First-row Transition Metal Research Articles

Anchoring and reactivation of single-site Co–porphyrin over TiO2 for the efficient photocatalytic CO2 reduction

Porphyrin and its derivatives have been often used for electrochemical and photocatalysis combined with first-row transition metals for sustainable applications. Cobalt–tetrakis(4-carboxyphenyl)porphyrin (Co–TCPP) was covalently anchored onto TiO2. Under CO2, H2, and UV–visible light irradiation, Co–TCPP anchored on TiO2 produced CO at a rate of 2.5 μmol h−1 (using 100 mg of catalyst and UV–visible light of 118 mW cm−2) when the Co–TCPP content was 2.5 wt %; however, the CO formation rate dropped to 0.3 μmol h−1 (using 100 mg of catalyst and the same intensity of light). The photoactivity drop to 12 % was solved by removing the hydroxy ligands coordinated to the central Co ions through ethanol treatment for 5 min of the Co–TCPP–TiO2 photocatalysts. This resulted in an increased CO photoformation rate to 7.3 μmol h−1 (using 100 mg of catalyst and the same intensity of light) because the dispersion of the J- and/or H-aggregates to the isolated Co–TCPP unit proceeded more with ethanol treatment and under UV–visible light. Conversely, to use ethanol as reductant was not effective because it reduced and deactivated Co–TCPP.

Iron-catalyzed cascade synthesis of nitrogen polycycles from alkynoic acids and functionalized amines

Catalysis by first-row transition metals is of increasing interest in the context of the scarcity of chemical resources. For instance, iron is promising due to its abundance, low toxicity and unique electronic features. Here we synthesized quinazoline alkaloids from alkynoic acids and functionalized amines in the presence of iron dibromide and pyridine in toluene or, alternatively, in a solventless reaction system. We studied iron sources, reaction media and the effect of additives. Results show 39–99% yields and regioselective preparation of nitrogen- and oxygen-containing scaffolds. This is the first example of a cascade process involving alkynoic acids catalyzed by iron. Fe is more abundant, cheaper and less toxic than other Au, Cu and Ru catalysts previously reported for similar transformations.

(Invited) Towards Entirely Platinum Group Metal-Free Water Electrolyzers: Innovative Electrocatalysts for Oxygen Evolution and Hydrogen Evolution Reactions

Making the production of “green” hydrogen (H2) cost-effective requires the development of high-performance and affordable low-temperature water electrolyzers (LTWE).1 Currently, the most mature technology for H2 production using renewable electricity is the liquid alkaline electrolysis (AE). This technology suffers several major drawbacks such as gas crossover, relatively low current density, and the use of highly corrosive concentrated alkaline solutions (20-40% KOH). Proton exchange membrane (PEM) electrolysis, a valid alternative to AE technology, already commercialized on a large scale, enables operation on pure water thus eliminating corrosion, reducing gas crossover and allowing higher current density. However, the main drawback of PEM electrolyzers is the need of very expensive and rare platinum group metals (PGMs) such as Ir and Pt as catalysts for oxygen evolution reaction (OER) at the anode and hydrogen evolution reaction (HER) at the cathode, respectively.2 Recent advancements in performance and stability of anion exchange membranes (AEMs) have enabled a new type of alkaline membrane-based LTWE operating on pure water and with PGM-free catalysts.3,4 If successful, this new AEM-LTWE technology will allow to overcome the drawbacks of AEs and PEM-LTWEs while benefiting from their respective advantages in a major breakthrough in the production of “green” H2 at a low cost. In this scenario crucial is the development of high-performance PGM-free electrocatalysts for both OER and HER.Due to the operation at high potentials, carbon-based catalysts and supports cannot be used at the anode. Therefore, the most common PGM-free anode catalysts are based on transition metal oxides, which suffer, however, from low surface area and electronic conductivity, limiting the electrocatalytic performance.5,6 The catalysts with the most promising OER activity in alkaline environment are Ni-based alloys, oxides, and (oxy)hydroxides.7 The combination of Ni with other first-row transition metals such as Fe and Co was found to increase the OER catalytic activity.8,9 In this work, we present a new method for synthesizing NiFe OER catalysts. The catalyst was synthesized via a sol-gel method, followed by a thermal treatment. The impact on the OER activity in alkaline liquid electrolyte of different synthesis parameters such as the Ni-to-Fe atomic ratio, the addition of a third transition metal (e.g., Co, Mn), the thermal treatment temperature and atmosphere were investigated. Then, the most promising electrocatalysts were tested in an AEM-LTWE operating with pure water and supporting electrolyte solution.Bimetallic HER PGM-free catalysts were also developed by combining one a first-row transition metal, e.g. Ni, with a second-row transition metal, e.g. Mo. These HER catalysts were synthesized by either (i) using the sol-gel approach described above or (ii) via a metal organic framework (MOF) method similar to the one used in the synthesis of “atomically dispersed” M-N-C catalysts for oxygen reduction reaction.10 References A. M. Oliveira, R. R. Beswick, and Y. Yan, Curr. Opin. Chem. Eng., 33, 100701 (2021).H. A. Miller et al., Sustain. Energy Fuels, 4, 2114–2133 (2020).J. Xiao et al., ACS Catal., 11, 264–270 (2021).D. Li et al., Nat. Energy, 5, 378–385 (2020).Q. Gao et al., Chem. Eng. J., 331, 185–193 (2018).D. Xu et al., ACS Catal., 9, 7–15 (2019).S. Fu et al., Nano Energy, 44, 319–326 (2018).G. Zhang et al., Appl. Catal. B Environ., 286, 119902 (2021).P. Chen and X. Hu, Adv. Energy Mater., 10, 1–6 (2020).Y. He et al., Energy Environ. Sci., 12, 250–260 (2019).

