Mo Center Research Articles

Upcycling polystyrene microplastics to Fe/Mo-doped sponge-carbon: Mo5+ enhanced electron transfer for boosting Fenton-like performance

The rate-limiting steps of promoting the conversion of Fe3+ to Fe2+ in Fenton-like systems are crucial for achieving efficient degradation of organic contaminants in aquatic environments. Herein, a novel magnetic Fe/Mo bimetallic doped sponge carbon (Fe/Mo-N-C) derived from polystyrene microplastics was successfully synthesized and the presence of metastable Mo5+ remarkably synergized the electron transfer of Fe2+ in internal microenvironment. In the Fe/Mo-N-C activating peroxymonosulfate (PMS) system, Mo5+ boosted the oxidation of Fe2+, and the conversion of Mo4+/Mo6+ accelerated the restoration of Fe2+ from Fe3+, resulting in nearly 100 % of 17α-ethinylestradiol (EE2) degradation with the kinetic rate constant of 0.343 min−1, which was 8.1 times faster than that of Fe-N-C. Moreover, Fe/Mo-N-C possessed excellent resistance to interference from various coexisting anions (especially chloride, sulfate, and nitrate ions up to 500 mM), natural organic matter, nano-plastics, and different water matrices. Density functional theory analysis demonstrated that Mo centers regulated the electron rearrangement of the Fe 3d orbital, enhancing the activation performance of Fe/Mo-N-C towards PMS. This study lays the groundwork for understanding the mechanism of metastable Mo, which holds significant importance for the up-recycling of polyethylene plastics and environmental remediation.

Engineering a Ce Promoter into a Three-Dimensional Porous Mo2C@NC Heterostructure for Hydrogen Evolution Electrocatalysis via Weakening the Mo-H Bond Strength.

The pursuit of highly efficient electrocatalysts for the alkaline hydrogen evolution reaction (HER) is of paramount importance for water splitting. However, it is still a formidable task in Mo2C-based materials because of the agglomeration and strong Mo-H binding of Mo2C units. Herein, a novel CeOCl-CeO2/Mo2C heterostructure nesting within a three-dimensional porous nitrogen-doped carbon matrix has been designed and used for catalyzing HER via simultaneous morphology and heterointerface engineering. As expected, the optimal CeOCl-CeO2(0.2)/Mo2C@3DNC exhibits impressive HER activity, with a low overpotential of 156 mV at a current density of 10 mA cm-2 coupled with a slight Tafel slope of 62.20 mV dec-1. Introducing a Ce promoter, that is CeOCl and CeO2, would endow the interface with an internal electric field and electron redistribution between CeOCl-CeO2 and Mo2C induced by the heterogeneous work function difference. Moreover, experimental investigation and density functional calculations confirm that the CeOCl-CeO2/Mo2C heterointerface can downshift the d-band center of the active Mo center, weakening the strength of the Mo-H coupling. This proposed concept, engineering Ce-based promoters into active entities involved in the heterostructure to modulate intermediate adsorption, offers a great opportunity for the design of superior electrocatalysts for energy conversion.

Synthesis of Isotypic Giant Polymolybdate Cages for Efficient Photocatalytic C-C Coupling Reactions.

The construction of isotypic high-nuclearity inorganic cages with identical pristine parent structure and increasing nuclearity is highly important for molecular growth and structure-property relationship study, yet it still remains a great challenge. Here, we provide an in situ growth approach for successfully synthesizing a series of new giant hollow polymolybdate dodecahedral cages, Mo250, Mo260-I, and Mo260-E, whose structures are growth based on giant polymolybdate cage Mo240. Remarkably, they show two pathways of nuclear growth based on Mo240, that is, the growth of 10 and 20 Mo centers on the inner and outer surfaces to afford Mo250 and Mo260-I, respectively, and the growth of 10 Mo centers both on the inner and outer surfaces to give Mo260-E. To the best of our knowledge, this is the first study to display the internal and external nuclear growth of a giant hollow polyoxometalate cage. More importantly, regular variations in structure and nuclearity confer these polymolybdate cages with different optical properties, oxidative activities, and hydrogen atom transfer effect, thus allowing them to exhibit moderate to excellent photocatalytic performance in oxidative cross-coupling reactions between different unactivated alkanes and N-heteroarenes. In particular, Mo240 and Mo260-E with better comprehensive abilities can offer the desired coupling product with yield up to 92% within 1 h.

