Oxidation State Of Copper Research Articles

Oxygen Nonstoichiometry of Tetragonal La2−xSrxCuO4−δ (x = 0.15−1.2) and in Situ XPS Studies at Elevated Temperatures

The peculiarities of oxygen nonstoichiometry (δ) in tetragonal La(2-x)Sr(x)CuO(4-δ) solid solution with x(Sr) = 0.15-1.2 were studied by XRD, NPD, in situ high-temperature XPS, and chemical analysis. Temperature dependences of oxygen nonstoichiometry, δ = δ(T), were obtained for different Sr contents at 1 bar of O(2). Two types of charge compensation during replacement of lanthanum by strontium are discussed: an increase of the average copper oxidation state and a formation of oxygen vacancies. The average copper oxidation state V(Cu) exhibits a maximum of 2.32 at x(Sr) = 0.6, while δ increases with x(Sr). Oxygen vacancies are unambiguously located on the 4c site ({CuO(2)} plane) for compositions with different strontium contents, which electronic state is described by the O 2p core electron peak at about 531 eV. Thermal stability of the solid solution in a vacuum is associated with the extraction of practically the entire oxygen from CuO(2) layers and the formation of Cu(+) at least in the near-surface region. The higher average copper oxidation state after synthesis in the Sr-rich phases in comparison with the Sr-poor compositions prevents oxygen removal and the formation of Cu(+) and, therefore, stabilizes the structure during heating in a vacuum.

Highly Stabilized and Finely Dispersed Cu2O/TiO2: A Promising Visible Sensitive Photocatalyst for Continuous Production of Hydrogen from Glycerol:Water Mixtures

Cu-doped TiO2 with varying amounts of Cu (0.2, 0.3, 0.5, 1, 2, and 5) are prepared by impregnation method and calcined at 350 and 450 °C for 5 h. These catalysts are characterized by X-ray diffraction, diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy energy-dispersive X-ray spectroscopy (EDAX), and transmission electron microscopy (TEM). The DRS studies are clearly showing the expanded photo response of TiO2 into the visible region on impregnation of copper ions. TEM images are depicting the fine dispersion of Cu particles on TiO2 surface. XPS studies are showing change in the binding energy values of Ti 2p, O 1s, and Cu 2p, indicating that copper ions are in interaction with TiO2. XPS results are also confirming that the oxidation state of copper is +2 in samples calcined at 350 °C and +1 in samples calcined at 450 °C. EDAX analysis supports the presence of copper species on the surface layers of TiO2. Photocatalytic hydrogen production activity...

Synthesis and Characterization of Oligonuclear Ru, Co and Cu Oxidation Catalysts

AbstractIn this work, we report the preparation and crystal structures of three new oligonuclear complexes, Ru2(bbpmp)(μ‐OAc)3 (4), [Co2(bbpmp)(μ‐OAc)(μ‐OMe)](PF6) (5), [Cu4(Hbbpmp)2(μ‐OAc)(H2O)2](OAc)(PF6)2 (6) {H3bbpmp = 2,6‐bis[(2‐hydroxybenzyl)‐(2‐pyridylmethyl)aminomethyl]‐4‐methyl‐phenol (3)}. The structures of the complexes were determined by single‐crystal X‐ray diffraction. The oxidation states of ruthenium, cobalt and copper in the complexes are +3, +3 and +2, respectively. In 4 and 5, RuIII and CoIII are coordinated to four oxygen and two nitrogen atoms in an octahedral geometry, while in 6, CuII adopts both octahedral (CuN2O4) and square‐pyramidal (CuN2O3) geometry. The potential of the three complexes as oxidation catalysts has been investigated.

