Cuprous State Research Articles

PREPARATIVE AND STRUCTURAL STUDIES ON THE SUPERCONDUCTING PHASE Tl2CaBa2Cu2O8

Previously others have reported the existence in the system Tl-Ca-Ba-Cu-O of two high T/sub c/ (above 100K) superconducting phases, namely Tl/sub 2/Ca/sub 2/Ba/sub 2/Cu/sub 3/O/sub 10+d/ (2223) and Tl/sub 2/CaBa/sub 2/Cu/sub 2/O/sub 8+d/ (2122). They did not get samples pure enough for detailed analysis of crystal structure. The authors have just finished determining the crystal structure of the superconducting phase Bi/sub 4/Ca/sub 2/Sr/sub 4/Cu/sub 4/O/sub 20-x/. This bismuth-containing phase displays onset temperatures and T/sub c/ at 113 and 80K respectively. However, the thallium-containing phase of a similar metal-ion stoichiometry, namely, 2122 has a higher T/sub c/. They have prepared a homogeneous sample for the phase and determined its crystal structure by powder XRD method. Then the structural features of the present phase is compared with that of the bismuth-containing phase 4244. No occupancy problem for oxygen and cupric state of copper have been found.

Linear-electric-field effect on g values of low-symmetry cupric sites.

We have investigated the linear\char21{}electric-field effect (LEFE) in cupric ions situated in ligand fields of low symmetry. General properties of LEFE signals resulting from various low-symmetry models are described. Treating g values, we show how hybrid-orbital ``united-atom'' models can be used for direct calculation of the LEFE signal expected from cupric sites of specific low-symmetry geometries. This hybrid\char21{}atomic-orbital approach is shown to give a straightforward method for interpreting LEFE data in terms of cupric electronic states that directly reflect the ligand environment. Results are presented which demonstrate the potential of calculations with this model to account quantitatively for the LEFE data from blue cupric proteins.

ESR studies of molecular interactions of Copper(II) nirvanol and Copper(II) diisopropylsalicylate with ehrlich ascites tumor cells

ESR spectra have been obtained after addition of either a cupric phenylhydantoin or a cupric diisopropylsalicylate complex to Ehrlich ascites tumor cells. It is shown that some of the complex remains in the cupric state. Because the ESR parameters of these complexes in the presence of cells differ from the ESR parameters for these complexes in the absence of cells, in the presence of cells either adducts or new cupric complexes are formed. The fast motion of these complexes, as determined from room temperature ESR spectra, is characteristic of complexes with molecular weights less than 1500.

Structural changes of glass-ceramics of the Cu2O-Al2O3-SiO2 system on heating in air

The behaviour of copper ions in low thermal expansion glass-ceramics prepared from Cu2O · Al2O3 ·nSiO2 glasses, or inβ-spodumene type Cu2O · Ae2O3 ·nSiO2 crystals included in the glass-ceramics on heating in air was investigated. On hewing at 300 to 500° C, the copper ions behaved as in the corresponding glasses. Cuprous ions in the glass-ceramics orβ-spondumene type crystals were oxidized into the cupric state, and at the same time an equal amount of cuprous ions to those oxidized were expelled out of the specimen for the requirement of electrical charge neutrality and then reacted with oxygen to form CuO on the surface. The oxidation of cuprous ions and the decrease of the copper content of theβ-spondumene type crystals brought about a considerable decrease in the lattice spooings.

Purification and some properties of tea leaf amine oxidase.

Tea leaf amine oxidase was purified by salting out and various column chromatographies. The molecular weight was estimated to be 162,000 daltons by gel filtration on a Sephadex G-200 column. This enzyme was determinated to be a dimer of which the molecular weight was found to be 81,000 daltons by SDS gel electrophoresis. The optimum pH for ethylamine oxidation by this enzyme was 7.0. The enzyme was stable up to 60°C. From the results of a inhibition study with chelating agents, the enzyme was found to contain copper in the cupric state. Carbonyl reagents such as semicarbazide, hydroxylamine and hydrazine strongly inhibited the activity. The enzyme oxidized alkylamines, ethanolamine and benzylamine rapidly, and also oxidized tyramine, histamine and other diamines slowly. The Km value for ethylamine was 8.8 x 10–5m. Polyamines, secondary amines and tertiary amines were not oxidized.