N2 Functionalization via Molybdenum‐Nitride Complex: Stepwise BH Bond Additions

AbstractReactivity of (triphosphine)MoIV‐nitrido complex generated by N2 splitting, toward boranes is reported. The simple adduct Mo≡N→BH3 is observed with BH3.SMe2 while 1,2 addition is evidenced with 9‐BBN leading to H−Mo=NBR2. A second addition of BH3.SMe2 is facile and forms an unprecedented complex featuring two bridging H between two B and the Mo centers. Addition of PMe3 or BH3.SMe2 promotes reductive elimination and N−H bond formation. The full sequence of functionalization at Mo≡N obtained after N2 splitting is therefore evidenced in this work.

Phase and Defect Engineering of MoSe2 Nanosheets for Enhanced NIR-II Photothermal Immunotherapy.

Inducing immunogenic cell death (ICD) during photothermal therapy (PTT) has the potential to effectively trigger photothermal immunotherapy (PTI). However, ICD induced by PTT alone is often limited by inefficient PTT, low immunogenicity of tumor cells, and a dysregulated redox microenvironment. Herein, we develop MoSe2 nanosheets with high-percentage metallic 1T phase and rich exposed active Mo centers through phase and defect engineering of MoSe2 as an effective nanoagent for PTI. The metallic 1T phase in MoSe2 nanosheets endows them with strong PTT performance, and the abundant exposed active Mo centers endow them with high activity for glutathione (GSH) depletion. The MoSe2-mediated high-performance PTT synergizing with efficient GSH depletion facilitates the release of tumor-associated antigens to induce robust ICD, thus significantly enhancing checkpoint blockade immunotherapy and activating systemic immune response in mouse models of colorectal cancer and triple-negative metastatic breast cancer.

N2 Functionalization via Molybdenum-Nitride Complex: Stepwise BH Bond Additions.

Reactivity of (triphosphine)MoIV-nitrido complex generated by N2 splitting, toward boranes is reported. The simple adduct Mo≡N→BH3 is observed with BH3.SMe2 while 1,2 addition is evidenced with 9-BBN leading to H-Mo=NBR2. A second addition of BH3.SMe2 is facile and forms an unprecedented complex featuring two bridging H between two B and the Mo centers. Addition of PMe3 or BH3.SMe2 promotes reductive elimination and N-H bond formation. The full sequence of functionalization at Mo≡N obtained after N2 splitting is therefore evidenced in this work.

Molybdenum(VI) Nitrido Complexes with Tripodal Silanolate Ligands. Structure and Electronic Character of an Unsymmetrical Dimolybdenum μ-Nitrido Complex Formed by Incomplete Nitrogen Atom Transfer.

