The Role of Reactive Natural Deep Eutectic Solvents in Sustainable Biocatalysis

Deep eutectic solvents (DESs) advanced in the past decade as the new generation of green and sustainable extraction and reaction media in biorefineries and in a multitude of chemical and biotechnological processes. Particularly, enzyme catalyzed reactions benefit from the specific properties of DESs, which not only ensure good substrate solubility but also enhance enzyme stability and operational efficiency. Recent studies showed that natural deep eutectic solvents (NADESs) comprising choline chloride or betaine as hydrogen bond acceptor and a large spectrum of natural compounds, such as carbohydrates, polyols carboxylic acids, as hydrogen bond donors, can have multiple functions, acting simultaneously as extraction solvent, reaction medium, source of substrate and source as catalyst. This novel approach for the utilization of multifunctional reactive natural deep eutectic solvents (R-NADESs) in catalytic conversions opens the way to the development of greener biocatalytic and chemo-catalytic processes, with simpler downstream processing and minimal discarded wastes, which will speed up their durable implementation in industry. This paper reviews the innovative applications of R-NADESs in biocatalytic reactions for the synthesis of a large diversity of high value chemicals and materials, including biosurfactants, flavors, biobased building blocks and biobased polymers, with highlight on esterification, transesterification, glycerolysis, polymerization, and redox reactions. Reactive natural deep eutectic solvents (R-NADESs) play multiple roles in enzyme-catalyzed reactions. This paper reviews single enzyme reactions and multienzyme cascades where the R-NADES is also the substrate or the initiator of the catalytic process. Highlighted are esterification, transesterification, glycerolysis, polymerization and redox reactions. image