The electrochemical oxidation of chalcopyrite in ammoniacal solutions

The anodic dissolution of chalcopyrite in ammoniacal solutions was investigated using electrochemical methods. At low overvoltages, the formation of a copper deficient sulfide layer, Cu1-xFeS2 through a charge transfer reaction is proposed based upon the dependence of the rest or open circuit potential on solution composition and the presence of a Tafel region of appropriate slope. In addition, a current peak that occurs at 10−4 A/cm2 is a function of the square root of the voltage scanning speed and is explained in terms of a charge transfer reaction. At larger overvoltages, constant potential experiments and mass balances performed at various anodic potentials indicate that the dissolution is consistent with the overall reaction, CuFeS2 + 4NH3 + 9OH- = Cu(NH3)4+2 + Fe(OH)3 + S2O3= + 3H2O +9e-, although some copper may be released to solution in the cuprous state and some ferrous iron has been identified in the product film. Currentvs time data taken during constant potential experiments were found to obey a linear rate relationship. This was interpreted in terms of the formation of a layer of constant thickness which is corroded at the outer interface at the same rate it is formed at the inner interface.. The model proposed is typical of the corrosion of some metals. An examination of the polarization curves shows the dissolution reaction to be first order with respect to [OH-]. The lack of dependence on [Cu2+] indicates that the catalytic effect of cupric ion during oxygen pressure leaching is related only to the cathodic reduction of O2 in agreement with the results of previous investigations.

The analogous mechanisms of enzymatic inactivation induced by ascorbate and superoxide in the presence of copper.

The mechanism of enzymatic inactivation of purified and membrane-bound acetylcholine esterase by ascorbate and copper was investigated. While the exposure of the enzyme to either ascorbate or copper did not cause enzymatic inactivation, the incubation of the enzyme with a combination of both ascorbate and copper resulted in a loss in acetylcholine esterase activity, which was time dependent. The enzymatic inactivation required either molecular oxygen or hydrogen peroxide under anaerobic conditions. Scavengers of hydroxyl radicals at concentrations of up to 100 mM did not provide protection to acetylcholine esterase. Only mannitol at very high concentrations (above 1 M) efficiently prevented the inactivation of the enzyme. The kinetics of the aerobic oxidation of reduced ascorbate in the presence of acetylcholine esterase and copper closely followed the rate of enzyme inactivation. Addition of the chelating agents EDTA and diethylenetriaminepentaacetic acid prevented both the oxidation of ascorbate and the inactivation of the enzyme. In the presence of low concentrations of histidine (0.5-2.0 mM), which forms high affinity complexes with copper, the rate of ascorbate oxidation was similar to that recorded in its absence. On the other hand, no enzyme inactivation was indicated in the presence of histidine. Low temperature EPR measurements have demonstrated the binding of copper to the enzyme, and have shown the reduction of the cupric enzyme to the corresponding cuprous complex. In view of these results, a general "site-specific" mechanism for biological damage can be offered, in which copper(II) ions are bound to enzymes or other biological macromolecules. Ascorbate plays a dual role: it reduces the cupric complex to the corresponding cuprous state and serves as a source for H2O2, which, in turn, reacts with the reduced copper complex, in a Fenton reaction. In this reaction, secondary hydroxyl radicals are site specifically formed, and react preferentially with the protein, at the site of their formation, causing its inactivation. This mechanism is analogous to that previously proposed (Samuni, A., Chevion, M., and Czapski, G. (1981) J. Biol. Chem. 256, 12632-12635) for the enhancement of the biological damage caused by superoxide in the presence of copper.

