This study introduces a new thermodynamic framework for aqueous binding equilibria that features an explicit consideration for the change in hydration that occurs when two solvated surfaces come into contact. As an outcome of this approach, the standard state free energy of binding is defined by the summation of two terms, the traditional term (-RTlnK) plus a desolvation free energy term that is weighted by the number of complexes formed atequilibrium. The governing equation suggests that the equilibrium ratio (K) is not a constant; this equation is supported firmly by results from isothermal titration calorimetry using thechelation of calcium(II) by EDTA as a model binding reaction. This study may have far-reaching implications for solution thermodynamics, including an explanation for the oft-noted discrepancy between enthalpy values obtained by calorimetry and the van't Hoff approach.

Neglect of water in binding equilibria: Why binding �constants� aren't constant with changing reactant concentration

246th National Meeting (2013)

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