Light-Activated Artificial CO-Reductase: Structure and Activity.

Light-dependent reduction of carbon dioxide (CO) into value-added products can be catalyzed by a variety of molecular complexes. Here we report a rare example of a structurally characterized artificial enzyme, resulting from the combination of a heme binding protein, heme oxygenase, with cobalt-protoporphyrin IX, with good activity for the photoreduction of CO to carbon monoxide (CO). Using a copper-based photosensitizer, thus making the photosystem free of noble metals, a large turnover frequency value of ∼616 h, a turnover value of ∼589, after 3 h reaction, and a CO vs H selectivity of 72% were obtained, establishing a record among previously reported artificial CO reductases.

[4Fe-4S]-dependent enzymes in non-redox tRNA thiolation.

Post-transcriptional modification of nucleosides in transfer RNAs (tRNAs) is an important process for accurate and efficient translation of the genetic information during protein synthesis in all domains of life. In particular, specific enzymes catalyze the biosynthesis of sulfur-containing nucleosides, such as the derivatives of 2-thiouridine (sU), 4-thiouridine (sU), 2-thiocytidine (sC), and 2-methylthioadenosine (msA), within tRNAs. Whereas the mechanism that has prevailed for decades involved persulfide chemistry, more and more tRNA thiolation enzymes have now been shown to contain a [4Fe-4S] cluster.

An organic O donor for biological hydroxylation reactions.

All biological hydroxylation reactions are thought to derive the oxygen atom from one of three inorganic oxygen donors, O, HO or HO. Here, we have identified the organic compound prephenate as the oxygen donor for the three hydroxylation steps of the O-independent biosynthetic pathway of ubiquinone, a widely distributed lipid coenzyme. Prephenate is an intermediate in the aromatic amino acid pathway and genetic experiments showed that it is essential for ubiquinone biosynthesis in under anaerobic conditions.

Zr-Based MOF-545 Metal-Organic Framework Loaded with Highly Dispersed Small Size Ni Nanoparticles for CO Methanation.

We report the use of Zr-based metal-organic frameworks (MOFs) MOF-545 and MOF-545(Cu) as supports to prepare catalysts with uniformly and highly dispersed Ni nanoparticles (NPs) for CO hydrogenation into CH. In the first step, we studied the MOF support under catalytic conditions using operando diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, ex situ characterizations (PXRD, XPS, TEM, and EDX-element mapping), and DFT calculations. We showed that the high-temperature conditions undoubtedly confer a potential for catalytic functionality to the solids toward CH production, while no role of the Cu could be evidenced.

Smart Electrode Surfaces by Electrolyte Immobilization for Electrocatalytic CO Conversion.

The activity and selectivity of molecular catalysts for the electrochemical CO reduction reaction (CORR) are influenced by the induced electric field at the electrode/electrolyte interface. We present here a novel electrolyte immobilization method to control the electric field at this interface by positively charging the electrode surface with an imidazolium cation organic layer, which significantly favors CO conversion to formate, suppresses hydrogen evolution reaction, and diminishes the operating cell voltage. Those results are well supported by our previous DFT calculations studying the mechanistic role of imidazolium cations in solution for CO reduction to formate catalyzed by a model molecular catalyst.

Activation of Coq6p, a FAD Monooxygenase Involved in Coenzyme Q Biosynthesis, by Adrenodoxin Reductase/Ferredoxin.

Adrenodoxin reductase (AdxR) plays a pivotal role in electron transfer, shuttling electrons between NADPH and iron/sulfur adrenodoxin proteins in mitochondria. This electron transport system is essential for P450 enzymes involved in various endogenous biomolecules biosynthesis. Here, we present an in-depth examination of the kinetics governing the reduction of human AdxR by NADH or NADPH.

Structure-based insights into the mechanism of [4Fe-4S]-dependent sulfur insertase LarE.

Several essential cellular metabolites, such as enzyme cofactors, contain sulfur atoms and their biosynthesis requires specific thiolation enzymes. LarE is an ATP-dependent sulfur insertase, which catalyzes the sequential conversion of the two carboxylate groups of the precursor of the lactate racemase cofactor into thiocarboxylates. Two types of LarE enzymes are known, one that uses a catalytic cysteine as a sacrificial sulfur donor, and the other one that uses a [4Fe-4S] cluster as a cofactor.

Silver and Copper Nitride Cooperate for CO Electroreduction to Propanol.

The need of carbon sources for the chemical industry, alternative to fossil sources, has pointed to CO as a possible feedstock. While CO electroreduction (CO R) allows production of interesting organic compounds, it suffers from large carbon losses, mainly due to carbonate formation. This is why, quite recently, tandem CO R, a two-step process, with first CO R to CO using a solid oxide electrolysis cell followed by CO electroreduction (COR), has been considered, since no carbon is lost as carbonate in either step.

