EXAFS study of binuclear hydroxo-bridged copper(II) complexes

Extended X-ray absorption fine structure (EXAFS) measurements have been recorded at the K-edge of copper in binuclear monohydroxo-bridged copper(II) complexes [(bpy)₂Cu–OH–Cu(bpy)₂](ClO₄)₃ (1) and [(phen)₂Cu–OH–Cu(phen)₂](C1O₄)₃ (2) and dihydroxo-bridged copper(II) complexes [Cu₂(μ–OH)₂(bipy)₂]SO₄?·?5H₂O (3) and [Cu₂(μ–OH)₂(phen)₂]SO₄?·?5H₂O (4) (where bpy and phen are 2,2′-bipyridine and 1,10-phenanthroline, respectively) using the dispersive EXAFS beamline at 2?GeV Indus-2 synchrotron source at RRCAT, Indore, India. The EXAFS data have been analyzed using the software, Athena and Artemis. Theoretical models have been generated for 1 and 3 using available crystallographic data and then fitted to their experimental EXAFS data to obtain the structural parameters, which include bond-lengths, coordination numbers, and thermal disorders. The results obtained have been found to be comparable with their crystallographic results. As the crystallographic data for 2 and 4 are not available in the literature, we have determined their structural parameters by fitting their experimental EXAFS data with the same theoretical models which were generated for their corresponding analogous complexes 1 and 3, respectively. The structural parameters thus determined have been reported. Also, on the basis of the analysis of the EXAFS data, these four complexes have been shown to be binuclear, i.e. they contain two metals. Further, the values of the chemical shifts suggest that copper is in +2 oxidation state in these complexes.     

Synthesis,spectroscopy and thermal analysis of copper(II) hydrazone complexes

The chelating behavior of some hydrazones towards Cu(II) has been investigated. The isolated complexes were characterized by elemental analysis, magnetic moment, spectra (electronic, IR and ms) and thermal measurements. The IR spectra showed that the ligands are deprotonated in the complexes as bidentate, tridentate and binegative tridentate. Protonation constants of the ligands and the stability constants of their Cu(II) complexes were calculated. Square-planar, square-pyramidal, tetrahedral and/or distorted octahedral structures are proposed. The TGA data help to confirm the chemical formula of the complexes and indicated the steps of their thermal degradations.     

The synthesis and characterization of three new vic -dioximes and their nickel(II), copper(II) and cobalt(II) complexes

Three new vic-dioximes, [L¹H₂], N-(4-ethylphenyl)amino-1-acetyl-1-cyclohexenylglyoxime, [L²H₂], N-(4-butylphenyl)amino-1-acetyl-1-cyclohexenylglyoxime, and [L³H₂], N-(4-methoxyphenyl)amino-1-acetyl-1-cyclohexenylglyoxime were synthesized from 1-acetyl-1-cyclohexeneglyoxime and the corresponding substituted aromatic amines. Metal complexes of these ligands were also synthesized with Ni(II), Cu(II), and Co(II) salts. These new compounds (ligands and complexes) were characterized with FT–IR, magnetic susceptibility measurement, molar conductivity measurements, mass spectrometry measurements, thermal methods (e.g. thermal gravimetric analysis), ¹H NMR (Nuclear Magnetic Resonance) and ¹³C NMR spectral data and elemental analyses.     

Redox-active antifungal cobalt(II) and copper(II) complexes with sterically hindered o-aminophenol derivatives

