Copper Imidazole Complexes Research Articles

Comprehensive structural {single crystal X-raydiffraction, spectroscopic & DFT computational simulation} and biological {in vitro DNA binding & antibacterial} studies of polymeric copper(Ⅱ)-based imidazole drug entity

A polymeric tetrakis N-imidazole copper(II) sulphate complex [Cu(imidazole)4(SO4)]n1, was synthesized and thoroughly characterized by various spectroscopic techniques, elemental analysis and single crystal X-ray crystallography. X-ray diffraction analysis confirmed that polymer complex 1 crystallized in a monoclinic C2/c space group possessing the lattice constants, a = 9.2213(1) Å, b = 17.6062(3) Å, c = 10.5710(2) Å, α = γ = 90˚ and β = 93.561˚ (1) per unit cell. Hirshfeld surface and DFT calculations were executed to simulate the electronic ground state energies in gas phase which showed that the HOMO and HOMO–1 were distributed on the axially coordinated SO42– moiety and considerable amount of electron density was present on Cu(II). Absorption and emission spectroscopic techniques were used to investigate the binding interaction of the copper(II) imidazole complex with the therapeutic target ct-DNA. The results suggested that the complex 1 binds to the ct-DNA through an electrostatic mode. The gel electrophoresis experiments of 1 were carried out with plasmid pBR322 which revealed that the polymer complex could unwind the plasmid DNA at 30 μM micromolar concentration via discernible oxidative cleavage pathway. Molecular docking studies were also carried out to support the results of DNA binding experiments. In addition, the antimicrobial potential of polymer complex was evaluated against various key pathogens viz., B. subtilis, E. coli, K. pneumonia and S. aureus. Antibiofilm behaviour of the complex 1 was examined against E. coli and S. aureus. The results demonstrated that 1 could act as an active antibacterial agent as it inhibited the bacterial growth in agar plates very efficiently.

Thermodynamic, spectroscopic and biological investigation of interaction of anionic surfactants with [Cu(im)6]F2·4H2O complex in aqueous solution

Present study describes the physicochemical behavior of the coordination complex of copper i.e. [Cu(im)6]F2.4H2O (Hexakis(imidazole)copper(II) fluoride tetrahydrate) and its solubilization by anionic surfactants sodium dodecyl sulphate (SDS) and sodium stearate (SS). The detailed investigation was accomplished by electrical conductivity measurements and UV–visible spectroscopy in aqueous solutions of anionic surfactants in the sub micellar and micellar concentration ranges. Furthermore, thermodynamic parameters of complex-surfactant interaction and CMC of both surfactants in the presence of copper imidazole complex were evaluated by electrical conductivity and experimental results revealed an increase in CMC of both surfactants in the presence of complex. CMC increases with rise in temperature and the trend of variation in thermodynamic parameters indicates that the solubilization of copper imidazole complex in micelles of both surfactants is spontaneous and enthalpy as well as entropy driven. Spectroscopic investigation indicates high degree of solubilization and strong interaction in case of complex and SDS than for SS.

An Undergraduate Experiment To Explore Cu(II) Coordination Environment in Multihistidine Compounds through Electron Spin Resonance Spectroscopy

Electron spin resonance (ESR) or electron paramagnetic resonance (EPR) spectroscopy is an incisive technique for the characterization of paramagnetic centers in inorganic, bioinorganic, and organic molecules and materials. These measurements are enabled with the help of paramagnetic species, such as organic free radicals and ions, electronically excited states, and metal–ligand compounds, some of which with biological importance. In this experiment, analogues of histidine–copper coordination compounds are investigated to show students how ESR line shapes depend on the complexed copper ion electronic structure as well as how the spectral features elucidate the coordination environment of copper. These coordinated compounds play an important role in metal ion coordination in proteins and peptides. The experiment has two parts. First, three copper–imidazole complexes that mimic copper–histidine compounds in the human body are synthesized. Second, the ESR spectrum of each complex is obtained at 77 K from frozen chloroform/methanol and acetonitrile/methanol matrixes and used to elucidate the ligand arrangement of the Cu2+ ion and the effect on the unpaired electron density.

Mixed-Metal Zeolitic Imidazolate Frameworks and their Selective Capture of Wet Carbon Dioxide over Methane.