Light-Driven Hydrogen Evolution Reaction Catalyzed by a Molybdenum-Copper Artificial Hydrogenase.

Orange protein (Orp) is a small bacterial metalloprotein of unknown function that harbors a unique molybdenum/copper (Mo/Cu) heterometallic cluster, [SMoSCuSMoS]. In this paper, the performance of Orp as a catalyst for the photocatalytic reduction of protons into H has been investigated under visible light irradiation. We report the complete biochemical and spectroscopic characterization of -Orp containing the [SMoSCuSMoS] cluster, with docking and molecular dynamics simulations suggesting a positively charged Arg, Lys-containing pocket as the binding site.

Shigella IpaA mediates actin bundling through diffusible vinculin oligomers with activation imprint.

Upon activation, vinculin reinforces cytoskeletal anchorage during cell adhesion. Activating ligands classically disrupt intramolecular interactions between the vinculin head and tail domains that bind to actin filaments. Here, we show that Shigella IpaA triggers major allosteric changes in the head domain, leading to vinculin homo-oligomerization.

The thiolation of uridine 34 in tRNA, which controls protein translation, depends on a [4Fe-4S] cluster in the archaeum Methanococcus maripaludis.

Thiolation of uridine 34 in the anticodon loop of several tRNAs is conserved in the three domains of life and guarantees fidelity of protein translation. U34-tRNA thiolation is catalyzed by a complex of two proteins in the eukaryotic cytosol (named Ctu1/Ctu2 in humans), but by a single NcsA enzyme in archaea. We report here spectroscopic and biochemical experiments showing that NcsA from Methanococcus maripaludis (MmNcsA) is a dimer that binds a [4Fe-4S] cluster, which is required for catalysis.

Oxygen-induced chromophore degradation in the photoswitchable red fluorescent protein rsCherry.

Reversibly switchable monomeric Cherry (rsCherry) is a photoswitchable variant of the red fluorescent protein mCherry. We report that this protein gradually and irreversibly loses its red fluorescence in the dark over a period of months at 4 °C and a few days at 37 °C. We also find that its ancestor, mCherry, undergoes a similar fluorescence loss but at a slower rate.

Identification of 2-Methylthio-methylenethio-N -(cis-4-hydroxyisopentenyl)adenosine (msms io A ) as a Novel Modification at Adenosine 37 of tRNAs from Salmonella typhimurium.

Post-transcriptional modifications of tRNA nucleotide are important determinants in folding, structure and function. We have successfully identified and characterized a new modified base named 2-methylthio-methylenethio-N -(cis-4-hydroxyisopentenyl)adenosine, which is present at position 37 in some tRNAs. We also showed that this new modified adenosine is derived from the known 2-methylthio-methylenethio-N -(isopentenyl)adenosine nucleoside by a catalytic cycle of the tRNA-diiron monooxygenase, MiaE, present in Salmonella typhimurium.

A subclass of archaeal U8-tRNA sulfurases requires a [4Fe-4S] cluster for catalysis.

Sulfuration of uridine 8, in bacterial and archaeal tRNAs, is catalyzed by enzymes formerly known as ThiI, but renamed here TtuI. Two different classes of TtuI proteins, which possess a PP-loop-containing pyrophosphatase domain that includes a conserved cysteine important for catalysis, have been identified. The first class, as exemplified by the prototypic Escherichia coli enzyme, possesses an additional C-terminal rhodanese domain harboring a second cysteine, which serves to form a catalytic persulfide.

Electrocatalytic Conversion of CO to Formate at Low Overpotential by Electrolyte Engineering in Model Molecular Catalysis.

An electrolyte engineering strategy was developed for CO reduction into formate with a model molecular catalyst, [Rh(bpy)(Cp*)Cl]Cl, by modifying the solvent (organic or aqueous), the proton source (H O or acetic acid), and the electrode/solution interface with imidazolium- and pyrrolidinium-based ionic liquids (ILs). Experimental and theoretical density functional theory investigations suggested that π -π interactions between the imidazolium-based IL cation and the reduced bipyridine ligand of the catalyst improved the efficiency of the CO reduction reaction (CO RR) by lowering the overpotential, while granting partial suppression of the hydrogen evolution reaction. This allowed tuning the selectivity towards formate, reaching for this catalyst an unprecedented faradaic efficiency (FE -) ≥90 % and energy efficiency of 66 % in acetonitrile solution.

CO Electroreduction in Water with a Heterogenized C-Substituted Nickel Cyclam Catalyst.

Molecular catalysis for selective CO electroreduction into CO can be achieved with a variety of metal complexes. Their immobilization on cathodes is required for their practical implementation in electrolytic cells and can benefit from the advantages of a solid material such as easy separation of products and catalysts, efficient electron transfer to the catalyst, and high stability. However, this approach remains insufficiently explored up to now.

