Influence of counterions on the structure of bis(oxazoline)copper(ii) complexes; an EPR and ENDOR investigation

X- and Q-band EPR and ENDOR spectroscopy was used to study the structure of a series of heteroleptic and homoleptic copper bis(oxazoline) complexes, based on the (-)-2,2'-isopropylidenebis[(4S)-4-phenyl-2-oxazoline] ligand and bearing different counterions (chloride versus triflate); labelled [Cu(II)()]. The geometry of the two heteroleptic complexes, [Cu(II)()] and [Cu(II)()], depended on the choice of counterion. Formation of the homoleptic complex was only evident when the Cu(II)(OTf)(2) salt was used (Cu(II)(Cl)(2) inhibited the transformation from heteroleptic to homoleptic complexes). The hyperfine and quadrupole parameters for the surrounding ligand nuclei were determined by ENDOR. Well resolved (19)F and (1)H couplings confirmed the presence of both coordinated water and TfO(-) counterions in [Cu()].     

Synthesis and characterization of a new Schiff base derived from 2,3-diaminopyridine and 5-methoxysalicylaldehyde and its Ni(II), Cu(II) and Zn(II) complexes. Electrochemical and electrocatalytical studies

We describe the synthesis and characterization of a new tetradentate Schiff base ligand obtained from 2,3-diaminopyridine and 5-methoxysalicylaldehyde. This ligand (H₂L) reacted with nickel(II), copper(II), and zinc(II) acetates to give complexes. The ligand and its metal complexes were characterized using analytical, spectral data (UV–vis, IR, and mass spectroscopy), and cyclic voltammetry (CV). The crystal structure of the copper complex was elucidated by X-ray diffraction studies. The electrochemical behavior of these compounds, using CV, revealed that metal centers were distinguished by their intrinsic redox systems, e.g. Ni(II)/Ni(I), Cu(II)/Cu(I), and Zn(II)/Zn(I). Moreover, the electrocatalytic reactions of Ni(II) and Cu(II) complexes catalyze the oxidation of methanol and benzylic alcohol.     

Reporting a unique example of electronic bistability observed in the form of valence tautomerism with a copper(II) helicate of a redox-active nitrogenous heterocyclic ligand

Valence tautomeric compounds involving nondixolene-type ligands are rare. The triple-helicate copper(II) complex [Cu(II)(2)(L)(3)](ClO(4))(4)·3CH(3)CN (1) containing a redox-active N-heterocyclic ligand (L) has been prepared and displays VT equilibrium in solution, as established by electronic spectroscopy, electron paramagnetic resonance spectroscopy, and cyclic and differential pulse voltammetry carried out at variable temperatures. The process involves intramolecular transfer of an electron from one of the L ligands to a copper(II) center, leading to the oxidation of L to an L(?+) radical with concomitant reduction of the Cu(II) center to Cu(I), as shown by the equilibrium [Cu(II)Cu(I)L(?+)L(2)](4+) ? [Cu(II)(2)L(3)](4+).     

Fine-tuning of properties of bismacrocyclic dinuclear cyclidene receptors by N-methylation

N-Methylated bismacrocyclic Cu and Ni complexes were synthesised and structurally characterised in the solid state. Their properties in solution were analysed by using NMR and ESR spectroscopies and electrochemical methods. Face-to-face biscyclidenes linked through polymethylene chains form rectangular boxlike cations. These moieties can host some small guest molecules (water, pi-electron donating compounds) and are stabilised by a shell of neighbouring counterions. For the bismacrocyclic dinuclear complexes containing two nickel or two copper ions, the intramolecular interactions between the metallic centres are strengthened through methylation of the macrocyclic components, as compared with the nonmethylated species. We report the electron coupling created by two unpaired electrons coming from two copper centres observed by ESR spectroscopy. Methylation weakens the electron-acceptor properties of the complexes, which leads to less effective binding of the pi-electron-donating guests. It also increases the stability of the lower oxidation states. In the case of the copper complexes, both Cu(II)/Cu(I) and Cu(II)/Cu(III) reversible one-electron transfers are seen in the voltammograms. These changes in properties are interpreted as the consequences of steric repulsion between the methyl substituents and the macrocyclic ring.     

