Stuart BROWN1, Qi HAN1, Calum DRUMMOND1, Tamar GREAVES1
1School of Science, RMIT, Melbourne, Australia
A proteins solvent environment is key to its stability due to the influence the environment has on protein aggregation and folding. For many proteins, aqueous buffer solutions do not provide the optimum solvent environment and so alternative solvents are required for protein stability. The use of ionic liquid-water mixtures has been shown to manipulate these protein properties, with certain ion combinations and concentrations greatly increasing protein stability or activity. These changes are based on the interactions occurring within the solution between protein-water, protein-ionic liquid and protein-protein. However, there is currently no working understanding of the relationship between ionic liquid (IL) structure and its effect on a protein making investigations of IL-protein systems a trial-and-error activity. To expedite this, our research presents 137 IL-water mixtures with 10 unique cations and 10 unique anions at 4 different concentrations to investigate the effect of IL structure and concentration on the model protein hen egg white lysozyme. It was found that the specific ion effects of a single ions structure are not consistent across ion pairs. Several trends were found at low IL concentrations, for example a hydroxyl group or the increased alkyl chain length of the cation reduced the size of lysozyme. It was also found that these trends were inconsistent across concentrations and highly specific to the ion series. The study of specific ion effects has shown great promise in relation to solvent effects on protein stability, however with the inclusion of ILs in this field it becomes necessary to incorporate a model of analysis that includes the ion pair and how combinations of ions affect a protein in solution.