N4 Coordination Research Articles

Tailoring O‐Monodentate Adsorption of CO2 Initiates C−N Coupling for Efficient Urea Electrosynthesis with Ultrahigh Carbon Atom Economy

AbstractThe thermodynamically and kinetically sluggish electrocatalytic C−N coupling from CO2 and NO3− is inert to initially take place while typically occurring after CO2 protonation, which severely dwindles urea efficiency and carbon atom economy. Herein, we report a single O‐philic adsorption strategy to facilitate initial C−N coupling of *OCO and subsequent protonation over dual‐metal hetero‐single‐atoms in N2−Fe−(N−B)2−Cu−N2 coordination mode (FeN4/B2CuN2@NC), which greatly inhibits the formation of C‐containing byproducts and facilitates urea electrosynthesis in an unprecedented C‐selectivity of 97.1 % with urea yield of 2072.5 μg h−1 mgcat.−1 and 71.9 % Faradaic efficiency, outperforming state‐of‐the‐art electrodes. The carbon‐directed antibonding interaction with Cu−B is elaborated to benefit single O‐philic adsorption of CO2 rather than conventional C‐end or bridging O,O‐end adsorption modes, which can accelerate the kinetics of initiated C−N coupling and protonation. Theoretical results indicate that the O‐monodentate adsorption pathway benefits the thermodynamics of the C−N coupling of *OCO with *NO2 and the protonation rate‐determining step, which markedly inhibits CO2 direct protonation. This oriented strategy of manipulating reactant adsorption patterns to initiate a specific step is universal to moderate oxophilic transition metals and offers a kinetic‐enhanced path for multiple conversion processes.

Coordination Number Regulation of Iron Single‐Atom Nanozyme for Enhancing H2O2 Activation and Selectively Eliminating Cephalosporin Antibiotics

AbstractNanozymes present promising alternatives to natural enzymes, but controlling nanozymes' performance and employing them for selectively removing antibiotics are extremely challenging. Employing theoretical calculations to design the coordination environments of mental and coordination atoms for directing single‐atom nanozymes synthesis emerges as a promising strategy to enhance their efficiency and selectivity in antibiotic elimination. In this study, the peroxidase‐like specificity of iron single‐atom nanozymes (FeSA‐Nx, x = 2,3, and 4) with specific Fe–N coordination numbers is demonstrated based on theoretical calculations. These calculations guide the synthesis of corresponding ultra‐thin FeSA‐Nx, achieving a high degree of consistency between theoretical predictions and experimental results. FeSA‐N3 with a Fe─N3 coordination number proves to be the most effective. The efficient electron transfer from Fe─N3 site to H2O2 reduces the free energy required for •OH generation. Quantitative structure‐activity relationship (QSAR) analysis reveals a strong positive correlation between degradation efficiency of cephalosporins and their electron‐donating capabilities (R2 = 0.820–0.929), realizing selectively eliminating cephalosporins. Integration FeSA‐N3 into ceramic membrane (FeSA‐N3/CM) improves hydrophilicity, achieving continuous and stable removal of cephalosporin. This study provides valuable insights into coordination number regulating nanozyme properties for selective antibiotics removal and offers novel perspectives for FeSA‐N3 application in integrated systems.

Cu single atoms anchored on hydrangea-like carbon nitride for facilitating photo-Fenton: Role of Cu2+/Cu+ cycle

Single-atom photo-Fenton (PF) reaction is widely employed for the degradation of antibiotics and water disinfection. However, the key fundamental issues of the valence state cycling of single-atom metals and the activation of hydrogen peroxide (H2O2) in the PF process remain indistinct. Herein, we developed a catalyst donated as Cu single atoms anchored hydrangea-like carbon nitride (Cu-SA/CNH) with Cu−N4 coordination for PF reaction. Compared to pristine CNH, the Cu-SA/CNH exhibited a 2.42-fold increase in PF kinetics. The Cu-SA/CNH/PF system achieved 98.1% degradation efficiency of tetracycline and effectively inactivated Escherichia coli within 30 min. Density functional theory calculations demonstrated that the formation of Cu−N4 effectively improved the energy of the Cu d orbitals, leading to the generation of intermediate states that facilitated the Cu2+/Cu+ cycle. The adsorption capacity of Cu dxz orbitals on H2O2 increased nearly 10 times. This work provides valuable insights for enhancing single-atom PF activity to address environmental pollution.

