Bifunctional COF-templated synthesis of immobilized enzyme catalysts for efficient bioconversion

Abstract

Rational design of immobilized enzyme catalysts based on covalent organic framework (COF) with high enzyme loading and superior robustness is highly desired. Herein, we designed an immobilized enzyme catalyst based on bifunctional COF. The quaternary ammonium-functionalized COF nanosheets adsorbed enzymes and subsequently induced the in-situ formation of silica coating without additional reagents. The ultrathin COF nanosheets guaranteed high enzyme loading of 3.4 mg mg⁻¹. Meanwhile, quaternary ammonium groups on COF induced the formation of silica coating on the surface of COF, where the as-formed silica coating protected the fragile enzyme. The stability of the enzyme in immobilization form increased by 165 %, 113 % and 44 %, respectively, compared to the enzyme directly adsorbed on COF under different conditions (50 °C, pH 11, or after five cycles). Furthermore, given the high enzyme loading of COF nanosheets, an immobilized multi-enzyme catalytic system was constructed to convert methanol to ethylene glycol via a four-enzyme cascade reaction, which exhibited 143 % increase in catalytic activity by contrast with free enzymes system. This study provides a promising approach for enzyme immobilization and extends the application of COF in biocatalysis.