(Digital Presentation) Ternary Nifetiooh Catalyst for the Oxygen Evolution Reaction: Study of the Effect of the Addition of Ti at Different Loadings

Ternary NiFeTiOOH Catalyst for the Oxygen Evolution Reaction: Study of the Effect of the Addition of Ti at Different Loadings Wenjamin Moschkowitsch and Lior Elbaz Chemistry Department, Bar-Ilan University, Ramat-Gan 5290002, IsraelThe demand for energy is expected to grow rapidly in the next decades, but it cannot be solely fulfilled with fossil fuel-based technologies without having a huge impact on the environment. The shift to production of clean energy from alternative sources, such as wind and sun, raise the importance of energy storage technologies. One of the most prominent solutions is storing surplus energy, harvested at peak production times and seasons, in hydrogen. However, the production of hydrogen with methods that require as little energy as possible, as well as being sustainable, environmentally friendly and cheap, are still considered to be a big challenge.Water electrolysis is the simplest industrial process for hydrogen production, and can be linked to fuel cells technology. Among the available electrolyzers, alkaline electrolyzers (ALE) are considered state-of-the-art. Although they can work with platinum-group metal-free (PGM-free) catalysts, unfortunately, this technology still requires the use of PGM catalysts in order to increase the current density, and lower the reaction activation energy.In electrolyzers, water splits into oxygen and hydrogen in two separate reactions, taking place at the anode and cathode. The cathodic reaction is the Hydrogen Evolution Reaction (HER), which is considered to be relatively facile. The anodic, Oxygen Evolution Reaction (OER), is considered to be much more difficult, since it is a four-electron process with very sluggish kinetics. The best known catalysts for this reaction in acidic medium are IrO2 and RuO2, oxides of very rare and precious metals (Ir is the scarcest metal on earth’s crust). In addition, in acidic medium, most PGM-free catalysts, based on earth abundant elements, are considered unstable (these conditions have also shown to be detrimental for Ir and Ru-based catalysts). In contrast, in ALEs, PGM-free catalysts have shown to be a good alternative to PGM catalysts. The most common OER PGM-free catalysts are first-row transition metals in their oxide, hydroxide and oxyhydroxide forms.One such catalyst is nickel oxyhydroxide (NiOOH). The structure of this specific catalyst has been studied in great detail by many different research groups, yet there are several open questions regarding the OER mechanism, i.e. the exact catalytic center and active phase.Recent studies suggest that pure NiOOH is not very active at all, and that all of the activity can be attributed to iron impurities.Indeed, NiFeOOH with iron content of 15-25 %at, has a much higher activity and a much lower overpotential compared to other PGM-free catalysts. It can thus be regarded as a benchmark for this class of OER catalysts.It is well accepted by now that the bimetallic catalyst further increases the intrinsic catalytic activity, and that addition of other transition metals,can further increase it.

