Binuclear Copper Research Articles

Binuclear copper complex as a new dual‐use catalyst for cycloaddition and coupling reactions: Synthesis, characterization, and application

Binuclear copper complex as a new dual‐use catalyst for cycloaddition and coupling reactions: Synthesis, characterization, and application

Chlorine bridge bond-enabled binuclear copper complex for electrocatalyzing lithium–sulfur reactions

Engineering atom-scale sites are crucial to the mitigation of polysulfide shuttle, promotion of sulfur redox, and regulation of lithium deposition in lithium–sulfur batteries. Herein, a homonuclear copper dual-atom catalyst with a proximal distance of 3.5 Å is developed for lithium–sulfur batteries, wherein two adjacent copper atoms are linked by a pair of symmetrical chlorine bridge bonds. Benefiting from the proximal copper atoms and their unique coordination, the copper dual-atom catalyst with the increased active interface concentration synchronously guide the evolutions of sulfur and lithium species. Such a delicate design breaks through the activity limitation of mononuclear metal center and represents a catalyst concept for lithium–sulfur battery realm. Therefore, a remarkable areal capacity of 7.8 mA h cm−2 is achieved under the scenario of sulfur content of 60 wt.%, mass loading of 7.7 mg cm−2 and electrolyte dosage of 4.8 μL mg−1.

Synthesis, characterization and biological applications of a new nano-sized binuclear copper(II) complex containing bathophenanthroline and ellagic acid as ligands

A new binuclear copper(II) complex, nano-[Cu2-(DIP)2-EA], was synthesized by using bathophenanthroline and ellagic acid ligands in a multi-component/one-pot method, and then characterized by electrospray ionization mass spectrometry (ESI-MS), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible spectrophotometry (UV–vis), thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FE-SEM). The antioxidant, antibacterial, and anticancer properties of the synthesized nano-[Cu2-(DIP)2-EA] were studied. The DPPH radical test pointed out that the nano-[Cu2-(DIP)2-EA] enjoys a good potential (28.4 %) to scavenge free radicals and the bacteria culture indicated a moderate ability of the complex to prevent the growth and proliferation of gram-positive bacteria (Staphylococcus aureus ATCC 29,213) and gram-negative ones (Pseudomonas aeruginosa ATCC 27,853). The cell culture displayed a superior ability of nano-[Cu2-(DIP)2-EA] to destroy breast cancer cells (MCF-7) compared to ellagic acid. In addition, the binding interaction of nano-[Cu2-(DIP)2-EA] with ct-DNA was studied in vitro (pH 7.40) by ultraviolet-visible absorption spectrophotometry, fluorescence emission spectrofluorimetry, circular dichroism (CD) spectropolarimetry, viscosity assessment technique, and molecular docking computer simulation. The results of the fluorescence enhancement spectra clearly showed a desirable affinity of nano-[Cu2-(DIP)2-EA] to ct-DNA. A hyperchromic effect was observed along with a slight red shift in the UV-visible spectra of nano-[Cu2-(DIP)2-EA]-DNA adduct, indicating that the nano-[Cu2-(DIP)2-EA] can form a conjugate with ct-DNA molecule. Thermodynamic properties exhibited an exothermic spontaneous formation of nano-[Cu2-(DIP)2-EA]-DNA adduct favored by H-bonds and van der Waals forces. The competitive emission investigations using methylene blue (MB) and Hoechst 33,258 demonstrated that the binuclear copper(II) can replace the DNA-bound Hoechst and interact via minor grooves, as confirmed also by negligible viscosity alterations. The CD observations proposed that the nano-[Cu2-(DIP)2-EA] induces conformational changes in the ct-DNA. Molecular docking modeling results recognized a minor groove mechanism of nano-[Cu2-(DIP)2-EA] to interact with ct-DNA, and the complexation process is supported by H-bonds and van der Waals interactions.

Improving sensitivity of XANES structural fit to the bridged metal-metal coordination.

