Oxidation State Of Copper Research Articles

A thermogravimetric study of the partial oxidation of methanol for hydrogen production over a Cu/ZnO/Al2O3 catalyst

The partial oxidation of methanol for the production of hydrogen was investigated in both a fixed-bed microreactor and in a thermogravimetric analyzer (TG-FTIR) from 180°C to 250°C using a commercial Cu/ZnO/Al2O3 catalyst. In the microreactor, a hot spot in the undiluted catalyst bed of 4K and 32K was observed at 180°C and 220°C, respectively. Methanol conversion was strongly accelerated between 180°C and 220°C. In the TG-FTIR experiments, the reduced copper was completely oxidized to cuprite, Cu2O, with increasing time-on-stream in the presence of oxygen and methanol (O2/MeOH=0.5) at 180°C. The selectivity to formaldehyde increased in the same manner as the catalyst was oxidized to cuprite. In contrast, at 250°C the catalyst remained completely reduced for the same O2/MeOH ratio. Two main reaction pathways are proposed explaining the influence of the copper oxidation state on the product distribution.

Mechanistic Studies of Cu(II) Binding to Amyloid-β Peptides and the Fluorescence and Redox Behaviors of the Resulting Complexes

Due in large part to the lack of crystal structures of the amyloid-beta (Abeta) peptide and its complexes with Cu(II), Fe(II), and Zn(II), characterization of the metal-Abeta complex has been difficult. In this work, we investigated the complexation of Cu(II) by Abeta through tandem use of fluorescence and electron paramagnetic resonance (EPR) spectroscopies. EPR experiments indicate that Cu(II) bound to Abeta can be reduced to Cu(I) using sodium borohydride and that both Abeta-Cu(II) and Abeta-Cu(I) are chemically stable. Upon reduction of Cu(II) to Cu(I), the Abeta fluorescence, commonly reported to be quenched upon Abeta-Cu(II) complex formation, can be regenerated. The absence of the characteristic tyrosinate peak in the absorption spectra of Abeta-Cu(II) complexes provides evidence that the sole tyrosine residue in Abeta is not one of the four equatorial ligands bound to Cu(II), but remains close to the metal center, and its fluorescence is sensitive to the copper oxidation state and perturbations in the coordination sphere. Further analysis of the quenching and Cu(II) binding behaviors at different Cu(II) concentrations and in the presence of the competing ligand glycine offers evidence supporting the operation of two binding regimes which demonstrate different levels of fluorescence recovery upon addition of the reducing agent. We provide results that suggest the fluorescence quenching is likely caused by charge transfer processes. Thus, by using tyrosine to probe the coordination site, fluorescence spectroscopy provides valuable mechanistic insights into the oxidation state of copper ions bound to Abeta, the binding heterogeneity, and the influence of solution conditions on complex formation.

The distribution of trace elements Ca, Fe, Cu and Zn and the determination of copper oxidation state in breast tumour tissue using μSRXRF and μXANES

A micro beam synchrotron x-ray fluorescence (μSRXRF) technique has been used to determine the localization of metals in primary invasive ductal carcinoma of breast. Nine samples were examined, all of which were formalin fixed tissues arranged as micro arrays of 1.0 mm diameter and 10 µm thickness. Cu was the particular interest in this study although 2D maps of the elements Ca, Fe and Zn, which are also of physiological importance, are presented. The distribution of these metals was obtained at approximately 18 µm spatial resolution and compared with light transmission images of adjacent sections that were H and E stained to reveal the location of the cancer cell clusters. Correlations were found between these reference images and the elemental distributions indicating an increase in all element concentrations in the tumour regions of all samples, with the exception of Fe, which in some cases showed a reverse of this trend. On average over all samples the percentage difference from the normal tissue elemental concentrations are Ca ≈ 67%, Cu ≈ 64% and Zn ≈ 145%. Micro x-ray absorption near edge spectroscopy (μXANES) was used to estimate the oxidation state of Cu in 19 normal and 17 tumour regions spread over five samples. The shape and the position of both normal and tumour regions suggest that they contain mixtures of copper ions with a significant fraction of Cu2+. However, the shape of the spectra does not exclude the presence of Cu+. Tumour regions were found to have a higher fraction of Cu+ compared to the normal samples.

