Inactivation of acetyl-CoA synthase/carbon monoxide dehydrogenase by copper

Two recent crystal structures of acetyl-CoA synthase (ACS) from Moorella thermoacetica exhibited different metal contents and geometries at their active site, called the A-cluster. This led to the proposal of two catalytic mechanisms, one Ni-based, the other Cu-based. ACS was studied with respect to synthase activity, methyl group transfer activity, metal content, and EPR spectroscopy. Our results indicate that Cu is not required for catalysis and that it inactivates ACS by binding to the proximal site of the A-cluster. With Cu in this site, the A-cluster cannot accept a methyl group from the corrinoid-iron-sulfur protein, nor can it exhibit the NiFeC EPR signal after treatment with CO.     

Activation of carbon dioxide and carbon monoxide at aluminium surfaces

Dynamic photoelectron spectroscopy has shown that the adsorption of carbon dioxide at aluminium surfaces is followed by a dissociative reaction leading to the formation of a metastable surface carbonate in the temperature range 80-120 K. The carbonate is subsequently reduced (120–475 K) (deoxygenated) to generate two different forms of surface carbon, one carbidic C^δ- (a) and the other less ionic C⁰(a) possibly graphitic. Quantification of the C(ls) and O(ls) spectra enable each of the species O^2-(a), CO₃^2-(a), C^δ-(a) and C⁰ (a) to be distinguished and their surface concentrations calculated over a wide temperature range. The temperature and pressure dependences of CO₂ reduction suggest the participation of a precursor dimer state (CO₂^---CO₂)(a) which then disproportionates. Furthermore studies of the coadsorption of ammonia and carbon dioxide in analogous systems indicate that a discrete and specifically reactive species, O^- (s), is formed during carbonate formation. The results are discussed in the context of recent theoretical studies of FREUND and MESSMER and also comparisons made with metal-CO₂ complexes.The facile surface reduction of CO₂ via a surface carbonate suggested that a possible route to carbon-oxygen bond cleavage in carbon monoxide interaction with an sp-metal surface (aluminium) was a step-wise oxidation to CO₂ leading to surface carbonate which was then readily deoxygenated. Studies of carbon monoxide: dioxygen mixtures (100: I) confirmed that this indeed occurred. A modified ELEY-RIDEAL type mechanism involving a hopping "non-adsorbed" CO molecule and a short-lived surface O^- (s) species is suggested.     

Synthesis and properties of copolymers of ethylene/carbon monoxide with styrene/carbon monoxide

The terpolymerization of ethylene, styrene, and carbon monoxide was accomplished by two different palladium‐based catalysts: a phosphine‐based ligand system and a nitrogen‐based ligand system. The range of possible compositions and the composition dependence of the properties of the resulting polymers were determined. These polymers were essentially carbon monoxide versions of the ethylene styrene interpolymers recently presented by Dow. A comparison between the two families of polymers is attempted. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 752–757, 2000     

Coadsorption of carbon monoxide and copper atoms on rhodium electroplates

The partial removal of copper atoms from a preliminarily formed Cu_ad layer and the adsorption of Cu²⁺ cations in the presence of a CO_ads monolayer were demonstrated for Rh/Pt electrodes by means of transients of current and potentiodynamic and analytical measurements. The electrooxidation of the mixed CO_ads + Cu_ad layer in the course of anodic potential scans is shown to be accompanied by simultaneous removal of both species in a wide potentials range.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 367–370.Original Russian Text Copyright © 2005 by Gladysheva, Podlovchenko.     

Simultaneous adsorption and dechlorination of carbon tetrachloride using copper nanoparticles@graphene oxide composites

Cu nanoparticles@graphene oxide composites (CGC) were synthesized by a simplistic and effective chemical reduction method. The resulting CGC composites were characterized by X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, transmission electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis. The performance of the CGC composites for dechlorination of carbon tetrachloride was evaluated. The batch investigations indicated that carbon tetrachloride could be almost completely removed by CGC after 75 min. The adsorption isotherm was also discussed. The high removal capacities of CGC with respect to the bare nanoscale zerovalent copper owe to the increased adsorption sites in the composites that are resulted from aggregation inhibition, which leads to the reduced Cu nanoparticles size.     

