Enzyme activation by water-mimicking dual-functionalized ionic liquids

Biocatalytic synthesis represents a green alternative to metal-catalyzed reactions. However, enzymes typically display much lower catalytic activities in nonaqueous solvents than in aqueous media. To mimic the aqueous environment for enzyme activation, this study designed a series of sixteen dual-functionalized ionic liquids (ILs) that comprising both glycol ether (hydrogen-bond acceptor) and tert-alcohol (hydrogen-bond donor) groups. These “water-like” ILs enabled high transesterification activities for immobilized Candida antarctica lipase B (CALB) known as Novozym 435 and immobilized Bacillus licheniformis protease (known as subtilisin A) respectively. Several water-mimicking ILs containing 2–3 v% water significantly increased the CALB activity by 1.8-fold of that in tert-butanol, and 1.6-fold of that in diisopropyl ether (both organic solvents are highly enzyme-compatible). To a smaller degree, subtilisin was activated by these ionic solvents up to 1.2-fold (with 100% selectivity at 2 v% water) than by diisopropyl ether. Fluorescence emission spectra suggested that the characteristic emission maximum peaks were maintained in “water-like” ILs in most cases.