Synthesis and structural analysis of copper(II) cysteine complexes

This report describes the synthesis and structural analysis of stable copper(II) cysteine complexes. Pale pink copper(II) cysteine complexes were synthesized in mole ratios of 1:2, 1:4, and 1:6 of copper(II):cysteine in ethanol. Infrared spectroscopy and X-ray absorption spectroscopy confirmed that copper(II) binding occurred via the thiol ligand of cysteine. XANES analysis showed that the oxidation state of copper remained as copper(II) and the local atomic geometry was similar in all of the cysteine complexes. The EXAFS data indicate that the copper(II) cysteine complexes are forming ring type structures with sulfur ligands from the cysteines acting as bridging ligands. X-ray diffraction revealed that the copper(II) cysteine complexes formed monoclinic cells with maximum crystallinity found in the 1:4 copper(II):cysteine complex.

Direct speciation of metals in copper-zinc superoxide dismutase isoforms on electrophoresis gels using X-ray absorption near edge structure

X-Ray absorption near edge structure (XANES) can be used for the speciation analysis of inorganic elements bound to proteins, after separation using polyacrylamide gel electrophoresis. In this paper, we report new methodological developments for the speciation of oxidation states in copper–zinc superoxide dismutase (CuZnSOD) isoforms separated in non-denaturing conditions according to their isoelectric point. The nature of CuZnSOD isoforms is still elusive, although differences in their metallation state have been suggested. A non-denaturing protocol for isoelectrofocusing electrophoresis was applied to preserve the metallation state of the proteins. XANES has been performed to study the copper and zinc oxidation states. As expected, zinc is present in its Zn(II) oxidation state in all analysed isoforms. Copper is present in the Cu(II) oxidation state in the main acidic isoform, while it is found in both Cu(II) and Cu(I) states in the main basic isoform. These methodological developments enable the direct speciation analysis of metals in CuZnSOD without any protein purification step that could modify their oxidation state.

Recycling the copper based spent catalyst for catalytic combustion of VOCs

The catalytic combustions of benzene, toluene and o-xylene (BTX) were investigated over the copper based spent catalyst and the pretreated copper based spent catalysts as well. Air, hydrogen and five different acid aqueous solution (HNO3, CH3COOH, H2SO4, HCl, and H3PO4) pretreatments were employed to recycle the spent catalyst from chemical industry. The properties of the pretreated spent catalysts were characterized by the Brunauer Emmett Teller (BET), elemental analyzer (EA), inductively coupled plasma (ICP), temperature programmed reduction (TPR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses. The results showed that while the air pretreatment had an insignificant effect on the catalytic activity of the spent catalyst, the hydrogen pretreatment significantly enhanced that of the spent catalyst. The temperature of hydrogen pretreatment also made a significant difference in its catalytic activity. Furthermore, the increasing pretreatment temperature increased the catalytic activity of the spent catalyst, which was associated with the lower copper oxidation state (or reduced state). In acid pretreatment, the order of catalytic performance of the pretreated spent catalyst according to each acid aqueous solution was found to be HNO3>CH3COOH>none>HCl>H3PO4>H2SO4. Nitric acid or acetic acid pretreatment slightly improved the catalytic activity of the spent catalyst by regenerating the active sites on the pretreated samples. The XRD, XPS and TPR results clearly supported that all copper species such as CuO, Cu2O and Cu0 were active, among which Cu0 was the most active for the removal of toluene. Hydrogen pretreatment was superior to air or acid pretreatments for regenerating the spent catalyst because it favored the generation of metallic coppers. Based on the results of a long-term test and the catalytic activity of BTX, we suggested that the copper based spent catalyst pretreated with hydrogen could be recycled for the removal of volatile organic compounds (VOCs).

