Oxidation of aqueous sulfur dioxide catalyzed by poly-4-vinylpyridine-Cu(II) complex. Part 1: Homogeneous phase oxidation

The oxidation of aqueous sulfur dioxide in the presence of polymer-supported copper(II) catalyst is also accompanied by homogeneous oxidation of aqueous sulfur dioxide catalyzed by leached copper(II) ions. Aqueous phase oxidation of sulfur dioxide of low concentrations by oxygen in the presence of dissolved copper(II) has therefore been studied. The solubility of SO2 in aqueous solutions is not affected by the concentration of copper(II) in the solution. In the oxidation reaction, only HSO3- is the reactive S(IV) species. Based on this observation a rate model which also incorporates the effect of sulfuric acid on the solubility of SO2 is developed. The rate model includes a power-law type term for the rate of homogeneous phase reaction obtained from a proposed free-radical chain mechanism for the oxidation. Experiments are conducted at various levels of concentrations of SO2 and O-2 in the gas phase and Cu(II) in the liquid phase. The observed orders are one in each of O-2, Cu(II) and HSO3-. This suggests a first-order termination of the free radicals of bisulfite ions.

Oxidation of aqueous sulphur dioxide catalysed by poly-4-vinylpyridine-Cu(II) complex .2. Combined homogeneous and heterogeneous phase oxidation

Aqueous phase oxidation of sulphur dioxide at low concentrations catalysed by a PVP-Cu complex in the solid phase and dissolved Cu(II) in the liquid phase is studied in a rotating catalyst basket reactor (RCBR). The equilibrium adsorption of Cu(II) and S(VI) on PVP particles is found to be of the Langmuir-type. The diffusional effects of S(IV) species in PVP-Cu resin are found to be insignificant whereas that of product S(VI) are found to be significant. The intraparticle diffusivity of S(VI) is obtained from independent tracer experiments. In the oxidation reaction HSO3- is the reactive species. Both the S(IV) species in the solution, namely SO2(aq) and HSO3- get adsorbed onto the active PVP-Cu sites of the catalyst, but only HSO3- undergoes oxidation. A kinetic mechanism is proposed based on this feature which shows that SO2(aq) has a deactivating effect on the catalyst. A rate model is developed for the three-phase reaction system incorporating these factors along with the effect of concentration of H2SO4 on the solubility of SO2 in the dilute aqueous solutions of Cu(II). Transient oxidation experiments are conducted at different conditions of concentration of SO2 and O-2 in the gas phase and catalyst concentration, and the rate parameters are estimated from the data. The observed and calculated profiles are in very good agreement. This confirms the deactivating effect of nonreactive SO2(aq) on the heterogeneous catalysis.

An enolato-bridged dinuclear Cu(II) complex with a coumarin-assisted precursor: a spectral, magnetic and biological study

A new, phenoxo-bridged Cu-II dinuclear complex Cu-2(L)(2)(DMF)(2)] (1) has been obtained by employing the coumarin-assisted tridentate precursor, H2L, benzoic acid(7-hydroxy-4-methyl-2-oxo-2H-chromen-8-ylmethylene)-hydrazide]. Complex 1 has been systematically characterized by FTIR, UV-Vis, fluorescence and PR spectrometry. The single crystal X-ray diffraction analysis of 1 shows that the geometry around each copper ion is square pyramidal, comprising two enolato oxygen atoms belonging to different ligands (which assemble the dimer bridging the two metal centers), one imine-N and one phenolic-O atoms of the Schiff base and one oxygen atom from the DMF molecule. The temperature dependent magnetic interpretation agrees with the existence of weak ferromagnetic interactions between the bridging dinuclear Cu(II) ions. Both the ligand and complex 1 exhibit anti-mycobacterial activity and considerable efficacy towards M. tuberculosis H37Rv ATCC 27294 and M. tuberculosis H37Ra ATCC 25177 strains. The cytotoxicity study on human adenocarcinoma cell lines (MCF7) suggests that the ligand and complex 1 have potential anticancer properties. Molecular docking of H2L with the enoyl acyl carrier protein reductase of M. tuberculosis H37R(v) (PDB ID: 4U0K) is examined and the best docked pose of H2L shows one hydrogen bond with Thr196 (1.99 angstrom).

