Solvate layers

Fig. 7. Stereoview of the crystal structure of water solvated host 5 (folded conformation). The structure is held together by host-host and host-solvent hydrogen bonding interactions. Within the solvation layer there are chains of circular H-bonds between the molecules of water (crystal data a - 8.227, b = 8.964, c - 16.945 A, a = 89.64, / = 97.51, y = 114.28°, space group Pi taken from Ref,3S>)...

Fig. 8. Stereoscopic illustration of the inclusion compound of host 5 (folded conformation) with acetic acid and 2 mol of water. Host-host and host-water hydrogen bonding interactions stabilize the structure. The solvation layers consist of cyclic carboxy dimers of acetic acid surrounded by water species (crystal data a = 7.857, b = 11.379,c = 13.831 A,a = 92.50,/i = 101.21, y = 101.12°, space group Pi taken from Ref. 351)...

There are basically two semicontinuum models one owing to Copeland, Kestner, andjortner (1970) (CKJ) and another to Fueki, Feng, and Kevan (1970, 1973 Fueki et al, 1971) (FFK). The calculations were designed for eh and eam,but have been extended to other polar media (Fueki et al., 1973 Jou and Dorfman, 1973). In these four or six solvent molecules form the first solvation layer in definite arrangement. Beyond that, the medium is taken as a continuum with two dielectric constants and a value of VQ, the lowest electron energy in the conduction state. 

Experimental mobility values, 1.2 X 10-2 cm2/v.s. for eam and 1.9 x 10-3 cm2/v.s. for eh, indicate a localized electron with a low-density first solvation layer. This, together with the temperature coefficient, is consistent with the semicontinuum models. Considering an effective radius given by the ground state wave-function, the absolute mobility calculated in a brownian motion model comes close to the experimental value. The activation energy for mobility, attributed to that of viscosity in this model, also is in fair agreement with experiment, although a little lower. 

Kujawa and Winnik [209] reported recently that other volumetric properties of dilute PNIPAM solutions can be derived easily from pressure perturbation calorimetry (PPC), a technique that measures the heat absorbed or released by a solution owing to a sudden pressure change at constant temperature. This heat can be used to calculate the coefficient of thermal expansion of the solute and its temperature dependence. These data can be exploited to obtain the changes in the volume of the solvation layer around a polymer chain before and after a phase transition [210], as discussed in more detail in the case of PVCL in Sect. 3.2.2. 

Additional information on the solvation layer around the polymers was obtained by PPC (Sect. 2.1), a technique that allows one to evaluate the changes in the partial volume of the polymer throughout the phase transition, and to obtain information on the temperature-dependant relative hydrophilicity/hydrophobicity of a polymer in solution [210]. Particular interest in the PPC studies was focused on the effect of the amphiphilic grafts on the volumetric properties of the polymers. 

However, picosecond resolution is insufficient to fully describe solvation dynamics. In fact, computer simulations have shown that in small-molecule solvents (e.g. acetonitrile, water, methyl chloride), the ultrafast part of solvation dynamics (< 300 fs) can be assigned to inertial motion of solvent molecules belonging to the first solvation layer, and can be described by a Gaussian func-tiona) b). An exponential term (or a sum of exponentials) must be added to take into account the contribution of rotational and translational diffusion motions. Therefore, C(t) can be written in the following form ... 

The effect of the ion on the strength of the hydrogen bond between water molecules dies off rapidly in the outer shells of the clusters. Almost the same values are observed in the third solvation layer and in tetrahedral water clusters. Chain structures discussed by Burton and Daly 220> show an analogous behavior (Table 19). 

Interactions between solute and solvent molecules can have a significant effect on the shape of a crystal. This can be accounted for by specific adsorption of the solvent molecule on ciystal faces. Current oystal growth theories indicate that when interactions between solute and solvent are strong the solute molecules are solvated and a solvation layer dsts at the oystal-liquid interface which likely can vary as a function of ciystal face. Crystal growth requires desolvation of die solute molecule and desolvation of the surface site on the crystal. The molecule then surface diffuses imtil it reaches an incorporation (kink) site. 

