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![a Atomic force microscopy image of the carboxylic acid functionalized single-walled carbon nanotube (SWCN-CO 2 H) bed layer on the cysteamine-modified gold electrode. b Carbodiimideassisted covalent linkage between the cysteamine layer at a gold electrode surface and SWCN-CO 2 H, and finally covalent hydrogenase linkage. Df [NiFe]-hase Desulfovibrio fructosovorans [NiFe] hydrogenase, DCC N,N 0dicyclohexylcarbodiimide, DMF N,N 0-dimethylformamide](profile/Elisabeth-Lojou/publication/5259733/figure/fig4/AS:668607654682626@1536419895241/a-Atomic-force-microscopy-image-of-the-carboxylic-acid-functionalized-single-walled.png)
a Atomic force microscopy image of the carboxylic acid functionalized single-walled carbon nanotube (SWCN-CO 2 H) bed layer on the cysteamine-modified gold electrode. b Carbodiimideassisted covalent linkage between the cysteamine layer at a gold electrode surface and SWCN-CO 2 H, and finally covalent hydrogenase linkage. Df [NiFe]-hase Desulfovibrio fructosovorans [NiFe] hydrogenase, DCC N,N 0dicyclohexylcarbodiimide, DMF N,N 0-dimethylformamide
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![Fig. 1 The 3D structure of Desulfovibrio fructosovorans [NiFe]...](profile/Elisabeth-Lojou/publication/5259733/figure/fig1/AS:394670665420800@1471108227057/The-3D-structure-of-Desulfovibrio-fructosovorans-NiFe-hydrogenase-was-obtained-from_Q320.jpg)
We report the modification of gold and graphite electrodes with commercially available carbon nanotubes for immobilization of Desulfovibrio fructosovorans [NiFe] hydrogenase, for hydrogen evolution or consumption. Multiwalled carbon nanotubes, single-walled carbon nanotubes (SWCNs), and amine-modified and carboxyl-functionalized SWCNs were used and...
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... was used to investigate the SWCN-CO 2 H arrangement on the electrode before hydrogenase coupling. As revealed by AFM (Fig. 2a), SWCN-CO 2 H are not protruding normal to the electrode surface, but form a network of nanotubes lying down on the electrode. Car- boxylic functions are described by the manufacturer to be positioned mainly on the walls of the nanotubes. Given these data along with the length of SWCN-CO 2 H (1 lm), a bed-like structure instead of a ...
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Citations
... Since the beginning of Protein Film Electrochemistry, a range of techniques to prepare the electroactive films were employed, from simply drop-casting the protein solution, sometimes with a co-adsorbant to help the adhesion to the electrode [1], to the chemical modification of electrodes and proteins to allow covalent grafting [29][30][31][32]. Films have also been made by slowly rotating an electrode in a buffer containing micromolar concentrations of enzyme under catalytic conditions, leading to a gradual increase over time of the catalytic current [17]. ...
Protein Film Electrochemistry is a technique in which a redox enzyme is directly wired to an electrode, which substitutes for the natural redox partner. In this technique, the electrical current flowing through the electrode is proportional to the catalytic activity of the enzyme. However, in most cases, the amount of enzyme molecules contributing to the current is unknown and the absolute turnover frequency cannot be determined. Here, we observe the formation of electrocatalytically active films of E. coli hydrogenase 1 by rotating an electrode in a sub-nanomolar solution of enzyme. This process is slow, and we show that it is mass-transport limited. Measuring the rate of the immobilization allows the determination of an estimation of the turnover rate of the enzyme, which appears to be much greater than that deduced from solution assays under the same conditions.
... The presence of an acidic patch of amino acids coupled to a dipole moment pointing toward the distal FeS cluster allowed the enzyme orientation to overturn as a function of the electrode surface charge. 24,29 In the case where no specific enzyme orientation was induced by an electrostatic interaction, the hydrophobicity/hydrophilicity of the electrochemical interface could be predominant. 25,30 For instance, the Aquifex aeolicus [NiFe]-hydrogenase yielded versatile enzyme− electrode interactions due to the lack of a preferential dipole moment direction. ...
... However, these studies are mainly centered on a few redox-enzymes and their metal cofactors. By exploiting the redox activity of metal cofactor, hydrogenase (a redox metalloenzyme) coated CNTs were used for HER and Hydrogen Oxidation Reactions (HOR) [23,24,28]. As the cofactors are susceptible to external stress (non-physiological conditions), the hydrogenase coated CNTs require delicate preparation steps to retain their active forms. ...
