Soluble Copper Species Research Articles

Antimicrobial mechanism of cuprous oxide (Cu2O) coatings

Some very effective antimicrobial coatings exploit copper or cuprous oxide (Cu2O) as the active agent. The aim of this study is to determine which species is the active antimicrobial – dissolved ions, the Cu2O solid, or reactive oxygen species. Copper ions were leached from Cu2O into various solutions and the leachate tested for both dissolved copper and the efficacy in killing Pseudomonas aeruginosa. The concentration of copper species leached from Cu2O into aqueous solution varied greatly with the composition of the aqueous solution. For a range of solution buffers, killing of P. aeruginosa was highly correlated with the concentration of copper in the leachate. Further, 10 µL bacterial suspension droplets were placed on Cu2O coatings, with or without a polymer barrier layer, and tested for bacterial kill. Killing occurred without contact between bacterium and solid, demonstrating that contact with Cu2O is not necessary. We therefore conclude that soluble copper species are the antimicrobial agent, and that the most potent species is Cu+. The solid quickly raises and sustains the concentration of soluble copper species near the bacterium. Killing via soluble copper ions rather than contact should allow copper coatings to kill bacteria even when fouled, which is an important practical consideration.

Compositionally Tuned Trimetallic Thiospinel Catalysts for Enhanced Electrosynthesis of Hydrogen Peroxide and Built-In Hydroxyl Radical Generation

On-site electrochemical production of hydrogen peroxide (H2O2), an oxidant and disinfectant with growing demand, could be realized through the selective two-electron oxygen reduction reaction (2e– ORR), but the widespread adoption of this method depends on robust and efficient electrocatalysts. Current catalysts have been limited by cost or toxicity and lack well-defined structures that can facilitate systematic tuning of activity and selectivity. Here, we demonstrate a series of CuCo2–xNixS4 (0 ≤ x ≤ 1.2) thiospinel catalysts for 2e– ORR with variable compositions that can be synthesized via hydrothermal conversion. Rotating ring disk electrode measurements show that these catalysts have high selectivity for 2e– ORR (>60%) and that their activity can be improved by increasing the nickel content without compromising selectivity. An acid treatment step is critical prior to employing the optimized CuCo0.8Ni1.2S4 catalyst for bulk electrosynthesis of H2O2 in 0.05 M H2SO4 solution. Various structural analyses, including synchrotron X-ray spectroscopy, confirm that the catalysts retain the spinel structure after acid treatment and H2O2 electrosynthesis. The acid treatment likely leaches the soluble copper species from the as-synthesized catalysts that would catalyze an electro-Fenton process to consume H2O2, generate hydroxyl radicals, and therefore prevent the accumulation of H2O2. This work demonstrates a general strategy for systematic tuning of metal compound catalysts for practical H2O2 electrosynthesis and facile generation of hydroxyl radicals.

Effect of NaOH concentration on antibacterial activities of Cu nanoparticles and the antibacterial mechanism.

A series of Cu nanoparticles (NPs) have been prepared by a facile hydrothermal method at 180°C using different concentrations of NaOH solutions and characterized by XRD, SEM, TEM and FT-IR spectra. Their antibacterial activities were assessed by means of Gram-positive S. aureus and Gram-negative E. coli bacteria, where various dosages (3, 5, 7, 10mg) of the antibacterial agents were applied, and compared with that of the commercial CuSO4 salt. The antibacterial mechanism was explored based on series of control experiments. The results show that the NaOH concentration affects the crystallinity, crystal size and surface hydroxyl content of the Cu NPs, which significantly influence the antibacterial activities. Compared to the commercial CuSO4 salt, the four Cu samples prepared using no <4molL-1 of NaOH display excellent antibacterial activities with low concentrations of copper leachates, which is great beneficial to the practical applications. The experimental results support that the highly reactive and soluble copper species in the antibacterial system of the Cu NPs is a Cu (II)-peptide complex, but not free Cu2+ ions.

