Enzymatic Reactions in Unusual Reaction Media

The performance of enzymatic reactions in unusual reaction media offers a wide range of possibilities. Polar and nonpolar organic solvents, supercritical fluids, ionic liquids, and deep eutectic solutions can be used as media for enzymatic reactions. The main motivations for this are to significantly increase the solubility of non- or low-water-miscible substrates and products compared to aqueous reaction systems, to simplify subsequent work-up, and to avoid microbial contamination as well as side and degradation reactions. Also, many enzymes exhibit different properties in unusual reaction media and catalyze different reactions than in aqueous systems. Hydrolytic enzymes can be successfully used for synthesis reactions, making specific use of their properties of regioselectivity, stereoselectivity, and substrate specificity. Therefore, the use of enzymes in unusual reaction media has gained great importance in recent years, e.g., for organic synthesis and in the chemical industry. This chapter describes the possibilities of carrying out enzymatic reactions in unusual reaction media. The different reaction media are presented in this chapter, and their influence on enzyme activity and stability is discussed. In all reactions, the consideration of water activity aW is an essential prerequisite for successful performance. Due to the reaction product water formed in the respective synthesis reactions, an equilibrium is reached above a certain concentration and should either be removed from the reaction preparations or its formation should be avoided by selecting suitable reaction conditions or substrates. Inactivation of enzymes in unusual reaction media can usually be avoided by immobilization.