Sacrificial Template-Assisted Mechanochemical Production of Highly Active Bifunctional Fe-N-C Catalysts

Bifunctional catalyst materials development for energy storage and conversion technologies is notoriously demanding in terms of electrochemistry (low stability, sluggish kinetics and high total overpotential (∆E)) and logistics (environmental safety, production methodologies and cost).Noble metal electrocatalysts are proven to be good bifunctional catalysts and as a result are being used as benchmark catalysts. However, the environmental and economic sustainability is severely compromised due to the scarcity of these metals. The alternative option is based on first-row transition metal heteroatom-doped carbon materials. Low cost, high availability, great electrocatalytic activity and stability promise to be a suitable noble metal free catalyst for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR).This work showcases a high performance Fe-N-C type material with sustainable synthesis and efficient activity towards ORR and OER. Unlike various classical methods for electrocatalyst synthesis, the developed methodology combines mechanochemistry and application of sacrificial template, which yields materials with superior bifunctional oxygen electrocatalytic performance.

(Invited) Elucidating the Electrochemically Active Site Density of PGM-Free ORR Catalysts in Situ Fuel Cells Using Fourier Transform Alternating Current Voltammetry

The rising interest in polymer electrolyte fuel cell (PEFC) technology, part of the global shift in energy production to clean sources, is accompanied by efforts to drive down the cost of this technology, which focus primarily on the cathode catalyst, the most expensive PEFC component. While platinum-group metals (PGMs) continues to be the materials of choice for oxygen reduction reaction (ORR) catalysts, use of these materials in PEFCs must be significantly reduced or eliminated without a penalty in the overall cell performance for PEFC technology to become fully viable.The most promising class ORR catalysts that do not utilize PGMs (i.e., PGM-free catalysts), involve first-row transition metals, such as iron and cobalt incorporated in a nitrogen-doped carbon (M-N-C catalysts). While advancements in M-N-C activity have been impressive, the much sought-after improvement in durability has been impeded by limited information on changes in the PGM-free catalyst active site density, activity and its degradation rate during fuel cell testing. Currently, degradation of PGM-free catalysts during fuel cell operation is often quantified using the low-current region of polarization curves. While this approach is well established, it neglects complications from such factors as catalyst pore structure, membrane conductivity, ionomer content, nature of the support, and the inhomogeneity of active sites. Hence, there exists a critical need for a method with high specificity towards catalytic activity.In this presentation we will report for the first time on the use of Fourier-transform alternating current voltammetry (FTacV) as an electrochemical method for accurately quantifying the electrochemically active site density of PGM-free ORR catalysts and following their degradation in situ during operation of polymer electrolyte fuel cells. Using this method, we were able to detect changes in performance of electrochemically active species (electrocatalytic centers in this case), allowing us to calculate the electrochemical active site density (EASD) for the first time, which is necessary to elucidate the degradation mechanisms of PGM-free ORR catalysts that occur in situ fuel cells. large-amplitude FTacV, a well-established electrochemical method with distinct advantages over dc methods, was utilized to quantify the electrochemically active site density of PGM-free FeNC catalysts in situ in PEFC. First, we will demonstrate that an accurate measurement of the EASD can be made using this method. To further emphasize the strength of the technique, we will present our findings during degradation of commercial FeNC catalysts in operating PEFC. The peak currents from higher harmonics produced by this method are correlated to the fuel cell performance, and decrease after durability tests in a manner that indicates EASD loss may not be the only catalyst degradation mechanism, thus inviting further studies of yet-unknown degradation pathway(s).

