Ion-pair formation of a copper(II)-ammine complex with an anionic surfactant and the recovery of copper(II) from ammonia medium by the surfactant-gel extraction method.

The extraction and separation of copper(II), zinc(II), cobalt(II), and cadmium(II) were investigated. Both copper(II) and zinc(II) formed ammine-complexes, while cadmium(II) and cobalt(II) formed hydroxide precipitates in an ammonia medium. By the addition of sodium dodecylsulfate (SDS), a copper(II) complex formed an ion-pair (copper-ammine-DS), which was extracted into the SDS phase. However, a zinc(II) complex did not form an ion-pair, and was soluble in water. Copper(II) ion was recovered by stripping (back-extraction) after the addition of hydrochloric acid. This method was applied to the separation of copper(II) in a brass alloy.     

Catalytic Oxidation of Iron(II) Aqua Complex by Oxygen in the Presence of Palladium(II) Tetraaqua Complex

The catalytic oxidation of iron(II) with oxygen occurs along with an autocatalytic reaction between palladium(II) tetraaqua complex and iron(II) aqua complex in an oxygen atmosphere. The reaction is catalyzed by a compound of palladium in an intermediate oxidation state, presumably by a small palladium cluster formed in the course of the reduction of palladium(II) tetraaqua complex with iron(II) aqua complex.     

Rational approach to endo/exocoordinated heteronuclear macrocyclic network: supramolecular Hg(ll), Cu(ll), and Hg(ll)/Cu(ll) complexes of a NS4 macrocycle

A rationally designed sulfur-rich macrocycle L incorporating one pyridine and one benzo subunit was synthesized and structurally characterized. From the assembly reactions of L with copper(II) nitrate and mercury(II) iodide, an endocyclic monocopper(II) complex and an exocyclic dimercury(II) complex were prepared, respectively. On the basis of these results, the construction of a Hg(II)/Cu(II) heteronuclear 1D network complex with an endo/exocyclic coordination mode was achieved by one-pot assembly reaction of L with mercury(II) iodide in the presence of copper(II) nitrate.     

Readily Available Fluorescence Probes for Zinc Ion in Aqueous Solution of Neutral pH

Zinc ion in aqueous solution of neutral pH was detected by a probe that is readily obtained by simply mixing commercially available cyclen (a Zn(II) receptor) and lumazine or lumichrome (a heterocyclic fluorophore containing an imide moiety as partial structure) in an equal molar ratio. The initially generated cyclen-Zn(II) complex interacts with lumazine to form a cyclen-Zn(II)-lumazine complex whereby the intensity of fluorescence is enhanced. These Zn(II) probes showed excellent selectivity for Zn(II) over other divalent metal ions such as Pb(II), Cu(II), Co(II), Ni(II), and good selectivity over Cd(II). The X-ray crystal structure of the cyclen-Zn(II)-lumazine complex revealed that the cyclen-chelated Zn(II) binds deprotonated lumazine at the N-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-.     

Cation complexation with p-tert-butylcalix[5]arene pentacarboxylic acid derivative: an allosteric regulation of the first metal ion for stepwise extraction of the second ion

A calix[5]arene based solvent extraction reagent 3, appending carboxylic acid groups at the lower rim, has been developed and its complexation behavior towards some transition metal ions has been studied. The host 3 can selectively and quantitatively extract Pb(II) ions above pH 1.8 while other divalent ions such as Cu(II), Zn(II), Co(II), Ni(II) are extracted quantitatively only above pH 3.0. The outstanding Pb(II) selectivity of 3 comes from the size fit complementarity effect of the Pb(II) ion in the calix[5]arene cavity. One molecule of 3 extracts two Pb(II) ions in a stepwise manner. The first Pb(II) ion is extracted into the deep cavity of the calix[5]arene defined by phenoxy oxygen atoms. The first complexed Pb(II) ion acts as a template to bring the host into a cone conformation and induces a positive allosteric effect for the extraction of the second Pb(II) ion at an oxygen rich coordinating site composed of carboxyl groups. Both the Pb(II) ions are extracted through an ion exchange mechanism and the electroneutral complex in the organic phase is formed by the release of an equivalent number of hydrogen ions into aqueous solution. The loaded Pb(II) is easily back-extracted from Pb(II)-complexed 3 using dilute acid solution.     