The influence of electrolyte usage on the growth of nanostructured anodic films on copper in sodium carbonate aqueous solution

Anodization of copper was performed in 0.1 M K2CO3 at 25 and 50 V. In order to study the influence of the electrolyte usage, samples were anodized in fresh electrolyte and electrolyte that was applied for anodizing for 2, 4 and 6 h. It was found that during anodization, the current oscillates with time. It means that there are cycles of adsorptions and delaminations of the anodic film of the samples. Moreover, the longer the electrolyte is used, the faster steady state of current densities without oscillations is achieved and the greater the current densities are. According to the Pourbaix diagram, the greater concentration of the water soluble copper species, the greater the CuO passivity field, thus the anodic oxides are formed much easier. For this reason, X-ray diffraction patterns revealed increasing content of tenorite phase (CuO) over cuprite (Cu2O) when the electrolyte is being re-used. For electrolytes pre-used for 6 h, no cuprite was found in the samples. Moreover, the longer the pre-usage of the electrolyte, the smaller the diameter of the grown nanowires. For anodizing performed at 25 V, nanowire diameter decreases from 55 ± 12 nm to 36 ± 7 nm (electrolyte pre-used for 6 h) in a linear manner.

Insights into relevant mechanistic aspects about the induction period of Cu(0)/Me(6)TREN-mediated reversible-deactivation radical polymerization.

There is a controversial debate about the mechanism of the Cu(0)-catalyzed radical polymerization. Herein, a comparative analysis of a series of reactions catalyzed by different valent copper shows that the induction period and the subsequent autoaccelerated polymerization of a Cu(0)/Me6TREN-catalyzed system originate from the accumulation of soluble copper species, and Cu(I) is still a powerful activator under its disproportionation favored conditions.

Oxidative IR spectroelectrochemistry of copper in methanol containing carbon monoxide.

IR spectroelectrochemistry was used to examine the electro-oxidation behavior of carbon monoxide in methanol at a polycrystalline copper electrode. Under such neutral conditions copper electrodes are coated with ill-defined copper oxides and hydroxides and at the oxidative potentials can be expected to generate soluble copper species. The electrochemistry displayed complex behavior suggesting that methanol oxidation was one prominent reaction. However, the spectroscopy revealed that very little methanol oxidation had occurred and that carbon monoxide was not adsorbed to the copper electrode. Instead, the electro-oxidation generated an intense IR band at 2107 cm(-1) that was attributed to a soluble [Cu(I)CO](+) species.

Reversible-Deactivation Radical Polymerization in the Presence of Metallic Copper. Comproportionation–Disproportionation Equilibria and Kinetics

This article is the first in a series of papers, describing reversible-deactivation radical polymerization (RDRP) in the presence of metallic copper. The aim of these papers is to determine the proportions and roles of Cu0, CuIBr/L, and CuIIBr2/L, and the overall reaction mechanism. This paper is focused on the comproportionation and disproportionation equilibrium between Cu0, CuIBr/L and CuIIBr2/L in dimethyl sulfoxide (DMSO) for various surface areas of Cu0 and different ligand concentrations, in both the absence and presence of methyl acrylate (MA). Comproportionation dominated disproportionation when there was enough ligand present in the reaction medium to stabilize all soluble copper species. The relative amount of CuI at comproportionation/disproportionation equilibrium increased with ligand concentration. CuI represents approximately 99.95% of all soluble Cu species in MA/DMSO = 2/1 (v/v) at the ratio [Me6TREN]0:[CuIIBr2]0 = 6:1. Under typical polymerization conditions, there is essentially no disproportionation, since the ratio [Me6TREN]:[CuII] is very large, starting from infinity and decreasing down to 6.7, for ∼3% terminated chains under the initial conditions [MA]0:[MBrP]0:[Me6TREN]0 = 222:1:0.1, in 33.3% (v/v) DMSO, with excess Cu0. The kinetics of comproportionation and disproportionation were both slow, requiring hours to reach equilibrium. The apparent rate coefficients for comproportionation and disproportionation were calculated as kcompapp = 9.0 × 10–4 cm s–1 and kdispapp = 2.0 × 10–5 cm s–1 in DMSO, as well as 3.5 × 10–3 cm s–1 and 3.1 × 10–6 cm s–1 in MA/DMSO = 2/1 (v/v), respectively. The results of this study invalidate the assumption of instantaneous and complete disproportionation, proposed in single-electron transfer living radical polymerization (SET-LRP). These findings agree with Cu0 acting as a supplemental activator and reducing agent in atom transfer radical polymerization (SARA ATRP).