Hard X-ray absorption spectroscopy is a valuable in situ probe for non-destructive diagnostics of metal sites. The low-energy interval of a spectrum (XANES) contains information about the metal oxidation state, ligand type, symmetry and distances in the first coordination shell but shows almost no dependency on the bridged metal-metal bond length. The higher-energy interval (EXAFS), on the contrary, is more sensitive to the coordination numbers and can decouple the contribution from distances in different coordination shells. Supervised machine-learning methods can combine information from different intervals of a spectrum; however, computational approaches for the near-edge region of the spectrum and higher energies are different. This work aims to keep all benefits of XANES and extend its sensitivity towards the interatomic distances in the first and second coordination shells. Using a binuclear bridged copper complex as a case study and cross-validation analysis as a quantitative tool it is shown that the first 170 eV above the edge are already sufficient to balance the contributions of Cu-O/N scattering and Cu-Cu scattering. As a more general outcome this work highlights the trivial but often overlooked importance of using `longer' energy intervals of XANES for structural refinement and machine-learning predictions. The first 200 eV above the absorption edge still do not require parametrization of Debye-Waller damping and can be calculated within full multiple scattering or finite difference approximations with only moderately increased computational costs.

Thermally Activated Delayed Fluorescent Binuclear Copper(I) Alkynyl Complexes with Cuprophilic Interactions.

Copper(I)-based thermally activated delayed fluorescence (TADF) emitters have been conceived to be promising candidates for display and lighting applications because of their multifarious structures and strong photoluminescence. Herein a string of binuclear Cu(I) complexes bearing pronounced cuprophilic interactions have been designed and synthesized. [Cu2(dppb)2(μ2-η1-C≡C-Ph)2] (1 a) and [Cu2(dppb)2(μ2-η1-C≡C-PPXZ)2] (1 b) display photoluminescence quantum yields of up to 67 % in doped films and solid states via TADF and exhibit reversible bicolor luminescence switching upon mechanical stimuli. Computational studies manifest that the metal-to-ligand charge transfer predominant transitions ensure a small energy splitting (ΔEST) between the lowest singlet (S1) and triplet (T1) excited states and cuprophilic interactions promote the spin-orbit coupling (SOC), favoring the reverse intersystem crossing (RISC) process. This study provides a new strategy for the construction of stimuli-responsive metal-based TADF materials.

Crystal structure of tetrakis(μ-2-hydroxy-3,5-diisopropylbenzoato)bis[(dimethyl sulfoxide)copper(II)

Metal complexes of 3,5-diisopropylsalicylate are reported to have anti-inflammatory and anti-convulsant activities. The title binuclear copper complex, [Cu2(C13H17O3)4(C2H6OS)2] or [Cu(II)2(3,5-DIPS)4(DMSO)2], contains two five-coordinate copper atoms that are bridged by four 3,5-diisopropylsalicylate ligands and capped by two axial dimethyl sulfoxide (DMSO) moieties. Each copper atom is attached to four oxygen atoms in an almost square-planar fashion, with the addition of a DMSO ligand in an apical position leading to a square-pyramidal arrangement. The hydroxy group of the diisopropylsalicylate ligands participates in intramolecular O—H...O hydrogen-bonding interactions.

Investigation of inhibition kinetics of various plant extracts on polyphenol oxidase enzyme from Paulownia Tomentosa and binding mechanism by molecular docking

Polyphenol oxidase/tyrosinase enzyme, which contains binuclear copper clusters play an important role in melanogenesis and enzymatic browning. Therefore, its inhibitors can be attractive in cosmetics and medicinal industries as depigmentation agents and also in food and agriculture industries as antibrowning compounds. Our aim in this study is to find natural plant extracts that will inhibit the polyphenol oxidase enzyme. The inhibitory effects of Verbascum thapsus, Tanacetum vulgare, Solanum nigrum and Datura stramonium herbal plant extracts obtained from Kosovo on the polyphenol oxidase enzyme activity were investigated. Polyphenol oxidase from the Poulownia tomentosa plant was purified using the three-phase purification method. It is determined that T. vulgare extract showed the most effective inhibitory effect with 0.43 mg/mL IC50 value. In order to explain and support the binding mechanism of the best inhibitor extract, the phenolic content of the T. vulgare extract was determined by LC-MS/MS and the mechanism of the inhibitory effect was explained by performing a molecular docking study for the phenolic compounds it contained at the highest rate.