Near-Quantitative Predictions of the First-Shell Coordination Structure of Hydrated First-Row Transition Metal Ions Using K-Edge X-ray Absorption Near-Edge Spectroscopy.

The solvation structure of transition metal ions is important for applications in geochemistry, biochemistry, energy storage, and environmental chemistry. We study the X-ray absorption pre-edge and near-edge spectra at the K-edge of a nearly complete series of hydrated first-row transition metal ions with d orbital occupancy from d2 to d10. We optimize all of the structures at the density functional theory (DFT) level with explicit solvation and then compute the pre-edge X-ray absorption spectra with time-dependent DFT (TDDFT) and restricted active space second-order perturbation theory (RASPT2). TDDFT provides accurate results for spectra that are dominated by single excitations, while RASPT2 correctly distinguishes between singly and doubly excited states with quantitative accuracy compared with experiment. We analyze the pre-edge features for each metal ion to reveal the impact of the variations in d orbital occupancy on the first-shell coordination environment. We also report the lowest-energy ligand field d-d transitions using complete active space second-order perturbation theory.

Manganese(I) Complex with Monodentate Arylisocyanide Ligands Shows Photodissociation Instead of Luminescence.

Recently reported manganese(I) complexes with chelating arylisocyanide ligands exhibit luminescent metal-to-ligand charge-transfer (MLCT) excited states, similar to ruthenium(II) polypyridine complexes with the same d6 valence electron configuration used for many different applications in photophysics and photochemistry. However, chelating arylisocyanide ligands require substantial synthetic effort, and therefore it seemed attractive to explore the possibility of using more readily accessible monodentate arylisocyanides instead. Here, we synthesized the new Mn(I) complex [Mn(CNdippPhOMe2)6]PF6 with the known ligand CNdippPhOMe2 = 4-(3,5-dimethoxyphenyl)-2,6-diisopropylphenylisocyanide. This complex was investigated by NMR spectroscopy, single-crystal structure analysis, high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) measurements, IR spectroscopy supported by density functional theory (DFT) calculations, cyclic voltammetry, and time-resolved as well as steady-state UV–vis absorption spectroscopy. The key finding is that the new Mn(I) complex is nonluminescent and instead undergoes arylisocyanide ligand loss during continuous visible laser irradiation into ligand-centered and charge-transfer absorption bands, presumably owed to the population of dissociative d–d excited states. Thus, it seems that chelating bi- or tridentate binding motifs are essential for obtaining emissive MLCT excited states in manganese(I) arylisocyanides. Our work contributes to understanding the basic properties of photoactive first-row transition metal complexes and could help advance the search for alternatives to precious metal-based luminophores, photocatalysts, and sensors.

Hydroboration of alkynes initiated by sodium triethylborohydride

Sodium triethylborohydride, a popular hydride transferring reagent, is commonly used as an activating agent for hydroboration catalysts based on the first-row transition metal complexes. It has been found that NaHBEt3 can be a selective catalyst for hydroboration of terminal alkynes with pinacolborane. Hydroboration of aromatic and aliphatic alkynes in the presence of 10 mol% of NaHBEt3 proceeded in a highly selective manner to give (E)-vinylboronate esters with high yields, whereas ethynylsilanes seem to be less reactive in this process. Internal alkynes can also be transformed into corresponding vinylboronate esters, however, this process require prolonged reaction times compared to their terminal counterparts.

Green-Light-Driven Fe(III)(btz)3 Photocatalysis in the Radical Cationic [4+2] Cycloaddition Reaction

Green-light-driven FeIII(btz)3 photocatalysis for the radical cationic [4+2] cycloaddition of terminal styrenes and nucleophilic dienes has been investigated. The Fe-MIC (mesoionic carbene) complex forms a ligand-to-metal charge-transfer transition state with relatively high excited-state reduction potentials that can selectively oxidize terminal styrene derivatives. Unique multisubstituted cyclohexenes and structurally complex biorelevant cyclohexenes were constructed, highlighting the usefulness of this mild and practical first-row transition metal complex system.

