Divalent Copper Ions Research Articles

EPR study of localized Cu2+ paramagnetic ions and Cu2+ pairs in the oxygen-deficient PrBa2Cu3O6+x and Pr0.5R0.5Ba2Cu3O6+x (R=Y,Er) compounds.

Low-temperature EPR measurements are presented for the ${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$ and ${\mathrm{Pr}}_{0.5}$${\mathit{R}}_{0.5}$${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$ (R=Y,Er) compounds with oxygen deficiency (tetragonal phase). The nuclear hyperfine interaction of the ${\mathrm{Cu}}^{2+}$ ions has been observed in both compounds. The origin of the ${\mathrm{Cu}}^{2+}$ EPR spectra has been associated with localized divalent copper ions in the Cu(1) sites. A time-induced transformation of the ${\mathrm{Cu}}^{2+}$ local crystal-field symmetry from orthorhombic to tetragonal, related to the oxygen distribution in the Cu(1) plane, has been detected. The EPR spectra of pairs of weakly exchange-coupled divalent copper ions were also observed. These copper pairs are suggested to occur in the Cu(1) planes and to be magnetically isolated from the antiferromagnetic ${\mathrm{CuO}}_{2}$ planes.

Evaluation of contaminant ion adsorption/desorption on goethite using pressure jump relaxation kinetics

The adsorption/desorption of contaminant ions on soil constituents such as metal oxides occurs within milliseconds. The rapid kinetics of Cu e+ and arsenate adsorption/ desorption on goethite (α-FeOOH) were investigated using the pressure-jump (p-jump) relaxation technique, which provides rate constants and mechanistic information for fast reactions. Results of p-jump experiments at 25°C revealed that both Cu 2+ and arsenate were specifically adsorbed on goethite. The divalent copper ion formed an inner-sphere monodentate surface complex, while arsenate formed an inner-sphere bidentate surface complex with goethite. In both cases, the rate constants for the adsorption reactions exceeded those for desorption, indicating that the desorption of Cu 2+ and arsenate from the goethite surface was the rate-limiting process. Pressure jump relaxation techniques can be used to predict the adsorption behavior of heavy metals in soil environments.

The Ternary Complexes of Bovine Serum Albumin and Polyacrylamide Derivatives in the Presence Copper Ions in Neutral Water

The formation of complexes between polyacrylamide which contains a glycine end group and BSA have been studied in neutral water. Water soluble or insoluble complexes are formed when divalent copper ions were added to these solutions. Contacts between protein and polyelectrolyte were achieved via chelate formation in which the copper ion is attached at the center. The solubility of the polycomplexes depends on the protein/polymer ratio. Starting with very low protein concentrations in the system, phase separation takes place. After a critical ratio of the protein/polymer was achieved the mixture exhibited water solubility. The kinetics of the formation of ternary complexes were studied. It was shown that water insoluble complexes are nonequilibrium complexes. A hypothetical structural model for the formation of soluble and insoluble ternary polycomplexes is proposed.

EPR study of Cu2+ ions in the Pr0.5RE0.5Ba2Cu3O6 + compounds in tetragonal phase at low temperatures

Abstract Powdered samples of the Pr 0.5 RE 0.5 Ba 2 Cu 3 O 6 + x compounds, where RE  Yb, Ho, Tm, Er, and Y, were investigated by the EPR technique at low temperatures in the range 2.8–20 K. In the EPR spectra of these non-superconducting materials in tetragonal phase, resonance lines arising from the exchange interaction of coupled pairs of divalent copper ions and Cu 2+ in the tetragonal local crystal field symmetry were recorded. Apart from the usually observed ΔM s = 1 and ΔM s = 2 transitions for the CuCu system, rarely reported singlet-triplet transitions were detected as well. The exchange parameter J has roughly the same value of about 0.12 cm −1 for all investigated samples and the zero-field splitting parameter D is of the order of 0.013 cm −1 . It is suggested that formation of Cu(1)OCu(2) copper coupled pairs is responsible for the observed EPR spectrum.

Probing of Phosphate Network Structure of an Alumina containing Phosphate Glass by using the d → d Absorption Properties of an Incorporated Transition Metal Ion

A significant change in the d → d absorption features of incorporated divalent copper ion has been noted in case of a phosphate glass with addition of alumina as one of its major components. The observed spectral change of the ion in the glass has been correlated to the structural change of the glass network that results due to the cross-linking of the phosphate chains of the glass by the alumina.