Capturing the Binuclear Copper State of Peptidylglycine Monooxygenase Using a Peptidyl-Homocysteine Lure.

Peptidylglycine monooxygenase is a copper-dependent enzyme that catalyzes C-alpha hydroxylation of glycine extended pro-peptides, a critical post-translational step in peptide hormone processing. The canonical mechanism posits that dioxygen binds at the mononuclear M-center to generate a Cu(II)-superoxo species capable of H atom abstraction from the peptidyl substrate, followed by long-range electron tunneling from the CuH center. Recent crystallographic and biochemical data have challenged this mechanism, suggesting instead that an "open-to-closed" transition brings the copper centers closer, allowing reactivity within a binuclear intermediate. Here we present the first direct observation of an enzyme-bound binuclear copper species, captured by the use of an Ala-Ala-Phe-hCys inhibitor complex. This molecule reacts with the fully reduced enzyme to form a thiolate-bridged binuclear species characterized by EXAFS of the WT and its M314H variant and with the oxidized enzyme to form a novel mixed valence entity characterized by UV/vis and EPR. Mechanistic implications are discussed.

Molecular engineering binuclear copper catalysts for selective CO2 reduction to C2 products

Molecular copper catalysts serve as exemplary models for correlating the structure-reaction-mechanism relationship in the electrochemical CO2 reduction (eCO2R), owing to their adaptable environments surrounding the copper metal centres. This investigation, employing density functional theory calculations, focuses on a novel family of binuclear Cu molecular catalysts. The modulation of their coordination configuration through the introduction of organic groups aims to assess their efficacy in converting CO2 to C2 products. Our findings highlight the crucial role of chemical valence state in shaping the characteristics of binuclear Cu catalysts, consequently influencing the eCO2R behaviour. Notably, the Cu(II)Cu(II) macrocycle catalyst exhibits enhanced suppression of the hydrogen evolution reaction (HER), facilitating proton transfer and the eCO2R process. Furthermore, we explore the impact of diverse electron-withdrawing and electron-donating groups coordinated to the macrocycle (R = –F, –H, and –OCH3) on the electron distribution in the molecular catalysts. Strategic placement of –OCH3 groups in the macrocycles leads to a favourable oxidation state of the Cu centres and subsequent C–C coupling to form C2 products. This research provides fundamental insights into the design and optimization of binuclear Cu molecular catalysts for the electrochemical conversion of CO2 to value-added C2 products.

Noble metal free double helix binuclear Cu(I) complex as catalyst for carboxylative cyclization of propargylamines with atmospheric carbon dioxide toward oxazolidinones synthesis under mild conditions

The application of economically abundant, renewable and C1-feedstock, carbon dioxide into organically important compounds is considered as the hot topic in modern aspects. In this prospective, a binuclear double helix copper (I) complex (1) was synthesized through insitu reaction between quinolone-2-carbaldehyde and succino-hydrazide with copper (II) nitrate hexahydrate. Single crystal X-ray analysis of complex 1, clearly explained that both tetra co-ordinated Cu(I) ions are in tetrahedral geometric environment, having suprmolecular network arrangement via weak interaction of H-bonding, π…π stacking and CH…π stacking. The complex 1 was found to be effectively active catalyst in carboxylative cyclization reaction of propargylic amines with carbon dioxide towards oxazolidinones synthesis under atmospheric pressure and mild reaction conditions. Due to the initiation of side reaction by –NH2 group of primary propargyliamines, which reduces the yield percentage of respective oxazolidinones as a result the carboxylative cyclization reaction of primary propargylic amines, was rarely developed. In this work both primary and secondary propargylamines smoothly undergoes through this catalytic reaction and produced high percentage of desired oxazolidinones product. Again neat condition for this catalytic reaction makes the methodology more environmentally benign and sustainable. The complex 1 showed luminescent property. Moreover DFT methods were utilized in order to explain the probable mechanistic pathway of carboxylative cyclization reaction.

