The reactions of octaethylporphyrin and its iron (II) and iron (III) complexes with free radicals

The reactions of dilute solutions of octaethylporphyrin and its iron (II) and iron (III) complexes with methyl, 2-cyanopropyl, t-butoxy, and benzoyloxy radicals are described. The results are summarized: (i) The reactivity of the porphyrin and its high-spin iron (II) and iron (III) complexes toward alkyl and t-butoxy radicals stands in the order: Fe^II > Fe^III ? free porphyrin. For benzoyloxy radicals the order is Fe^II > Porp > Fe^III. (ii) The exclusive path of reaction of high-spin iron (II) porphyrin with radicals is the rapid reduction of the radical and generation of an iron (III) porphyrin. The dominant path of reaction of high-spin iron (III) porphyrin with alkyl and (presumably) t-butoxy radicals is a rapid axial inner sphere reduction of the porphyrin. An axial ligand of iron is transferred to the radical. (iv) The reaction of benzoyloxy radicals with high or low-spin iron (III) porphyrins occurs primarily at the meso position. With the low-spin dipyridyl complex in pyridine the attendant reduction to iron (II) can be observed spectrally. Methyl radicals also reduce this complex by adding to the meso position. (v) The reaction of a radical with either an iron (II) or an iron (III) porphyrin results in the generation of the other valence state of iron and consequently oxidation and reduction products emanating from both iron species are obtained. (vi) No evidence for an iron (IV) is intermediate is apparent. (vii) Iron (II) porphyrins in solvents that impart either spin state are easily oxidized by diacyl peroxides. The occurrence of both axial and peripheral redox reactions with the iron complexes supports an underlying premise of a recent theory of hemeprotein reactivity. The relevance of the work to bioelectron transfer and heme catabolism is noted.     

The coordination chemistry of N-(2-aminophenyl)- and N-(3-aminophenyl)quinoline-2′-carboxamide; two potentially tridentate ligands containing secondary amide and N-donor groups

New complexes of the general formulae Co(o-LH)₂X₂ (XCl, NCS), Co(o-LH)₂Br₂·EtOH (EtOHethanol), M(o-LH)(NO₃)₂ (MCo, Ni), Ni(o-LH)₂X₂ (XCl, Br, NCS), Cu(o-L)X (XCl, Br), Zn(o-LH)X₂ (XCl, Br), Pd(o-L)Cl, Pt(o-LH)₂Cl₂·H₂O, M(m-LH)Cl₂·nH₂O (MCo, Ni, Pd; n=0, 0.5, 1), Cu(m-LH)Cl₂·EtOH, M(m-LH)₂Cl₂·nH₂O (MCo, Zn, Pt; n=0, 1), M(m-LH)Br₂ (MCu, Zn), M(m-LH)₂Br₂ (MCo, Ni), Co(m-LH)(NCS)₂ and Co(m-LH)₂(NCS)₂, where o-LH=N-(2-aminophenyl)quinoline-2′-carboxamide and m-LH=N-(3-aminophenyl)quinoline-2′-carboxamide, have been prepared. The complexes were characterised by elemental analyses, conductivity measurements, X-ray powder patterns, thermogravimetric analyses, magnetic moments and spectral (¹H NMR, IR, and electronic) studies. Copper(II) and palladium(II) promote amide deprotonation at nearly acidic pH on coordination with o-LH. A variety of stereochemistries is assigned for the complexes prepared. The deprotonated copper(II) and the nickel(II) and palladium(II) complexes of m-LH appear to be polymeric. The neutral amide group of the ligands is coordinated to the metal ions through oxygen, while N(amide)-coordination is observed for the deprotonated complexes. Coordination of the secondary amide group is not observed for Zn(m-LH)₂Cl₂, Pd(m-LH)Cl₂·0.5H₂O and platinum(II) complexes. The neutral ligand o-LH shows bidentate N(ring), O-behaviour, while the anion o-L⁻ exhibits tridentate N,N,N-coordination. m-LH acts as a monodentate, bidentate and tridentate ligand depending on the metal ion, the anion and the preparative conditions.     

The formation and characterization of copper(II) 1,4-benzenediolate and p-semiquinonate complexes

Strongly oxidizing p-quinones such as tetrachloro-1,4-benzoquinone and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone undergo stepwise oxidative addition reactions with copper(I) chloride and bromide in pyridine resulting in copper(II) p-semiquinone and dinuclear copper(II) 1,4-benzenediolate pyridine complexes.     

Sheet and chain polymeric transition metal complexes formed by N,N-o-phenylenedimethylenebis(pyridin-4-one)

The preparations are reported of the ‘extended reach’ ligand N,N^′-o-phenylene-dimethylenebis(pyridin-4-one) (o-XBP4) and of a range of its metal complexes with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II), two of which have been shown by X-ray studies to have polymeric structures. In the compound [Mn(o-XBP4)(H₂O)₂(NO₃)](NO₃) the o-XBP4 ligands link ‘Mn(H₂O)₂(NO₃)’ units into chains which are then cross-linked into sheets by the bridging action of the coordinated nitrate. In [Cu(o-XBP4)(NO₃)₂] chains are also formed by the bridging action of the o-XBP4 ligands but here they simply pack trough-in-trough with no nitrate cross-linking. X-band EPR spectra are reported for these and the other Mn and Cu compounds as are relevant spectroscopic results for the other complexes.     

