Micro volume changes due to Pb(II) and Cu(II) sorption on amorphous Fe(III) hydroxide

Micro volume changes due to Pb(II) and Cu(II) sorption on amorphous Fe(III) hydroxide (AFH) were determined by a dilatometer at pH 4.50. Volume change is attributed to change in hydration status of dissolved and/or suspended substances. The volume of the system increased due to Pb(II) and Cu(II) sorption, suggesting that water molecules hydrated around Pb(II) or Cu(II) ions and AFH were released during sorption. Volume increases due to Pb(II) and Cu(II) sorption were smaller than those due to bulk precipitation of Pb and Cu hydroxides. Precipitation of Pb(II) and Cu(II) was not likely to occur at pH 4.50 in the presence of AFH. In conclusion, Pb(II) and Cu(II) formed an inner-sphere complex on AFH at pH 4.50, keeping hydrated water on the adsorbed species. Adsorbed Cu(II) kept more hydrated water than adsorbed Pb(II) on AFH.     

Insights into the N-terminal Cu(II) and Cu(I) binding sites of the human copper transporter CTR1

Abstract

Copper transporter 1 (CTR1) is the main copper transporter in the eukaryotic system. CTR1 has several important roles: It binds Cu(II) ions that are present in the blood; it reduces those Cu(II) ions to Cu(I); and it subsequently transfers Cu(I) to the cytoplasmic domain, where the ion is delivered to various cellular pathways. Here, we seek to identify CTR1 binding sites for Cu(II) and Cu(I) and to shed light on the Cu(II)-to-Cu(I) reduction process. We focus on the first 14 amino acids of CTR1. This N-terminal segment is rich with histidine and methionine residues, which are known to bind Cu(II) and Cu(I), respectively; thus, this region has been suggested to have an important function in recruiting Cu(II) and reducing it to Cu(I). We utilize electron paramagnetic resonance (EPR) spectroscopy together with nuclear magnetic resonance (NMR) and UV-VIS spectroscopy and alanine substitution to reveal Cu(II) and Cu(I) binding sites in the focal 14-amino-acid segment. We show that H5 and H6 directly coordinate to Cu(II), whereas M7, M9, and M12 are involved in Cu(I) binding. This research is another step on the way to a complete understanding of the cellular copper regulation mechanism in humans.     

Electrochemistry of the system Cu(II)Cu(I)Cu(0) in acidified thiocyanate solutions

The system Cu(II)Cu(I)Cu(0) in acidified thiocyanate medium was investigated at carbon, mercury, and copper amalgam electrodes using cyclic voltammetry, normal, differential and reverse pulse voltammetry, double potential step chronocoulometry, and exhaustive coulometry. Reduction of Cu(II) to Cu(I) on carbon electrodes proceeds quasireversibly. At moderate concentrations of Cu(II) and SCN^? the reduction of Cu(II) leads to three-dimensional precipitation of CuSCN which can be deposited at the electrode surface. At high concentration of SCN^? complexation dominates over precipitation and only soluble species are formed. At mercury and copper amalgam electrodes the situation is more complicated. The three- dimensional precipitation is preceded by strong thiocyanate-induced adsorption of Cu(I) which results in formation of a mono layer at potential well-separated from those where diffusing product is formed.     

Copper(II) and nickel(II) complexes of binucleating macrocyclic bis(disulfide)tetramine ligands

