Heterogeneous Catalysis Mediated Cofactor NADH Regeneration for Enzymatic Reduction

Abstract

Enzymatic reduction using oxidoreductases is important in commercial chemical production. This enzymatic action requires a cofactor (e.g., NADH) as a hydrogen source that is consumed during reaction and must be regenerated. We present, for the first time, an in situ NADH regeneration (NAD + → NADH) using a heterogeneous catalyst (Pt/Al 2 O 3 ) and H 2 coupled with an enzymatic reduction. This regeneration system can be operated at ambient pressure where NADH yield and turnover frequency (TOF) increased with temperature (20−37 °C) and pH (4.0−9.9) delivering full selectivity to enzymatically active NADH. Cofactor regeneration by heterogeneous catalysis represents a cleaner (H + as sole byproduct) alternative to current enzymatic and homogeneous (electro-and photo-) catalytic methods with the added benefit of facile catalyst separation. The viability of coupling cofactor regeneration with enzymatic (alcohol dehydrogenase, ADH) reaction is established in aldehyde reduction (propanal to propanol) where 100% alcohol yield was achieved. The potential of this hybrid inorganic−enzymatic system is further demonstrated in the continuous (fed-batch) conversion of propanal with catalyst (activity/selectivity) stability for up to 100 h.

Photoelectrochemical NADH Regeneration using Pt‐Modified p‐GaAs Semiconductor Electrodes

“…Prior studies of NADH regeneration at metallic Pt electrodes—as opposed to the Pt/Al 2 O 3 system coupled with alcohol dehydrogenase, which exhibited 100% selective generation of 1,4‐NADH at low TOF—only partially characterized the products obtained. Yun et al .…”

“…A similar argument holds for surfaces modified by immobilized enzymes or metal complexes . Both electroenzymatic and enzyme‐supported NADH regeneration processes have also been reported, though these studies often sacrifice turnover frequency for selectivity and low applied potential, or vice versa . Consequently, several studies began focusing on “all‐solid” systems for electrochemical NADH regeneration.…”

Creating a Low‐Potential Redox Polymer for Efficient Electroenzymatic CO2 Reduction

“…[10] Furthermore,the electroreduction of NAD + commonly results in the formation of enzymatically inactive dimers. [11] Themore recently studied metal-dependent FDHs, which typically contain molybdenum (Mo-FDH) or tungsten (W-FDH), are more efficient biocatalysts for CO 2 reduction. [9b, 12] In addition, their tightly associated cofactors make them attractive biocatalysts for immobilized electroenzymatic biotechnologies.W -FDH has been reported by Reda and coworkers for its high efficiency in reversibly interconverting CO 2 and formate.…”

Creating a Low‐Potential Redox Polymer for Efficient Electroenzymatic CO2 Reduction

“…The NAD + ‐dependent FDH, which requires the unstable, expensive, and diffusive cofactor (NAD + or NADH) as the electron donor or acceptor, is well understood but typically has poor CO 2 reduction activity . Furthermore, the electroreduction of NAD + commonly results in the formation of enzymatically inactive dimers . The more recently studied metal‐dependent FDHs, which typically contain molybdenum (Mo‐FDH) or tungsten (W‐FDH), are more efficient biocatalysts for CO 2 reduction .…”