Showing papers on "Copper published in 1971"

Thermal decomposition of vinylic copper(I) and silver(I) organometallic compounds

Abstract: The thermal decomposition of cis-and tans-l-propenylcopper(I) and cis-and. trctns-l-propenyl(tri-n-butylphosphine)copper(t) yields copper(O) and 2.4-hexadienes with i.t.niion of configuration at the olefinic double bcnds. This stereochemical result, when interpreted in light of the known rate of inversion of configuration of vinylradicirl, is sufhcic'nt to establish that free propenyl radicais are not intermediates in these thermal coupling re-ttctions. A comparison of the retention of stereochemistry observed on decomposition of the analogous 2-butenyl-copper(t) and-silver([) compounds with the complete loss of stereochcmistry; observed on reduction of cis-and rruns-2-bromo-2-butene with tri-n-butyltin hydride undcr free-radical conditions qualitatively supports a similar conclusion. A sltrvey of the yietd and stcreochcmistry of the conversion of trun.t-propt-'nyllithium to 2.4-hexadienes on oxidation rvith a variety of transition metalsalts suggests that frec propenytradicais atio arc not inv,olved in these co uplings. fhe reaction of arylrlagnesium and-lithiunr re-I *gents wirh transition nretal halides is widely usecl s.v\"ntheticerlly as a nlerhod lor preparing biarvls.r-; Thesc reactions are believed in most instances to irrvolve transitiorr metal aryls as internrecliates; the isolatecl products result fronr the rapid decomposition of these thermally unstable intermediates under the conditions of the reactions. Alttrough idenrification of the inrer-nrediare orgirnometallic conlpounds in these reactions and independent derlonstration that their thernral decomposition yields coupleci proc-luct have proved possible in special cases,','6 in general the thermal stability of transition metal organometallic compounds has ap-pearc'd suftrciently low to discourage attenrpts to examine the mechanisnrs of this interesting crass of coupling reactions in detail. A number of studies have establisheci copper(l) and silv'er([) as among the nlost usefur oi the transition nretals for the oxidative coupling of arvl and vinylic Grignard reagents.s'7-rr During these studies several-qroups have prepared and characterizecl authentic aromatic and vinylic organonretallic compounds of these me[als.'-r'r The thernial stability of this class of compounds , although low conrpared with the stabilities ol nrain group organometallic cotltpounds, appeared tu Lrs to be sullicient to make a derailed investigation ot' the ir thernral decom position a practical enterprisc. Therefore. in consequence of our in[erest in the mechanisms and synthetic applicarions oi the Ullman and related coupling reactions,r{-r6 as well as in the variety ttt-other organic reactions catalyzeci by compounds of copper .''t'17 we have examined the mechanism of thermal decomposition of vinylic copper(l) and silver(l) organo-metallic conrpounds to butadiene s. A question of fundamental interest in discussion ot' these reactions concerns the mechanism of the step in which the carbon-metal bond is broken and the …

Neonatal copper deficiency.

Abstract: PURE copper deficiency in man has probably never been observed. When it occurs other deficiencies complicate the picture. In infants, a disorder characterized by hypocupremia, hypoferremia, neutrop...

The computed distribution of copper(II) and zinc(II) ions among seventeen amino acids present in human blood plasma.

Abstract: The equilibrium distribution of copper(II) and zinc(II) ions among a mixture of 17 amino acids has been computed from stability-constant and blood-plasma-composition data. At pH7.4, 98% of the copper(II) in the simulated plasma solution is co-ordinated to histidine and cystine, predominantly as the mixed-ligand complexes [Cu.His.Cystine](-) and [Cu.H.His.Cystine]. Approximately half of the zinc(II) is co-ordinated to cysteine and histidine, but appreciable complex-formation occurs with most of the other amino acids. Stability constants are given for copper(II) and zinc(II) amino acid complexes, including some mixed-ligand species, at 37 degrees C and I=0.15m.

