Chemistry Of Cu Research Articles

Role of Cu Oxide and Cu Adatoms in the Reactivity of CO2 on Cu(110).

We investigate the interaction of CO2 with metallic and oxidized Cu(110) surfaces using a combination of near-ambient pressure scanning tunneling microscopy (NAP-STM) and theoretical calculations. While the Cu(110) and full CuO films are inert, the interface between bare Cu(110) and the CuO film is observed to react instantly with CO2 at a 10 mbar pressure. The reaction is observed to proceed from the interfacial sites of CuO/Cu(110). During reaction with CO2, the CuO/Cu(110) interface releases Cu adatoms which combine with CO3 to produce a variety of added Cu-CO3 structures, whose stability depends on the gas pressure of CO2. A main implication for the reactivity of Cu(110) is that Cu adatoms and highly undercoordinated CuO segments are created on the Cu(110) surface through the interaction with CO2, which may act as reaction-induced active sites. In the case of CO2 hydrogenation to methanol, our theoretical assessment of such sites indicates that their presence may significantly promote CH3OH formation. Our study thus implies that the CuO/Cu(110) interfacial system is highly dynamic in the presence of CO2, and it suggests a possible strong importance of reaction-induced Cu and CuO sites for the surface chemistry of Cu(110) in CO2-related catalysis.

Role of Cu Oxide and Cu Adatoms in the Reactivity of CO2 on Cu(110)

AbstractWe investigate the interaction of CO2 with metallic and oxidized Cu(110) surfaces using a combination of near‐ambient pressure scanning tunneling microscopy (NAP‐STM) and theoretical calculations. While the Cu(110) and full CuO films are inert, the interface between bare Cu(110) and the CuO film is observed to react instantly with CO2 at a 10 mbar pressure. The reaction is observed to proceed from the interfacial sites of CuO/Cu(110). During reaction with CO2, the CuO/Cu(110) interface releases Cu adatoms which combine with CO3 to produce a variety of added Cu−CO3 structures, whose stability depends on the gas pressure of CO2. A main implication for the reactivity of Cu(110) is that Cu adatoms and highly undercoordinated CuO segments are created on the Cu(110) surface through the interaction with CO2, which may act as reaction‐induced active sites. In the case of CO2 hydrogenation to methanol, our theoretical assessment of such sites indicates that their presence may significantly promote CH3OH formation. Our study thus implies that the CuO/Cu(110) interfacial system is highly dynamic in the presence of CO2, and it suggests a possible strong importance of reaction‐induced Cu and CuO sites for the surface chemistry of Cu(110) in CO2‐related catalysis.

Ultra-pure hydrogen from chemical looping preferential oxidation of CO over a Cu–O–Ce based dual function material

Hydrogen from hydrocarbon reforming contains small amounts of CO, necessitating further purification for its use in fuel cell applications. In this work, a novel chemical looping preferential oxidation (CL-PROX) process is proposed for efficient hydrogen purification. Enabled by a Cu–O–Ce based dual function material (DFM), the process uniquely combines both catalytic CO preferential oxidation and in-situ immobilization. This results in near-complete CO conversion and < 20 ppm COx concentration with hydrogen recovery of 97 % in the purification step. Experimental characterizations indicate that CO is converted into formate and carbonate on the DFM, which can easily decompose to CO2 during the regeneration step. The interaction between copper and ceria species increased the reducibility of the DFM, as well as the CO activation and immobilization. Facile and reversible transformations between Cu2+/Ce4+ and Cu+/Ce3+ were observed throughout the reduction and re-oxidation stages. This work suggests an intensification strategy for selective hydrogen purification, and provides insights into the redox chemistry of Cu–O–Ce DFMs.

