Protease activation in glycerol-based deep eutectic solvents

Deep eutectic solvents (DESs) consisting of mixtures of a choline salt (chloride or acetate form) and glycerol are prepared as easily accessible, biodegradable, and inexpensive alternatives to conventional aprotic cation–anion paired ionic liquids. These DES systems display excellent fluidity coupled with thermal stability to nearly 200 °C. In this work, the transesterification activities of cross-linked proteases (subtilisin and α-chymotrypsin), immobilized on chitosan, were individually examined in these novel DESs. In the 1:2 molar ratio mixture of choline chloride/glycerol containing 3% (v/v) water, cross-linked subtilisin exhibited an excellent activity (2.9 μmol min−1 g−1) in conjunction with a selectivity of 98% in the transesterification reaction of N-acetyl-l-phenylalanine ethyl ester with 1-propanol. These highly encouraging results advocate more extensive exploration of DESs in protease-mediated biotransformations of additional polar substrates and use of DESs in biocatalysis more generally.

Graphical abstractThe deep eutectic ionic liquid, choline chloride/glycerol (1:2, molar ratio), is shown to be friendly and compatible with subtilisin Carlsberg (protein image from PDB ID: 1SBC).Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Deep eutectic solvents (DESs) consisting of a choline salt (chloride or acetate form) and glycerol are biodegradable and inexpensive solvents for biocatalysis. ► These DES systems display excellent fluidity and high thermal stability. ► High transesterification activity and selectivity of immobilized subtilisin were observed in choline chloride/glycerol (1:2) containing 3% (v/v) water.