Showing papers on "Copper published in 1999"

Undetectable intracellular free copper: the requirement of a copper chaperone for superoxide dismutase.

Abstract: The copper chaperone for the superoxide dismutase (CCS) gene is necessary for expression of an active, copper-bound form of superoxide dismutase (SOD1) in vivo in spite of the high affinity of SOD1 for copper (dissociation constant = 6 fM) and the high intracellular concentrations of both SOD1 (10 μM in yeast) and copper (70 μM in yeast). In vitro studies demonstrated that purified Cu(I)-yCCS protein is sufficient for direct copper activation of apo-ySOD1 but is necessary only when the concentration of free copper ions ([Cu] free ) is strictly limited. Moreover, the physiological requirement for yCCS in vivo was readily bypassed by elevated copper concentrations and abrogation of intracellular copper-scavenging systems such as the metallothioneins. This metallochaperone protein activates the target enzyme through direct insertion of the copper cofactor and apparently functions to protect the metal ion from binding to intracellular copper scavengers. These results indicate that intracellular [Cu] free is limited to less than one free copper ion per cell and suggest that a pool of free copper ions is not used in physiological activation of metalloenzymes.

The role of zinc oxide in Cu/ZnO catalysts for methanol synthesis and the water–gas shift reaction

Abstract: All commercial catalysts for methanol synthesis and for the water–gas shift reaction in the low temperature region contain zinc oxide in addition to the main active component, copper. The varied benefits of zinc oxide are analysed here. The formation of zincian malachite and other copper/zinc hydroxy carbonates is essential in the production of small, stable copper crystallites in the final catalyst. Further, the regular distribution of copper crystallites on the zinc oxide phase ensures long catalyst life. Zinc oxide also increases catalyst life in the water–gas shift process by absorbing sulphur poisons but it is not effective against chloride poisons. In methanol synthesis, zinc oxide (as a base) removes acidic sites on the alumina phase which would otherwise convert methanol to dimethyl ether. Although bulk reduction of zinc oxide to metallic zinc does not take place, reduction to copper–zinc alloy (brass) can occur, sometimes as a surface phase only. A new interpretation of conflicting measurements of adsorbed oxygen on the copper surfaces of methanol synthesis catalysts is based on the formation of Cu–O–Zn sites, in addition to oxygen adsorbed on copper alone. The possible role of zinc oxide as well as copper in the mechanisms of methanol synthesis is still the subject of controversy. It is proposed that, only under conditions of deficiency of adsorbed hydrogen on the copper phase, hydrogen dissociation on zinc oxide, followed by hydrogen spillover to copper, is significant.

Rotaxanes Incorporating Two Different Coordinating Units in Their Thread: Synthesis and Electrochemically and Photochemically Induced Molecular Motions

Abstract: Three different multicomponent molecular systems have been synthesized by means of the three-dimensional template effect of copper(I). These systems incorporate both a coordinating ring (2,9-diphenyl-1,10-phenanthroline-containing 30-membered ring) and a molecular string which consists of two different coordination sites (2,9-disubstituted-1,10-phenanthroline and 5,5‘ ‘-disubstituted-2,2‘:6‘,2‘ ‘-terpyridine unit). Each end of the string could be functionnalyzed by a small group or by a bulky stopper (tris(p-tert-butylphenyl)(4-hydroxyphenyl)methane), leading to an unstoppered compound, to a semi-rotaxane, or to a real rotaxane. As in the case of a disymmetrical copper [2]-catenane, large reversible molecular motions have been induced both electrochemically and photochemically. The driving force of the rearrangement processes is the high stability of two markedly different coordination environments for the copper(I) and copper(II) ions. In the copper(I) state, two phenanthroline units (one of the ring, on...

