Showing papers on "Copper published in 2007"

Short communication Susceptibility constants of Escherichia coli and Bacillus subtilis to silver and copper nanoparticles

Abstract: Nanoparticle susceptibility constants were defined and used to evaluate the antimicrobial characteristics of silver and copper nanoparticles against Escherichia coli and Bacillus subtilis. Reaction of copper nanoparticles of 100 nm with B. subtilis showed the highest susceptibility (Z=0.0734 mL/μg) whereas the reaction of silver nanoparticles of 40 nm with E. coli showed the lowest one (Z=0.0236 mL/μg). © 2006 Elsevier B.V. All rights reserved.

Synthesis of size-controlled and shaped copper nanoparticles.

Abstract: The synthesis of stable, monodisperse, shaped copper nanoparticles has been difficult, partially because of copper's propensity for oxidation. This article reports the findings of an investigation of a synthetic route for the synthesis of size-controllable and potentially shape-controllable molecularly capped copper nanoparticles. The approach involved the manipulation of reaction temperature for the synthesis of copper nanoparticles in organic solvents in the presence of amine and acid capping agents. By manipulating the reaction temperature, this route has been demonstrated for the production of copper nanoparticles ranging from 5 to 25 nm. The size dependence of the melting temperature of copper nanoparticles, especially for surface melting, is believed to play an important role in interparticle coalescence, leading to size growth as the reaction temperature is increased. Control of the reaction temperature and capping molecules has also been demonstrated to produce copper nanoparticles with different ...

Intracellular Copper Does Not Catalyze the Formation of Oxidative DNA Damage in Escherichia coli

Abstract: Because copper catalyzes the conversion of H2O2 to hydroxyl radicals in vitro, it has been proposed that oxidative DNA damage may be an important component of copper toxicity. Elimination of the copper export genes, copA, cueO, and cusCFBA, rendered Escherichia coli sensitive to growth inhibition by copper and provided forcing circumstances in which this hypothesis could be tested. When the cells were grown in medium supplemented with copper, the intracellular copper content increased 20-fold. However, the copper-loaded mutants were actually less sensitive to killing by H2O2 than cells grown without copper supplementation. The kinetics of cell death showed that excessive intracellular copper eliminated iron-mediated oxidative killing without contributing a copper-mediated component. Measurements of mutagenesis and quantitative PCR analysis confirmed that copper decreased the rate at which H2O2 damaged DNA. Electron paramagnetic resonance (EPR) spin trapping showed that the copper-dependent H2O2 resistance was not caused by inhibition of the Fenton reaction, for copper-supplemented cells exhibited substantial hydroxyl radical formation. However, copper EPR spectroscopy suggested that the majority of H2O2-oxidizable copper is located in the periplasm; therefore, most of the copper-mediated hydroxyl radical formation occurs in this compartment and away from the DNA. Indeed, while E. coli responds to H2O2 stress by inducing iron sequestration proteins, H2O2-stressed cells do not induce proteins that control copper levels. These observations do not explain how copper suppresses iron-mediated damage. However, it is clear that copper does not catalyze significant oxidative DNA damage in vivo; therefore, copper toxicity must occur by a different mechanism.

Selective CO oxidation in excess H2 over copper-ceria catalysts: identification of active entities/species.

Abstract: Catalysts based on combinations between copper and cerium oxides are analyzed with respect to their catalytic properties for preferential oxidation of CO in a H2-rich stream (CO-PROX) by means of DRIFTS, XANES, and Raman under Operando conditions. The results allow analyzing entities/species responsible for the CO and H2 oxidation reactions taking place during the CO-PROX process. While CO oxidation takes place at copper oxide support interfacial sites and its activity correlates with the degree of reduction achieved on the dispersed copper oxide particles, H2 oxidation apparently proceeds when a massive copper oxide reduction occurs. This opens the possibility to modulate the catalytic behavior of these types of catalysts by acting, respectively, on the interfacial redox properties and on the dispersed copper oxide redox properties.