Poly(vinylpyrrolidone)‐based films grown on copper surfaces

The influence of molecular weight and the amount of the poly(vinylpyrrolidone) (PVP) on the growth of poly(vinylpyrrolidone)–based films on copper surfaces was studied by electrochemical, infrared and electronic spectroscopy, and thermogravimetric methods. Complex polymer/metal ions were deposited onto a copper surface, as the result of the electrochemically generated reaction of copper cations with PVP and SCN^?, in sulfuric acid media. Spontaneous film growth on copper surfaces was generated and characterized as a Cu(II)/PVP/SCN^? complex. Infrared spectra and thermal gravimetric curves of the films generated at + 0.7 V were compared with the chemically synthesized complex, and show the same patterns. The oxidation process can be described as: Cu(0)→Cu(I) and Cu(I)→Cu(II), and the copper complex formed at more positive potentials was characterized as Cu(II)/PVP/SCN^?, with copper bonded to the oxygen atom of PVP and thiocyanate ligand N‐linked. This study focuses on the complex formation on a copper surface in acid media and its characterization through electrochemical and spontaneously generated reactions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2206–2214, 2009     

Cathodic and anodic stripping determination of traces of adenine and adenosine based on accumulation of copper(I) compounds at mercury or amalgam electrodes

In the presence of adenine and adenosine, the copper(II)/copper(Hg) couple splits to the copper(II)/copper(I) and copper(I)/copper(Hg) couples. Sparingly soluble complexes of copper(I) with adenine and adenosine can be accumulated on the electrode surface either by reduction of Cu(II) ions or by oxidation of the copper amalgam electrode. The copper(I)/adenine deposit can be stripped either cathodically or anodically with detection limits of 5×10^?9 and 2×10^?8 mol dm^?3, respectively. The copper(I)/ adenosine complex yields only the cathodic stripping peak with a detection limit of 9×10^?6 mol dm^?3. The stripping peaks obtained for the copper(I)/adenine and copper(I)/ adenosine complexes are better defined and appear over a wider range of pH than the peaks related to the corresponding mercury compounds. Adenosine cannot be determined in the presence of adenine bur adenine can be determined in the presence of moderate amounts of adenosine.     

SELENOETHER COMPLEXES OF COPPER(II) ‐ SYNTHESIS,SPECTROSCOPY AND STRUCTURES

Abstract

The red-brown copper(II) diselenoether complexes, [Cu (L-L)₂][BF₄]₂ (L-L = MeSeCH₂CH₂SeMe, MeSeCH₂CH₂CH₂SeMe or PhSeCH₂CH₂SePh) have been prepared from copper(II) fluoroborate and the ligands in anhydrous dichloromethane. Some new dithioether analogues are also described. The reaction of MeSeCH₂CH₂SeMe and copper(II) fluoroborate in ethanol led to an unstable dark green substance which appeared to contain both copper(I) and copper(II) and was formulated [Cu(MeSeCH₂CH₂SeMe)₂] [BF₄]_x. The complexes were characterised by analysis, UV-visible and e.p.r. spectroscopy, and magnetic measurements, and cyclic voltammetry has been used to probe the Cu (II)/Cu(I) redox couples. The complexes are too unstable in solution to obtain crystals for an X-ray study, but structural data has been obtained for both the Cu(II) and Cu(I) complexes by copper K-edge EXAFS studies. Ditelluroethers reduce copper(II) salts to copper(I) complexes.     