The DNA solvation shell consists of about 20-22 water molecules per nucleotide of these, — 15-17 waters associate with the nucleoside and —5 waters associate with the phosphate group [13,14]. Water outside the solvation layer is termed bulk water. Upon freezing, the DNA solvation water forms two primary phases the ice phase, consisting of one or more of the crystalline forms of ice, and a DNA-associated phase, consisting of ordered water which comes in direct contact with the DNA (primary layer) and disordered water in the secondary layer. DNA hydration is expressed in terms of F, the number of water molecules per nucleotide. 

Fig. 1. Overview of the regions defined in a QMCF simulation the chemically most relevant part is treated by QM while MM is applied in the remaining part. The QM region is further separated into the QM core and the QM (solvation) layer. ...

This approach requires that all atoms of the solute species remain close to the QM center—if a solute particle were located too close to the interface between QM and MM region, in addition to the Coulombic interactions, non-Coulombic potentials would be required and the advantages of the QMCF methodology lost. This also implies that only species for which non-Coulombic potentials are available are allowed in the QM layer region. Hence, this second QM zone is also referred to as solvation layer as it is exclusively composed of solvent particles. Besides solvent molecules this could also apply to other species such as counterions assuming that non-Coulombics are provided for these species as well. 

Solvation in water was extensively studied and processes on different timescales were described ranging from 30 fs to several ps [8]. Due to our experimental resolution the shortest decay time we measure contains various superimposed contributions from the ultrafast processes presumably the inertial response of water and initial librational motions of molecules in the first solvation layer. 

Wetting. Removal of the air from the surface of the pigment particles and formation of a solvate layer [1.65], [1.66]. 

Stabilization. Maintenance of the disperse state by creating repulsive forces between the particles (e.g., by coating them with solvate layers). These forces must be greater than the van der Waals attraction forces [1.67] that cause flocculation [1.68], [1.69]. 

The first conclusion is that solvated electrons no longer exist in appreciable quantities. The most direct determination has been by Beckman and Pitzer (2) who do not find the famous 1.5/z peak at concentrations above 1M. Indeed, it would be difficult to understand how the solvation layer might be maintained around electrons with the high thermal velocities characteristic of a degenerate electron gas. One may also note that at the concentrations in question the mole ratio n (= moles solvent/mole solute) is rapidly approaching unity, so that fewer solvent molecules are available for the solvation process. At the onset of the... 

A totally different view was proposed by Becker, Lindquist, and Alder (2) who considered the electron to be trapped at a solvated cation site in which the solvated metal cation has its valence electron localized on the protons of the ammonia molecules of the innermost solvation layer. This species, with its valence electron in a sort of enlarged Rydberg orbital, may then dissociate or undergo dimerization. 

PCS measurements yield the hydrodynamic size. This size includes any coating, solvation layer, surface attached molecules (surfactants), entrapped solvent (swelling), or any other matter which moves with the particle. This size may be quite different than the "dry" diameter. 

When two surfaces are immersed in a liquid, the force between them can be greatly affected by the interaction of the liquid with the surface. In this case the surface may be solvated in a particular way. An isolated surface will thereby modify the structure of the liquid adjacent to it. The nature and thickness of the solvation layer depend on properties of surface and liquid. The solvation force in water is called the hydration force. 

Regarding the electrode as a giant ion, the solvent molecules form its first solvation layer the IHP is the plane that passes through the centre of these dipoles and specifically adsorbed ions. In a similar fashion, OHP refers to adsorption of solvated ions that could be identified with a second solvation layer. Outside this comes the diffuse layer. Note that the actual profile of electrostatic potential variation with distance (Fig. 3.9b) is the same in qualitative terms as in the Grahame model (Fig. 3.8b). 

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