Raman spectroelectrochemical studies and crystal structure of a binuclear copper(I) complex with a bridging diimine ligand

Raman spectroelectrochemical and X-ray crystallographic studies have been made for the binuclear copper(I) complex, [(Ph(3)P)(2)Cu(dpq)Cu(PPh(3))(2)][BF4](2), where dpq is the bridging ligand 2,3-di(2-pyridyl)quinoxaline. The X-ray data show that the pyridine rings are twisted out of plane with respect to the quinoxaline ring which is itself non-planar. The UV/VIS spectra of the metal-to-ligand charge-transfer excited state and those of the electrochemically reduced complex are similar. The resonance-Raman spectrum of the latter species exhibits little change in the frequency of the pyridinylquinoxaline inter-ring C-C bond stretching mode, compared to the ground electronic state. This suggests minimum change in the inter-ring C-C bond order in the electrochemically or charge-transfer generated radical anion. Semiempirical molecular-orbital calculations on both the neutral dpq and radical anion show two near-degenerate lowest unoccupied orbitals in the neutral species. One is strongly bonding across the inter-ring C-C bond while the other is almost nun-bonding. The Raman data suggest that it is this latter orbital which is populated in the transient and electrochemical experiments.

Transformation of vaterite into calcite in the absence and the presence of copper(II) species. Thermal analysis, IR and EPR study

The transformation of vaterite into calcite may be performed by heating in the presence and the absence of oxygen. Vaterite remains thermally stable until a calcination temperature of 450°C. It transforms progressively to calcite up to 500°C giving two exothermic peaks: 1) at 481°C due to the transformation of vaterite surface which is in contact with a small amount of calcite phase already formed with the time on the solid surface from the humidity atmosphere; 2) at 491°C due to the transformation of pure vaterite bulk. The calcite phase remains stable until 700°C. Above this temperature the formation of CaO is observed.

A simple method for assessing copper-mediated oxidation of very-low-density lipoprotein isolated by rapid ultracentrifugation

The association of very-low-density lipoprotein (VLDL) with atherosclerosis remains controversial. However, studies have shown that oxidative modification of VLDL can promote foam cell formation, leading to the development of atherosclerosis. A rapid method is described which will allow the significance of VLDL oxidation to be assessed in clinical studies. VLDL was isolated from heparinized plasma by a 1-h, single spin ultracentrifugation. Total protein was standardized to 25 mg/L. Oxidation was promoted by the addition of copper ions (17.5 mu mol/L, final concentration) incubated at 37 degrees C. Conjugated diene production was followed at 234 nm. Total assay preparation time was 2 h. Urate greatly inhibited the oxidation of VLDL and was successfully removed by size exclusion chromatography. VLDL isolated from frozen plasma (-70 degrees C) was stable for 15 weeks. This simple, rapid method for the isolation of VLDL may be applied to assess the significance of VLDL oxidation in disease.

Facile in situ synthesis of nanofluids based on ionic liquids and copper oxide clusters and nanoparticles

Two stable nanofluids comprising of mixed valent copper(_I,_II) oxide clusters (<1 nm) suspended in 1-butyl-3-methylimidazolium acetate, [C(₄)mim][OAc], and copper(_II) oxide nanoparticles (<50 nm) suspended in trioctyl(dodecyl) phosphonium acetate, [P-₈₈₈₁₂][OAc], were synthesised in a facile one-pot reaction from solutions of copper(_II) acetate hydrate in the corresponding ionic liquids. Formation of the nanostructures was studied using ¹³C NMR spectroscopy and differential scanning calorimetry (DSC). From a solution of Cu(OAc)₂ in 1-ethyl-3-methylimidazolium acetate, [C₂mim][OAc], crystals were obtained that revealed the structure of [C₂mim][Cu₃(OAc)₅(OH)₂(H₂O)]center dot H₂O, indicating the formation of copper hydroxo-clusters in the course of the reaction. Synthesised nanostructures were studied using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Physical properties of the prepared IL-nanofluids were examined using IR and UV-VIS spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and densitometry. 