Haems as potential reagents for carbon monoxide

A study of the potential of a myoglobin model system based on dipiperidyltetraphenylporphinatoiron(II) for the spectrophotometric determination of carbon monoxide is reported. At room temperature, oxygen does not bind strongly at the iron centre and does not interfere. Nitric oxide, hydrogen sulphide and carbon dioxide interfere and must be removed before the determination if present in significant amounts. The main disadvantage of this novel method is the low sensitivity (about 300 ppm CO). Possible means of modifying the system to enhance the sensitivity and to further reduce the number of interfering species are discussed.     

Polyethylene powder as an absorbent for preconcentration of aluminium, beryllium and thallium

Polyethylene powder has been shown to function effectively as an adsorbent for the preconcentration of complexing agents and their metal complexes. The adsorbed trace compound can easily be eluted from the polyethylene by use of polar organic solvents and subsequently be determined by AAS or spectrophotometry. In this paper, the adsorptivity of chrome azurol S and rhodamine B and their complexes with aluminium, beryllium and thallium (as [Tl Br₄]^–) on polyethylene was investigated. The influence of the pH and the effect of the saline concentration of the solution were studied. From the preconcentration of aluminium and beryllium with chrome azurol S, enrichment factors up to 10 and 20, respectively, could be achieved. For thallium with rhodamine B the factor was 50. With this analytical procedure, recoveries of 92–110%, 94–103% and 96–104% with relative standard deviations of 3.4–5.4%, 2.6–5.3 and 1.6–7.2% for aluminium, beryllium and thallium respectively, were achieved. The method was used for the preconcentration of trace amounts of the metals from tap water, dialysis solutions and solid salts.     

Palladium-catalyzed addition reaction of olefins,carbon tetrachloride and carbon monoxide in alcohols to give 2-alkyl-4,4,4-trichlorobutanoates

Pd(OAc)₂ combined with PPh₃ is a good catalyst for the addition reaction of CCl₄ and CO to olefins in ethanol to afford ethyl 2-alkyl-4,4,4-trichlorobutanoates. The esters were obtained in satisfactory yields when the reaction was carried out at 50° in the presence of K₂CO₃ under CO pressure.     

Oxidation of carbon monoxide over a copper(II) oxide catalyst

Transient FTIR observations in conjuction with gas phase CO conversion measurements indicate an adsorbed CO species which seems not to participate directly in the oxidation reaction over a silica supported copper(II) oxide catalyst. This observation together with order of reaction determinations suggest that oxidation occurs via an Eley-Rideal mechanism.

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CO CO, (II), . , , , -.

     

Electroreduction of carbon monoxide on palladium electrodeposits in solutions containing copper ions

It is shown that the electroreduction of CO proceeds on electrolytic deposits of palladium (edPd) in 0.5 M H₂SO₄ + (1–5) mM CuSO₄ + CO(sat) solutions at the potentials more positive than the Cu²⁺/Cu equilibrium potential. Among the CO reduction products, methanol and formaldehyde are identified. The current efficiency with respect to CH₃OH exceeds 75% on edPd formed in 1% PdCl₂+0.5 M H₂SO₄ solutions. In addition, Cu⁺ ions, which probably form complexes with CO, are detected in the solution and are assumed to play the role of intermediate species in the mediator catalysis along with copper adatoms.     

Cobalt promoted copper manganese oxide catalysts for ambient temperature carbon monoxide oxidation

Low levels of cobalt doping (1 wt%) of copper manganese oxide enhances its activity for carbon monoxide oxidation under ambient conditions and the doped catalyst can display higher activity than current commercial catalysts.     

State of the copper ions in the catalysts for oxidation of carbon monoxide to carbon dioxide

The state of the copper ions in the catalysts for the oxidation of carbon monoxide to carbon dioxide, prepared by dissolving an activated copper-containing aluminum alloy in water followed by calcination (method A) and by impregnation of the support produced by dissolving activated aluminum in water with copper nitrate solution (method B), was investigated by diffuse reflection electronic spectroscopy. It was established that the catalysts contain Cu ²⁺ ions stabilized in fields of octahedral symmetry. The concentration of these ions depends on the method of synthesis of the catalyst, its copper content, and the pretreatment temperature. It is higher in the samples produced by impregnation than in the samples produced by fusion; increase in the amount of copper leads to a decrease while increase in the calcination temperature leads to an increase in the concentration of the above-mentioned ions. Treatment of the oxide systems with the reaction mixture does not affect the state and concentration of Cu ²⁺. The catalytic activity of the samples depends on the method of preparation and increases with decrease in the amount of Cu ²⁺ (O_h) and with increase in the content of the CuO phase in the system.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 786–790, April, 1992.     