A presynthesized, square planar copper imidazole complex, [Cu(imidazole)4](NO3)2, was utilized as a precursor in the synthesis of a new series of zeolitic imidazolate frameworks, termed ZIF-202, -203, and -204. The structures of all three members were solved by single-crystal X-ray diffraction analysis, which revealed ZIF-203 and -204 having successfully integrated square planar units within the backbones of their respective frameworks. As a result of this unit, the structures of both ZIF-203 and -204 were found to adopt unprecedented three-dimensional nets, namely, ntn and thl, respectively. One member of this series, ZIF-204, was demonstrated to be highly porous, exhibit exceptional stability in water, and selectively capture CO2 over CH4 under both dry and wet conditions without any loss in performance over three cycles. Remarkably, the regeneration of ZIF-204 was performed under the mild conditions of flowing a pure N2 gas through the material at ambient temperature.

Synergistic effect of sandwich polyoxometalates and copper–imidazole complexes for enhancing the peroxidase-like activity

Two inorganic–organic hybrids based on copper(ii)–imidazole complex modified sandwich-type tungstobismuthate or tungstoantimonite, have been synthesized, demonstrating higher peroxidase-like activity using TMB as a peroxidase substrate.

The X-ray absorption spectroscopic model of the copper(II) imidazole complex ion in liquid aqueous solution: a strongly solvated square pyramid.

Cu K-edge extended X-ray absorption fine structure (EXAFS) and Minuit X-ray absorption near-edge structure (MXAN) analyses were combined to evaluate the structure of the copper(II) imidazole complex ion in liquid aqueous solution. Both methods converged to the same square-pyramidal inner coordination sphere [Cu(Im)(4)L(ax)](2+) (L(ax) indeterminate) with four equatorial nitrogen atoms at EXAFS, 2.02 ± 0.01 Å, and MXAN, 1.99 ± 0.03 Å. A short-axial N/O scatterer (L(ax)) was found at 2.12 ± 0.02 Å (EXAFS) or 2.14 ± 0.06 Å (MXAN). A second but very weak axial Cu-N/O interaction was found at 2.9 ± 0.1 Å (EXAFS) or 3.0 ± 0.1 Å (MXAN). In the MXAN fits, only a square-pyramidal structural model successfully reproduced the doubled maximum of the rising K-edge X-ray absorption spectrum, specifically excluding an octahedral model. Both EXAFS and MXAN also found eight outlying oxygen scatterers at 4.2 ± 0.3 Å that contributed significant intensity over the entire spectral energy range. Two prominent rising K-edge shoulders at 8987.1 and 8990.5 eV were found to reflect multiple scattering from the 3.0 Å axial scatterer and the imidazole rings, respectively. In the MXAN fits, the imidazole rings took in-plane rotationally staggered positions about copper. The combined (EXAFS and MXAN) model for the unconstrained cupric imidazole complex ion in liquid aqueous solution is an axially elongated square-pyramidal core, with a weak nonbonded interaction at the second axial coordination position and a solvation shell of eight nearest-neighbor water molecules. This core square-pyramidal motif has persisted through [Cu(H(2)O)(5)](2+), [Cu(NH(3))(4)(NH(3),H(2)O)](2+), (1, 2) and now [Cu(Im)(4)L(ax))](2+) and appears to be the geometry preferred by unconstrained aqueous-phase copper(II) complex ions.

A Binder-Free Ag Paste Using a Chemically Adsorbed Monolayer

We developed a binder-free Ag paste using reactive chemically absorbed monolayers (CAMs), such as epoxy-terminated CAMs. Ag paste was prepared by forming an epoxy-terminated CAM with 2-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane (ECHxES) on the surface of Ag particles, followed by adding 2-methyl-imidazole (2-MeIm) as a cross-linker into a suspension of dispersed Ag particles modified with ECHxES. To increase electrical conductivity, a mixture of large (average diameter D = 1.0 µm) and small (D = 0.5 µm) Ag particles was used. When the ratio in the mixture of large: small was 7:3, the best conductivity, 4.0 ×104 S/cm, was obtained. To prepare rigid wires from Ag paste, a cross-linker of a copper imidazole complex, instead of 2-MeIm, was added to the mixture of the Ag particles covered with ECHxES CAMs. The best pencil hardness and the best electrical conductivity obtained with the Ag paste wire were F and 2.5 ×105 S/cm, respectively, which exceeded the values of commercially available Ag pastes.

