Enzymes in nearly anhydrous deep eutectic solvents: Insight into the biocompatibility and thermal stability

With the development of green chemistry, the demand for environmentally friendly and biocompatible solvents for non-aqueous enzymatic catalysis is increasingly urgent. Deep eutectic solvents (DESs) are viewed as the most promising alternatives to traditional organic solvents in non-aqueous biocatalysis. To expand the types of DESs and provide guidance for DESs design for non-aqueous enzymatic catalysis, the enzyme performance in aqueous buffer after incubation in nearly anhydrous DESs was associated with the properties and component structures of DESs. Almond β- Glucosidase (β-GC) and Candida antarctica lipase B (CALB) were selected as model enzymes. Physico-chemical properties of DESs (as inferred by their solvatochromic parameters) were applied to explore the influences of DESs properties on enzyme activity. For DESs with the same HBD, the biocompability of DESs and thermal stability of enzymes in DESs were negatively associated with the polarity and hydrogen bond acidity of DESs, and were positively associated with hydrogen bond basicity of DESs. Whereas an opposite trend was observed in DESs with the same HBA. Analyzing from the DESs components, the biocompatibility of hydrophobic DESs for enzyme was much lower than that of hydrophilic DESs. Generally, the amount of hydroxyl group and the length of carbon chain represent advantageous ingredients for maintaining natural structure of enzyme molecule. The presence of carboxyl group in hydrophilic DESs and carbon-carbon double bond may impair enzyme structure and activity. This work is hoped to be helpful in expanding the applications of DESs in non-aqueous biocatalysis.