In recent years, there has been an increasing interest in designing economically viable metal-free carbon-supported catalysts for hydrogen-based energy technologies. Here we propose carbon nanotubes (CNTs) covalently functionalized with peptides or proteins as effective catalysts for electrochemical hydrogen evolution reaction (HER). We demonstrate that the HER activity of pristine CNTs can be greatly enhanced via simple functionalization by electrically insulating macromolecules. The roles of the conductive residues and the nitrogen content of the proteins, as well as the importance of their covalent connectivity with the CNTs, have been established. Moreover, we have observed a multifold enhancement in the HER current density due to electrochemical protein denaturation induced by the acidic medium used for HER. We have provided mechanistic insights into the HER activity of different metal-free peptides and proteins. Our work opens up new avenues in carbon-based metal-free HER catalysis, where, by careful selection of natural proteins, both the onset potential and the current density of the HER can be augmented.
... Some of the heme-containing enzymes (e.g., cytochrome c peroxidase, horseradish peroxidase, lignin peroxidase, manganese peroxidase) could also transfer electrons directly to the electrode surface [37,38]. It was noticed that oxidoreductases containing copper ion-based cofactors (e.g., laccase and bilirubin oxidase) [39], as well as NiFe and FeS hydrogenases [40,41], are also capable of DET. However, the DET phenomenon is not easily implemented-approximately only 100 out of 1700 known oxidoreductases have been shown to operate in DET applications [42,43]. ...
Direct electron transfer (DET)-capable oxidoreductases are enzymes that have the ability to transfer/receive electrons directly to/from solid surfaces or nanomaterials, bypassing the need for an additional electron mediator. More than 100 enzymes are known to be capable of working in DET conditions; however, to this day, DET-capable enzymes have been mainly used in designing biofuel cells and biosensors. The rapid advance in (semi) conductive nanomaterial development provided new possibilities to create enzyme-nanoparticle catalysts utilizing properties of DET-capable enzymes and demonstrating catalytic processes never observed before. Briefly, such nanocatalysts combine several cathodic and anodic catalysis performing oxidoreductases into a single nanoparticle surface. Hereby, to the best of our knowledge, we present the first review concerning such nanocatalytic systems involving DET-capable oxidoreductases. We outlook the contemporary applications of DET-capable enzymes, present a principle of operation of nanocatalysts based on DET-capable oxidoreductases, provide a review of state-of-the-art (nano) catalytic systems that have been demonstrated using DET-capable oxidoreductases, and highlight common strategies and challenges that are usually associated with those type catalytic systems. Finally, we end this paper with the concluding discussion, where we present future perspectives and possible research directions.
... [NiFe]-hydrogenases catalyzing H 2 oxidation possess a [NiFe] catalytic site accompanied by Fe−S clusters distant less than 10 Å to facilitate intra-then intermolecular ET between the catalytic site and either c-type or the b-type cytochromes ( Figure 6D). 88,228,229 On the cathodic side, the copper site T1 of multicopper oxidases (MCOs) is the site where the natural substrate binds. It is located near the shell of the enzyme allowing ET with the electrode surface. ...
The ever-increasing demands for clean and sustainable energy sources combined with rapid advances in biointegrated portable or implantable electronic devices have stimulated intensive research activities in enzymatic (bio)fuel cells (EFCs). The use of renewable biocatalysts, the utilization of abundant green, safe, and high energy density fuels, together with the capability of working at modest and biocompatible conditions make EFCs promising as next generation alternative power sources. However, the main challenges (low energy density, relatively low power density, poor operational stability, and limited voltage output) hinder future applications of EFCs. This review aims at exploring the underlying mechanism of EFCs and providing possible practical strategies, methodologies and insights to tackle these issues. First, this review summarizes approaches in achieving high energy densities in EFCs, particularly, employing enzyme cascades for the deep/complete oxidation of fuels. Second, strategies for increasing power densities in EFCs, including increasing enzyme activities, facilitating electron transfers, employing nanomaterials, and designing more efficient enzyme-electrode interfaces, are described. The potential of EFCs/(super)capacitor combination is discussed. Third, the review evaluates a range of strategies for improving the stability of EFCs, including the use of different enzyme immobilization approaches, tuning enzyme properties, designing protective matrixes, and using microbial surface displaying enzymes. Fourthly, approaches for the improvement of the cell voltage of EFCs are highlighted. Finally, future developments and a prospective on EFCs are envisioned.