Rationalizing the effects of amino acid side chain, pyridine, and imidazole on the assembly and reversible disassembly of a octanuclear Cu(III) complex

This paper reports the observation of a reversible disassembly process for a previously reported octanuclear Cu(II) complex with imidazole. To identify the factors responsible for the process, five Cu(II) complexes of different nuclearity with different amino acid-derived tetradentate ligands were structurally characterized. The results show that the coordination geometry preference of Cu(II), the tendency of imidazole to act as in-plane ligand, and H-bonding played important role in the formation and disassembly of the octanuclear complex. A general scheme describing the effect of different amino acid side arms, solvents, and exogenous ligands on the nuclearity of the Cu(II) complexes has been presented. The crystals of the complexes also showed formation of multifaceted networks in the resulting complexes.

Synthesis and characterization of cobalt(II), nickel(II), copper(II) and zinc(II) complexes of 2-nitrobenzoic acid with methyl carbazate as ancillary ligand. Crystal structure of the copper(II) complex

Divalent metal complexes of general formula M(2-nb)(2)(mc)(2)].2(2-nbH), where M = Co(II), Ni(II), Cu(II) or Zn(II), 2-nbH = 2-nitrobenzoic acid and mc = methyl carbazate (NH2NHCOOCH3), have been prepared and characterized by physicochemical and spectroscopic methods. Single-crystal X-ray study of the Cu(II) complex revealed that the molecule is centrosymmetric, with two N,O-chelating mc ligands in equatorial positions and a pair of monodentate 2-nb anions in the axial positions. The lattice 2-nbH molecules help to establish the packing of monomers through hydrogen-bonding interactions. Thermal stability and reactivity of the complexes were studied by TG-DTA. Emission studies show that these complexes are fluorescent.

Electrochemical reduction of Cu(II)-CyDTA complex at dropping mercury electrode. An impedance approach

The electrochemical reduction of Cu(II)-CyDTA (CyDTA — trans 1,2-cyclohexanediamine N, N, N′, N′ tetraacetic acid) by impedance method reveals the unusual behaviour of complex plane polarograms owing to potential dependence of double layer capacitance. The impedance plane plots by frequency variation method indicates the quasi-reversible nature of the system. From these plots the chargetransfer resistance at various potentials was evaluated. The standard rate constant was evaluated which complements the prediction of impedance plots for the quasireversible behaviour of the system.

Electrochemical reduction of Cu(II)-EDTA complex at dropping mercury electrode. An impedance approach

The study of electrochemical reduction of Cu(II)-EDTA system by phase sensitive a.c. impedance method at dropping mercury electrode reveals several interesting features. The complex plane polarograms exhibit loop like shape in contrast to the classical zinc ion reduction where crest like shape is found. Again, the relative placement of peaks of in-phase and quadrature components, and the relative placement of portions before and after the peaks of complex plane polarograms are different from that of zinc ion reduction. The complex plane plots suggest that electrochemical reduction of Cu-EDTA is charge transfer controlled.

Structural model for the Cu-B site of dopamine beta-hydroxylase: Crystal structure of a copper(II) complex showing N3OS coordination with an axial sulfur ligation

A copper(II) complex containing a NSO-donor Schiff base and NN-donor 2,2'-bipyridine has been prepared and structurally characterized. The square pyramidal complex with an axial sulfur ligation is a structural model for the CUB site of dopamine-hydroxylase in its oxidized form. The copper(II) complex is catalytically active in the oxidation of ascorbic acid by dioxygen mediated by a copper(I) species which is proposed to have a four-coordinate structure with a N3S coordination geometry.