In contrast to a tungsten nitrido complex endowed with a tripodal silanolate ligand framework, which was reported in the literature to be a dimeric species with a metallacyclic core, the corresponding molybdenum nitrides 3 are monomeric entities comprising a regular terminal nitride unit, as proven by single-crystal X-ray diffraction (SC-XRD). Their electronic character is largely determined by the constraints imposed on the metal center by the podand ligand architecture. 95Mo nuclear magnetic resonance (NMR) and, to a lesser extent, 14N NMR spectroscopy allow these effects to be studied, which become particularly apparent upon comparison with the spectral data of related molybdenum nitrides comprising unrestrained silanolate, alkoxide, or amide ligands. Attempted nitrogen atom transfer from these novel terminal nitrides to [(tBuArN)3Mo] (Ar = 3,5-dimethylphenyl) as the potential acceptor stopped at the stage of unsymmetric dimolybdenum μ-nitrido complex 13a as the first intermediate along the reaction pathway. SC-XRD, NMR, electron paramagnetic resonance, and ultraviolet-visible spectroscopy as well as magnetometry in combination with density functional theory allowed a clear picture of the geometric and electronic structure of this mixed-valent species to be drawn. 13a is formally best described as an adduct of the type [(Mo[O])+III-(μN)-III-(Mo[N])+VI], S = 1/2 complex with (Mo[O])+III in the low-spin configuration, whereas related complexes such as [(AdS)3Mo-(μN)-Mo(NtBuAr)3] (19; Ad = 1-adamantyl) have previously been regarded in the literature as mixed-valent Mo+IV/Mo+V species. The spin population at the two Mo centers is uneven and notably larger at the more reduced Mo[O] atom, whereas the only spin present at the (μN) bridge is derived from spin polarization.

Alkane Elimination Preparation of Heterobimetallic MoAl Tetranuclear and Binuclear Complexes Promoting THF Ring Opening

We report a straightforward alkane elimination strategy to prepare well-defined heterobimetallic Al/Mo species. Notably, the reaction of the monohydride complex of molybdenum, Cp*MoH(CO)3, with triisobutyl aluminum affords a new heterobimetallic [MoAl]2 tetranuclear compound, [Cp*Mo(CO)(µ-CO)2Al(iBu)2]2, (1), featuring a 12-membered C4O4Mo2Al2 ring in which isocarbonyls bridge the Mo and Al centers. The addition of pyridine to this complex successfully results in the dissociation of the dimer into a new discrete binuclear complex, [Cp*Mo(CO)2(µ-CO)Al(Py)(iBu)2], (2). Switching the nature of the Lewis base from pyridine to tetrahydrofuran does not lead to the THF analogue of adduct 2, but rather to a complex reaction where one of the identified products corresponds to a tetranuclear species, [Cp*Mo(CO)3(μ-CH2CH2CH2CH2O)Al(iBu)2]2, (3), featuring two bridging alkoxybutyl fragments originating from the C-O ring opening of THF. Compound 3 adds to the unusual occurrences of THF ring opening by heterobimetallic complexes, which is evocative of masked metal-only frustrated Lewis pair behavior and highlights the high reactivity of these Al/Mo assemblies.

Flash Joule‐heating synthesis of MoO2 nanocatalysts in graphene aerogel for deep catalytic oxidative desulfurization

AbstractUltra‐high‐temperature flash Joule‐heating of organometallic precursor‐embedded reduced graphene oxide (rGO) aerogel represents a highly efficient approach for the ultrafast production of nanocatalysts, while such a methodology has been scarcely applied to 3D nanocarbon‐based aerogel monoliths. Herein, we demonstrate the rapid synthesis of MoO2 nanoparticles within the aerogel matrix via a 1‐s high‐temperature flash Joule‐heating process (~1700°C), resulting in the formation of the hybrid MoO2@rGO aerogel with uniformly distributed nanoparticles. Nitrogen adsorption/desorption analysis indicates discernible internal microstructural disparities attributed to the additional 1‐s flash‐heating and the substantial generation of MoO2 nanoparticles. This aerogel exhibits exceptional catalytic functionality, achieving up to 99.8% efficiency in converting dibenzothiophene to dibenzothiophene sulfone. Density functional theory calculations provide insights into the catalytic mechanism, revealing that the Mo center shows accumulated electron density contributed from the electron‐rich graphene substrate. This electron density enhancement significantly enhances the catalytic activity, enabling deep desulfurization. The proposed flash nanocatalyst synthesis approach presented here can be extended to fabricate multimetallic nanocatalysts and high‐entropy alloys within the cylindrical aerogel entity, exhibiting great potential for applications in industry‐relevant flow chemistry, electrochemistry, industrial catalysis, and beyond.