Novel macrocyclic bis(disulfide)tetramine ligands and several Cu(II) and Ni(II) complexes of them with additional ligands have been synthesized by the oxidative coupling of linear tetradentate N2S2 tetramines with iodine. Facile demetalation of the Ni(II) oxidation products affords the free 20-membered macrocycles meso-9 and rac-9 and the 22-membered macrocycle 16, all of which are potentially octadentate N4S4 ligands. X-ray structure analyses reveal distinctly different conformations for the two isomers of 9; meso-9 shows a stepped conformation in profile with the disulfide groups corresponding to the rise of the step, whereas rac-9 exhibits a V conformation with the disulfide groups near the vertex of the V. No metal complexes of rac-9 have been isolated. Crystallographic studies of three Cu(II) complexes reveal that depending upon the size of the macrocyclic ligand and the nature of the additional ligands (I-, NCO-, and CH3CN), the Cu(II) coordination geometry shows considerable variation (plasticity), with substantial changes in the Cu(II)-disulfide bonding. Thus, a diiodide salt contains six-coordinate Cu(II) to which all four bridging disulfide sulfur atoms form strong equatorial bonds. In contrast, isocyanato complexes of the 20- and 22-membered macrocycles exhibit trigonal-bipyramidal Cu(II) and distorted cis-octahedral Cu(II) geometries, respectively, having only one and no short equatorially bound sulfur atoms. The coordination geometry of the latter complex can also be described as four-coordinate seesaw with two semicoordinated S(disulfide) ligands. Disulfide-->Cu(II) ligand-to-metal charge transfer absorptions of both isocyanato-containing Cu(II) species appear too weak to observe, probably because of poor overlap of the sulfur orbitals with the Cu(II) d-vacancy. The dual disulfide-bridged Ni(II) units of the crystallographically characterized octahedral Ni(II) complex of meso-9 with axial iodide and acetonitrile ligands promote substantial antiferromagnetic coupling (J = -13.0(2) cm-1).     

EDTA effect on the removal of Cu(II) onto TiO2

The adsorption of Cu(II) and Cu(II)-EDTA onto TiO2 with variations in the pH, concentration, and molar ratio of Cu(II) to EDTA has been studied. The adsorption of Cu(II) and Cu(II)-EDTA onto TiO2 showed typical cationic- and anionic-type behavior, respectively. The removal of Cu(II) in an EDTA-excess system was less than that in an equimolar Cu(II)/EDTA system due to the competitive adsorption of EDTA and Cu(II)-EDTA onto the TiO2. The removal of Cu(II) was favorable at low pH for both the equimolar and EDTA-excess systems, while significant Cu(II) removal was observed over the entire pH range in a copper-excess system. For model predictions, the MINTEQA2 program employing an inner-sphere complexation and a diffuse layer model was used; the surface complexes used included Ti(OH2)OCu+, Ti(OH)EDTAH2-(2), and Ti(OH)EDTACu2-.     

2-Benzoylpyridine thiosemicarbazone as a novel reagent for the single pot synthesis of dinuclear Cu(I)-Cu(II) complexes: formation of stable copper(II)-iodide bonds

2-Benzoylpyridine thiosemicarbazone {R(1)R(2)C(2)=N(2)·N(3)H-C(1)(=S)-N(4)H(2), R(1) = py-N(1), R(2) = Ph; Hbpytsc} with copper(I) iodide in acetonitrile-dichloromethane mixture has formed stable Cu(II)-I bonds in a dark green Cu(II) iodo-bridged dimer, [Cu(2)(II)(μ-I)(2)(η(3)-N(1),N(2),S-bpytsc)(2)] 1. Copper(I) bromide also formed similar Cu(II)-Br bonds in a dark green Cu(II) bromo-bridged dimer, [Cu(2)(II)(μ-Br)(2)(η(3)-N(1),N(2),S-bpytsc)(2)] 3. The formation of dimers 1 and 3 appears to be due to a proton coupled electron transfer (PCET) process wherein copper(I) loses an electron to form copper(II), and this is accompanied by a loss of -N(3)H proton of Hbpytsc ligand resulting in the formation of anionic bpytsc(-). When copper(I) iodide was reacted with triphenylphosphine (PPh(3)) in acetonitrile followed by the addition of 2-benzoylpyridine thiosemicarbazone in dichloromethane (Cu?:?PPh(3)?:?Hbpytsc in the molar ratio 1:1:1), both Cu(II) dimer 1 and an orange Cu(I) sulfur-bridged dimer, [Cu(2)(I)I(2)(μ-S-Hbpytsc)(2)(PPh(3))(2)] 2 were formed. Copper(I) bromide with PPh(3) and Hbpytsc also formed Cu(II) dimer 3 and an orange Cu(I) sulfur-bridged dimer, [Cu(2)(I)Br(2)(μ-S-Hbpytsc)(2)(PPh(3))(2)] 4. While complexes 2 and 4 exist as sulfur-bridged Cu(I) dimers, 1 and 3 are halogen-bridged. The central Cu(2)S(2) cores of 2 and 4 as well as Cu(2)X(2) of 1 (X = I) and 3 (X = Br) are parallelograms. One set of Cu(II)-I and Cu(II)-Br bonds are short, while the second set is very long {1, Cu-I, 2.565(1), 3.313(1) ?; 3, Cu-Br, 2.391(1), 3.111(1) ?}. The Cu···Cu separations are long in all four complexes {1, 4.126(1); 2, 3.857(1); 3, 3.227(1); 4, 3.285(1) ?}, more than twice the van der Waals radius of a Cu atom, 2.80 ?. The pyridyl group appears to be necessary for stabilizing the Cu(II)-I bond, as this group can accept π-electrons from the metal.     