... Multiple enzymes have been reported for their ability to undergo direct electron transfer with electrode surfaces, including isoforms of hydrogenase and formate dehydrogenase. [29][30][31][32][33][34][35][36] Further, we recently reported that a mixture of Hdr complexes from M. maripaludis could adsorb to carbon electrodes and reduce 2H + or CO2 to H2 or formate, for an extended period of time. 14 As such, we explored the possibility of electronically contacting the Hdr complexes isolated in this study with an electrode, for bioelectrochemical evaluation of FBEB. ...
Hydrogenotrophic methanogens oxidize molecular hydrogen to reduce carbon dioxide to methane. In methanogens without cytochromes, the initial endergonic reduction of CO2 to formylmethanofuran with H2-derived electrons is coupled to the exergonic reduction of a heterodisulfide of coenzymes B and M, by flavin-based electron bifurcation (FBEB). In Methanococcus maripaludis, FBEB is performed by a heterodisulfide reductase (Hdr) enzyme complex that involves hydrogenase (Vhu), although formate dehydrogenase (Fdh) has been proposed as an alternative to Vhu. We have identified and purified three Hdr complexes of M. maripaludis, where homodimeric Hdr complexes containing (Vhu)2 or (Fdh)2 were found, in addition to a heterocomplex that contains both Vhu and Fdh. Formate was found in in vitro assays using purified Hdr complex to act directly as the electron donor for FBEB via the associated Fdh. Furthermore, while ferredoxin was slowly reduced to 30% (-360 mV vs. SHE) by H2 and formate (0.8 atm and 30 mM, according to thermodynamics), the addition of CoBS -S-CoM as the high potential electron acceptor (E 0' =-140 mV vs. SHE; to induce FBEB) resulted in the rapid and more complete reduction of Fd to 94% (-455 mV vs. SHE).
... The catalyst layer on the cathode side contains electron conductive nanoparticles, binder, and enzymes. Both anode and cathode catalyst layers contain porous electron conductive matrixes, which are formed out of carbon, gold nanoparticles, or polymer materials [51][52][53][54]. Most recent studies have concentrated on the use of carbon nanomaterials [54]. ...
Efficient electron transfer between redox enzymes and electrocatalytic surfaces plays a significant role in development of novel energy conversion devices as well as novel reactors for production of commodities and fine chemicals. Major application examples are related to enzymatic fuel cells and electroenzymatic reactors, as well as enzymatic biosensors. The two former applications are still at the level of proof-of-concept, partly due to the low efficiency and obstacles to electron transfer between enzymes and electrodes. This chapter discusses the theoretical backgrounds of enzyme/electrode interactions, including the main mechanisms of electron transfer, as well as thermodynamic and kinetic aspects. Additionally, the main electrochemical methods of study are described for selected examples. Finally, some recent advancements in the preparation of enzyme-modified electrodes as well as electrodes for soluble co-factor regeneration are reviewed.
... The most common hydrogenases contain a catalytic cofactor (typically [NiFe] or [FeFe]) that is buried within the enzyme structure alongside accompanying FeS clusters that facilitate ET from the surface of the protein (figure 6a) [60][61][62]. These two types of hydrogenases can usually facilitate the reduction of 2H þ to H 2 and the oxidation of H 2 to 2H þ , and their electrochemistry has been explored for over 30 years [63][64][65][66]. ...
... In 2008, Lojou et al. demonstrated that the orientation of hydrogenase ([NiFe] from Desulfovibrio fructosovorans) significantly impacted the direct bioelectrocatalysis response observed at an electrode surface. Direct bioelectrocatalytic H 2 -oxidation and 2H þ -reduction currents were observed at modified gold electrode surfaces, where a combination of thiol and/ or carbon nanotube modifications was employed [64]. As discussed above for the case of MCOs, orientational studies provide strong evidence to suggest that the observed bioelectrocatalytic response is in fact due to holo-enzyme. ...
... Proposed ET pathway of bacterial FAD-dependent glucose dehydrogenase (bFAD-GDH), as described in[64].(Online version in colour.) ...