Simultaneous, long-term monitoring of valve and cardiac activity in the blue mussel Mytilus edulis exposed to copper

Valve and cardiac activity were simultaneously measured in the blue mussel (Mytilus edulis) in response to 10 d copper exposure. Valve movements, heart rates and heart-rate variability were obtained non-invasively using a Musselmonitor(R) (valve activity) and a modified version of the Computer-Aided Physiological Monitoring system (CAPMON; cardiac activity). After 2 d exposure of mussels (4 individuals per treatment group) to a range of dissolved copper concentrations (0 to 12.5 mu M as CuCl2) median valve positions (% open) and median heart rates (beats per minute) declined as a function of copper concentration. Heart-rate variability (coefficient of variation for interpulse durations) rose in a concentration-dependent manner. The 48 h EC50 values (concentrations of copper causing 50% change) for valve positions, heart rates and heart-rate variability were 2.1, 0.8, and 0.06 mu M, respectively. Valve activity was weakly correlated with both heart rate (r = 0.48 +/- 0.02) and heart-rate variability (r = 0.32 +/- 0.06) for control individuals (0 mu M Cu2+). This resulted from a number of short enclosure events that did not coincide with a change in cardiac activity. Exposure of mussels to increasing copper concentrations (greater than or equal to 0.8 mu M) progressively reduced the correlation between valve activity and heart rates (r = 0 for individuals dosed with greater than or equal to 6.3 mu M Cu2+), while correlations between valve activity and heart-rate variability were unaffected. The poor correlations resulted from periods of valve flapping that were not mimicked by similar fluctuations in heart rate or heart-rate variability. The data suggest that the copper-induced bradycardia observed in mussels is not a consequence of prolonged valve closure.

The initial mode of action of copper on the cardiac physiology of the blue mussel, Mytilus edulis

Previous studies have shown that low levels of copper (down to 0.8 muM) induce bradycardia in the blue mussel (Mytilus edulis) and that this is not caused by prolonged Valve closure. The aim of this study was to determine the precise mechanism responsible. To establish if copper was directly affecting heart cell physiology, recordings of contractions from isolated ventricular strips were made using an isometric force transducer, in response to copper concentrations (as CuCl2) ranging between 1 muM and 1 mM. Inhibition of mechanical activity only occurred at 1 mM copper, suggesting that the copper-induced bradycardia observed in whole animals cannot be attributed to direct cardiotoxicity. Effects of copper on the cardiac nerves were subsequently examined. Following removal of visceral ganglia (from where the cardiac nerves originate), exposure to 12.5 muM copper had no effect on the heart rate of whole animals. The effect of copper on the heart rate of mussels could not be abolished by depletion of the monoamine content of the animal using reserpine. However, pre-treatment of the animals with alpha -bungarotoxin considerably reduced the sensitivity of the heart to copper. These results indicated that the influence of copper on the heart of M. edulis might be mediated by a change in the activity of cholinergic nerves to heart. In the final experiments, mussels were injected with either benzoquinonium or D-tubocurarine, prior to copper exposure, in an attempt to selectively block the inhibitory or excitatory cholinoreceptors of the heart. Only benzoquinonium decreased the susceptibility of the heart to copper, suggesting that copper affects the cardiac activity of blue mussels by stimulating inhibitory cholinergic nerves to the heart. (C) 2001 Elsevier Science B.V. All rights reserved.

Preferential CO oxidation over a copper-cerium oxide catalyst in a microchannel reactor

The activity of a 5-wt% Cu/CeO2-x catalyst during preferential CO oxidation in hydrogen-rich gas mixtures was studied in a microchannel reactor. The CO concentration dropped from 1 vol.% to 10 ppm at a selectivity of 60%, at a temperature of 190 degrees C, and a weight hour space velocity (WHSV) of 55,000 cm(3) g(-1) h(-1). Both the CO concentration and the temperature increased when the WHSV was increased from 50,000 to 500,000 cm(3) g(-1) h(-1). An increase of the O-2 concentration from a 1.2 to 3 fold excess reduced the CO concentration to 10 ppm in a broad temperature interval of 50 degrees C at WHSVs up to 275,000 cm(3) g(-1) h(-1). The preferential CO oxidation could be carried out at higher flow rates and at higher selectivities in the microchannel reactor compared to a fixed-bed flow reactor. (C) 2008 Elsevier B.V. All rights reserved.