Optical Spectra of Copper‐Doped Zn‐Phosphate Glasses

Copper‐containing, binary, Zn‐phosphate glasses were melted under reductive conditions. The profile of their optical spectra and their color change drastically when the ZnO content of the host is modified. An increase in the host's ZnO concentration tilts the copper oxidation state's equilibria toward the reduced species Cu+ and Cu0. In hosts containing more than 52 mol% ZnO, the Cu0 aggregates precipitate upon melt cooling to form ruby glasses. The ruby color also appears in glasses including 50 mol% ZnO, after thermal treatments. The effect of ZnO increase, in the composition of binary Zn‐phosphate glasses, on the redox equilibria of a copper dopant, is inverse to that caused by increase of Na2O content in the case of Na‐phosphate hosts.

Redox Reactions of Copper Complexes Formed with Different β-Amyloid Peptides and Their Neuropathalogical Relevance

The binding stoichiometry between Cu(II) and the full-length beta-amyloid Abeta(1-42) and the oxidation state of copper in the resultant complex were determined by electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) and cyclic voltammetry. The same approach was extended to the copper complexes of Abeta(1-16) and Abeta(1-28). A stoichiometric ratio of 1:1 was directly observed, and the oxidation state of copper was deduced to be 2+ for all of the complexes, and residues tyrosine-10 and methionine-35 are not oxidized in the Abeta(1-42)-Cu(II) complex. The stoichiometric ratio remains the same in the presence of more than a 10-fold excess of Cu(II). Redox potentials of the sole tyrosine residue and the Cu(II) center were determined to be ca. 0.75 and 0.08 V vs Ag/AgCl [or 0.95 and 0.28 V vs normal hydrogen electrode (NHE)], respectively. More importantly, for the first time, the Abeta-Cu(I) complex has been generated electrochemically and was found to catalyze the reduction of oxygen to produce hydrogen peroxide. The voltammetric behaviors of the three Abeta segments suggest that diffusion of oxygen to the metal center can be affected by the length and hydrophobicity of the Abeta peptide. The determination and assignment of the redox potentials clarify some misconceptions in the redox reactions involving Abeta and provide new insight into the possible roles of redox metal ions in the Alzheimer's disease (AD) pathogenesis. In cellular environments, the reduction potential of the Abeta-Cu(II) complex is sufficiently high to react with antioxidants (e.g., ascorbic acid) and cellular redox buffers (e.g., glutathione), and the Abeta-Cu(I) complex produced could subsequently reduce oxygen to form hydrogen peroxide via a catalytic cycle. Using voltammetry, the Abeta-Cu(II) complex formed in solution was found to be readily reduced by ascorbic acid. Hydrogen peroxide produced, in addition to its role in damaging DNA, protein, and lipid molecules, can also be involved in the further consumption of antioxidants, causing their depletion in neurons and eventually damaging the neuronal defense system. Another possibility is that Abeta-Cu(II) could react with species involved in the cascade of electron transfer events of mitochondria and might potentially sidetrack the electron transfer processes in the respiratory chain, leading to mitochondrial dysfunction.

Copper(II) and Copper(III) Complexes of Pyrrole-Appended Oxacarbaporphyrin

The reaction of an O-confused porphyrin with a pendant pyrrole 4 and copper(II) acetate yields an organocopper(III) diamagnetic complex 4-Cu(III) substituted at the C(3) position by the pyrrole and H. The transformation of 4-Cu(III), performed in aerobic conditions, gave a rare copper(II) organometallic compound 6-Cu(II). In the course of this process, the tetrahedral-trigonal rearrangement originated at the C(3) atom but effects the whole structure. The electron paramagnetic resonance spectroscopic features correspond to a copper(II) oxidation state. A crystallographic analysis of 6-Cu(II) confirmed the formation of a direct metal-C bond [Cu(II)-C 1.939(4) A]. It was found that the Cu(II) complex of O-confused oxaporphyrin is sensitive to oxidative conditions. The degradation of 6-Cu(II) to yield copper(II) tripyrrinone complexes has been observed, which was considered as a peculiar case of dioxygen activation in a porphyrin-like environment. This process is accompanied by regioselective oxygenation at the inner C to form the 2-oxa-3-(2'-pyrrolyl)-21-hydroxycarbaporphyrinatocopper(II) complex ((pyrr)OCPO)CuII (8). The reaction of 6-Cu(II) with hydrogen peroxide, performed under heterophasic conditions, resulted in quantitative regioselective hydroxylation centered at the internal C(21) atom, also producing 8. Treatment of 8 with acid results in demetalation to form the nonaromatic 21-hydroxy O-confused porphyrin derivative ((pyrr)OCPOH)H (9).

