Coordination Of Cu Research Articles

The possible role of Gly residues in the prion octarepeat region in the coordination of Cu2+ ions

Spectroscopic and potentiometric data have shown that insertion of tripeptides other than the Gly3 peptide fragment, Ala3 or Lys3, into the prion octarepeat region destabilizes the biologically relevant Cu2+ complex with the metal ion bound equatorially through the {Nimid,2N−} donor set. The other likely role of the high glycine content could be enforcement of the high flexibility of the N-terminal prion region resulting in the unstructured protein organization. However, the insertion of bulkier amino acid residues does not change the basic coordination mode at physiological pH which involves imidazole nitrogen and two amide nitrogen donors from the third and fourth residues.

Coordination polymers based on porphyrin and copper: the influence of the crystallization solvents on the dimensionality of the network

The α2β2 atropoisomer of meso-tetrakis(o-nicotinoylamidophenyl)–copper porphyrin leads in the presence of Cu(II) cation to coordination polymers in the crystalline phase. The networks are generated by interconnection of metalloporphyrin units through the coordination of Cu centres adopting an octahedral coordination geometry by two pyridines belonging to consecutive complexes. Depending on the solvent systems used, the 1-D coordination network based on 1α2β2 and Cu dication was shown to form a 3-D network based on a combination of three distinct supramolecular forces.

Carbon Monoxide Oxidation on Nanostructured CuO x/CeO 2 Composite Particles Characterized by HREM, XPS, XAS, and High-Energy Diffraction

Nonstoichiometric CuO x /CeO 2 nanocomposite particles have been synthesized by inert gas condensation (IGC) over the whole compositional range (2 to 98 at.% Cu). The composition influences greatly the formation of various nanostructures, such as core-shells. A wide range of techniques were used to characterize the catalysts: high-resolution TEM and X-ray photoelectron spectroscopy, as well as high-energy diffraction (HED) and X-ray absorption spectroscopy (XANES and EXAFS) using synchrotron radiation. Catalytic oxidation of carbon monoxide was performed on catalysts with equal specific surface area, using both a batch reactor and a fixed-bed flow reactor. X-ray absorption spectroscopy showed that copper was present as a mixture of Cu(I) and Cu(II) species ranging from ca. 36% Cu(I) in one of the fresh samples to less than 5% in the activated samples. The coordination of Cu(I) was found to be mostly linear 2-coordinate as in the model compound Cu 2O or alternatively 3-coordinate planar, while Cu(II) was found to present a mixture of tetrahedral and highly distorted octahedral coordination. EXAFS showed that both copper species were part of a very dispersed and highly disordered structure. The main chemical factors that control the activity for the oxidation of carbon monoxide are (i) the nanostructured morphology, (ii) the X-ray crystallinity as determined by HED, and (iii) the dispersion of copper at the surface. These three factors can be tailored during the IGC synthesis, but they can also change during the thermal activation. Copper ions migrate toward the particle surface and create new and highly dispersed superficial copper species/clusters, accompanied by a slight reduction of the CeO 2 surface. This favorable morphological evolution, or diminutive structural rearrangement, which was not adequately resolved by HREM, can be monitored as a shift of the light-off temperature. The wide variation in X-ray crystallinity between the catalysts can be used to quantify the processes occurring during the thermal activation. Easily reducible, high-energy surfaces of CeO 2 are better in stabilizing extremely dispersed copper species by a close synergistic interaction, which promotes a rapid change of valency and supply of oxygen.

Carbon Monoxide Oxidation on Nanostructured CuOx/CeO2 Composite Particles Characterized by HREM, XPS, XAS, and High-Energy Diffraction