On the Relationship between Protein-Forced Ligand Fields and the Properties of Blue Copper Centers

Abstract The stable conformation of blue copper proteins forces the metal ion into a unique geometrical ligand arrangement. Spectroscopic data suggest that at least 70 kJmol−1 would be required to twist the protein into a conformation that would allow the cupric ion to occupy a square planar site. The observation that the γ S→ Cu(x2-y2) transition energy does not change with increasing ligand field strength is interpreted in terms of a model in which Cu(xz, yz)ligand back bonding enhances the splitting between the Cu(x2-y2 ) and Cu(xz, yz) levels in blue sites with high chemical reduction potentials, thereby providing an explanation of the special stability of the cuprous state.

Active site of copper oxidases

Copper amine oxidases catalyse the oxidative deamination of biological amines according to the following equation: RCH 2NH 2 + O 2 + H 2O → RCHO + H 2O 2 + NH 3 It should be recalled that another class of amine oxidases was described. They contain FAD as a prosthetic group, but will not be discussed here. All copper amine oxidases have molecular weight higher than 100,000: some of them appear to contain two equivalent subunits which are probably not linked by disulfide bridges [1,2]. All these enzymes contain at least two copper atoms and one carbonyl group per molecule. The nature of the carbonyl cofactor is a controversial issue: many data suggest that it could be identified as pyridoxal-5-phosphate [1]. Electron spin resonance (ESR) spectra show that the two copper atoms are in an equivalent environment and in the cupric state [3, 4]. The spectrum is typical of Cu(II) in a complex of tetragonal symmetry [3]. the use of 15N labeled putrescine demonstrated that the substrate is not directly bound to copper [3]. Magnetic resonance studies [3, 5] and the comparison of the absorption and ESR spectra of the bovine enzyme with a model complex [6] suggest that in these enzymes at least two nitrogen atoms and 2 oxygen (from water) are coordinated around the copper ion. When copper amine oxidases were treated with phenyllhydrazine, 1 carbonyl group/mol was titrated [1] and an enzymatically inactive irreversible adduct was formed: its formation requires the presence of cupric copper[7]. After treatment with phenylhydrazine the bovine plasma enzyme shows changes in the ESR parameters of only one copper [7], indicating that the two copper sites are not identical. The non-identity of copper sites was demonstrated also in the pig plasma enzyme by magnetic studies [5]. The copper atoms however, become equivalent after treatment with strong ligands like N 3− and CN− [5]. These results indicate a functional significance of the difference between the two copper atoms. Since the enzyme molecule contains two non identical copper ions and only carbonyl group, these findings suggest that only one of the two coppers has a role in the substrate oxidation. If the second prosthetic group is pyridoxal-5-phosphate, one of the copper ligands could be the nitrogen of the pyridine ring [1]. The substrate may bind the carbonyl cofactor and copper may have a catalytic role in oxygen activation [7].

Intermediates in the reduction of dioxygen by cytochrome c oxidase and in the photosynthetic water oxidation

