Showing papers on "Copper published in 1988"

Copper complexation in the Northeast Pacific

Abstract: Copper titrations were conducted at sea with differential pulse anodic stripping voltammetry to examine the degree to which copper was associated with organic ligands. Greater than 99.7% of the total dissolved copper in surface waters of the central Northeast Pacific shallower than 200 m was estimated to be associated with strong organic complexes. Below 200 m, increasing proportions of inorganic or labile copper spccics were observed. At middepths (1,000 m), about 50-70% of the total dissolved copper was in the organically complexed form. Whereas total copper varies by a factor of only three from the surface to middepths (0.6-I .8 nM), copper complexation gives rise to extremely low cupric ion activities in surface waters ({Cu!‘} = 1.4 x lo-l4 M) and higher values at middepth ({Cuz-I} = lo- I1 M)-a variation of three orders of magnitude. Two classes of copperbinding ligands were found to be responsible for this complexation: an extremely strong ligand class [log K’cond (cu,j = 11.5 J at low concentrations (- 1.8 nM) -which dominated copper complexation in the surface waters and decreased with depth, and a weaker class of ligands [log K’cond(Cu3 = 8.51 at higher concentrations (8-10 nM) which was observed throughout the water column and showed no apparent structure in its vertical distribution. These findings have significant implications concerning the toxicity and bioavailability of copper in open ocean systems.

The Molecular Mechanisms of Copper and Silver Ion Disinfection of Bacteria and Viruses

Abstract: Disinfection due to copper or silver ions may result from action at the cell or capsid protein surface or on the nucleic acid of cells or viruses. Metals may alter enzyme structure and function or facilitate hydrolysis or nucleophilic displacement. The means by which cells may reduce the toxic effect of metal ions include: biomethylation, complexation with metallothionen, development of efflux pumps, the binding of metal ions to cell surfaces, and the removal of metal ions by precipitation. The phenomenon of “multiplicity of reactivation” may reduce the effect of a disinfectant on a virus by allowing a clump of partially inactivated viruses to produce a productive infection in a susceptible cell. Conditions which may affect metal ion‐biomolecule interaction include: pH, ionic strength, temperature, dissolved oxygen, presence of interfering substances or light, the chemical form and valency of the metal ion, and the condition of the microorganisms.

High-temperature thermal expansion of six metallic elements measured by dilatation method and X-ray diffraction

Abstract: The thermal expansion of silver, gold, copper, nickel, molybdenum and tungsten has been measured by the dilatation method. The thermal expansion values of silver, gold, copper and nickel have also been evaluated from lattice parameter measurements by X-ray diffraction. These six metals were found to exhibit a nearly uniform expansion over the temperature ranges covered. The thermal expansion values obtained by the dilatation method are in good agreement with those determined by X-ray diffraction. The present results appear also to agree well with those reported previously in the literature.

Semicorrin metal complexes as enantioselective catalysts. Part 2. Enantioselective cyclopropane formation from olefins with diazo compounds catalyzed by chiral (semicorrinato)copper complexes

Abstract: Copper complexes of chiral, C2-symmetric semicorrin ligands were found to be efficient catalysts for the cyclopropane formation from olefins with diazo compounds. In the presence of 1 mode-% of catalyst, alkyl diazoacetates reacted smoothly with terminal olefins such as styrene, butadiene, and 1-heptene to give the corresponding optically active cyclopropanecarboxylic-acid derivatives (Table 1 Scheme 2). With one of the catalysts, enantioselectivities up to 97% ee were obtained (Table 2). Usually, the reactions were carried out using bis(semicorrinato)copper(II) complexes as precatalysts. In order to produce active catalysts, these complexes had to be activated first by heating in the presence of diazoacetate or by treatment with phenylhydrazine. Experiments with (semicorrinato)copper(I) complexes, prepared in situ from copper(I) tert-butoxide (Scheme 4), suggest that the actual catalyst is a [mono(semicorrinato)]copper(I).

