Relation between Preferential Solvation and Measurable Quantities

Relation between Preferential Solvation and Measurable Quantities 

We assume that S is highly diluted in a solvent mixture of A and B at composition Xa - Let / denote the liquid mixture of A and B. In this system, the chemical potential of the solute S is 

Note that 77 is a measurable quantity through the inversion of the Kirkwood-Buff theory. Since 77 0, the entire quantity kT pA + Pb) It] is always positive. Therefore, the sign of the derivative is the same as the sign of Gbs Gas- 

FIGURE 6.14. Solvation Gibbs energy of methane in mixtures of water and ethanol, as a function of the mole fraction of ethanol, at two temperatures. 

Relation (6.17.17) is useful for a solute for which the solvation Gibbs energy can be determined. If we are interested in proteins as solutes, then (6.17.17) is impractical. However, we can still measure the solvation free energy of 5 in / relative to, say, pure A (e.g., solvation of protein in a solution relative to the solvation in pure water). The relevant relation is 

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