Structure−Activity Relationship in Nanostructured Copper−Ceria-Based Preferential CO Oxidation Catalysts

Abstract: Two series of nanostructured oxidized copper−cerium catalysts with varying copper loadings, and prepared, respectively, by impregnation of ceria and by coprecipitation of the two components within ...

Role of Lattice Strain and Defects in Copper Particles on the Activity of Cu/ZnO/Al2O3 Catalysts for Methanol Synthesis

Abstract: Copper-based catalysts are industrially applied in various reactions including water-gas shift, synthesis of fatty alcohols from fatty acid methyl esters, and methanol synthesis. Today, methanol is produced at low pressures (35-55 bar) and 200-300°C over Cu/ZnO/Al2O3 catalysts. Due to the great commercial relevance, Cu/ZnO-based catalysts have been extensively studied and many different models have been proposed regarding the nature of active sites and the valence of copper under conditions of methanol formation, such as Cu dispersed in ZnO, metallic copper supported on ZnO, dynamic surface and bulk alloy formation depending on the reduction potential of the synthesis gas, Cu at the so-called Schottky junction between metallic Cu and the semiconductor ZnO, and ZnO segregated on Cu. The catalytic activity of the binary catalyst has been reported to be several orders of magnitude greater than that of metallic Cu or pure ZnO, respectively, indicating a synergetic interaction of the two components. ZnO is regarded either as provider of atomic spillover hydrogen for further hydrogenation of adsorbed reaction intermediates on Cu sites, or as a structure directing support controlling dispersion, morphology, and specific activity of the metal particles. Strong interaction between the metal and the support, especially in the case of large lattice mismatch, is known to cause strain in the metal particles, to which an increase in catalytic performance has been attributed. On the other hand, 1-ML-high and thicker Cu islands epitaxially grown on the ZnO (000⎯1) surface were experimentally found to be strain-free. In most of the earlier studies model catalysts with low Cu loadings (Cu/Zn 1) and the ZnO particles, acting rather as a spacer than as a support, are comparable in size, or even smaller than the Cu particles. In this paper we report the results of TEM and in situ XRD characterization of a series of Cu/ZnO/Al2O3 catalysts exhibiting different catalytic activities. The molar ratio Cu:Zn:Al = 60:30:10 is characteristic of commercial catalysts. The microstructural features of the materials prepared by coprecipitation with sodium carbonate from metal nitrate solution are analyzed after calcination in air at 330°C and subsequent reduction in hydrogen at 250°C. A quantitative estimation of imperfections in metal particles determined by combination of independent TEM and in situ XRD investigations is established. The implications of strain in Cu crystallites and the defect frequency associated therewith on the catalytic activity of Cu/ZnO/Al2O3 catalysts in methanol synthesis are discussed. The TEM and HRTEM images shown in Figure 1 illustrate the microstructure typical of the catalysts studied. Generally, 10 to 15 clusters similar to the one shown in Figure 1a, which had the size that varied from 100 nm to several micrometers, were analyzed in each of the catalysts with Energy-Dispersive X-Ray spectroscopy (EDX) to determine the concentrations of Al, Cu, and Zn. The average value (Al: 10.6 ±4.5 at.%; Cu: 62.7 ±7.2 at.%; Zn: 26.7 ±4.2 at.%) is close to the nominal composition. Figure 2 that contains data of all catalysts illustrates the scattering due to local inhomogeneities. The particles of Cu and ZnO form an irregular framework (Figure 1b). The particles of ZnO, which are comparable in size or smaller than the Cu particles, serve as spacers between the latter, preventing them from sintering.