Humic Acid Complexation of Calcium and Copper

Abstract: High-affinity metal binding by isolated humic acids has been observed for both copper and calcium in metal titration experiments. Results of titrations of humic acids with a single metal (either calcium or copper) are consistent with a discrete ligand site model of humate-metal binding. However, copper titrations in the presence of excess calcium do not show competitive effects predicted by such a model. Hence, different ligand sites must be involved in calcium and copper binding, or a binding mechanism other than discrete ligand binding must be operative.

Magnetic recording medium

Abstract: There is provided a magnetic medium in which the non-magnetic layer is a nickel-copper-phosphorus film containing 20 to 65 wt% of copper, which layer is formed by electroless plating It does not become magnetic even after heat treatment at 200 DEG C or above

Enhanced formation of ethylene and alcohols at ambient temperature and pressure in electrochemical reduction of carbon dioxide at a copper electrode

Abstract: In the electroreduction of CO2 at a copper cathode in aqueous solution at ambient temperature and pressure the faradaic yield of C2H4 amounted to 48%, and appreciable amounts of EtOH and PrnOH were formed; the selectivity of the products depends strongly upon the electrolytes.

Ultraviolet photoelectron spectroscopy of copper clusters

Abstract: Using a new magnetically focused time‐of‐flight photoelectron spectrometer, the ultraviolet photoelectron spectra (UPS) of mass‐selected negative copper clusters have been measured at photon energy of 4.66 eV for all clusters in the range from 6 through 41 copper atoms. These UPS data provide the first detailed probe of the 4s valence band structure of such medium size negative copper clusters, and extend previous approximate measures of the electron affinity of the corresponding neutral species. The results are in accord with the predictions of the ellipsoidal shell model for monovalent metal clusters. In particular, clusters 8, 20, and 40 (which correspond to spherical shell closings in this simple model) are found to have unusually low electron affinities and large HOMO–LUMO gaps. Subshell closings at 14 and 34 also appear special in this new UPS data.

Kinetics of trace metal complexation: role of alkaline-earth metals

Abstract: The rate of reaction of inorganic copper with the model ligand ethylenediaminetetraacetic acid (EDTA) is significantly retarded in the presence of calcium at seawater concentrations. The half-life for inorganic copper reacting with EDTA in seawater is /similar to/2 h at 10/sup /minus/7/M EDTA. This kinetic hindrance to the formation of the thermodynamically favored CuEDTA species results from several factors: (1) the preponderance of the calcium complex in the speciation of EDTA, (2) the competition of calcium and copper for reaction with any free EDTA formed by the dissociation of CaEDTA, and (3) the slow kinetics of direct attack of copper on CaEDTA compared to reaction with free or protonated EDTA species. If metal-complexing agents in natural waters behave as discrete ligands, then the reaction of a metal at strong binding sites may also be kinetically hindered at high alkaline-earth concentrations. In contrast with the reaction of EDTA, however, the rate of completion of copper by humic acid is not observably affected by high calcium concentrations.

Electrodeposited Cu‐Ni Textured Superlattices

Abstract: Artificially layered materials of alternating 2–3 nm thick copper and nickel layers have been produced by electrodeposition on oriented single‐crystal copper substrates. X‐ray diffraction examination of thin layers chemically removed from the substrate showed that a coherent, relatively homogeneous coating, with a strong epitaxial relationship, had been produced. In particular, artificially layered Cu‐Ni alloys displaying a textured [110] orientation were obtained by electrodeposition. Noncoherent nucleation leads to the presence of various amounts of randomly oriented alloy grains on all substrates but, in particular, for the [100] orientation.

A study of the structural, electrical and optical properties of copper tellurium oxide glasses

Abstract: The results of an investigation of some properties of CuO-TeO2 glasses are reported. X-ray diffraction, differential scanning calorimetry and optical absorption measurements are discussed with respect to the compositions. D.c. conductivity is measured in the temperature range 293 to 453 K and discussed in terms of small polaron theory.