The cycle of oxygen in the biosphere is totally dominated by two processes, photosynthetic oxidation of water to dioxygen on the one hand and reduction of dioxygen to water on the other. There is one problem common to the mechanism of these two reactions; at least at some point, electrons are carried one at a time, whereas the dioxygen-water reaction requires a total of four electrons. In some cases thermodynamic requirements effectively prevent four consecutive one-electron transfers, which, in addition, would lead to some very reactive and harmful intermediates. In mitochondria the reduction of oxygen occurs through the action of cytochrome c oxidase. Electrons are transferred from reduced cytochrome c, presumably via a heme (cytochrome a) and a copper ion (Cu A), to a binuclear center consisting of one heme (cytochrome a 3) and one copper ion (Cu B). The individual steps of the reaction can be followed at sub-zero temperature with optical and EPR spectroscopy. It seems that only the binuclear center is directly involved in the dioxygen reduction, and the initial steps after mixing dioxygen with the fully reduced enzyme are: ▪ The structure of the last species is derived from its unusual EPR spectrum [1], which indicates the presence of a weak antiferromagnetic interaction between a Cu 2+ ion and an S = 1 or 2 heme. Further support for this structure comes from 17O hyperfine structure in experiments with isotopically enriched dioxygen. In the reaction above, dioxygen is formally reduced in a process consisting of two two-electron transfer, thereby circumventing the O − 2 and OH· states. The catalytic cycle is completed by the transfer of three more electrons to the binuclear center, reducing the heme and the copper ion to the ferrous and cupric states, respectively. Much less is known about the reverse reaction, the oxidation of water to dioxygen in the photosynthetic systems. Manganese ions most likely are involved, and so far the only paramagnetic intermediate detected suggests the presence of antiferromagnetically interacting Mn ions [2, 3]. However, from such observations and analogies with the cytochrome c oxidase reaction, a model can be proposed that again involves two two-electron transfers [4].

Colorimetric Determination of Monovalent Copper in Copper Ruby Glass by Complexing with 2, 2′-Biquinoline

2, 2′-biquinoline forms a very sensitive coloured cationic complex with monovalent copper and is used for determination of trace amount of copper. So far, no use have been made of this reagent for direct estimation of monovalent copper in cuprous compounds or materials containing monovalent copper due to instability in acid solution. In the present investigation, attempts have been made to utilize this reagent in the direct estimation of monovalent copper in copper-ruby silicate glass. The existing method has been modified to carry out the estimation in 50% aqueous isopropyl alcohol to shorten the time to arrest the oxidation of monovalent copper to bivalent state. Glass samples were dissolved in hydrochloric and hydrofluoric acid in presence of the reagent and the optical density of colour developed at a pH about 5 was measured at a wavelength of 545 nm. Experiments were carried out to determine the monovalent copper in actual copper glasses melted with and without tin. The results showed that major part of the copper in copper-ruby silicate glasses is present in cuprous state.

The oxidation of Cu(I) by oxygen gas in concentrated NaCl solutions: A kinetic study

The oxidation of Cu(I) by oxygen gas in concentrated NaCl solutions was studied in a standard stirred reactor. Each test was carried out at constant pH and under stable hydrodynamic conditions. The effect of stirring speed, solution volume, temperature, pH, oxygen partial pressure, chloride and copper ion concentration of the solution were evaluated. The oxidation of Cu(I) followed linear kinetics up to 85% of the copper ions in the cupric state. The experimental results were interpreted by using the film theory of mass transfer with chemical reaction. In the linear range, the chemical reaction was found to be first order with respect to oxygen concentration. The kinetic constant is given. The flux equation was specific of a fast reaction regime and the overall reaction rate was independent of the mass transfer coefficient k L up to a k L -value of about 10 −2 cm/sec. A parallel study of the oxidation of SO 3 2− by oxygen gas was carried out in the same reactor. The effects of stirring speed and solution volume were similar for both systems.