Exploring haem-based alternatives for oxygen reduction catalysis in fuel cells—a statusreport of our first principles calculations

For hydrogen fuel cells to become commercially viable, an alternative catalyst to platinumsurfaces that is both efficient and affordable must be discovered. We considerhaem and haem derivatives as potentials substitutes. In this paper, we discussthe oxygen reduction reaction on both the platinum surface and on haem. Wethen introduce our suggestions based on density-functional studies on how toimprove haem’s oxygen-reduction capabilities, which can be summarized as follows:inducing the singlet state, inducing side-on interaction, mimicking cytochromec oxidase by adding a copper–imidazole complex, using platinum deposited ontin porphyrin instead of haem, and using oxomolybdenum porphyrin instead ofhaem. We shall focus on the last three methods because of their experimentalpracticability.

Some biochemical properties of cytokinin oxidase/dehydrogenase in Cucurbita pepo L. (zucchini) leaves

Cytokinin oxidase/dehydrogenase (CKX) was extracted and partially purified from intact leaves of Cucurbita pepo (zucchini) and its activity determined by an in vitro assay based on the measurement of the rate of conversion of [2- 3 H]iP to [2- 3 H] adenine. The optimum incubation time of the enzyme reaction under standard assay conditions was 3 h. Under these conditions the conversion of the substrate was almost linear and did not exceed 20%. The addition of copper-imidazole complex to the assay mixture resulted in a significant increase in the enzyme activity compared with the standard assay, especially during the first 6 h of incubation. The partially-purified enzyme extract exhibited a pH optimum at pH7.0-7.5 (Tris–HCl). The biochemical properties of zucchini enzyme preparations are discussed in view of the existing evidence for biochemical diversity of CKX.

Small heterocyclic ligands improve the copper-catalyzed oxidative coupling of 2,6-dimethylphenol to poly(2,6-dimethyl-1,4-phenylene ether)

Poly(2,6-dimethyl-1,4-phenylene ether) (PPE) [J. Polym. Sci. A 36 (1998) 505], which is widely used in high-performance engineering plastics, is obtained by the copper-catalyzed oxidative coupling of 2,6-dimethylphenol. The oxidative polymerizations have been carried out in acetonitrile with copper-imidazole complexes as the catalyst precursor compounds, which appeared to be extremely active. Different substituents on the imidazole ring showed that both the ligand basicity and the steric hindrance close to the coordinated nitrogen atom are important factors to increase the catalytic activity. Higher activities are always found with an excess of ligand and when using monodentate ligands instead of didentate ones. Most likely, the imidazole moieties may also act as base. Another nitrogen donor ligand, viz. 2-methyl-oxazoline, has been successfully tested, showing a very good activity in this oxidative coupling reaction.

Synthesis, characterization and reactivity of copper(I) imidazole complexes based on a cavitand ligand design†

Two new cavitand-based imidazolyl ligands and their corresponding copper(I) complexes are reported; the tris(imidazole) complex is substitutionally inert while the bis(imidazole) complex readily reacts with CO, PMe3, N3− and SCN−.

An ESEEM investigation of single crystals and powders of copper-dopedl-histidine hydrochloride monohydrate

In this paper we present an investigation of the remote nitrogen of imidazole in copper-dopedl-histidine hydrochloride monohydrate, which is a model system for a wide range of biologically important copper-imidazole complexes. Since these systems are mostly not available in a crystalline form it is interesting to investigate to what extent information that can be obtained from these disordered systems using ESEEM techniques is reliable. From single crystal ESEEM and HYSCORE experiments we have determined the hyperfine and quadrupole coupling tensors of the remote nitrogen in this model system. Additionally, we determined information on these tensors from powdered material, independent of the single crystal results, using orientation selective multifrequency and two-dimensional experiments. The availability of the coupling tensors from the single crystal investigation allowed an assessment of the applicability of the employed powder techniques to this important class of systems. The two-dimensional stimulated echo experiment was found to be a very useful spectroscopic tool for the study of these systems when combined with simulations.

Cytokinin oxidase from auxin- and cytokinin-dependent callus cultures of tobacco (Nicotiana tabacum L.)