Spacer-dependent structural and physicochemical diversity in copper(II) complexes with salicyloyl hydrazones: a monomer and soluble polymers

Complexation of copper(II) with a series of heterodonor chelating Schiff bases (LL) of salicylic acid hydrazide and aliphatic or cycloaliphatic ketones affords soluble one-dimensional (1D) metallopolymers containing Schiff bases as bridging ligands. Single-crystal X-ray diffraction results reveal nanometer-sized metallopolymeric wires [Cu(μ-LL)(2)](n) with off-axis linkers and a zigzag geometry. Octahedrally coordinated copper centers, exhibiting a Jahn-Teller distortion, are doubly bridged by two Schiff-base molecules in the μ(2)-η(1),η(2) coordination mode. The use of dibutylketone with long alkyl chains as a component for Schiff base formation leads to a distorted square planar monomeric copper(II) complex [Cu(LL)(2)], as evidenced by its X-ray crystal structure. The compounds are characterized by elemental analyses and IR and UV-vis spectroscopy, as well as magnetic susceptibility and cyclic voltammetry measurements. Electrochemical studies on the complexes reveal an existence of polymeric and monomeric forms in solution and the dependence of Cu(II)/Cu(I) reduction potentials on alkyl groups of salicyloyl hydrazone ligands. Polymeric complexes form conducting films on Pt electrodes upon multicycle potential sweeps.     

Tetraalkoxyaluminates of nickel(II), copper(II), and copper(I)

The syntheses and structural details of tetraisopropoxyaluminates and tetra-tert-butoxyaluminates of nickel(II), copper(I), and copper(II) are reported. Within the nickel series, either Ni[Al(OiPr)4]2.2HOiPr, with nickel(II) in a distorted octahedral oxygen environment, or Ni[Al(OiPr)4]2.py, with nickel(II) in a square-pyramidal O4N coordination sphere, or Ni[(iPrO)(tBuO)3Al]2, with Ni(II) in a quasi-tetrahedral oxygen coordination, has been obtained. Another isolated complex is Ni[(iPrO)3AlOAl(OiPr)3].3py (with nickel(II) being sixfold-coordinated), which may also be described as a "NiO" species trapped by two Al(OiPr)3 Lewis acid-base systems stabilized at nickel by three pyridine donors. Copper(I) compounds have been isolated in three forms: [(iPrO)4Al]Cu.2py, [(tBuO)4Al]Cu.2py, and Cu2[(tBuO)4Al]2. In all of these compounds, the aluminate moiety behaves as a bidentate unit, creating a tetrahedrally distorted N2O2 copper environment in the pyridine adducts. In the base-free copper(I) tert-butoxyaluminate, a dicopper dumbbell [Cu-Cu 2.687(1) A] is present with two oxygen contacts on each of the copper atoms. Copper(II) alkoxyaluminates have been characterized either as Cu[(tBuO)4Al]2, {Cu(iPrO)[(iPrO)4Al]}2, and Cu[(tBuO)3(iPrO)Al]2 (copper being tetracoordinated by oxygen) or as [(iPrO)4Al]2Cu.py (pentacoordinated copper similar to the nickel derivative). Finally, a copper(II) hydroxyaluminate has been isolated, displaying pentacoordinate copper (O4N coordination sphere) by dimerization, with the formula {[(tBuO)4Al]Cu(OH).py}2. The formation of all of these isolated products is not always straightforward because some of these compounds in solution are subject to decomposition or are involved in equilibria. Besides NMR [copper(I) compounds], UV absorptions and magnetic moments are used to characterize the compounds.     

Blue copper model complexes with distorted tetragonal geometry acting as effective electron-transfer mediators in dye-sensitized solar cells

