Thiol and H2S Mediated NO Generation from Nitrate at Copper(II)

Nitrate fertilizer runoff poses chemical challenge for their remedial as relatively inert nitrate-oxoanions require stringent conditions for reduction. We present a novel strategy of using thiols RSH that represent biologically relevant reductants to convert nitrate to NO at a Cu(II) center under mild conditions with formation of disulfides RSSR. The bidentate b-diketiminato complex [Cl2NNF6]Cu(κ2-O2NO) engages in O-atom transfer (OAT) with various thiols (RSH) to form sulfenic acid (RSOH). Mechanistic studies indicate formation of the copper(II) nitrite complex [Cl2NNF6]Cu(κ2-O2N) upon OAT that further reacts with RSH to give S-nitrosothiols RSNO and [CuII]2(m-OH)2 en route to NO formation with [CuII]-SR intermediates. H2S, a physiologically potent agent and thiol congener, also reduces nitrate at copper(II) to NO generation, providing a lens into NO3-/H2S cross-talk in the biological milieu

Activation of Co(I) State in a Cobalt-Dithiolato Catalyst for Selective and Efficient CO₂ Reduction to CO

Reduction of CO₂ holds the key to solving two major challenges taunting the societyclean energy and clean environment. There is an urgent need for the development of efficient non-noble metal-based catalysts that can reduce CO₂ selectively and efficiently. Unfortunately, activation and reduction of CO₂ can only be achieved by highly reduced metal centers jeopardizing the energy efficiency of the process. A carbon monoxide dehydrogenase inspired Co complex bearing a dithiolato ligand can reduce CO₂, in wet acetonitrile, to CO with ∼95% selectivity over a wide potential range and 1559 s^–1 rate with a remarkably low overpotential of 70 mV. Unlike most of the transition-metal-based systems that require reduction of the metal to its formal zerovalent state for CO₂ reduction, this catalyst can reduce CO₂ in its formal +1 state making it substantially more energy efficient than any system known to show similar reactivity. While covalent donation from one thiolate increases electron density at the Co­(I) center enabling it to activate CO₂, protonation of the bound thiolate, in the presence of H₂O as a proton source, plays a crucial role in lowering overpotential (thermodynamics) and ensuring facile proton transfer to the bound CO₂ ensuring facile (kinetics) reactivity. A very covalent Co­(III)–C bond in a Co­(III)-COOH intermediate is at the heart of selective protonation of the oxygen atoms to result in CO as the exclusive product of the reduction

Electrocatalytic Ammonia Oxidation by a Low Coordinate Copper Complex

Molecular catalysts for ammonia oxidation to dinitrogen represent enabling components to utilize ammonia as a fuel and/or source of hydrogen. Ammonia oxidation requires not only the breaking of multiple strong N-H bonds, but also controlled N-N bond formation. We report a novel β-diketiminato copper complex [iPr2NNF6]Cu-NH3 ([Cu(I)]-NH3 (2)) as a robust electrocatalyst for NH3 oxidation in acetonitrile under homogeneous conditions. Complex 2 operates at a moderate overpotential (700 mV) with a TOFmax = 940 h-1 as determined from CV data in 1.3 M NH3 MeCN solvent. Prolonged (>5 h) controlled potential electrolysis (CPE) reveals the stability and robustness of the catalyst under electrocatalytic conditions. Detailed mechanistic investigations indicate that electrochemical oxidation of [Cu(I)]-NH3 forms {[Cu(II)]-NH3}+ (4) which undergoes deprotonation by excess NH3 to form reactive copper(II)-amide [Cu(II)]-NH2 (6) unstable towards N-N bond formation to give the dinuclear hydrazine complex [Cu(I)]2(mu-N2H4). Electrochemical studies reveal that the bisammine complex [Cu(I)](NH3)2 (7) forms at high ammonia concentration as part of the {[Cu(II)](NH3)2}+/[Cu(I)](NH3)2 redox couple that is electrocatalytically inactive. DFT analysis reveals a much higher thermodynamic barrier for deprotonation of {[Cu(II)](NH3)2}+ (8) by NH3 to give the four-coordinate copper(II) amide [Cu(II)](NH2)(NH3) (9) (dG = 31.7 kcal/mol) as compared to deprotonation of the three coordinate {[Cu(II)]-NH3}+ by NH3 to provide the reactive three coordinate parent amide [Cu(II)]-NH2 (dG = 18.1 kcal/mol) susceptible to N-N coupling to form [Cu(I)]2(mu-N2H4) (dG = -11.8 kcal/mol)

