Stability and stabilization of biocatalysts by ionic liquids

As a new generation of nonaqueous solvents, ionic liquids (ILs) have attracted much attention in biocatalysis as (co)solvents. This chapter systematically discusses how ILs influence enzyme stability and how ILs have been used to stabilize enzymes in ionic environments. Several major factors in terms of IL properties have been surveyed on their impact on enzyme stability, which include IL network structure, IL polarity and hydrophobicity, hydrogen-bond basicity and nucleophilicity of anions, ion specificity and Hofmeister series, viscosity, and surfactant effect. The roles of ILs in improving the enzyme activity and stability are discussed in two categories: the modification of enzyme’s microenvironment and the design of enzyme-compatible functionalized ILs. The goal of this chapter is to provide some fundamental understandings of enzyme stability in ILs and point out some new direction in enzyme stabilization through using ILs.