Nonstoichiometric CuOx/CeO2 nanocomposite particles have been synthesized by inert gas condensation (IGC) over the whole compositional range (2 to 98 at.% Cu). The composition influences greatly the formation of various nanostructures, such as core-shells. A wide range of techniques were used to characterize the catalysts: high-resolution TEM and X-ray photoelectron spectroscopy, as well as high-energy diffraction (HED) and X-ray absorption spectroscopy (XANES and EXAFS) using synchrotron radiation. Catalytic oxidation of carbon monoxide was performed on catalysts with equal specific surface area, using both a batch reactor and a fixed-bed flow reactor. X-ray absorption spectroscopy showed that copper was present as a mixture of Cu(I) and Cu(II) species ranging from ca. 36% Cu(I) in one of the fresh samples to less than 5% in the activated samples. The coordination of Cu(I) was found to be mostly linear 2-coordinate as in the model compound Cu2O or alternatively 3-coordinate planar, while Cu(II) was found to present a mixture of tetrahedral and highly distorted octahedral coordination. EXAFS showed that both copper species were part of a very dispersed and highly disordered structure. The main chemical factors that control the activity for the oxidation of carbon monoxide are (i) the nanostructured morphology, (ii) the X-ray crystallinity as determined by HED, and (iii) the dispersion of copper at the surface. These three factors can be tailored during the IGC synthesis, but they can also change during the thermal activation. Copper ions migrate toward the particle surface and create new and highly dispersed superficial copper species/clusters, accompanied by a slight reduction of the CeO2 surface. This favorable morphological evolution, or diminutive structural rearrangement, which was not adequately resolved by HREM, can be monitored as a shift of the light-off temperature. The wide variation in X-ray crystallinity between the catalysts can be used to quantify the processes occurring during the thermal activation. Easily reducible, high-energy surfaces of CeO2 are better in stabilizing extremely dispersed copper species by a close synergistic interaction, which promotes a rapid change of valency and supply of oxygen.

On the existence of CuI pairs in ZSM-5--a computational study.

The siting and coordination of Cu(I) pairs in zeolite ZSM-5 have been studied by means of a combined quantum mechanics/interatomic potential function technique (QM-Pot). It couples a density functional theory (DFT) description employing a hybrid functional (B3LYP) for copper ions, including their local environment, with a DFT-parameterized shell model ion-pair potential for the periodic ZSM-5 structure. A missing Cu(I)-Cu(I) interaction potential term in the force field has been parameterized on the basis of DFT results. Several distinct coordination sites for Cu(I) pairs have been identified within the ZSM-5 framework. These have been classified as open, nest, open-nest, and cage pairs, owing to the shape of their local environment in the crystal. A nest-shaped, bridged eight-membered ring constitutes the most probable site for the existence of Cu(I) ion pairs. It is energetically favored over all isolated Cu(I) sites. The excitation and emission energies for the singlet-triplet transition of the Cu(I) pairs have been studied. Earlier assignment of an emission band at 520 nm to Cu(I) pairs by others is not supported by our computed results.

Single Crystal EPR and Optical Studies of Cu(II) Doped Zinc Ammonium Phosphate Hexahydrate: A Case of Rhombic Distortion

Single crystal EPR and optical studies of Cu(II) doped ZnNH4PO4 · 6H2O (Zinc struvite) have been carried out at room and liquid nitrogen temperatures. The g and A tensors indicate that the impurity has entered the lattice substitutionally. Even though the coordination polyhedron around the host Zn(II) is a compressed octahedron of oxygen atoms of water, the Cu(II) ion has an elongated octahedron corresponding to dx2-y2 ground state. The optical spectrum shows four bands at 1205, 1095, 833 and 805 nm, which confirms the octahedral coordination of Cu(II) with rhombic (C2V) distortion.

Effects of Water and Ion-Exchanged Counterion on the FTIR Spectra of ZSM-5. II. (Cu+–CO)-ZSM-5: Coordination of Cu+–CO Complex by H2O and Changes in Skeletal T–O–T Vibrations

The 2157 cm−1 (strong) and 2108 cm−1 (very weak) ν(CO) IR bands due to Cu+–CO in ZSM-5 zeolite with 12C and 13C isotopes, respectively, are reversibly red-shifted by subsequent adsorption of H2O at 293 K. On the contrary, the locally perturbed internal (T–O–T) asymmetric stretching framework vibration [νasint(TOT)(Cu+–CO)=965 cm−1] is reversibly blue-shifted. The courses of the band shifts revealed notable features. Charge transfers from water to Cu+ ions, changes in coordination spheres of Cu+(CO)(H2O)n aqua complexes and secondary (solvent-like) effects were considered to explain the results.

Semicarbazone of starch dialdehyde and its complexes with metal ions

Potato starch was oxidised with periodate to 14% dialdehyde product that was converted into its semicarbazone. Complexes of the semicarbazone with Ca, Cd, Co (II), Cu (II), Fe (II), Mg, Mn (II), Ni (II), Pb (II) and Zn are described. IR spectral analyses on the soluble fractions of the complexes showed that the carbonyl oxygen atoms and the CN nitrogen atoms of the semicarbazone are involved in chelation of the metal atoms. The thermal analysis of complexes revealed two-step decomposition of the ligand and three-step decomposition of complexes. Particular metal ions are chelated to a different extent. One in six semicarbazone moiety is engaged in co-ordination of Cu (II), and in bonding of Mn (II) one in 40 semicarbazone moiety is involved.