Evidence for the formation of (NN)xMN(M=Os and Ru) (x=1–3) complexes

MN and their N2 complexes (NN)MN, (NN)2MN, and (NN)3MN (M=Os and Ru) were obtained in the reaction of laser-ablated transition metal Os and Ru atoms with nitrogen in excess solid argon at 4 K through matrix isolation infrared spectroscopy and quantum chemical calculations. The maximum coordinated N2 number is got according to the energy surface. With the increase of coordinated number, the M-N bond length increase in accordance with the red shift of M-N stretching mode from 1130.2 cm−1 to 1052.1 cm−1 for OsN series and from 1119.1 cm−1 to 984.1 cm−1 for RuN series. In addition, a new product (NN)2NOsOsN(NN)2 was discovered in the reaction of laser-ablated Os with N2 in N2 matrix, which could be regarded as NOsOsN coordinated by four N2 molecules. The reason that growth of M-N bond length in (NN)xMN with the N2 coordination was explained in detail, which was mainly caused by relativistic effect.

Optimization of Carbon-Defect Engineering to Boost Catalytic Ozonation Efficiency of Single Fe─N4 Coordination Motif.

Carbon-defect engineering in single-atom metal-nitrogen-carbon (M─N─C) catalysts by straightforward and robust strategy, enhancing their catalytic activity for volatile organic compounds, and uncovering the carbon vacancy-catalytic activity relationship are meaningful but challenging. In this study, an iron-nitrogen-carbon (Fe─N─C) catalyst is intentionally designed through a carbon-thermal-diffusion strategy, exposing extensively the carbon-defective Fe─N4 sites within a micro-mesoporous carbon matrix. The optimization of Fe─N4 sites results in exceptional catalytic ozonation efficiency, surpassing that of intact Fe─N4 sites and commercial MnO2 by 10 and 312 times, respectively. Theoretical calculations and experimental data demonstrated that carbon-defect engineering induces selective cleavage of C─N bond neighboring the Fe─N4 motif. This induces an increase in non-uniform charges and Fermi density, leading to elevated energy levels at the center of Fe d-band. Compared to the intact atomic configuration, carbon-defective Fe─N4 site is more activated to strengthen the interaction with O3 and weaken the O─O bond, thereby reducing the barriers for highly active surface atomic oxygen (*O/*OO), ultimately achieving efficient oxidation of CH3SH and its intermediates. This research not only offers a viable approach to enhance the catalytic ozonation activity of M─N─C but also advances the fundamental comprehension of how periphery carbon environment influences the characteristics and efficacy of M─N4 sites.

Porous C3N4 nanosheet supported Au single atoms as an efficient catalyst for enhanced photoreduction of CO2 to CO

Artificial photosynthesis utilizing solar energy to convert carbon dioxide (CO2) and water (H2O) into fuels and high-value chemicals offers a promising technology for mitigating energy consumption and environmental pollution. However, the development of efficient photocatalysts with high product selectivity remains a big challenge due to the sluggish dynamic transfer of photogenerated charge carriers. Herein, porous C3N4 nanosheet supported Au single atoms photocatalyst (Au1@CN) with AuN4 coordination is fabricated via a facile “impregnation + freeze-drying” process. The as-synthesized Au1@CN exhibits efficient and stable CO2 photoreduction activity with a CO evolution rate of 0.58 μmol h−1 (amount of catalyst: 10 mg), CO selectivity of 94 %, and a turnover frequency (TOF) of 10.0 h−1 using H2O as the reductant, which exceed most previous works on C3N4-based single-atom photocatalysts for CO2 reduction. Experimental studies and density functional theory (DFT) calculations reveal that the unique Au—N4 coordination promotes the dynamic transfer of photogenerated charge carriers, facilitates the adsorption/activation of CO2 molecules and generation of *COOH intermediate, thereby significantly enhancing the CO2 photoreduction activity with high CO selectivity. This study demonstrates an effective strategy for the design of M—N4 coordinated single-atom catalyst toward efficient and selective photoreduction of CO2 to CO.