Synthesis, crystal structure and DNA cleavage activity of (aqua)bis(dipyridophenazine)copper(II) complex

A copper(II) complex of dipyridophenazine, viz., [Cu(dppz)(2)(H2O)](ClO4)(2) (I), has been prepared and structurally characterized by X-ray crystallography. The crystal structure of the complex shows a five-coordinate structure in which two N,N-donor dipyridophenazine (dppz) and one aqua ligand bind to the copper(II) center giving Cu-O and Cu-N bond distances in the range of 1.981(6) to 2.043(6) angstrom. The ESI-MS spectrum of 1 in MeCN shows a peak at m/z value of 313 (100%) indicating the dissociation of the aqua ligand in the solution phase. The complex is one-electron paramagnetic (mu(eff), 1.86 mu(B)). It displays a quasi-reversible Cu(II)/Cu(I) redox process at 0.096 V. The complex is an avid binder to CT DNA giving a binding constant value of 3.5 x 10(5) M-1. It shows significant hydrolytic cleavage of supercoiled pUC19 DNA in dark ill the absence of any external agents. The complex exhibits chemical nuclease activity oil treatment with 3-mercaptopropionic acid as a reducing agent forming hydroxyl radicals. Complex 1 is a model synthetic nuclease and hydrolase showing both modes of DNA cleavage under different reaction conditions. The DNA cleavage activity of 1 is significantly better than its phen analogue but similar to that of the bis-dpq complex.

Metal chelates in vinyl polymerization: Bulk polymerization of acrylonitrile initiated by Cu(II)-imine complexes

This article deals with the kinetics and mechanism of acrylonitrile (AN) polymerization initiated by Cu(II)-4-anilino 3-pentene 2-one[Cu(II)ANIPO], Cu(II)-4-p-toluedeno 3-pentene 2-one [Cu(II)TPO], and Cu(II)-4-p-nitroanilino 3-pentene 2-one [Cu(II)NAPO] in bulk at 60°C. The polymerization is free radical in nature. The exponent of initiator(I) is 0.5. The initiation step is a complex formation between the chelate and monomer and subsequent decomposition of the intermediate complex giving rise to free radical and Cu(I). This is substantiated by ultraviolet (UV) and electron spin resonance (ESR) studies. The activation energies and kinetic and chain transfer constants have also been evaluated.

Metal chelates in vinyl polymerization: Kinetics and mechanism of acrylonitrile polymerization initiated by Cu(II) imine complexes

The free radical polymerization of acrylonitrile (AN) initiated by Cu(II) 4-anilino 2-one [Cu(II) ANIPO] Cu(II), 4-p-toluedeno 3-pentene 2-one [Cu(II) TPO], and Cu(II) 4-p-nitroanilino 3-pentene 2-one [Cu(II) NAPO] was studied in benzene at 50 and 60°C and in carbon tetrachloride (CCl4), dimethyl sulfoxide (DMSO), and methanol (MeOH) at 60°C. Although the polymerization proceeded in a heterogeneous phase, it followed the kinetics of a homogeneous process. The monomer exponents were 2 at two different temperatures and in different solvents. The square-root dependence of Rp on initiator concentration and higher monomer exponents accounted for a 1:2 complex formation between the chelate and monomer. The complex formation was shown by ultraviolet (UV) study. The activation energies, kinetics, and chain transfer constants were also evaluated.

A Comparative Study of Electrochemical Kinetic Parameters by the Potential Step Method. Electrode Reactions of CyDTA and EDTA Complexes of Cu(II) at DME

By using the same current-time (I-t) curves, electrochemical kinetic parameters are determined by two methods, (a) using the ratio of current at a given potential to the diffusion-controlled limiting current and (b) curve fitting method, for the reduction of Cu(II)–CyDTA complex. The analysis by the method (a) shows that the rate determining step involves only one electron although the overall reduction of the complex involves two electrons suggesting thereby the stepwise reduction of the complex. The nature of I-t curves suggests the adsorption of intermediate species at the electrode surface. Under these circumstances more reliable kinetic parameters can be obtained by the method (a) compared to that of (b). Similar observations are found in the case of reduction of Cu(II)–EDTA complex.