Some Factors Governing Ag+ and Cu+ Low Coordination in Chalcogenide Environments

The factors influencing the low coordination of Cu+ and Ag+d10 cations in chalcogenides are analyzed by means of FLAPW band structure calculations. The study shows that the metal s/d orbital mixing is the predominant factor, in agreement with most previous research reports. It also quantitatively shows that the d10 cation polarization is reduced when the chalcogen electronegativity decreases, thus the coordination increases when going from the oxides to the tellurides. The calculation results make clear the fact that the d10 element low coordination can be raised for a given chalcogen by enhancing the polarization influence of the chalcogen through a charge transfer from an alkali metal. Finally, the shift in behavior from Cu+ to Ag+ is shown to be related to their different polarizabilities.

ChemInform Abstract: Coordination of Cu+ and Cu2+ Ions in ZSM‐5 in the Vicinity of Two Framework Al Atoms.

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Studies on synthesis and adsorption properties of chitosan cross-linked by glutaraldehyde and Cu(II) as template under microwave irradiation

A series of cross-linked chitosan resins have been synthesized by forming chitosan coordination of Cu(II) as template in dilute acetic acid solutions under microwaves irradiation, then reacting the Cu(II)–chitosan complex with glutaraldehyde as cross-linking agent under microwave irradiation, and finally removing off the Cu(II ) with dilute acid. The adsorption capacity and selectivity of the cross-linked chitosan for Cu 2+, Ni 2+ and Co 2+ have also been investigated. The experimental results show that these resins obtained have better adsorption capacity for Cu 2+ than Ni 2+ and Co 2+, very good stability and reusability in acidic solutions.

Copper(II)-lincomycin: complexation pattern and oxidative activity.

Coordination of Cu(II) to lincomycin was studied by potentiometry, UV-Vis, circular dichroism (CD), EPR, NMR, cyclic voltammetry (CV) and ESI-MS. Only mononuclear complexes of stoichiometries ranging from CuL to CuH(-3)L were found. In the main species present at neutral pH, CuH(-2)L, lincomycin bonds Cu(II) through both of its nitrogen donors, and a deprotonated oxygen donor at C4 of the sugar moiety. High pressure liquid chromatography (HPLC) of products of 2'-deoxyguanosine (dG) oxidation and agarose gel electrophoresis of plasmid DNA confirmed that lincomycin complexes effectively facilitate dG oxidation by H2O2, but are not able to cleave double-stranded plasmid DNA.

Coordination of Cu+ and Cu2+ ions in ZSM-5 in the vicinity of two framework Al atoms

A combined quantum mechanics/interatomic potential function technique has been used to examine Cu+/Al− sites in the vicinity of H+Al− sites and Cu2+ in the vicinity of two framework Al atoms under dehydrated conditions. The symmetrical coordination of Cu2+ ions to four framework oxygen atoms is the most stable site and Cu2+ is hard to reduce at these sites. In agreement with EPR measurements a square-pyramidal coordination of Cu2+ at these sites is suggested. However, this symmetrical coordination is attained only for specific positions of the framework aluminium pair. Coordination changes upon reduction of divalent to monovalent copper ions and upon excitation of Cu+ ions in the first triplet excited state are also investigated. The coordination of the copper ions does not significantly change during reduction in the dehydrated state. Coordination changes of Cu+ upon excitation in the triplet state and calculated transition energies for Cu+/Al− sites in the vicinity of H+Al− sites are identical to those observed for isolated Cu+/Al− sites.

Monolayers of novel amphiphile with schiff base moiety as headgroup and its complex of copper(II)

A novel amphiphile 2,4-dihydroxy- N-octadecylbenzylideneamine (abbreviated as SBC 18) bearing a schiff base moiety as headgroup, and its complex Bis(2,4-dihydroxy- N-octadecylbenzylideneaminato) Copper(II) (abbreviated as Cu(SBC 18) 2) were synthesized successfully. The π -A isotherms were conducted to explore their monolayer behavior. The π -A isotherm of an SBC 18 monolayer shows that an orientational change may be accompanied by increase of intramolecular hydrogen bonds in the plateau-like region, which were further confirmed by FTIR and UV-Vis spectroscopic results. By Comparison the plateau-like region disappeared in π-A isotherms of surface film and subphase film of Cu (SBC 18) 2 which may be due to coordination of Cu 2+ to SBC 18 eliminating conversion of intermolecular to intramolecular hydrogen bonds.

