Asymmetric Sulfoxidation Catalyzed by Horseradish Peroxidase in Hydrophilic Ionic Liquid

摘要

The effect of seven different hydrophilic ionic liquids (ILs) on the activity and enantioselectivity of horseradish peroxidase (HRP) was investigated through the enzymatic sulfoxidation of thioanisole in homogeneous phosphate buffer/ionic liquid co-solvents, using hydrogen peroxide or t-butyl hydroperoxide as oxygen donor. HRP displayed higher activity and enantioselectivity in the systems containing [C2mim] [BF4], [C4mim][BF4], [C6mim][BF4],[C4mim]Cl, [C4mim]HSO4, and [C4mim]NO3 with proper content than that in phosphate buffer. It showed that the anions of ILs have a significant effect on the reaction. And the IL [C4mim]Cl,which shows to be the most suitable for the reaction, gave the highest initial rate and enantioselectivity among various ILs which were studied. Furthermore, the enzymatic sulfoxidation in [C4mim]Cl-containing solvent was strongly dependent on [C4mim]Cl content and the optimum content was 15% (v/v). Activity and enantioselectivity of HRP in the system with [C4mim][CF3CO2] decreased dramatically. In addition the initial reaction rates of sulfoxidation of the substrate thioanisole in different co-solvents were observed to be 0.6-fold to 1.5-fold compared to that in phosphate buffer, using hydrogen peroxide as oxygen donor. But under higher substrate concentration, these rates were tens to hundreds of times faster than in phosphate buffer.