Decoding Key Transient Inter-Catalyst Interactions in a Reductive Metallaphotoredox-Catalyzed Allylation Reaction.

Metallaphotoredox chemistry has recently witnessed a surge in interest within the field of synthetic organic chemistry through the use of abundant first-row transition metals combined with suitable photocatalysts. The intricate details arising from the combination of two (or more) catalytic components during the reaction and especially the inter-catalyst interactions remain poorly understood. As a representative example of a catalytic process featuring such intricacies, we here present a meticulous study of the mechanism of a cobalt-organophotoredox catalyzed allylation of aldehydes. Importantly, the commonly proposed elementary steps in reductive metallaphotoredox chemistry are more complex than previously assumed. After initial reductive quenching, a transient charge-transfer complex forms that interacts with both the transition-metal catalyst and the catalytic base. Surprisingly, the former interaction leads to deactivation due to induced charge recombination, while the latter promotes deprotonation of the electron donor, which is the crucial step to initiate productive catalysis but is often neglected. Due to the low efficiency of this latter process, the overall catalytic reaction is photon-limited and the cobalt catalyst remains in a dual resting state, awaiting photoinduced reduction. These new insights are of general importance to the synthetic community, as metallaphotoredox chemistry has become a powerful tool used in the formation of elusive compounds through carbon–carbon bond formations. Understanding the underlying aspects that determine the efficiency of such reactions provides a conceptually stronger reactivity paradigm to empower future approaches to synthetic challenges that rely on dual metallaphotoredox catalysis.

Structural diversity in transition metal-doped titanium oxo-alkoxy complexes: Potential sol-gel intermediates for doped titania nanoparticles and complex titanates

Since the discovery of its photocatalytic properties, titanium dioxide has remained one of the most popular and widely used metal oxide photocatalysts. Its major drawback, however, lies in the narrow region (UV) of sunlight necessary to produce reactive oxygen species. This have been countered by sensitizing with organic dyes to red-shift the absorption spectrum but also with doping of other metals and non-metals. Volume doping or surface modification have demonstrated improved photocatalytic efficiency, mainly via red-shifted absorption by introduction of intermediate energy states between the valence band (VB) and conduction band (CB) and increased number of surface hydroxyl groups (which can form reactive hydroxyl radicals) from charge compensation, and in some cases by improved surface-adsorption of organic molecules. Doped titania and complex titanates have traditionally been produced via, for instance, co-precipitation of mixed metal salts or via solid-state synthesis. While these methods usually are simple, they offer limited control over size, shape, and phase composition. An alternative is the use of single-source precursors (SSPs), i.e., molecules already containing the desired metal ratio in a homogenous distribution. The last one or two decades have seen an increased number of reported transition metal-doped titanium oxo-alkoxides (TOA), particularly for the first-row transition metals as potential single-source precursors (SSP) for doped titania and complex titanates. This review aims at providing an overview of TM-doped TOAs, focusing on first and second row TM elements, with special emphasis on their synthesis, photochemical properties, and their applications as SSPs.Graphical abstract

Recent Advances in Porphyrin-Based Systems for Electrochemical Oxygen Evolution Reaction.

Oxygen evolution reaction (OER) plays a pivotal role in the development of renewable energy methods, such as water-splitting devices and the use of Zn–air batteries. First-row transition metal complexes are promising catalyst candidates due to their excellent electrocatalytic performance, rich abundance, and cheap price. Metalloporphyrins are a class of representative high-efficiency complex catalysts owing to their structural and functional characteristics. However, OER based on porphyrin systems previously have been paid little attention in comparison to the well-described oxygen reduction reaction (ORR), hydrogen evolution reaction, and CO2 reduction reaction. Recently, porphyrin-based systems, including both small molecules and porous polymers for electrochemical OER, are emerging. Accordingly, this review summarizes the recent advances of porphyrin-based systems for electrochemical OER. Firstly, the electrochemical OER for water oxidation is discussed, which shows various methodologies to achieve catalysis from homogeneous to heterogeneous processes. Subsequently, the porphyrin-based catalytic systems for bifunctional oxygen electrocatalysis including both OER and ORR are demonstrated. Finally, the future development of porphyrin-based catalytic systems for electrochemical OER is briefly prospected.