Structural and functional aspects of copper transporting proteins

The biogenic nature and esssentiality of copper in biological systems is well known. Due to both its oxidations–reduction activity and the intriguing coordination of chemistry, copper is most suited to play a vital role in cellular biochemistry. Hydrated copper ions themselves are highly reactive and would be in a position to interfere in many a biochemical pathway. For example, the Fenton Type generation of ·OH radicals would destroy the cellular architecture in an uncontrolled manner. Unwanted and non-specific binding of ionic copper to functional and/or structurally important biopolymers must be considered hazardous for living system. In electron transport and oxygen reduction the specific reaction of the bound copper is dictated by the macromolecular protein portion [1,2]. While some progress has been made on the structure-function correlation of some of these copper proteins little is known how the metal is implanted into these functionally important copper proteins. In order to avoid the uncontrolled reactivity of copper and to ascertain the proper insertion of this metal into a specific enzyme the need of an efficient transportation is obvious. At present only three copper-transporting proteins including the cupreins, caeruloplasmin and copper-thionein are fairly well characterized. The binding site of the cuprein copper has been elucidated by X-ray crystallography. The other two proteins have been chemically and spectroscopically studied, in the serum protein caeruloplasmin three different types of copper coordination are known while the copper chromophore in copperthionein appears to be homogeneous. Special emphasis will be placed on this thiolate rich copper protein. This type of copper binding protein appears to be very old origin. It is found in microorganisms as well as in animal cells. Its amino acid composition is even more simple compared to the amino acid residues found in the iron sulphur proteins. A striking phenomenon is the extraordinarily high cysteine content ranging up to 30%. In freshly isolated Cuthionein the copper is the cuprous state. Apart from the copper transportation in either protein some of these proteins display catalytic functions. For example, some of the copper in caerulophenoloxidase and is reported to function like a terminal cytochrome c oxidase. Furthermore, the function of a more or less specific iron oxidase has been suggested. The cupreins are discussed with great enthusiasm to catalyse the spontaneous superoxide dismutation. In the case of the copper-thioneins their role apparently remains to lie exclusively in metal transport.

Characterization of the intermediates in the reaction of mixed-valence state soluble cytochrome oxidase with oxygen at low temperatures by optical and electron-paramagnetic-resonance spectroscopy.

The reaction of soluble mixed-valence-state (a3+CuA 2+.CuB + A32+) cytochrome oxidase with O2 at low temperature was studied by optical and e.p.r. spectroscopy. The existence of three intermediates [Clore & Chance (1978) Biochem. J. 173, 799-8101] was confirmed. From the e.p.r data it is clear that cytochrome a and CuA remain in the low-spin ferric and cupric states respectively throughout the reaction. No e.p.r. signals attributable to cytochrome a3 or CuB were seen in the intermediates. The difference spectra (intermediates minus unliganded mixed-valence-state cytochrome oxidase) and absolute spectra of the three intermediates were obtained. The chemcal nature of the three intermediates is discussed in terms of their spectroscopic properties. A catalytic cycle for cytochrome oxidase is proposed.

Characterization of the low-temperature intermediates of the reaction of fully reduced soluble cytochrome oxidase with oxygen by electron-paramagnetic-resonance and optical spectroscopy.

The reaction of fully reduced soluble bovine heart cytochrome oxidase with O2 at 173K was investigated by low-temperature optical and e.p.r. spectroscopy, and the kinetics of the reaction were analysed by non-linear optimization techniques. The only e.p.r. signals seen during the course of the reaction are those attributable to low-spin cytochrome a3+ and CuA2+. Quantitative analysis of e.p.r. signals shows that, at the end point of the reaction at 173K, nearly 100% of CuA is in the cupric state but only about 40% of cytochrome a is in the ferric low-spin state. The optical spectra recorded at this stage of the reaction show incomplete oxidation of haem and the absence of a 655 nm absorption band. The only reaction scheme that accounts for both the e.p.r. and optical data is a four-intermediate mechanism involving a branching pathway. The reaction is initiated when fully reduced cytochrome oxidase reacts with O2 to form intermediate I. This is then converted into either intermediate IIA or intermediate IIB. Of these, intermediate IIB is a stable end product at 173 K, but intermediate IIA is converted into intermediate III, which is the stable state at 173 K in this branch of the mechanism. The kinetic analysis of the e.p.r. data allows the unambiguous assignments of the valence states of cytochrome a and CuA in the intermediates. Intermediate I contains cytochrome a2+ and CuA+, intermediate IIA contains low-spin cytochroma a3+ and CuA+, intermediate IIB contains cytochrome a2+ and CuA2+, and intermediate III contains low-spin cytochrome a3+ and CuA2+. The electronic state of the O2-binding CuBa3 couple during the reoxidation of cytochrome oxidase is discussed in terms of an integrated structure containing CuB, cytochrome a3 and O2.