X-ray structure and the reaction mechanism of bovine heart cytochrome c oxidase

X-ray structure of bovine heart cytochrome c oxidase in the fully oxidized state shows a peroxide bridging between Fe 3+ and Cu 2+ in the O 2 reduction site. The bond distances for Fe–O and Cu–O are 2.52 and 2.16 Å, respectively. The structure is consistent with antiferromagnetic coupling between the two metals, which has long been known and to recent redox titration results [J. Biol. Chem. 274 (1999) 33403]. The trigonal planer coordination of Cu 1+ in the O 2 reduction site is consistent with the very weak interaction between Cu 1+ and O 2 bound at Fe 2+ revealed by time-resolved resonance Raman investigations. One of the three histidine imidazoles coordinated to the Cu ion in the O 2 reduction site fixes a tyrosine phenol group near the O 2 reduction site with the direct covalent link between the two groups. The structure suggests that the phenol group is the site for donating protons to the bound O 2. Redox-coupled conformational change in an extramembrane loop indicates that an aspartate (Asp51) in the loop apart from the O 2 reduction site is the site for proton pumping.

EXAFS study on the local environment of Cu + ions in glasses of the Cu 2O–Na 2O–Al 2O 3–SiO 2 system prepared by Cu +/Na + ion exchange

The local environment around Cu + in Cu +/Na + ion-exchanged sodium aluminosilicate glasses was investigated as a function of the ratio x (x= Cu +/[ Cu ++ Na +]) by extended X-ray absorption fine structure spectroscopy (EXAFS). Glass specimens with various ratios were prepared by ion exchange in 20Na 2O–10Al 2O 3–70SiO 2 (mol%) glass at 400°C followed by concentration equalizing treatment. The coordination number N of Cu + in the glasses of x20Cu 2O–(1− x)20Na 2O–10Al 2O 3–70SiO 2 (mol%) increased accompanying the increase of the interatomic distance r Cu–O with increasing x: N=2.2, 2.8 and 3.7, and r Cu– O =0.184, 0.188 and 0.191 nm for the samples of x=0.2, 0.4 and 0.63, respectively. The change in the coordination of Cu + was discussed in relation to the structural evolution caused by ion exchange. These changes seem to induce a change in the environment around Cu + from twofold to fourfold coordination structure. The fourfold site for Cu + offered a favorable situation for ionic conduction, because these highly ion-exchanged glass samples showed high electrical conductivity.

The crystal structure of namibite, Cu(BiO)2VO4(OH), and revision of its symmetry

The crystal structure of namibite, Cu(BiO)2VO4(OH) [triclinic, space group P1̄, a = 6.210(1), b = 7.398(1), c = 7.471(1) Å, α = 90.10(1), β = 108.73(1), γ = 107.47(1)°, V = 308.22(8) Å3, Z = 2] was determined using single-crystal X-ray diffraction data. The refinement, based on 2140 unique reflections with Fo > 4σ(Fo), gave R1 = 3.61%. The structure determination showed namibite to be triclinic-pseudomonoclinic; the previously reported C-centered monoclinic cell is a pseudocell. The structure contains two unique Bi atoms, with nine Bi-O bonds between 2.17 and 3.39 Å. The Bi coordinations show some stereochemical influence of the lone pair of electrons on Bi3+. A threedimensional network is formed by linkages of Bi-O polyhedra to one slightly distorted V5+O4 tetrahedron that decorates chains of corner-sharing CuO6 polyhedra extending parallel to the b axis. The CuO6 polyhedra show the Jahn-Teller-distorted [4+2]-coordination of Cu2+. Layers of Bi atoms parallel to (100) alternate with layers of parallel heteropolyhedral [Cu(VO4)O2(OH)] chains. According to bond-valence calculations and geometrical considerations, the H atom of the OH group is probably involved in disordered or trifurcated H bonding. The structure of namibite represents a slightly distorted ordered variant of the monoclinic structure of brendelite, (Bi,Pb)2(Fe3+,Fe2+)O2(OH)(PO4). Further relations to synthetic Cu3Bi4V2O14, to the 7 Å chain-structure phosphates and sulfates, and to linarite are outlined.