The electron self-exchange rate constants of blue copper model complexes, [(-)-sparteine-N,N'](maleonitriledithiolato-S,S')copper ([Cu(SP)(mmt)])(0/)(-), bis(2,9-dimethy-1,10-phenanthroline)copper ([Cu(dmp)(2)](2+/+)), and bis(1,10-phenanthroline)copper ([Cu(phen)(2)](2+/+)) have been determined from the rate constants of electron transfer from a homologous series of ferrocene derivatives to the copper(II) complexes in light of the Marcus theory of electron transfer. The resulting electron self-exchange rate constant increases in the order: [Cu(phen)(2)](2+/+) < [Cu(SP)(mmt)](0/)(-) < [Cu(dmp)(2)](2+/+), in agreement with the order of the smaller structural change between the copper(II) and copper(I) complexes due to the distorted tetragonal geometry. The dye-sensitized solar cells (DSSC) were constructed using the copper complexes as redox couples to compare the photoelectrochemical responses with those using the conventional I(3)(-)/I(-) couple. The light energy conversion efficiency (eta) values under illumination of simulated solar light irradiation (100 mW/cm(2)) of DSSCs using [Cu(phen)(2)](2+/+), [Cu(dmp)(2)](2+/+), and [Cu(SP)(mmt)](0/)(-) were recorded as 0.1%, 1.4%, and 1.3%, respectively. The maximum eta value (2.2%) was obtained for a DSSC using the [Cu(dmp)(2)](2+/+) redox couple under the light irradiation of 20 mW/cm(2) intensity, where a higher open-circuit voltage of the cell was attained as compared to that of the conventional I(3)(-)/I(-) couple.     

A new dinuclear heme-copper complex derived from functionalized protoporphyrin IX

A new biomimetic model for the heterodinuclear heme/copper center of respiratory oxidases is described. It is derived from iron(III) protoporphyrin IX by covalent attachment of a Gly-L-His-OMe residue to one propionic acid substituent and an amino-bis(benzimidazole) residue to the other propionic acid substituent of the porphyrin ring, yielding the Fe(III) complex 1, and subsequent addition of a copper(II) or copper(I) ion, according to needs. The fully oxidized Fe(III)/Cu(II) complex, 2, binds azide more strongly than 1, and likely contains azide bound as a bridging ligand between Fe(III) and Cu(II). The two metal centers also cooperate in the reaction with hydrogen peroxide, as the peroxide adducts obtained at low temperature for 1 and 2 display different optical features. Support to this interpretation comes from the investigation of the peroxidase activity of the complexes, where the activation of hydrogen peroxide has been studied through the phenol coupling reaction of p-cresol. Here the presence of Cu(II) improves the catalytic performance of complex 2 with respect to 1 at acidic pH, where the positive charge of the Cu(II) ion is useful to promote O-O bond cleavage of the iron-bound hydroperoxide, but it depresses the activity at basic pH because it can stabilize an intramolecular hydroxo bridge between Fe(III) and Cu(II). The reactivity to dioxygen of the reduced complexes has been studied at low temperature starting from the carbonyl adducts of the Fe(II) complex, 3, and Fe(II)/Cu(I) complex, 4. Also in this case the adducts derived from the Fe(II) and Fe(II)/Cu(I) complexes, that we formulate as Fe(III)-superoxo and Fe(III)/Cu(II)-peroxo exhibit slightly different spectral properties, showing that the copper center participates in a weak interaction with the dioxygen moiety.     

New heteroleptic bis-phenanthroline copper(I) complexes with dipyridophenazine or imidazole fused phenanthroline ligands: spectral, electrochemical, and quantum chemical studies