Determination of cobalt at ng ml(-1) level in water using the electrophilic substiution complexation between co(II) and chlorophosphonazo-p-CL-Cu(II) complex

The chromophore chlorophosphonazo-p-Cl (PCCPA) was used to complex Co(II) and Cu(II) at pH 9.18. The formation of Co(PCCPA)2 and Cu(PCCPA)2 complexes were characterized by the spectral correction technique. Co(II) could competitively substitute Cu(II) from the Cu(II)-PCCPA complex via electrophilic effect. With the assistance of the light-absorption ratio variation approach, the electrophilic substitution complexation showed a high selectivity and good sensitivity with 1.9 ng mL(-1) of LOD. The proposed method has been applied to the direct detection of Co(II) in surface water and wastewater with good percent of recovery.     

Compositions and structures of copper hexacyanoferrates(II) and (III): experimental results

The preparation, composition and structure of copper hexacyanoferrates have been investigated. Three methods were used: precipitation, local growth in an aqueous solution, and growth in a gel. Four compounds were obtained, either in powdered form or as single crystals: Cu(II)(2)Fe(II)(CN)(6) . xH(2)O, Cu(II)(3)[Fe(III)(CN)(6)](2) . xH(2)O, Na(2)Cu(II)Fe(II)(CN)(6) . 10H(2)O and K(2)Cu(II)Fe(II)(CN)(6). Powders of Cu(II)(2)Fe(II)(CN)(6) . xH(2)O and Cu(II)(3)[Fe(III) (CN)(6)](2) . xH(2)O are easily prepared by precipitation and can also be obtained by local growth. They crystallise generally with cubic symmetry, in space group Fm3m, and are structurally disordered. The mixed copper hexacyanoferrates of general formulae M(1)(2)Cu(II)Fe(II)(CN)(6) or M(I)Cu(II)Fe(III)(CN)(6) (here M(I) is Na, K) were not obtained by precipitation. The appropriate method was local growth for the preparation of powders of K(2)Cu(II)Fe(II)(CN)(6). Single crystals of Na(2)Cu(II)Fe(II)(CN)(6) were obtained by growth in a gel, and their study using single crystal X-ray diffraction revealed a new monoclinic structure.     