Reaction pathways over copper and cerium oxide catalysts for direct synthesis of imines from amines under aerobic conditions

Copper(II) oxide, cerium oxide, and several copper(II) oxide supported on cerium oxide catalysts are explored in the aerobic oxidative homocoupling of benzylamine to form N-benzylidenebenzylamine in DMSO at 110°C. Although both CuO and CeO2 alone are shown to catalyze the reaction, CuOCeO2 catalysts are shown to most efficiently catalyze the reaction, providing higher rates (per g Cu) due to the presence of both copper and ceria species in the reactor. Catalysts with lower copper loadings and increased ceria content reduce the product yield, as ceria domains can catalyze the decomposition of the desired product as well. The amine conversion occurs with a significant induction period, associated with the putative formation of an initial benzylimine intermediate in the case of catalysis with CeO2 alone or from slow copper solubilization in cases where supported or unsupported copper catalysts are used, followed by rapid conversion to the N-benzylidenebenzylamine product. Copper leaching studies clearly demonstrate that catalysis using copper-containing catalysts is primarily associated with turnover by soluble copper species. A series of experiments targeted at elucidating the reaction pathway suggests that copper oxide domains promote the coupling of the initial intermediate, benzylimine, with benzylamine to produce the N-benzylidenebenzylamine product (path A), with a maximum production rate of 888μmol/m2h (13.3mmol/gCuh) over the pure CuO catalyst or 22.9μmol/m2h (26.1mmol/gCuh) over the CuOCeO2 catalyst. In contrast, cerium oxide domains are suggested to primarily convert the benzylimine to benzaldehyde, followed by condensation of the benzaldehyde with benzylamine in a rapid step to yield the N-benzylidenebenzylamine product (path B), with a maximum amine production rate of 2.74μmol/m2h. Both ceria and copper(II) oxide domains promote the initial benzylimine formation at comparable rates. Although the CuOCeO2 catalyst leaches about 11% of the copper during the reaction, and these soluble copper species are largely responsible for the catalytic turnover, the recovered solid can be recycled until the copper is depleted, catalyzing the reaction with an identical rate per g Cu in a second cycle, after calcination. The copper–ceria family of catalysts offers an alternative, potentially lower cost composition for the target oxidative homocoupling reaction than previously studied precious metal catalysts, although copper leaching is a distinct drawback to the catalyst composition.

Investigation of copper solubilization and reaction in micronized copper treated wood by electron paramagnetic resonance (EPR) spectroscopy

Abstract The purpose of this study was to compare the reaction chemistry of micronized copper and alkaline copper treatments with wood and to determine how fast copper is solubilized during the reaction between the acidic functionality in wood and the basic copper carbonate (CuCO3). Copper species produced in wood by various treatment methods were analyzed by electron paramagnetic resonance (EPR) spectroscopy. The effects of time and solution concentration on the spectral parameters of copper complexes in sawdust treated with copper sulfate solutions were examined, followed by study on the structure and the rate of formation of the copper complexes in sawdust treated with basic CuCO3 suspension. The study further attempted to identify the soluble copper species formed in wood during treatment with micronized copper preservatives. Comparisons were made among the fixed copper complexes in wood treated with micronized copper preservatives, copper sulfate solutions, basic CuCO3 suspensions and alkaline copper solution. The results showed rapid formation of fixed copper complexes in wood treated with aqueous suspensions of basic CuCO3. These complexes can resist leaching, and they have similar stereochemistry to those formed between wood and copper sulfate. This finding supports the premises that soluble copper is generated during the treatment of sawdust with basic CuCO3, and it can bond to wood cell components by migrating into the cell wall in a manner similar to other soluble copper species. Such copper complexes formed are different from those of alkaline copper treated wood, which can be easily distinguished by EPR.