Thermal enrichment and speciation of copper in rice husk ashes

Copper(II) was considerably enriched in the residual ash via thermal treatment of copper-sorbed rice husk at 700–1100°C for 2h, and the copper speciation was quantitatively determined with X-ray absorption spectroscopy. After the thermal process, the resulting ash only represents by weight 18.7–26.4% of the pre-heated samples. Copper content in the ashes is >7% which is far above the required minimum copper content in copper ores for the copper smelting sector, 0.5%. Crystalline SiO2 is observed only in the ash generated at 1100°C, with more copper in this ash being available for leaching in acidic solution. It is suggested that this is due to the considerable dissimilarity in crystalline structure between copper compounds and crystalline SiO2. No chemical reaction between copper and SiO2 is observed in any ash. In fact, we suggest that the SiO2 crystalline phase repels copper during the thermal process; this would make it easy to extract copper from the ashes. For copper speciation in the ashes, CuO merely represents 0–12% of the total copper, while Cu2O and Cu(0) represent 34–42% and 46–63%, respectively. The lower copper oxidation state would be beneficial for the copper smelting process due to less usage of coke.

The determination of zinc, copper and iron oxidation state in invasive ductal carcinoma of breast tissue and normal surrounding tissue using XANES

X-ray absorption near-edge structure (XANES) spectroscopy was used to examine the oxidation state of Zn, Fe and Cu in 22 normal and 23 tumour regions spread over 30 formalin-fixed, paraffin-embedded tissue samples of human primary invasive breast cancer. A micro-mapping analysis of the metal distribution in the tissue was performed prior to the XANES analysis to identify and localise the metals in the tumour and normal tissue regions. The aim of this study was to identify the oxidation state of Zn, Fe and Cu in normal and tumour tissues of the breast, in order to correlate the oxidation state of these elements with the carcinogenesis process. The position of the Zn K-edge in normal and tumour tissues suggests that Zn exists in a bounded form. The shape of the Cu K-edge XANES spectra and the first derivative spectra of normal and tumour tissues shows that a significant portion of the total copper is present as Cu (I). Nevertheless, the position of the edges in the normal and tumour tissue spectra does not exclude the presence of Cu (II). The shape and position of both normal and tumour regions of the tissue suggest that they contain mixtures of Fe (II) and Fe (III) ions with a significant fraction being Fe (III). However, normal tissue regions were found to have a higher fraction of Fe (II) compared to the tumour tissues. In order to estimate the best target for therapy, more information is required about the relative abundance of Zn, Fe and Cu binding proteins, their oxidation state and their localisation at the subcellular level. Copyright © 2010 John Wiley & Sons, Ltd.

Influence of copper chloride for the formation of aromatic compounds during polyethylene pyrolysis

Infrared image furnace ion-attachment mass spectrometry (IIF-IAMS) experiments have been conducted to elucidate the effects of copper(II) chloride on the formation of aromatic compounds during the pyrolysis of polyethylene. Under the time-resolved pyrolysis conditions of IIF-IAMS, the effects of CuCl 2 were measured to compare the variation in ratios of alkenes and aromatics during polyethylene thermal degradation when pyrolysis temperature was increased. Thermogravimetry experiments and X-ray powder diffraction analysis conducted under similar conditions to those used for IIF-IAMS enabled us to characterize the oxidation states of copper prevailing during the thermal degradation process of polyethylene in the presence of CuCl 2. Reduction of Cu(II) into Cu(I) during the pyrolysis process was characterized. The IIF-IAMS method demonstrates its advantage for on-line detection of reaction products during time-resolved pyrolysis experiments.

Hydrogen purification for fuel cell using CuO/CeO 2–Al 2O 3 catalyst

CuO/CeO 2, CuO/Al 2O 3 and CuO/CeO 2–Al 2O 3 catalysts, with CuO loading varying from 1 to 5 wt.%, were prepared by the citrate method and applied to the preferential oxidation of carbon monoxide in a reaction medium containing large amounts of hydrogen (PROX-CO). The compounds were characterized ex situ by X-ray diffraction, specific surface area measurements, temperature-programmed reduction and temperature-programmed reduction of oxidized surfaces; XANES-PROX in situ experiments were also carried out to study the copper oxidation state under PROX-CO conditions. These analyses showed that in the reaction medium the Cu 0 is present as dispersed particles. On the ceria, these metallic particles are smaller and more finely dispersed, resulting in a stronger metal–support interaction than in CuO/Al 2O 3 or CuO/CeO 2–Al 2O 3 catalysts, providing higher PROX-CO activity and better selectivity in the conversion of CO to CO 2 despite the greater BET area presented by samples supported on alumina. It is also shown that the lower CuO content, the higher metal dispersion and consequently the catalytic activity. The redox properties of the ceria support also contributed to catalytic performance.