Competition between Cu-Br semi-coordinate bond and C-H∙∙∙Br, C-H∙∙∙S and S∙∙∙S interactions; new two thioalkylazothiophenol (SNS) copper (II) dimers [Cu(L)(µ-Br)

Two new copper dimers [Cu(L)(µ-Br)]2, HL = 2(RS)C6H4N = NC(COCH3)-SC6H5, where R = CH3 (1), C6H5 (2) were synthesized and characterized using a variety of physicochemical methods, including single crystal X-ray diffraction. The molecular structures of the two binuclear copper(II) complexes show that Cu∙∙∙Cu inter-nuclei distances are 3.662 \\AA and 3.392 \\AA in 1 and 2, respectively. Structural analysis of the two dimers supported by QTAIM analysis of electron density indicates the presence of competition between Cu∙∙∙Br semi-coordinate bond and CH∙∙∙Br and CH∙∙∙S hydrogen bonding interactions and S∙∙∙S chalcogen bonding interactions. In complex 1, CH∙∙∙Br and CH∙∙∙S hydrogen bonding interactions exist, in contrast, they are absent in 2. Cu∙∙∙Br semi-coordinate bonds are stronger in 2 as indicated by Cu∙∙∙Br bond distances; Cu∙∙∙Br bond distances are 2.955 and 2.858 Å in 1 and 2.746 Å in 2. There are two weaker S∙∙∙S interactions in 2 and one stronger interaction in 1 as indicated by S∙∙∙S interatomic distances. The two copper dimers and their ligands exhibited good anticancer efficacy against breast (MCF-7), lung (HCT115), and colon human (A549) cancer cell lines. Complex 1 demonstrated strong cancer cell death compared to complex 2. Additionally, the complexes exhibited higher activity than the ligands. Dimer 2 exhibits two quasi-reversible one-electron reduction waves at −0.05 V and −0.37 V. The comproportionating constant for forming the Cu(I/II) mixed-valence complex was 2.57 × 105. The absence of Intervalence transfer (IT) bands in the electronic absorption spectrum for the mixed-valence complex suggested that a single unpaired electron is localized on one copper center.

Competition between Mononuclear and Binuclear Copper Sites across Different Zeolite Topologies.

A key challenge for metal-exchanged zeolites is the determination of metal cation speciation and nuclearity under synthesis and reaction conditions. Copper-exchanged zeolites, which are widely used in automotive emissions control and potential catalysts for partial methane oxidation, have in particular evidenced a wide variety of Cu structures that are observed to change with exposure conditions, zeolite composition, and topology. Here, we develop predictive models for Cu cation speciation and nuclearity in CHA, MOR, BEA, AFX, and FER zeolite topologies using interatomic potentials, quantum chemical calculations, and Monte Carlo simulations to interrogate this vast configurational and compositional space. Model predictions are used to rationalize experimentally observed differences between Cu-zeolites in a wide-body of literature, including nuclearity populations, structural variations, and methanol per Cu yields. Our results show that both topological features and commonly observed Al-siting biases in MOR zeolites increase the population of binuclear Cu sites, explaining the small population of mononuclear Cu sites observed in these materials relative to other zeolites such as CHA and BEA. Finally, we used a machine learning classification model to determine the preference to form mononuclear or binuclear Cu sites at different Al configurations in 200 zeolites in the international zeolite database. Model results reveal several zeolite topologies at extreme ends of the mononuclear vs binuclear spectrum, highlighting synthetic options for realization of zeolites with strong Cu nuclearity preferences.

An immunogenic anti-cancer stem cell bi-nuclear copper(II)-flufenamic acid complex.

An asymmetric bi-nuclear copper(II) complex with both cytotoxic and immunogenic activity towards breast cancer stem cells (CSCs) is reported. The bi-nuclear copper(II) complex comprises of two copper(II) centres bound to flufenamic acid and 3,4,7,8-tetramethyl-1,10-phenanthroline. The bi-nuclear copper(II) complex exhibits sub-micromolar potency towards breast CSCs grown in monolayers and three-dimensional cultures. Remarkably, the bi-nuclear copper(II) complex is up to 25-fold more potent toward breast CSC mammospheres than salinomycin (a gold standard anti-breast CSC agent) and cisplatin (a clinically administered metallodrug). Mechanistic studies showed that the bi-nuclear copper(II) complex readily enters breast CSCs, elevates intracellular reactive oxygen species levels, induces apoptosis, and promotes damage-associated molecular pattern release. The latter triggers phagocytosis of breast CSCs by macrophages. As far as we are aware, this is the first report of a bi-nuclear copper(II) complex to induce engulfment of breast CSCs by immune cells.