Lanthanide Complexes of Related Click Tripodal 1,2,3-Triazole-Containing Ligands on the Ph3P(O) Platform. The N2 and N3 Coordination of Triazole Fragments

Lanthanide Complexes of Related Click Tripodal 1,2,3-Triazole-Containing Ligands on the Ph3P(O) Platform. The N2 and N3 Coordination of Triazole Fragments

Single-atom Pt–N4 active sites anchored on porous C3N4 nanosheet for boosting the photocatalytic CO2 reduction with nearly 100% CO selectivity

Photoreduction of CO2 and H2O into fuels and value-added chemicals is a promising green technology for solar-to-chemical conversion. However, improving the conversion efficiency with regulated product selectivity is a big challenge due to the sluggish dynamic transfer and insufficient active sites. Herein, we report on Pt single atoms anchored porous C3N4 nanosheet photocatalyst (Pt1@CN) with Pt–N4 coordination for stable and efficient CO2 photoreduction using H2O as reductant. The Pt1@CN exhibits an evolution rate of 84.8 μmol g−1 h−1 with nearly 100% CO selectivity, outperforming most previous C3N4-based single-atom photocatalysts. Experimental and DFT calculation results reveal that the Pt–N4 coordinated active sites promote the photogenerated electron transfer, CO2 adsorption/activation, *COOH generation, and *CO desorption, thus accounting for the significantly improved CO2 photoreduction activity with ∼100% CO selectivity. This study provides a deep insight into the significant roles of single-atom active sites in enhancing the CO2 photoreduction activity and regulating the product selectivity.

Synergy between palladium single atoms and small nanoparticles co-anchored on carbon atom self-doped graphitic carbon nitride boosting photocatalytic H2 generation

Supramolecule self-assembly of dicyandiamide and uracil followed by thermal polymerization route is designed to prepare carbon atom self-doped g-C3N4 (CCNx), and then wet reduction is applied to fabricate Pd single atoms (Pd1) and nanoparticles (PdNPs) co-anchored CCNx heterojunctions (Pd1+NPs/CCNx). In Pd1+NPs/CCNx structure, interlayer Pd−N4 coordination is the most favorable for chemically stabilizing Pd1, while PdNPs accumulate on the in-plane of CCNx. Pd1+NPs/CCNx heterojunctions exhibit remarkably enhanced photocatalytic H2 evolution reaction (HER) activity, and HER rate and AQY value reach up to 24.1 mmol g−1 h−1 and 17.1% (400 nm) over the optimized Pd1+NPs/CCNx catalyst. Mechanism studies unveil that synergy of as-built interlayer N−Pd−N electron transfer channels at the atomic-scale and surface Mott–Schottky effect of small Pd nanoparticles notably accelerates migration of photogenerated electrons, which leads to plentiful electrons accumulation around Pd single atoms and small nanoparticles to decrease the energy barrier of H* activation and boost HER photodynamics significantly.

Iron(II) spin crossover complexes of tetradentate Schiff-bases: tuning T1/2 by choice of formyl-heterocycle component.

Four new tetradentate Schiff-base ligands were prepared in situ from the 1 : 2 condensation of 1,3-diaminopropane and either 2-thiazolecarboxaldehyde (L2thiazole), 4-thiazolecarboxaldehyde (L4thiazole), 4-oxazolecarboxaldehyde (L4oxazole), or 5-bromopyridine-2-aldehyde (L5Br-pyridine), and complexed with [Fe(NCS)2(pyridine)4] to give four monometallic FeII complexes, [Fe(Lheterocycle)(NCS)2]. Structural characterisation shows the expected octahedral FeII centres in all cases, with Lheterocycle occupying the equatorial plane and the two thiocyanate ligands trans to each other, resulting in an N6 coordination sphere. Solid state magnetic measurements showed that the two complexes with the thiazole-based ligands exhibit the beginning of a spin transition above 300 K, with T1/2 = 350 K for [Fe(L4thiazole)(NCS)2] and 400 K for [Fe(L2thiazole)(NCS)2], whereas the 4-oxazole-based ligand gives [Fe(L4oxazole)(NCS)2] which remains high spin at all measured temperatures (50-400 K). Interestingly, [Fe(L5Br-pyridine)(NCS)2] crystallised as two solvent-free polymorphs: magnetic measurements on samples with both polymorphs present showed a two step SCO with an abrupt transition at T1/2 = 245 K assigned to the transition in polymorph A (as this was also seen in a sample of pure polymorph A), and a gradual transition at T1/2 = 304 K assigned to polymorph B. These findings show that the order of increasing ligand field strength for these heterocycles is 4-oxazole ≪ 5Br-pyridine < 4-thiazole < 2-thiazole.

