Improving the Enzyme Catalytic Efficiency Using Ionic Liquids with Kosmotropic Anions

Abstract

The kosmotropicity of cations and anions in ionic liquids has a strong influence on the enzyme catalytic efficiency in aqueous environments. The kosmotropic anion CF 3 COO -seemed to activate the protease, and the chaotropic anions tended to destabilize the enzyme.

Enhancing protease enantioselectivity by ionic liquids based on chiral- or ω-amino acids

“…The [EMIM] + cation was chosen because it is a chaotrope, 33 and stabilizes the enzyme. [8][9][10] As seen in Figure 1, a high enantiomeric excess (ee, 92.2%) and yield (97.2%) of L Lphenylalanine were obtained in a low IL concentration (0.5 M), suggesting high enzyme activity in this medium. These values are very comparable with those in pure water (94.2% ee and 94.6% yield).…”

“…The reason for the former IL is that OTs À was suspected to be a chaotrope based on our previous enzyme-stability studies. 8,9 The reason for the later IL could be explained by the kosmotropicity of amino acids. As discussed in detail by our recent review on this subject, 28 On the other hand, the ions of amino acids are more kosmotropic than zwitterionic amino acids (AA) in a decreasing order of anion > cation > AA; 28 for example, B-coefficients of glycine ions at 25°C are in the order of 0.242 (Gly À ) > 0.160 (Gly + ) > 0.143 (Gly).…”

“…1 In particular, the ion-specific interaction has been an attractive focus for many scientists who routinely work with proteins and enzymes. Such an interaction was recently adopted by our group to help explain the effect of ionic liquids (ILs) as new ionic solvents on the enzyme stability 8,9 and enantioselectivity. 10 Our studies suggested that in aqueous solutions, kosmotropic anions and chaotropic cations of ILs stabilize the enzyme activity and enantioselectivity since hydrophilic ILs dissociate into individual cations and anions in water.…”

Using ionic liquid [EMIM][CH3COO] as an enzyme-‘friendly’ co-solvent for resolution of amino acids

“…[22][23][24] In diluted IL aqueous solutions, the enzyme is typically well hydrated; also, the medium viscosity and solution dissolution ability (towards substrates) are adjustable through varying the IL content. However, since hydrophilic ILs dissociate into cations and anions in water, the overall solvent properties (such as polarity) do not always account for the enzymatic behaviors in these media.…”

“…In other words, the mechanism of solvent effect on the enzyme function in IL aqueous solutions is different from that in nearly dry ILs. Our recent studies [22][23][24] suggested that the individual ion's kosmotropicity, following the Hofmeister ion series of protein stabilization, 11,[25][26][27] is responsible for the enzyme stability and enantioselectivity in IL aqueous solutions. The general conclusion was that ILs consisting of a kosmotropic anion and chaotropic cation can stabilize or even activate the enzyme in aqueous solutions.…”