Solution studies of some new oxamides – Co-ordination behaviour towards Cu(II) ions

The co-ordination chemistry of some new oxamides towards Cu(II) ions was studied using various techniques: potentiometry, voltammetry, spectroscopy (UV–Vis, CD and EPR) and ESI–MS spectrometry. All tested compounds chelate the copper(II) ions with formation of 1:1 and 1:2 (metal-to-ligand ratio) complexes. The Cu(II) ions are bound by 1N, 2N or 3N nitrogen donor systems. Additionally, an unusual co-ordination to amide N-atoms without additional anchoring site is suggested. The 14N hyperfine splitting observed for the system ox6–Cu(II) above pH 10 clearly indicates the involvement of at least three N donor atoms in the copper ion binding. Moreover, the surrounding by three amide-N and one carbonyl-O stabilizes the high oxidation state of copper(III), although such complexes are very unstable in solution.

Density Functional Theory Studies on Copper Phenanthroline Complexes

Density functional theory calculations have been employed to investigate the role of structural properties of copper phenanthroline complexes for DNA-cleavage activity. Structural changes imposed on the coordination geometries of Cu(phen)(2)(+,2+) (phen = 1,10-phenanthroline) linked by a serinol bridge (abbreviated as Clip) were studied, as well as their energetic profiles. Our calculations show that structures of these copper complexes (in this work named as clipped complexes) strongly depend on the position of the link, rather than on the copper oxidation state. Ionization energies slightly differ among the three selected complexes, while inner-sphere reorganization energies more markedly depend on the serinol link. However, the relative rates of the redox reaction of Cu(phen)(2), Cu(2-Clip-phen), and Cu(3-Clip-phen) were found not to correlate with their relative DNA-cleavage activity experimentally observed. Thus, the serinol link mainly affects the structural properties of copper phenanthroline complexes rather than their electronic properties. Docking simulations of clipped and nonclipped Cu(I) phenanthroline complexes on a DNA 16mer, d[CGCTCAACTGTGATAC](2), were finally performed to assess how different structural properties could affect the formation of DNA adducts. This analysis revealed that the most stable adducts of Cu(phen)(2+) and Cu(3-Clip-phen)(+) with DNA bind in the minor groove, whereas Cu(2-Clip-phen)(+) binds preferentially into the major groove.

Structural characterization of alachlor complexes with transition metal ions by electrospray ionization tandem mass spectrometry

Electrospray ionization mass (ESI-MS) spectrometry was used to investigate the nature of metal complexes of alachlor and their dissociations on activation. Ions of the first row transition metal series were employed to react with alachlor and the products were subjected to collision-induced dissociation (CID) for further structural characterization. The formation of diverse complex ions including doubly charged metal/alachlor complexes; [3L + M] 2+ and [4L + M] 2+ (L: alachlor and M: transition metal ions) were observed depending on the experimental conditions including the tube lens offset voltage (TLOV) and relative concentrations of alachlor and transition metal ions. It is clear that complexation with transition metal ions alters the reactive site of alachlor, promoting the loss of chlorine over the loss of CH 3OH that is the major reaction pathway in uncomplexed system. Direct elimination of chlorine from alachlor molecule was confirmed by the use of MnBr 2 instead of MnCl 2. These evidences clearly illustrate the catalytic activities of the metal ions through insertion mechanism. The function of transition metal ions in complexation was emphasized comparing the fragmentation patterns with those of protonated molecule. A change in the oxidation state of copper from + 2 to + 1 during the dissociation of metal complex was observed in company with elimination of radicals which is specific for the copper complex ions.

