Designing a biocatalytic process involving deep eutectic solvents

During the last decade, deep eutectic solvents (DESs) have emerged as a promising alternative to traditional organic solvents, from both environmental and technological perspectives. The number of structural combinations encompassed by DESs is tremendous; thus, it is possible to design an optimal DES for each specific enzymatic reaction system. In (bio)catalytic processes, a DES can serve as solvent/co‐solvent, as an extractive reagent for an enzymatic product, and as a pretreatment solvent of enzymatic biomass. To date, hydrolases are the most studied enzymes in DESs, which is not surprising given that lipases are the most important industrial enzymes. At the same time, there are a limited number of papers dealing with synthetic reactions in DESs involving other hydrolytic enzymes (epoxide hydrolases, phospholipase, proteases and haloalkane dehalogenases), lyases, and dehydrogenases (as a part of the whole Saccharomyces cerevisae and Escherichia coli cell biocatalysis). When designing efficient biocatalytic processes involving DESs, independent of the reaction type and enzyme used, the following steps should be included: (i) preparation and characterisation of the DES, (ii) screening of the DES for optimal enzyme performance, (iii) selection and optimisation of the biocatalytic protocol, and (iv) recovery of the product/DES and DES recycling with possible scale‐up. In this paper, we will present some practical aspects that we experienced while working with these solvents, together with some major observations that are available in the literature. © 2020 Society of Chemical Industry