Environment-friendly biocatalytic processes using natural deep eutectic solvents

Green chemistry is a prevention approach to designing products and processes that minimize the use of materials hazardous to human health and environment. Biocatalysis, green solvents, reducing energy consumption by using alternative energy sources (e.g. microwave, ultrasound) are most important tools of green chemistry. The biocatalysis (whole cells, cell extracts, or purified enzymes) has the ability to catalyse organic reactions in the high chemo-, regio-, and stereoselectivity under mild reaction conditions and therefore represents an environment-friendly method of performing reactions that are known to require highly acidic or alkaline levels, high energy consumption for heating or even highly toxic metal catalysts. During the last 10 years, in order to find an alternative to conventional organic solvents, natural deep eutectic solvents (NADES) have started to be assessed as tools for biocatalysis, either as solvents or as separative agents, to overcome challenging workup procedures. A number of enzymes have shown enhanced activity and stability in the presence of cholinium-based NADES. The possibility to design an optimal NADES for each specific biocatalytic reaction system allows to improve substrate/product solubility ; enhance enzyme activity, enantioselectivity, regioselectivity and stability ; or to tailor the reaction rate. Herein, the behavior of industrial biocatalyst, Candida antarctica lipase B, carrot root and yeast Saccharomyces cerevisiae in the asymmetric hydrolysis of prochiral compounds and asymmetric reduction of prochiral ketones in natural deep eutectic solvents was studied. The effects of NADES on the synthetic activity and enantioselectivity of selected biocatalysts (as solvents, co- solvents or immiscible second phase), as well as some key parameters of processes involving them, will be presented.