Galactose oxidase models: solution chemistry, and phenoxyl radical generation mediated by the copper status

Galactose oxidase (GO) is an enzyme that catalyzes two-electron oxidations. Its active site contains a copper atom coordinated to a tyrosyl radical, the biogenesis of which requires copper and dioxygen. We have recently studied the properties of electrochemically generated mononuclear Cu(II)-phenoxyl radical systems as model compounds of GO. We present here the solution chemistry of these ligands under various copper and dioxygen statuses: N(3)O ligands first chelate Cu(II), leading, in the presence of base, to [Cu(II)(ligand)(CH(3)CN)](+) complexes (ortho-tert-butylated ligands) or [(Cu(II))(2)(ligand)(2)](2+) complexes (ortho-methoxylated ligands). Excess copper(II) then oxidizes the complex to the corresponding mononuclear Cu(II)-phenoxyl radical species. N(2)O(2) tripodal ligands, in the presence of copper(II), afford directly a copper(II)-phenoxyl radical species. Addition of more than two molar equivalents of copper(II) affords a Cu(II)-bis(phenoxyl) diradical species. The donor set of the ligand directs the reaction towards comproportionation for ligands possessing an N(3)O donor set, while disproportionation is observed for ligands possessing an N(2)O(2) donor set. These results are discussed in the light of recent results concerning the self-processing of GO. A path involving copper(II) disproportionation is proposed for oxidation of the cross-linked tyrosinate of GO, supporting the fact that both copper(I) and copper(II) activate the enzyme.     

Polyethyleneimine Methylenephosphonic Acid for the Solid-Phase Sorption of Lead(II)

Abstract

In the first part of this work, polyethyleneimine methylenephosphonic acid (PEIMPA) was used as an effective sorbent for solid-phase extraction of Pb(II) ions from an aqueous solution. Conditions for effective sorption are optimized with respect to different experimental parameters in a batch process. The results showed that the amount of extraction decreases with solution pH in the range between 3.5 and 5.8. The sorption capacity is 609 mg·g^?1. The second part of the study focuses on the recovery of Pb(II) from a synthesized binary solution of Pb(II)–Zn(II) and from real Zn(II)-electrolyzed wastewaters. The presence of Cd(II), Co(II), Cu(II), Fe(III), Ni(II), and Zn(II) in large concentrations has a significantly negative effect on extraction properties.     

On the mechanism of the palladium(II)-catalyzed decarboxylative olefination of arene carboxylic acids. Crystallographic characterization of non-phosphine palladium(II) intermediates and observation of their stepwise transformation in Heck-like processes

Mechanistic studies of a palladium-mediated decarboxylative olefination of arene carboxylic acids are presented, providing spectroscopic and, in two instances, crystallographic evidence for intermediates in a proposed stepwise process. Sequentially, the proposed pathway involves carboxyl exchange between palladium(II) bis(trifluoroacetate) and an arene carboxylic acid substrate, rate-determining decarboxylation to form an arylpalladium(II) trifluoroacetate intermediate (containing two trans-disposed S-bound dimethyl sulfoxide ligands in a crystallographically characterized form), then olefin insertion and beta-hydride elimination. Because of the unique mode of generation of the arylpalladium(II) trifluoroacetate intermediate, a species believed to be substantially electron-deficient relative to phosphine-containing arylpalladium(II) complexes previously studied, it has been possible to gain new insights into those steps that are common to the Heck reaction, namely, olefin insertion and beta-hydride elimination. The present results show that there are notable differences in reactivity between arylpalladium(II) intermediates generated by decarboxylative palladation and those produced in conventional Heck reactions. Specifically, we have found that more electron-rich alkenes react preferentially with an arylpalladium(II) trifluoroacetate intermediate formed by decarboxylative palladation, whereas an opposite trend is found in conventional Heck reactions. In addition, we have found that the aralkylpalladium(II) trifluoroacetate intermediates that are formed upon olefin insertion in the present study are stabilized with respect to beta-hydride elimination as compared to the corresponding phosphine-ligated aralkylpalladium(II) complexes. We have also crystallographically characterized an aralkylpalladium(II) trifluoroacetate intermediate derived from arylpalladium(II) insertion into norbornene, and this structure, too, contains an S-bound dimethyl sulfoxide ligand; the ipso-carbon of the transferred aryl group and trifluoroacetate function as the third and fourth ligands in the observed distorted square-planar palladium(II) complex.     

Investigations on the effect of aqueous acetone medium on separation of metal ions on Chelex 100 ion-exchanger

The use of glycine as a complexing agent in acetone-water medium for the separation of metal ions with Chelex 100 chelating resin has been investigated. The affinity of metal ions for Chelex 100 in the presence of glycine in acetone-water and aqueous medium was determined as a function of acidity and it was established that the presence of acetone is an essential factor in production of differentiation in the selectivity and for consequent separation of a number of mixtures of metal ions [Cu(II)Co(II); Cu(II)Al(III)Pb(II); Cu(II)Ni(II)Co(II); Cu(II)Ni(II)Pb(II)]. The mechanism of the effect of acetone is discussed.     

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.     