Probing the Bioinorganic Chemistry of Cu(I) with 111Ag Perturbed Angular Correlation (PAC) Spectroscopy

The two most common oxidation states of copper in biochemistry are Cu(II) and Cu(I), and while Cu(II) lends itself to spectroscopic interrogation, Cu(I) is silent in most techniques. Ag(I) and Cu(I) are both closed-shell d10 monovalent ions, and to some extent share ligand and coordination geometry preferences. Therefore, Ag(I) may be applied to explore Cu(I) binding sites in biomolecules. Here, we review applications of 111Ag perturbed angular correlation (PAC) of γ-ray spectroscopy aimed to elucidate the chemistry of Cu(I) in biological systems. Examples span from small blue copper proteins such as plastocyanin and azurin (electron transport) over hemocyanin (oxygen transport) to CueR and BxmR (metal-ion-sensing proteins). Finally, possible future applications are discussed. 111Ag is a radionuclide which undergoes β-decay to 111Cd, and it is a γ-γ cascade of the 111Cd daughter nucleus, which is used in PAC measurements. 111Ag PAC spectroscopy may provide information on the coordination environment of Ag(I) and on the structural relaxation occurring upon the essentially instantaneous change from Ag(I) to Cd(II).

Stability and Reversible Oxidation of Sub-Nanometric Cu5 Metal Clusters: Integrated Experimental Study and Theoretical Modeling.

Sub-nanometer metal clusters have special physical and chemical properties, significantly different from those of nanoparticles. However, there is a major concern about their thermal stability and susceptibility to oxidation. In situ X-ray Absorption spectroscopy and Near Ambient Pressure X-ray Photoelectron spectroscopy results reveal that supported Cu5 clusters are resistant to irreversible oxidation at least up to 773 K, even in the presence of 0.15 mbar of oxygen. These experimental findings can be formally described by a theoretical model which combines dispersion-corrected DFT and first principles thermochemistry revealing that most of the adsorbed O2 molecules are transformed into superoxo and peroxo species by an interplay of collective charge transfer within the network of Cu atoms and large amplitude "breathing" motions. A chemical phase diagram for Cu oxidation states of the Cu5 -oxygen system is presented, clearly different from the already known bulk and nano-structured chemistry of Cu.

Aquatic photochemistry of Cu(II) in the presence of As(III): Mechanistic insights from Cu(III) production and As(III) oxidation under neutral pH conditions

Surface complexation between arsenite (As(III)) and colloidal metal hydroxides plays an important role not only in the immobilization and oxidation of As(III) but also in the cycle of the metal and the fate of their ligands. However, the photochemical processes between Cu(II) and As(III) are not sufficiently understood. In this work, the photooxidation of As(III) in the presence of Cu(II) under neutral pH conditions was investigated in water containing 200 μM Cu(II) and 5 μM As(III) under simulated solar irradiation consisting of UVB light. The results confirmed the complexation between As(III) and Cu(II) hydroxides, and the photooxidation of As(III) is attributed to the ligand-to-metal charge transfer (LMCT) process and Cu(III) oxidation. The light-induced LMCT process results in simultaneous As(III) oxidation and Cu(II) reduction, then produced Cu(I) undergoes autooxidation with O2 to produce O2•⁻ and H2O2, and further the Cu(I)-Fenton reaction produces Cu(III) that can oxidize As(III) efficiently (kCu(III)+As(III) = 1.02 × 109 M–1 s–1). The contributions from each pathway (ρrCu(II)-As(III)+hv = 0.62, ρrCu(III)+As(III) = 0.38) were obtained using kinetic analysis and simulation. Sunlight experiments showed that the pH range of As(III) oxidation could be extended to weak acidic conditions in downstream water from acid mine drainage (AMD). This work helps to understand the environmental chemistry of Cu(II) and As(III) regarding their interaction and photo-induced redox reactions.

Generation and Aerobic Oxidative Catalysis of a Cu(II) Superoxo Complex Supported by a Redox-Active Ligand.