Quantum oscillations and the Fermi surface in an underdoped high-Tc superconductor

Despite twenty years of research, the phase diagram of high-transition-temperature superconductors remains enigmatic. A central issue is the origin of the differences in the physical properties of these copper oxides doped to opposite sides of the superconducting region. In the overdoped regime, the material behaves as a reasonably conventional metal, with a large Fermi surface. The underdoped regime, however, is highly anomalous and appears to have no coherent Fermi surface, but only disconnected 'Fermi arcs'. The fundamental question, then, is whether underdoped copper oxides have a Fermi surface, and if so, whether it is topologically different from that seen in the overdoped regime. Here we report the observation of quantum oscillations in the electrical resistance of the oxygen-ordered copper oxide YBa2Cu3O6.5, establishing the existence of a well-defined Fermi surface in the ground state of underdoped copper oxides, once superconductivity is suppressed by a magnetic field. The low oscillation frequency reveals a Fermi surface made of small pockets, in contrast to the large cylinder characteristic of the overdoped regime. Two possible interpretations are discussed: either a small pocket is part of the band structure specific to YBa2Cu3O6.5 or small pockets arise from a topological change at a critical point in the phase diagram. Our understanding of high-transition-temperature (high-T(c)) superconductors will depend critically on which of these two interpretations proves to be correct.

Wet peroxide oxidation and catalytic wet oxidation of stripped sour water produced during oil shale refining

Catalytic wet oxidation (CWO) and wet peroxide oxidation (WPO) of stripped sour water (SSW) from an oil shale refinery was investigated. Greater than 70% total organic carbon (TOC) removal from SSW was achieved using Cu(NO 3) 2 catalysed WO under the following conditions using a glass lined reaction vessel: 200 °C, pO 2 = 0.5 MPa, 3 h, [Cu(NO 3) 2] = 67 mmol/L. Significant TOC removal (∼31%) also occurred in the system without added oxygen. It is proposed that this is predominantly due to copper catalysed oxidative decarboxylation of organics in SSW based on observed changes in copper oxidation state. Greater than 80% TOC removal was achieved using WPO under the following conditions: 150 °C, t = 1.5 h, [H 2O 2] = 64 g/L. Significantly more TOC could be removed from SSW by adding H 2O 2 in small doses as opposed to adding the same total amount in one single dose. It was concluded that WPO was a far more effective process for removing odorous compounds from SSW.

Fabrication of optical layers containing Er(III) and Cu(I) in silicate glasses

Optical materials containing Cu + have recently become a subject of considerable interest for their potential application in tunable lasers emitting in the blue-green spectral region. The emission is the result of the Cu + transition 3d 10↔3d 94s 1. One of the main problems we solved was the sufficient stabilization of Cu + and the prevention of its oxidation to Cu 2+. We present our approach to the fabrication of Cu + containing slab waveguides up to 10 μm deep in specially designed sodium-zincsilicate glasses doped with erbium. The erbium atoms when present in a glass matrix lower its permeability for diffusing ions. Therefore, we formulated novel glasses with a higher sodium content having more open structure and stabilizing the Cu + ions. The Cu + waveguides were fabricated using the ion exchange technology in melts where CuI was a key component. The characterization of prepared samples included composition analysis with special attention paid to the oxidation states of copper and optical/waveguiding properties’ measurements focused on the blue-green emission. Our experiments revealed that the coordination of copper ions in a glass matrix significantly influences the position of the blue-green luminescence band that can be tuned by modifying a glass composition.

Room temperature ferromagnetism in Zn1−xCuxO thin films

Here the authors report systematic studies on the epitaxial growth and properties of Zn1−xCuxO (x=0.02–0.1) thin films deposited onto sapphire c-plane single crystals using pulsed-laser deposition. X-ray diffraction and high resolution transmission electron microscopy (HRTEM) were employed to study the epitaxial relations of Zn1−xCuxO with the substrate, and x-ray photoelectron spectroscopy was used to establish the bonding characteristics and oxidation states of copper inside the ZnO host. Room temperature ferromagnetism was observed in the Zn1−xCuxO films with magnetic moment per Cu atom decreasing with an increasing Cu content. The presence of any magnetic phase was ruled out using HRTEM. Thus, the ferromagnetism was attributed to Cu ions substituted into the ZnO lattice.

