Abundant Transition Metal Research Articles

Metabolic-scale gene activation screens identify SLCO2B1 as a heme transporter that enhances cellular iron availability

Iron is the most abundant transition metal essential for numerous cellular processes. Although most mammalian cells acquire iron through transferrin receptors, molecular players of iron utilization under iron restriction are incompletely understood. To address this, we performed metabolism-focused CRISPRa gain-of-function screens, which revealed metabolic limitations under stress conditions. Iron restriction screens identified not only expected members of iron utilization pathways but also SLCO2B1, a poorly characterized membrane carrier. SLCO2B1 expression is sufficient to increase intracellular iron, bypass the essentiality of the transferrin receptor, and enable proliferation under iron restriction. Mechanistically, SLCO2B1 mediates heme analog import in cellular assays. Heme uptake by SLCO2B1 provides sufficient iron for proliferation through heme oxygenases. Notably, SLCO2B1 is predominantly expressed in microglia in the brain, and primary Slco2b1-/- mouse microglia exhibit strong defects in heme analog import. Altogether, our work identifies SLCO2B1 as a microglia-enriched plasma membrane heme importer and provides a genetic platform to identify metabolic limitations under stress conditions.

Cooperative redox and spin activity from three redox congeners of sulfur-bridged iron nitrosyl and nickel dithiolene complexes

The synthesis of sulfur-bridged Fe-Ni heterobimetallics was inspired by Nature's strategies to "trick" abundant first row transition metals into enabling 2-electron processes: redox-active ligands (including pendant iron-sulfur clusters) and proximal metals. Our design to have redox-active ligands on each metal, NO on iron and dithiolene on nickel, resulted in the observation of unexpectedly intricate physical properties. The metallodithiolate, (NO)Fe(N2S2), reacts with a labile ligand derivative of [NiII(S2C2Ph2)]0, NiDT, yielding the expected S-bridged neutral adduct, FeNi, containing a doublet {Fe(NO)}7. Good reversibility of two redox events of FeNi led to isolation of reduced and oxidized congeners. Characterization by various spectroscopies and single-crystal X-ray diffraction concluded that reduction of the FeNi parent yielded [FeNi]-, a rare example of a high-spin {Fe(NO)}8, described as linear FeII(NO-). Mössbauer data is diagnostic for the redox change at the {Fe(NO)}7/8 site. Oxidation of FeNi generated the 2[FeNi]+⇌[Fe2Ni2]2+ equilibrium in solution; crystallization yields only the [Fe2Ni2]2+ dimer, isolated as PF6- and BArF- salts. The monomer is a spin-coupled diradical between {Fe(NO)}7 and NiDT+, while dimerization couples the two NiDT+ via a Ni2S2 rhomb. Magnetic susceptibility studies on the dimer found a singlet ground state with a thermally accessible triplet excited state responsible for the magnetism at 300 K (χMT = 0.67 emu·K·mol-1, µeff = 2.31 µB), and detectable by parallel-mode EPR spectroscopy at 20 to 50 K. A theoretical model built on an H4 chain explains this unexpected low energy triplet state arising from a combination of anti- and ferromagnetic coupling of a four-radical molecular conglomerate.

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.

Fe‐based catalysts for nitrogen reduction toward ammonia electrosynthesis under ambient conditions

AbstractAs one of the most important chemicals and carbon‐free energy carriers, ammonia (NH3) has significant energy‐related applications in industry and agriculture. Ninety percent of NH3 is produced by the Haber–Bosch process using high‐purity N2 and H2 at high temperatures and pressures, which consumes about 1% of the total energy production and causes 1.4% of global CO2 emissions. The environmentally friendly electrochemical nitrogen reduction reaction (NRR) with low energy consumption is a promising alternative to the conventional Haber–Bosch process. However, the main issue is the low Faradaic efficiency and NH3 selectivity of electrochemical NRR, caused by inert nitrogen molecules and competitive hydrogen evolution reaction. As one of the cheapest and most abundant transition metals widely utilized in the Haber–Bosch process, the Fe element has presented the potential high performance for the electrochemical NRR. This article summarizes recent advances and research progress in non‐noble Fe‐based catalysts used for NH3 electrosynthesis. Various synthetic protocols, structure/morphology modification, performance improvement, and reaction mechanisms are comprehensively presented. Based on recent experimental and theoretical studies, we aim to illuminate the structure–property relationship and offer an excellent opportunity for engineering advanced Fe‐based catalysts for nitrogen fixation. The most critical challenges and opportunities for Fe‐based catalysts are also provided. This review would open up a promising avenue toward developing platinum‐group‐metal‐free catalysts for electrochemical NRR applications in the future.