Cytokinin oxidase was extracted and partially purified from auxin- and cytokinin-dependent callus tissue of tobacco (Nicotiana tabacum L. cv. Wisconsin 38). The activity of the enzyme preparation was examined using an assay based on the conversion of tritiated N6-(Δ2-isopentenyl)adenine ([2,8-3H]iP) to adenine. Cytokinin oxidase exhibited a temperature optimum at 45–50°C and a relatively high pH optimum (8.5–9.0). The apparent Km value of the enzyme was 4.3 μM for iP. On the basis of the substrate competition assays, iP was determined to be the preferred substrate of the enzyme. Substrate competition was also observed with zeatin and the cytokinin-active urea derivative Thidiazuron. Cytokinins bearing saturated isoprenoid side chains or cyclic side chain structures, as well as auxins and abscisic acid, had no effect on the conversion of [2,8-3H]iP. The cytokinin oxidase exhibited increased activity in the presence of copper-imidazole complex in the reaction mixture. Under optimal concentrations of copper (15 mM CuCl2) and imidazole (100 mM), the enzyme activity was enhanced ca. 40-fold. Under these conditions the pH optimum was lowered to pH 6.0, whereas the temperature optimum, the apparent Km value, and the substrate specificity were not altered. Most of the enzyme moiety did not bind to the lectin concanavalin A. The characteristics of cytokinin oxidase presented here suggest that a novel molecular form of the enzyme, previously identified and characterized in Phaseolus lunatus callus cultures (Kaminek and Armstrong (1990) Plant Physiol 93:1530), also occurs in cultured tobacco tissue.

Synthesis and Characterization of 2,2-Biimidazole Complexes of Oxocations of Molybdenum (VI, V) and Uranium(VI)

Abstract 2,2′-Biimidazole complexes of MoO2 +2, MoO2 + and UO2 +2 have been prepared and characterized by elemental analysis, conductance; and 1H NMR, IR and electronic spectra. Two types of complexes have been identified. Those obtained from slightly acidic solutions have the formulae MoO2 (H2bim)Cl2.2H2O 1, UO2(H2bim) (Ac)2 2 and UO2(H2bim)Cl2.2H2O 3; whereas those from alkaline solutions have the formulae Mo2O4(Hbim)2.2H2O 4, and MO2(Hbim)2 (M = Mo(VI) 5, U(VI) 6). The infrared spectra of these complexes show characteristic biimidazole frequencies in the 3200–2500, 1550–1000 and 750 cm−1 regions as well as metal oxygen double bonds in the 900 cm−1 region. The stoichiometries of the acetate complex has been confirmed from 1H NMR signal ratios of bimidazole to acetate protons at 7.3 and 2.3 ppm, respectively. The electronic spectrum of molybdenum(V) complex showed d-d transition band at ≃13,500 cm−1 in accord with that reported for copper (d9) imidazole complexes; as well as peaks due to charge transfer ...

Synthesis, spectroscopic and structural characterization of bis(acetato)tetrakis(imidazole)copper(II): a model complex for DNA binding

The complex bis(acetato)tetrakis(imidazole)copper(II), [Cu(Im)4(OAc)2] (2), has been prepared by the reaction of excess imidazole with Cu2(OAc)4. Complex 2 exhibits a magnetic moment of 1.88 BM, consistent with one unpaired electron and the formulation of the complex as a Cu(II) monomer. The frozen-solution ESR spectrum exhibits axial symmetry with g∥ and g⊥ values of 2.221 and 2.040, respectively, and A∥(Cu)=181×10−4 cm−1. The g⊥ signal and lowest-field component of the g∥ signal exhibit 14N super-hyperfine structure that consists of nine lines with A⊥(N)=15×10−4 and A∥(N)=10×10−4 cm−1. The ESR data are consistent with the tetragonally elongated chromophore CuN4···O2. Complex 2 crystallizes in the space group C2/c with a=13.187(2), b=8.591(1), c=17.644(2) Å, β=104.13(1), V=1938.4(5) Å3, Z=4, Dcalc=1.556 g/cm3. The relevance of complex 2 to DNA binding of copper(II) imidazole complexes is discussed.

Copper imidazole complexes as synthetic biomimics.

Copper imidazole complexes as synthetic biomimics.

Genotypic Variation in Cytokinin Oxidase from Phaseolus Callus Cultures

Genotypic variation in cytokinin oxidase has been detected in enzyme preparations from Phaseolus vulgaris L. cv Great Northern and Phaseolus lunatus L. cv Kingston callus cultures. Although cytokinin oxidase preparations from Great Northern and Kingston callus tissues appear to have very similar substrate specificities, the cytokinin oxidase activities from the two callus tissues were found to differ in a number of other properties. The cytokinin oxidase from P. vulgaris cv Great Northern callus tissue exhibited a pH optimum of 6.5 (bisTris) and had a strong affinity for the lectin concanavalin A. The cytokinin oxidase from P. lunatus cv Kingston callus tissue exhibited a pH optimum of 8.4 (Taps) and did not bind to concanavalin A. The two enzymes also differed in position of elution when chromatographed on DEAE-cellulose. Both cytokinin oxidase activities exhibited enhanced activity and lower pH optima in the presence of copper-imidazole complexes, but the optimum copper-imidazole ratio and the magnitude of enhancement differed for the two activities. In both callus tissues, transient increases in the supply of exogenous cytokinins induced increases in cytokinin oxidase activity. The differences in pH optima and in glycosylation (as evidenced by the observed difference in lectin affinity) of the cytokinin oxidases from Great Northern and Kingston callus tissues suggest that the compartmentation of cytokinin oxidase may differ in the two callus tissues. The possibility that enzyme compartmentation and isozyme variation in cytokinin oxidase may play a role in the regulation of cytokinin degradation in plant tissues is discussed in relation to known differences in the rates of cytokinin degradation in Great Northern and Kingston callus tissues.