The reaction of lithium with CuCr2S4—lithium intercalation and copper displacement/extrusion

The electrochemical reduction of CuCr2S4 by Li was shown to occur in two steps, involving first a combined Cu extrusion/Li insertion leading to a Li1.75Cu0.25Cr2S4 phase that, upon further lithiation, undergoes a conversion reaction. Analytical transmission electron microscopy, high resolution electron energy loss spectroscopy and neutron diffraction experiments have been used to elucidate the copper, sulphur and chromium oxidation states during the first electrochemical step. HRTEM shows the growth of copper dendrites during the discharge of the compound and their disappearance upon subsequent re-oxidation, while EDS analysis indicates that all of the copper cannot be extruded from the pristine phase upon discharge, nor be fully reinserted on charging. HR-EELS confirms the following oxidation state Cu+Cr23+(S2−)3S− for the pristine material and demonstrates that the insertion of lithium in the sample only corresponds to a change of the sulphur oxidation state whereas the valence of chromium was not modified. This observation was directly confirmed by neutron data that show an increase in the S–S bond length upon lithium insertion.

Copper oxidation state in chalcopyrite: Mixed Cu d9 and d10 characteristics

The determination of the oxidation states of copper and iron in sulfides, and chalcopyrite (CuFeS 2) in particular, using 2 p X-ray photoemission spectroscopy (XPS) and L 2,3-edge X-ray absorption spectroscopy (XAS) is revisited. Reassessment of the published spectra derived by these methods produces consistent results and reveals the ‘ d count’ in the copper compounds to be intermediate between d 9 and d 10. Nevertheless, these covalent copper compounds can be divided into those nominally monovalent and those nominally divalent. The Fe L 2,3-edge XAS of chalcopyrite, along with Mössbauer data, confirm the presence of high-spin Fe 3+. Chalcopyrite, despite recent published reports to the contrary, clearly belongs to the monovalent copper class.

X-ray absorption spectroscopy and high-energy XRD study of the local environment of copper in antibacterial copper-releasing degradable phosphate glasses

Phosphate-based glasses of the general formula Na2O–CaO–P2O5 are degradable in an aqueous environment, and therefore can act as antibacterial materials through the inclusion of ions such as copper. In this study, CuO and Cu2O were added to Na2O–CaO–P2O5 glasses (1–20mol% Cu) and X-ray absorption spectroscopy (XAS) and high-energy X-ray diffraction (HEXRD) used to probe the local environment of the copper ions. Copper K-edge X-ray absorption near-edge structure (XANES) spectra confirm the oxidation state of copper to be predominantly 2+ in all samples regardless of which copper oxide was used in the preparation. The XANES results suggest the structural environment of copper to be octahedral with respect to oxygen in all samples. The HEXRD results yield a Cu–O nearest-neighbour distance of 1.98Å and associated coordination number of approximately six, both consistent with octahedral coordination. Analysis of the extended X-ray absorption fine structure (EXAFS) data also yields structural parameters consistent with copper in an octahedral environment. The HEXRD and EXAFS results reveal a Cu–P distance of 3.13Å, which confirms that the copper ions are coordinated within the phosphate glass network and not phase-separated in domains of copper oxide.

Stabilization of the trivalent oxidation state of copper by tridentate imine–oxime–amine ligands

Two tridentate imine–oxime–amine ligands have been synthesized and their corresponding copper(II) complexes have been isolated. These copper(II) complexes are readily oxidized both chemically and electrochemically to give relatively stable copper(III) complexes. In the pH range 1.5–3.0 the electron transfer process is electrochemically reversible with Δ E p = 60 mV and i pa/ i pc ∼ 1. Plots of E 1/2 versus pH are linear with a slope = −60 indicating the involvement of one proton in the electron transfer process. Aqueous solutions of copper(III) complexes have high molar absorption at λ max with ε > 10 4 M −1 cm −1. Solid samples of the complexes are diamagnetic consistent with a d 8 square planar geometry. It seems that only imine–oxime nitrogens are coordinated to copper(II) with the NH 2 group being free as indicated by i.r. spectra. Substitution of a –CH 3 group on the carbon atom adjacent to the oxime group by the more electron donating group –CH(CH 3) 2 lowers electrode potential by more than 90 mV. This is consistent with an earlier observation that electron-donating substituents on the carbon atom adjacent to the oxime group lower the potential of Cu III/Cu II couples and stabilize the higher oxidation state.