Repurposing a Bio-Inspired NiFe Hydrogenase Model for CO2 Reduction with Selective Production of Methane as the Unique C-Based Product

International audienceIn the current environmental and economic context, there is an urgent need to develop catalytic systems to efficiently activate and transform abundant small molecules while demonstrating selectivity when multielectron processes are involved. This is especially true for catalytic production of CH4 from CO2, as a limited number of active photo- or electro-catalysts have been described to date. Herein, we report the unprecedented reactivity of a molecular electrocatalyst physiadsorbed on a graphite electrode: the bioinspired [(LNiFeCp)-Ni-N2S2-Fe-II-Cp-II(CO)]+ (L-N2S2 = 2,2'-(2,2'-bipryridine-6,6'-diyl)bis- (1,1'-diphenylethanethiolate) complex selectively and catalytically reduces CO2 in acidic aqueous solution to produce a mixture of CH4 and H-2. Under optimized conditions, at pH 4, Faradaic yields of 12% and 66% for CH4 and H-2 production (TOFCH4 = 214 s(-1), TOFH2 approximate to 5.1 x 10(3) s(-1)) are measured, respectively. We demonstrate that this binuclear NiFe catalyst is stable for hours under controlled potential electrolysis conditions

An [FeFe]-Hydrogenase Mimic Immobilized through Simple Physiadsorption and Active for Aqueous H-2 Production

International audienceMimicking hydrogenases with synthetic complexes is a promising strategy for the design of Earth-abundant electrocatalysts for H$_2$ evolution as alternative to platinum. Here, we describe a bio-inspired FeFe electrocatalyst, with a semi-bridging $\mu$-CO ligand, active and stable for H$_2$ evolution in acidic aqueous solutions after its physiadsorption onto carbon-based electrodes

Elon Musk’s Neuralink Brain Chip: A Review on ‘Brain-Reading’ Device

With its novel bidirectional communication method, Neuralink, the brain-reading gadget created by Elon Musk, is poised to transform human-machine relations. It represents a revolutionary combination of health science, neurology, and artificial intelligence. Neuralink is a potentially beneficial brain implant that consists of tiny electrodes placed behind the ear and a small chip. It can be used to treat neurological conditions and improve cognitive function. Important discussions are nevertheless sparked by ethical worries about abuse, privacy, and security. It is important to maintain a careful balance between the development of technology and moral issues, as seen by the imagined future in which people interact with computers through thinking processes. In order for Neuralink to be widely accepted and responsibly incorporated into the fabric of human cognition and connectivity, ongoing discussions about ethical standards, regulatory frameworks, and societal ramifications are important. Meanwhile, new advancements in Brain-Chip-Interfaces (BCHIs) bring the larger context into focus. By enhancing signal transmission between nerve cells and chips, these developments offer increased signal fidelity and improved spatiotemporal resolution. The potential revolutionary influence of these innovations on neuroscience and human-machine symbiosis raises important considerations about the ethical and societal consequences of these innovations

A bidirectional bioinspired [FeFe]-hydrogenase model

International audienceWith the price-competitiveness of solar and wind power, hydrogen technologies may be game changers for a cleaner, defossilized, and sustainable energy future. H$_2$ can indeed be produced in electrolyzers from water, stored for long periods, and converted back into power, on demand, in fuel cells. The feasibility of the latter process critically depends on the discovery of cheap and efficient catalysts able to replace platinum group metals at the anode and cathode of fuel cells. Bioinspiration can be key for designing such alternative catalysts. Here we show that a novel class of iron-based catalysts inspired from the active site of [FeFe]-hydrogenase behave as unprecedented bidirectional electrocatalysts for interconverting H$_2$ and protons efficiently under near-neutral aqueous conditions. Such bioinspired catalysts have been implemented at the anode of a functional membrane-less H$_2$/O$_2$ fuel cell device

Hydrogen evolution from aqueous solution mediated by a heterogenized [NiFe]-hydrogenase model: low pH enables catalysis through enzyme-relevant mechanism.

International audience[NiFe]-hydrogenase enzymes are efficient catalysts for H2 evolution but their synthetic models have not been reported to be active under aqueous conditions, so far. Here we show that a close model of the [NiFe]-hydrogenase active site can work as a very active and stable heterogeneous H2 evolution catalyst under mildly acid aqueous conditions. Entry in catalysis is a NiIFeII complex, with electronic structure analogous to the Ni-L state of the enzyme, corroborating the mechanism modification recently proposed for [NiFe]-hydrogenases