An understanding of the x-ray absorption near-edge structure of copper(II) imidazole complexes

Detailed multiple scattering calculations have been carried out to understand the K-edge X-ray absorption near-edge structure (XANES) of a number of copper(II) imidazole compounds. Results are presented which show that each of the spectral features observed in the XANES can be understood as arising primarily from electron-scattering effects. The calculations suggest that contributions to the XANES from secondary processes (e.g., shake-off effects) are negligible. Evidence is presented for the existence of electron scattering between the imidazole ligands.

FURTHER STUDIES ON THE KINETICS AND MECHANISM OF THE COPPER-IMIDAZOLE CATALYSED DECOMPOSITION OF HYDROGEN PEROXIDE

Abstract The catalytic decomposition of hydrogen peroxide in the presence of the tetrakis(imidazole)copper(II) complex was investigated. The kinetics, based on the rates of oxygen evolution, indicated that a ternary copper(I1)-imidazole-peroxo complex is involved in the rate-determining step. The equilibrium constant for the coordination of hydrogen peroxide to the cupric ion, and the acid dissociation constant for the coordinated H202 ligand were calculated as 1.7 M1 and 2.1 × 109 M, respectively. The ternary complex undergoes intramolecular electron transfer, with k = 4 s1, generating Cu(1) species which can react with hydrogen peroxide or dioxygen, returning to the catalytic cycle. A complete mechanism is proposed, based on the kinetics of oxygen and on the electrocatalytic behdviour observed for the copperimidazole complexes under a dioxygen atmosphere.

ChemInform Abstract: X‐Ray Absorption Spectroscopy of Metal‐Histidine Coordination in Metalloproteins. Exact Simulation of the EXAFS of Tetrakis(imidazole)copper(II) Nitrate and Other Copper‐Imidazole Complexes by the Use of a Multiple‐Scattering Treatment.

ChemInformVolume 19, Issue 10 Physical Organic Chemistry ChemInform Abstract: X-Ray Absorption Spectroscopy of Metal-Histidine Coordination in Metalloproteins. Exact Simulation of the EXAFS of Tetrakis(imidazole)copper(II) Nitrate and Other Copper-Imidazole Complexes by the Use of a Multiple-Scattering Treatment. R. W. STRANGE, R. W. STRANGE S. E. R. C. Daresbury Lab., Warrington, Cheshire WA4 4AD, UKSearch for more papers by this authorN. J. BLACKBURN, N. J. BLACKBURN S. E. R. C. Daresbury Lab., Warrington, Cheshire WA4 4AD, UKSearch for more papers by this authorP. F. KNOWLES, P. F. KNOWLES S. E. R. C. Daresbury Lab., Warrington, Cheshire WA4 4AD, UKSearch for more papers by this authorS. S. HASNAIN, S. S. HASNAIN S. E. R. C. Daresbury Lab., Warrington, Cheshire WA4 4AD, UKSearch for more papers by this author R. W. STRANGE, R. W. STRANGE S. E. R. C. Daresbury Lab., Warrington, Cheshire WA4 4AD, UKSearch for more papers by this authorN. J. BLACKBURN, N. J. BLACKBURN S. E. R. C. Daresbury Lab., Warrington, Cheshire WA4 4AD, UKSearch for more papers by this authorP. F. KNOWLES, P. F. KNOWLES S. E. R. C. Daresbury Lab., Warrington, Cheshire WA4 4AD, UKSearch for more papers by this authorS. S. HASNAIN, S. S. HASNAIN S. E. R. C. Daresbury Lab., Warrington, Cheshire WA4 4AD, UKSearch for more papers by this author First published: March 8, 1988 https://doi.org/10.1002/chin.198810042AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume19, Issue10March 8, 1988 RelatedInformation