Protein Denaturation by Ionic Liquids and the Hofmeister Series: A Case Study of Aqueous Solutions of Ribonuclease A

Abstract

The rating game: The effect of cations and anions of ionic liquids (ILs) on the stability of ribonuclease A in aqueous solutions was studied by differential scanning calorimetry (DSC thermogram shown). The salt‐induced shifts of the transition temperature are used to rank the cations and anions of ILs in the Hofmeister series.

How ionic liquids can help to stabilize native proteins

“…85 Using k cat /K M as the ordering scheme both, the cation and anion dependences, agree with the above-mentioned Hofmeister series deduced from thermal stability data for RNase A. 34 Moreover, the results in Table 2 reproduce the transition from stabilizing to destabilizing behaviour in these series. Thus, the results are ''universal'' with regard to both, the protein and the experimental property considered.…”

“…This high stability is surprising because the addition of hydrophobic ILs to aqueous protein solutions imposes strong denaturation. 34 Results for lipases, which are often tolerant to non-aqueous solvents, confirm the picture deduced from molecular solvents. For example, candida antarctica lipase B (CALB) maintained its activity in [C 4 82 We have attempted to characterize the effect of a hydrophobic IL on the melting temperature T m of a protein from dilute aqueous solutions to the neat IL.…”

“…95,96 Such correlations have also been discussed at length for ILs, 96 but have never been very precise. Referring to the anion series quoted above, 34 Ball 90 has noted that the observations do not seem to fit into any ordering scheme that can be conveniently interpreted on the basis of putative chaotropic and kosmotropic hydration.…”

“…1, both with regard to the thermodynamic stability of the species and kinetic barriers of the reactions. 4,8,15,16 Solvent modification can stabilize or destabilize the native fold, [27][28][29][30][31][32][33][34] enhance refolding, 42,43 optimize protein crystallization, 44 disrupt aggregates, 32 or steer the formation of intermediates. 32,45,46 The literature contains many useful, but more-or-less empirical guide lines for solvent optimization.…”

Single-walled Carbon Nanotube-triethylammonium Ionic Liquid as a New Catalytic System for Michael Reaction

“…5,6 ILs have proven to be promising solvents for various applications such as organic synthesis, protein folding, materials science, electrochemistry and separation technology. [9][10][11][12][13][14][15] On the other hand, the carbon nanotube (CNTs) due to their large surface area and exceptional electric properties are being exploited for the development of nanostructured materials with various applications.…”