Hydration shell properties

Monophosphabutadienes, 33 281-283 Monophosphacarbodiimides, 33 322 preparation, 33 323 reactivity, 33 322-325 stereoselective reaction, 33 324 Monophosphahexadienes, 33 305, 307-310 Monoterpyridine complexes of copper, 45 288 Monovalent cations hydration shell properties, 34 203-204 structure, 34 202-205... 

Hydration Shell Properties of Transition Metal Ions°... 

Hydration Shell Properties for Rare Earth Ions°... 

Hydration Shell Properties of Tetra- and Hexavalent Cations... 

The interplay between ion adsorption and ion hydration, and the relation between thermodynamic quantities like the free energy of adsorption and microscopic structure, characterized, e.g., by hydration shell properties and hole formation, has been elucidated. 

A fourth solvent structural effect refers to the average properties of solvent molecules near the solute. These solvent molecules may have different bond lengths, bond angles, dipole moments, and polarizabilities than do bulk solvent molecules. For example, Wahlqvist [132] found a decrease in the magnitude of the dipole moment of water molecules near a hydrophobic wall from 2.8 D (in their model) to 2.55 D, and van Belle et al. [29] found a drop from 2.8 D to 2.6 D for first-hydration-shell water molecules around a methane molecule. 

After this computer experiment, a great number of papers followed. Some of them attempted to simulate with the ab-initio data the properties of the ion in solution at room temperature [76,77], others [78] attempted to determine, via Monte Carlo simulations, the free energy, enthalpy and entropy for the reaction (24). The discrepancy between experimental and simulated data was rationalized in terms of the inadequacy of a two-body potential to represent correctly the n-body system. In addition, the radial distribution function for the Li+(H20)6 cluster showed [78] only one maximum, pointing out that the six water molecules are in the first hydration shell of the ion. The Monte Carlo simulation [77] for the system Li+(H20)2oo predicted five water molecules in the first hydration shell. A subsequent MD simulation [79] of a system composed of one Li+ ion and 343 water molecules at T=298 K, with periodic boundary conditions, yielded... 

The average DNA helix diameter used in modeling applications such as the ones described here includes the diameter of the atomic-scale B-DNA structure and— approximately—the thickness of the hydration shell and ion layer closest to the double helix [18]. Both for the calculation of the electrostatic potential and the hydrodynamic properties of DNA (i.e., the friction coefficient of the helix for viscous drag) a helix diameter of 2.4 nm describes the chain best [19-22]. The choice of this parameter was supported by the results of chain knotting [23] or catenation [24], as well as light scattering [25] and neutron scattering [26] experiments. 

The amount of adsorbed chemical is controlled by both properties of the chemical and of the clay material. The clay saturating cation is a major factor affecting the adsorption of the organophosphorus pesticide. The adsorption isotherm of parathion from an aqueous solution onto montmorillonite saturated with various cations (Fig. 8.32), shows that the sorption sequence (Al > Na > Ca ) is not in agreement with any of the ionic series based on ionic properties. This shows that, in parathion-montmoriUonite interactions in aqueous suspension, such factors as clay dispersion, steric effects, and hydration shells are dominant in the sorption process. In general, organophosphorus adsorption on clays is described by the Freundhch equation, and the values for parathion sorption are 3 for Ca +-kaoUnite, 125 for Ca -montmorillonite, and 145 for Ca -attapulgite. 

The more exact forms of the aqueous cations, with their primary hydration shells, are normally omitted from the diagrams. As is the case with Crvl, which in acid solution exists as the dichromate ion, Cr2072-, the forms of any oxo anions are indicated by their formulae in the diagrams. The diagram for chromium summarizes the following important properties ... 

Cations and anions with a strong solvation shell retain their solvation shell and thus interact with the electrode surface only through electrostatic forces. Since the interaction is exclusively electrostatic, the amount of these ions at the interface is defined by the electrostatic bias between the sample and the counter electrodes and independent from the chemical properties of the electrode surface non-specific adsorption. Considering the size effect of their hydration shell, these ions are able to approach the electrode to a distance limited by the size of the solvation shell of the ion. The center of these ions at a distance of closest approach defined by the size of the solvation shell is called the outer Helmholtz layer. The electrode surface and the outer Helmholtz layer have charges of equal magnitude but opposite sign, resulting in the formation of an equivalent of a plate condenser on a scale of a molecular layer. Helmholtz proposed such a plate condenser on such a molecular scale for the first time in the middle of the nineteenth century. 

A whole series of known anomalies in. the static and mnetie properties of the proton in aqueous solution may he explained by the assumption that it is present as the hydrated hydroninm ion. Earlier considerations [1 j have already resulted in the following most probable model for the hydration shell of the proton (Pig. I). H3(F as centre is strongly... 

The experimentally fitted hydrate guest Kihara parameters in the cavity potential uj (r) of Equation 5.25 are not the same as those found from second virial coefficients or viscosity data for several reasons, two of which are listed here. First, the Kihara potential itself does not adequately fit pure water virials over a wide range of temperature and pressure, and thus will not be adequate for water-hydrocarbon mixtures. Second, with the spherical Lennard-Jones-Devonshire theory the point-wise potential of water molecules is smeared to yield an averaged spherical shell potential, which causes the water parameters to become indistinct. As a result, the Kihara parameters for the guest within the cavity are fitted to hydrate formation properties for each component. 

The ion content of the organic phase of ethylenoxid-products indicate that under saturation conditions there are some water molecules whose properties are not too different from normal water. Polypropyleneoxide products which contain much less water, release under similar conditions water with a reduced ion content147. From this experience one gets a working hypothesis for the mechanism of semipermeable membranes. The membranes should have some secondary hydrate shell with movable water but by reason of solubility or steric effects, not too much secondary hydrate water to avoid normal water with common solubility properties. 

The presence of chemical guest species in the water pool of soft-core RMs can modify the organization of the micellar components. The chemical guest species may compete with the surfactant for water molecules to build its own hydration shell. Ions may be specifically bound to the charged groups of the micellar wall resulting in dramatically changed properties of micelles. 

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