Synthesis, structure, and electronic and EPR spectra of copper(II) complexes containing the [CuBr4]2- anion and triphenylarsine oxide

The preparation and characterization of (Ph3AsOH)2[CuBr4] and [Cu(Ph3AsO)4][CuBr4] are reported (Ph3AsO = triphenylarsine oxide). Crystallographic analysis of the monoclinic crystals of (Ph3AsOH)2[CuBr4] (space group C2/c, a = 17.569 (3) Å, b = 13.090 (2) Å, c = 16.933 (2) Å, and β = 105.64 (2)°, R = 0.055 and Rw = 0.057) revealed the presence of compressed [CuBr4]2- tetrahedra of C2 symmetry with Cu-Br distances of 2.340 (1) and 2.437 (1) Å and trans-Br-Cu-Br angles of 139.2 (1) and 122.4 (1)°. The oxonium cations hydrogen bond to the bromine atoms involved in the longer Cu-Br bonds and the smaller trans-Br-Cu-Br angle. Single-crystal electronic and EPR spectra are interpreted in terms of the observed [CuBr4]2- geometry. Analysis of the electronic and EPR spectra of [Cu(Ph3AsO)4][CuBr4] led to the postulation of the presence of planar [Cu(Ph3AsO)4]2+ cations and distorted tetrahedral [CuBr4]2- anions. © 1992 American Chemical Society.

Adsorption and structure of copper(II) complexes on a silica gel surface chemically modified with 2-aminothiazole

The isotherms of adsorption of CuX2 (X=Cl-, Br-, ClO- 4) by silica gel chemically modified with 2-aminothiazole were studied in acetone and EtOH solutions, at 25°C. The 2-aminothiazole molecule, covalently bond to the silica gel surface, adsorbs CuX2 from solvent by forming a surface complex. At low loading, the electronic and E.S.R. spectral parameters indicate that the Cu2+ complexes have a distorted tetragonal symmetry. The d-d eletronic transition spectra show that for ClO- 4 complex, the peak of absorption do not change for any degree of metal loading whilst for Cl- and Br- complexes, the peak maxima shift to higher energy with lower metal loading. © Elsevier Science Ltd.

Research of new mixed-chelate copper complexes with quinoxaline N 1,N 4,-dioxide derivatives and alanine as ligands, potential antimycobacterial agents

Three new mixed-chelate copper complexes with 3-aminoquinoxaline-2-carbonitrile N 1,N 4-dioxide derivatives and alanine as ligands were synthesized in solid state. The spectroscopic characterization (FTIR, EPR, UV-Vis) showed that copper coordinated through the amine and the N-oxide groups of the quinoxaline derivatives and the amine and carboxylate moieties from alanine forming a dimeric species. The tree complexes showed in vitro activity against M. tuberculosis H 37Rv (ATCC 27294) similar to that of ethambutol while they are inactive against E. coli and S. aureus.

Determination of Glycerol in Biodiesel Using a Nickel(II) Oxyhydroxide Chemically Modified Electrode by Cyclic Voltammetry

A glassy carbon electrode chemically modified with nickel oxyhydroxide from a nickel hexacyanoferrate (NiHCF) film was used to determine glycerol in biodiesel by cyclic voltammetry. The modified electrode exhibited a linear response to glycerol concentration in the range from 0.05 to 0.35mmol L-1, and a detection limit of 0.030mmol L-1. The glycerol concentration found in the biodiesel sample was 0.156mmol L-1. The method developed in this study showed a recovery of (100.3±5.0)%. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electrochemical behaviour of copper electrode in concentrated sulfuric acid solutions

The electrochemical behaviour of copper in 6.0 mol 1-1 sulfuric acid at 30°C, was studied by means of the potentiodynamic method. At low potential sweep rates, v < 200 m V s-1, the data reveal that the anodic process is basically constituted of copper dissolution and a film formation which inhibits further metal oxidation and which may undergo further dissolution. For higher potential sweep rates, a modification in the passivation region of the voltammogram is observed. It can be ascribed to a change in the passivation mechanism which possibly involves different surface species. The kineticrelationships derived from the potentiodynamic I/E curves obtained at low v suggest a film formation via a dissolution/precipitation mechanism. © 1993.

