Mol Of Copper Research Articles

Cu 2+ in NaF: EPR study of a dynamic center

An EPR study has been carried out on a Cu 2+ center in NaF single crystals (with 2 % mole of copper) from 1.6 k – 150 K. The symmetry of the EPR spectra is triclinic at 1.6 K, monoclinic at 4.2 K, tetragonal at T ⩾ 40 K. No hyperfine structure has been observed. Models which include both the Jahn-Teller effect and a low symmetry crystal field are proposed.

Determination of the two-phase equilibrium constants of copper(II)-modified silica gels used in liquid chromatography

Silica gels modified with copper(II) are currently used in ligand-exchange liquid chromatography. The main species present at the surface of the stationary phase is shown to be (SiO) 2Cu(NH 3) 2(H 2O) x. Measurements of the ammonia concentration in the mobile and stationary phases are combined with computer-assisted calculations to determine the following apparent equilibrium constants: for SiOH + NH 3 ⇌ SiO −NH + 4, log K = −0.2; for (SiO) 2Cu + NH 3 ⇌ (SiO) 2Cu(NH 3), log β 1 = 2.8; and for (z.tbnd;SiO) 2Cu + 2NH 3 ⇌ (SiO) 2Cu(NH 3) 2, log β 2 = 4.0. A distribution diagram of the different species present at the surfac of copper-modified silica gel is given. Under the usual operating conditions for ligand-exchange chromatography (pNH 3 < 1), more than 60% of the silanol groups which fix copper(II) have a silicate structure with two moles of ammonia per mole of copper(II).

Purification and characterization of the cytochrome oxidase from alkalophilic Bacillus firmus RAB.

A cytochrome oxidase was purified 52-fold from membranes of alkalophilic Bacillus firmus RAB by extraction with Triton X-100, ion-exchange and hydroxyapatite chromatography, and gel filtration. On denaturing gels, the purified enzyme dissociated into two subunits of 56,000 and 40,000 Mr as well as a cytochrome c with an Mr of approximately 14,000. Heme contents calculated for an enzyme with a molecular weight of 110,000 were found to be 2 mol of heme a and 1 mol of heme c per mol of cytochrome oxidase; approximately 2 mol of copper per mol of purified enzyme was also found. Enzyme activity was observed in assays using reduced yeast or horse heart cytochrome c. Activity of the purified enzyme was optimal at pH 6.0 and in the presence of added lipids. Impure, membrane-associated activity exhibited a broader pH range for optimal activity extending to alkaline values.

Two-stage nuclear demagnetization refrigerator reaching 27 �K

A two-stage nuclear demagnetization refrigerator with large cooling capacity has been constructed and successfully operated. The first stage consists of 11 moles of the Van Vleck paramagnet PrNi5 in an initial field of 6 T, and the second stage consists effectively of 19 moles of copper in an initial field of 7.6 T. The minimum temperature as measured with pulsed platinum NMR is 27 µK, the lowest ever obtained in a low-field experimental region.

Inactivation of beef plasma amine oxidase by sulfide.

Sulfide irreversibly inactivates beef plasma amine oxidase in a time-dependent reaction. Mercaptoacetic acid and 2-mercaptoethanol do not inactivate the enzyme. The sulfide complex displayed an intense absorption band at 360 nm (epsilon = 6000 M-1 cm-1, per mol of copper) that is assigned as sigma S leads to Cu(II) ligand to metal charge-transfer transition. However, this band slowly decreased in intensity; the final spectrum resembles the spectrum of the dithionite-reduced enzyme. Bleaching at approximately 450-500 nm specifically indicates that the organic cofactor is reduced. EPR parameters for the sulfide complex differ significantly from those observed for the native amine oxidase. Superhyperfine structure, attributable to coordinated nitrogens, is clearly evident. Time-dependent reduction of Cu(II) that parallels the kinetics and absorbance changes was also observed by EPR. The amine oxidaseazide complex was inactivated by sulfide at a considerably slower rate than the resting enzyme. Since azide is known to coordinate to Cu(II) in beef plasma amine oxidase, the data strongly suggest that enzyme-bound copper is the site of action for inhibition by sulfide.