Co(II), Ni(II), and Cu(II) complexes derived from 1,2,4-triazine: synthesis, characterization, anticancer activity, DFT, and molecular docking studies with a COVID-19 protein receptor

1,2,4-Triazine derivatives showed a significant role in the biological and pharmacological fields, which motivated us to study the biological and cytotoxicity activity of its first-row transition metal complexes. Three new complexes of Co(II), 1; Ni(II), 2; and Cu(II), 3 with 3-(2-benzylidenehydrazinyl)-5-(4-isobutylphenyl)-1,2,4-triazine, L were synthesized and characterized by standard physicochemical and theoretical methods. The structure of these complexes was evidenced by IR and 1H NMR spectroscopies, elemental analysis, magnetic measurements, molar conductance, mass spectrometry, and DFT modeling. The ligand behaved as a bidentate chelator that coordinates by triazine nitrogen-2 and azomethine nitrogen in a 2:1 (ligand : metal) ratio. The anticancer activity of the compounds was investigated against breast cancer cells (Mcf7 cell line). The antimicrobial activities of the ligand and its complexes were evaluated against different types of bacteria. Cu(II) was the most efficacious antimicrobial, with greater inhibition zones than the other complexes. The molecular docking studies were implemented to consider the binding attraction of the compounds with the receptors of breast cancer oxidoreductase (PDB:3HB5) and those of the COVID-19 main protease viral protein (PDB ID: 6LU7). The DFT calculations were used to confirm the molecular geometry of the new complexes.

Efficient Triplet-Triplet Annihilation Upconversion Sensitized by a Chromium(III) Complex via an Underexplored Energy Transfer Mechanism.

Sensitized triplet‐triplet annihilation upconversion (sTTA‐UC) mainly relies on precious metal complexes thanks to their high intersystem crossing (ISC) efficiencies, excited state energies, and lifetimes, while complexes of abundant first‐row transition metals are only rarely utilized and with often moderate UC quantum yields. [Cr(bpmp)2]3+ (bpmp=2,6‐bis(2‐pyridylmethyl)pyridine) containing earth‐abundant chromium possesses an absorption band suitable for green light excitation, a doublet excited state energy matching the triplet energy of 9,10‐diphenyl anthracene (DPA), a close to millisecond excited state lifetime, and high photostability. Combined ISC and doublet‐triplet energy transfer from excited [Cr(bpmp)2]3+ to DPA gives 3DPA with close‐to‐unity quantum yield. TTA of 3DPA furnishes green‐to‐blue UC with a quantum yield of 12.0 % (close to the theoretical maximum). Sterically less‐hindered anthracenes undergo a [4+4] cycloaddition with [Cr(bpmp)2]3+ and green light.

Cooperative C-H Bond Activation by a Low-Spin d6 Iron-Aluminum Complex.

The reactions of transition metal complexes underpin numerous synthetic processes and catalytic transformations. Typically, this reactivity involves the participation of empty and filled molecular orbitals centered on the transition metal. Kinetically stabilized species, such as octahedral low-spin d6 transition metal complexes, are not expected to participate directly in these reactions. However, novel approaches that exploit metal–ligand cooperativity offer an opportunity to challenge these preconceptions. Here, we show that inclusion of an aluminum-based ligand into the coordination sphere of neutral low-spin d6 iron complex leads to unexpected reactivity. Complexes featuring an unsupported Fe–Al bond are capable of the intermolecular C–H bond activation of pyridines. Mechanistic analysis suggests that C–H activation proceeds through a reductive deprotonation in which the two metal centers (Fe and Al) act like a frustrated Lewis pair. The key to this behavior is a ground state destabilization of the d6 iron complex, brought about by the inclusion of the electropositive aluminum-based ligand. These findings have immediate implications for the design of reagents and catalysts based on first-row transition metals.