Co(II) complexes with 4,6-di(tert-butyl)-2-aminophenol (HL^I) and 2-anilino-4,6-di(tert-butyl)phenol (HL^II) have been synthesized and characterized by means of physico-chemical methods. The compounds HL^I and HL^II coordinate in their singly deprotonated forms and behave as bidentate O,N-coordinated ligands; their low-spin Co(II) complexes are characterized by CoN₂O₂ coordination modes and square planar geometry. Both the free ligands and their Co(II) and Cu(II) complexes (we have produced and characterized the latter before) exhibit a pronounced antifungal activity against Aspergillus niger, Fusarium spp., Mucor spp., Penicillium lividum, Botrytis cinerea, Alternaria alternata, Sclerotinia sclerotiorum, Monilia spp., which in a number of cases is comparable with that of Nystatin and Terbinafine or even higher. The reducing properties of the ligands and their metal(II) complexes, as well as their antifungal activities, were found to decrease in the order: Cu(L^I)₂ > Cu(L^II)₂ ? Co(L^I)₂ > Co(L^II)₂ > HL^I > HL^II.     

Thermogravimetric investigation of thermal decomposition of copper(II) complexes with methylpyrido[2,3-d]imidazole derivatives

Solid-state complexes with the formulae CuL _x X₂·nH₂O, wereL=2-methyl-, 5-methyl-, or 7-methylpyrido[2,3-d]imidazole,X=NO ₃ ^– or Cl^–,x=2 or 3, andn=1 or 2, were subjected to thermogravimetric analyses. The kinetic parameters were calculated according to the Coats-Redfern method. Reactions paths are proposed and their agreement with the data obtained from TG curves is checked.The authors thank Dr. W. Surga for XRD analyses, and Dr. B. Kowalczyk and Dr. M. Czerwinski from the Pedagogical University in Czestochowa for providing access to the computer application allowing calculation of the kinetic parameters.     

Synthesis,characterization, antimicrobial activity, 3D-QSAR,DFT, and molecular docking of some ciprofloxacin derivatives and their copper(II) complexes

Six new derivatives of ciprofloxacin compounds and their copper(II) complexes were synthesized, characterized by spectroscopic methods (ultraviolet–visible [UV–vis], Fourier transform infrared [FTIR], nuclear magnetic resonance [NMR], mass spectrometry [MS], and electron paramagnetic resonance [EPR]), and tested for antibacterial activities against gram-negative and gram-positive bacteria. The data showed that ciprofloxacin derivatives act as bidentate ligands and the metal ions coordinate through the pyridone carbonyl and the carboxylate oxygen atoms. Tetragonally distorted octahedral ligand fields were assumed for all complexes based on their spectral studies. Copper(II) complexes of the synthesized ciprofloxacin derivatives revealed higher antibacterial activities against gram-positive and gram-negative bacterial species than the parent ciprofloxacin antibiotic. Furthermore, three-dimensional quantitative structure–activity relationship (3D-QSAR) models were evaluated by studying 30 antibiotic compounds of the quinolone class. Density function theory (DFT) calculations were applied to evaluate the optimized geometrical structures using the B3LYP method and 6-311G(d,p) basis set. The 3D-QSAR study revealed that there are eight optimum parameters that give the best predictive modulation with good reliability (R² = 0.996, F = 12.004, sigma = 0.426). In silico molecular docking was also performed on the derivatives, and the results revealed the presence of two types of interactions between the Escherichia coli and the derivatives, H-bonding and Van der Waals interactions, and an effective inhibition at the docked site.     

Molecular complexes of hydrazides with copper(II)

Summary The reaction of substituted hydrazides with copper(II) chloride was investigated in the solid state or in solution in order to account for substituent effects. Spectroscopic results and values of the formation constants indicate the occurrence of strong complexes.

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Molekulare Komplexe von Hydraziden mit Kupfer(II)

Zusammenfassung Die Reaktionen von substituierten Hydraziden mit Kupfer(II)chlorid wurden im Festzustand und in Lösung untersucht. Die spektroskopischen Ergebnisse und die Werte der Bildungskonstanten zeigen die Koordinierung zu starken Komplexen an.

