Oxidation Of Cu Research Articles

Discrete and Polymeric Coordination Assemblies Derived from 3-Pyridyl Attached Flexible Phosphoric Triamide Ligand and Copper Salts

A new example of phosphonium cation, [P(NH3Py)4]+, (2) featuring 3-pyridyl substituents has been reported. Reactivity of 2 with KOH in methanol have resulted in the formation of a neutral phosphine imine [P(N3Py)(NH3Py)3], 2-H. Treatment of 2 with various metal salts of copper have resulted in a P–N bond cleavage in which the in situ generated phosphoramide ligand [PO(NH3Py)3], 1, has shown to yield interesting kinds of self-assembled structures in macrocyclic, cage and 2D-coordination polymers. Thus, the reaction of 2 with Cu(NO3)2 in methanol gave the supramolecular [M6L8]12+ type cage reported earlier with the phosphoramide 1. Treatment of 2 with a Cu(I) salt in CHCl3 under ambient conditions have lead to the formation of a 20-membered macrocyclic Cu(II) compound [(PO(NH3Py)3)CuCl2]2, 3, via the in situ oxidation of Cu(I). In another reaction, treatment of 1 or 2 with Cu(NO3)2 in a reducing solvent such as dimethylformamide (DMF) under hydrothermal conditions gave a Cu(I) coordination polymer {[Cu2(PO(NH3Py)3)3](NO3)2}n, 4. Crystallographic studies on all these newly synthesized compounds have shown interesting kinds of supramolecular organization for these molecules. New examples of a phosphonium cation, [P(NH3Py)4]+, and a phosphine imine, [P(N3Py)(NH3Py)3] featuring 3-pyridyl substituents have been reported. Treatment of the phosphonium cation with various metal salts of copper have resulted in a P–N bond cleavage in which the in situ generated phosphoramide ligand [PO(NH3Py)3], has shown to yield interesting kinds of self-assembled structures in macrocyclic, cage and 2D-coordination polymers.

Biomolecular mode of action of metformin in relation to its copper binding properties.

Metformin (Metf), the most commonly used type 2 diabetes drug, is known to affect the cellular housekeeping of copper. Recently, we discovered that the structurally closely related propanediimidamide (PDI) shows a cellular behavior different from that of Metf. Here we investigate the binding of these compounds to copper, to compare their binding strength. Furthermore, we take a closer look at the electronic properties of these compounds and their copper complexes such as molecular orbital interactions and electrostatic potential surfaces. Our results clearly show that the copper binding energies cannot alone be the cause of the biochemical differentiation between Metf and PDI. We conclude that other factors such as pKa values and hydrophilicity of the compounds play a crucial role in their cellular activity. Metf in contrast to PDI can occur as an anion in aqueous medium at moderate pH, forming much stronger complexes particularly with Cu(II) ions, suggesting that biguanides but not PDI may induce easy oxidation of Cu(I) ions extracted from proteins. The higher hydrophobicity and the lack of planarity of PDI may further differentiate it from biguanides in terms of their molecular recognition characteristics. These different properties could hold the key to metformin's mitochondrial activity because they suggest that the drug could act at least in part as a pro-oxidant of accessible protein-bound Cu(I) ions.

Structure-Stability Correlations in Li-ion Battery Cathode Materials

ABSTRACTDetailed structural studies of two lithiated metal oxides, Li2CuO2 and nanoscale LiCoO2, have been carried out using ex situ high-energy X-ray diffraction (XRD) and in situ X-ray absorption spectroscopy (XAS) with the objective of understanding structural changes that might cause capacity loss during cycling. XRD on the cuprate was studied at various states of charge and phase composition, and the bulk state was determined by Rietveld refinement and pair density function (PDF) analysis. Results showed a largely irreversible structural change of the material upon oxidation of Cu2+ as well as CuO formation. The in-situ XAS of the LiCoO2 was analyzed through a difference method to extract the changes in the local structure that occur upon cycling in both the near edge (XANES) and extended region (EXAFS). Results suggest that cycling causes site exchange of the Co and Li ions near the surface of the nanoscale LiCoO2.

Dichotomous effect of caffeine, curcumin, and naringenin on genomic DNA of normal and diabetic subjects.