Synthesis and Characterization of NMC622 Cathode Material Modified by Various Cheap and Abundant Transition Metals for Li-ion Batteries

Synthesis and Characterization of NMC622 Cathode Material Modified by Various Cheap and Abundant Transition Metals for Li-ion Batteries

Theoretical study of single transition metal atom catalysts supported on two-dimensional Nb2NO2 for efficient electrochemical CO2 reduction to CH4

The design of highly efficient catalysts for electrochemical reduction CO2 (ECR) to value-add chemicals and fuels is important for CO2 conversion technologies. In this work, earth abundant transition metal (TM = V, Cr, Mn, Fe, Co and Ni) atoms embedded into two-dimensional (2D) Nb2NO2 (TM@Nb2NO2) as single-atom catalysts (SACs) for ECR was investigated by first-principles study. We demonstrated that Nb2NO2 can be an excellent substrate for anchoring single TM atom due to its excellent stability and electronic conductivity. Besides, V, Cr and Ni@Nb2NO2 could effectively promote CO2 adsorption and reduction. All TM@Nb2NO2 exhibit high selectivity towards CH4, and V, Cr and Ni@Nb2NO2 show low limiting potentials. The activity origin was revealed by analysing adsorption energy, d band centre, bonding/antibonding population and the change of valence state of TM atoms.

Deep‐Red Luminescent Molybdenum(0) Complexes with Bi‐ and Tridentate Isocyanide Chelate Ligands

AbstractIn octahedral complexes, molybdenum(0) has the same 4d6 valence electron configuration as ruthenium(II), which is beneficial for establishing energetically low‐lying metal‐to‐ligand charge transfer (MLCT) excited states. Those MLCT states often show luminescence, and they can furthermore undergo photoinduced electron and energy transfer reactions that are of interest in the context of solar energy conversion, sensing, or photocatalysis. Molybdenum is roughly 100 times more abundant than ruthenium, and it seems desirable to increase our fundamental understanding of the photophysical properties of complexes made from non‐precious metals. We report here on the luminescence behavior of two new homoleptic molybdenum(0) isocyanide complexes, one with three bidentate, the other with two tridentate chelate ligands. The key novelty is the incorporation of thiophene units into the ligand backbones, causing strongly red‐shifted photoluminescence with respect to comparable molybdenum(0) isocyanides with phenylene units in the ligand backbones. Combined experimental and computational studies provide detailed insight into the photophysical properties of this compound class. This work is relevant for the development of new luminescent compounds with possible applications in lighting and sensing, and it complements current research efforts on photoactive complexes with other abundant transition metal and main group elements.

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.

Iron metabolism in the social amoeba Dictyostelium discoideum: A role for ferric chelate reductases

Iron is the most abundant transition metal in all living organisms and is essential for several cellular activities, including respiration, oxygen transport, energy production and regulation of gene expression. Iron starvation is used by professional phagocytes, from Dictyostelium to macrophages, as a form of defense mechanism against intracellular pathogens. Previously, we showed that Dictyostelium cells express the proton-driven iron transporter Nramp1 (Natural Resistance-Associated Macrophage Protein 1) and the homolog NrampB (Nramp2) in membranes of macropinosomes and phagosomes or of the contractile vacuole network, respectively. The Nramp-driven transport of iron across membranes is selective for ferrous ions. Since iron is mostly present as ferric ions in growth media and in engulfed bacteria, we have looked for proteins with ferric reductase activity. The Dictyostelium genome does not encode for classical STEAP (Six-Transmembrane Epithelial Antigen of Prostate) ferric reductases, but harbors three genes encoding putative ferric chelate reductase belonging to the Cytochrome b561 family containing a N terminus DOMON domain (DOpamine β-MONooxygenase N-terminal domain). We have cloned the three genes, naming them fr1A, fr1B and fr1C. fr1A and fr1B are mainly expressed in the vegetative stage while fr1C is highly expressed in the post aggregative stage. All three reductases are localized in the endoplasmic reticulum, but Fr1A is also found in endolysosomal vesicles, in the Golgi and, to a much lower degree, in the plasma membrane, whereas Fr1C is homogeneously distributed in the plasma membrane and in macropinosomal and phagosomal membranes. To gain insight in the function of the three genes we generated KO mutants, but gene disruption was successful only for two of them (fr1A and fr1C), being very likely lethal for fr1B. fr1A- shows a slight delay in the aggregation stage of development, while fr1C- gives rise to large multi-tipped streams during aggregation and displays a strong delay in fruiting body formation. The two single mutants display altered cell growth under conditions of ferric ions overloading and, in the ability to reduce Fe3+, confirming a role of these putative ferric reductases in iron reduction and transport from endo-lysosomal vesicles to the cytosol.