Oxide film formation and oxygen adsorption on copper in aqueous media as probed by surface-enhanced raman spectroscopy

Abstract: The electrode potential-dependent formation of oxygen species on copper in noncomplexing aqueous media, encompassing oxide phase films and adsorbed oxygen/hydroxide, are explored at different pH values by means of surface-enhanced Raman spectroscopy (SERS). This technique provides a monolayer-sensitive in- situ vibrational probe, which can follow potential-dependent surface speciation on voltammetric or longer time scales. In alkaline NaClO4 electrolytes (pH 13), the cyclic voltammetric peaks associated with copper oxide phase-film formation and removal are correlated quantitatively with simultaneously acquired SER spectral sequences. The latter indicate the sequential formation of Cu2O and then mixed Cu2O/Cu(OH)2 layers, diagnosed by the appearance of metal−oxygen lattice vibrations at 625/525 and 460 cm-1, respectively. The potential-dependent speciation is in concordance with the Pourbaix diagram, certifying the “bulk-phase” nature of the films. The Raman band intensity−film thickness correlation (the ...

A structure-based mechanism for copper-zinc superoxide dismutase.

Abstract: A reaction cycle is proposed for the mechanism of copper-zinc superoxide dismutase (CuZnSOD) that involves inner sphere electron transfer from superoxide to Cu(II) in one portion of the cycle and outer sphere electron transfer from Cu(I) to superoxide in the other portion of the cycle This mechanism is based on three yeast CuZnSOD structures determined by X-ray crystallography together with many other observations The new structures reported here are (1) wild type under 15 atm of oxygen pressure, (2) wild type in the presence of azide, and (3) the His48Cys mutant Final R-values for the three structures are respectively 200%, 173%, and 209% Comparison of these three new structures to the wild-type yeast Cu(I)ZnSOD model, which has a broken imidazolate bridge, reveals the following: (i) The protein backbones (the "SOD rack") remain essentially unchanged (ii) A pressure of 15 atm of oxygen causes a displacement of the copper ion 037 A from its Cu(I) position in the trigonal plane formed by His46, His48, and His120 The displacement is perpendicular to this plane and toward the NE2 atom of His63 and is accompanied by elongated copper electron density in the direction of the displacement suggestive of two copper positions in the crystal The copper geometry remains three coordinate, but the His48-Cu bond distance increases by 018 A (iii) Azide binding also causes a displacement of the copper toward His63 such that it moves 128 A from the wild-type Cu(I) position, but unlike the effect of 15 atm of oxygen, there is no two-state character The geometry becomes five- coordinate square pyramidal, and the His63 imidazolate bridge re-forms The His48-Cu distance increases by 070 A, suggesting that His48 becomes an axial ligand (iv) The His63 imidazole ring tilts upon 15 atm of oxygen treatment and azide binding Its NE2 atom moves toward the trigonal plane by 028 and 066 A, respectively, in these structures (v) The replacement of His48 by Cys, which does not bind copper, results in a five-coordinate square pyramidal, bridge-intact copper geometry with a novel chloride ligand Combining results from these and other CuZnSOD crystal structures, we offer the outlines of a structure-based cyclic mechanism

The Alzheimer's disease amyloid precursor protein modulates copper-induced toxicity and oxidative stress in primary neuronal cultures.

Abstract: The amyloid precursor protein (APP) of Alzheimer's disease can reduce copper (II) to copper (I) in a cell-free system potentially leading to increased oxidative stress in neurons. We used neuronal cultures derived from APP knock-out (APP(-/-)) and wild-type (WT) mice to examine the role of APP in copper neurotoxicity. WT cortical, cerebellar, and hippocampal neurons were significantly more susceptible than their respective APP(-/-) neurons to toxicity induced by physiological concentrations of copper but not by zinc or iron. There was no difference in copper toxicity between APLP2(-/-) and WT neurons, demonstrating specificity for APP-associated copper toxicity. Copper uptake was the same in WT and APP(-/-) neurons, suggesting APP may interact with copper to induce a localized increase in oxidative stress through copper (I) production. This was supported by significantly higher levels of copper-induced lipid peroxidation in WT neurons. Treatment of neuronal cultures with a peptide corresponding to the human APP copper-binding domain (APP142-166) potentiated copper but not iron or zinc toxicity. Incubation of APP142-166 with low-density lipoprotein (LDL) and copper resulted in significantly increased lipid peroxidation compared to copper and LDL alone. Substitution of the copper coordinating histidine residues with asparagines (APP142-166(H147N, H149N, H151N)) abrogated the toxic effects. A peptide corresponding to the zinc-binding domain (APP181-208) failed to induce copper or zinc toxicity in neuronal cultures. These data support a role for the APP copper-binding domain in APP-mediated copper (I) generation and toxicity in primary neurons, a process that has important implications for Alzheimer's disease and other neurodegenerative disorders.

