Quantifying the roles of water and solutes (denaturants, osmolytes, and Hofmeister salts) in protein and model processes using the solute partitioning model.

Salts and uncharged solutes in aqueous solution exert effects on a wide range of processes in which large amounts ofbiopolymer surface are buried or exposed (folding/unfolding, complexation/dissociation, or precipitation/dissolution). A simple two-state solute partitioning model (SPM, where the solute is partitioned between the bulk and surface water) allows the interpretation and prediction of the thermodynamic effects of various uncharged solutes (e.g., urea, glycine betaine) on protein and nucleic acid processes in terms of structural information. The correlation of solute effects with various coarse-grained types of biopolymer surface exposed or buried in a process provides a novel probe for investigation of large-scale conformational changes. Solutes that are fully excluded from one or more types of biopolymer surface are useful to quantify changes in water of hydration of these surfaces in biopolymer processes. Additionally, application of the SPM to the analysis of non-Coulombic salt effects on various model processes provides an estimate for the hydration layer at surfaces and shows that ion effects are additive and independent of the nature of the counterion.