Two new sterically challenged diimine ligands L(1) (2,9-dimesityl-2-(4'-bromophenyl)imidazo[4,5-f][1,10]phenanthroline) and L(2) (3,6-di-n-butyl-11-bromodipyrido[3,2-a:2',3'-c]phenazine) have been synthesized with the aim to build original heteroleptic copper(I) complexes, following the HETPHEN concept developed by Schmittel and co-workers. The structure of L(1) is based on a phen-imidazole molecular core, derivatized by two highly bulky mesityl groups in positions 2 and 9 of the phenanthroline cavity, preventing the formation of a homoleptic species, while L(2) is a dppz derivative, bearing n-butyl chains in α positions of the chelating nitrogen atoms. The unambiguous formation of six novel heteroleptic copper(I) complexes based on L(1), L(2), and complementary matching ligands (2,9-R(2)-1,10-phenanthroline, with R = H, methyl, n-butyl or mesityl) has been evidenced, and the resulting compounds were fully characterized. The electronic absorption spectra of all complexes fits well with DFT calculations allowing the assignment of the main transitions. The characteristics of the emissive excited state were investigated in different solvents using time-resolved single photon counting and transient absorption spectroscopy. The complexes with ligand L(2), bearing a characteristic dppz moiety, exhibit a very low energy excited-state which mainly leads to fast nonradiative relaxation, whereas the emission lifetime is higher for those containing the bulky ligand L(1). For example, a luminescence quantum yield of about 3 × 10(-4) is obtained with a decay time of about 50 ns for C2 ([Cu(I)(nBu-phen)(L(1))](+)) with a weak influence of strong coordinating solvent on the luminescence properties. Overall, the spectral features are those expected for a highly constrained coordination cage. Yet, the complexes are stable in solution, partly due to the beneficial π stacking between mesityl groups and vicinal phenanthroline aromatic rings, as evidenced by the X-ray structure of complex C3 ([Cu(I)(Mes-phen)(L(2))](+)). Electrochemistry of the copper(I) complexes revealed reversible anodic behavior, corresponding to a copper(I) to copper(II) transition. The half wave potentials increase with the steric bulk at the level of the copper(I) ion, reaching a value as high as 1 V vs SCE, with the assistance of ligand induced electronic effects. L(1) and L(2) are further end-capped by a bromo functionality. A Suzuki cross-coupling reaction was directly performed on the complexes, in spite of the handicapping lability of copper(I)-phenanthroline complexes.     

Interaction of copper(II) complex of compartmental Schiff base ligand N,N'-bis(3-hydroxysalicylidene)ethylenediamine with bovine serum albumin

Circular dichroism (CD) spectroscopy, cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to investigate the interaction between copper(II) complex of compartmental Schiff base ligand (L), N,N'-bis(3-hydroxysalicylidene)ethylenediamine, and bovine serum albumin (BSA) in 0.1 mol dm(-3) phosphate buffer solution adjusted to physiological pH 7.0 containing 20% (w/w) dimethylsulfoxide at room temperature. CD spectra show that the interaction of the copper(II) complex with BSA leads to changes in the alpha-helical content of BSA and therefore changes in secondary structure of the protein with the slight red shift (2 nm) in CD spectra. From the voltammetric data, i.e. changes in limiting current with addition of BSA, the binding constant (K) of the interaction of copper(II) complex with BSA was found to be 1.96 x 10(4)dm(3)mol(-1). From the shifts in potential with the addition of BSA, the equilibrium constant ratio (K(2)/K(1)) for the binding of the oxidized Cu(II)L (K(1)) and reduced Cu(I)L (K(2)) species to BSA was found to be 3.77, which shows that the reduced form Cu(I)L is bound more strongly to BSA than the oxidized form Cu(II)L.     

Mononuclear and binuclear copper(I) complexes ligated by bis(3,5-diisopropyl-1-pyrazolyl)methane: insight into the fundamental coordination chemistry of three-coordinate copper(I) complexes with a neutral coligand

