Molybdenum sulfides are very attractive noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER) from water. The atomic structure and identity of the catalytically active sites ...have been well established for crystalline molybdenum disulfide (c-MoS2) but not for amorphous molybdenum sulfide (a-MoSx), which exhibits significantly higher HER activity compared to its crystalline counterpart. Here we show that HER-active a-MoSx, prepared either as nanoparticles or as films, is a molecular-based coordination polymer consisting of discrete Mo3S13(2-) building blocks. Of the three terminal disulfide (S2(2-)) ligands within these clusters, two are shared to form the polymer chain. The third one remains free and generates molybdenum hydride moieties as the active site under H2 evolution conditions. Such a molecular structure therefore provides a basis for revisiting the mechanism of a-MoSx catalytic activity, as well as explaining some of its special properties such as reductive activation and corrosion. Our findings open up new avenues for the rational optimization of this HER electrocatalyst as an alternative to platinum.
Superoxide reductases (SORs) are mononuclear non-heme iron enzymes involved in superoxide radical detoxification in some microorganisms. Their atypical active site is made of an iron atom ...pentacoordinated by four equatorial nitrogen atoms from histidine residues and one axial sulfur atom from a cysteinate residue, which plays a central role in catalysis. In most SORs, the residue immediately following the cysteinate ligand is an asparagine, which belongs to the second coordination sphere and is expected to have a critical influence on the properties of the active site. In this work, in order to investigate the role of this asparagine residue in the
Desulfoarculus baarsii
enzyme (Asn117), we carried out, in comparison with the wild-type enzyme, absorption and resonance Raman (RR) studies on a SOR mutant in which Asn117 was changed into an alanine. RR analysis was developed in order to assign the different bands using excitation in the (Cys116)-S
−
→ Fe
3+
charge transfer band. By investigating the correlation between the (Cys116)-S
−
→ Fe
3+
charge transfer band maximum with the frequency of each RR band in different SOR forms, we assessed the contribution of the
ν
(Fe-S) vibration among the different RR bands. The data showed that Asn117, by making hydrogen bond interactions with Lys74 and Tyr76, allows a rigidification of the backbone of the Cys116 ligand, as well as that of the neighboring residues Ile118 and His119. Such a structural role of Asn117 has a deep impact on the S-Fe bond. It results in a tight control of the H-bond distance between the Ile118 and His119 NH peptidic moiety with the cysteine sulfur ligand, which in turn enables fine-tuning of the S-Fe bond strength, an essential property for the SOR active site. This study illustrates the intricate roles of second coordination sphere residues to adjust the ligand to metal bond properties in the active site of metalloenzymes.
Superoxide reductase Asn117 residue, by making hydrogen bonds with neighboring residues, enables fine-tuning of the Fe-S(Cys116) bond strength.
In this study, the PAH-degrading bacteria of a constructed wetland collecting road runoff has been studied through DNA stable isotope probing. Microcosms were spiked with
13C-phenanthrene at 34 or ...337 ppm, and bacterial diversity was monitored over a 14-day period. At 337 ppm, PAH degraders became dominated after 5 days by Betaproteobacteria, including novel
Acidovorax,
Rhodoferax and
Hydrogenophaga members, and unknown bacteria related to Rhodocyclaceae. The prevalence of Betaproteobacteria was further demonstrated by phylum-specific quantitative PCR, and was correlated with a burst of phenanthrene mineralization. Striking shifts in the population of degraders were observed after most of the phenanthrene had been removed. Soil exposed to 34 ppm phenanthrene showed a similar population of degraders, albeit only after 14 days. Results demonstrate that specific Betaproteobacteria are involved in the main response to soil PAH contamination, and illustrate the potential of SIP approaches to investigate PAH biodegradation in soil.
► We explored PAH-degrading bacteria on a chronically polluted site by stable isotope probing. ► Betaproteobacteria appeared as the main phenanthrene degraders in soil. ► Most soil PAH degraders were poorly related to bacteria isolated so far. ► Diversity shifts occurred in the community of degraders when the PAH became less available.
On a site collecting road runoff, implementation of stable isotope probing to identify soil bacteria responsible for phenanthrene degradation, led to the discovery of new Betaproteobacteria distantly related to known PAH degraders.
Dioxygen activation by copper complexes is a valuable method to achieve oxidation reactions for sustainable chemistry. The development of a catalytic system requires regeneration of the CuI active ...redox state from CuII. This is usually achieved using extra reducers that can compete with the CuII(O2) oxidizing species, causing a loss of efficiency. An alternative would consist of using a photosensitizer to control the reduction process. Association of a RuII photosensitizing subunit with a CuII pre‐catalytic moiety assembled within a unique entity is shown to fulfill these requirements. In presence of a sacrificial electron donor and light, electron transfer occurs from the RuII center to CuII. In presence of dioxygen, this dyad proved to be efficient for sulfide, phosphine, and alkene catalytic oxygenation. Mechanistic investigations gave evidence about a predominant 3O2 activation pathway by the CuI moiety.
