cosolutes

Cosolutes are solutes added to a solvent that modify the properties of the solvent and, in turn, influence the behavior of other solutes in the solution. They can change aspects such as solvent polarity, dielectric constant, hydrogen-bonding networks, ionic strength, viscosity, and osmotic pressure. Through these changes, cosolutes alter solubility, reaction rates, and phase behavior.

Mechanisms by which cosolutes act include altering solvent quality for solutes and, in biological contexts, preferential exclusion or binding to macromolecules. Depending on the system, cosolutes can stabilize or destabilize structures such as proteins or nucleic acids. For example, some osmolytes stabilize biomolecules by being excluded from their surfaces, while others modify solvation shells and folding landscapes through changes in solvent properties.

Common cosolutes in aqueous solutions span inorganic salts (for example sodium chloride), sugars and polyols (such as glucose and glycerol), and alcohols (like ethanol). Organic denaturants (for example urea and guanidinium salts) and stabilizing osmolytes (such as trimethylamine N-oxide, TMAO) illustrate the range of possible effects on solubility and stability.

Applications of cosolutes include tuning solubility and crystallization in chemical and biochemical workflows, controlling protein folding and stability in solution, and adjusting solvent quality in polymer science and pharmaceutical formulations. Effects are highly system-specific, requiring empirical or theoretical characterization for each solute–solvent combination.