Characterization of localized hole states inPr1+xBa2−xCu3O6+yby nuclear magnetic resonance

We investigated the charge distribution in Pr_{1+x}Ba_{2-x}Cu_3O_{6+y}-crystals at liquid-He temperature by means of ^{63,65}Cu- and ^{141}Pr-NMR and NQR. The electric field gradients determined for the different oxygen coordinations of Cu(1) on the chains confirm the model that the hole states are localized in the O 2p - pi-orbitals of the CuO_(2)-planes. The intensity and line-shape analysis of the Cu(1)- and Pr-resonances in the oxygen doping series (x approx 0, y=0..1) and in the Pr/Ba solid-solution series (at y=1) allows us to assign the Pr-resonance to Pr at RE-sites. Therefore, we can investigate the charge distribution in the CuO_(2)-Pr-CuO_(2)-layers by crystal field analysis of the Pr-signal. To consistently describe our results with neutron scattering data we propose that two Pr-states are present in the RE-layer, and ascribe them to Pr with and one without a hole localized in the oxygen coordination shell. NMR detects only the former, with a virtually nonmagnetic singlet ground state, while space-integral techniques are dominated by the latter, due to a quasi-doublet ground state and antiferromagnetism of its Pr-moments at low temperature.

New cell volume expanded, elevated temperature orthorhombics YBa 2Cu 3O 6.5 and their Tc∼50 K plateau on time dependent transitions to volume contracted orthorhombics at room temperature.

A range of strongly cell volume ( V) expanded orthorhombics YBa 2Cu 3O y , diagnosed as partly based on three fold O coordination of Cu(1), is found to be stable for y=6.5 when fast quenched from near 670 K. These materials can rapidly transform, presumably in a series of infinitely adaptable ladder structures, to more V contracted orthorhombics at lower T and constant y=6.5. The transformation rates (of order h) can be slowed by partial Ni substitutions. A T c∼50 K plateau extends from V=173.0 to 174.8 A 3, is followed by T c collapse, but T c can reappear with roughly doubled values (extrapolated) for the highest V (>176 Å 3) obtained by a different method. The cell volume expanded varieties suggest a new paradigm for massive selfdoping involving Cu + and O −. This massive selfdoping is held responsible for T c plateaus and also for strong T c of complex cuprates such as Bi 2Sr 2Ca n−1 Cu n O 2 n+4 or HgBa 2CuO 4. The new concepts have far ranging implications for existing literature on physical properties or questions of doping, charge transfer or lattice gas calculations. They support a subperoxide–metal adduct state model for superconductivity.

Domains I and III of the human copper chaperone for superoxide dismutase interact via a cysteine-bridged Dicopper(I) cluster.

Copper binding to the human copper chaperone for superoxide dismutase (hCCS) has been investigated by X-ray absorption spectroscopy. Stoichiometry measurements on the dialyzed, as-isolated protein indicated that up to 3.5 Cu ions bound per hCCS molecule. Reduction with either sodium dithionite or dithiothreitol decreased the copper binding ratio to 2 coppers per hCCS monomer. Analysis of the as-isolated EXAFS data indicated coordination of Cu by a mixture of S and N backscatterers, suggestive of heterogeneous binding of copper between Cu-cysteine binding sites of domain I or III and copper-histidine SOD1-like metal binding sites of domain II. The best fit was obtained with 1.6 Cu-S (cysteine) at 2.24 A (2sigma(2) = 0.011 A(2)) and 1.1 N (histidine) at 1.98 A (2sigma(2) = 0.005 A(2)). A peak of variable intensity in the Fourier transform (FT) of the as-isolated protein at 2.7 A was suggestive of the presence of a heavy atom scatterer such as Cu. Analysis of the dithionite- and DTT-reduced derivatives indicated that copper was lost from the histidine coordinating sites, resulting in a S-only environment with copper coordinated to three S backscatterers at 2. 26 A. The heavy atom scatterer peak was now prominent in the FT and could be well fit by a Cu-Cu interaction at 2.72 A. The data were best interpreted by a dinuclear mu(2)()-bridged cluster with doubly bridging cysteine ligands similar to the cluster proposed to exist in the cytochrome c oxidase chaperone COX17. Analysis of primary sequence and X-ray structural information on yeast CCS strongly suggests that this cluster bridges between domains I and III in hCCS. A mechanism for copper translocation is briefly discussed.