Nutraceutical compounds show antioxidant and prooxidant properties under stress conditions like cancer, diabetes, and other diseases. The objective of this study is to find the dichotomic behavior of caffeine, curcumin, and naringenin on DNA of diabetic and normal subjects in the presence and absence of copper, hydrogen peroxide, and complex of copper-hydrogen peroxide. Hydrogen peroxide releases hydroxyl free radicals (•OH) on oxidation of Cu (I) to Cu (II) through Fenton-type reaction to cause DNA damage. In the results, agarose gel electrophoretic pattern speculates the prooxidant effect of caffeine and antioxidant effect of curcumin on DNA in the presence of copper and hydrogen peroxide. UV-Vis spectral analysis shows hyperchromism on addition of DNA to caffeine, hypochromism with curcumin, and subtle changes with naringenin. The chosen nutraceuticals act as inducers and quenchers of oxidative free radicals arising from diabetes.

Anodic Stripping Determination of Pt (IV) Based on the Anodic Oxidation of Cu from the Intermetallic Phase of Cu3Pt

It is shown that platinum can be determined by anodic stripping voltammetry at the peak of selective electrooxidation of copper from intermetallic phase with platinum of Cu3Pt composition. The composition of intermetallic copper-platinum phase formed on the electrode during pre-electrolysis was calculated on the amount of potential displacement (ΔЕ) of copper electrooxidation.

Copper-manganese mixed oxides: CO2-selectivity, stable, and cyclic performance for chemical looping combustion of methane.

Chemical looping combustion (CLC) is a key technology for oxy-fuel combustion with inherent separation of CO2 from a flue gas, in which oxygen is derived from a solid oxygen carrier. Multi-cycle CLC performance and the product selectivity towards CO2 formation were achieved using mixed oxide of Cu and Mn (CuMn2O4) (Fd3[combining macron]m, a = b = c = 0.83 nm) as an oxygen carrier. CuMn2O4 was prepared by the co-precipitation method followed by annealing at 900 °C using copper(II) nitrate trihydrate and manganese(II) nitrate tetrahydrate as metal precursors. CuMn2O4 showed oxygen-desorption as well as reducibility at elevated temperatures under CLC conditions. The lattice of CuMn2O4 was altered significantly at higher temperature, however, it was reinstated virtually upon cooling in the presence of air. CuMn2O4 was reduced to CuMnO2, Mn3O4, and Cu2O phases at the intermediate stages, which were further reduced to metallic Cu and MnO upon the removal of reactive oxygen from their lattice. CuMn2O4 showed a remarkable activity towards methane combustion reaction at 750 °C. The reduced phase of CuMn2O4 containing Cu and MnO was readily reinstated when treated with air or oxygen at 750 °C, confirming efficient regeneration of the oxygen carrier. Neither methane combustion efficiency nor oxygen carrying capacity was altered with the increase of CLC cycles at any tested time. The average oxygen carrying capacity of CuMn2O4 was estimated to be 114 mg g(-1), which was not altered significantly with the repeated CLC cycles. Pure CO2 but no CO, which is one of the possible toxic by-products, was formed solely upon methane combustion reaction of CuMn2O4. CuMn2O4 shows potential as a practical CLC material both in terms of multi-cycle performance and product selectivity towards CO2 formation.

CuO‐In2O3Core‐Shell Nanowire Based Chemical Gas Sensors

The CuO‐In2O3 core‐shell nanowire was fabricated by a two‐step method. The CuO nanowire core (NWs) was firstly grown by the conventional thermal oxidation of Cu meshes at 500°C for 5 hours. Then, the CuO nanowires were immersed into the suspension of amorphous indium hydroxide deposited from the In(AC)3 solution by ammonia. The CuO nanowires coated with In(OH)3 were subsequently heated at 600°C to form the crystalline CuO‐In2O3 core‐shell structure, with In2O3 nanocrystals uniformly anchored on the CuO nanowires. The gas sensing properties of the formed CuO‐In2O3 core‐shell nanowires were investigated by various reducing gases such as hydrogen, carbon monoxide, and propane at elevated temperature. The sensors using the CuO‐In2O3 nanowires show improved sensing performance to hydrogen and propane but a suppressed response to carbon monoxide, which could be attributed to the enhanced catalytic properties of CuO with the coated porous In2O3 shell and the p‐n junction formed at the core‐shell interface.

