Progress in Scaling up and Streamlining a Nanoconfined, Enzyme‐Catalyzed Electrochemical Nicotinamide Recycling System for Biocatalytic Synthesis

Abstract

An electrochemically driven nicotinamide recycling system, referred to as the ‘electrochemical leaf’ has unique attributes that may suit it to the small‐scale industrial synthesis of high‐value chemicals. A complete enzyme cascade can be immobilized within the channels of a nanoporous electrode, allowing complex reactions to be energized, controlled and monitored continuously in real time. The electrode is easily prepared by depositing commercially available indium tin oxide (ITO) nanoparticles on a Ti support, resulting in a network of nanopores into which enzymes enter and bind. One of the enzymes is the photosynthetic flavoenzyme, ferredoxin NADP+ reductase (FNR), which catalyzes the quasi‐reversible electrochemical recycling of NADP(H) and serves as the transducer. The second enzyme is any NADP(H)‐dependent dehydrogenase of choice, and further enzymes can be added to build elaborate cascades that are driven in either oxidation or reduction directions through the rapid recycling of NADP(H) within the pores. In this Article, we describe the measurement of key enzyme/cofactor parameters and an essentially linear scale‐up from an analytical scale 4 mL reactor with a 14 cm2 electrode to a 500 mL reactor with a 500 cm2 electrode. We discuss the advantages (energization, continuous monitoring that can be linked to a computer, natural enzyme immobilization, low costs of electrodes and low cofactor requirements) and challenges to be addressed (optimizing minimal use of enzyme applied to the electrode).

Green Chemistry, Biocatalysis, and the Chemical Industry of the Future

“…In the “electrochemical leaf” concept, [45] a minimum of two enzymes operating in a cascade are entrapped in a nanoporous metal oxide (e. g., indium‐tin oxide) electrode. One of these enzymes is ferredoxin nicotinamide adenine dinucleotide phosphate (NADP + ) reductase (FNR), a small photosynthetic flavoenzyme that is ubiquitous in vivo where it channels electrons into biosynthesis [46] .…”

Bioelectrocatalytic Cofactor Regeneration Coupled to CO2 Fixation in a Redox‐Active Hydrogel for Stereoselective C−C Bond Formation

“…While the rate for NADPH production remained significant, the competing O 2 reduction by the redox‐active polymer [19–21] strongly decreased the faradaic efficiency. Therefore, the bioelectrocatalyic NADP + reduction was carried out under inert atmosphere in analogy to previously reported electrochemical NAD(P)H regenerating systems [10, 22–24] …”

“…Therefore, the bioelectrocatalyic NADP + reduction was carried out under inert atmosphere in analogy to previously reported electrochemical NAD(P)H regenerating systems. [ 10 , 22 , 23 , 24 ]…”

“…While the rate for NADPH production remained significant, the competing O 2 reduction by the redox-active polymer [19][20][21] strongly decreased the faradaic efficiency.T herefore,the bioelectrocatalyic NADP + reduction was carried out under inert atmosphere in analogy to previously reported electrochemical NAD(P)H regenerating systems. [10,[22][23][24] Thee ffect of the film thickness on the catalytic current was tested by modulating the total amount of polymer and enzyme used for electrode modification while maintaining their previously optimized ratio constant [19] (Figure 1D and Figure S5B). Thec atalytic current for NADP + reduction increases with polymer and enzyme amount up to at otal loading of 60 mgcm À2 and is mostly independent of loading for values above 100 mgcm À2 .A ccording to theoretical kinetic models of thin electrocatalytic films [16,25] the initial linear regime can be assigned to current limited by catalyst loading while the thickness-independent currents are due to electron transfer and/or catalysis limitations within the film.…”

Bioelektrokatalytische Cofaktor‐Regeneration und CO2‐Fixierung in einem redoxaktiven Hydrogel durch stereoselektive C‐C‐Bindungsknüpfung

“…Während die Rate fürd ie NADPH-Produktion dabei signifikant blieb,v erringerte die durch das redoxaktive Polymer [19][20][21] konkurrierende O 2 -Reduktion die faradaysche Effizienz stark. Daher wurde die bioelektrokatalytische NADP + -Reduktion unter inerter Atmosphäre in Analogie zu früher berichteten elektrochemischen NAD(P)H-Regenerations-Systemen [10,[22][23][24] durchgeführt.…”