The Eggers laboratory proposes to develop and test a thermodynamic framework for aqueous reaction equilibria that treats the solvent as a co-reactant. The new approach is motivated by the fact that the numbers and orientations of hydrogen bonds in liquid water are altered near a solute, and by the fact that the rearrangement in water structure, which accompanies the conversion of the traditional reactants to products, should be included in the total free energy change of the system. Although the solvent contribution may be negligible for chemical reactions involving formation and/or breakage of covalent bonds, changes in water structure may play a dominant role in binding equilibria and conformational equilibria. Consequently, this research is expected to enhance our understanding of the role of water in many important biological reactions, including protein folding and the structure of the polynucleic acids, DNA and RNA. A combination of biophysical techniques, including two types of calorimetry experiments, will be implemented to test the validity of the new framework. Enthalpy and entropy values of bulk water will be measured and tabulated for many solutions of interest, including neutral salts, osmolytes, chaotropes, and crowding agents. Application of the new framework to the solubility of model compounds should lead to a quantitative assessment of hydration forces in macromolecular structure. This research provides an alternative view for understanding the effects of solutes on biological equilibria, a view that may be deemed as more intuitive and more widely applicable than current models. In addition, this research may yield new insights into molecular recognition and drug design. The experimental data obtained from this work may be extremely useful to computational scientists in developing realistic force fields for water at interfaces, an important consideration for computer simulations of biological processes.