Formation of an unusual copper(II) complex from the degradation of a novel tricopper(II) carbohydrazone complex

An unusual copper(II) complex [Cu(L-1a)(2)Cl-2] CH3OH center dot H2O center dot H3O+Cl- (1a) was isolated from a solution of a novel tricopper(II) complex [Cu-3(HL1)Cl-2]Cl-3 center dot 2H(2)O (1) in methanol. where L-1a is 3-(2-pyridyl)triazolo [1,5-a]-pyridine, and characterized with single crystal X-ray diffraction study. The tricopper(II) complex of potential ligand 1,5-bis(di-2-pyridyl ketone) carbohydrazone (H2L1) was synthesized and physicochemically characterized, while the formation of the complex la was followed by time-dependant monitoring of the UV-visible spectra. which reveals degradation of ligand backbone as intensity loss of bands corresponding to O -> Cu(II) charge transfer.

Cu-II-Azide Polymers of Cu-3 and Cu-6 Building Units: Synthesis,Structures, and Magnetic Exchange Mechanism

Two new neutral copper-azido polymers [Cu-3(N-3)(6)(tmen)(2)](n)(1)and [Cu-6(N-3)(12)(deen)(2)](n) (2) [tmen = N,N,N, N-tetramethylethylenediamine and deen = N,N-diethylethylenediamine] have been synthesized by using lower molar equivalents of the chelating diamine ligands with Cu(NO3)(2)center dot 3H(2)O and an excess of NaN3. The single crystal X-ray structure shows that in the basic unit of the 1D complex 1, the three Cu-II ions are linked by double end-on azido bridges with Cu-N-EO-Cu angles on both sides of the magnetic exchange critical angle of 108 degrees. Complex 2 is a 3D framework of a basic u-6 cluster. Cryomagnetic susceptibility measurements over a wide range of temperature exhibit dominant ferromagnetic behavior in both the complexes. Density functional theory calculations (B3LYP functional) have been performed on the trinuclear unit to provide a qualitative theoretical interpretation of the overall ferromagnetic behavior shown by the complex 1.

Anion directed template synthesis of Cu(II) complexes of a N,N,O donor mono-condensed Schiff base ligand: A molecular scaffold forming highly ordered H-bonded rectangular grids

Anion directed, template syntheses of two dinuclear copper(II) complexes of mono-condensed Schiff base ligand Hdipn (4-[(3-aminopentylimino)-methyl]-benzene-1,3-diol) involving 2,4- dihydroxybenzaldehyde and 1,3-diaminopentane were realized in the presence of bridging azide and acetate anions. Both complexes, [Cu-2(dipn)(2)(N-3)(2)] (1) and [Cu-2(dip(n))(2)(OAc)(2)] (2) have been characterized by X-ray crystallography. The two mononuclear units are joined together by basal-apical, double end-on azido bridges in complex 1 and by basal-apical, double mono-atomic acetate oxygen-bridges in 2. Both complexes form rectangular grid-like supramolecular structures via H-bonds connecting the azide or acetate anion and the p-hydroxy group of 2,4- dihydroxybenzaldehyde. Variable-temperature (300-2 K) magnetic susceptibility measurements reveal that complex 1 has antiferromagnetic coupling (J = -2.10 cm (1)) through the azide bridge while 2 has intra-dimer ferromagnetic coupling through the acetate bridge and inter-dimer antiferromagnetic coupling through H-bonds (J = 2.85 cm (1), J' = -1.08 cm (1)). (C) 2009 Elsevier B. V. All rights reserved.