Copper chemical-mechanical-polishing (CMP) dishing

Abstract: A method is disclosed for forming inlaid copper interconnects in an insulating layer without the normally expected dishing that occurs after chemical-mechanical polishing of the excess copper. This is accomplished by forming a conformal blanket barrier layer over a substrate including a composite groove/hole structure already formed in an insulating layer and then growing a copper seed layer over the barrier layer. A layer of photoresist is next deposited over the substrate filling the composite structure. The photoresist layer, seed layer and the barrier layer are then removed by chemical-mechanical polishing, leaving the seed layer and the barrier layer on the inside walls of the composite structure, however. Then the photoresist is removed from the composite structure, and replaced, in its place, with electroless plated copper, which forms a dome-like protrusion extending from the composite structure. When the substrate is subjected to chemical-mechanical polishing in order to remove the excess copper, the dome-like structure prevents the dishing of the copper metal. In a second embodiment, the seed layer and the barrier layer are chemical-mechanical polished without first depositing a photoresist layer. Copper metal is next selectively formed by electroless plating having a dome-like protrusion, which in turn is removed by chemical-mechanical polishing without the detrimental formation of dishing in the copper metal.

Copper interconnection structure incorporating a metal seed layer

Abstract: The present invention discloses an interconnection structure for providing electrical communication with an electronic device which includes a body that is formed substantially of copper and a seed layer of either a copper alloy or a metal that does not contain copper sandwiched between the copper conductor body and the electronic device for improving the electromigration resistance, the adhesion property and other surface properties of the interconnection structure. The present invention also discloses, methods for forming an interconnection structure for providing electrical connections to an electronic device by first depositing a seed layer of copper alloy or other metal that does not contain copper on an electronic device, and then forming a copper conductor body on the seed layer intimately bonding to the layer such that electromigration resistance, adhesion and other surface properties of the interconnection structure are improved.

Furfural hydrogenation over carbon‐supported copper

Abstract: Furfural hydrogenation over copper dispersed on three forms of carbon – activated carbon, diamond and graphitized fibers – were studied. Only hydrogenation of the C=O bond to form either furfuryl alcohol or 2‐methyl furan occurred at temperatures from 473 to 573 K. Reduction at 573 K gave the most active catalysts, all three catalysts had activation energies of 16 kcal/mol, and turnover frequencies were 0.018–0.032 s-1 based on the number of Cu0 + Cu+ sites, which were counted by N2O adsorption at 363 K and CO adsorption at 300 K, respectively. The Cu/activated carbon catalyst showed no deactivation during 10 h on stream, in contrast to the other two catalysts. A simple Langmuir–Hinshelwood model invoking two types of sites was able to fit all kinetic data quite satisfactorily, thus it was consistent with the presence of both Cu0 and Cu+ sites.

Atomic Layer Deposition of Copper Seed Layers

Abstract: Deposition of thin and conformal copper films has been examined using atomic layer deposition as possible seed layers for subsequent electrodeposition. For this investigation, the copper films were deposited on glass plates as well as on , , and films on silicon wafers. Typical resistivities of these films ranged from for thick copper films to for thick films. The adhesion of the copper films deposited on and at was excellent. These films were highly conformal over high aspect ratio trenches. ©2000 The Electrochemical Society

Copper-induced release of complexing ligands similar to thiols by Emiliania huxleyi in seawater cultures