Dual‐Functional Artificial Peroxidases with Ferriporphyrin Centers for Amplifying Tumor Immunotherapies via Immunogenic Cell Death

AbstractConstructing highly effective sonosensitizers that integrate tumor microenvironment (TME)‐adaptive and ultrasound (US)‐controllable production of reactive oxygen species (ROS) to amplify tumor immunotherapies is extremely desirable but remains challenging. Here, inspired by the coordination structure and biocatalytic effects of Fe‐based peroxidase, a dual‐functional artificial peroxidase is synthesized with ferriporphyrin networks (FePorNW‐DAP) to serve a TME‐adaptive and US‐controllable ROS‐generator for amplifying tumor immunotherapies in breast cancer via immunogenic cell death. Owing to the structural advantages of the ferriporphyrin‐based large d–π‐conjugated networks with the monatomic Fe─N4 coordination center, moderate interaction with H2O2, and decreased bandgap, the FePorNW‐DAP displays efficient dual‐functional ROS production capabilities to combat tumor cells and amplify the tumor immunotherapies, 1) utilize locally produced H2O2 in the TME to catalytically generate potent •OH and other ROS species; simultaneously, 2) external US irradiation can further boost the generation of •OH and 1O2. This work provides not only critical evidence that the proposed dual‐functional artificial peroxidases can induce a strong antitumor immune response and immune memory but also offers essential guidance for creating a high‐performance and biocompatible strategy to regulate the immunosuppression TME and enhance the antitumor immune responses of breast cancer.

Cryo-IR spectroscopy and cryo-kinetics of cluster N2 adsorbate complexes of tantalum cluster cations Ta5-8.

We present an IR-PD study of tantalum cluster adsorbate complexes [Tan(N2)m]+, abbreviated (n,m), n = 5-8. We utilize infrared spectroscopy of isolated and size selected clusters as prepared and characterized by a cryogenic tandem ion trap setup, and we augment our experiments with quantum chemical simulations at the level of density functional theory. The cluster adsorbate complexes (n,m) reveal vibrational bands above 2000cm-1, which indicate end-on coordinated μ1-N2 oscillators, and bands below 2000cm-1, which indicate side-on μ2-κN:κN,N coordinated ones. We observe a general increase in spectral complexity and an inhomogeneous broadening, mainly towards the red, at certain points of N2 loading m, which originates from an increasingly higher amount of double and triple N2 coordination at Ta sites, eventually at all of them. Other than the small tantalum clusters Tan+, n = 2-4, the IR-PD spectra of the initial N2 adsorbate species (n,1), n = 5-8, provide strong evidence for a lack of spontaneous N2 cleavage. Spontaneous N2 cleavage by Tan+, n = 5-8, seems suppressed. Therefore, the ability of a small Ta cluster to cleave dinitrogen disappears with one more tantalum core atom. The study of stepwise N2 adsorption on size selected Tan+, n = 5-8 clusters revealed adsorption limits m(max) of [Tan(N2)m]+ that are independent of cluster size within this size range. Cryo-adsorption kinetics at 26K allowed for kinetic fits to consecutive N2 adsorption steps, and the fits revealed significant N2 desorption rates upon higher N2 loads, and the cluster adsorbate complexes eventually reached equilibrium. Some enhanced N2 desorption rates point towards likely adsorbate shell reorganization, and there is also some evidence for the coexistence of isomeric cluster adsorbate complexes.

Cryo IR spectroscopy and cryo kinetics of dinitrogen activation and cleavage by small tantalum cluster cations.