Copper mediated controlled radical polymerization of methyl acrylate in the presence of ascorbic acid in a continuous tubular reactor

Controlled radical polymerization of methyl acrylate catalyzed by copper was conducted in a continuous tubular reactor. A length of copper tubing was used to initiate polymerization and generate soluble copper species, while the bulk of polymerization took place in inert stainless steel tubing. To mediate polymerization in the absence of copper surface, environmentally benign ascorbic acid was used for the first time in single electron transfer-living radical polymerization (SET-LRP) as a reducing agent to regenerate activating copper species. Polymerizations were conducted at ambient temperature with 30 wt% DMSO as solvent, producing well defined living polymer at a steady state conversion of 78% for a residence time of 62 min. Chain extensions using outlet polymer solutions were well-controlled and proceeded to high conversion in a short period of time, with a final concentration of 10 ppm of residual copper. The results illustrate the significant potential of using a continuous tubular reactor with ascorbic acid as a reducing agent as an efficient means to scale-up production of well controlled polyacrylics and other multiblock copolymers.

FTIR Characterization of Surface Interactions of Cyanide and Copper Cyanide with a Platinum Electrode in Alkaline Solution

In this paper, the nature of the species formed in theelectrochemical interactions between a polycrystalline platinum surface and cyanide and copper−cyanide species in alkaline solution (pH 13) has been investigated by combining cyclic voltammetry with in situ FTIR spectroscopy. This study was performed because electrochemical reactors for the treatment of cyanide-containing industrial wastewaters have been shown to achieve viable destruction rates when copper ions are present in the alkaline solution through the formation of copper oxide films [Palmer, S. A. K.; Breton, M. A.; Nunno, T. J.; Sullivan, D. M.; Surprenant, N. F.Metal/Cyanide Containing Wastes; Noyes Data Corp.: Park Ridge, New Jersey, 1988. Monteagudo, J. M.; Rodríguez, L.; Villaseñor, J.Advanced oxidation processes for destruction of cyanide from thermoelectric power station waste waters. J. Chem. Technol. Biotechnol. 2004, 79, 117−125. Sax, N. I., Ed.Dangerous Properties of Industrial Materials, 5th ed.; Van Nostrand-Reinhold: New York, 1979; p 526]. It has been found that the complexation of cyanide ions by copper species hinders the adsorption of the anion at the electrode, thus avoiding the characteristic electrode poisoning by CO that occurs in the absence of soluble copper species. Conversely, soluble copper−cyanide complexes can be electrooxidized at the platinum surface through the formation of cyanate species as an intermediate, and of HCOO− and NO as end products. The addition of copper species to the electrolyte also facilitates this route for cyanide oxidation to occur at higher rates without poisoning the platinum electrode.

SET‐LRP of N,N‐dimethylacrylamide and of N‐isopropylacrylamide at 25 °C in protic and in dipolar aprotic solvents

AbstractThe single‐electron transfer living radical polymerization (SET‐LRP) of water‐soluble monomers, N,N‐dimethylacrylamide (DMA) and N‐isopropylacrylamide (NIPAM), initiated with 2‐methylchloropropionate (MCP) in dipolar aprotic and protic solvents is reported. The radical polymerization of acrylamides is characterized by higher rate constants of propagation and bimolecular termination than acrylates. Therefore, the addition of CuCl2 is required to mediate deactivation in the early stages of the reaction. Through the use of Cu(0)‐wire/Me6‐TREN catalysis, conditions were optimized to minimize the amount of externally added CuCl2 required to maintain a linear evolution of molecular weight and narrow molecular weight distribution. By using less CuCl2 additive, the amount of soluble copper species that must ultimately be removed from the reaction mixture is reduced. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1752–1763, 2010

Effect of copper speciation at different pH on temporal sensory attributes of copper

The effect of copper solubility on temporal characteristics of copper sensation was investigated by evaluating bitterness, astringency, and metallic sensory characteristics of samples containing copper (39.4 and 78.8 μM) at two pH levels (pH 5.5 and pH 7.5) using the time–intensity test. Concentration of soluble copper in samples was measured with atomic absorption spectroscopy after filtering samples through 0.2 μm filter to remove insoluble copper particles. Decrease in copper concentration significantly inhibited metallic flavor. Astringency was not significantly affected by copper concentration, but changed as a function of pH. The level of soluble copper at pH 7.5 decreased by 50% compared to that at pH 5.5. There was a significant positive relationship between soluble copper concentration, overall sensory response, and intensity of metallic flavor. The result suggested that soluble copper species influence the perception of copper sensation by controlling metallic flavor.