Determination of Tocopherols (Vitamin E) by Reduction of Cupric Ion

Abstract This research details the principal characteristics of a new chemical reaction for the determination of tocopherols (vitamin E). The proposed technique is based on the reduction of Cu(II) to Cud) by the tocopherols. The reduced ion is then available to form a complex with 2,2'-biquinoline (cuproine) and with 2,9-dimethyl - 4,7-diphenyl-l,10-phenanthroline (bathocuproine), which have maximum absorbances at 545 and 478 nm, respectively. One mole of tocopherol reduces 2 moles of copper. When urea is used as a catalyst in the reaction, α-tocopherol and γ-tocopherol react completely in 10 s; δ-tocopherol reacts in 90 s. The reaction is not affected by exposure to light. The method was compared with 2 other methods: reduction of Fe(III) to Fe(II) and complexation with 2,2'-bipyridine (conventional Emmerie- Engel method), and reduction of the free radical l,l'-diphenyl-2-picrylhydrazyl (DPPH) to the corresponding hydrazine. Absorptivities of the complexes Cu(cuproine)+2, Cu(bathocuproine)+2, Fe-(bipyridine)++, and DPPH, in terms of concentration of tocopherol were: 30.89,61.87,39.91, and 48.86 Lg-1 cm-1, respectively.

Spectroscopic studies on the copper(II) complexes of carnosine

Carnosine complexes with copper(II) ions were studied with magnetic resonance techniques over a wide range of ligand to metal ratios at various pH values. Water proton relaxation rates increased with decreasing carnosine to copper ratios until a molar ratio of 48 was reached. Over the ratio range of 48–2 carnosine molecules per copper ion, the relaxation rate decreased so that in the 2:1 carnosine-copper(II) complex, the water-copper(II) distance was estimated to be 1.92 Å. Proton NMR studies revealed the broadening of imidazole proton lines at high mole ratios followed by other histidyl protons as the ratio decreased. The β-alanyl methylene protons were the last to be broadened by the addition of copper(II) ions. Carbon to copper(II) distances were determined for the carnosine to copper mole ratios of 500:1 and 5000:1. EPR spectra obtained at 93°K revealed the probable existence of four carnosine imidazoles as the sole coordinated ligands to copper(II) at high dipeptide-to-metal ratios (>10). At mole ratios below four, nuclear hyperfine lines characteristic of both monomeric and dimeric carnosine-copper(II) forms were observed. These results reveal that imidazole from carnosine is the sole ligand contributed to copper(II) for coordination over the pH range 5 to 7 at high carnosine to copper(II) ratios

Copper(II)‐Binding Ability of Human Alpha‐fetoprotein

Our previous sequence study showed that alpha‐fetoprotein (AFP) had one histidyl residue at position 3 or 4 from the N‐terminus (heterogeneous N‐terminus). Since human serum albumin also has a cupric chelate locus histidine at the third position from N‐terminus, copper(II)‐binding ability of AFP was examined by equilibrium dialysis and gel‐filtration method. AFP could bind one mole of copper(II) ion per mole of protein above pH 6.0 and the pH‐dependence of copper(II)‐binding ability of AFP was quite similar to that of albumin. AFP bound 0.5 mole of copper(II) ion at pH 5.4 which is close to the pK value of imidazole of histidine. Photo‐oxidation of AFP in the presence of methylene blue showed that the loss of copper(II)‐binding ability of the protein was parallel to the destruction of histidine. These results indicate that histidyl residues play some important role in this copper(II)‐binding ability of the protein. Reduced and S‐carboxymethylated AFP also had this ability.

Structural and functional determinants of Mucor miehei protease VI. Inactivation of the enzyme by diazoacetyl norleucine methyl ester, pepstatin and [formula omitted

Mucor miehei protease (EC 3.4.23—), an acid protease of fungal origin, was rapidly inhibited at pH 5.0 and 10°C by a 78-fold molar excess of diazoacetyl norleucine methyl ester (N 2Ac-Nle-OMe) when simultaneously added with a 78-fold molar excess of Cu(II). Preincubation with Cu(II) before the addition of N 2Ac-Nle-OMe reduced the initial rate of activity loss presumably due to a copper-induced structural change as deduced from an examination of CD spectra. Complete inactivation was associated with the incorporation of 1.6 ± 0.12 residues of norleucine and 1.02 ± 0.041 mol of copper. The conformation of the N 2Ac-Nle-OMe-inhibited enzyme appeared to be somewhat altered since the rate of H- 3H exchange determined for the slowest exchanging class of hydrogens was reduced by more than 10-fold although the estimated number of hydrogens in this class remained constant. Mucor miehei protease was also inhibited by pepstatin; complete inactivation required a 6-fold molar excess of inhibitor and was associated with a major conformational change as determined from CD spectra. Loss of activity also occurred in the presence of 1,2- epoxy-3-(p- nitrophenoxy)propane (EPNP).