Cu systems feature prominently in aerobic oxidative catalysis in both biology and synthetic chemistry. Metal ligand cooperativity is a common theme in both areas as exemplified by galactose oxidase and by aminoxyl radicals in alcohol oxidations. This has motivated investigations into the aerobic chemistry of Cu and specifically the isolation and study of Cu-superoxo species that are invoked as key catalytic intermediates. While several examples of complexes that model biologically relevant Cu(II) superoxo intermediates have been reported, they are not typically competent aerobic catalysts. Here, we report a new Cu complex of the redox-active ligand tBu,TolDHP (2,5-bis((2-t-butylhydrazono)(p-tolyl)methyl)-pyrrole) that activates O2 to generate a catalytically active Cu(II)-superoxo complex via ligand-based electron transfer. Characterization using ultraviolet (UV)-visible spectroscopy, Raman isotope labeling studies, and Cu extended X-ray absorption fine structure (EXAFS) analysis confirms the assignment of an end-on κ1 superoxo complex. This Cu-O2 complex engages in a range of aerobic catalytic oxidations with substrates including alcohols and aldehydes. These results demonstrate that bioinspired Cu systems can not only model important bioinorganic intermediates but can also mediate and provide mechanistic insight into aerobic oxidative transformations.

CO Hydrogenation to Methanol over Cu/MgO Catalysts and Their Synthesis from Amorphous Magnesian Georgeite Precursors

AbstractThe synthesis of Mg‐substituted copper hydroxycarbonates by constant‐pH co‐precipitation with subsequent ageing of the precipitate has been studied in detail. This allowed the retrieval of crystalline magnesian malachite samples, which showed a “radical‐sign‐shaped” pH drop and the blue/green color change during ageing that is well‐known from the analogous Cu/Zn system. The crystallization of Cu‐rich samples has been studied elaborately by means of powder diffraction, pair distribution function (PDF), and infrared spectroscopy, thus elucidating the ageing chemistry of Cu,Mg hydroxycarbonates in general. It was found that up to 17 % Mg can be incorporated into the crystalline malachite using a synthesis route comparable to that established for Cu/ZnO catalysts, but with drastically elongated precipitate ageing times. For higher Mg contents, a step‐like pH drop was observed instead, and an amorphous variant of the hydroxycarbonate, referred to as “magnesian georgeite”, could be isolated. From such a Mg‐rich sample (Cu/Mg 70 : 30 at. %), a Cu/MgO catalyst has been prepared that shows high activity and good stability in CO hydrogenation to methanol over 800 hrs. time on stream.

Characterization of Chalkophomycin, a Copper(II) Metallophore with an Unprecedented Molecular Architecture.

Metals play essential roles in life by coordination with small molecules, proteins, and nucleic acids. Although the coordination of copper ions in many proteins and methanobactins is known, the coordination chemistry of Cu(II) in natural products and their biological functions remain underexplored. Herein, we report the discovery of a Cu(II)-binding natural product, chalkophomycin (CHM, 1), from Streptomyces sp. CB00271, featuring an asymmetric square-coordination system of a bidentate diazeniumdiolate and a conjugated 1H-pyrrole 1-oxide-oxazoline. The structure of 1 may inspire the synthesis of Cu(II) chelators against neurodegenerative diseases or Cu(II)-based antitumor therapeutics.

Correlation of the mechanical properties of Cu/C composite materials with the chemistry of Cu C interfacial zone

In the frame of thermal management applications, copper metal matrix reinforced by carbon fibers (CF) are undoubtedly one of the most promising composites for heat sinks. In this work, two types of composite materials were produced: Cu(CuTi)x/CF composites fabricated with a mixture of Cu and CuTi powders by a solid-liquid co-existent phase process and Cu/CF composites fabricated without the CuTi powder. The mechanical properties and post-deformation microstructures of both composite materials have been investigated. Compression tests were performed at room temperature under constant strain-rate deformation condition. Elastic properties were examined using a dynamic resonant method over the temperature range 20 °C - 250 °C. The results show that the addition of Ti and the resulting formation of the TiC interphase at the Cu-CF interfaces are able to create strong interfacial bonding evidenced by a deformation without pull-out. When the volume fraction of CFs reaches 40%, crack percolation occurs in the Cu(CuTi)/CF composite leading to the sample ruin in case of strong interfaces. In the case of Cu/CF, fiber pull-out allows for deformation.

