Intersolute

The McMillan-Mayer theory allows us to develop a fomialism similar to that of a dilute interacting fluid for solute dispersed in the solvent provided that a sensible description of W can be given. At the Ihnit of dilution, when intersolute interactions can be neglected, we know that the chemical potential of a can be written as = W (a s) + IcT In where W(a s) is the potential of mean force for the interaction of a solute... 

The great disadvantages of fractionation of dipolar ions such as proteins using media of reduced dielectric constant are the increased lability of the solutes and the tendency to form intersolute complexes due to the increased electrostatic interactions between the different solute species. 

The general principle is to treat AG o, as die sum of eontributions from dre three types of pairwise interactions solvent-solvent interactions, which give rise to the general medium effect, solvent-solute interactions, or the solvation effect, and solute-solute interactions (the intersolute effect in the present eontext). Thus we write. 

There are two contributions to the intersolute effect. One of these eomes from solute-solute interactions in the pure solute, which for solid solutes constitutes the crystal lattice energy. We will make the assumption that this contribution is independent of die nature (identity and composition) of the solvent. Usually this is a valid assumption, but exceptions are known in which the composition of the solid depends upon the composition of the solvent Theophylline, for example, forms a hydrate in water-rich solvents, but exists as the anhydrous form in water-poor solvents thus its crystal energy varies with the solvent composi-tion. " Although the final theory is capable of empirically describing the solubility of such systems, it lacks a valid physical interpretation in these cases. Fortunately such solid solute behavior is not common, and our assumption that the pure solute interaction energy is solvent-independent is usually a good one. 

Barbari, T.A. Kasargod, S S., and Fieldson, G.T., Effect of unequal transport rates and intersolute solvation on the selective batch extraction of a dilute mixture with a dense polymeric sorbent, Ind. Eng. Chem. Res., 35(4), 1188-1194(1996). 

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