Mechanism of superoxide anion scavenging reaction by bis-(salicylato)-copper(II) complex

The mechanism of the reaction of bis-(salicylato)-copper(II) with superoxide anion has been studied by utilizing electron paramagnetic resonance and polarographic techniques. The proposed reaction sequence is as follows: Cu(II) + O 2 − ← Cu(II) O 2 −← Cu(I) O 2 −← Cu(I) + O 2 Cu(I) + O 2 −← Cu(I)O 2 −← Cu(II)O 2 2−← 2H + Cu(II)O + H 2 O 2 Using the xanthine-xanthine oxidase system as a superoxide generator, it was found that the concentration of this copper complex for 50% inhibition of the xanthine-cytochrome c reductase activity was about 1000 times more per mole of copper than that of erythrocyte superoxide dismutase.

Purification and characterization of dopamine beta-hydroxylase from bovine adrenal medulla.

A new purification procedure that permits large-scale purification of dopamine beta-hydroxylase from bovine adrenal medulla was developed. Whole adrenal medullas were extracted with 0.1% Triton X-100, and the enzyme was purified by precipitation with polyethylene glycol, chromatography on DEAE-cellulose, and adsorption to concanavalin A linked to agarose. The yield of protein and the specific activity were high compared with previously published methods. The enzyme appeared essentially homogenous by the criteria of polyacrylamide gel electrophoresis in the presence or absence of dodecylsulfate, and sedimentation velocity analysis. The purified protein was subjected to amino acid and carbohydrate analyses, and the results were compared with previously published data. We found about 3 mol of copper per mol of protein (tetramer of 290000 daltons). No free sulfhydryl groups could be found. Analysis for NH2-terminal amino acids with [14C]dansyl chloride revealed 2 residues of alanine and 2 residues of serine per tetramer. We found the NH2-terminal amino acid of chromogranin A to be leucine. The results of our analysis for amino acid composition and NH2-terminal amino acids do not support the suggestion that dopamine beta-hydroxylase and chromogranin A contain identical peptide chains.

Citric acid enhancement of copper solubility and toxicity in bicarbonate solutions

Copper solubility and cupric ion toxicity to photosynthesis of isolated chloroplasts and algal cells in bicarbonate solutions were enhanced by the addition of citric acid. The toxicity of cupric ions to algal growth during the first 2 days of incubation was increased by the presence of citric acid in the growth medium. No adverse effects of citric acid on cupric sulfate as an algicide were detected. Sulfhydryls were oxidized in the presence of cupric ions to disulfides with one mole of oxygen taken up for every 4 mol of sulfhydryls oxidized. In bicarbonate solutions, this reaction was stimulated by the addition of citric acid. A four to one ratio of citric acid to cupric sulfate pentahydrate on a weight to weight basis, 5.2 mol citric acid per mol copper, appeared to be the most efficient ratio. The citric acid influence on copper solubility and cupric ion toxicity was not due to a pH effect.

Activity of a new polyoxime‐copper complex in the reversible uptake of molecular oxygen and carbon monoxide, in the polymerization of acrylonitrile, and in the addition reaction of alcohols to acrolein

AbstractA new polyoxime‐copper complex was prepared from cupric acetate and a polyoxime which is considered to consist largely of 1,2‐bis(hydroxyimino)trimethylene units. The properties of the complex were studied. Its ESR spectrum was found to be similar to that of the low molecular weight copper(II) complex, whose intensity decreases with increasing copper content. The complex shows a catalytic activity in the Michael type addition reaction of alcohols to acrolein, yielding exclusively β‐alkoxypropionaldehyde. In addition, it initiates the polymerization of acrylonitrile under hydrogen pressure (40 to 90 kg/cm2). Furthermore, the complex with a composition ratio Cu: OX ≈ 1:4 (Cu: number of copper atoms, OX: number of hydroxyimino groups in the complex), after being treated with hydrazine hydrate in methanol under nitrogen, can reversibly take up and release ca. 3,2dm3 of molecular oxygen (in water) and 0,8dm3 of carbon monoxide (in methanol) per mole of copper. These activities decrease remarkably with decreasing copper content of the complex.

CHELATION STUDY OF COPPER (II): FULVIC ACID SYSTEM

The chelation reaction between Cu (II) and fulvic acid has been investigated using a relatively new direct approach — that of titration with a cupric ion-selective electrode. The results of different investigators are in fair agreement with each other if they are interpreted in terms of both pH and mole fraction of reactants. In 0.1 M sodium nitrate solutions with a copper mole fraction equal to 0.5 ± 0.2, the equilibrium quotient at 25 C and pH 3 was found to be 2.2 ± 0.1.

Purification of superoxide dismutase from fungi and characterization of the reaction of the enzyme with catechols by electron spin resonance spectroscopy.