Investigation on chloro-bridged binuclear copper(ii) complexes as potent metallodrug candidates against colon cancer via chemical and biological assessments

Synthesized binuclear copper(ii) complexes have been utilized for catechol oxidase mimicking activity, DNA/BSA interactions, molecular docking and pharmacological potential assessment against colon cancer and normal skin cells through in vitro method.

Synthesis, structural analysis, DFT study, and catalytic performance of a glycine-Schiff base binuclear copper(ii) complex

We report the synthesis of a binuclear copper(ii) complex with a Schiff base ligand from glycine, showing excellent catalytic performance in olefin cyclopropanation and C–S cross-coupling, with high yields, selectivity, and versatility.

Electro-enzymatic processes in mitochondria

Four enzymatic complexes form the electron transport chain of the mitochondrion. Complexes I and II are current generator half-elements, that create electron flows with the participation of the enzymes NADH dehydrogenase and Succinate dehydrogenase, oxidizing NADH·H into NAD+, and succinate into fumarate, respectively. Electrons are transferred throw the iron-sulfur clusters system, participate reduction enzymatic reaction of CoQ10 into CoQ10Н2. The proton pumping into the mitochondrial intermembrane space, as well as the regeneration of CoQ10 occur when electrons transferred by ubiquinone-cytochrome-c-oxidoreductase enzyme to the Riske iron-sulfur protein (Fe2S2). The Riske protein regulates electron flows: it transfers one electron to the bL,bН (III) complex, and the other to cytochrome c. Cytochrome c directs electrons to the ΙV complex electrolysis system. The binuclear copper center [CuA-CuB] of the ΙV complex is the anode, where oxygen is formed. Electrons along the galvanic pair chain from paired copper Cu2++ e- ↔ Cu+ and iron Fe2+- е- ↔Fe3+ are transferred to the cathode, copper ion (Сu+), where the electrochemical reaction occurs O2 + 4e- + 4H+ → 2H2O, with the pumping of 4 protons into the mitochondrial intermembrane space.

An engineered POSS drug delivery system for copper(II) anticancer metallodrugs in a selective application toward melanoma cells.

In this work, a polyhedral silsesquioxane (POSS) was used as an engineered drug delivery system for two oxindolimine-copper(II) anticancer complexes, [Cu(isaepy)]+ and [Cu(isapn)]+. The interest in hybrid POSS comes from the necessity of developing materials that can act as adjuvants to improve the cytotoxicity of non-soluble metallodrugs. Functionalization of POSS with a triazole ligand (POSS-atzac) permitted the anchorage of such copper complexes, producing hybrid materials with efficient cytotoxic effects. Structural and morphological characterizations of these copper-POSS systems were performed by using different techniques (IR, NMR, thermogravimetric analysis). A combination of continuous-wave (CW) and pulsed EPR (HYSCORE) spectroscopies conducted at the X-band have enabled the complete characterization of the coordination environment of the copper ion in the POSS-atzac matrix. Additionally, the cytotoxic effects of the loaded materials, [Cu(isapn)]@POSS-atzac and [Cu(isaepy)]@POSS-atzac, were assessed toward melanomas (SK-MEL), in comparison to non-tumorigenic cells (fibroblast P4). Evaluation of their nuclease activity or ability to facilitate cleavage of DNA indicated concentrations as low as 0.6 μg mL-1, while complete DNA fragmentation was observed at 25 μg mL-1. By using adequate scavengers, investigations on active intermediates responsible for their cytotoxicity were performed, both in the absence and in the presence of ascorbate as a reducing agent. Based on the observed selective cytotoxicity of these materials toward melanomas, investigations on the reactivity of these complexes and corresponding POSS-materials with melanin, a molecule that contributes to melanoma resistance to chemotherapy, were carried out. Results indicated the main role of the binuclear copper species, formed at the surface of the silica matrix, in the observed reactivity and selectivity of these copper-POSS systems.

