Showing papers on "Copper published in 1994"
TL;DR: In this article, it was shown that the presence of copper is not a prerequisite for the existence of superconductivity in a layered perovskite, and that the low value of the superconducting transition temperature (Tc = 0.93 K) points towards a special role for copper in the high-temperature superconductors.
Abstract: FOLLOWING the discovery of superconductivity at ∼30 K in La2−xBaxCuO4 (ref. 1), a large number of related compounds have been found that are superconducting at relatively high temperatures. The feature common to all of these materials is a layered crystal structure based on a perovskite template and containing planar networks of copper and oxygen. This raises the question of whether superconductivity can occur in layered perovskites that do not contain copper. To the best of our knowledge, no such material has been found to date, despite nearly a decade of searching. We describe here the discovery of superconductivity in Sr2RuO4, a layered perovskite isostructural with La2−xBaxCuO4 (Fig. 1). Our results demonstrate that the presence of copper is not a prerequisite for the existence of superconductivity in a layered perovskite. But the low value of the superconducting transition temperature (Tc = 0.93 K) points towards a special role for copper in the high-temperature superconductors.
1,977 citations
787 citations
TL;DR: In this paper, the antioxidative effects of wine phenolics on the catalysis of lipid peroxidation by biological catalysts such as myoglobin, cytochrome c, iron ascorbate, and copper ions were determined.
Abstract: The concentrations of phenolics of three grape varieties and two red wines were determined. The red grape variety and the red wines contain phenolics at concentrations of 920 mg/kg and 1800 and 3200 mg/L, respectively. The antioxidative effects of wine phenolics on the catalysis of lipid peroxidation by biological catalysts such as myoglobin, cytochrome c, iron ascorbate, and copper ions were estimated. Lipid peroxidation catalyzed by myoglobin, cytochrome c, and iron ascorbate was inhibited (I 50 ) by wine phenolics at concentrations of 0.2, 0.35, and 0.9 μg of phenolics/mL
501 citations
Book•
01 Aug 1994
TL;DR: CVD of aluminium tungsten copper from Cu(II) percursors gold and silver precursors platinum, pallaium, and nickel assorted metals is given in this article.
Abstract: CVD of aluminium tungsten copper from Cu(II) percursors copper from Cu(I) precursors gold and silver platinum, pallaium, and nickel assorted metals.
469 citations
421 citations
TL;DR: The CTR1 gene of Saccharomyces cerevisiae encodes a protein required for high affinity copper uptake, which is expressed on the plasma membrane, is heavily glycosylated with O-linkages, and exists as an oligomer in vivo.
416 citations
TL;DR: Bacterial mechanisms of copper resistance are related to reduced copper transport, enhanced efflux of cupric ions, or copper complexation by cell components, and the metallothionein chelation mechanism has been approached with molecular detail.
Abstract: Copper is both an essential micronutrient and a toxic heavy metal for most living cells. The presence of high concentrations of cupric ions in the environment promotes the selection of microorganisms possessing genetic determinants for copper resistance. Several examples of chromosomal and plasmid copper-resistance systems in bacteria have been reported, and the mechanisms of resistance have started to be understood at the molecular level. Bacterial mechanisms of copper resistance are related to reduced copper transport, enhanced effiux of cupric ions, or copper complexation by cell components. Copper tolerance in fungi has also been ascribed to diverse mechanisms involving trapping of the metal by cell-wall components, altered uptake of copper, extracellular chelation or precipitation by secreted metabolites, and intracellular complexing by metallothioneins and phytochelatins; only the metallothionein chelation mechanism has been approached with molecular detail.
374 citations
TL;DR: In this paper, the third-order nonlinearities of glasses doped with a large number of copper or silver particles are studied by degenerate four-wave mixing with an emphasis on particle size dependence.
Abstract: Third-order nonlinearities of glasses doped with a large number of copper or silver particles are studied by degenerate four-wave mixing with an emphasis on particle-size dependence. The nonlinear susceptibility χ(3) exhibits a peak at the wavelength of the absorption peak, with a maximum value of the order of 10−7 esu. The value of χ(3)/α is roughly independent of the absorption coefficient α and increases as the particle radius increases. This result is well explained by the size dependence of the imaginary part of the dielectric constant of metal particles and the local-field factor. The time response of the nonlinearity exhibits two-component behavior: the fast decay time is shorter than the pulse width of the laser (~12 ps), whereas the slow one is 120–200 ps, being weakly dependent on the radius.