Ion-selective chalcogenide electrodes for a number of cations

Ion-selective chalcogenide disc electrodes have been developed which are responsive to cations such as silver, lead, chromium(III), nickel, cobalt(II), cadmium, zinc, copper(II) and manganese(II) ions. Each was prepared by using the corresponding metal chalcogenide with silver sulphide. An electrode was assembled with both a compacted and a sintered disc. The sintered electrodes were more sensitive and stable than the compacted ones. Response to silver ion was 59.5 mV pAg , to lead, nickel, cadmium, zinc and copper(II) 29.5 mV pM and to chromium(III) 20 mV pM . Cobalt(II) and manganese(II) electrodes had a non-Nernstian response of 25 mV pM . Both selenides and tellurides can be used for potentiometric determination, but the manganese(II) electrode serves as an analytical tool only when the disc consists of manganese(II) telluride and silver sulphide.     

Preparation and characterization of Cr(III), Mn(II), Fe(II), Co(II) and Ni(II) complexes of a hexaazadithiophenolate macrocycle

The ligating properties of the 24-membered macrocyclic dinucleating hexaazadithiophenolate ligand (L(Me))2- towards the transition metal ions Cr(II), Mn(II), Fe(II), Co(II), Ni(II) and Zn(II) have been examined. It is demonstrated that this ligand forms an isostructural series of bioctahedral [(L(Me))M(II)2(OAc)]+ complexes with Mn(II) (2), Fe(II) (3), Co(II) (4), Ni(II) (5) and Zn(II) (6). The reaction of (L(Me))2- with two equivalents of CrCl2 and NaOAc followed by air-oxidation produced the complex [(L(Me))Cr(III)H2(OAc)]2+ (1), which is the first example for a mononuclear complex of (L(Me))2-. Complexes 2-6 contain a central N3M(II)(mu-SR)2(mu-OAc)M(II)N3 core with an exogenous acetate bridge. The Cr(III) ion in is bonded to three N and two S atoms of (L(Me))2- and an O atom of a monodentate acetate coligand. In 2-6 there is a consistent decrease in the deviations of the bond angles from the ideal octahedral values such that the coordination polyhedra in the dinickel complex 5 are more regular than in the dimanganese compound 2. The temperature dependent magnetic susceptibility measurements reveal the magnetic exchange interactions in the [(L(Me))M(II)2(OAc)]+ cations to be relatively weak. Intramolecular antiferromagnetic exchange interactions are present in the Mn(II)2, Fe(II)2 and Co(II)2 complexes where J = -5.1, -10.6 and approximately -2.0 cm(-1) (H = -2JS1S2). In contrast, in the dinickel complex 5 a ferromagnetic exchange interaction is present with J = +6.4 cm(-1). An explanation for this difference is qualitatively discussed in terms of the bonding differences.     

Rearrangement of the tris(2-pyridylthio)methanido ligand in an iron(II) complex containing an Fe-C bond

Iron(II) tris(2-pyridylthio)methanido (1) containing an Fe-C bond, obtained from the reaction of tris(2-pyridylthio)methane (HL(1)) and iron(II) triflate, reacts with protic acid to generate iron(II) bis(2-pyridylthio)carbene (1a). The carbene complex is converted to an iron(II) complex (2) of the 1-[bis(2-pyridylthio)methyl]pyridine-2-thione ligand (L(3)) upon treatment with a base. Complex 2 reversibly transforms to 1a in the presence of an acid. During the transformation of 1 to 2, a novel rearrangement of L(1) to L(3) takes place. The iron(II) complexes are reactive toward dioxygen to form the corresponding iron(III) complexes.     

Protonation constant of salicylidene (N-benzoyl)glycyl hydrazone and its coordination behaviour towards some bivalent metal ions

Protonation constant of an unsymmetrical Schiff base, salicylidene(N-benzoyl)glycyl hydrazone (SalBzGH), and formation constants of its complexes have been determined potentiometrically at different temperatures in aqueous dioxane medium. Complexes of SalBzGH with VO(IV), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) have been prepared. Elemental analyses, pH-metric, molar conductance, magnetic susceptibility, electronic, IR, ESR, XRD (powder) and NMR studies have been carried out to study the coordination behaviour of SalBzGH toward these metal ions. pH-metric and 1H NMR studies show the presence of two dissociable protons in the ligand. IR and NMR spectra suggest the tridentate nature of the ligand, coordinating as a uninegative species in the Mn(II) complex and as a dinegative species in all the other complexes. Presence of two different conformers of the ligand at room temperature and stabilization of a single conformer upon complex formation have been established from¹H NMR spectra of the metal-free ligand, Zn(II) and Hg(II) complexes recorded at 296 K. Electronic and ESR spectra indicate highly distorted tetragonal geometry for VO(IV) and Cu(II) complexes. XRD powder patterns of the Zn(II) complexes are indexed for an orthorhombic crystal system.     

