Design and Evolution of an Enzyme for the Asymmetric Michael Addition of Cyclic Ketones to Nitroolefins by Enamine Catalysis.

Consistent introduction of novel enzymes is required for developing efficient biocatalysts for challenging biotransformations. Absorbing catalytic modes from organocatalysis may be fruitful for designing new-to-nature enzymes with novel functions. Herein we report a newly designed artificial enzyme harboring a catalytic pyrrolidine residue that catalyzes the asymmetric Michael addition of cyclic ketones to nitroolefins through enamine activation with high efficiency. Diverse chiral γ-nitro cyclic ketones with two stereocenters were efficiently prepared with excellent stereoselectivity (up to 97 % e.e., >20 : 1 d.r.) and good yield (up to 86 %). This work provides an efficient biocatalytic strategy for cyclic ketone functionalization, and highlights the usefulness of artificial enzymes for extending biocatalysis to further non-natural reactions.

A novel magnetic nanoscaled Fe3O4/CeO2 composite prepared by oxidation-precipitation process and its application for degradation of orange G in aqueous solution as Fenton-like heterogeneous catalyst.

In this work, magnetic nanoparticles (MNPs) Fe3O4/CeO2 were firstly synthesized using three different preparation methods, including coprecipitation, impregnation oxidation-precipitation and impregnation reduction-precipitation, respectively. The catalytic activities of Fe3O4/CeO2 MNPs, prepared by above three methods, were compared systematically in terms of the degradation of orange G (OG). The impregnation oxidation-precipitation process was economical and maneuverable due to the usage of air, no need of nitrogen protection and higher utilization efficiency of iron. Response surface methodology based on central composite design were used to investigate the individual and interactive effects of three process parameters on the OG degradation, i.e. the initial pH of the solution, the dosage of H2O2 and the initial concentration of OG. Under the optimal conditions of pH 2.5, H2O2 30 mM, OG 50 mg L-1, catalyst 2.0 g L-1 and 35 °C, the degradation percentage of OG was 98.2% within 120 min, which agreed well with the modeling prediction (R2 = 0.9984, and Adj-R2 = 0.9969). And the degradation reaction well followed the first-order kinetic with R2 = 0.9969. The Fe3O4/CeO2-OX MNPs showed high catalytic activity, stability and reusability in the degradation of OG.