Semi-vacant Wells-Dawson anions. Synthesis of tri-tungsten-vacant derivatives and crystallographic studies of [alphabetabetaalpha-(Cu(II)OH2)2(Cu(II))2(AsW15(OH2)3(OH)O52)2]12-

The tri-tungsten-vacant polyoxometalate, [alpha-AsW15(OH)4O52]13-, derived from the semi-vacant Wells-Dawson complex [alpha-AsW18(OH)4O58]7-, reacts with the late-transition metal cations, Cu(II) or Zn(II), to form sandwich-type species; the X-ray crystal structure of [alphabetabetaalpha]-(Cu(II)OH2)2(Cu(II))2(AsW15(OH2)3(OH)O52)2]12-, prepared by the acidification of [alphabetabetaalpha]-(Cu(II)OH2)2(Cu(II))2(AsW15(OH)4O52)2]18-, reveals that the missing heteroatoms are distal to the central Cu4 unit and the vertices of the vacant tetrahedron are occupied by one OH- and three OH2 groups.     

The solvent extraction of Cu(II), Ni(II) and Co(II) with benzil mono(2-quinolyl)hydrazone

Benzil mono(2-quinolyl)hydrazone, BmQH, has been studied as an extracting agent for Cu(II), Ni(II) and Co(II). Though the uncomplexed ligand remains undissociated in the pH range 3.5-10, it can lose a proton on complexation with metals, owing to the electron-withdrawing effects of neighbouring groups. The dependence of degree of extraction on pH indicates that complexes of both Cu(2+) and Cu(OH)(+) are extracted. Cu(BmQH)(2) and Cu(OH)BmQH species are extracted into MIBK, and the Cu(OH)BmQH complex is extracted into benzene. In the vicinity of pH 5.5-6, extraction efficiencies greater than 95% can be achieved with both solvents. Both Ni(II) and Co(II) also show dependence of extraction on pH, but precipitation of both metals in the vicinity of pH 6 limits further studies.     

An unusual dimeric structure of a Cu(I) bis(thiosemicarbazone) complex: implications for the mechanism of hypoxic selectivity of the Cu(II) derivatives

The electrochemical reduction of Cu(II) bis(thiosemicarbazone) complexes [Cu(II)(btsc)] is accompanied by protonation to give an unstable Cu(I) intermediate [Cu(btscH(2))](+). The nature of this intermediate was probed by reaction of bis(thiosemicarbazone) ligands with a Cu(I) precursor which gave a novel helical dimeric dicationic complex. The dependence of these reactions on the ligand backbone substituents is discussed together with their possible relevance to the use of Cu(II) bis(thiosemicarbazone) ligands as hypoxic selective imaging and therapeutic agents.     

A fluorescent chemosensor for copper(II) based on a carboxylic acid-functionalized tris(2,2'-bipyridine)-ruthenium(II) complex.

In this research, bis(2,2'-bipyridine)(4-methyl-2,2'-bipyridine-4'-carboxylic acid)ruthenium(II).2PF(6)- complex (1), was first used as a fluorescent chemosensor to recognize Cu(II) in EtOH/H(2)O (1:1, v/v) solution. The response of the sensor is based on the fluorescence quenching of complex 1 by binding with Cu(II). The analytical performance characteristics of the proposed Cu(II)-sensitive chemosensor were investigated. The sensor can be applied to the quantification of Cu(II) with a linear range covering from 5.0 x 10(-8) to 1.0 x 10(-4) M and a detection limit of 4.2 x 10(-8) M. The experiment results show that the response behavior of 1 to Cu(II) is pH independent in medium condition (pH 4.0 - 8.0), and show excellent selectivity for Cu(II) over other transition metal cations.     

Copper(II) ion-selective microelectrochemical transistor

A device has been developed for the measurement of copper(II) ions (Cu⁺⁺) in aqueous medium. The device reported here is an electrochemical transistor that consists of two platinum electrodes separated by 100-μm spacing and bridged with an anodically grown polycarbazole film. The undoped polycarbazole film is observed to be highly selective for the Cu(II) ions. In a completed device, the conductivity of the polycarbazole film changes on addition of Cu (II)ions. This change in conductivity is attributed to the conformational changes in the polymer phase on occupation of the Cu(II) ions, without affecting electron/proton transfer. The device turns on by adding 2.5×10⁻⁶ M Cu(II) ions and reaches a saturation region above a concentration of 10⁻⁴ M Cu(II) ions. In this concentration range, the plot of I _D vs log[Cu(II)] is linear. The selectivity of the device for other metal ions such as Cu(I), Co(II), Fe(II), Fe(III), Zn(II), and Pb(II) is also studied.     