Benzotriazole as Corrosion Inhibitor for Copper

Abstract: The effect of benzotriazole (BTA) on corrosion of copper in 5% NaCl has been studied by immersion tests, potentiostatic polarization, AC impedance measurements, and ellipsometric investigations. It was found that BTA when present in the corrosive environment is a good inhibitor. The good electronic conductivity of the film formed on copper, the decreased double capacity, small film thickness, and decreased current on anodic polarization curves indicate that BTA is chemisorbed on the surface. This prevents adsorption of oxygen and formation of a prenucleation layer which is the forerunner of oxide formation. Discrepancies with results obtained by other investigators using infrared reflectance techniques are discussed.

The weak beam technique as applied to the determination of the stacking-fault energy of copper

Abstract: The weak beam technique is used to obtain a value for the stacking-fault energy of copper. The observed partial dislocation image spacings are compared with many-beam computational models and it is demonstrated that anisotropic elasticity theory breaks down for small partial dislocation spacings in copper.

Native Copper, Silver, and Gold Accessible to Early Metallurgists

Abstract: The weathered zones of ore deposits, which no longer exist, are reconstructed by inference to provide estimates of relative abundances of usable nuggets of native copper, silver, and gold in ancient times. New analyses and selected data from the literature summarize metallic impurities in native copper, silver, gold, and lead and in the oxidized copper minerals, oxide, silicate, carbonate, chloride, and sulfate, together with impurities in lead carbonate and silver halide minerals. The influence that these occurrences and compositions exerted upon the origin and development of metallurgy in Mesoamerica and South America is discussed in relation to new analyses of artifacts and selected data from the literature. Topics emphasized are: the discovery of smelting and melting by the Moche; the inability of New World metallurgists to smelt copper from sulfide ores or silver from lead ores; and the lack of influence by transoceanic contacts. This paper is contribution number 1702 of the Division of Geological Sciences, C.I.T.

Kupfer(I)-diazabutadien-halogenide

Abstract: 14-Diaza-butadiene-(13) bilden mit Kupfer(I)-halogeniden stark farbige, monomere 1:1-Komplexe 2-11, 16-20, 24, 25 mit dreifach koordiniertem Kupfer Diese Koordination bestimmt das elektronenspektroskopische Verhalten Wahrend in Diazabutadien-Komplexen anderer Metalle in niedrigen Oxydationsstufen die langstwellige Absorption sehr starken Metall-Ligand-charge-transfer-Charakter hat, fehlt hier bei etwa gleich starker Beteiligung von Metalltermen im Grundzustand und angeregten Zustand die typische Solvatochromie und die extrem hohe Intensitat des farbgebenden Ubergangs Copper(I)-diazabutadiene Halides 1,4-Diazabuta-1,3-dienes react with cuprous halides to form strongly coloured, monomeric 1:1 adducts 2-11, 16-20, 24, 25, containing copper with threefold coordination This coordination number determines the spectroscopic behaviour While diazabutadiene complexes of other metals in low oxidation states show a long-wavelength absorption with strong metal-to-ligand CT character, in the copper complexes 2-11, 16-20, 24, 25 the metal terms are about equally important in the ground and excited state without showing the typical solvatochromism and the extremely high intensity of the chromogenic transition

The effect of copper additions on electromigration in aluminum thin films

Abstract: Copper additions reduce the rate of electromigration in aluminum thin film conductors subjected to dc currents of high density. The results of experiments conducted with the goal of understanding the mechanism of this effect are presented. The relationships between lifetimes and the mode of preparation, the composition, and the heat treatment of the samples are explored. The lifetimes of copper bearing aluminum conductors vary in the same way, with respect to temperature and current density, as conductors made of pure aluminum. Data obtained with an electron microprobe on samples which have failed electrically, after prolonged exposure to current, show the coincidence of crack formation and copper depletion in the surrounding area. Analysis along the length of current stressed samples, also with the microprobe, indicates that under the effect of current, copper atoms migrate at a considerably faster rate than aluminum atoms. Gold and silver additions in aluminum do not have the same effect as copper additions. It is believed that this difference is due to variations in adsorption of different atomic species on aluminum grain boundaries.