     

Studies of copper (Ⅱ) complexes as catalysts for the hydrolysis of DNA

Hydrolysis of DNA is an important enzymatic reaction , but it is exceedingly difficult to mimic in the laboratory because of the stability of hydrolysis of DNA. In this paper, the cleavage activity of complexes formed between Cu(Ⅱ) and four different amino acid or amino acid methyl ester on DNA is studied by gel elec-trophoresis. It is found that DNA could be cleaved by Cu(Ⅱ)-L-His and Cu(Ⅱ)-L-His methyl ester complexes and the efficiency of cleavage is largely dependent on the metal ion-to-ligand ratio. Further experiments show that the cleavage of DNA mediated by Cu(Ⅱ)-L-His complexes occurs via a hydrolytic mechanism and the active chemical species that affects DNA cleavage is proposed to be MI2H and ML2H22 .     

Design,synthesis, characterization and antibacterial properties of copper(II) complexes with chromone‐derived compounds

A new series of six chromone‐derived compounds and their Cu(II) complexes was synthesized and characterized by their physical, spectral and analytical data The elemental analysis data of the complexes agree well with the proposed composition of the compounds, which were found to be dimeric in nature with two hydrazine molecules bridging the two copper atoms through coordination. The ligands and their Cu(II) complexes were screened for their in‐vitro antibacterial activity against four Gram‐negative (Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, Shigella flexneri) and two Gram‐positive (Bacillus subtilis, Staphylococcus aureus) bacterial strains by the agar‐well diffusion method. The ligands were found to exhibit either no or low to moderate activities against one or more of the bacterial species, whereas all the metal complexes exhibited moderate to high activities against different bacterial species. The ligands which were inactive before complexation turned active and less active ones became more active upon coordination with copper ions. Overall, the complexes 7–12 showed comparatively much higher activities than the ligands. Copyright © 2009 John Wiley & Sons, Ltd.     

TG,DTA and electrical conductance properties of some Cu(II) AND Mn(II) bisazo- dianils complexes

The TG and DTA of a new series of Mn(II) and Cu(II) complexes with a number of newly prepared bisazo-dianil ligands were studied in the temperature range (20-700°C). The TG and DTG curves display to main steps, the first one within the temperature range (25-330°C) correspond to the elimination of water or and ethanol from the complexes. The second step within the range (350-625°C) is due to the decomposition of the complexes yielding the metal oxides as the final product. The rate constants of the dehydration and decomposition reactions were determined, from which some kinetic parameters were evaluated. The DTA curves show that the dehydration of the metal complexes is an endothermic reaction. In all cases the anhydrous metal complexes undergo exothermic decomposition reactions to give the metal oxide. The thermodynamic parameters (ΔE, ΔH, ΔS, ΔG) for the occurring processes are calculated. The electrical conductivities of the solid complexes were measured and the activation energy of the complex and its free ligand are also calculated. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal behaviour of hydrated copper(II) complexes

Dehydration steps of aquacopper(II) complexes with homogeneous and heterogeneous coordination sphere are investigated from the view point of structural changes taking place under their heating to the decomposition temperature and during the dehydration. The role of loosening of intra-and intermolecular hydrogen bonds in the decomposition reaction for the structure changes of the remainder, the structural presumptions of the reactants for lower hydrates formation are discussed. Activation parameters of dehydration were found to be the lower, the smaller are the structure differences between the reactants and products. They do not reflect the bond length central atomvolatile ligand, much more the overall structure differences between the starting and resulting compounds. From all data on crystal and molecular structures of dehydrated compounds is the reaction pathway best indicated by anisotropic temperature parameters of donor atoms corrected for the thermal movement of the central atom: the higher these values in the bond direction are, the lower the values of activation energies of dehydration are.     

On the relationship between the structures of Cu(II) complexes and their chemical transformations

The thermal dehydration of pentacoordinate complexes [Cu(maleinate)(H₂O)] (I), [Cu₂(citrate) (H₂O)₂] (II) and [Cu(phenoxyacetate)₂(H₂O₃] (III) was investigated and correlated with the structural changes occurring during the dehydration. It was found that the activation parameters of the reactions do not follow the lengths of the split Cu?OH₂ bonds. The lowestE _a and lgA values were found for compound I, the highest ones for compound III. The most expressive changes of the anionic ligand binding mode take place during the dehydration of this compound.     