Low Temperature EPR Spectra of the (Pr, RE)BaCuO Ceramics in the Orthorhombic Phase

AbstractThe EPR spectra of the members of the series Pr0.5RE0.5Ba2Cu3O6+x (RE = Pr, La, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, Tm, Yb, and Lu) in the orthorhombic phase are investigated at low temperature. The EPR spectra arise from two different paramagnetic centers, one from divalent copper ions in orthorhombic local crystal field symmetry and another from exchange coupled pairs of copper ions whose origin is discussed. The EPR spectra essentially depend on the time exposition. The EPR spectra of some divalent and trivalent rare earth ions are recorded. The crystal field analysis is done for the trivalent ytterbium ions. The semiconducting behaviour of the dc conductivity can be attributed to thermally activated small polaron hopping motion.

Specific Protein Attachment to Artificial Membranes via Coordination to Lipid-Bound Copper(II)

A versatile and convenient method for targeting proteins to lipid assemblies using metal ion coordination is described. Mixed lipid bilayers and Langmuir monolayers containing a metal-chelating lipid and divalent copper ions are shown to bind protein via surface-accessible histidine residues. Cu^(2+) chelated by iminodiacetate (IDA) in the headgroup serves as an affinity ligand to target the protein to the interface. The compact, uncharged Cu^(2+)-IDA headgroup can be incorporated into lipid assemblies without disrupting the lipid packing. Surface pressure-area isotherms of DSPC monolayers containing 5 mol % of IDA-lipid show that Cu^(2+) enhances the rate and extent of myoglobin association with the interface. Myoglobin binds to small unilamellar vesicles containing 2% Cu^(2+)-IDA lipid (48% DSPC and 50% cholesterol) at least an order of magnitude more tightly than to vesicles without metal or loaded with Ca^(2+). The Cu^(2+)-IDA lipid more than doubles the amount of protein targeted to the interface. Cu^(2+) ESR parameters g_∥ and A_∥, measured for liposomes with native and DEPC-modified myoglobin, support coordination of surface histidine side chains to Cu^(2+) as the binding interaction.

Removal of Divalent Metal Cations and Their Mixtures from Aqueous Streams Using Micellar-Enhanced Ultrafiltration

ABSTRACT Micellar-enhanced ultrafiltration (MEUF) is a novel membrane-based separation technique that can be used to remove multivalent metal cations from aqueous streams. In this technique an anionic surfactant is added to the aqueous stream containing the metal cations to be removed. The surfactant forms highly charged aggregates called micelles onto which the metal cations adsorb or bind. The aqueous stream is then passed through an ultrafiltration membrane with pores small enough to block the passage of the micelles and adsorbed metal cations. In this study, MEUF has been shown to remove divalent cadmium, zinc, copper, and calcium ions and their mixtures with rejections of at least 96%. A previously developed equilibrium binding model describes the results successfully. Under reasonable conditions the flux rates are not substantially below that of pure water, indicating the feasibility of MEUF for industrial application.

Equilibrium studies for the interaction of aqueous metal ions and polyacrylic acid by a batch ultrafiltration method

Equilibrium constants for the complexation reactions of divalent copper and zinc ions and polyacrylic acid (PAA) were determined at 25°C from batch ultrafiltration results at an initial concentration ratio of PAA to metal ion of 2 and a pH value lower than ca. 3.50. The average coordination number of negatively charged PAA groups interacting with one metal ion was also obtained, with initial concentration ratios of PAA to copper ion up to 15. A simple equilibrium model proposed in this work enabled us to satisfactorily predict the rejection coefficient of metal ions in the presence of PAA. In addition, the effect of the formation of soluble metal hydroxy complexes on the rejection coefficient of the metal ions was examined.

Removal of copper and zinc from aqueous sulfate solution with polyacrylic acid by a batch complexation-ultrafiltration process

The removal of divalent copper and zinc ions from an aqueous sulfate solution with polyacrylic acid (PAA) was examined by a batch complexation-ultrafiltration process. Factors affecting the rejection and permeate flux such as the membrane pore size and the applied pressure were investigated. In addition, on the basis of the known chemical equilibrium constants obtained from a mono-ionic system, a rejection mechanism taking into account the formation of soluble metal hydroxy complexes was proposed to predict the rejection coefficient of metal ions and the separation factor in a bi-ionic solution.

