Co-immobilization of galactose oxidase, catalase, and Mn-superoxide dismutase for efficient conversion of 5-hydroxymethylfurfural to 2,5-diformylfuran in water.

The three enzymes galactose oxidase (GO), catalase (CAT), and Mn-superoxide dismutase (SOD) were simultaneously immobilized by coordinating to Cu in phosphate buffer saline. The biocatalyst GO&CAT&SOD@Cu was used for the conversion of 5-hydroxymethylfurfural (HMF). The immobilized GO catalyzes the oxidation of HMF to 2,5-diformylfuran (DFF), concomitantly the co-substrate O is reduced to hydrogen peroxide (HO). A portion of the byproduct HO is broken down to O and HO by the co-immobilized CAT, and the evolved O can be recycled and used as the co-substrate. A portion of the byproduct HO is broken down to produce hydroxyl radicals •OH under the synergistic catalysis of the immobilized SOD and coordinated Cu, and the produced •OH can reactivate the immobilized galactose oxidase. Two aspects contribute to the high catalytic efficiency by GO&CAT&SOD@Cu: the reactivation of the immobilized galactose oxidase by producing •OH and the enrichment of the co-substate O by recycling the produced O. For the conversion of 10 mM HMF, GO&CAT&SOD@Cu (with encapsulated GO 0.2 mg/mL) achieved 97% HMF conversion within 2 h reaction. In contrast, free galactose oxidase M variant (ACS Catalysis 2018, 8, 4025) (0.2 mg/mL) achieved 25.3% HMF conversion within 2 h reaction. All the reactions were carried out in pure water, not in PBS.