Dating of U-rich heterogenite: New insights into U deposit genesis and U cycling in the Katanga Copperbelt

The Katanga Copperbelt region of the Democratic Republic of Congo hosts world-class cobalt deposits accounting for ∼50% of the world reserves. Heterogenite (CoOOH) is the most abundant Co-bearing secondary mineral in the region. Its occurrence is the result of oxidation of Cu–Co-sulfides and associated Co reprecipitation in the uppermost part of the deposits, during the Pliocene. In addition to sediment-hosted copper and cobalt ore deposits, the Katanga Copperbelt also hosts numerous uraniferous mineral occurrences and deposits, which can be associated with heterogenite. Within these deposits, heterogenite can have high concentrations of U (up to 3.5%) and Pb (up to ∼4%).In situ SIMS U–Pb ages were obtained for heterogenite samples from the U deposits of Shinkolobwe, Kalongwe and Kambove. These analyses yield distinct Neoproterozoic ages, at ∼876Ma, ∼823Ma and in the ∼720 to ∼670Ma age range. As the geological context prevailing at those times was not favorable for heterogenite formation, these ages most probably record geological events that are not the formation of the mineral itself. For instance, the heterogenites could have inherited the U–Pb signature of a U-rich mineral, most likely uraninite, formed and/or yet reworked at ∼876Ma, ∼823Ma and in the ∼720 to ∼670Ma time interval and spatially associated with primary Co-sulfides. In this hypothesis, the ages obtained in this paper are significant for understanding the cycling and re-deposition of U at given moments in the regional geological history.In such context, the ∼876Ma and the ∼823Ma age are consistent with syn-early diagenetic concentration of uranium in sediments of the Katanga basin. The ∼720 to ∼670Ma ages are interpreted as a phase of U remobilization related to hydrothermal fluid circulation induced by late Nguba proto-oceanic rifting or by early stages of Congo-Kalahari craton convergence, and associated hydrothermal circulation.

Protective CuO Coating Synthesis via Electrodeposition of Copper on AISI 430 Ferritic Steel for SOFC Interconnect Applications

In this work, electrodeposition of copper on AISI 430 steels substrate with relatively low current density followed by oxidation of Cu to form protective and conductive oxide layer is examined. Result shows that the activation by Ni strike plating on AISI 430 steels substrate prior to electroplating improves the coating ability of copper. Phase identification by XRD on the oxidized sample confirms that as coated Cu layer was transformed into CuO. The growth of CuO scales was relatively low and effectively prevents Cr outward diffusion from the ferritic steels.

Correction to Oxidation of Cu(I) in Seawater at Low Oxygen Concentrations

Correction to Oxidation of Cu(I) in Seawater at Low Oxygen Concentrations

Degradation of bisphenol A by hydrogen peroxide activated with CuFeO2 microparticles as a heterogeneous Fenton-like catalyst: Efficiency, stability and mechanism

CuFeO2 microparticles were prepared, characterized and used as a heterogeneous Fenton-like catalyst. The as-prepared CuFeO2 microparticles were composed of pure rhombohedral crystalline particles with sizes in the range of 2–3μm. As a composite oxide of Cu and Fe elements, the CuFeO2 microparticles showed much stronger catalytic ability toward the activation of H2O2 than Cu2O microparticles and Fe3O4 nanoparticles did. The catalytic activation of H2O2 produced hydroxyl radicals (OH), causing rapid degradation and mineralization of bisphenol A (BPA). The use of 1.0gL−1 CuFeO2 microparticles and 20mmolL−1 H2O2 yielded a nearly complete removal of the added BPA (0.1mmolL−1) in 120min and 85% removal of TOC in 180min. The microscaled CuFeO2 catalyst was confirmed to have merits of easy recycling and good stability by successive degradation experiments. The generation of OH from the catalytic activation of H2O2 over CuFeO2 microparticles was evidenced using electron spin resonance spectroscopy, quenching experiment and coumarin fluorescent probe technique. This activation was confirmed to be initiated by surface Cu(I) and Fe(III).

Crystal‐Plane‐Controlled Surface Chemistry and Catalytic Performance of Surfactant‐Free Cu2O Nanocrystals

Surfactant-free Cu2 O nanocrystals, including cubes exposing {100} crystal planes, octahedra exposing {111} crystal planes, and rhombic dodecahedra exposing {110} crystal planes, were used as model catalysts to study the effect of the crystal plane on the surface chemistry and catalytic performance for CO oxidation of Cu2 O nanocrystals. The catalytic performance follows the order of octahedra rhombic dodecahedra>cubes; this suggests that Cu2 O(111) is most active in catalyzing CO oxidation among Cu2 O (111), (110), and (100) surfaces. CO temperature-programmed reduction results demonstrate that Cu2 O octahedra are the most easily reduced of the Cu2 O cubes, octahedra, and rhombic dodecahedra. Diffuse reflectance FTIR spectra show that CO chemisorption on Cu2 O nanocrystals depends on their shape and the chemisorption temperature. CO chemisorption is strongest on rhombic dodecahedra at 30°C, but at 150°C on octahedra. Both the reducibility and chemisorption ability of various Cu2 O nanocrystals toward CO are consistent with their catalytic performance in CO oxidation. The observed surface chemistry and catalytic performance in CO oxidation of various Cu2 O nanocrystals can be well correlated with their exposed crystal plane and surface composition/structure. Cu2 O octahedra expose the {111} crystal plane with coordinated, unsaturated Cu(I) sites, and thus, are most active in chemisorbing CO and catalyzing CO oxidation. These results nicely demonstrate the crystal-plane-controlled surface chemistry and catalytic performance of oxide catalysts.