We investigate small tantalum clusters Tan+, n = 2-4, for their capability to cleave N2 adsorption spontaneously. We utilize infrared photon dissociation (IR-PD) spectroscopy of isolated and size selected clusters under cryogenic conditions within a buffer gas filled ion trap, and we augment our experiments by quantum chemical simulations (at DFT level). All Tan+ clusters, n = 2-4, seem to cleave N2 efficiently. We confirm and extend a previous study under ambient conditions on Ta2+ cluster [Geng et al., Proc. Natl. Acad. Sci. U. S. A. 115, 11680-11687 (2018)]. Our cryo studies and the concomitant DFT simulations of the tantalum trimer Ta3+ suggest cleavage of the first and activation of the second and third N2molecule across surmountable barriers and along much-involved multidimensional reaction paths. We unravel the underlying reaction processes and the intermediates involved. The study of the N2 adsorbate complexes of Ta4+ presented here extends our earlier study and previously published spectra from (4,m), m = 1-5 [Fries et al., Phys. Chem. Chem. Phys. 23(19), 11345-11354 (2021)], up to m = 12. We confirm the priory published double activation and nitride formation, succeeded by single side-on N2 coordination. Significant red shifts of IR-PD bands from these side-on coordinated μ2-κN:κN,N N2 ligands correlate with the degree of tilting towards the second coordinating Ta center. All subsequently attaching N2 adsorbates onto Ta4+ coordinate in an end-on fashion, and we find clear evidence for co-existence of end-on coordination isomers. The study of stepwise N2 adsorption revealed adsorption limits m(max) of [Tan(N2)m]+ which increase with n, and kinetic fits revealed significant N2 desorption rates upon higher N2 loads. The enhanced absolute rate constants of the very first adsorbate steps kabs(n,0) of the small Ta3+ and Ta4+ clusters independently suggest dissociative N2 adsorption and likely N2 cleavage into Ta nitrides.

An Iron-Sulfur Cluster with a Highly Pyramidalized Three-Coordinate Iron Center and a Negligible Affinity for Dinitrogen.

Attempts to generate open coordination sites for N2 binding at synthetic Fe-S clusters often instead result in cluster oligomerization. Recently, it was shown for Mo-Fe-S clusters that such oligomerization reactions can be prevented through the use of sterically protective supporting ligands, thereby enabling N2 complex formation. Here, this strategy is extended to Fe-only Fe-S clusters. One-electron reduction of (IMes)3Fe4S4Cl (IMes = 1,3-dimesitylimidazol-2-ylidene) forms the transiently stable edge-bridged double cubane (IMes)6Fe8S8, which loses two IMes ligands to form the face-bridged double-cubane, (IMes)4Fe8S8. The finding that the three supporting IMes ligands do not confer sufficient protection to curtail cluster oligomerization prompted the design of a new N-heterocyclic carbene, SIArMe,iPr (1,3-bis(3,5-diisopropyl-2,6-dimethylphenyl)-2-imidazolidinylidene; abbreviated as SIAr), that features bulky groups strategically placed in remote positions. When the reduction of (SIAr)3Fe4S4Cl or [(SIAr)3Fe4S4(THF)]+ is conducted in the presence of SIAr, the formation of (SIAr)4Fe8S8 is indeed suppressed, permitting characterization of the reduced [Fe4S4]0 product. Surprisingly, rather than being an N2 complex, the product is simply (SIAr)3Fe4S4: a cluster with a three-coordinate Fe site that adopts an unusually pyramidalized geometry. Although (SIAr)3Fe4S4 does not coordinate N2 to any appreciable extent under the surveyed conditions, it does bind CO to form (SIAr)3Fe4S4(CO). This finding demonstates that the binding pocket at the unique Fe is not too small for N2; instead, the exceptionally weak affinity for N2 can be attributed to weak Fe-N2 bonding. The differences in the N2 coordination chemistry between sterically protected Mo-Fe-S clusters and Fe-only Fe-S clusters are discussed.