Evaluation of Copper Speciation and Water Quality Factors That Affect Aqueous Copper Tasting Response

This study determined taste thresholds for copper as its speciation was varied among free cupric ion, complexed cupric ion, and precipitated cupric particles. The impact of copper chemistry on taste is important as copper is added to many beverages and can be present in drinking water as a natural mineral or due to corrosion of copper plumbing. A one-of-five test was used to define thresholds with solutions containing 0.025-8 mg/l Cu (from copper sulfate) in distilled or mineralized water of varying pH. The mineralized water was designed to mimic the composition of a typical tap water. Group thresholds for copper in either distilled-deionized water or mineralized water were not significantly different and ranged from 0.4 to 0.8 mg/l Cu. A difference from control test was used to assess the impact of soluble and particulate copper on taste. Soluble copper species, including free cupric ion and complexed copper species, were readily tasted, while particulate copper was poorly tasted.

A Rigorous Calculation Method for Determining Potential-pH Diagrams Part I: Copper in Aqueous Solutions of Various Complexing Agents

The main aim of this research is to determine optimal leaching conditions; Eh, pH and complexing agent concentrations, for recovery of Copper from hydroxide sludges such as those produced by electroplating shops, metal finishers, treatment of acid mine drainage, and industrial wastewater in general. This has been preceded by a theoretical approach and numerical and computer calculation. Potential-pH diagrams for the copper-water-ammonia, copper-water- cyanide, copper-water-glycine, copper-water-ethylenediamine (En) and copper-water-ethylene- diaminetetraacetic acid (EDTA) systems are derived at different total copper and complexing agent concentrations. The originality of our method is the introduction of a rigorous calculating method; we don't neglect any equilibrium or species for Eh-pH diagrams and with the free concentration of complexing agent (pL-pH) diagram to show the stable regions of soluble copper species.

Recyclable polymerization catalysts: methyl methacrylate polymerization with silica-supported CuBr–bipyridine atom transfer radical polymerization catalysts

CuBr/Bipyridine (Bpy) atom transfer radical polymerization (ATRP) catalysts are physisorbed and covalently tethered to nonporous fumed silica and are characterized by elemental analysis, thermogravimetric analysis, and UV/vis spectroscopy. The supported catalysts are used for the polymerization of methyl methacrylate (MMA), promoting the polymerization to moderate conversions with good control, with molecular weights similar to theoretical values and low polydispersity indices (PDIs). The used, Cu(II)-containing catalysts are subjected to a regeneration process with AIBN as a reductant, producing increased concentrations of Cu(I) species on the surface for the tethered system. Leaching experiments indicate that the tethered systems result in no detectable soluble copper species and that the majority of the catalytic transformations occur with sites tethered to the surface. In contrast, use of the physisorbed catalyst results in a substantial amount of leached copper species, and the soluble species are capable of controlling the polymerization in the absence of the solid, although with extremely low polymerization rates.

The effect of citrate ions on the stress corrosion cracking of Al-Brass in acidic sulphate solutions

The addition of tri-sodium citrate to acidic copper sulphate solutions produces contrasting effects on the occurrence of the stress corrosion cracking (SCC) in Al-brass. Stimulating effects are observed in a wide range of low citrate concentrations (5 × 10−6 to 10−2 M) in which the formation of Cu2O deposits is delayed or suppressed. Inhibitive effects are observed at higher citrate concentrations at which the formation of crystalline copper citrate deposits takes place. The contrasting effects produced by citrates on the corrosive process are discussed in terms of the different weight that the formation of cuprous citrate complexes can have on the activity of the soluble copper species and, consequently, on the chemical and electrochemical equilibria at the metal/solution interface.

Catalytic activity of cupric oxide in addition reactions of alkyl cyanoacetates with 1-alkenes

In the presence of cupric oxide as the catalyst, ethyl cyanoacetate reacts with 1-alkenes to form 1 : 1 adducts in high yields. The active catalytic component was found to be a soluble copper species generated in the absence of oxygen in 10-3 to 10-5 M concentrations by a partial dissolution of cupric oxide in ethyl cyanoacetate. The homogeneous catalytic reaction proceeds already at temperatures about 80 °C at a fast rate and with high selectivity. Results of inhibition experiments in the presence of α-naphthol and galvinoxyl support strongly the view on a free-radical mechanism of the addition reaction.