Efficient NADH Regeneration by a Redox Polymer-Immobilized Enzymatic System

Abstract

Given the high costs and stoichiometric amounts of reduced nicotinamide adenine dinucleotide (NADH) required by the many oxidoreductases used for organic synthesis and the pharmaceutical industry, there is a need for the efficient reductive regeneration of NADH from its oxidized form, NAD + . Bioelectrocatalytic methods for NADH regeneration involving diaphorase and a redox mediator have shown promise; however, strong reductive mediators needed for this system are scarce, generally unstable, and require downstream separation. The immobilization of diaphorase in cobaltocene-modified poly-(allylamine) redox polymer is presented which is capable of producing bioactive 1,4-NADH with yields between 97% and 100%, faradaic efficiencies between 78% and 99%, and turnover frequencies between 2091 h −1 and 3680 h −1 over a range of temperatures spanning 20 to 60 °C. By using this system, methanol and propanol production by an NADH-dependent alcohol dehydrogenase were enhanced 7.1-and 5.2-fold, respectively, compared with a negative control. Finally, the efficiency of this approach coupled with its high operational stability (91% of the maximum activity after five experimental cycles) renders it among the most promising means of NADH regeneration yet developed.

Electroenzymatic Nitrogen Fixation Using a MoFe Protein System Immobilized in an Organic Redox Polymer

“…Aliquots of the resulting electrolyte solutions were analyzed by fluorescence spectroscopy, confirming that N 2 reduction to NH 3 was attained at potentials as high as À0.3 V, and the maximum yield of NH 3 was achieved at an applied potential of À0.8 V. This result suggests that at a sufficiently high applied overpotential the majority of the polymer-tethered NR moieties would be in their reduced state following the Nernst equation, leading to a high electrocatalytic driving force consistent with Butler-Volmer kinetics. [20,26,31,32]…”

“…Hence, electron transfer (ET) becomes independent of the electrode-enzyme distance and orientation via a mediated charge transfer. [17][18][19][20][21] The potential of a redox polymer to electrically communicate with nitrogenase via the MoFe protein should be < À0.49 V vs. SCE. [4,5,11] Accordingly, there are only a few potential redox mediators that could provide a sufficient reducing power, such as a variety of viologen-modified polymers, [22][23][24] which offer sufficient reducing power with redox potentials of around À0.69 V vs. SCE.…”

Elektroenzymatische Stickstofffixierung unter Verwendung eines MoFe‐Proteinsystems immobilisiert in einem organischen Redoxpolymer

“…Dieses Ergebnis lässt vermuten, dass bei einem ausreichend hohen angelegten Überpotential die Mehrzahl der polymergebundenen NR-Einheiten nach der Nernst-Gleichung in ihrem reduzierten Zustand vorliegen, was zu einer hohen elektrokatalytischen Triebkraft führt, die mit der Butler-Volmer-Kinetik im Einklang steht. [20,26,31,32] Experimente mit 15 [11,33] Das charakteristische Signalmuster für 15…”

“…Im Prinzip sind die polymergebundenen Redoxmediatoren in der Lage, jede beliebige Orientierung eines Redoxenzyms effizient mit der Elektrode zu kontaktieren, sodass der Elektronentransfer (ET) unabhängig vom Abstand und der Ausrichtung zwischen Elektrode und Enzym über einen mediierten Ladungstransfer gewährleistet wird. [17][18][19][20][21] Das Potential eines Redoxpolymers zur elektrischen Kommunikation mit der Nitrogenase über das MoFe-Protein sollte < À0.49 V vs. SCE liegen. [4,5,11] Dementsprechend gibt es nur wenige potentielle Redoxmediatoren, die ein ausreichendes Reduktionspotential aufweisen, wie z.…”

Enhanced Electrosynthetic Hydrogen Evolution by Hydrogenases Embedded in a Redox‐Active Hydrogel

“…Cc‐PAA has been shown to mediate electron transfer from an electrode to formate dehydrogenase and diaphorase, however other enzyme classes remain to be tested . Concurrently, the NiFe hydrogenase HynAB from Desulfovibrio gigas has been shown to accept electrons from cobaltocene‐functionalized branched polyethylenimine (Cc‐BPEI) in a photoelectrochemical setup .…”