Silver in biology and medicine: opportunities for metallomics researchers.

The antibacterial properties of silver have been known for centuries and the threat of antibiotic-resistant bacteria has led to renewed focus on the noble metal. Silver is now commonly included in a range of household and medical items to imbue them with bactericidal properties. Despite this, the chemical fate of the metal in biological systems is poorly understood. Silver(I) is a soft metal with high affinity for soft donor atoms and displays much similarity to the chemistry of Cu(I). In bacteria, interaction of silver with the cell wall/membrane, DNA, and proteins and enzymes can lead to cell death. Additionally, the intracellular generation of reactive oxygen species by silver is posited to be a significant antimicrobial action. While the antibacterial action of silver is well known, bacteria found in silver mines display resistance against it through use of a protein ensemble thought to have been specifically developed for the metal, highlighting the need for judicious use. In mammals, ∼10-20% of ingested silver is retained by the body and thought to predominantly localize in the liver or kidneys. Chronic exposure can result in argyria, a condition characterized by blue staining of the skin, resulting from subdermal deposition of silver [as Ag(0)/sulfides], but more insidious side effects, such as inclusions in the brain, seizures, liver/kidney damage, and immunosuppression, have also been reported. Here, we hope to highlight the current understanding of the biological chemistry of silver and the necessity for continued study of these systems to fill existing gaps in knowledge.

Copper(II) Binding to PBT2 Differs from That of Other 8-Hydroxyquinoline Chelators: Implications for the Treatment of Neurodegenerative Protein Misfolding Diseases.

PBT2 (5,7-dichloro-2-[(dimethylamino)methyl]-8-hydroxyquinoline) is a small Cu(II)-binding drug that has been investigated in the treatment of neurodegenerative diseases, namely, Alzheimer's disease (AD). PBT2 is thought to be highly effective at crossing the blood-brain barrier and has been proposed to exert anti-Alzheimer's effects through the modulation of metal ion concentrations in the brain, specifically the sequestration of Cu(II) from amyloid plaques. However, despite promising initial results in animal models and in clinical trials where PBT2 was shown to improve cognitive function, larger-scale clinical trials did not find PBT2 to have a significant effect on the amyloid plaque burden compared with controls. We propose that the results of these clinical trials likely point to a more complex mechanism of action for PBT2 other than simple Cu(II) sequestration. To this end, herein we have investigated the solution chemistry of Cu(II) coordination by PBT2 primarily using X-ray absorption spectroscopy (XAS), high-energy-resolution fluorescence-detected XAS, and electron paramagnetic resonance. We propose that a novel bis-PBT2 Cu(II) complex with asymmetric coordination may coexist in solution with a symmetric four-coordinate Cu(II)-bis-PBT2 complex distorted from coplanarity. Additionally, PBT2 is a more flexible ligand than other 8HQs because it can act as both a bidentate and a tridentate ligand as well as coordinate Cu(II) in both 1:1 and 2:1 PBT2/Cu(II) complexes.

Thiosulphate leaching of gold in the Cu–NH3–S2O32−–H2O system: An updated thermodynamic analysis using predominance area and species distribution diagrams

Thiosulphate, as an environmentally friendly lixiviant, is currently identified as the most promising alternative to cyanide for the extraction of gold from ores in sensitive locations. The Cu(II) ammine complexes acts as the catalytic oxidant to increase the thiosulphate leaching rate of gold, which also causes an undesirable high consumption of thiosulphate. Due to the complex solution chemistry of Cu–NH3–S2O32−–H2O system, fundamentally supported mechanisms to justify the catalytic effects and the consumption of thiosulphate are yet to be developed. Thermodynamic analysis offers essential information on which chemical species that could form and how these species influence the solution chemistry under various conditions. In this paper, predominance area and species distribution diagrams for gold leaching in the Cu–NH3–S2O32−–H2O system were constructed from a series of calculations using updated thermodynamic data. The diagrams reveal insights into the thermodynamics of gold dissolution, thiosulphate stability and redox behaviour of Cu(II)/Cu(I) couples. Analysis of the results presented in this paper can provide a theoretical basis for the complex thiosulphate leach solution chemistry that allows for a better understanding on the relationships between the redox behaviour of Cu(II)/Cu(I) couples and the behaviours of gold leaching and thiosulphate decomposition.