Abstract: Marine microalgae (Emiliania huxleyi) were grown in seawater enriched only with nitrogen and phosphorus, without control of free metal concentrations using synthetic chelators. Complexing ligands and thiol compounds were determined by cathodic stripping volt-ammetry. Copper was added to these cultures, and ligands were produced in response to the copper addition. Parallel measurements of thiols showed that glutathione and other unidentified thiols (electrochemically similar to thioacetamide) were produced by the algae at rates and concentrations similar to those of the complexing ligands. Smaller amounts of thiols were produced when ligands including thiols were added to the culture. The results indicate that thiols can account for a major part or most of the copper-complexing ligands produced by these algae. Furthermore, a feedback mechanism exists in which the production of thiol-type complexing ligands is controlled by the free copper concentration, production already being stimulated by an increase of [Cu 21 ] from 0.4 to 1.5 pM. Incubations with added exudates, thiols, and salicylaldoxime (SA) showed much reduced copper toxicity even though copper uptake was increased by the exudates and the SA.

Effect of kinetics of complexation by humic acid on toxicity of copper to Ceriodaphnia dubia

Abstract: The rate of reaction of trace metal ions is an important consideration when studying the chemistry of trace metals in natural waters. The application of speciation models to natural water systems requires knowledge of kinetics if reactions are slow. Most bioassay and toxicity tests conducted in static and flow-through systems have not taken reaction kinetics into account. Therefore, results from these studies may overestimate the toxicity in the receiving waters. In the present study, the kinetics of the interaction of Cu(II) with humic acid (HA) and its influence on the toxicity of copper to Ceriodaphnia dubia were investigated by both chemical kinetic studies using a copper ion selective electrode and bioassay tests using a continuous flow-through bioassay system. A two-ligand site with first-order rate constants model gave a very good description of experimental kinetic data of the change of free Cu2+ concentration. Average k1 was 1.85/h and average k2 was 0.094/h. Bioassay tests indicated that different reaction times of copper with HA solution produced different toxic effects to organisms. We determined the hydrodynamic characteristics of the bioassay chambers to better describe the exposure of the organisms to free Cu2+. The bioassays supported the free ion activity model that the bioavailability and therefore toxicity of copper was directly correlated to the free Cu2+ concentration rather than to the total copper concentration. It was further shown that conventional chemical kinetics can be used to predict the toxicity of copper in these bioassays. This study supports the importance of considering reaction kinetics when studying the chemistry of trace metals in natural waters.

Metal Removal from Contaminated Soil and Sediments by the Biosurfactant Surfactin

Abstract: Batch soil washing experiments were performed to evaluate the feasibility of using surfactin from Bacillus subtilis, a lipopeptide biosurfactant, for the removal of heavy metals from a contaminated soil and sediments. The soil contained high levels of metals and hydrocarbons (890 mg/kg of zinc, 420 mg/kg of copper, and 12.6% oil and grease), and the sediments contained 110 mg/kg of copper and 3300 mg/kg of zinc. The contaminated soil was spiked to increase the levels of copper, zinc, and cadmium to 550, 1200, and 2000 mg/kg, respectively. Water alone removed minimal amounts of copper and zinc (less than 1%). Results showed that 0.25% surfactin/1% NaOH could remove 25% of the copper and 6% of the zinc from the soil and 15% of the copper and 6% of the zinc from the sediments. A series of five washings of the soil with 0.25% surfactin (1% NaOH) was able to remove 70% of the copper and 22% of the zinc. The technique of ultrafiltration and the measurement of octanol−water partitioning and ζ-potential were used...