Effect of Polyethylenimine on the Selectivity of Determining Silver(I) by Stripping Voltammetry in the Presence of Copper(II)

It has been proposed that a water-soluble complexing polymer, polyethylenimine (PEI), be used to lower intermetallic interactions at the surface of solid electrodes in the determination of Ag(I) by stripping voltammetry in the presence of Cu(II). The introduction of PEI in the binary Ag(I)–Cu(II) system weakened the effect of Cu(II) on the anodic peak of Ag(I) and enhanced the selectivity in determining Ag(I) in the presence of excess amounts of Cu(II). With the use of PEI, Ag(I) can be determined at a Cu(II)-to-Ag(I) concentration ratio of 1000 : 1, compared to that of 20 : 1 in the absence of the polymer.     

Perturbation of the Electronic Structure of a Copper(II) ion by a Cu(I)Cl Moiety in a Class I Mixed Valence Copper Complex, Cu(II)(Me(5)dien)Cl(2)(Cu(I)Cl)

A new mixed valence copper complex Cu(II)(Me(5)dien)Cl(2)(Cu(I)Cl) (2) was obtained from the reaction of CuCl with Cu(II)(Me(5)dien)Cl(2) (1) in acetonitrile. The structures of 1 and 2 have been determined by single-crystal X-ray diffraction analyses. Compound 1 crystallizes in the monoclinic space group P2(1)/n with a = 8.374(5) ?, b = 17.155(3) ?, c = 23.806(5) ?, beta = 94.40(4) degrees, Z = 8, and V = 3398(1) ?(3) while compound 2 crystallizes in orthorhombic space group Pbcn with a = 14.71(1) ?, b = 16.06(2) ?, c = 13.38(1) ?, Z = 8, and V = 3159(5) ?. The Cu(II)(Me(5)dien)Cl(2) unit in both compounds has a similar distorted square-pyramidal geometry. The Cu(I)Cl moiety in 2 is attached to the Cu(II) unit via two bridging chlorine atoms and has a distorted trigonal planar geometry. UV-vis and EPR spectroscopic studies and molecular orbital calculations established the presence of significant perturbation of the Cu(I)Cl unit to the electronic structure of the Cu(II) ion in compound 2.     

Electrochemical detection of Cu(I) and Cu(II) in styrene media

A method is described to detect Cu(II) and Cu(I) added as bromide simultaneously in styrene solution containing tetrahexylammoniumperchloraat (THAP) as supporting electrolyte. It was found that Cu(II) and Cu(I) behave similarly in styrene and in aqueous solution. Reduction of Cu(II) and Cu(I) to metallic copper, as well as oxidation of Cu(I) to Cu(II) and the dissolution of a deposited metallic copper layer are observed. Ohmic drop problems were circumvented by adding THAP to the styrene solution and using ultramicro electrodes. The simultaneous detection of Cu(II) and Cu(I) is based on recording a cyclic voltammetric curve in a mixture of these compounds and calculating their concentration from the cathodic limiting current obtained at −0.80 V vs. RE and the anodic stripping peak corresponding to the dissolution of metallic copper. A detection limit of 2.0×10⁻⁴ mol l⁻¹ was obtained for both Cu(II) and Cu(I) and reproducible results were obtained concerning sensitivity and stability of the calibration curves.     