351 citations
TL;DR: In this paper, a multi-method approach was used to investigate the chemical speciation of dissolved copper and nickel in South San Francisco Bay and determined dissolved copper speciation by four different analytical approaches: competitive ligand equilibration-cathodic stripping voltammetry [CLE-CSV], differential pulse anodic stripping (DPSV), DPASV(TMF-RGCDE) and chelating resin column partitioning-graphite furnace atomic absorption spectrometry [CRCP-GFAAS].
324 citations
TL;DR: In this paper, the structural changes previously initiated by the thermodynamic effects of high pressure are induced chemically under ambient conditions, resulting in a superconducting oxy-fluoride in which fluorine plays a dominant structural role, rather than merely being an electronic dopant.
Abstract: HIGH-PRESSURE synthesis has proved a useful technique for obtaining new, metastable copper oxide superconductors; for example, oxygen insertion into Sr2CuO3 at 6 GPa (ref. 1) yields superconducting Sr2CuO3.i, with transition temperature Tc = 70 K, in which the superconducting CuO2 layers are generated by pressure-induced oxygen migration from apical to equatorial sites. Although the simple structure and high transition temperatures make this family (general formula Srn+1CunO2n + 1+ δ) of interest, the stringent synthesis conditions limit its value for applications. Here we report that fluorine insertion into Sr2CuO3 at ambient pressure causes related structural rearrangements to give superconducting Sr2CuO2F2 + δ with a maximum Tc of 46 K. In this synthesis, the structural changes previously initiated by the thermodynamic effects of high pressure are induced chemically under ambient conditions. The result is a superconducting oxy-fluoride in which fluorine plays a dominant structural role, rather than merely being an electronic dopant as in La2CuO4Fx (ref. 2) and Nd2CuO4−xFy (ref. 3).
301 citations
TL;DR: In this article, the authors measured reaction rates and activation energies for carbon monoxide oxidation over thin films of metallic copper, copper (I) oxide, and copper (II) oxide grown on graphite.
TL;DR: In this article, electron paramagnetic resonance (EPR) spectroscopy was used to probe the oxidation state and coordination environment of copper in ion-exchanged CuZSM-5.
Abstract: Electron paramagnetic resonance (EPR) spectroscopy was utilized to probe the oxidation state and coordination environment of copper in ion-exchanged CuZSM-5. EPR spectra of hydrated samples were consistent with octahedral coordination. Square pyramidal and square-planar sites were identified in pretreated CuZSM-5 samples, and the relative concentration of square-pyramidal sites in these samples was linearly correlated with the copper-exchange level. The extent of autoreduction was monitored by EPR and it was determined that a substantial fraction (approximately 40-60%) of the copper was reduced and the reduction process was reversible in the presence of water. A mechanism for the autoreduction of copper is proposed that is consistent with the EPR results. Further, the reactivity of the proposed copper species was probed in reducing and oxidizing environments and in the presence of nitric oxide. The increase in EPR signal intensity that was observed after room-temperature NO exposure of pretreated and oxidized CuZSM-5 is attributed to the formation of copper nitrite and nitrate species. High-temperature in situ EPR experiments revealed that on the time scale of the EPR experiment, the paramagnetic copper environment did not change at elevated temperatures in the presence of nitric oxide. 39 refs., 13 figs., 3 tabs.
TL;DR: The bulk properties of [ital d]-wave superconductors relevant to high-[ital T][sub [ital c]] copper oxides within weak-coupling theory are studied and strong anisotropy in the ultrasonic attenuation when a sound wave is propagated within the [ital a]-[ital b] plane is predicted.
Abstract: We study the bulk properties of d-wave superconductors relevant to high-${\mathit{T}}_{\mathit{c}}$ copper oxides within weak-coupling theory. The superfluid density, the tunneling conductance, and the frequency-dependent electric conductivity appear to be quite consistent with some of the experimental data from single crystals of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ and ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCuO}}_{8}$. We also predict strong anisotropy in the ultrasonic attenuation when a sound wave is propagated within the a-b plane.