Superoxide dismutase catalyzes the conversion of the single electron reduced species of molecular oxygen to hydrogen peroxide and oxygen. The widely distributed copper enzyme has been purified from two fungi. Identical chromatographic and electrophoretic behavior of the enzyme isolated from different sources indicates great similarity in the molecular properties of the enzyme from eucaryotic organisms. A photosensitized recording assay procedure for the enzyme was developed which elminates the use of a second enzyme system for generating the substrate, superoxide anion. Kinetic data indicate that the reaction between enzyme and superoxide anion shows a logarithmic dependence on concentration under the conditions of the method.The fungal enzyme contains 2 mol of zinc and 2 mol of copper per mole of holoenzyme. The reaction between the enzyme-bound copper and several catechol derivatives has been examined through the use of electron spin resonance spectroscopy. It was concluded from these studies that these compounds reduce a portion of the copper to the cuprous form and also may form a complex with enzyme copper. The substituted catechols are oxidized noncatalytically by the enzyme to the semiquinone forms in the presence of oxygen. Much higher concentrations of the semiquinones are formed in the presence of the enzyme than are possible with oxygen alone at pH 8. Catechols also react readily with superoxide anion. Because of the complex relationships between catechols, superoxide anion, and superoxide dismutase, it is difficult to assess the effect of catechols on the catalytic activity of the enzyme.

Determination of bacitracin in animal feeds that contain copper.

A modification of the method involving the use of acidified methanol for the analysis of animal feeds that contain bacitracin and copper sulphate as additives has been developed. Because of the interference of copper in the bacitracin assay, the copper is precipitated by the addition of 3 to 4 mol of sulphide ions per mole of copper. The method has been used for feed samples that contain 5 to 20 p.p.m. of bacitracin and 100 to 300 p.p.m. of copper

Degradation of rutin by Aspergillus flavus. Studies on specificity, inhibition, and possible reaction mechanism of quercetinase.

The dioxygenase produced by Aspergillus flavus that oxidizes quercetin contains 2 moles of copper per mole of enzyme and binds at least 2 moles of substrate. The enzyme is not inhibited by sulfhydryl reagents or affected by H2O2, but is inhibited by copper-chelating agents and reducing agents. Nitrogen bases with chelating ability are more effective inhibitors than those that do not form metal chelates.The dioxygenase oxidizes flavones that possess a double bond between carbons-2 and -3 and a hydroxyl on carbon-3. Hydroxyls at other positions affect both the relative rates of enzymatic oxidation and the concentration of substrate required to attain half maximal rate (Km). The evidence indicates that the substrate binds to the copper of the enzyme via the 3-hydroxyl and 4-carbonyl groups of the substrate. A possible mechanism for the reaction is presented.

The Conformational Transition of Sperm Whale Ferrimyoglobin in the Presence of Several Equivalents of Cupric Ion

Abstract When sperm whale ferrimyoglobin is mixed, at pH 6.6 to 6.7 and 23°, with 2 to 7 moles of copper(II) ion per mole of protein, at a concentration of the latter of 0.2 mm, the copper(II) ions become bound to the protein within a few seconds, as shown by electron paramagnetic resonance spectroscopy. In a slower process, which can be correlated with a previously described conformational transition, the characteristic high spin iron(III) signal at g = 6 is reduced in intensity without change in shape. The extent of the reduction in the heme iron(III) signal at equilibrium depends linearly on the mole ratio of the copper(II); it is essentially complete at a mole ratio of 7, but not observable at a mole ratio of 1. Throughout most of the course of the process, the reduction in the iron(III) signal parallels the reduction in the Soret peak intensity at 409 mµ. The loss of the signal may be caused by dipolar coupling between paramagnetic ions, but it is significant that it may be produced by zinc ions, which are not paramagnetic but do promote the conformational transition in a similar way. At equilibrium, the copper(II) signal is reduced in intensity and somewhat broadened, but without other striking changes in form, and some degree of dipolar coupling of neighboring paramagnetic ions is indicated. Binding of the 1st copper(II) ion is relatively strong, but the binding of the additional 6 copper(II) ions in the altered complex cannot be distinguished according to a gradation of binding strengths.

Spectrophotometric Titration of Divalent Metals with 1-Nitroso-2-naphthol in N,N-Dimethylformamide

1-Nitroso-2-naphthol, an organic precipitating agent, can be used as a volumetric reagent for the titration of micro amounts of divalent metals in a N,N- diraethylforraamide solution. Spectrophotometric titrations of 0.01 mu mole of copper(II) and 10.0 mu moles of Ni(II) in 40 nfl of solvent can be perforraed with a precision of 2 parts per 1000. Pb(II), Zn(II), and uranyl ions also chelate with nitrosonaphthol in dimethylfornnannide. The usefulness of nitrosonaphthol as a titrant in dimethylfornnannide is limited somewhat by its gradual decomposition in this solvent. (auth)

Interaction of one mole of copper with the alpha amino group of bovine serum albumin

Interaction of one mole of copper with the alpha amino group of bovine serum albumin