Copper(II) complexes with pyrazole derivatives – Synthesis, crystal structure, DFT calculations and cytotoxic activity

The series of pyrazole derivatives (1a–4a) were used as bidentate N,N′ ligands to obtain neutral Cu(II) complexes of ML2Cl2 type (1b–4b). The molecular structures of ligand 1a and Cu(II) complex 4b were determined by X-ray crystallography and theoretical DFT calculations. In this study, three functionals B3LYP, BP86 and mPW1PW91 with different basis sets and two effective core potentials Los Alamos and Stuttgart/Dresden were performed. The DFT study disclosed the usefulness of BP86 functional with SDD-ECP for Cu(II) ion and dedicated D95 basis set for other non-transition metal atoms, with the exclusion of Cl for which 6-31++G(2df,2pd) were used. The structural analysis shows that the presence of phenyl substituent in a pyrazole ring contributed to Cu–N bond elongation, which can result in different reactivity of complexes 1b and 3b. The cytotoxicity of the obtained compounds was evaluated on three cancer cells lines: HL-60, NALM-6 and WM-115. The complexes have exhibited similar moderate antiproliferative activity. All the complexes, except for 1b, were found to be more active against three cancer cell lines than uncomplexed pyrazoles. The lipophilicity and electrochemical properties of ligands and complexes was also studied. For complexes with ligand 1a and 3a only one reduction process at the metal centre occurs (Cu(II)→Cu(I)) with oxidization of Cu(I)–Cu(II) in the backward step.

Microwave assisted growth of copper germanide thin films at very low temperatures

Herein the synthesis of Cu3Ge films by exposing Cu-Ge alloy films to microwave radiation is reported. It is shown that microwave radiation led to the formation of copper germanide at temperatures ca. 80 °C. The electrical properties of the Cu3Ge films are presented and compared for various annealing times. X-ray diffraction shows that the Cu3Ge films formed after microwave annealing is crystalline in the orthorhombic phase. Rutherford backscattering and X-ray photoelectron spectroscopy confirms the formation of copper oxide encapsulation layer. Despite the slight oxidation of Cu during the microwave anneal the lowest resistivity of Cu3Ge films obtained is 14 μΩ-cm.

Monitoring Localized Initial Atmospheric Corrosion of Alkanethiol-Covered Copper Using Sum Frequency Generation Imaging Microscopy: Relation between Monolayer Properties and Cu2O Formation

In order to evaluate the interfacial monolayer order on copper surfaces in two-dimensions, the tilt angle distribution and orientation-conformation correlation maps were investigated using sum frequency generation imaging microscopy (SFGIM). In this paper, these methods of analyses were further utilized in evaluating the effect of the formation of a thin oxide film on the monolayer order of octadecanethiol (ODT) deposited on Cu. By chemically stripping the native oxide of the copper surface using amidosulfonic acid (ASA), the spontaneous atmospheric oxidation of Cu from an initial reduced state was observed as a change in the nonresonant phase response of the sum frequency generation (SFG) spectral line shape obtained from the SFGIM setup configured with a 1064 nm probe beam. Statistical calculations and contour maps for the CH-stretch modes of the terminal methyl and methylene group showed the overall decrease in the mean tilt angle and increase in the amount of alkyl gauche defects as a result of the ox...

Electrochemical Behavior of Cu-Ag Alloys in Perchlorate Solutions Using Cyclic Voltammetric and Current Transients Techniques