By using the neutral bidentate nitrogen-containing ligand, bis(3,5-diisopropyl-1-pyrazolyl)methane (L1' '), the copper(I) complexes [Cu(L1' ')2](CuCl2) (1CuCl2), [Cu(L1' ')2](ClO4) (1ClO4), [Cu(L1' ')]2(ClO4)2 (2ClO4), [Cu(L1' ')]2(BF4)2 (2BF4), [Cu(L1' ')(NCMe)](PF6) (3PF6), [Cu(L1' ')(PPh3)](ClO4) (4ClO4), [Cu(L1' ')(PPh3)](PF6) (4PF6), [{Cu(L1' ')(CO)}2(mu-ClO4)](ClO4) (5ClO4), and the copper(II) complexes [{Cu(L1' ')}2(mu-OH)2(mu-ClO4)2] (6), and [Cu(L1' ')Cl2] (7) were systematically synthesized and fully characterized by X-ray crystallography and by IR and 1H NMR spectroscopy. In the case of copper(II), ESR spectroscopy was also applied. In comparison with the related neutral tridentate ligand L1', bis-chelated copper(I) complexes and binuclear linear-coordinated copper(I) complexes are easy to obtain with L1' ', like 1CuCl2, 1ClO4, 2ClO4, and 2BF4. Importantly, stronger and bulkier ligands such as acetonitrile (3PF6) and especially triphenylphosphine (4ClO4 and 4PF6) generate three-coordinate structures with a trigonal-planar geometry. Surprisingly, for the smaller ligand carbon monoxide, a mononuclear three-coordinate structure is very unstable, leading to the formation of a binuclear complex (5ClO4) with one bridging perchlorate anion, such that the copper(I) centers are four-coordinate. The same tendency is observed for the copper(II) bis(mu-hydroxo) compounds 6, which is additionally bridged by two perchlorate anions. Both copper(II) complexes 6 and 7 were obtained by molecular O2 oxidation of the corresponding copper(I) complexes. A comparison of the new copper(I) triphenylphosphine complexes 4ClO4 and 4PF6 with corresponding species obtained with the related tridentate ligands L1' and L1 (8ClO4 and 9, respectively) reveals surprisingly small differences in their spectroscopic properties. Density functional theory (DFT) calculations are used to shed light on the differences in bonding in these compounds and the spectral assignments. Finally, the reactivity of the different bis(pyrazolyl)methane complexes obtained here toward PPh3, CO, and O2 is discussed.     

SiO2/graphene composite for highly selective adsorption of Pb(II) ion

SiO(2)/graphene composite was prepared through a simple two-step reaction, including the preparation of SiO(2)/graphene oxide and the reduction of graphene oxide (GO). The composite was characterized by UV-Vis spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscope, and X-ray photoelectron spectroscopy, and what is more, the adsorption behavior of as-synthesized SiO(2)/graphene composite was investigated. It was interestingly found that the composite shows high efficiency and high selectivity toward Pb(II) ion. The maximum adsorption capacity of SiO(2)/graphene composite for Pb(II) ion was found to be 113.6 mg g(-1), which was much higher than that of bare SiO(2) nanoparticles. The results indicated that SiO(2)/graphene composite with high adsorption efficiency and fast adsorption equilibrium can be used as a practical adsorbent for Pb(II) ion.     

Thiohydrazone copper(II) complexes. The relationship between redox properties and superoxide dismutase mimetic activity

The redox behaviour of copper(II) complexes with the open chain ligand, benzilbisthiosemicarbazone, and the macrocyclic one [3,4,10,11-tetraphenyl-1,2,5,8,9,12,13-octaazacyclotetradeca-7,14- dithione- 2,4,9,11-tetraene] has been explored by cyclic voltammetry. The half-wave potential values for the copper(II)/copper(I) redox couple and the spectral data obtained on dimethylsulfoxide (DMSO) solution agree with the superoxide dismutase (SOD)-mimetic activity of the complexes. The macrocyclic complexes show more positive reduction potential and more activity than the open chain derivatives. From our results it follows that the structure and conformation of ligand has influence on the redox potential of central atom in coordination compound. The changes in the coordination sphere are connected with the change of biological function of compounds represented by SOD-mimic activity. In addition, the L1H6 derivatives show quasireversible waves associated to Cu(II)/Cu(III) process.     

Click chemistry meets polymerization: Controlled incorporation of an easily accessible ruthenium(II) complex into a PMMA backbone via RAFT copolymerization

The copper(I)-catalyzed azide-alkyne cycloaddition provided an easy and efficient access to a functionalized heteroleptic ruthenium(II) complex monomer. A grafted copolymer with the heteroleptic ruthenium(II) complex and methyl methacrylate (MMA) as comonomer was synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization. The product was characterized by means of ¹H NMR spectroscopy, UV/vis spectroscopy and size exclusion chromatography coupled with a photodiode array detector. The RAFT process itself led to a grafted copolymer with a low polydispersity index.     