Mechanochemical synthesis of calcium and copper ferrite catalysts for medium-temperature carbon monoxide conversion

The mechanochemical synthesis of calcium and copper ferrites has been investigated by X-ray powder diffraction, X-ray crystallography, thermogravimetric analysis, IR spectroscopy, sedimentation analysis, and chromatography. The effects of mechanical activation and heat treatment on the formation of calcium ferrite with a perovskite structure and copper ferrite with a mixed spinel structure are demonstrated. Calcium and copper ferrites calcined at low temperatures (450–500°C) are catalytically very active in the water-gas shift reaction. CO conversion on calcium and copper ferrites yields a number of by-products. The concentrations of these by-products in the condensate have been determined.     

Robust copper nanocrystal/nitrogen-doped carbon monoliths as carbon monoxide-resistant electrodes for methanol oxidation reaction

Noble metal-based electrocatalysts present high activities for methanol oxidation reaction (MOR),but are limited by their high cost,low stability and poor resis...     

Reduction of nitrobenzene catalyzed by immobilized copper catalyst under carbon monoxide and water

Catalytic activity for reduction of nitrobenzene to aniline (98%) and azobenzene (2%) using a poly(4-vinylpyridine)-immobilized Cu catalyst [Cu(II)/P(4-VP)] under a CO atmosphere in aqueous 2-ethoxyethanol was studied as a function of the various reaction parameters ([Cu], P(CO), T, and nitrobenzene/Cu molar ratio). Reaction rates were first-order in [Cu]_tot over 1.0–12.0?wt.% range and in P(CO) over the 6.8–27.2?atm range. The catalytic activity proved to be non-linear in nitrobenzene/Cu ratio over 41–500 molar ratio range. These results suggest that the rate-limiting step is preceded by reversible coordination of nitrobenzene to a carbonyl–Cu(I) immobilized species. A catalytic mechanism consistent with the data is proposed.     

Photoelectric properties of aluminium/copper phthalocyanine/gold photovoltaic cells

Solid-state photovoltaic cells based on the semiconductor copper phthalocyanine depend on the presence of dopants for their operation. Electronegative dopants such as oxygen, iodine and water form trap levels in the semiconductor, which aid the dissociation of photoproduced excited states into charge carriers. The cross section for this reaction has been estimated to be about the same as the molecular cross section of phthalocyanine.     

Preparation and characterization of silicon monoxide/graphite/carbon nanotubes composite as anode for lithium-ion batteries

Silicon monoxide/graphite/multi-walled carbon nanotubes (SiO/G/CNTs) material was prepared by ball milling followed by chemical vapor deposition method and characterized by X-ray diffraction, scanning electron microscopy (SEM), galvanostatic charge–discharge, and AC impedance spectroscopy, respectively. The results revealed that SiO/G/CNTs exhibited an initial specific discharge capacity of 790 mAh g⁻¹ with a columbic efficiency of 65%. After 100 cycles, a high reversible capacity of 495 mAh g⁻¹ is still retained. The improved electrochemical properties were due to beneficial SEI by the SEM and EIS results.     

Substitution of silver for copper in the binuclear Mo/Cu center of carbon monoxide dehydrogenase from Oligotropha carboxidovorans

Carbon monoxide dehydrogenase from Oligotropha carboxidovorans catalyzes the aerobic oxidation of carbon monoxide to carbon dioxide, providing the organism both a carbon source and energy for growth. The active site of the native enzyme is a unique binuclear molybdenum- and copper-containing center. Here we show that silver can be substituted for copper in the active site to yield a functional enzyme. The characteristic hyperfine coupling of the I = ? nucleus of Ag is evident in the EPR signal of the binuclear active site observed upon reduction with CO, indicating both the incorporation of silver into the active site and, remarkably, retention of the catalytic activity. The silver-substituted enzyme is reduced by CO with an observed limiting rate constant of 8.1 s(-1), which can be compared with the value of 51 s(-1) for the wild-type enzyme. Steady-state kinetics for the Ag-substituted enzyme yielded k(cat) = 8.2 s(-1) and K(m) = 2.95 μM at pH 7.2.