Kinetics and thermodynamics of copper(II) binding to apoazurin

The binding of copper(II) to apoazurin has been probed by isothermal titration calorimetry in cholamine buffer at pH 7.0. The standard enthalpy change was determined to be -10.0 +/- 1.4 kcal/mol. Each calorimetric trace reveals an initial exothermic phase followed by an endothermic phase. The calorimetric data could be fit to a kinetic model involving a bimolecular combination of copper(II) and apoazurin in an exothermic process (k = 2 +/-1 x 103 M-1 s-1, DeltaH degrees = -19 +/- 3 kcal/mol) to form an intermediate that spontaneously converts to Cu(II)-azurin in an endothermic process (k = 0.024 +/- 0.01 s-1, DeltaH degrees = +9 +/- 3 kcal/mol). These data suggest that copper(II) first combines with apoazurin in an irreversible process to form an intermediate that converts to copper(II)-azurin in a process driven by the release of water. The overall standard free energy of copper(II) binding to apoazurin is estimated to be -18.8 kcal/mol.     

Metal ion detection using a fluorogenic ‘click’ reaction

A fluorogenic Cu(I)-catalyzed azide-alkyne cycloaddition reaction (CuAAC) of 3-azido-7-hydroxycoumarin has been used to detect metal ions in solution. The formation of a highly fluorescent triazole product signals the presence of Cu(I) or Cu(II) ions at micromolar concentrations. CuAAC can be modified by using an exogenous ligand like EDTA to detect and quantify Zn(II), Ca(II), and Cd(II) ions at micromolar concentrations by an allosteric mechanism. The increase in the formation of the triazole product is regulated by the release of Cu(II) from the Cu(II)-EDTA complex by the addition of a second metal ion, the allosteric effector.     

桥联双核铜席夫碱配合物的合成和晶体结构

利用1-苯基-3-甲基-5-吡唑啉酮和水杨酰胺制备了PMP缩水杨酰胺席夫碱及其铜(Ⅱ ) 配合物,根据红外和紫外光谱数据表征了它的结构.利用X射线衍射方法研究了配合物的晶体结构,结果表明配合物为桥联双核铜结构,铜原子为五配位的四方锥构型,每个铜原子与一个配体中吡唑啉酮上的氧原子、席夫碱上的N原子、水杨酰的酚氧原子和溶剂DMF中的氧原子配位,而相邻配体中水杨酰的酚氧原子也参加配位并将两个铜原子连接起来形成桥联双核铜配合物,两个Cu(Ⅱ )原子间的距离为0.3268 nm.芳环堆积作用和分子内及分子间氢键的存在增强了配合物分子的稳定性.     

Electrocatalytic reduction of oxygen at electrodes coated with a bimetallic cobalt(II)/platinum(II) porphyrin

Edge plane pyrolytic graphite (EPG) electrodes coated with 5-(4-pyridyl)-10,15,20-tris(3-methoxy-4-hydroxyphenyl)porphyrin and its Pt(II) and Co(II)/Pt(II) analogs undergo an electrochemical-chemical-electrochemical (ECE) reaction when anodically scanned in 1.0 M HClO4. The new redox couple formed from this anodic conditioning of the coated electrode is dependent on the pH of the solution. Roughened EPG electrodes coated with the Co(II)/Pt(II) bimetallic porphyrin show a catalytic shift of 500 mV for the reduction of O2 when compared to the reduction of O2 at a bare EPG electrode. An additional catalytic shift of ca. 100 mV is observed for O2 reduction at an EPG electrode coated with the Co(II)/Pt(II) porphyrin which has been oxidized in 1.0 M HClO4. In addition to the added electrocatalysis a significant percentage of O2 reduced at the oxidized Co(II)/Pt(II) EPG electrode is converted to H2O as determined by rotating disk electrode measurements.     

Electroreduction of Ammonia and Hydroxyammonia Complexes of Divalent Metals: Effect of the Ligand Concentration and the EDL Structure

Kinetics and mechanism of electroreduction of complexes Pd(NH₃)₄ ²⁺ on a dropping mercury electrode (DME) and a Pd electrode, as well as ammonia complexes of Co(II), Ni(II), and Zn(II) and hydroxyammonia complexes of Zn(II) on DME at different concentrations of ammonia and supporting electrolytes and different pH values are discussed. The half-wave potentials of electroreduction of ammonia complexes of Pd(II) and Ni(II) on DME in the absence of a polarographic maximum obey an equation that takes into account the effect the EDL structure has on the rate of a slow outer-sphere electrochemical stage. As opposed to Pd(II) complexes, the reduction of the other complexes involves preceding reversible chemical stages, which yield diammonia complexes undergoing a direct reduction on DME. The reasons for the emergence of a polarographic maximum upon an increase in the concentration of reduced complexes and the time of recording an instant current are discussed.