Copper Thin-Film Dissolution/Precipitation Kinetics in Organic HF Containing Cleaning Solution

The corrosion behavior of electrochemically deposited copper thin films in deaerated and non-deaerated commercial cleaning solution containing HF has been investigated. Thin-film copper dissolution and reaction kinetics were investigated by monitoring , employing inductively coupled plasma–mass spectroscopy, and the oxidation states of copper on Si wafer surface, employing X-ray photoelectron spectroscopy. It was determined that the reaction kinetics is first order with respect to both HF and oxygen concentrations. A kinetic scheme involving reduction of oxygen and oxidation of and is proposed, which is consistent with the experimentally determined reaction kinetic orders and the observed deposition of undesired copper residues on semiconductor wafers during the cleaning process.

Complexes of Gilman Reagents with C−S and C−N Double Bonds: σ or π Bonding?

Upon rapid injection, a variety of thiocarbonyl compounds react with the Gilman reagent Me(2)CuLi at -100 degrees C inside the probe of an NMR spectrometer to give high yields of complexes. Typical examples of substrates include carbon disulfide, methyl dithioacetate, methyl dithiobenzoate, thiobenzophenone, ethylene trithiocarbonate, and phenyl isothiocyanate. Evidence suggesting the formal oxidation state of copper in these complexes to be Cu(III) is presented. The last example was particularly interesting, since it involved a transient intermediate that was identified as a complex with a C-N double bond. Methyl isothiocyanate gave a stable C-N double-bond complex.

Evidence for Conformational Changes upon Copper Binding to Cupriavidus metallidurans CzcE

CzcE is a periplasmic protein from Cupriavidus metallidurans CH34 that can bind four copper atoms per dimer. We have crystallized the apo form of the protein and determined its structure at 1.85 A resolution. Three Cu atoms were localized by soaking apo-CzcE crystals into a CuCl(2) solution. We identified His24 as a Cu(II) ligand in each protomer and Asp100 as a key residue for Cu binding at the interface of the dimer. The role of these amino acids was confirmed by site-directed mutagenesis and UV-visible spectroscopy. The fourth Cu atom was not located. The oxidized form of CzcE contains four Cu(II) atoms, while the reduced form contains four Cu(I) atoms. Average coordination spheres of four N or O atoms for Cu(II) and of one N or O atom and two S atoms for Cu(I) were determined by X-ray absorption spectroscopy. As there is no evidence for preformed metal-binding sites in apo-CzcE, we suggest that different conformational changes occurred upon Cu(II) or Cu(I) binding. These changes were further demonstrated by digestion experiments that gave different proteolysis patterns depending not only on the presence of the metal but also on its speciation. The ability of CzcE to bind copper and to adapt its conformation to different copper oxidation states could be related to a role in copper sensing for this protein.

Nature and Location of Copper Nanospecies in Mesoporous Molecular Sieves

Copper-mesoporous molecular sieves type MCM-41 have been successfully prepared by different direct incorporation methods of the metal in the initial synthesis gel. Various techniques including XRD, AAS, adsorption/desorption of N2, UV−vis−DR, TPR, and XPS were employed for the materials characterization. All of the materials exhibited a good structural regularity, even for loadings of copper of ∼10 wt %, besides high specific surface areas and pore volumes. An extended and detailed study about the nature of copper oxidation state as well as of the copper species distribution on the siliceous nanostructure has been made. It was found that copper is present on the mesoporous silica in the form of various species: isolated mononuclear Cuδ+ cations possibly in coordination with the lattice oxygen; linear oligonuclear [Cuδ+···Oδ−···Cuδ+]n clusters probably inserted into mesoporous channels; and bulky CuO oxide segregated of the structure. The distribution of copper species in the final solid depends on the preparation method used as well as of the copper content in the initial gel. Moreover, we infer the coexistence of the both copper oxidation states +1 and +2 (+δ) in the major species of these materials: isolated and oligonuclear copper species.

