Electrochemical Regeneration of NADH Enhanced by Platinum Nanoparticles

Abstract

Herein, we report the application of nanoparticulate platinum (nPt) to enhancing the heterogeneous electron transfer between NAD + (nicotinamide adenine dinucleotide, oxidized form) and electrodes in the presence of an organometallic mediator.(Pentamethylcyclopentadienyl-2,2'-bipyridinechloro)rhodium(III) (M = [Cp*Rh(bpy)Cl] + ; Cp* = C 5 Me 5 , bpy = 2,2'-bipyridine) was used as a primary mediator to shuttle electrons between NAD + and electrodes. nPt functioned as a homogeneous catalyst and also as a secondary mediator to improve the turnover kinetics of M.Pyridine nucleotides (NAD(P)H) or their oxidized counterparts (NAD(P) + ) are used as cofactors that are critically required for redox reactions catalyzed by various oxidoreductases. [1,2] In biocatalytic reactions, NADH should be regenerated to allow the enzymes to continue their turnover. Electrochemical regeneration has been chosen as an attractive strategy that is an alternative to enzymatic regeneration.[3] In electrochemical regeneration, however, the first drawback to overcome is the slow electron transfer between NAD + and the electrodes, even at a potential where the reduction of NAD + into NADH is thermodynamically favorable. The use of a homogeneous mediator to shuttle electrons between electrodes and NAD + can be one solution to solve the problem. [4][5][6] The rhodium complex M was successfully used as an electron shuttle for NAD + in electrolyte, which improved the kinetics of NADH regeneration. [7][8][9] The active reduced form M red2 that enables NADH to be generated is made through a typical electrochemical/chemical (EC) process (Scheme 1).M ox is reduced to M red1 by accepting two electrons from the electrodes (E step). Successively, M red1 is chemically converted into M red2 without any change in the total number of electrons, by taking up one proton from solution (C step). NADH is generated from NAD + with the active form M red2 by accepting one proton plus two electrons from M red2 and returning M red2 to the initial state M ox (Scheme 2).The chemical step from M red1 to M red2 (the uptake of a proton into the ligand sphere of M red1 ) is the rate-determining step of NADH generation, specifically at high rates, even though it was reported to proceed quite fast.[8] Figure 1 a shows cyclic voltammograms obtained at various scan rates. The intensity of the anodic peak increased with scan rate, whereas the peak was not apparently observed at scan rates

Bio‐Inspired Catalytic Imine Reduction by Rhodium Complexes with Tethered Hantzsch Pyridinium Groups: Evidence for Direct Hydride Transfer from Dihydropyridine to Metal‐Activated Substrate

“…For example, although this example is driven by formate ion, which is a renewable reductant, [22] it is also likely that these reductions can be driven electrochemically or photochemically. [7,8] We note that 1 is axially chiral. It remains to be seen whether the enantiomers of 1 or other chiral metal-OHD conjugates are active for asymmetric reduction.…”

“…[6] Electrolytic reduction of [Cp*Rh III (NN)L] n+ affords the corresponding Rh I complex, which is rapidly protonated at low pH to give the active hydrido-Rh III species for hydride transfer to NAD(P) + . [6][7][8][9] Conveniently, catalytic regeneration of OHDs using [Cp*Rh III (NN)L] n+ can be driven directly by electricity, by light and a photosensitizer, or by renewable chemical reductants, such as formate. [7][8][9] We employed a Hantzsch…”

Human Urine‐Fueled Light‐Driven NADH Regeneration for Redox Biocatalysis

“…Cp*Rh(bpy)(H 2 O) 2 + was synthesized according to the literature. [27] Synthesis of a-Fe 2 O 3 nanowire film: We synthesized a-Fe 2 O 3 nanowire films by using a hydrothermal method. [13] After sequentially washing an FTO substrate in acetone, ethanol, and 2-propanol for 15 min each, we put the substrate in a solution of 0.15 m iron(III) chloride and 1 m sodium nitrate and incubated it in an autoclave.…”

Nanomaterial-Based Electrochemical and Colorimetric Sensors for On-Site Detection of Small-Molecule Targets

“…83 The electrochemical oxidation of NADH at the electrode surface has garnered a lot of interest in the area of biosensors, because of the commercially available nature of these dehydrogenase enzymes, that can be applicable in clinical, environmental, and food analysis. 80,83,97 Drug screening usually utilizes these dehydrogenase-based systems to generate NADH as a signal indicator for the presence of target. Biosample matrix such as saliva is probably the idea matrix for on-site drug detection owing to its non-invasive procurement, relatively clean, and ease of accessibility.…”

“…95 Nicotinamide adenine dinucleotide (reduced) itself is electrochemically active, and the conventional solid electrodes such as gold, 96 platinum, 97 and glassy carbon 98 have been used as electrodes for NADH oxidation. However, NADH can only be oxidized on these electrodes at potentials above +1.0 V. [96][97][98] Consequently, various electron mediators such as organic dyes, 201 conducting polymers 202 and thio-substituted nucleobases 203 have been employed or modified on the electrode surface to facilitate NADH oxidation. Although the use of such electron mediators seems promising, problems such as defects of surface modification, the relatively cumbersome nature of these assays, lack of long-term electrode stability, low sensitivity and toxicity limit their practical applications.…”