Corrosion of Lithium‐Ion Battery Current Collectors

Abstract: The primary current‐collector materials being used in lithium‐ion cells are susceptible to environmental degradation: aluminum to pitting corrosion and copper to environmentally assisted cracking. Localized corrosion occurred on bare aluminum electrodes during simulated ambient‐temperature cycling in an excess of electrolyte. The highly oxidizing potential associated with the positive‐electrode charge condition was the primary factor. The corrosion mechanism differed from the pitting typically observed in aqueous electrolytes because each site was filled with a mixed metal/metal‐oxide product, forming surface mounds or nodules. Electrochemical impedance spectroscopy was shown to be an effective analytical tool for characterizing the corrosion behavior of aluminum under these conditions. Based on X‐ray photoelectron spectroscopy analyses, little difference existed in the composition of the surface film on aluminum and copper after immersion or cycling in electrolytes made with two different solvent formulations. Although Li and P were the predominant adsorbed surface species, the corrosion resistance of aluminum may simply be due to its native oxide. Finally, copper was shown to be susceptible to environmental cracking at or near the lithium potential when specific metallurgical conditions existed (work hardening and large grain size). © 1999 The Electrochemical Society. All rights reserved.

Factors controlling copper solubility and chalcopyrite deposition in the Sungun porphyry copper deposit, Iran

Abstract: The Sungun porphyry copper deposit is hosted in a Diorite/granodioritic to quartz-monzonitic stock that intruded Eocene volcanosedimentary and Cretaceous carbonate rocks Copper mineralization is associated mainly with potassic alteration and to a lesser extent with sericitic alteration Based on previously published fluid inclusion and isotopic data by Hezarkhani and Williams-Jones most of the copper is interpreted to have deposited during the waning stages of orthomagmatic hydrothermal activity at temperatures of 400 to 300 °C These data also indicate that the hydrothermal system involved meteoric waters, and boiled extensively In this work, thermodynamic data are used to delineate the stability fields of alteration and ore assemblages as a function of fS2, fO2 and pH The solubility of chalcopyrite was evaluated in this range of conditions using recently published experimental data During early potassic alteration (>450 °C), Copper solubility is calculated to have been >50 000 ppm, whereas the copper content of the initial fluid responsible for ore deposition is estimated, from fluid inclusion data, to have been 1200–3800 ppm This indicates that initially the fluid was highly undersaturated with respect to chalcopyrite, which agrees with the observation that veins formed at T > 400 °C contain molybdenite but rarely chalcopyrite Copper solubility drops rapidly with decreasing temperature, and at 400 °C is approximately 1000 ppm, within the range estimated from fluid inclusion data, whereas at 350 °C it is only 25 ppm These calculations are consistent with observations that the bulk of the chalcopyrite deposited at Sungun is hosted by veins formed at temperatures of 360 ± 60 °C Other factors that, in principle, may reduce chalcopyrite solubility are increases in pH, and decreases in fO2 and aCl− Our analysis shows, however, that most of the change in pH occurred at high temperature when chalcopyrite was grossly undersaturated in the fluid, and that the direction of change in fO2 increased chalcopyrite solubility We propose that the Sungun deposit formed mainly in response to the sharp temperature decrease that accompanied boiling, and partly as a result of the additional heat loss and decrease in aCl−, which occurred as a result of mixing of acidic Cu-bearing magmatic waters with cooler meteoric waters of lower salinity

Copper chaperones: function, structure and copper-binding properties.

Abstract: Copper is an absolute requirement for living systems and the intracellular trafficking of this metal to copper-dependent proteins is fundamental to normal cellular metabolism. The copper chaperones perform the dual functions of trafficking and the prevention of cytoplasmic exposure to copper ions in transit. Only a small number of copper chaperones have been identified at this time but their conservation across plant, bacterial and animal species suggests that the majority of living systems utilise these proteins for copper routing. The available data suggest that each copper-dependent protein in the cell is served by a specific copper chaperone. Although copper chaperones cannot be substituted for one another in a given cell type, copper chaperones that deliver to the same protein in different cell types appear to be functionally equivalent. The majority of the copper chaperones identified thus far have an "open-faced β-sandwich" global fold with a conserved MXCXXC metal-binding motif. Specificity for a given copper-dependent protein appears to be mediated by the residues surrounding the copper-binding motif. Copper binds to such proteins as Cu(I) in a trigonal complex with three sulfur ligands. Only the copper chaperone specific for cytochrome-c-oxidase, Cox17, deviates from this design.