EXAFS analysis of a human Cu,Zn SOD isoform focused using non-denaturing gel electrophoresis

Isoelectric point isoforms of a metalloprotein, copper-zinc superoxide dismutase (CuZnSOD), separated on electrophoresis gels were analyzed using X-ray Absorption Spectroscopy. Mutations of this protein are involved in familial cases of amyotrophic lateral sclerosis. The toxicity of mutants could be relied to defects in the metallation state. Our purpose is to establish analytical protocols to study metallation state of protein isoforms such as those from CuZnSOD. We previously highlighted differences in the copper oxidation state between CuZnSOD isoforms using XANES. Here, we present the first results for EXAFS analyses performed at Cu and Zn K-edge on the majoritary expressed isoform of human CuZnSOD separated on electrophoresis gels.

Low-Temperature, Highly Selective, Gas-Phase Oxidation of Benzyl Alcohol over Mesoporous K-Cu-TiO2 with Stable Copper(I) Oxidation State

A newly developed mesoporous mixed metal oxide (K-Cu-TiO(2)) catalyst is capable of highly selective, gas-phase benzyl alcoholbenzaldehyde transformation at excellent yields (>99%) under surprisingly low temperatures (203 degrees C, bp of benzyl alcohol). The low-temperature reaction conditions and integration of K and Cu(I) components into the TiO(2) matrix are of vital importance for the stabilization of an active Cu(I) oxidation state and resultant stable, excellent catalytic performance.

Room Temperature Ferromagnetism and Structure of Zn1−xCuxO Films Synthesized by Radio Frequency Magnetron Sputtering

Zm1−xCuxO thin films were synthesized by the radio frequency (R.F) magnetron sputtering technique using a ZnO target containing different pieces of small Cu-chips. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to analyze the crystalline and microstructure of the film, and X-ray photoelectron spectroscopy (XPS) was used to establish the bonding characteristics and oxidation states of copper inside the ZnO host. Room temperature (RT) ferromagnetism was observed in the Zn1−xCuxO films by a Quantum Design superconducting quantum interference device (SQUID) and the saturation magnetic moment of the films was found to decrease with the increase in Cu content.

CuOx−TiO2 Photocatalysts for H2 Production from Ethanol and Glycerol Solutions

Hydrogen production by photocatalytic reforming of aqueous solutions of ethanol and glycerol was studied with the use of impregnated and embedded CuO(x)/TiO(2) photocatalysts. Embedded CuO(x)@TiO(2) was prepared by a water-in-oil microemulsion method, which consists in the formation of Cu nanoparticles in the microemulsion followed by controlled hydrolysis and condensation of tetraisopropyl orthotitanate with the aim of covering the protected metal particles with a surrounding layer of porous titanium oxyhydroxide. Mild calcination leads to the complete removal of the organic residues, the crystallization of TiO(2), and an unavoidable oxidation of copper. Two reference samples were prepared by classical wet impregnation of preformed TiO(2) with different ratios of anatase, rutile, and brookite polymorphs. The two supports were prepared by sol-gel (TiO(2)-SG) and microemulsion (TiO(2)-ME) methods. Superior performances have been observed for the embedded system, which shows higher hydrogen production rates with respect to the impregnated systems using either ethanol or glycerol as sacrificial molecules. Deep structural characterization of the materials has been performed by coupling high resolution transmission electron microscopy (HRTEM), high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), X-ray absorption fine structure (XAFS), and electron paramagnetic resonance (EPR) techniques. Correlation between copper oxidation state and its dispersion and reactivity has been attempted. Finally, the stability of the CuO(x)/TiO(2) catalysts was also studied with respect to carbonaceous deposits and copper leaching.

