Aqueous solubilities with cosolvents coefficient

In the present section, the expression obtained for the protein solubility will be extended to the solubility of a sparingly soluble gas in an aqueous electrolyte solution. Eq. (14) will be used for the derivative of the activity coefficient of an infinitely dilute gas with respect to the mole fraction of the cosolvent (electrolyte). While there are no experimental results for the preferential binding parameter for the systems water (1) + gas (2) + electrolyte (3), Eq. (14) can be still used by assuming, however, in analogy with the protein solutions that = 6X3, where e is a constant. Because for the derivative of the logarithm of the Henry constant H2t in a binary solvent with respect to the mole fraction of the electrolyte one can write [27]... 

The paper is organized as follows first, an equation for the activity coefficient of a solute at infinite dilution in a binary nonideal mixed solvent (Ruckenstein and Shulgin, 2003) is employed to derive an expression for its solubility in terms of the properties of the mixed solvent. Second, various expressions for the activity coefficients of the cosolvents are inserted into the above equation. Finally, the obtained equations are used to correlate the drug solubilities in binary aqueous mixed solvents and the results are compared with experimental data and other models available in the literature. 

Different scientific groups have demonstrated that there are direct connections between the solubility of proteins in aqueous solutions and both the osmotic second virial coefficient and the preferential binding parameter. The osmotic second virial coefficient B22 is a measure of the intermolecular protein-protein interaction and the preferential binding parameter is an indicator of the redistributions of water and cosolvent in the vicinity of a protein surface, hence a measure of their interactions with the solvent and cosolvent. The preferential binding parameter is defined at infinite dilution of a protein... 

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