Lumenal loop M672-P707 of the Menkes protein (ATP7A) transfers copper to peptidylglycine monooxygenase

Copper transfer to cuproproteins located in vesicular compartments of the secretory pathway depends on activity of the copper-translocating ATPase (ATP7A), but the mechanism of transfer is largely unexplored. Copper-ATPase ATP7A is unique in having a sequence rich in histidine and methionine residues located on the lumenal side of the membrane. The corresponding fragment binds Cu(I) when expressed as a chimera with a scaffold protein, and mutations or deletions of His and/or Met residues in its sequence inhibit dephosphorylation of the ATPase, a catalytic step associated with copper release. Here we present evidence for a potential role of this lumenal region of ATP7A in copper transfer to cuproenzymes. Both Cu(II) and Cu(I) forms were investigated since the form in which copper is transferred to acceptor proteins is currently unknown. Analysis of Cu(II) using EPR demonstrated that at Cu:P ratios below 1:1 (15)N-substituted protein had Cu(II) bound by 4 His residues, but this coordination changed as the Cu(II) to protein ratio increased toward 2:1. XAS confirmed this coordination via analysis of the intensity of outer-shell scattering from imidazole residues. The Cu(II) complexes could be reduced to their Cu(I) counterparts by ascorbate, but here again, as shown by EXAFS and XANES spectroscopy, the coordination was dependent on copper loading. At low copper Cu(I) was bound by a mixed ligand set of His + Met, whereas at higher ratios His coordination predominated. The copper-loaded loop was able to transfer either Cu(II) or Cu(I) to peptidylglycine monooxygenase in the presence of chelating resin, generating catalytically active enzyme in a process that appeared to involve direct interaction between the two partners. The variation of coordination with copper loading suggests copper-dependent conformational change which in turn could act as a signal for regulating copper release by the ATPase pump.     

Copper in Acid Chloride Solutions: Electrochemical Behavior by Quartz Microgravimetry and Voltammetry

The cathodic deposition of copper on a gold electrode and its subsequent anodic dissolution in an acid chloride solution, where two successive stages of a one-electron transfer are distinguishable because of the stability of chloride complexes of Cu(I), is studied by voltammetry and quartz microgravimetry. The formation of a film of an intermediate compound of Cu(I) during the deposition and dissolution of copper is revealed experimentally. Techniques for identifying the intermediate solid species are suggested. During a cathodic polarization, a film of intermediate compound CuCl forms at a reduced concentration of chloride ions in the Cu(II)/Cu(I) process, while during the anodic dissolution of the copper deposit formed during the cathodic polarization the intermediates appear in the Cu(0)/Cu(I) process, the concentration of chloride ions notwithstanding. The change in the electrochemical behavior of the system caused by a decrease in the concentration of chloride ions is explained.     

An electrochemical study on interaction of copper ions with three isomers,picolinic, nicotinic and isonicotinic acids at physiological pH

The electrochemical behaviors of copper ions complexed with picolinic, nicotinic and isonicotinic acids (2-, 3- and 4-pyridinecarboxylic acids) in Britton–Robinson buffer (pH 7.4) was studied by polarographic and voltammetric techniques on a mercury electrode. This study showed that the reduction of complexed copper ions in the presence of nicotinic acid (NA) was carried out in two one-electron steps [Cu(II)/Cu(I) and Cu(I)/Cu(0)] whereas this cathodic process in the presence of picolinic acid (PA) or isonicotinic acid (INA) occurred in one two-electron step [Cu(II)/Cu(0)]. The stability of the Cu(I) complex can be sourced from the positions of carboxylate substituents on these isomeric ligands, binding to the copper center.