Metal-Organic Frameworks as a Tunable Platform to Deconvolute Stereoelectronic Effects on the Catalytic Activity of Thioanisole Oxidation.

The local environment of a metal active site plays an important role in affecting the catalytic activity and selectivity. In recent studies, tailoring the behavior of a molybdenum-based active site via modulation of the first coordination sphere has led to improved thioanisole oxidation performance, but disentangling electronic effects from steric influences that arise from these modifications is nontrivial, especially in heterogeneous systems. To this end, the tunability of metal-organic frameworks (MOFs) makes them promising scaffolds for controlling the coordination sphere of a heterogeneous, catalytically active metal site while offering additional attractive features such as crystallinity and high porosity. Herein, we report a variety of MOF-supported Mo species, which were investigated for catalytic thioanisole oxidation to methyl phenyl sulfoxide and/or methyl phenyl sulfone using tert-butyl hydroperoxide (tBHP) as the oxidant. In particular, MOFs of contrasting node architectures were targeted, presenting a unique opportunity to investigate the stereoelectronic control of Mo active sites in a systematic manner. A Zr6-based MOF, NU-1000, was employed along with its sulfated analogue Zr6-based NU-1000-SO4 to anchor a dioxomolybdenum species, which enabled examination of support-mediated active site polarizability on catalytic performance. In addition, a MOF containing a mixed metal node, Mo-MFU-4l, was used to probe the stereoelectronic impact of an N-donor ligand environment on the catalytic activity of the transmetalated Mo center. Characterization techniques, including single crystal X-ray diffraction, were concomitantly used with reaction time course profiles to better comprehend the dynamics of different Mo active sites, thus correlating structural change with activity.

Catalytic hydrogenation of olefins by a multifunctional molybdenum-sulfur complex

Exploration of molybdenum complexes as homogeneous hydrogenation catalysts has garnered significant attention, but hydrogenation of unactivated olefins under mild conditions are scarce. Here, we report the synthesis of a molybdenum complex, [Cp*Mo(Ph2PC6H4S−CH = CH2)(Py)]+ (2), which exhibits intriguing reactivity toward C2H2 and H2 under ambient pressure. This vinylthioether complex showcases efficient catalytic activity in the hydrogenation of various aromatic and aliphatic alkenes, demonstrating a broad substrate scope without the need for any additives. The catalytic pathway involves an uncommon oxidative addition of H2 to the cationic Mo(II) center, resulting in a Mo(IV) dihydride intermediate. Moreover, complex 2 also shows catalytic activity toward C2H2, leading to the production of polyacetylene and the extension of the vinylthioether ligand into a pendant triene chain.

Aldehyde and Ketone Hydroboration Mediated by a Heterogeneous Single‐Site Molybdenum‐Dioxo Catalyst: Scope and Mechanistic Implications

AbstractEfficient hydroboration of aldehydes and ketones is demonstrated using a single‐site MoO2 catalyst supported on activated carbon. Under mild conditions with low catalytic loadings, the reaction exhibits chemoselectivity towards carbonyl reduction over halides, alkene, alkyne, nitrile, and ester groups, affording high yields of desired products. Furthermore, competition studies between aldehyde and ketone reduction using HBpin and HBcat indicate that HBpin preferably functionalizes aldehydes, while HBcat can functionalize either substrate under specific conditions. Mechanistic studies suggest that the reaction proceeds via the initial formation of a molybdenum‐hydride species upon B−H activation and subsequent molybdenum‐alkoxide species upon carbonyl activation by the Mo center. The experimental activation energy of 14.3 kcal/mol alignssatisfactorily with the DFT computed ΔH≠ of 18.7 kcal/mol, further supporting the proposed mechanism. Combined experimental/computational analyses reveal that excess HBpin can possibly deactivate the catalyst. The presence of excess benzaldehyde efficiently mitigates deactivation by HBpin, providing significantly higher catalyst recyclability. Overall, this non‐toxic, air‐ and moisture‐stable, active, and selective catalyst demonstrates significant potential for green processes.