Formate Dehydrogenase Mimics as Catalysts for Carbon Dioxide Reduction.

Formate dehydrogenases (FDH) reversibly catalyze the interconversion of CO to formate. They belong to the family of molybdenum and tungsten-dependent oxidoreductases. For several decades, scientists have been synthesizing structural and functional model complexes inspired by these enzymes.

Electrocatalytic metal hydride generation using CPET mediators.

Transition metal hydrides (M-H) are ubiquitous intermediates in a wide range of enzymatic processes and catalytic reactions, playing a central role in H/H interconversion, the reduction of CO to formic acid (HCOOH) and in hydrogenation reactions. The facile formation of M-H is a critical challenge to address to further improve the energy efficiency of these reactions. Specifically, the easy electrochemical generation of M-H using mild proton sources is key to enable high selectivity versus competitive CO and H formation in the CO electroreduction to HCOOH, the highest value-added CO reduction product.

Selective Ethylene Production from CO and CO Reduction via Engineering Membrane Electrode Assembly with Porous Dendritic Copper Oxide.

Gas-fed zero-gap electrolyzers have recently emerged as attractive systems for limiting ohmic losses and costs associated with electrolytes and for optimizing energy efficiencies. Here, we report that using a dendritic Cu oxide (D-CuO) material deposited on a gas diffusion layer as the cathode of a gas-fed zero-gap membrane electrode assembly (MEA) system results in a very selective conversion of CO to ethylene. More specifically, CO reduction yielded ethylene with an FE up to 68% at 100-125 mA·cm with H as the only other gaseous product and the electrolysis could be carried out for several hours with good stability.

Heterogenised Molecular Catalysts for Sustainable Electrochemical CO Reduction.

There has been a rapid rise in interest regarding the advantages of support materials to protect and immobilise molecular catalysts for the carbon dioxide reduction reaction (CO RR) in order to overcome the weaknesses of many well-known catalysts in terms of their stability and selectivity. In this Review, the state of the art of different catalyst-support systems for the CO RR is discussed with the intention of leading towards standard benchmarking for comparison of such systems across the most relevant supports and immobilisation strategies, taking into account these multiple pertinent metrics, and also enabling clearer consideration of the necessary steps for further progress. The most promising support systems are described, along with a final note on the need for developing more advanced experimental and computational techniques to aid the rational design principles that are prerequisite to prospective industrial upscaling.

Electrochemical CO reduction on Cu single atom catalyst and Cu nanoclusters: an approach.

The electrochemical CO reduction presents a sustainable route to the production of chemicals such as ethylene or ethanol, however the design of selective catalysts is still challenging. The use of single site copper nitrogen doped carbon materials with porphyrin-like Cu graphene structures have shown a significant improvement towards the production of multi carbon products, particularly ethanol. Nonetheless, during reaction the porphyrin like Cu sites transiently convert into metallic copper nanoclusters in a reversible process, making difficult to understand the actual role of each phase.

Dihydrouridine in the Transcriptome: New Life for This Ancient RNA Chemical Modification.

Until recently, post-transcriptional modifications of RNA were largely restricted to noncoding RNA species. However, this belief seems to have quickly dissipated with the growing number of new modifications found in mRNA that were originally thought to be primarily tRNA-specific, such as dihydrouridine. Recently, transcriptomic profiling, metabolic labeling, and proteomics have identified unexpected dihydrouridylation of mRNAs, greatly expanding the catalog of novel mRNA modifications.

Molecular Inhibition for Selective CO Conversion.

Electrochemical CO reduction presents a sustainable route to the production of chemicals and fuels. Achieving a narrow product distribution with heterogeneous Cu catalysts is challenging and conventional material modifications offer limited control over selectivity. Here, we show that surface-immobilised molecular species can act as inhibitors for specific carbon products to provide rational control over product distributions.

Keeping sight of copper in single-atom catalysts for electrochemical carbon dioxide reduction.

Carbon dioxide can be electrochemically converted into valuable multi-carbon products using Cu-based single-atom catalysts. However, transient cluster formation, which is undetectable using ex-situ techniques, may be responsible for C products. Here we discuss these observations to highlight the need for characterisation when defining active sites.

Carbon Dioxide Reduction: A Bioinspired Catalysis Approach.

While developed in a number of directions, bioinspired catalysis has been explored only very recently for CO reduction, a challenging reaction of prime importance in the context of the energetic transition to be built up. This approach is particularly relevant because nature teaches us that CO reduction is possible, with low overpotentials, high rates, and large selectivity, and gives us unique clues to design and discover new interesting molecular catalysts. Indeed, on the basis of our relatively advanced understanding of the structures and mechanisms of the active sites of fascinating metalloenzymes such as formate dehydrogenases (FDHs) and CO dehydrogenases (CODHs), it is possible to design original, active, selective, and stable molecular catalysts using the bioinspired approach.