Stability of Enzymes in Nearly Anhydrous Ionic Liquids

The redox protein cytochrome c dissolved in both [BMPrl][H2P04] and [H0EtMe3N][H2P04] [87] indicating that a hydrogen-bonding capability of the cation is not required, in contrast with the above example. FT-IR measurements showed that cyt c maintained its native secondary structure upon dissolution in these ionic liquids. 

Alternatively, the enzyme can be modified such that it dissolves in a hydrophobic ionic liquid with retention of activity. This approach was demonstrated with cyt c, which, when covalently modified with polyethylene glycol (PEG), dissolved in [EMIm][ Tf2N] with retention of activity. The best results were obtained when the molecular weight of the polymer chain was 2000 [88]. Similarly, a copolymer of PEG and maleic anhydride solubilized subtilisin in [EMIm][NTf2] and a range of similar ionic liquids with good retention of activity and operational stability [89, 90]. 

Stability of Enzymes in Nearly Anhydrous Ionic Liquids 

Proteases have received less attention than lipases, but in one of the earliest papers on biocatalysis in ionic liquids it was noted that the activity loss of thermo-lysin during preincubation proceeded much more slowly in [BMIm][PF6] than in ethyl acetate [8]. The storage stability of a-chymotrypsin in the ionic liquid [EMIm][ Tf2N] was compared with that in water, 3 M sorbitol, and 1-propanol. The residual hydrolytic activity (after dilution with aqueous buffer) was measured vs time, and structural changes were monitored by fluorescence and CD spectroscopy as well as DSC [98]. The enzyme s life-time in [EMIm][ Tf2N] at 30°C was more than twice that in 3 M sorbitol, six times as long as that in water, and 96 times as long as that in 1-propanol. 

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