New procedure for determination of [Cu-O]+p charge and oxygen content in high Tc copper oxides

Abstract: The properties of High Tc Superconductors are critically dependent on the degree of oxidation, i.e., on the average [Cu-O]+p charge (or formal oxidation state Cu+2+p of copper). This fact makes it important to accurately characterize High Tc copper oxide samples in term of this key parameter. We describe here a simple and reliable procedure for determining the effective copper oxidation level and, as a result, the oxygen content. Using a modification of standard iodometric titration techniques, our procedure involves the ratio of the results of two titrations: one to determine the copper concentration in the sample and the second to measure the degree of oxidation beyond Cu+. Using this ratio, numerous errors and difficulties are minimized. In addition, the exact stoichiometry of the sample need not be known. Experimental results on YBa2Cu3Oy are discussed which demonstrate the accuracy, reproducibility and reliability of our procedure.

In-Plane Structure of Underpotentially Deposited Copper on Gold (111) Determined by Surface EXAFS (Extended X-Ray Absorption Fine Structure).

Abstract: : The Surface Extended X Ray Absorption Fine Structure (SEFAFS) spectrum of an electrochemically deposited ad-layer of copper on a gold (111) electrode immersed in solution and under potential control was obtained by employing fluorescence detection and grazing incidence geometry. The x-rays were polarized parallel to the plane of the gold surface. Two peaks were observed in the radial distribution function, indicating two different near neighbors for copper. The near neighbors were determined to be gold at 2.58 plus or minus 0.03 angstrom and copper at 2.92 plus or minus 0.03 angstroms. The copper-copper distance is identical to the gold-gold lattice spacing showing that at full coverage, the copper ad-layer forms at 1 x 1 commensurate layer on the gold (111) substrate. The intensity of the gold-copper scattering relative to the copper-copper suggests the copper atoms sit in 3 fold hollows sites.

Metallic, but not superconducting, La-Ba (and La-Sr) copper oxides.

Abstract: New measurements are reported on three La-Ba (and La-Sr) copper-oxide compounds, including one new compound. These materials have metallic conductivities, comparable to those of the high-${T}_{c}$ copper oxides in the normal state, but they are not superconducting down to 5 K. Their magnetic susceptibility and structural features are also similar. These data provide a new challenge and test for the numerous theories of high ${T}_{c}$ to account also for its absence in these three closely related materials.

The reactive chemisorption of carbon dioxide at magnesium and copper surfaces at low temperature

Abstract: X-ray photoelectron spectroscopic studies reveal that the following species are present when carbon dioxides reactively chemisorbed at magnesium and copper surfaces: CO2(phys) CO3(a), CO 2 − (a) CO(a) and C(a). At Mg(0001) surfaces, it has been shown that there is a step-wise process, with a whole range of metastable species formed above 80 K. By contrast, at copper surfaces the chemistry is less complex, the most significant species being CO 2 − (a); these form preferentially under conditions which favour high surface concentrations of CO2(a) and therefore co-operative effects within the adlayer. The need to develop experimental methods for studying surface processes at high pressures is well recognised, however the present work shows that for some systems low temperatures (and pressures) offer a possible alternative strategy for delineating the step-wise nature of the reaction.

Characterization of haze-forming precipitates in silicon

Abstract: The defects leading to haze formation after diffusion of the transition metals cobalt, nickel, copper, and palladium have been studied by means of transmission electron microscopy and preferential etching. In all cases crystalline metal silicide particles have been observed. Both cobalt and nickel form disilicide particles of different morphologies in the surface regions of silicon wafers, whereas copper and palladium form metal‐rich silicide particles causing a supersaturation of Si self‐interstitials or undersaturation of vacancies and leading to the formation of extrinsic dislocation loops.