Dynamic deformation of aluminium and copper at elevated temperatures

Abstract: T he mechanical behaviour of two annealed face-centred cubic metals, aluminium and copper, at elevated temperatures has been investigated experimentally to determine their rate sensitivity. The results indicate that hot compression is a thermally-activated process. The experimental value of the activation energy for aluminium obtained from the present work is almost similar to that for creep and self-diffusion. This indicates that hot dynamic compression may be a diffusion-controlled thermally-activated process. However, the experimental activation energy of 74 kcal/mole obtained from the present work for copper is higher than that observed both for creep and self-diffusion. Experimental evidence (D. Hardwick and W.J. McG. Tegart in 1961) suggests that recrystallization is the rate-controlling process in dynamic deformation, while in creep it is usually recovery in the form of sub-grain formation. For aluminium specimens the dislocation density decreases with increasing temperature; for increasing strain rate the dislocation density remains almost constant, while the size of dislocation cells diminishes. If the dislocation density did not change substantially, one should conclude (as did L. Taborský in 1969) that the rise in flow stress caused by high strain rate is due to the reduction of the size of dislocation cell structure and by the increased rate of movement of the moving individual dislocations.

Copper Tolerance in Some Californian Populations of the Monkey Flower, Mimulus guttatus

Abstract: A preliminary investigation had been made into the evolution of copper tolerance in some Californian populations of Mimulus guttatus growing on abandoned copper mines. It has been shown that populations growing on soil with normally toxic levels of copper were tolerant to this heavy metal. There was also some indication of an increase in tolerance to zinc, lead and nickel in the copper tolerant populations, even when the soil was not particularly rich in these other metals. With one exception, populations on non-contaminated soils were non-tolerant as judged by root growth in aqueous solutions or soil containing copper. Furthermore, there was a marked difference in germination and seedling establishment on copper soil between stocks originating from mine and from non-mine environments. The superiority of the mine populations under such circumstances was less marked when established plants were potted up in mine soil. By testing the F$_{1}$ progeny of crosses involving tolerant and non-tolerant parents it was found that copper tolerance is dominant in effect at low copper concentrations, intermediate at intermediate concentrations, and recessive in effect at high copper concentrations. When the plants had been grown on normal soil there appeared to be a requirement for copper at low concentrations among the offspring of tolerant parents. It is suggested that this may result from the mechanism of tolerance by complexing the copper and thus making it unavailable to the plant. The genetic control of zinc and lead tolerance is not clear, but there is evidence that zinc tolerance may be dominant at concentrations of zinc in solution of 15 parts/10$^{6}$.

Zoning in the White Pine copper deposit, Ontonagon County, Michigan

Abstract: Cu-Fe sulfides, introduction of copper into Nonesuch shale (Precambrian) from underlying Copper Harbor conglomerate, sulfur-rich reducing environment of the Nonesuch, replacement of original pyrite along an upward advancing mineralization front, metals more soluble than copper swept upward before copper front

DNA-copper (II) complex and the DNA conformation.