Modeling and dynamical analysis of the full-length structure of factor XII with zinc.

Zinc (II), the second most abundant transition metal in blood, binds to the initiator of the contact pathway, factor XII (FXII). This binding induces conformational changes in the structure of FXII eventually leading to its activation. Despite many in vitro and in vivo studies on zinc-mediated activation of FXII, its molecular mechanism remains elusive mainly due to absence of a full-length structural model of FXII. To this end, this study investigated the role of zinc in the structure and dynamics of the full-length structure FXII that was obtained through molecular modeling. We have used four structural templates covering more than 70% of the FXII sequence and the remaining interconnecting regions were built by loop modeling. The resulting full-length structure of FXII contained disordered regions, but in comparison to the AlphaFold (AF) prediction, our full-length model represented a more realistic structure because of the disordered regions which were modeled to yield a more compact full-length structure in our model than the AF structure. Other than the disordered regions, our model and AF prediction were highly similar. The resulting full-length FXII structure was used to generate different systems representing the zinc-bound form (holo). Further to assess the contribution of the disulfide bridges, we also analyzed the apo and holo FXII structures with oxidized or reduced cysteine side-chains. Simulations suggested zinc binding conferred rigidity to the structure, particularly to the light chain of FXII. Zinc binding alone was sufficient to limit the backbone flexibility while 15 disulfide bonds, which were scattered throughout the structure, made a less significant contribution to the backbone rigidity. Altogether our results provide insights into the first realistic full-length structure of FXII focusing on the impact of structural zinc and disulfide bridges in the dynamics of this structure.

N-Heterocyclic Carbene Complexes of Nickel(II) from Caffeine and Theophylline: Sustainable Alternative to Imidazol-2-ylidenes.

Xanthines, such as caffeine and theophylline, are abundant natural products that are often present in foods. Leveraging renewable and benign resources for ligand design in organometallic chemistry and catalysis is one of the major missions of green and sustainable chemistry. In this Special Issue on Sustainable Organometallic Chemistry, we report the first nickel-N-heterocyclic carbene complexes derived from Xanthines. Well-defined, air- and moisture-stable, half-sandwich, cyclopentadienyl [CpNi(NHC)I] nickel-NHC complexes are prepared from the natural products caffeine and theophylline. The model complex has been characterized by x-ray crystallography. The evaluation of steric, electron-donating and π-accepting properties is presented. High activity in the model Suzuki-Miyaura cross-coupling is demonstrated. The data show that nickel-N-heterocyclic carbenes derived from both Earth abundant 3d transition metal and renewable natural products represent a sustainable alternative to the classical imidazol-2-ylidenes.

Single‐Vesicle Electrochemistry Following Repetitive Stimulation Reveals a Mechanism for Plasticity Changes with Iron Deficiency

Single‐Vesicle Electrochemistry Following Repetitive Stimulation Reveals a Mechanism for Plasticity Changes with Iron Deficiency

Single-Vesicle Electrochemistry Following Repetitive Stimulation Reveals a Mechanism for Plasticity Changes with Iron Deficiency.

Deficiency of iron, the most abundant transition metal in the brain and important for neuronal activity, is known to affect synaptic plasticity, causing learning and memory deficits. How iron deficiency impacts plasticity by altering neurotransmission at the cellular level is not fully understood. We used electrochemical methods to study the effect of iron deficiency on plasticity with repetitive stimulation. We show that during iron deficiency, repetitive stimulation causes significant decrease in exocytotic release without changing vesicular content. This results in a lower fraction of release, opposite to the control group, upon repetitive stimulation. These changes were partially reversible by iron repletion. This finding suggests that iron deficiency has a negative effect on plasticity by decreasing the fraction of vesicular release in response to repetitive stimulation. This provides a putative mechanism for how iron deficiency modulates plasticity.