Novel Fenton-like Catalyst HKUST-1(Cu)/MoS2-3-C with Non-Equilibrium-State Surface for Selective Degradation of Phenolic Contaminants: Synergistic Effects of σ-Cu-Ligand and ≡Mo–OOSO3− Complex

Novel Fenton-like catalyst HKUST-1(Cu)/MoS2-3-C with a non-equilibrium-state surface was constructed for selective degradation of phenolic contaminants. Electron-polarized distribution facilitated the formation of σ-Cu-ligand between electron-poor Cu centre and phenolic compounds, which not only enhanced radicals generation but also accelerated the Cu(I)/Cu(II) redox. Meanwhile, ≡Mo–OOSO3− complexes formed by the electron-rich Mo centre and peroxymonosulfate (PMS), could directly oxidize phenolic contaminants with the generation of SO4•−. The radical quenching experiments and EPR tests indicated that both SO4•− and •OH played a dominant role in the reaction. Additionally, O2 could be reduced to O2•− by OVs and subsequently converted into 1O2 over the Mo centre. DFT calculation, FT-IR, and in situ Raman spectra analysis results demonstrated that phenolic compounds and PMS were respectively adsorbed by electron-poor Cu centre and electron-rich Mo centre, favouring the electrons transfer from phenolic contaminants to Mo centre for PMS activation. With synergistic effects of σ-Cu-ligand and ≡Mo–OOSO3− complexes, HKUST-1(Cu)/MoS2-3-C achieved a high degradation rate of phenolic contaminants and utilization efficiency of PMS.

Thiomolybdate Clusters: From Homogeneous Catalysis to Heterogenization and Active Sites.

Thiomolybdates are molecular molybdenum-sulfide clusters formed from Mo centers and sulfur-based ligands. For decades, they have attracted the interest of synthetic chemists due to their unique structures and their relevance in biological systems, e.g., as reactive sites in enzymes. More recently, thiomolybdates are explored from the catalytic point of view and applied as homogeneous and molecular mimics of heterogeneous molybdenum sulfide catalysts. This review summarizes prominent examples of thiomolybdate-based electro- and photocatalysis and provides a comprehensive analysis of their reactivities under homogeneous and heterogenized conditions. Active sites of thiomolybdates relevant for the hydrogen evolution reaction are examined, aiming to shed light on the link between cluster structure and performance. The shift from solution-phase to surface-supported thiomolybdates is discussed with a focus on applications in electrocatalysis and photocatalysis. The outlook highlights current trends and emerging areas of thiomolybdate research, ending with a summary of challenges and key takeaway messages based on the state-of-the-art research.

Metal–organic supramolecular architecture of oxo-bridged molybdenum(VI) complexes: Synthesis, structural elucidation and Hirshfeld surface analysis

New Binuclear monooxo, Mo2O4L21(H2O)CHCl3 (1), tetranuclear tetraoxo, Mo4O8L41 (2) and binuclear dioxo, Mo2O4L22 (3) bridged molybdenum(VI) complexes have been synthesized using two diprotic tridentate ONS donor Schiff base ligands H2L1 and H2L2 (H2L1 = S-benzyl-β-N-(2-hydroxyphenyl) methylene dithiocarbazate and H2L2 = S-benzyl-β-N-(5‑bromo-2-hydroxyphenyl) methylene dithiocarbazate. All the three complexes have been characterized by elemental analyses and IR, UV–vis and 1H NMR spectroscopies and their crystal structures were solved by single crystal X-ray diffraction technique. Complexes (1) and (3) crystallized in triclinic space group P-1 and complex (2) in monoclinic space group P21/n. Complexes 1, 2 and 3 exhibit distorted octahedral geometry around Mo(VI) center. X-ray crystallography reveals that in the crystal packing of the complexes C–H···O, O–H···O, O–H···N, C–X···π (X = Br) and π···π stacking interactions cooperatively take part. A detailed analysis of Hirshfeld surfaces and fingerprint plots facilitates a comparison of intermolecular interactions which are crucial in building different supramolecular architectures of three molybdenum complexes. Crystal structure analysis supported with the Hirshfeld surface and fingerprint plots enabled the identification of the significant intermolecular interactions. The intermolecular interactions are further characterized by analyzing the topological parameters through Bader's theory of ‘atoms in molecule’ (QTAIM) along with the ‘non-covalent interaction’ (NCI) plot index. The investigation of topological parameters of electron density at the (3, −1) bond critical point classified the interactions as ‘closed-shell’ interactions.