Cobalt(II), nickel(II), and copper(II) complexes of 14-membered hexaazamacrocycles: synthesis and characterization

Cobalt(II), nickel(II), and copper(II) complexes containing 5,12-di(4-bromophenyl)-7,14-dimethyl-1,2,4,8,9,11-hexaazacyclotetradeca-7,14-diene-3,10-dione (H₂L¹) and 5,12-diphenyl-7,14-dimethyl-1,2,4,8,9,11-hexaazacyclotetradeca-7,14-diene-3,10-dione (H₂L²) have been synthesized. All complexes were characterized by elemental analysis, MALDI TOF-MS spectrometry, and electronic absorption spectroscopy. The crystal structures of two compounds, [Cu₂(H₂L¹)Cl₄]_n and [NiL²], were determined by X-ray powder diffraction. In the polymeric [Cu₂(H₂L¹)Cl₄]_n, the Cu₂Cl₄ units and H₂L¹ molecules are situated on inversion centers. Each Cu(II) has a distorted trigonal-bipyramidal coordination environment formed by N and O from H₂L¹ [Cu–N 2.340(14)?Å, Cu–O 1.952(11)?Å], two bridging chlorides [Cu–Cl 2.332(5), 2.279(5)?Å] and one terminal chloride [Cu–Cl 2.320(6)?Å]. In the [NiL²] complex, the Ni(II) situated on inversion center has a distorted square-planar coordination environment formed by four nitrogens from L² [Ni–N 1.860(11), 1.900(11)?Å].     

Rhodium(III), palladium(II) and platinum(II) complexes of Bis(o-aminobenzenesulfonyl)ethylenediamine

New complexes of the formulae K₃[RhL ₃]·2 H₂O, [PdL]·H₂O and [M(LH₂)Cl₂] [whereM = Pd, Pt andLH₂ = bis(o-aminobenzenesulfonyl)ethylenediamine] have been prepared and characterized by conductivity measurements, thermogravimetric analysis, X-ray powder patterns and IR, Ligand Field and¹H-NMR spectroscopy.

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Rhodium(III), Palladium(II)- und Platin(II)-Komplexe mit Bis(o-aminobenzolosulfonyl)ethylendiamin (Kurze Mitteilung)

Zusammenfassung Neue Komplexe der allgemeinen Formeln K₃[RhL ₃]·2H₂O, [PdL]·H₂O und [M(LH₂)Cl₂] mitM = Pd, Pt undLH₂ = Bis(o-aminobenzolosulfonyl)ethylendiamin wurden dargestellt und mit Konduktionsmessungen, thermogravimetrischen Analysen, Röntgenstrukturanalysen, IR, Ligandfeld- und¹H-NMR-Spektroskopie charakterisiert.

     

Antioxidant,DNA interaction,molecular docking and cytotoxicity studies of aminoethylpiperazine‐containing macrocyclic binuclear copper(II) complexes

A series of new macrocyclic binuclear copper(II) complexes of the type [Cu₂L^1–5(ClO₄)](ClO₄) ( 1 – 5 ) were synthesized by template condensation between precursor compounds 2,6‐bis(4‐aminoethylpiperazin‐1‐ylmethyl)‐4‐substituted phenols and 2,6‐diformyl‐4‐substituted phenols. The synthesized precursors and complexes were characterized using regular physicochemical techniques. The rate constant values obtained for the hydrolysis of 4‐nitrophenylphosphate were in the range 1.83 × 10⁻²–4.19 × 10⁻² min⁻¹. Antioxidant studies against 2,2′‐diphenyl‐1‐picrylhydrazyl revealed the antioxidant potency of the synthesized complexes. Binding studies of the complexes with calf thymus DNA were conducted using electronic, viscometric and voltammetric techniques, and the obtained results suggested a non‐covalent groove mode of binding. The oxidative cleavage of pBR322 DNA in the presence of co‐reactant H₂O₂ and radical scavengers showed single strand scission and involvement of H₂O₂ radical in the cleavage process. Molecular docking studies were performed to insert complexes into the crystal structures of 1BNA and VEGFR kinase at active sites to determine the possible binding mode and predominant binding interactions. In vitro cytotoxicity of the complexes was tested against human epidermoid carcinoma cells (A431) by MTT assay, which revealed the effective anticancer activity of the complexes. Live cell and fluorescent imaging of A431 cells showed that the complexes induce cell death through apoptosis.     