O2 activation oxidation: A new Ru‐Cu dyad has been isolated and confirmed to be efficient for the photocatalytic oxygenation of organic substrates. Mechanistic investigations confirmed a photoinduced electron transfer from the photosensitizer to the copper catalytic center prior to O2 activation. X=substrate (sulfides, alkenes, phosphines).
Abstract
MiaE (2-methylthio-N6-isopentenyl-adenosine37-tRNA monooxygenase) is a unique non-heme diiron enzyme that catalyzes the O2-dependent post-transcriptional allylic hydroxylation of a ...hypermodified nucleotide 2-methylthio-N6-isopentenyl-adenosine (ms2i6A37) at position 37 of selected tRNA molecules to produce 2-methylthio-N6–4-hydroxyisopentenyl-adenosine (ms2io6A37). Here, we report the in vivo activity, biochemical, spectroscopic characterization and X-ray crystal structure of MiaE from Pseudomonas putida. The investigation demonstrates that the putative pp-2188 gene encodes a MiaE enzyme. The structure shows that Pp-MiaE consists of a catalytic diiron(III) domain with a four alpha-helix bundle fold. A docking model of Pp-MiaE in complex with tRNA, combined with site directed mutagenesis and in vivo activity shed light on the importance of an additional linker region for substrate tRNA recognition. Finally, krypton-pressurized Pp-MiaE experiments, revealed the presence of defined O2 site along a conserved hydrophobic tunnel leading to the diiron active center.
The development of catalytic systems for the oxidation of organic substrates using renewable sources such as water and dioxygen remains challenging. In this paper we report the synthesis and full ...characterization of a new dyad combining a ruthenium(II)‐based chromophore and a bio‐inspired copper(II) pre‐catalyst. In particular, photo‐induced electron transfer from the photosensitized RuII subunit toward the CuII center is highlighted. The photogenerated CuI moiety proves to be catalytically efficient for sulfides oxidation by 3O2 in the presence of a sacrificial electron source. Finally, the covalent association of the two partners favors Cu/O2‐based catalysis at the expense of a 1O2‐centered reactivity for a bimolecular mixture.
Covalent association of a Ru photosensitizable unit with a Cu‐based catalyst proves to be efficient for substrates oxygenation in the presence of molecular O2 as unique O‐atom source and limits the involvement of 1O2 side pathway.
Metallaphotoredox catalyzed cross-coupling of an arylbromide (Ar-Br) with an alkyl bis-catecholato silicate (R-Si⊖) has been analyzed in depth using a continuum of analytical techniques (EPR, ...fluorine NMR, electrochemistry, photophysics) and modeling (micro-kinetics and DFT calculations). These studies converged on the impact of four control parameters consisting in the initial concentrations of the iridium photocatalyst (Ir0), nickel precatalyst (Ni0) and silicate (R-Si⊖0) as well as light intensity I0 for an efficient reaction between Ar-Br and R-Si⊖. More precisely, two regimes were found to be possibly at play. The first one relies on an equimolar consumption of Ar-Br with R-Si⊖ smoothly leading to Ar-R, with no side-product from R-Si⊖ and a second one in which R-Si⊖ is simultaneously coupled to Ar-Br and degraded to R-H. This integrative approach could serve as a case study for the investigation of other metallaphotoredox catalysis manifolds of synthetic significance.
Due to their redox capabilities, thiols have an important role in biological oxidative/reductive processes through the formation of disulfides or their oxidation to into sulfenic, sulfinic, or ...sulfonic derivatives being also relevant for specific enzyme activities. The mechanisms of these biological pathways often involve metal ion(s). In this case, deciphering metal-assisted transformation of the S–S bond is of primary interest. This report details the reactivity of the disulfide-containing 2,6-bis(bis(pyridylmethyl)amino)methyl-4-methylmercaptophenyldisulfide (LMe(BPA)S–S) ligand with Cu(II) using different experimental conditions (anaerobic, H2O-only, H2O/O2, or O2-only). Crystallographic snapshots show the formation of tetranuclear disulfide, dinuclear sulfinate, and sulfonate complexes. Mechanistic investigations using Zn(II) as control indicate a non-metal-redox-assisted process in all cases. When present, water acts as nucleophile and attacks at the S–S bond. Under anhydrous conditions, a different pathway involving a direct O2 attack at the disulfide is proposed.
The emergence of superbugs developing resistance to antibiotics and the resurgence of microbial infections have led scientists to start an antimicrobial arms race. In this context, we have previously ...identified an active RiPP, the Ruminococcin C1, naturally produced by Ruminococcus gnavus E1, a symbiont of the healthy human intestinal microbiota. This RiPP, subclassified as a sactipeptide, requires the host digestive system to become active against pathogenic Clostridia and multidrug-resistant strains. Here we report its unique compact structure on the basis of four intramolecular thioether bridges with reversed stereochemistry introduced posttranslationally by a specific radical-SAM sactisynthase. This structure confers to the Ruminococcin C1 important clinical properties including stability to digestive conditions and physicochemical treatments, a higher affinity for bacteria than simulated intestinal epithelium, a valuable activity at therapeutic doses on a range of clinical pathogens, mediated by energy resources disruption, and finally safety for human gut tissues.
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