Hydrazinium thiocyanate as a reagent for determination of copper

Hydrazinium thiocyanate, N 2H 5SCN, has been used for the determination of copper in copper salts. The reagent reduces the copper ions to the cuprous state and precipitates cuprous thiocyanate Cu 2(SCN) 2, quantitatively.

Use of ESCA for a convenient and semi-quantitative state analysis of copper-nickel alloy surfaces

A semi-quantitative technique by means of ESCA was applied to the surface state analysis of copper-nickel alloys. With area integrated intensity of peaks at the L3M4, 5M4, 5 region of copper and 2 p 3/2 region of nickel, cuprous state and nickel oxide state on alloys could be semi-quantitatively determined. As to oxygen states on alloy surfaces, interstitial (Cu2O and NiO states), non-stoichiometric (represents -OH) and molecular states (adsorbed) were estimated. Further, the surface composition of alloys after heating under high vacuum was discussed.

Thiol complexes of copper as possible biological models

The reactions and properties of 2-aminothiophenol complexes of copper have been investigated under differing conditions. Inconsistencies among earlier reports arise from previously unrealised effects of atmospheric conditions and counter ion. It is suggested that the ligand is unusual in the sense that it stabilises the cupric and cuprous states to the same extent; some of the properties of its copper complexes are thereby understood. Three ligands similar to 2-amino-thiophenol have been studied. Spectral and magnetic measurements are presented; attention is drawn to unexpected results, especially in the d-d region of electronic spectra.

Superoxide Dismutase Inactivation by Radiation-Induced Radicals: Evidence for Histidine Residues in the Active Site

The inactivation of superoxide dismutase from bovine and human erythrocytes brought about by ionizing radiation has been studied. Both enzymes have similar radiation sensitivities, but, whereas the solvated electron is almost completely ineffective as an inactivating species, the probabilities of an OH radical or H atom inactivating a native enzyme molecule at pH 7.2 are about 0.04 and 0.1, respectively. H atoms are more effective when the enzyme copper is in the cuprous state, suggesting a conformational difference between the two oxidation states of the enzyme. Inactivation by ${\rm Br}_{2}{}^{-}$ radicals is negligible at pH 7 but increases sharply above pH 10. The effect of pH upon enzyme inactivation by ${\rm Br}_{2}{}^{-}$ has been compared with pH effects upon the rate and product absorption spectrum of the ${\rm Br}_{2}{}^{-}-\text{enzyme}$ reaction. In this way, ${\rm Br}_{2}{}^{-}$ was shown to inactivate the hol...

Conversion of metallothionein into Cu-thionein, the possible low molecular weight form of neonatal hepatic mitochondrocuprein

FEBS LettersVolume 44, Issue 3 p. 293-297 Full-length articleFree Access Conversion of metallothionein into Cu-thionein, the possible low molecular weight form of neonatal hepatic mitochondrocuprein Heinz Rupp, Heinz Rupp Physiologisch-chemisches Institut der Universität Tubingen, W. GermanySearch for more papers by this authorUlrich Weser, Corresponding Author Ulrich Weser Physiologisch-chemisches Institut der Universität Tubingen, W. GermanyTo whom reprint requests should be addressed.Search for more papers by this author Heinz Rupp, Heinz Rupp Physiologisch-chemisches Institut der Universität Tubingen, W. GermanySearch for more papers by this authorUlrich Weser, Corresponding Author Ulrich Weser Physiologisch-chemisches Institut der Universität Tubingen, W. GermanyTo whom reprint requests should be addressed.Search for more papers by this author First published: August 30, 1974 https://doi.org/10.1016/0014-5793(74)81161-0Citations: 80AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume44, Issue3August 30, 1974Pages 293-297 ReferencesRelatedInformation