The electrochemical behavior of Cu-Ag system was studied in 0.5 M NaOH and sodium perchlorate by means of cyclic voltammetry, potentiodynamic anodic polarization and current/ time transients techniques. SEM and EDX microanalysis were used to examine the changes caused by the electrochemical perturbations. In perchlorate free alkali solution the anodic portion of the voltammogram was characterized by the existence of two potential regions I and II. In the first potential region copper dissolves preferentially and exhibits three anodic peaks A1, A2 and A3. The anodic peak A1 was related to the formation of Cu2O while the anodic peaks A2 and A3 are related to the oxidation of Cu and Cu2O, respectively to CuO and Cu(OH)2. The preferential dissolution of copper was enhanced and the simultaneous dissolution of silver was retarded on increasing the silver content in the alloy. The potential region II was characterized by the appearance of three anodic peaks A4, A5 and A6 which are related o the formation of mono-layer, and multi-layers of Ag2O, AgO and Ag2O3, respectively. The addition of increasing amounts of ClO4 - increases the heights of the anodic peaks and above a limiting value breakdown the anodic passivity and initiate pitting corrosion. The pitting potential decreases linearly with ClO4 - concentration but increases with increasing scan rate. The potentiostatic current time transients show that the pitting corrosion can be described in terms of an instantaneous three dimensional grows under diffusion control. X-ray diffraction analysis was used to determine the composition of the corrosion products on the electrode surface. Scanning electron microscope was used to monitor pitting corrosion and to elucidate the effect of constituents on the alloy dissolution.

Single-crystalline CuO nanowire growth and its electrode-dependent resistive switching characteristics

Resistive switching characteristics of single-crystalline CuO nanowires grown by thermal oxidation was investigated. The compressive stress developed in Cu2O layer prevented further oxidation of Cu and caused CuO nanowire growth, which was driven by the total Gibbs free energy minimization. CuO nanowire with Pt electrode showed Ohmic below 1.1 V and space charge limited current above 1.1 V, while that with Cu electrode showed resistive switching characteristics with sufficient Cu ions to form the metallic filaments from the electrodes.

Mechanistic study of glucose oxidation on copper sulfide modified glassy carbon electrode

By studying the reduction of hydrogen peroxide and oxidation of glucose on the CuS nanoparticles modified glassy carbon electrode (CuS/chitosan/GCE), a mechanism of the oxidation of glucose was proposed. It was believed that there is no direct electron transfer between glucose and the electrode surface. Although CuS is a weak oxidant, the glucose was oxidized by CuS while Cu(II) was reduced to Cu(I). The produced Cu(I) undergoes two competing reactions. One reaction is the electro-oxidation of Cu(I) to Cu(II) on the electrode surface which induces the increase of the anodic peak current of the Cu(II)/Cu(I) redox couple in the presence of glucose. Another is the oxidation of Cu(I) by dissolved oxygen to produce H2O2 which was subsequently reduced on the electrode surface.

Copper-Catalyzed Hydroquinone Oxidation and Associated Redox Cycling of Copper under Conditions Typical of Natural Saline Waters

A detailed kinetic model has been developed to describe the oxidation of Cu(I) by O2 and the reduction of Cu(II) by 1,4-hydroquinone (H2Q) in the presence of O2 in 0.7 M NaCl solution over a pH range of 6.5-8.0. The reaction between Cu(I) and O2 is shown to be the most important pathway in the overall oxidation of Cu(I), with the rate constant for this oxidation process increasing with an increasing pH. In 0.7 M NaCl solutions, Cu(II) is capable of catalyzing the oxidation of H2Q in the presence of O2 with the monoanion, HQ(-), the kinetically active hydroquinone form, reducing Cu(II) with an intrinsic rate constant of (5.0 ± 0.4) × 10(7) M(-1) s(-1). Acting as a chain-propagating species, the deprotonated semiquinone radical (SQ(•) (-)) generated from both the one-electron oxidation of H2Q and the one-electron reduction of 1,4-benzoquinone (BQ) also reacts rapidly with Cu(II) and Cu(I), with the same rate constant of (2.0 ± 0.5) × 10(7) M(-1) s(-1). In addition to its role in reformation of Cu(II) via continuous oxidation of Cu(I), O2 rapidly removes SQ(•) (-), resulting in the generation of O2(•) (-). Agreement between half-cell reduction potentials of different redox couples provides confirmation of the veracity of the proposed model describing the interactions of copper and quinone species in circumneutral pH saline solutions.

ChemInform Abstract: Copper‐Mediated Fluorination of Arylboronate Esters. Identification of a Copper(III) Fluoride Complex.

A method for the direct conversion of arylboronate esters to aryl fluorides under mild conditions with readily available reagents is reported. Tandem reactions have also been developed for the fluorination of arenes and aryl bromides through arylboronate ester intermediates. Mechanistic studies suggest that this fluorination reaction occurs through facile oxidation of Cu(I) to Cu(III), followed by rate-limiting transmetalation of a bound arylboronate to Cu(III). Fast C–F reductive elimination is proposed to occur from an aryl–copper(III)–fluoride complex. Cu(III) intermediates have been generated independently and identified by NMR spectroscopy and ESI-MS.