Enzymatic bioelectrocatalysis is being increasingly exploited to better understand oxidoreductase enzymes, to develop minimalistic yet specific biosensor platforms, and to develop alternative energy conversion devices and bioelectrosynthetic devices for the production of energy and/or important chemical commodities. In some cases, these enzymes are able to electronically communicate with an appropriately designed electrode surface without the requirement of an electron mediator to shuttle electrons between the enzyme and electrode. This phenomenon has been termed direct electron transfer or direct bioelectrocatalysis. While many thorough studies have extensively investigated this fascinating feat, it is sometimes difficult to differentiate desirable enzymatic bioelectrocatalysis from electrocatalysis deriving from inactivated enzyme that may have also released its catalytic cofactor. This article will review direct bioelectrocatalysis of several oxidoreductases, with an emphasis on experiments that provide support for direct bioelectrocatalysis versus denatured enzyme or dissociated cofactor. Finally, this review will conclude with a series of proposed control experiments that could be adopted to discern successful direct electronic communication of an enzyme from its denatured counterpart. © 2017 The Author(s) Published by the Royal Society. All rights reserved.
... 79 CNTs can be arranged in a multitude of different geometries (isolated tubes, planar arrays, random networks, or forests) that are currently explored for H 2 oxidation and O 2 reduction. 92,98,99 They can be compacted into disks, 100 arranged to form exible buckypaper lms with mm thickness, 101 deposited at electrode surfaces by layer-by-layer drop casting, 53,94,96 or painted as an ink. 102 Although catalytic currents are enhanced in all the cases, the respective role of increase in the electroactive surface area, in the heterogeneous electron transfer rate or in the loading of electroactive enzymes need to be elucidated. ...
... The immobilization of Df hydrogenase on amino-modied CNTs is fully consistent with a structure of the enzyme showing high value of dipole moment and a strong acidic patch of glutamate residues around the distal FeS. 94,141 The case of Re MbH is more astonishing. Re and Aa MbHs share more than 60% of homology. ...
Intensive research during the last 15 years on mechanistic understanding of hydrogenases, the key enzyme for H2 transformation in many microorganisms, has authorized the concept of green energy producing through H2/O2 enzymatic fuel cells (EFCs), in which enzymes are used as biodegradable and bioavailable biocatalysts. More recently, great effort has been put in the improvment of the interfacial electron transfer process between the enzymes and high surface area conductive materials in order to shift from the proof-of-concept to usable power device. Herein, we analyze the main issues that have been adressed during the last 5 years to make this breakthrough. After a brief introduction on the structure of hydrogenases and bilirubin oxidases, a widely used enzyme for O2 reduction, we compare their activity with platinum. We introduce the first H2/O2 EFCs and discuss their main limitations mainly related to the sensitivity of hydrogenases to O2 and oxidative potentials. We then review the discovery of new enzymes in the biodiversity and the advances in the control of the functionnal immobilization of these enzymes on electrodes that have permitted to overcome these limitations. We finally present all the reported H2/O2 EFCs, with a critical discussion on the perspectives of such devices.
... The nickel-iron hydrogenase absorbs directly on a graphite electrode [6] and also on carbon-nanotube-coated pyrolytic graphite electrodes [7] to, here, catalyze the consumption of H2 (see Figure 2). When adsorbed on an electrode, the hydrogenase enzyme produces high catalytic current and occurs at potentials expected for this half-cell reaction [2]. ...
Biohydrogen is a versatile energy carrier for the generation of electric energy from renewable sources. Hydrogenases can be used in enzymatic fuel cells to oxidize dihydrogen. The rate of electron transfer (ET) at the anodic side between the [NiFe]-hydrogenase enzyme distal iron-sulfur cluster and the electrode surface can be described by the Marcus equation. All parameters for the Marcus equation are accessible from DFT calculations. The distal cubane FeS-cluster has a three cysteine and one histidine coordination [Fe4S4](His)(Cys)3 first ligation sphere. The reorganization energy (inner- and outer-sphere) is almost unchanged upon a histidine-to-cysteine substitution. Differences in rates of electron transfer between the wild-type enzyme and the all-cysteine mutant can be rationalized by a diminished electronic coupling between the donor and acceptor molecules in the [Fe4S4](Cys)4 case. The fast and efficient electron transfer from the distal iron-sulfur cluster is realized by a fine-tuned protein environment which facilitates the flow of electrons. This study enables the design and control of electron transfer rates and pathways by protein engineering.