Copper Catalyzed Autoxidation of Sulphur Dioxide and Inhibition by Methanoic Acid

Background:: Today, acid rain problem is one of the serious global problems to the environment in which pH of the rain water decreases, causing harmful effect to nature, buildings, monuments, vegetation and human being as well. Therefore, the objective of the paper to find out some organic inhibitors present in the atmosphere that inhibited the acid rain. Objective:: In this paper, we studied the chemistry of Cu (II)-methanoic acid-S(IV)-O2 in acetate buffered medium by earlier reported methods in literature. Gravimetric analysis was carried out to find the end product and confirmed that it was sulphate with 98 % recovery. Methods:: Experiments were carried out at 303 ≤ T/K ≤ 313, 4.0 ≤ pH ≤ 5.35, 1.0×10−3 mol/dm3 ≤ S(IV) ≤ 10.0×10−3 mol/dm3, 5×10−6 mol/dm3 ≤ [Cu(II)] ≤ 2.5×10−5 mol/dm3, 6×10−6 mol/dm3≤[methanoic acid]≤7×10-4 mol/dm3. The value of apparent activation energy and inhibition parameter B was calculated in the presence of methanoic acid found as 29.07 kJ mol-1and 3.18 x 103 mol dm-3, respectively. The thermodynamic parameters were found as frequency factor (1.59 x 10-6s-1), entropy (-358.92 J K-1 mol-1), enthalpy (20.97 k J mol-1), and Gibbs free energy (172.83k J mol-1), respectively. Results:: We observed that methanoic acid acts as an inhibitor in copper catalyzed autoxidation of SO2 in acidic medium. Therefore, on the basis of the observed results a free radical mechanism has been identified. The results are useful for modeling rain water acidity and therefore a great use of meteorology and atmospheric chemistry. This study is important in understanding the mechanism of the oxidation of S(IV) by O2. Conclusion:: This study suggests that since organic inhibitors are found in the atmosphere, their concentrations and their influence on the oxidation of aqueous SO2 should be taken into account. The intervention of methanoic acid in the autoxidation of aqueous SO2 plays a role in deciding the fate of both methanoic acid and SO2. The influence of inhibitors may be used to calculate the lifetime of SO2, Methanoic acid has high values of kinh and, therefore, it would be degraded by sulfate radical anions in atmospheric waters.

Unusual chemistry of Cu(ii) salan complexes: synthesis, characterization and superoxide dismutase activity

Cu(ii)-salan complexes: structural and spectral characterization, solvent assisted ring cleavage and correlation of superoxide dismutase activity with cyclic voltammetry data and steric effects.

Role of oligomer structures in the surface chemistry of amidinate metal complexes used for atomic layer deposition of thin films

Abstract

Identification of a haptoglobin-hemoglobin complex in human blood plasma

Blood plasma metalloproteins that contain copper (Cu), iron (Fe), zinc (Zn) and/or other metals/metalloids are potential disease biomarkers because the bloodstream is in permanent contact with organs. Their quantification and/or the presence of additional metal-entities or the absence of certain metalloproteins in blood plasma (e.g. in Wilson's disease) may provide insight into the dyshomeostasis of the corresponding metal (s) to gain insight into disease processes. The first step in investigating if the determination of plasma metalloproteins is useful for the diagnosis of diseases is their definitive qualitative identification. To this end, we have added individual highly pure Cu, Fe or Zn-containing metalloproteins to plasma (healthy volunteer) and analyzed this mixture by size-exclusion chromatography (SEC) coupled to an inductively coupled plasma atomic spectrometer (ICP-AES), simultaneously monitoring the emission lines of Cu, Fe and Zn. The results clearly identified ceruloplasmin (Cp), holo-transferrin (hTf), and α2-macroglobulin (α2M), which verifies our previous assignments. Interestingly, another major Fe-peak in plasma was identified as a haptoglobin (Hp)-hemoglobin (Hb) complex. This Hp-Hb complex is formed after Hb, which is released during the hemolysis of erythrocytes, binds to the plasma protein Hp. The Hp-Hb complex formation is known to be one of the strongest interactions in biochemistry (Kd≈1pmol/L) and is critical because it prevents kidney toxicity of free Hb. Hence, the simultaneous determination of Cp, hTf, α2M and the Hp-Hb complex in plasma in <25min has the potential to provide new insight into disease processes associated with the bioinorganic chemistry of Cu, Fe and Zn.

