How to improve the efficiency of biocatalysis in non-aqueous pure deep eutectic solvents: A case study on the lipase-catalyzed transesterification reaction

Non-aqueous biocatalysis has been expanding the application fields of biocatalysis and is playing an increasingly important role in industrial biocatalysis. Deep eutectic solvents (DESs) have been recognized as green reaction media of non-aqueous biocatalysis. To provide guidance for improving the catalytic performance of enzymes in pure DESs, Candida antarctica lipase B (CALB) catalyzed transesterification reaction was chosen as the model reaction to assess the catalytic efficiency in different series of pure DESs. The catalytic efficiency of CALB was strongly influenced by the properties of DESs. Hydrophobic DESs caused less inactivation of CALB than hydrophilic DESs. The highest yield in hydrophobic DESs reached 56.75% after 12 h. The amount of carboxyl group in hydrophobic DESs, the amount of hydroxyl group in hydrophilic DESs, and the length of carbon chain had positive impacts on the catalytic efficiency of CALB in DESs. Learning from the CALB behaviors in DESs, a preliminary attempt in rational design DESs for higher transesterification efficiency was provided. Except for reaction media, the catalytic activity of CALB in DESs was improved by medium engineering means and enzyme engineering measures, such as adding a trace amount of water, imprinting CALB with pH buffer or inorganic salt, and protecting CALB by lyoprotectants. Synergistic effect of multiple activation methods could also be observed in improving the catalytic efficiency. This study can provide insights into expanding the application of DESs in non-aqueous biocatalysis.