Increasing the activity of copper(II) complexes against Leishmania through lipophilicity and pro-oxidant ability

Copper complexes with fluorinated beta-diketones were synthesized and characterized in terms of lipophilicity and peroxide-assisted oxidation of dihydrorhodamine as an indicator of redox activity. The biological activity of the complexes was tested against promastigotes of Leishmania amazonensis. Inhibition of trypanosomatid-specific trypanothione reductase was also tested. It was found that the highly lipophilic and redox-active bis(trifluoroacetylacetonate) derivative had increased toxicity towards promastigotes. These results indicate that it is possible to modulate the activity of metallodrugs based on redox-active metals through the appropriate choice of lipophilic chelators in order to design new antileishmanials. Further work will be necessary to improve selectivity of these compounds against the parasite.

Local electrochemical investigation of copper patina

The patination of copper is known for its complexity and heterogeneous formation. For a deeper investigation, a locally resolved surface analysis was considered. An exact determination of the accessed area and a potentiostatic control in a three-electrode configuration was reached with the use of the electrochemical microcell technique, which enables local electrochemical measurement such as local electrochemical impedance spectroscopy and cyclic voltammetry. Such a technique provides a unique way for performing the investigation of heterogeneities on electrode surfaces. The local electrochemical measurements on the artificially patinated surface have allowed distinguishing areas of different reactivity even when the analysis of the surface revealed a homogenous chemical composition of patina. Local measurements with the electrochemical microcell showed the presence of small defects on the patina layer that can be modelled by considering a hemispherical diffusion process at small active areas surrounded by larger less reactive domains.

Cyclic Voltammetry and Computational Chemistry Studies on the Evaluation of the Redox Behavior of Parabens and other Analogues

Parabens are antimicrobial preservatives widely used in pharmaceutical, cosmetic and food industries. The alkyl chain connected to the ester group defines some important physicochemical characteristics of these compounds, including the partition coefficient and redox properties. The voltammetric and computational analyses were carried out in order to evaluate the redox behavior of these compounds and other phenolic analogues. A strong correlation between chemical substituents inductive effects of parabens with redox potentials was observed. Using cyclic voltammetry and glassy carbon working electrode, only one irreversible anodic peak was observed around 0.8 V for methylparaben (MP), ethylparaben (EP), propylparaben (PP), butylparaben (BP), benzylparaben (BzP) and p-substituted phenolic analogues. The electrodonating inductive effect of alkyl groups was demonstrated by the anodic oxidation potential shift to lower values as the carbon number increases and, therefore the parabens (and other phenolic analogues) oxidation processes to the quinonoidic forms showed great dependence on the substituent pattern.

Cyclic voltammetry and computational chemistry studies on the evaluation of the redox behavior of parabens and other analogues

Parabens are antimicrobial preservatives widely used in pharmaceutical, cosmetic and food industries. The alkyl chain connected to the ester group defines some important physicochemical characteristics of these compounds, including the partition coefficient and redox properties. The voltammetric and computational analyses were carried out in order to evaluate the redox behavior of these compounds and other phenolic analogues. A strong correlation between chemical substituents inductive effects of parabens with redox potentials was observed. Using cyclic voltammetry and glassy carbon working electrode, only one irreversible anodic peak was observed around 0.8 V for methylparaben (MP), ethylparaben (EP), propylparaben (PP), butylparaben (BP), benzylparaben (BzP) and p-substituted phenolic analogues. The electrodonating inductive effect of alkyl groups was demonstrated by the anodic oxidation potential shift to lower values as the carbon number increases and, therefore the parabens (and other phenolic analogues) oxidation processes to the quinonoidic forms showed great dependence on the substituent pattern.