Experimental studies of the EuBa2-xEuxCu3O7- delta compound in the tetragonal phase

EPR and magnetic measurements were carried out on specially prepared samples of the EuBa2-xEuxCu3O7- delta compound in the tetragonal phase, in the temperature range 100-4.2 K. The EPR spectra of Eu2+, Cu2+, coupled pairs of divalent copper ions and the superexchange interaction between Cu ions over oxygen bridges have been observed. The EPR spectrum of europium ions indicates the existence of a crystal-field splitting of the 8S7/2 ground state of Eu2+ ions with a value of the spin-Hamiltonian parameter b20 of about 14*10-2 cm-1. This parameter is analysed within the framework of Newman's superposition model. Anomalies in the temperature variation of the magnetic susceptibility are attributed to the presence of divalent and trivalent europium ions. The susceptibility of Eu3+ ions is non-zero because the excited states are thermally populated and they contribute to the result of the ground state with J=0.

Sorption of copper and zinc from aqueous sulfate solutions with bis(2-ethylhexyl)phosphoric acid-impregnated macroporous resin

Equilibrium studies were thermodynamically made for the sorption of divalent copper and zinc ions from aqueous sulfate solutions with bis(2-ethylhexyl)phosphoric acid-impregnated hydrophobic macroporous resins, by employing either Bromley or the simplified Pitzer equations to estimate the stoichiometric activity coefficient of various species in the aqueous phase. The mechanisms of copper and zinc sorption were found to be the same as those of the solvent extraction

Electron paramagnetic resonance studies of the oxygenated and non-oxygenated LaBa2Cu3O7- delta compounds

The EPR spectra of polycrystalline oxygenated and non-oxygenated (large oxygen deficiency) LaBa2Cu3O7- delta compounds, obtained at various temperatures, were studied and analysed. The oxygenated samples showed a transition temperature Tc at about 50 K. The EPR spectrum of the Cu2+ ions in the orthorhombic local symmetry was observed. It was found that these spectra are essentially influenced by an oxygen deficiency and thermal treatment. In the non-oxygenated samples, at a certain stage of the annealing process an EPR spectrum was detected at low temperatures. After the final anneal, this EPR spectrum showed significant changes. Changes were also observed in the corresponding XRD spectra indicating reductions in the concentrations of the CuO and BaCuO2 impurity phases. Additionally, the EPR spectrum of divalent copper ions in the axial local symmetry in the dx2-y2 ground state was observed.

EPR spectrum of Tm 2+ ions in the tetragonal phase of (La, Tm)-Ba-Cu-O compound

EPR measurements at room temperature (RT) on the oxygen deficient (La, Tm)-Ba-Cu-O compound (tetragonal phase) revealed a line centered at g=2.895(5) with linewidth Δ H=0.015(1)T. The line is ascribed to Tm 2+ ions (4f 13, 2F 7/2) assuming that the Γ(7) doublet is the ground state. A characteristic EPR spectrum of divalent copper ions was also observed.

Electron-paramagnetic-resonance study of silver halide photochromic glasses: Darkening mechanism

The mechanism of darkening of standard silver halide photochromic glass is studied by electron paramagnetic resonance (EPR) of photogenerated divalent copper ions. A time resolution of the EPR spectra was obtained by recording the evolution with the irradiation time of the EPR intensity at various magnetic-field strengths. It is shown that only one copper species is photogenerated during darkening. This species is a CuII-silver vacancy complex oriented along a [110] direction. The electron ground state has a predominantly dz2 character. The activation energy of the formation of this complex, E=0.06±0.01 eV, is controlled by the migration of interstitial silver ions. It is also shown that the silver vacancy of the complex is generated during the hole trapping by the monovalent copper ion.