Comparative analysis of CO2 reduction by soluble Escherichia coli formate dehydrogenase H and its selenocysteine-to-cysteine substitution variant

Metal-dependent formate dehydrogenases (Me-FDHs) are highly active CO2-reducing enzymes operating at low redox potentials and employ either molybdenum or tungsten to reduce the bound substrate. This makes them suitable for electrochemical applications such as fossil-free production of commodity chemicals utilizing renewable energy. Electrocatalytic CO2 reduction by cathode-immobilized Me-FDHs has been recently demonstrated and rational protein engineering can be used to optimize Me-FDHs for various carbon reduction reactions. In the present study, CO2 reduction by soluble monomeric Escherichia coli formate dehydrogenase H (EcFDH-H) was demonstrated and the function of its nucleophilic selenocysteine residue as a transient ligand of a centrally bound molybdenum atom was investigated. Kinetic analysis of the wildtype enzyme revealed maximum CO2 reduction rates of 44 ± 6 s−1 at pH 5.8 that was decreased to 19% and 0% in the case of selenocysteine substitution with the structural homologues cysteine and serine, respectively. Further selenocysteine-to-cysteine substitution effects included an increased acid tolerance as well as stronger inhibition by nitrate and azide indicating a shift of the Mo oxidation state from IV to VI. Conversely, a destabilizing effect on the oxidized Mo(VI) center could be assigned to the native selenocysteine residue that may facilitate the observed efficient CO2 reduction by rapid transition between Mo oxidation states. Taken together, the performed characterization of EcFDH-H as a catalyst for CO2 reduction and the selenocysteine substitution analysis furthers the understanding of the active-site structure of Me-FDHs and thereby supports the development of more efficient biocatalysts for CO2 reduction.

Phase Engineering of Molybdenum Carbide-Cobalt Heterostructures for Long-Lasting Zn-Air Batteries.

Developing highly active and robust oxygen catalysts is of great significance for the commercialization of Zn-air batteries (ZABs) with long-life stability. Herein, heterostructured catalysts comprising molybdenum carbide and metallic Co are prepared by a simple dicyandiamide-assisted pyrolysis strategy. Importantly, the crystalline phase of molybdenum carbide in the catalysts can be carefully regulated by adjusting the CoMo-imidazole precursor and dicyandiamide ratio. The electronic configuration of Co and Mo centers as well as the phase-dependent oxygen reduction reaction performance of these heterostructures (β-Mo2C/Co, β-Mo2C/η-MoC/Co, and η-MoC/Co) was disclosed. A highly active η-MoC/Co cathode enables ZABs with outstanding long-term stability over 850 h with a low voltage decaying rate of 0.06 mV·h-1 and high peak power density of 162 mW·cm-2. This work provides a new idea for the rational design of efficient and stable cathode catalysts for ZABs.