Cobalt-N-Heterocyclic Carbene Complexes in Catalysis.

Cobalt-NHC complexes have emerged as an attractive class of 3d transition metal catalysts for a broad range of chemical processes, including cross-coupling, hydrogenation, hydrofunctionalization and cycloaddition reactions. Herein, we present a comprehensive review of catalytic methods utilizing cobalt-NHC complexes with a focus on catalyst structure, the role of the NHC ligand, properties of the catalytic system, mechanism and synthetic utility. The survey clearly suggests that the recent emergence of well-defined cobalt-NHC catalysts may have a tremendous utility in the design and application of catalytic reactions using more abundant 3d transition metals.

Photoactive Fe Catalyst for Light-Triggered Alkyd Paint Curing.

Herein, we show that the photoactive complexes [(Cp)Fe(arene)]+ (Cp = cyclopentadienyl; arene = C6H6, C6H5Me) act as latent catalysts that allow for photochemical control over the onset of alkyd paint curing, without the need for antiskinning agents such as the volatile 2-butanone oxime normally used to prevent curing during paint storage. The highly soluble neutral complexes [(Cp)Fe(Ch)] and [(Cp)Fe(Ch′)] (Ch = cyclohexadienyl, Ch′ = methylcyclohexadienyl) readily convert to the photoactive complexes [(Cp)Fe(arene)]+ upon oxidation in alkyd, allowing the latter to be dosed in a wide range of concentrations. Infrared and Raman studies show similar spectral changes of the alkyd paint matrix as have been observed in alkyd curing mediated by well-known, industrially applied cobalt- and manganese-based catalyst Co(neodecanoate)2 and [(Me3TACN)2Mn2(μ-OOCR)3](OOCR). The [(Cp)Fe(Ch)]/[(Cp)Fe(arene)]+ system performs equally well as these cobalt- and manganese-based catalysts in terms of drying time and outperform the manganese catalyst by showing a hardness development (increase) similar to that of the cobalt-based catalyst. Based on electron paramagnetic resonance and light–activity studies, we propose that photolysis of [(Cp)Fe(arene)]+ generates short-lived active FeII species, explaining the desired latency. The [(Cp)Fe(Ch)]/[(Cp)Fe(arene)]+ alkyd curing systems presented herein are unique examples of intrinsically latent paint curing catalysts that (1) are based on an abundant and harmless transition metal (Fe), (2) do not require any antiskinning agents, and (3) show favorable performance in terms of drying times and hardness development.

Advanced MoS2 nanocomposite materials for the synthesis of valuable pharmaceuticals

Rampant industrialization has played pivotal role in generation of polluting materials threatening ecology, environment and biosphere reserves. Amongst various pollutants, nitroarmatics are key components of non-biodegradable organic dyes, insecticides having toxic and carcinogenic effect on human health. Furthermore, aromatic hydrocarbons are widespread contaminants of ground water. Therefore, these waste materials are generally degraded by advanced oxidation process to carbon dioxide and water. But, these organic waste materials instead of complete mineralization can be valorized to valuable pharmaceuticals. For example, nitroaromatics can be valorized to tertiary amine or N-Mannich bases. N-Mannich bases are important pharmacophores and used as anti-microbial, anti-viral, anti-HIV, anti-inflammatory, analgesics and RSK2 inhibitory. Ethylbenzene is an important industrial waste can be used as building block for the synthesis of α-ketoamides. These α-ketoamides are significant pharmacophores can be used as the broad-spectrum antibiotics for COVID-19. Presently, COVID-19 is a global pandemic affecting billions of people. To deliver doses to such a big population would be a challenge. Therefore, we can use the industrial waste materials for the synthesis of valuable pharmacophors to boost the economy. To effectively catalyze the transformation of these industrial wastes into valuable products, cost-effective, readily available catalytic materials will be investigated. Earth abundant transition metals like Cu, Co, Zn, Ni, Zr etc. supported over 2D transition metal dichalcogenides can be used as the desirable candidates for the synthesis of pharmacophors from industrial waste. These catalytic materials will be prepared by hydrothermal or reverse micelle microemusion technique form metal salts or metal dithiocarbamates based single source molecular precursors.

Recent Advances in the High-Valent Cobalt-Catalyzed C-H Functionalization of N-Heterocycles.