Adsorption of Cu(II) and Ni(II) on solid humic acid from the Azraq area, Jordan

Isotherms of adsorption of Cu(II) and Ni(II) onto solid Azraq humic acid (AZHA) were studied at different pH (2.0-3.7) values and 0.1 M NaClO4 ionic strength. The Langmuir monolayer adsorption capacity was found to range from 0.1 to 1.0 mmol metal ion/g AZHA, where Cu(II) has higher adsorptivity than Ni(II). The previously reported NICA-Donnan parameters for sorption of Cu(II) on HA fit the amount of Cu(bound) determined in the present study at pH 3.7 but underestimates those at pH values of 3.0, 2.4, and 2.0. The contribution of low affinity sites to binding of metal ions increases with decreasing pH and increasing metal ion loading. The aggregation of HA, which is facilitated by decreasing pH and increasing metal loading, may increase the ability of low-affinity sites to encapsulate metal ions. The binding of Ni(II) to HA exhibits less heterogeneity and less multidentism than that of Cu(II). AZHA loaded with Cu(II) and Ni(II) was found to be insoluble in water with no measurable amount of desorbed metal ions.     

Studies in nickel(IV) Chemistry. Kinetics of the aquacopper(II)-catalyzed oxidation of phenylhydrazine by tris(dimethylglyoximato)-nickelate(IV) in aqueous medium

The kinetics of electron transfer in the redox system containing phenylhydrazine (S) and tris(dimethylglyoximato)nickelate(IV), in the presence of catalytic amounts of added Cu(II)_aq, have been studied in aqueous medium at an ionic strength of 0.25M in the pH range of 6.01–9.06. The kinetics exhibit pseudo-zero-order disappearance of Ni(IV) when an excess of [S]₀ and small amounts of Cu(II) are present. While the pseudo-zero-order rate constants are almost linearly dependent on [S]₀ at constant [Cu(II)] and pH tending to become non-linearly dependent on higher relative [S]₀, they are linearly dependent on [Cu(II)] in a 20-fold range. The pH-rate profiles with low [S]₀ and [Cu(II)] show a monotonic decrease in rates with increasing pH, the rates tending to attain limiting values at higher relative pH. Results are interpreted in terms of a probable mechanism involving the formation of precursor complexes of phenylhydrazine and Cu(II) species in the medium, followed by the rate-determining breakdown of the precursors with concomitant electron transfer. The hydrolyzed species of Cu(II) reacts more slowly than does the aquacopper(II). Ni(IV) does not appear to have any kinetic role in the redox system and is involved only in rapid product formation steps. The oxidation product of phenylhydrazine is 4-hydroxyazobenzene.     

Charge-transfer photochemistry of the ternary complex (dithio-diseleno-carbamato)copper(II)

Photolysis of the ternary system consisting of diethyldithiocarbamate (Et2dtc), diethyldiselenocarbamate (Et2dsc) and copper(II) (1:1:1) has been studied in isobutylmethylketone (IBMK), toluene, chloromethane and chloromethane/ROH solutions (chloromethane = CCl4, CHCl3 or CH2Cl2 and ROH = EtOH or i-PrOH). The results obtained by EPR techniques and UV-Vis data indicate that a homolytic Cu-S bond cleavage involving the dithiocarbamate (dtc) ligand appears as the primary photo-process in Cu(Et2dtc)(Et2dsc) photolysis. Further conversion of the primary photoproduct Cu(I)(Et2dsc) is discussed in terms of a specific interaction with the solvent. In chloromethanes and chloromethane/ROH Cu(I)(Et2dsc) is oxidised by the solvent to give the corresponding paramagnetic mixed-ligand Cu(II)(Et2dsc)Cl complex and/or its chloride-bridged and EPR silent dimer Cu2(Et2dsc)2Cl2. The formation of the monomeric species occurs through a co-ordination of the alcohol molecule in the xy plane of the complex. Because of its co-ordination inertness, toluene poorly stabilises the primary photoproduct Cu(I)(Et2dsc), thus providing an effective primary recombination process and lower efficiency of Cu(Et2dtc)(Et2dsc) photolysis. The formation of the bis-solvated mixed-ligand complex Cu(II)(Et2dsc)+ in IBMK is also discussed.