Solvation processes

Our starting point is the general expression for the chemical potential of a molecule s in any liquid /, which we write as 

From now on we shall assume that qs is the same PF of a single molecule s, whether in an ideal gas or in the liquid. Our focus in the study of solvation will be on the coupling work W s l). We have seen in Chapters 5 and 6 that this quantity conveys the effect of molecular interactions between the particles on the chemical potential. In the limit of very low densities, or when interactions are negligible, this term vanishes and the chemical potential (6.13.1) reduces to that of a molecule of species s in an ideal gas. In section 5.9.3 we presented a convenient interpretation of the pseudochemical potential p7 as the work involved in placing 5 at a fixed location in the liquid. Within the classical treatment of our systems the process of fixing the location of a specific particle is meaningful. We shall adopt this interpretation of p7 throughout the book. 

We define the solvation process of a molecule. s in a fluid / as the process of transfering the molecule s from a fixed position in an ideal gas phase g into a fixed position in the fluid or liquid phase /. The process is carried out at constant temperature T and pressure P. Also, the composition of the system is unchanged. 

When such a process is carried out, we shall say that the molecule s is being solvated by the liquid phase /. If 5 is a simple spherical molecule, it is sufficient to require that the center of the molecule be fixed. On the other hand, if. s is a more complex molecule, such as -alkane or a protein, we require that the center of mass of the molecule be at a fixed position. We note, also, that in complex molecules the geometrical location of the center of mass might change upon changing the conformation of the molecule. In such cases we need to distinguish between the process of solvation of the molecule at a particular conformation and an average solvation process over all possible conformations of the molecule. 

One could also define the solvation process as above, but at constant volume rather than constant pressure. The definition given above is the one which may be related more directly to experimental quantities. However, for some theoretical considerations it might be more convenient to treat the constant-volume solvation process. The relation between the two is discussed in Appendix E. 

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Lian T, Kholodenko Y and Hochstrasser R M 1995 Infrared probe of the solvent response to ultrafast solvation processes J. Rhys. Chem. 99 2546-51... 

Solvation Process of swelling of a resin or plastic. Can be caused by... 

An empirical solution of Eq. (1) consists of analysis of the solvation process of the target molecule in solute, finding descriptors, which govern each phase and using them to calculate logP. This was done, for example, in the LSER approach which considered that the process of any solvation involves (i) endoergic creation of a cavity in the solvent and (ii) incorporation of the solute in the cavity with consequent setting up of various solute-solvent interactions [4—6]. Each of these steps... 

The small size of the proton relative to its charge makes the proton very effective in polarizing the molecules in its immediate vicinity and consequently leads to a very high degree of solvation in a polar solvent. In aqueous solutions, the primary solvation process involves the formation of a covalent bond with the oxygen atom of a water molecule to form a hydronium ion H30 +. Secondary solvation of this species then occurs by additional water molecules. Whenever we use the term hydrogen ion in the future, we are referring to the HsO + species. 

Abstract This chapter reviews the theoretical background for continuum models of solvation, recent advances in their implementation, and illustrative examples of their use. Continuum models are the most efficient way to include condensed-phase effects into quantum mechanical calculations, and this is typically accomplished by the using self-consistent reaction field (SCRF) approach for the electrostatic component. This approach does not automatically include the non-electrostatic component of solvation, and we review various approaches for including that aspect. The performance of various models is compared for a number of applications, with emphasis on heterocyclic tautomeric equilibria because they have been the subject of the widest variety of studies. For nonequilibrium applications, e.g., dynamics and spectroscopy, one must consider the various time scales of the solvation process and the dynamical process under consideration, and the final section of the review discusses these issues. 

Scheme 8 Fragmentation, rearrangement, and solvation processes of 2-methyl-3-phenyl-3-(diphenylphosphatoxy)-2-propyl radical and associated contact ion pair...

With taken into account, that the constants of the reaction rates are determined via the equilibrium constants of the activated reactive complex formation, and the last in part depend on the solvation processes, it was proposed by Koppell and Palm [22] the following equation in order to determine the influence of medium properties on the reaction rates of processes proceeding in it ... 

AH% would be the heat of reaction of (41). Note that AHX is dependent on n and when n is small it differs from the conventional heat of vaporization. Neglecting surface effects, the whole single-ion solvation processes can be constructed from reactions (40 c) and (41)... 

In conclusion of this short account on experiments, which is clearly far from complete, detailed structural data for solutions will be available in the near future. They may serve well to support theoretical calculations of solvation processes and to present challenges for theoretical considerations, which will in any case have to be dynamic ones. Data which may be compared quantitatively with molecular calculations will, however, have to come from gas-phase solvation experiments. There already exists a great variety of according data and their number will certainly increase further. 

In accordance with the limited aim of this article, in the following subsections we shall consider only two of the individual contributions to the highly complex solvation process dealing with structural problems of solutions. No attempt is made to treat other aspects, which might well be of considerable theoretical interest, like electronic spectra 189 244> or dynamic properties 13> of liquid mixtures. 

Electron transfer reactions, treated by continuum theory, suggested that the Franck-Condon barrier (the barrier for the vertical transition of electrons), which is about four times the activation barrier for the isotopic electron transfer in solution, is due to Bom continuum solvation processes. Specific contributions for the activation of ions come from the solvent continuum far from the ion the important contribution from the solvent molecules oriented toward the central ion in the first and second solvation shells is neglected. ... 

For the acidic proton transfer of Eqn. 3-44, the proton solvation processes of Eqns. 3-32 and 3-42 are represented by the proton level versus concentration curves of Eqns. 3-39 and 3-43, respectively, as shown in Fig. 3-19. In this proton level diagram, the proton level in an acetic acid solution is given by the intersecting point (mH,o - where cross each other the occupied proton level versus concentration curve of H3O ion and the vacant proton level versus concentration curve of Ac" ion, as expressed in Eqn. 3-46 ... 

Generally, the solubihty characteristics of organic compounds depend on several properties of the participating components. For the solute, these properties are the molecular size and structure, polarity, dipole moment, va-por/sublimation pressure, and, in the case of a sohd solute, also its melting characteristics. When using SCCO2 as the solvent, mainly its dipole moment and quadrupole moment influence the solvatation process (Sect. 2.2). 

These expressions appear more applieable to nonpolar solvents or mixtures than to polar solvents. The nature of the solvation process (and the radii and so forth of the solvated reactants) may stay approximately constant in the first situation but almost certainly will not in the seeond. The function (E>op A ) features in the reorganisation term Xq which is used for estimating rate constants for redox reactions (Eqn. 5.23). is the optical dielectric constant and Dj the static dielectric constant (= refractive index ). 

When a solute particle is introduced into a liquid, it interacts with the solvent particles in its environment. The totality of these interactions is called the solvation of the solute in the particular solvent. When the solvent happens to be water, the term used is hydration. The solvation process has certain consequences pertaining to the energy, the volume, the fluidity, the electrical conductivity, and the spectroscopic properties of the solute-solvent system. The apparent molar properties of the solute ascribe to the solute itself the entire change in the properties of the system that occur when 1 mol of solute is added to an infinite amount of solution of specified composition. The solvent is treated in the calculation of the apparent molar quantities of the solute as if it had the properties of the pure solvent, present at its nominal amount in the solution. The magnirndes of quantities, such as the apparent molar volume or heat content, do convey some information on the system. However, it must be realized that both the solute and the solvent are affected by the solvation process, and more useful information is gained when the changes occurring in both are taken into account. 

The electroconstriction contribution derives from the structural collapse of the solvent in the immediate neighborhood of the ion and by the ion-solvation process... 

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