Synthesis and characterization of a tetramethyl furanone functionalized diiminedioxime,a potential ligand for Cu radiopharmaceuticals,and its copper(II) and nickel(II) complexes

As part of our on-going effort to develop ⁶⁴Cu-based radiopharmaceuticals for PET (positron emission tomography) imaging of multidrug resistance in cancer, we prepared a tetramethylfuranone-functionalized diiminedioxime ligand, TMFPreH (TMFPreH = 4-[3-(4-hydroxyimino-2,2,5,5-dimethyl-dihydro-furan-3-ylideneamino)-propylimino]-2,2,5,5-tetramethyl-dihydrofuran-3(2H)-one oxime) and its Cu(II) and Ni(II) complexes. When the copper(II) complex was prepared from Cu(ClO₄)₂ in ethanol, it was isolated as a Cu(II)-bridged dimer, but when it was prepared from Cu(OAc)₂ and heated in acetone, an unusual example of an acetone adduct of the ligand is formed by reduction of one of the imine double bonds by the solvent. The Ni(II) complex is square pyramidal with the perchlorate counterion at the apex.     

Synthesis,characterization and biological applications of new copper(II) complexes of aryl hydrazones

On treatment of copper(II) acetate with aryl hydrazone ligands, four new solid derivatives of copper(II) were produced in appreciable yields. Various characterization techniques including infrared, UV–visible, NMR, electron paramagnetic resonance and mass spectroscopies, elemental analysis, scanning electron microscopy, powder X‐ray diffraction and thermogravimetric analysis revealed a tetra‐coordination in all the mononuclear crystalline complexes with high thermal stability. Further, significant interaction of these novel complexes with calf thymus DNA via intercalative mode of binding was revealed by electronic absorption spectroscopy. The chemical nuclease activity of the complexes on pBR322 DNA was investigated in the presence and absence of oxidizing agent (H₂O₂). A potent nuclease activity was observed only in the presence of H₂O₂. Further, antibacterial and antifungal studies of the new ligands and complexes revealed that the latter possessed comparatively better activity.     

Oxidative DNA cleavage by copper ternary complexes of 1,10-phenanthroline and ethylenediamine-sulfonamide derivatives

Ternary copper(II) complexes (1–3) of 1,10-phenanthroline and ethylenediamine-R-sulfonamide derivatives (R = benzene, toluene and naphthalene rings) have been synthesized and characterized with the aid of X-ray diffraction and spectroscopic and electrochemical techniques. The crystal structures of the complexes show that the coordination polyhedron around copper(II) is distorted square planar. Both 1,10-phenanthroline and ethylenediamine-R-sulfonamide act as bidentate ligands. The three structures are stabilized by π–π stacking interactions. The interaction of the complexes with calf thymus DNA has been investigated by thermal denaturation studies which indicated that DNA was stabilized in the presence of the compounds. The increase in DNA stability induced by the complexes follows the order: 3 > 2 > 1. All three complexes were found to be very efficient agents of plasmid DNA cleavage in the presence of ascorbate as reducing agent. Mechanistic studies of the DNA cleavage process performed with radical scavengers show that the reactive oxygen species involved in the DNA damage are the hydroxyl radical, singlet oxygen-like species, the superoxide* and hydrogen peroxide.