Metal-Ligand Cooperativity in Iron Dinitrogen Complexes: Proton-Coupled Electron Transfer Disproportionation and an Anionic Fe(0)N2 Hydride.

Metal-ligand cooperativity and redox-active ligands enable the use of open-shell first-row transition metals in catalysis. However, the fleeting nature of the reactive intermediates prevents direct inspection of the relevant catalytic species. By employing phosphine α-iminopyridine (PNN)-based complexes, we show that chemical and redox metal-ligand cooperativity can be combined in the coordination sphere of iron dinitrogen complexes. These systems show dual activation modes either through deprotonation, which triggers reversible core dearomatization, or through reversibly accepting one electron by reducing the imine functionality. (PNN)Fe(N2) fragments can be obtained under mildly reducing conditions. Deprotonation of such complexes induces dearomatization of the pyridine core while retaining a terminally coordinated N2 ligand. This species is nevertheless stable in solution only below -30 °C and undergoes unusual ligand-assisted redox disproportionation through proton-coupled electron transfer at room temperature. The origin of this phenomenon is the significant lability of the α-imine C-H bonds in the dearomatized species, where the calculated bond dissociation free energy is 48.7 kcal mol-1. The dispropotionation reaction yields an overreduced iron compound, demonstrating that the formation of such species can be triggered by mild bases, and does not require harsh reducing agents. Reaction of the dearomatized species with dihydrogen yields a rare anionic Fe hydride that binds dinitrogen and features a rearomatized core.

Catalytic reductive ring opening of epoxides enabled by zirconocene and photoredox catalysis

Catalytic reductive ring opening of epoxides enabled by zirconocene and photoredox catalysis

Zng1 is a GTP-dependent zinc transferase needed for activation of methionine aminopeptidase.

The evolution of zinc (Zn) as a protein cofactor altered the functional landscape of biology, but dependency on Zn also created an Achilles' heel, necessitating adaptive mechanisms to ensure Zn availability to proteins. A debated strategy is whether metallochaperones exist to prioritize essential Zn-dependent proteins. Here, we present evidence for a conserved family of putative metal transferases in human and fungi, which interact with Zn-dependent methionine aminopeptidase type I (MetAP1/Map1p/Fma1). Deletion of the putative metal transferase in Saccharomyces cerevisiae (ZNG1; formerly YNR029c) leads to defective Map1p function and a Zn-deficiency growth defect. Invitro, Zng1p can transfer Zn2+ or Co2+ to apo-Map1p, but unlike characterized copper chaperones, transfer is dependent on GTP hydrolysis. Proteomics reveal mis-regulation of the Zap1p transcription factor regulon because of loss of ZNG1 and Map1p activity, suggesting that Zng1p is required to avoid a compounding effect of Map1p dysfunction on survival during Zn limitation.

Accurate, affordable, and generalizable machine learning simulations of transition metal x-ray absorption spectra using the XANESNET deep neural network.

The affordable, accurate, and generalizable prediction of spectroscopic observables plays a key role in the analysis of increasingly complex experiments. In this article, we develop and deploy a deep neural network-XANESNET-for predicting the lineshape of first-row transition metal K-edge x-ray absorption near-edge structure (XANES) spectra. XANESNET predicts the spectral intensities using only information about the local coordination geometry of the transition metal complexes encoded in a feature vector of weighted atom-centered symmetry functions. We address in detail the calibration of the feature vector for the particularities of the problem at hand, and we explore the individual feature importance to reveal the physical insight that XANESNET obtains at the Fe K-edge. XANESNET relies on only a few judiciously selected features-radial information on the first and second coordination shells suffices along with angular information sufficient to separate satisfactorily key coordination geometries. The feature importance is found to reflect the XANES spectral window under consideration and is consistent with the expected underlying physics. We subsequently apply XANESNET at nine first-row transition metal (Ti-Zn) K-edges. It can be optimized in as little as a minute, predicts instantaneously, and provides K-edge XANES spectra with an average accuracy of ∼±2%-4% in which the positions of prominent peaks are matched with a >90% hit rate to sub-eV (∼0.8eV) error.