Catalytic oxidation of CO on CuO x revisited: Impact of the surface state on the apparent kinetic parameters

Analysis of kinetic features of the copper oxides reduction by CO pulses as related to mechanism of CO catalytic oxidation by oxygen combined with monitoring the state of the surface by an electrochemical technique using a solid electrolyte—Pyrex glass and high resolution TEM data on the defect structure of CuO allowed us to suggest a partially “flexible” model of CuO surface. This model, with a due regard for the data of FTIR spectroscopy of adsorbed CO test molecules, assigns the most active surface sites able to coordinate highly reactive CO and O forms to clusters of Cu + cations located at outlets of extended defects (dislocations, twins). Variation of the number, size and structure of these clusters under the reaction medium effect allows explaining the difference between quasi-steady and true steady states of copper oxides in catalytic CO oxidation reaction as well as the difference between kinetic parameters of reaction estimated at quasi-steady and constant states of the surface following Boreskov's approach. Kinetic features of the reaction agree with the Langmuir–Hinshelwood reaction mechanism operating for clustered defect centers of CuO.

New Roles for Copper Metabolism in Cell Proliferation, Signaling, and Disease

Over the past 2 decades, the molecular mechanisms by which cells acquire, distribute, and utilize copper have been under intense investigation. Significant progress has been made in the identification of genes encoding copper homeostasis proteins and in fundamental aspects of their structure, function, and mechanisms of action in copper balance. A number of more comprehensive reviews of the field with respect to the genetics, structure, function, and physiology of copper metabolism have recently appeared elsewhere (1–4). Here, we review general mechanisms for eukaryotic copper metabolism at the cellular level in the context of recent discoveries in the field, identifying potential new functions for copper and copper metabolism proteins in cell signaling, gene expression, tumor cell metastasis, and resistance to anti-neoplastic drugs.

Obtention of low oxidation states of copper from Cu 2+–Al 3+ layered double hydroxides containing organic sulfonates in the interlayer

A series of hydrotalcite-type compounds containing Cu(II) and Al(III) in the layers, and carbonate or different alkylsulfonates in the interlayer, have been prepared and studied. Calcination of these solids gives rise to formation of metallic copper and Cu 2+ and Cu + oxides or sulfates, depending on the calcination temperature and on the precise nature of the interlayer alkylsulfonate.

Characterization and oxidation states of Cu and Pd in Pd–CuO/ZnO/ZrO2 catalysts for hydrogen production by methanol partial oxidation

Abstract Copper and zinc oxide based catalysts prepared by coprecipitation were promoted with palladium and ZrO2, and their activity and selectivity for methanol oxidative reforming was measured and characterized by N2O decomposition, X-ray absorption spectroscopy, BET, X-ray photoelectron spectroscopy, X-ray diffraction, and temperature programmed reduction. Addition of ZrO2 increased copper dispersion and surface area, with little effect on activity, while palladium promotion significantly enhanced activity with little change of the catalytic structure. A catalyst promoted with both ZrO2 and palladium yielded hydrogen below 150 °C. EXAFS results under reaction conditions showed that the oxidation state of copper was influenced by palladium in the catalyst bulk. A palladium promoted catalyst contained 90% Cu0, while the copper in an unpromoted catalyst was 100% Cu1+ at the same temperature. Palladium preferentially forms an unstable alloy with copper instead of zinc during reduction, which persists during reaction regardless of copper oxidation state. A 100-h time on stream activity measurement showed growth in copper crystallites and change in copper oxidation state resulting in decreasing activity and selectivity. A kinetic model of the reaction pathway showed that palladium and ZrO2 promoters lower the activation energy of methanol combustion and steam reforming reactions.

Copper(II) organic compounds as intermediates of photochemical transformations of quaternary ammonium tetrachlorocuprates

171 Stable organometallic compounds with a Cu(II)–C σ bond have not been described [1]. Pulse radiolysis and photolysis of divalent copper salts in aqueous solutions [2, 3] and in n -donor solvents [4] gave short-lived copper complexes with organic radicals in which the copper oxidation state was presumably two. Dissociation [2] CuR + Cu + + R • and bimolecular processes [3] 2CuR + 2Cu + + R 2 , CuR + + H 3 O + Cu 2+ + RH + H 2 O, were considered as the key routes for the destruction of these complexes. Copper(II) Organic Compounds as Intermediates of Photochemical Transformations of Quaternary Ammonium Tetrachlorocuprates E. N. Golubeva a, A. V. Lobanov a , V. I. Pergushov a , N. A. Chumakova a, and A. I. Kokorin b Presented by Academician A.L. Buchachenko February 5, 2008