Direct functionalization of heterocycles using C-H activation widely relies on the precious metal complexes. In past decade, the use of earth abundant and inexpensive transition metal to functionalize heterocycles has become an attractive alternate strategy. This concept is also interesting due to the unique reactivity pattern of these inexpensive metals. In this context we and other research groups have utilized the high-valent cobalt complexes as an inexpensive and readily available catalyst for the functionalization of heterocycles. In this review, we intend to brief recent progress made in the area of high-valent cobalt complexes catalyzed C-H functionalization of N-containing heterocycles.

Aqueous aging of secondary organic aerosol coating onto black carbon: Insights from simultaneous L-ToF-AMS and SP-AMS measurements at an urban site in southern China

Secondary organic aerosol (SOA) in the atmosphere can be formed from the gas phase precursors and evolve in the particle phase. Compared to numerous studies on gas phase oxidation of volatile organic compounds (VOCs), the evolution of OA and corresponding mechanisms in the particle phase are still unclear. In this study, a thermodenuder (TD) was coupled with both a long time-of-flight aerosol mass spectrometer (L-ToF-AMS) and a soot particle aerosol mass spectrometer (SP-AMS) at an urban site in southern China during wintertime of 2018, to explore whether there is significant difference for OA evolution on black carbon (BC) aerosols. The OA measured by L-ToF-AMS and SP-AMS were resolved into different primary and secondary factors, with the OA factors on BC particles showed different volatilities to that on the bulk aerosol. The more-oxidized oxygenated OA (MO-OOA, an agent of aged SOA) exhibited a unique preference on BC particles compared to other OA components. The abundant transition metals detected on BC particles was possibly the catalyser for the transformation from less oxidized OOA (LO-OOA, an agent of fresh SOA) to MO-OOA in aerosol aqueous-phase on BC particles and thus facilitates SOA formation. More studies are needed to further explore the potential role of BC and transition metals as catalysers for OA aging and the co-benefit of BC and transition metals pollution control on SOA reduction in the atmosphere.

Efficient UV–visible photodetector based on single CuO/Cu2O core-shell nanowire

One-dimensional nanostructures such as nanowires show better photoresponse than that of their bulk counterparts because of unidirectional transport that significantly reduces recombination and scattering of photo-generated charge carriers. CuO and Cu2O are relatively abundant transition metal oxides with optical band gaps suitable for efficient detection of UV and visible radiation. In addition, they form type-II heterojunction for efficient charge separation. Here, we report the fabrication of CuO/Cu2O core-shell nanowire arrays by chemical bath deposited Cu2O layer over thermally grown CuO nanowires. Photodetector devices based on individual CuO and CuO/Cu2O core-shell nanowire are fabricated through photolithography using Pd metal contact for studying response under UV and visible light illumination. Core-shell nanostructures show better performance in terms of responsivity, detectivity, external quantum efficiency, faster response, and recovery times over that of bare CuO nanowires. This is attributed to the Ohmic junction formed at the Pd-Cu2O interface that ensures barrierless hole transport for the core-shell photodetector. Further, the type-II heterojunction formed at CuO/Cu2O interface enhances hole concentration in the Cu2O shell layer, which is responsible for better photoresponse in core-shell nanostructures. The results establish that CuO/Cu2O core-shell nanowires offer simplified design and highly efficient photodetectors that can be used in several optoelectronic devices.

Trace Single‐Atom Iron‐Decorated Nitrogen‐Doped Carbons Enable Highly Efficient Selective Oxidation of Ethyl Benzene

AbstractThe hybridization of abundant transition metals with facile nitrogen‐doped carbons is an effective strategy to fabricate advanced functional materials for targeted applications. Herein, we demonstrate a novel and straightforward synthetic approach of preparing a series of different transition metal‐modified nitrogen‐doped carbons (M/NC, M=Fe, Co, Ni) through the addition of corresponding metal sulfates during the polymerization of aniline, followed by high‐temperature (873–1273 K) pyrolysis treatment. While Fe/NC features predominantly single Fe atoms, nanoparticles of mixed metal oxides and or carbonates are formed on Co/NC and Ni/NC. When employed in the selective oxidation of ethyl benzene by using tert‐butyl hydroperoxide both as the solvent and the oxidant, these materials showed promoted catalytic response with the order of Fe>Co>Ni as compared with the metal‐free analogue. The performance can be further tuned by controlling the pyrolysis temperature, and the best performance can be achieved over Fe/NC‐1273 (0.153 wt.% Fe), affording an unprecedented acetophenone yield of 98 % and excellent cycling performance.