Synthesis, characterization, crystal structure, hirshfeld surface analysis and chromotropic properties of halo- bridged copper(II) complexes

In this study, two novel chromotropic binuclear copper(II) complexes were introduced. The complexes were denoted as [LCu(μ-Cl)Cl]2, 1 and [LCu(μ-Br)Br]2, 2 with L representing the chelating ligand N,N-dimethyl-N'-(9-methylanthracenyl)ethylenediamine. To investigate the structures of these complexes, various analytical techniques were employed, including FT-IR, EPR, UV–Vis spectroscopy, TG-DTA, molar conductivity measurements, and elemental analysis. The geometrical property of [LCu(μ-Br)Br]2 was determined using X-ray crystallography, while the intermolecular interactions were studied through Hirshfeld surface analysis. The characterization data provided strong evidence supporting the proposed binuclear structure, wherein two copper (II) centers are connected by two halogen bridges. Remarkably, these complexes exhibit solvatochromism and thermochromism properties, displaying a diverse range of colors in solutions with varying polarities and/or temperatures. Experimental findings suggest that the observed chromotropism can be attributed to the substitution of solvent molecules with the coordinated halogens in the complexes.

Synthesis, Crystal Structure, Hirshfeld Surface Analysis, and DFT Calculations of the Novel Binuclear Copper(I) Complex Containing 2-Benzimidazolethiole and Triphenylphosphine Ligands.

The reaction of 2-benzimidazolethiole (2-BIT) with copper dichloride in the presence of two equivalents of triphenylphosphine led to a binuclear complex of the type [Cu(µ-S-2-BIT)2(Ph3P)2Cl2]: dichloridobis(μ-1,3-dihydro-2H-benzimidazole-2-thione)bis(triphenylphosphi ne)-di-copper. The Cu(I) compound has been fully identified by elemental analysis, molar conductivity, FT-IR, UV/Vis, and single-crystal X-ray diffraction (XRD). The XRD study reveals that the complex has distorted tetrahedral geometry around the Cu(I)center, which contains two bridge sulfur atoms. The Hirshfeld surface mappedover dnorm, shape index, and curvature revealed important H...H, H... C/C...H, and H... Cl/Cl...H intermolecular interactions as the main contributors to crystal packing. The natural bond orbital (NBO) was applied to understand the strength of nucleophilic and electrophilic attack between ligands and Cu(I)ions. Furthermore, density functional theory (DFT) was employed to demonstrate the molecular reactivity and stability of the ligands and coppercomplex.

Heterogenized Molecular Electrocatalyst Based on a Hydroxo-Bridged Binuclear Copper(II) Phenanthroline Compound for Selective Reduction of CO2 to Ethylene.

Molecular copper catalysts have emerged as promising candidates for the electrochemical reduction of CO2 . Notable features of such systems include the ability of Cu to generate C2+ products and the well-defined active sites that allow for targeted structural tuning. However, the frequently observed in situ formation of Cu nanoclusters has undermined the advantages of the molecular frameworks. It is therefore desirable to develop Cu-based catalysts that retain their molecular structures during electrolysis. In this context, a heterogenized binuclear hydroxo-bridged phenanthroline Cu(II) compound with a short Cu···Cu distance is reported as a simple yet efficient catalyst for electrogeneration of ethylene and other C2 products. In an aqueous electrolyte, the catalyst demonstrates remarkable performance, with excellent Faradaic efficiency for C2 products (62%) and minimal H2 evolution (8%). Furthermore, it exhibits high stability, manifested by no observable degradation during 15 h of continuous electrolysis. The preservation of the atomic distribution of the active sites throughout electrolysis is substantiated through comprehensive characterizations, including X-ray photoelectron and absorption spectroscopy, scanning and transmission electron microscopy, UV-vis spectroscopy, as well as control experiments. These findings establish a solid foundation for further investigations into targeted structural tuning, opening new avenues for enhancing the catalytic performance of Cu-based molecular electrocatalysts.