TL;DR: In this article, Salicylaldoxime (SA) was used to detect copper complexing ligands in sea water using cathodic stripping voltammetry (CSV) at a detection window intermediate to that and overlapping with those currently available using other electroactive ligands.
TL;DR: An unusual mechanism of metal resistance is found in certain plant pathogenic strains of Pseudomonas syringae that are exposed to high levels of copper compounds used in disease control on agricultural crops, and part of this copper sequestering activity is determined by copper-binding protein products of the copper resistance operon (cop).
Abstract: An unusual mechanism of metal resistance is found in certain plant pathogenic strains of Pseudomonas syringae that are exposed to high levels of copper compounds used in disease control on agricultural crops. These bacteria accumulate blue Cu2+ ions in the periplasm and outer membrane. At least part of this copper sequestering activity is determined by copper-binding protein products of the copper resistance operon (cop). Potential copper-binding sites of the periplasmic CopA protein show conservation with type-1, type-2, and type-3 copper sites of several eukaryotic multi-copper oxidases. In addition to compartmentalization of copper in the periplasm, two components of the cop operon, copC and copD, appear to function in copper uptake into the cytoplasm. Copper resistance operons related to cop have been described in the related plant pathogen Xanthomonas campestris and in Escherichia coli, but these resistance systems may differ functionally from the Pseudomonas syringae system.
TL;DR: In this paper, the selective catalytic reduction of nitric oxide with ammonia in the presence of oxygen has been studied on Cu2+ ion-exchanged zeolite catalysts.
TL;DR: It is shown that the LDL lag time decreases with increasing copper concentration, leveling out at a relatively high copper‐to‐LDL ratio, demonstrating the existence of a finite number of saturable pro‐oxidant copper binding sites within the LDL particle.
TL;DR: The X-ray structures of three functional derivatives of ascorbate oxidase from Zucchini have been determined and are compared to the "native" oxidized form.
TL;DR: Copper(I)-catalyzed aminations of propargyl phosphates and acetates proceed under mild reaction conditions to give the corresponding propargylamines which are precursors of 1-alken-3-yamines and (Z)-allylamines as mentioned in this paper.
Abstract: Copper(I)-catalyzed aminations of propargyl phosphates and acetates proceed under mild reaction conditions to give the corresponding propargylamines which are precursors of 1-alken-3-ylamines and (Z)-allylamines
Patent•
08 Jun 1994
TL;DR: In this article, a method for mechanically and electrically bonding metallic materials and semiconductor materials was described, for example, in forming a semiconductor electrical heater, particularly for use in electrical smoking articles.
Abstract: A method is disclosed for mechanically and electrically bonding metallic materials and semiconductor materials. The method according to the invention may be used, for example, in forming a semiconductor electrical heater, particularly for use in electrical smoking articles. A metallic element, such as a copper alloy power supply tab, is laser welded to a semiconductor element, such as a doped silicon resistive heater element. A laser beam is directed through a hole in the copper alloy tab to melt some silicon material, which flows into the hole in the copper tab, reacts and intermixes with the copper and solidifies to form a slug containing copper silicide. A protective material such as nickel may be applied to protect the copper silicide from oxidation if desired. An ohmic, low resistance contact and high strength bond is provided between the parts.
Patent•
IBM1
TL;DR: In this paper, a high speed electrochemical metal removal technique was used for planarization of multilayer copper interconnection in thin film modules, which uses a neutral salt solution, is compatible with the plating process and has minimum safety and waste disposal problems.
Abstract: A high speed electrochemical metal removal technique provides for planarization of multilayer copper interconnection in thin film modules. The process uses a neutral salt solution, is compatible with the plating process and has minimum safety and waste disposal problems. The process offers tremendous cost advantages over previously employed micromilling techniques for planarization.
TL;DR: The high correlation between the copper level in the membranes and enzymatic activity as well as the high reactivity of the reduced copper clusters toward dioxygen strongly indicate that the membrane-bound copper ions constitute the active sites of the pMMO.
TL;DR: In this article, N -(3-Trimethoxysilyl-propyl)pyrrole was applied as a primer to adhere poly(3,4-ethylenedioxythiophene) (PEDOT) to the substrate.
TL;DR: The growth kinetics of intermetallic compound layers formed between four hot-dipped solder coatings and copper by solid state, thermal aging were examined in this paper, where solders were l00Sn, 50In-50Sn, 100In, and 63Sn-37Pb (wt.%); the substrate material was oxygen free, high conductivity Cu.