Abstract: Spectrophotometric, sedimentation, infrared, optical rotatory dispersion (ORD), and circular dichroism (CD) methods have been used to demonstrate the structural changes in DNA induced by the interaction of copper(II) with bases and to elucidate the complex binding sites. As shown by the electrolyte-induced reversion (addition of salts) of temperature-denatured copper DNA the effectiveness of re-formation of the double-stranded structure depends on the temperature, copper(II) ion concentration, and on the base composition of the DNA. Exposure of heat-denatured copper DNA to higher temperatures decreases the reversion effect on addition of electrolyte. The results indicate that a greater fraction with a cooperative transition appears on heating DNA to 80 or 100°C at a Cu2+/DNA-P ratio of 2 : 1 than at a Cu2+/DNA-P ratio of 1 : 1. With AT-rich copper DNA, reversion to the native DNA structure was not observed. Selective methylation of guanine residues in DNA also affects the electrolyte-induced reversion, indicating the importance of GC pairs for copper(II) binding and the reversion to the native structure. Temperature-denatured copper DNA shows an increased sedimentation coefficient Which decreases again after electrolyte-induced reversion. This change in s is reduced by selective methylation of DNA. Complex formation between copper(II) and the bases is accompanied by a conformational change of the DNA double-helical structure as demonstrated by ORD and CD experiments. The ORD profile of GC-rich DNA is much more affected by copper(II) than that of AT-rich ones. Even at very low copper(II) concentrations, e.g., at 0.02 and 0.2 Cu2+/DNA-P, the ORD and CD measurements exhibit conformational changes of the DNA secondary structure at room temperature. By comparing the infrared spectra of deoxynucleosides with that of DNA of different GC content it has been shown that both guanine and cytosine are involved in the formation of the complex of copper(II) with DNA. N-7 and O at C-6 in guanine and N-3 as well as O of C-2 in cytosine are discussed as the most probable binding sites in DNA. A binding model for the coordination of the copper(II) ion between guanine and cytosine of the opposite strands is suggested. The results are in good agreement with the assumptions and predictions made by Eichhorn and Clark about the complexing of copper(II) with DNA. The recent proposal made by Schreiber and Daune about an interaction of the type guanine–Cu2+–guanine cannot be excluded as an additional kind of coordination of copper(II) in DNA.

The Reactions of Grignard Reagents with Transition Metal Halides: Coupling, Disproportionation, and Exchange with Olefins

Abstract: The reactions of transition metal halides (Mn, Fe, Co, Ni, Pd, Cu, and Ag) with the low-molecular-weight alkyl Grignard reagents in tetrahydrofuran and diethyl ether, especially in the presence of styrene were reinvestigated. An alkyl transition metal species formed in situ by metathesis decomposed to a dialkyl (oxidative dimerization) or to an alkene and an alkane (oxidative disproportionation). Silver(I) and copper(II) were particularly effective in oxidative dimerization of primary alkyl groups. Alkyl groups which contain no β-hydrogen were also coupled by iron, cobalt, nickel, palladium, and copper(I) halides with varying degrees of efficiency. Oxidative disproportionation was generally the more common route to decomposition for alkyl groups which have β-hydrogens. It seemed to proceed directly via a bimolecular interaction of alkylmetals or indirectly by elimination of a hydrido-metal species. If the latter added to an alkene reversibly, exchange was observed between Grignard reagent and alkene. Styr...

Mechanism of the Green-Copper Luminescence in ZnS Crystals. I. Direct Evidence for the Pair Emission Mechanism

Abstract: Using a ZnS:Cu, Al crystal grown from the melt, precise measurements were made at liquid helium temperature on the relationship between the decay rate of the green-copper luminescence and those of two kinds of photoinduced absorptions, one due to holes created at copper acceptors, and the other due to electrons trapped at aluminum donors. It was found that the decay rates of the two kinds of absorptions are equal to each other, and are about one half of that of the luminescence. This fact clearly incicates that the green-copper luminescence is caused by the recombination of electrons trapped at aluminum donors with holes trapped at copper acceptors according to the bimolecular kinetics, and provides the direct experimental evidence for the conclusion of the donor-acceptor pair emission mechanism for this luminescence presented in the previous investigations.

The Effect of Zinc and Copper on the Osmolality of Blood Serum of the Channel Catfish, Ictalurus punctatus Rafinesque, and Golden Shiner, Notemigonus crysoleucas Mitchill

Abstract: A new, and possibly primary, effect of heavy metals on fishes is described. It is demonstrated that heavy metals so affect fishes as to cause a drop in the salt concentration in the blood serum. This change in the ionic content of the blood can cause the fish to become weakened, and pronounced change can be fatal. Salt changes in the blood were monitored by osmometry. The effects of both zinc and copper were evaluated.