Effect of the coordination environment on the ability of iron to bind/activate N2: A theoretical study with relevance to the nitrogenase mechanism

Activation of molecular dinitrogen to ammonia (and an accompanying metal-hydride formation) occurs in nitrogenases at an iron-sulfur active site. Iron-sulfur centers normally feature Fe(II) and/or Fe(III) oxidation states, which in general are not known to bind N2 or H+. Two peculiarities of the nitrogenase active site may be responsible for their unusual reactivity: an unusually reduced Mo(III) center in some of the nitrogenases (possibly suggesting an ability to also generate super-reduced Fe), and the presence of a central carbide anion, inverse-coordinated by 6 Fe centers within the iron-sulfur cluster. To try and deconvolute the factors that may allow the nitrogenase Fe to bind molecular nitrogen, we report here a density functional theory (DFT) study on the ability of a series of mononuclear Fe complexes to bind and activate N2. Structures of the type Fe(H2O)nR(N2) were examined, with the formal oxidation state of the iron varied from 0 to + 3, with octahedral or tetrahedral geometry, where R = H2O, HO–, CH3–, CH22–, H2S, H−. Iron-dinitrogen complexes only appear straightforward with lower oxidation states (0, +1), and the carbanion ligands appear distinctly better than oxygen or sulfur at facilitating N2 binding as well as activation/weakening of the NN bond. For Fe(II), higher spin states and carbanion ligation may in fact allow N2 binding as well – thus raising the question whether in nitrogenases (where sulfur and carbanion-ligated high-spin Fe(II) is present) do require Fe(I) in the catalytic cycle – at least from the point of view of initial N2 ligation.

An Important Photocatalysis Oxidation: Selective Oxidation of Aniline to Azobenzene over a {P4Mo6}-based Crystalline Catalyst Under Visible-light Irradiation at Room Temperature.

Selective oxidation of aniline to azobenzene with a higher economic value is significant for modern industrial production. However, the high reaction temperature and undefined catalytic reaction center always limit the promotion of this reaction. Here, we designed and synthesized a new [P4MoV6O31]12--based cobalt-containing complex (Hbiz)5{Co(H2O)3[Co(H2O)2]2}{Co[Mo6O12(OH)3(PO4)(HPO4)3][Mo6O12(OH)3(PO4)2(HPO4)2]}·3H2O (1; biz = benzimidazole) under solvothermal conditions. Using 1 as the photocatalyst, the visible-light-driven conversion of aniline to azobenzene at room temperature was realized for the first time (conversion rate 97%, selectivity 96% of azobenzene, reaction time of 12 h). Additionally, real sunlight irradiation can produce a comparable outcome in 48 h. The mechanism investigation manifested that the Mo and Co centers in 1 acted as Brönsted and Lewis acid centers, synergistically promoting the aniline oxidation reaction. This research advances the application of polyoxometalate-based photocatalysts while also offering a sustainable and effective method for producing azobenzene.

Mechanistic complexities of sulfite oxidase: An enzyme with multiple domains, subunits, and cofactors

Sulfite oxidase (SO) deficiency, an inherited disease that causes severe neonatal neurological problems and early death, arises from defects in the biosynthesis of the molybdenum cofactor (Moco) (general sulfite oxidase deficiency) or from inborn errors in the SUOX gene for SO (isolated sulfite oxidase deficiency, ISOD). The X-ray structure of the highly homologous homonuclear dimeric chicken sulfite oxidase (cSO) provides a template for locating ISOD mutation sites in human sulfite oxidase (hSO). Catalysis occurs within an individual subunit of hSO, but mutations that disrupt the hSO dimer are pathological. The catalytic cycle of SO involves five metal oxidation states (MoVI, MoV, MoIV, FeIII, FeII), two intramolecular electron transfer (IET) steps, and couples a two-electron oxygen atom transfer reaction at the Mo center with two one-electron transfers from the integral b-type heme to exogenous cytochrome c, the physiological oxidant. Several ISOD examples are analyzed using steady-state, stopped-flow, and laser flash photolysis kinetics and physical measurements of recombinant variants of hSO and native cSO. In the structure of cSO, Mo…Fe = 32 Å, much too long for efficient IET through the protein. Interdomain motion that brings the Mo and heme centers closer together to facilitate IET is supported indirectly by decreasing the length of the interdomain tether, by changes in the charges of surface residues of the Mo and heme domains, as well as by preliminary molecular dynamics calculations. However, direct dynamic measurements of interdomain motion are in their infancy.