Hydroxynitrile Lyase Catalysis in Ionic Liquid-containing Systems

On the background of enhanced stability and reusability of enzymes in ionic liquids

The ability of ILs (ionic liquids) to provide an environment of increased stability and, in this way, improve the recyclability of enzymes has been studied. The description of this phenomenon is not easy; there are several approaches for explanation. In this mini-review, the results from different research groups are summarized, with the aim of explaining the strong stability effect of ILs on several enzymes. Spectroscopic methods (e.g. fluorescence and CD, IR spectroscopy, mass spectroscopy and NMR) and investigations of polarity and kosmotropicity of ions are promising methods. Since higher stability means that we may be able to reuse enzymes more times, the recyclability of enzymes was also in the focus. From this point of view, the advantages and disadvantages of applying monophasic or biphasic systems are discussed too, presenting the coupled techniques as well.

Efficient kinetic resolution of (R,S)-1-trimethylsilylethanol via lipase-mediated enantioselective acylation in ionic liquids

Efficient enantioselective acylation of (R,S)-1-trimethylsilylethanol {(R,S)-1-TMSE} with vinyl acetate catalyzed by immobilized lipase from Candida antarctica B (i.e., Novozym 435) was successfully conducted in ionic liquids (ILs). A remarkable enhancement in the initial rate and the enantioselectivity of the acylation was observed by using ILs as the reaction media when compared to the organic solvents tested. Also, the activity, enantioselectivity, and thermostability of Novozym 435 increased with increasing hydrophobicity of ILs. Of the six ILs examined, the IL C4MIm.PF6 gave the fastest initial rate and the highest enantioselectivity, and was consequently chosen as the favorable medium for the reaction. The optimal molar ratio of vinyl acetate to (R,S)-1-TMSE, water activity, and reaction temperature range were 4:1, 0.75, and 40 -50 degrees C, respectively, under which the initial rate and the enantioselectivity (E value) were 27.6 mM/h and 149, respectively. After a reaction time of 6 h, the ee of the remaining (S)-1-TMSE reached 97.1% at the substrate conversion of 50.7%. Additionally, Novozym 435 was effectively recycled and reused in C4MIm.PF6 for five consecutive runs without substantial lose in activity and enantioselectivity. The preparative scale kinetic resolution of (R,S)-1-TMSE in C4MIm.PF6 is shown to be very promising and useful for the industrial production of enantiopure (S)-1-TMSE.