Structural studies of copper(II)-amine terminated dendrimer complexes by EXAFS

The three-dimensional branched nature of dendritic macromolecules provides many potential sites per molecule for the complexation of metal ions. Therefore, dendrimers may act as hosts for metals with coordination potentially occurring at the periphery, the interior, or both. To understand further the complexation of dendrimers with metal ions EXAFS experiments were carried out. In this work, the interaction of amine-terminated polyamido(amine), PAMAM, dendrimer with copper(II) ions determined by EXAFS is reported. It was found that a model consisting of the copper(II) ion forming five- and six-membered rings by chelating with the primary amine, amide, and tertiary amine nitrogen donors of the PAMAM dendrimer could describe the experimental EXAFS data well. Corroborative evidence for binding to amide nitrogen donors comes from the broadening of NMR resonances of a copper(Il)-PAMAM mixture revealing the presence of paramagnetic copper(II) ions at these sites. The significance of the results presented in this paper is that copper(II) ions form complexes within the dendrimer structure and not just at the periphery. The current study may have implications for the use of PAMAM dendrimers as effective ligands in sensing systems.

Novel one-dimensional structures and solution behaviour of copper(II) bromide and chloride complexes of a new pentapyridyldiamine ligand

Copper(II) bromide and chloride complexes of the new heptadentate ligand 2,6-bis(bis(2-pyridylmethyl)amino)methylpyridine (L) have been prepared. For the bromide complexes, chains of novel, approximately C-2-symmetric, chiral [Cu-2(L)Br-2](2+) 'wedge-shaped' tectons are found. The links between the dicopper tectons and the overall chirality and packing of the chains are dictated by the bromide ion content, not the counter anion. In contrast, the chloride complexes exhibit linked asymmetric [Cu-2(L)Cl-3](+) tectons with distinct N3CuCl2 and N4CuCl2 centres in the solid. The overall structures of the dicopper bromide and chloride units persist in solution irrespective of the halide. The redox chemistry of the various species is also described.

Cobalt complexes of tripodal hexadentate ligands: Electrochemically driven rearrangements

The Co-III complexes of the hexadentate tripodal ligands HOsen (3-(2'-aminoethylamino)-2,2-bis((2 ''-aminoethylamino) methyl) propan-1-ol) and HOten (3-(2'-aminoethylthia)-2,2-bis((2 ''-aminoethylthia) methyl) propan-1-ol) have been synthesized and fully characterized. The crystal structures of [Co(HOsen)]Cl-3 center dot H2O and [Co(HOten)](ClO4)Cl-2 are reported and in both cases the ligands coordinate as tripodal hexadentate N-6 and N3S3 donors, respectively. Cyclic voltammetry of the N3S3 coordinated complex [Co(HOten)](3+) is complicated and electrode dependent. On a Pt working electrode an irreversible Co-III/II couple ( formal potential - 157 mV versus Ag-AgCl) is seen, which is indicative of dissociation of the divalent complex formed at the electrode. The free HOten released by the dissociation of [Co(HOten)](2+) can be recaptured by Hg as shown by cyclic voltammetry experiments on a static Hg drop electrode ( or in the presence of Hg2+ ions), which leads to the formation of an electroactive Hg-II complex of the N3S3 ligand (formal potential + 60 mV versus Ag-AgCl). This behaviour is in contrast to the facile and totally reversible voltammetry of the hexaamine complex [Co(HOsen)](3+) ( formal potential (Co-III/II) - 519 mV versus Ag-AgCl), which is uncomplicated by any coupled chemical reactions. Akinetic and thermodynamic analysis of the [Co(HOten)](2+)/[Hg(HOten)](2+) system is presented on the basis of digital simulation of the experimental voltammetric data.

Synthesis and characterization of copper(II) complexes of pyridine-2-carboxamidrazones as potent antimalarial agents

Copper(II) complexes of some pyridine-2-carboxamidrazones have been prepared and characterized. The crystal structures of the copper complex cis-[dichloro(N1-2-acetylthiophene-pyridine-2-carboxamidrazone) copper(II)] 8a and one of the free ligands, viz. {(p-chloro-2-thioloxy-benzylidine-pyridine-2-carboxamidrazone)} 6, have been determined. The former shows a highly distorted square planar geometry around copper, with weak intermolecular coordination from the thiophenyl sulfur resulting in a stacking arrangement in the crystal lattice. The in vitro activities of the synthesized compounds against the malarial parasite Plasmodium falciparum are reported for the first time, which clearly shows the advantage of copper complexation and the requirement of four coordinate geometry around copper as some of the key structural features for designing such metal-based antimalarials. © 2003 Elsevier Science B.V. All rights reserved.