Interaction of Sulfur Dioxide, Polyphenols, and Oxygen in a Wine-Model System: Central Role of Iron and Copper

Abstract: The rate of oxidation of SO2 was studied in a wine-model system under aerial oxygen saturation conditions to gain further insight into its mechanism of action in wine. When SO2 was studied alone, no significant oxidation was observed unless iron and copper were introduced. When these metals were added a slow oxidation was observed and bound SO2 also increased to a small but significant extent. These results are consistent with a radical chain mechanism initiated by metal catalysis, in which powerful oxidizing radicals, capable of oxidizing ethanol to acetaldehyde, are produced. This increase in bound SO2 is prevented by 4-methylcatechol (4-MeC) in keeping with the known ability of polyphenols to scavenge these intermediate radicals and thus to inhibit SO2 autoxidation, which consequently should not occur in wine. When 4-MeC was introduced at a concentration that simulated the reducing capacity of red wine, again no significant SO2 oxidation was observed without addition of iron and copper. Had the catechol been oxidized, hydrogen peroxide would have been generated and reacted with the SO2. In the presence of both metals the rate of SO2 oxidation was markedly increased compared to SO2 alone and then was dependent on the concentration of the catechol. These results demonstrate the crucial importance of metals in allowing polyphenol oxidation and that the rate of SO2 consumption is dependent on the rate of catechol oxidation. When iron and copper were added separately, only a modest increase in rate of catechol oxidation resulted. However, when combined, marked synergism was observed and the rate then became very sensitive to copper concentration. It is proposed that copper, by interacting with oxygen, facilitates redox cycling of iron. Exposure of a red wine to the conditions used in this study produced similar results regarding SO2 oxidation to those observed.

Effect of Particle Shape on Thermal Conductivity of Copper Reinforced Polymer Composites

Abstract: Thermal conductivity of copper powder filled polyamide composites are investigated experimentally in the range of filler content 0-30% by volume for particle shape of short fibers and 0-60% by volume for particle shapes of plates and spheres. The thermal conductivity of polymer composites is measured by the Hot-Disk method. It is seen that the experimental values for all the copper particle shapes are close to each other at low particle content, φ<10, as the particles are dispersed in the polyamide matrix and they are not interacting with each other. For particle content greater than 10% by volume, a rapid increase occurs in the thermal conductivity for the copper fibers filled polymer composite. As a result of this study, thermal conductivity of copper filled polyamide composites depends on the thermal conductivity of the filler particles, filler particle shape and size, and the volume fraction and spatial arrangement of the filler particles in the polymer matrix.

Size, composition and optical properties of copper nanoparticles prepared by laser ablation in liquids

Abstract: Colloidal copper nanoparticles were prepared by pulsed Nd:YAG laser ablation in water and acetone. Size and optical properties of the nanoparticles were characterized by transmission electron microscopy and UV–visible spectrophotometry, respectively. The copper particles were rather spherical and their mean diameter in water was 30 nm, whereas in acetone much smaller particles were produced with an average diameter of 3 nm. Optical extinction immediately after the ablation showed surface plasmon resonance peaks at 626 and 575 nm for the colloidal copper in water and acetone, respectively. Time evaluation showed a blue shift of the optical extinction maximum, which is related to the change of the particle size distribution. Copper nanoparticles in acetone are yellowish and stable even after 10 months. In water, the color of the blue-green solution was changed to brown-black and the nanoparticles precipitated completely after two weeks, which is assigned to oxidation of copper nanoparticles into copper oxide (II) as was confirmed by the electron diffraction pattern and optical absorption measurements. We conclude that the ablation of bulk copper in water and acetone is a physical and flexible method for synthesis of stable colloidal copper and oxidized copper nanoparticles.

Human copper transporter 2 is localized in late endosomes and lysosomes and facilitates cellular copper uptake.