Copper-Promoted Functionalization of Organic Molecules: from Biologically Relevant Cu/O2 Model Systems to Organometallic Transformations.

Copper is one of the most abundant and less toxic transition metals. Nature takes advantage of the bioavailability and rich redox chemistry of Cu to carry out oxygenase and oxidase organic transformations using O2 (or H2O2) as oxidant. Inspired by the reactivity of these Cu-dependent metalloenzymes, chemists have developed synthetic protocols to functionalize organic molecules under enviormentally benign conditions. Copper also promotes other transformations usually catalyzed by 4d and 5d transition metals (Pd, Pt, Rh, etc.) such as nitrene insertions or C-C and C-heteroatom coupling reactions. In this review, we summarized the most relevant research in which copper promotes or catalyzes the functionalization of organic molecules, including biological catalysis, bioinspired model systems, and organometallic reactivity. The reaction mechanisms by which these processes take place are discussed in detail.

Antimicrobial Titanium Surface via Click-Immobilization of Peptide and Its in Vitro/Vivo Activity.

The use of antimicrobial peptides (AMPs)-functionalized titanium implants is an efficient method for preventing bacterial infection. However, the attachment of AMPs to the surface of titanium implants remains a challenge. In this study, a "clickable" titanium surface was developed by using a silane coupling agent with an alkynyl group. The antimicrobial titanium implant was then constructed through the reaction between the "clickable" surface and azido-AMPs (PEG-HHC36:N3-PEG12-KRWWKWWRR) via click chemistry of Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). Such an antimicrobial titanium implant, with an AMP density of 897.4 ± 67.3 ng/cm2 (2.5 ± 0.2 molecules per nm2) on the surface, exhibited good and stable antimicrobial activity, inhibited 90.2% of Staphylococcus aureus and 88.1% of Escherichia coli after 2.5 h of incubation, and even inhibited 69.5% of Staphylococcus aureus after 4 days of degradation. The CCK-8 assay indicated that the antimicrobial titanium implant exhibited negligible cytotoxicity to mouse bone mesenchymal stem cells. In vivo assay illustrated that this implant could kill 78.8% of Staphylococcus aureus after 7 days. This method has great potential for the preparation of antimicrobial titanium implants and the prevention of infections in the clinic.

Structure and Chemistry of Cu–Fe–Al Nanocomposite Catalysts for CO Oxidation

High-active Fe–Al and Cu–Fe–Al nanocomposite catalysts were synthesized by fusion of aluminium, iron, and copper salts and then tested in the oxidation of CO. It was found that the activity of Fe–Al catalysts depends on the Fe concentration and the maximum is achieved when the Fe2O3 content is approximately 82 wt%. The addition of Cu leads to a significant increase in activity. Using adsorption techniques, X-ray diffraction, X-ray absorption spectroscopy, and Fourier-transform infrared spectroscopy, morphology, structure, and chemistry of the catalysts were studied. It was shown that the Fe–Al catalysts consist of Fe2O3 and Al2O3 phases mainly. Alumina is in an amorphous state whereas iron oxide forms nanoparticles with the protohematite structure. The Al3+ cations partially dissolute in the Fe2O3 lattice. X-ray absorption spectroscopy indicated that the Cu–Fe–Al catalysts in addition contain CuO and CuFe2O4 oxides in an amorphous state.