Selective Photocatalytic Reduction of CO2 to CO Mediated by Silver Single Atoms Anchored on Tubular Carbon Nitride

AbstractArtificial photosynthesis is a promising strategy for converting carbon dioxide (CO2) and water (H2O) into fuels and value‐added chemical products. However, photocatalysts usually suffered from low activity and product selectivity due to the sluggish dynamic transfer of photoexcited charge carriers. Herein, we describe anchoring of Ag single atoms on hollow porous polygonal C3N4 nanotubes (PCN) to form the photocatalyst Ag1@PCN with Ag−N3 coordination for CO2 photoreduction using H2O as the reductant. The as‐synthesized Ag1@PCN exhibits a high CO production rate of 0.32 μmol h−1 (mass of catalyst: 2 mg), a high selectivity (&gt;94 %), and an excellent stability in the long term. Experiments and density functional theory (DFT) reveal that the strong metal–support interactions (Ag−N3) favor *CO2 adsorption, *COOH generation and desorption, and accelerate dynamic transfer of photoexcited charge carriers between C3N4 and Ag single atoms, thereby accounting for the enhanced CO2 photoreduction activity with a high CO selectivity. This work provides a deep insight into the important role of strong metal–support interactions in enhancing the photoactivity and CO selectivity of CO2 photoreduction.

Understanding the Electronic Structure Basis for N2 Binding to FeMoco: A Systematic Quantum Mechanics/Molecular Mechanics Investigation.

The FeMo cofactor (FeMoco) of Mo nitrogenase is responsible for reducing dinitrogen to ammonia, but it requires the addition of 3-4 e-/H+ pairs before N2 even binds. A binding site at the Fe2/Fe3/Fe6/Fe7 face of the cofactor has long been suggested based on mutation studies, with Fe2 or Fe6 nowadays being primarily discussed as possibilities. However, the nature of N2 binding to the cofactor is enigmatic as the metal ions are coordinatively saturated in the resting state with no obvious binding site. Furthermore, the cofactor consists of high-spin Fe(II)/Fe(III) ions (antiferromagnetically coupled but also mixed-valence delocalized), which are not known to bind N2. This suggests that an Fe binding site with a different molecular and electronic structure than the resting state must be responsible for the experimentally known N2 binding in the E4 state of FeMoco. We have systematically studied N2 binding to Fe2 and Fe6 sites of FeMoco at the broken-symmetry QM/MM level as a function of the redox-, spin-, and protonation state of the cofactor. The local and global electronic structure changes to the cofactor taking place during redox events, protonation, Fe-S cleavage, hydride formation, and N2 coordination are systematically analyzed. Localized orbital and quasi-restricted orbital analysis via diamagnetic substitution is used to get insights into the local single Fe ion electronic structure in various states of FeMoco. A few factors emerge as essential to N2 binding in the calculations: spin-pairing of dxz and dyz orbitals of the N2-binding Fe ion, a coordination change at the N2-binding Fe ion aided by a hemilabile protonated sulfur, and finally hydride ligation. The results show that N2 binding to E0, E1, and E2 models is generally unfavorable, likely due to the high-energy cost of stabilizing the necessary spin-paired electronic structure of the N2-binding Fe ion in a ligand environment that clearly favors high-spin states. The results for models of E4, however, suggest a feasible model for why N2 binding occurs experimentally in the E4 state. E4 models with two bridging hydrides between Fe2 and Fe6 show much more favorable N2 binding than other models. When two hydrides coordinate to the same Fe ion, an increased ligand-field splitting due to octahedral coordination at either Fe2 or Fe6 is found. This altered ligand field makes it easier for the Fe ion to acquire a spin-paired electronic structure with doubly occupied dxz and dyz orbitals that backbond to a terminal N2 ligand. Within this model for N2 binding, both Fe2 and Fe6 emerge as possible binding site scenarios. Due to steric effects involving the His195 residue, affecting both the N2 ligand and the terminal SH- group, distinguishing between Fe2 and Fe6 is difficult; furthermore, the binding depends on the protonation state of His195.

