Ionic liquids (ILs) are used in a variety of technological and biological applications. Recent experimental and simulation results reveal the influence of aqueous ionic liquids on the stability of protein and enzyme structures. Depending on different parameters like the concentration and the ion composition, one can observe distinct stabilization or denaturation mechanisms for various ILs. In this review, we summarize the main findings and discuss the implications with regard to molecular theories of solutions and specific ion effects. A preferential binding model is introduced in order to discuss protein-IL effects from a statistical mechanics perspective. The value of the preferential binding coefficient determines the strength of the ion influence and indicates a shift of the chemical equilibrium either to the native or the denatured state of the protein. We highlight the role of water in order to explain the self-association behavior of the IL species and discuss recent experimental and simulation results in the light of the observed binding effects.

We present a theoretical and numerical framework for the study of molecular attraction mechanisms between species in solution. The respective approach provides detailed insight into the enthalpic contributions of solvation and relies on molecular exchange reactions in combination with electronic perturbations. Associated values for chemical reactivity indices such as the electronegativity, the chemical hardness, and the electrophilicity are obtained from straightforward conceptual density functional theory calculations. Further analysis of corresponding reaction energies allows us to estimate the enthalpic stability of solvent–solute, solvent–ion, and ion–ion complexes. The validity of our approach is demonstrated by the calculation of donor numbers for distinct solvents. Our results reveal a reasonable agreement between calculated and experimental outcomes which highlights the applicability of our combined theoretical and computational approach.

We have performed Molecular Dynamics simulations of ectoine, hydroxyectoine and urea in explicit solvent. Special attention has been spent on the local surrounding structure of water molecules. Our results indicate that ectoine and hydroxyectoine are able to accumulate more water molecules than urea by a pronounced ordering due to hydrogen bonds. We have validated that the charging of the molecules is of main importance resulting in a well defined hydration sphere. The influence of a varying salt concentration is also investigated. Finally we present experimental results of a DPPC monolayer phase transition that validate our numerical findings.