Abstract: High-affinity cellular copper uptake is mediated by the CTR (copper transporter) 1 family of proteins. The highly homologous hCTR (human CTR) 2 protein has been identified, but its function in copper uptake is currently unknown. To characterize the role of hCTR2 in copper homoeostasis, epitope-tagged hCTR2 was transiently expressed in different cell lines. hCTR2–vsvG (vesicular-stomatitis-virus glycoprotein) predominantly migrated as a 17 kDa protein after imunoblot analysis, consistent with its predicted molecular mass. Chemical cross-linking resulted in the detection of higher-molecular-mass complexes containing hCTR2–vsvG. Furthermore, hCTR2–vsvG was co-immunoprecipitated with hCTR2–FLAG, suggesting that hCTR2 can form multimers, like hCTR1. Transiently transfected hCTR2–eGFP (enhanced green fluorescent protein) was localized exclusively to late endosomes and lysosomes, and was not detected at the plasma membrane. To functionally address the role of hCTR2 in copper metabolism, a novel transcription-based copper sensor was developed. This MRE (metal-responsive element)–luciferase reporter contained four MREs from the mouse metallothionein 1A promoter upstream of the firefly luciferase open reading frame. Thus the MRE–luciferase reporter measured bioavailable cytosolic copper. Expression of hCTR1 resulted in strong activation of the reporter, with maximal induction at 1 μM CuCl2, consistent with the Km of hCTR1. Interestingly, expression of hCTR2 significantly induced MRE–luciferase reporter activation in a copper-dependent manner at 40 and 100 μM CuCl2. Taken together, these results identify hCTR2 as an oligomeric membrane protein localized in lysosomes, which stimulates copper delivery to the cytosol of human cells at relatively high copper concentrations. This work suggests a role for endosomal and lysosomal copper pools in the maintenance of cellular copper homoeostasis.

A copper(II) ion-selective on-off-type fluoroionophore based on zinc porphyrin-dipyridylamino.

Abstract: A new copper(II) fluorescent sensor 5,10,15,20-tetra((p-N,N-bis(2-pyridyl)amino)phenyl)porphyrin zinc (1) has been designed and synthesized by the Ullmann-type condensation of bromoporphyrin zinc with 2,2‘-dipyridylamine (dpa) under copper powder as a catalyst as well as with K2CO3 as the base in a DMF solution. It consists of two separately functional moieties: the zinc porphyrin performs as a fluorophore, and the dpa-linked-to-zinc porphyrin acts as a selected binding site for metal ions. It displays a high selectivity and antidisturbance for the Cu2+ ion among the metal ions examined (Na+, Mg2+, Cr3+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Ag+, Zn2+, Cd2+, Hg2+, and Fe3+) and exhibits fluorescence quenching upon the binding of the Cu2+ ion with an “on−off”-type fluoroionophoric switching property. The detection limit is found to be 3.3 × 10-7 M (3s blank) for Cu2+ ion in methanol solution, and its fluorescence can be revived by the addition of EDTA disodium solution. The design strategy and remarkable photophy...

The effect of boron on the corrosion resistance of the high entropy alloys Al0.5CoCrCuFeNiBx

Abstract: High entropy alloys are a newly developed family of multicomponent alloys that consist of various major alloying elements, including copper, nickel, aluminum, cobalt, chromium, iron, and others. Each element in the alloy system is present at between 5 and 35 atom %. A high entropy alloy has numerous beneficial mechanical, magnetic, and electrochemical characteristics. This investigation discusses the corrosion resistance of the Al 0.5 CoCrCuFeNiB x alloys with various amounts of added boron. Surface morphological and chemical analyses verified that the addition of boron produced Cr, Fe, and Co borides. Therefore, the fraction of Cr outside borides precipitates was scant. The anodic polarization curves and electrochemical impedance spectra of the Al 0.5 CoCrCUFeNiB x alloys, obtained in 1 N H 2 SO 4 aqueous solution, clearly reveal that the general corrosion resistance decreases as the concentration of boron increases.

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

Abstract: The binding stoichiometry between Cu(II) and the full-length β-amyloid Aβ(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 Aβ(1−16) and Aβ(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 Aβ(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 075 and 008 V vs Ag/AgCl [or 095 and 028 V vs normal hydrogen electrode (NHE)], respectively More importantly, for the first time, the Aβ−Cu(I) complex has been generated electrochemically and was found to catalyze the reduction of ox