Turning the Inert Element Zinc into an Active Single‐Atom Catalyst for Efficient Fenton‐Like Chemistry

AbstractAmongst various Fenton‐like single‐atom catalysts (SACs), the zinc (Zn)‐related SACs have been barely reported due to the fully occupied 3d10configuration of Zn2+being inactive for the Fenton‐like reaction. Herein, the inert element Zn is turned into an active single‐atom catalyst (SA−Zn−NC) for Fenton‐like chemistry by forming an atomic Zn−N4coordination structure. The SA−Zn−NC shows admirable Fenton‐like activity in organic pollutant remediation, including self‐oxidation and catalytic degradation by superoxide radical (O2⋅−) and singlet oxygen (1O2). Experimental and theoretical results unveiled that the single‐atomic Zn−N4site with electron acquisition can transfer electrons donated by electron‐rich pollutants and low‐concentration PMS toward dissolved oxygen (DO) to actuate DO reduction into O2⋅−and successive conversion into1O2. This work inspires an exploration of efficient and stable Fenton‐like SACs for sustainable and resource‐saving environmental applications.

Turning the Inert Element Zinc into an Active Single-Atom Catalyst for Efficient Fenton-Like Chemistry.

Amongst various Fenton-like single-atom catalysts (SACs), the zinc (Zn)-related SACs have been barely reported due to the fully occupied 3d10 configuration of Zn2+ being inactive for the Fenton-like reaction. Herein, the inert element Zn is turned into an active single-atom catalyst (SA-Zn-NC) for Fenton-like chemistry by forming an atomic Zn-N4 coordination structure. The SA-Zn-NC shows admirable Fenton-like activity in organic pollutant remediation, including self-oxidation and catalytic degradation by superoxide radical (O2 ⋅- ) and singlet oxygen (1 O2 ). Experimental and theoretical results unveiled that the single-atomic Zn-N4 site with electron acquisition can transfer electrons donated by electron-rich pollutants and low-concentration PMS toward dissolved oxygen (DO) to actuate DO reduction into O2 ⋅- and successive conversion into 1 O2 . This work inspires an exploration of efficient and stable Fenton-like SACs for sustainable and resource-saving environmental applications.

The built-in electric field across FeN/Fe3N interface for efficient electrochemical reduction of CO2 to CO

Nanostructured metal-nitrides have attracted tremendous interest as a new generation of catalysts for electroreduction of CO2, but these structures have limited activity and stability in the reduction condition. Herein, we report a method of fabricating FeN/Fe3N nanoparticles with FeN/Fe3N interface exposed on the NP surface for efficient electrochemical CO2 reduction reaction (CO2RR). The FeN/Fe3N interface is populated with Fe−N4 and Fe−N2 coordination sites respectively that show the desired catalysis synergy to enhance the reduction of CO2 to CO. The CO Faraday efficiency reaches 98% at −0.4 V vs. reversible hydrogen electrode, and the FE stays stable from −0.4 to −0.9 V during the 100 h electrolysis time period. This FeN/Fe3N synergy arises from electron transfer from Fe3N to FeN and the preferred CO2 adsorption and reduction to *COOH on FeN. Our study demonstrates a reliable interface control strategy to improve catalytic efficiency of the Fe–N structure for CO2RR.

Binding profile of a mixed-ligand silver(I) complex with DNA and Topoisomerase I

A new mixed-ligand Ag(I) complex, [Ag(daf)(phen)]NO3 (daf = 4,5-diazafluoren-9-one and dian = N-(4,5-diazafluoren-9-ylidene)aniline), was synthesized. The elemental analysis, FTIR, 1HNMR, UV–Vis spectroscopy, cyclic voltammetry, and DFT (Density Functional Theory) geometry optimization method were applied in order to predict the Ag(I) complex structure which concluded to a distorted tetrahedral N4 coordination around the Ag(I) center. A detailed in silico analysis of the bioaffinity of the complex to DNA and human DNA-Topoisomerase I was conducted using molecular docking simulations and ONIOM (Our own N-layered Integrated molecular Orbital and molecular Mechanics) techniques. In this overall scenario, the results suggest the dominance of π-π stacking interactions of the heteroaromatic ligands in the intercalating pocket of DNA and the active site of the enzyme and the rational correlation between being a good intercalator and a potent Topoisomerase I inhibitor. In vitro DNA-binding experiments by spectrophotometric, spectrofluorometric, Voltammetric, and viscometric techniques at physiological pH also confirmed the computational results. The complex inhibited MCF-7 cell growth in a dose-dependent manner while being nontoxic on HUVEC normal cells.