Simultaneous spectrophotometric determination of metal ions with 4-(pyridyl-2-azo)resorcinol (PAR)

A new method for the simultaneous determination of the divalent ions of cadmium, cobalt, copper, lead, manganese, nickel and zinc in binary, ternary and quaternary mixtures based on the application of a multiple linear regression programme to the spectra of the complexes of these ions with 4-(pyridyl-2-azo)resorcinol (PAR) was developed. The detection limits afforded by the proposed method range from 0.02 μg/ml for Co(II), Mn(II), Ni(II) and Zn(II) to 0.10 μg/ml for Pb(II). The method is rapid and quite simple as it entails no prior separation, and was successfully applied to the analysis for the above-mentioned ions in synthetic samples and real alloys.

Synthesis and characterization of square planar and pseudo-tetrahedral M(II)N 2S 2

Copper(II), nickel(II) and zinc(II) complexes of methyl-2-amino-1-cyclopentenedithiocarboxylate and N,N′-pentamethylene-bis(methyl-2-amino-1-cyclopentenedithiocarboxylate) have been prepared and characterized in order to provide a basis for comparison of neutral molecules involved in planar and pseudo-tetrahedral coordination geometries with similar N 2S 2 ligand donor sets. Methyl-2-amino-1- cyclopentenedithiocarboxylate chelates as a bidentate ligand through a thioketonate sulfur and an imine nitrogen, forming planar complexes with the divalent ions of copper(II), nickel(II) and zinc(II). The Cu(II) complex exhibits EPR spin Hamiltonian parameters typical of an axial system with g∥=2.139 and A∥=175x10 −4. N,N′-pentamethylene-bis(methyl-2-amino-1-cyclopentenedithiocarboxylate) coordinates as a tetradentate ligand, where the pentamethylene bridge between the nitrogens introduces steric strain forcing distortion of the inner coordination sphere. Spectral data support pseudo-tetrahedral coordination geometries for both Cu(II) and Ni(II). The EPR spectrum of this Cu(II) complex is characteristic of a large tetrahedral distortion with g∥=2.146 and A∥=133x10 −4cm −1, while 1H NMR studies on the Ni(II) analogue indicate paramagnetic contact shifts of resonances, also indicative of tetrahedral distortion. The complexes are examined as possible spectral models of N 2S 2 coordination environments at the active sites of metalloproteins such as in the type I blue copper(II) and nickel hydrogenase proteins.

EPR of complexes of divalent copper ions with organophosphorus derivatives of 2-aminopyridine

The complexation of copper(II) ion with organophosphorus derivatives of 2-aminopyridine was studied with EPR. It was found that, compared with 2-aminopyridine, the presence of a P-N bond in its derivatives substantially changes the character of the coordination of the ligand with respect to divalent copper, which includes an aminic nitrogen atom in the coordination sphere of the metal, and results in the formation of a four-membered chelate ring. The parameters of the EPR spectra and evaluations of the stability constants are given.

Oxidation of low-density lipoprotein by Cu 2+ and lipoxygenase: an electron spin resonance study

The aim of this work was to obtain spectroscopic evidence for free radicals formed during copper ion- and lipoxygenase-catalyzed oxidation of the low-density lipoprotein. During the initial oxidation phase, a free-radical metabolite derived from the endogeneous α-tocopherol present in the low-density lipoprotein was detected by the electron spin resonance technique. The divalent copper ions were bound to the residual EDTA present in the low-density lipoprotein and to the protein. Production of the α-tocopherol radical was suppressed in the presence of spin traps. Evidence for the low-density lipoprotein-lipid derived radicals was obtained by ESR-spin trapping methods. Implications of these findings in the oxidative modification of the low-density lipoprotein are discussed.

Simultaneous purification of nickel sulphate solutions from di-valent iron, copper and zinc ions

On the basis of kinetic data optimal conditions for simultaneous hydrolytic purification of low-acid nickel sulphate solutions from divalent ions of iron, copper and zinc were established. The residual content of Fe, Cu and Zn in the purified solutions is about or less than 1 mgl −1. Only 9–11% of nickel co-precipitates with the admixtures. At a mole ratio Fe 2+:Cu 2+ of about 1 the oxidation of Fe 2+ proceeds totally without addition of an oxidizing agent. The precipitates were analyzed by X-ray micro-analysis, X-ray diffraction and Mössbauer spectroscopy. The data obtained along with the kinetic data concerning the precipitation of all elements made it possible to propose a mechanism of the process studied.