Abstract: The growth kinetics of intermetallic compound layers formed between four hot-dipped solder coatings and copper by solid state, thermal aging were examined. The solders were l00Sn, 50In-50Sn, 100In, and 63Sn-37Pb (wt.%); the substrate material was oxygen-free, high conductivity Cu. The total intermetallic layer of the 100Sn/Cu system exhibited a combination of parabolic growth at lower aging temperatures and t0.42 growth at the higher temperatures. The combined apparent activation energy was 66 kJ/mol. These results are compared to the total layer growth observed with the 63Sn-37Pb/Cu system which showed parabolic kinetics at similar temperatures and an apparent activation energy of 45 kJ/mol. Both 100Sn and 63Sn-37Pb diffusion couples showed a composite intermetallic layer comprised of Cu3Sn and Cu6Sn5. The intermetallic compound layer formed between In and Cu changed from a CuIn2 stoichiometry at short annealing times to a Cu57In43 composition at longer periods. The growth kinetics were parabolic with an apparent activation energy of 20 kJ/mol. The intermetallic layer growth of the 50In-50Sn/Cu system exhibited extreme variations in the layer thicknesses which prohibited a quantitative assessment of the growth kinetics. The layer was comprised of two compounds: Cu26Sn13In8 which was the dominant phase and a thin layer of Cu17Sn9In24 adjacent to the solder.
TL;DR: The results of these experiments unambiguously show that zinc and copper bind at separate noninteracting sites on this protein, and it is found that dog serum albumin has a specific high affinity site for copper.
TL;DR: Crystallographic analysis shows that NIR is a trimer composed of three identical subunits, and that the ligands to the type I and type II copper atoms are the same as those of the Achromobacter cycloclastes NIR.
Abstract: Nitrite reductase (NIR) from the denitrifying bacterium Alcaligenes faecalis S-6 is a copper-containing enzyme which requires pseudoazurin, a low molecular weight protein containing a single type I copper atom, as a direct electron donor in vivo. Crystallographic analysis shows that NIR is a trimer composed of three identical subunits, each of which contains one atom of type I copper and one atom of type II copper, and that the ligands to the type I and type II copper atoms are the same as those of the Achromobacter cycloclastes NIR. An efficient NIR expression-secretion system in Escherichia coli was constructed and used for site-directed mutagenesis. An NIR mutant with a replacement of the type II copper ligand, His135, by Lys still retained a type II copper site as well as a type I copper atom, but it completely lost nitrite-reducing activity as measured with methyl viologen as an electron donor. On the other hand, another mutant with a replacement of the type I copper ligand, Met150, by Glu contained only a type II copper atom, but it still retained significant nitrite-reducing activity with methyl viologen. When pseudoazurin was used as an electron donor for the reaction, however, Met150Glu failed to catalyze the reduction of nitrite. Kinetic analysis of the electron transfer between NIR and pseudoazurin revealed that the electron-transfer rate between Met150Glu and pseudoazurin was reduced 1000-fold relative to that of wild-type NIR.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: In this paper, high density preparation of single wall tubes in the presence of mixed catalysts of the types Fe/Ni and Co/Ni, in the soot as well as in the weblike deposits forming in the chamber was reported.
Abstract: We report here on the high‐density preparation of single‐wall tubes in the presence of mixed catalysts of the types Fe/Ni and Co/Ni, in the soot as well as in the weblike deposits forming in the chamber. The yield is much higher than previously reported, and gram quantities can be obtained. Diameters cover the range from 0.9 to 3.1 nm, larger than previously reported, with the histogram showing only one peak at 1.7 nm. Evidence of an epitaxial action between C60 and single‐walled nanotubes is presented. Results from the mixed catalysts Co/Cu, Ni/Mg, and Ni/Ti are also reported.
TL;DR: In this article, the reduction of Ni 2+ (aq), Ni 2 + (diglyme) and Cu 2+ by NaBH 4 has been studied with mechanistic and stoichiometric factors as the focus.
Abstract: The reduction of Ni 2+ (aq), Ni 2+ (diglyme), Cu 2+ (aq), and Cu 2+ (diglyme) by NaBH 4 has been studied with mechanistic and stoichiometric factors as the focus