Molecular Scale Solvation in Complex Solutions

Abstract

Complex solution environments are ubiquitous in nature. Most life science systems contain hydrated macromolecules whose solubility, function and stability are modulated by several small organic molecules or salts (cosolutes) present simultaneously. This Perspective discusses solvation of mixed cosolutes in water. Recent computer simulations and experiments have shown that nonadditive cosolute effects on the water solubility of thermoresponsive polymers and on protein stability have a common physical origin, rooted in solvent-excluded volume effects determined by mutually enhanced cosolute hydration in bulk. We discuss mixtures of weakly and strongly hydrated salts in the anionic Hofmeister series and mixtures of urea and trimethylamine N-oxide. Nonadditive phenomena in these mixtures lead to intriguing effects including consecutive polymer collapse and swelling transitions and counteraction of denaturant-induced protein unfolding. The combination of today’s advanced simulation methods and spectroscopy techniques should be used to improve further the understanding of these complex aqueous solubility problems.

A cosolvent surfactant mechanism affects polymer collapse in miscible good solvents

“…By contrast, cosolvents that are depleted from the polymer surface favor the globule state over the coil state and therefore decrease polymer solubility and the LCST. Although this simple picture applies in many cases, it is not generic and a recent paradigm shift followed several intriguing observations that polymer collapse could in fact be triggered by preferential interactions with cosolvents [13][14][15][16][17][18][19] , specific salts [20][21][22][23] , or cosolutes 6,7,[24][25][26][27][28][29] that partition at the polymer surface.…”

Unifying the Ambivalent Mechanisms of Protein-Stabilising Osmolytes

“…Rather it was the average conformation of the protein which was analyzed for preferential interaction. 41,42 and hydrophobic interactions. 25 It will be interesting to see how the proposed conformation dependence of osmolytes' individual preferential interaction with protein plays out in the case of mixtures.…”

Nanopore Sensing Technique for Studying the Hofmeister Effect

“…However, cosolutes, like salts, may have a significant impact on the solution desolvation effect regardless of whether cations or anions are attracted to or excluded from the surfaces of these protein molecules. [ 4 ] The ions from the Hofmeister series affect the salting‐out process based on factors such as the ionic strength and hydration energy, with widely varied effectiveness. [ 5 ]…”

“…He employed salts with typical ions and observed their salting abilities. [3] The typical order of the ions from the Hofmeister series is generally applied to cations, i.e., NH 4 + > K + > Na + > Cs + > Li + > Rb + > Mg 2+ > Ca 2+ > Ba 2+ , and anions, i.e., SO 4 2-> OH -> F -> Cl -> Br -> NO 3 -> I -> SCN -> ClO 4 -. In a solution, desolvation is the most crucial factor in maintaining the connection between solutes and solvents.…”