion, even in ice. In fact, the translational and rotational mobility of water directly determines its availability. Water mobility can be measured by a number of physical methods, including NMR, dielectric relaxation, ESR, and thermal analysis (Chinachoti, 1993). The mobility of water molecules in biological systems may play an important role in a biochemical reaction s equilibrium and kinetics, formation and preservation of chemical gradients and osmotic pressure, and macromolecular conformation. In food systems, the mobility of water may influence the engineering processes — such as freezing, drying, and concentrating chemical and microbial activities, and textural attributes (Ruan and Chen, 1998). 

At low concentrations just above the CMC and at low ionic strengths ( < 0.2 M NaCl), nearly all simple bile salt micellar solutions contain spherical or nearly spherical micellar particles [5,6,12,146]. Intrinsic viscosity measurements [162,170-172] are in agreement with this and also indicate that the micelles are highly hydrated, cholates2 DC [162,172]. The maximum size of these globular micelles falls in the range Ry, = 10-16 A with h = 10-12 [146]. In the case of NaTC, the water of hydration amounts to about 30 moles H20/mole of monomer in the micelle [162]. By employing the translational mobility of H20, Lindman et al. [173]... 

The structure of water next to the metal is strongly perturbed only over two layers, and the range of other inhomogeneities and anisotropies appears to be not more than four layers at most. Detailed structural information has been derived. It has been demonstrated that the translational and rotational mobility of water and ions near a metal surface is reduced compared to the bulk. 

Affected by the forces of inter-atomic and inter-molecular interactions, almost all atoms in ground water turn out to be to some extent associated. Numerous weak intermolecular bonds, not taken into account at chemical analysis, whose effect grows with increase in pressure, salinity and with the decrease in temperature and rate of flow, have special significance. All these bonds obstruct translation mobility of individual atoms and thereby facilitate the formation of some structure of the solution, which determines its physical and chemical properties in reservoir conditions. Aqueous solution structure is some relatively stable in space and time optimum orderliness of inter-atomic and inter-molecular bonds in the specifically set conditions. This structme depends on temperature, pressure and composition of water in the reservoir conditions. 

The translational mobility of the water located in the region of z = 9-15 A, where rather highly packed hydrophobic chains and ester groups are found, is significantly low. 

Numerous studies have shown that water acts as a plasticizer when it is absorbed into amorphous sohds, resulting in reductions in [42a], decreases in NMR relaxation times [99b, 100], and increases in translational diffusion of water [99b] and other solutes [100b]. Plasticization of amorphous solids by water has also been a subject of several MD simulations where increasing water content has been associated with increases in polymer mobility and increases in diffusivities of water or other low-molecular-weight solutes [56, 61, 96,101],... 

Relaxation phenomena (TSDC), molecular mobility (NMR, TPDMS), and chemical reactions (TPDMS of associative desorption of water) are observed for adsorbed water/LiChrolut EN adsorbent over a wide temperature range. These phenomena are characterized by very different activation energies from 10 kJ/mol (rotational mobility of hydroxyls in WAW molecules), 20-40 kJ/mol (rotational mobility of the molecules in SAW), 40-80 kJ/mol (rotational and translational mobility of the water molecules in pores of different sizes), and 60-200 kJ/mol (molecular and associative desorption of water) (Figure 5.34). As a whole, all the distribution functions of activation energy fiJS) obtained using different methods are well concordant. This is caused by the nature of activated processes whereas all the processes are caused by the molecular mobility of water dependent on the topological and chemical characteristics of confined space in nano- and mesopores in LiChrolut EN adsorbent. 

In addition to the well-established molecular relaxations, the TSC spectrum shows a weak / relaxation, ascribed to rotation of trace amounts of absorbed water, and a weak [3 relaxation, a dielectric signal that may correspond to translational mobility of charges, hindered sidechain motions, or even structural relaxation effects [see, e.g., Muzeau et al. (1995) Kalogeras (2004). The a relaxation has a peak at = 110 °C, near the DSC Tg (Kalogeras and Neagu 2004). The intrachain effect of the stiffness of individual chain segments is—at least in the case of PMMA and some other poly(n-alkyl metharylate)s— more important than the interchain effect of the cohesive (attractive) forces... 

Pulsed field gradient (PFG)-NMR experiments have been employed in the groups of Zawodzinski and Kreuer to measure the self-diffusivity of water in the membrane as a function of the water content. From QENS, the typical time and length scales of the molecular motions can be evaluated. It was observed that water mobility increases with water content up to almost bulk-like values above T 10, where the water content A = nn o/ nsojH is defined as the ratio of the number of moles of water molecules per moles of acid head groups (-SO3H). In Perrin et al., QENS data for hydrated Nation were analyzed with a Gaussian model for localized translational diffusion. Typical sizes of confining domains and diffusion coefficients, as well as characteristic times for the elementary jump processes, were obtained as functions of A the results were discussed with respect to membrane structure and sorption characteristics. ... 

Translational entropy of mobile ions and water molecules (i A, C, OH—,... 

Water mobility from molecular reorientation and diffusion. Evidence for the motion of the water molecules in crystal structures is typically provided by XH NMR (Davidson and Ripmeester, 1984). At very low temperatures (<50 K) molecular motion is frozen in so that hydrate lattices become rigid and the hydrate proton NMR analysis suggests that the first-order contribution to motion is due to reorientation of water molecules in the structure the second-order contribution is due to translational diffusion. 2H NMR has been also used to measure the reori-entational rates of water and guest molecules in THF hydrate (Bach-Verges et al., 2001). Spin lattice relaxation rates (fy) have been measured during THF hydrate... 

The great distinction between the relaxation spectra of water and ice originates due to the phase transition occurring near 0°C. Because of the latter the translational mobility is extremely low in ice, unlike in water. However, an evident resemblance of the FIR spectra of water and ice, demonstrated in Fig. 64, suggests an idea that the rotational mobility does not differ so much in these two phase states of H20. If we apply the hat-curved model also for ice I, the fitted form factor / obviously should be less than /(H20) to give narrower rotational band. The intermolecular potential should be spread in ice at longer distances than in water, just as the steepness of such potential is less in water than in a nonassociated liquid (see Section VII). 

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