Homoleptic platinum(II) and palladium(II) complexes of 1,5,9-trithiacyclododecane: the crystal structures of [Pt(12S3)2](PF6)2 · 2CH3NO2 and [Pd(12S3)2](BF4)2 · 0.5H2O

The synthesis, spectroscopy, electrochemistry, and crystal structures of two new mononuclear homoleptic Pt(II) and Pd(II) complexes with the crown trithioether 1,5,9-trithiacyclododecane (12S3) are reported. In contrast to behavior with analogous smaller ring trithiacrowns, both metal complexes exhibit exodentate axial sulfur donors, a consequence of the preferred conformation of the 12S3 ligand. The lack of two axial metal-sulfur interactions correlates with the observed electronic spectroscopy and oxidative electrochemistry displayed by the complexes and contrasts with properties exhibited by complexes containing smaller polythioether macrocycles. The two complexes have electronic spectra dominated by charge transfer, not d-d bands and show no M²⁺/M³⁺ couples. Both complexes show a fluxional 12S3 ligand in solution due to a 1,5-metallotropic shift, an uncommon observation of this particular type of intramolecular ligand exchange. The ¹⁹⁵Pt NMR chemical shift of −4201 ppm for [Pt(12S3)₂]²⁺ is consistent with an alternating positioning of the four sulfur lone pairs on the coordinated thioethers. Although 12S3 is poorly pre-organized for facial complexation, its flexibility to position a sulfur in an exodentate fashion enables it to form stable complexes with d⁸ metal ions such as Pt(II) and Pd(II).     

花色苷的酶降解

综述了降解花色苷的酶类及其降解机理的研究进展.降解花色苷的酶有花色苷酶、多酚氧化酶、过氧化物酶和果胶酶.花色苷酶和果胶酶均能水解花色苷糖苷键产生花色素和糖,花色素很不稳定,因吡喃烊环极易开环可自发转换成无色衍生物.花色苷不能直接作为PPO或POD的底物;PPO和POD氧化、降解花色苷须依赖具邻二酚结构的其他酚类的存在,...     

Antidiabetic Drug Sitagliptin with Divalent Transition Metals Manganese and Cobalt: Synthesis,Structure, Characterization Antibacterial and Antioxidative Effects in Liver Tissues

Metals and their complexes have an increasing number of medical applications. Sitagliptin (STG) acts as an antidiabetic drug. Mn(II) and Co(II) complexes were studied and characterized based on physical characterization, FT-IR, DG/TG, XRD, ESM, and TEM. Data revealed that STG acts as a bidentate ligand through the oxygen atom of a carbonyl group and the nitrogen atom of an amino group. Magnetic measurement data revealed that the Mn/STG metal complex has a square planner geometry. The experiment was performed on 40 male albino rats who were divided into four groups: the control group, STG group, group treated with STG/Mn, and group treated with Co/STG. Biomarkers for hepatic enzymes and antioxidants were found in the blood, and hepatic tissue histology was evaluated. STG in combination with Mn and Co administration showed potent protective effects against hepatic biochemical alterations induced by STG alone, as well as suppressing oxidative stress and structural alterations. These complexes prevented any stress and improved hepatic enzymatic levels more than STG alone. The STG/Mn complex was highly effective against Bacillus subtilis and Streptococcus pneumonia, while STG/Co was highly effective against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureas. Therefore, STG combined with Mn and Co produced a synergistic effect against oxidative stress and improved the histological structure of the liver tissues. STG metal complexes with Mn and Co showed the most potential ameliorative antioxidant and hepatoprotective effects.     

Cobalt(III) complexes of some aromatic thiohydrazides - Synthesis, characterization and structure

[Co(NH₃)₅Cl]Cl₂ forms neutral 1:3 complex by reaction with aromatic thiohydrazides, i.e. thiobenzhydrazide, o-hydroxythiobenzhydrazide, thiophen-2-thiohydrazide and furan-2-thiohydrazide. All these complexes are diamagnetic and have been characterized by elemental analysis and combination of spectroscopic methods. Cyclic voltammometry of the complexes shows irreversible metal centered and ligand centered electron transfer reactions. One complex, tris-o-hydroxythiobenzhydrazidocobalt(III), has been crystallized from DMSO solution to produce solvated crystals and its structure has been established by X-ray crystallography. Cobalt(III) ion is linked through three hydrazinic nitrogen and three sulfur atoms of three identical deprotonated ligand molecules in a distorted octahedral environment. Involvement of -OH group in intramolecular and intermolecular hydrogen bonding is crucial for crystal formation.     

Synthesis,spectroscopy, electrochemistry,and photochemistry of a series of M(bpym)2Cl2 (M=Mn(II), Co(II), Ni(II), and Cu(II)) complexes. Precursor complexes in the preparation of polymetallic systems

The synthesis, aqueous absorption and reflectance spectra, cyclic voltammetry and ligand field photochemistry of a series of M(bpym)₂Cl₂ (M=Mn(II), Co(II), Ni(II), Cu(II) and bpym=2,2′-bipyrimidine) are reported here. Ligand field electronic spectral assignments are made by comparison to analogous M(bpy)₂Cl₂(s) (bpy=2,2′-bipyridine) and M(bpym)₃²⁺ complexes. Ligand field absorption maxima are shifted to lower energy as a result of bpym loss vs. M(bpym)₃²⁺ complexes. Metal to ligand charge transfer absorption energies increase as a result of d_M orbital stabilization vs. M(bpym)₃²⁺ complexes. Cyclic voltammetry indicates ring opening upon reduction of the complexes. The complexes are photochemically inert (φ_max<0.002) at the irradiated wavelengths.     

Kinetics and mechanism of the oxidative addition of iodomethane to β-diketonatobis(triphenylphosphite)rhodium(I) complexes

The kinetics and mechanism of the oxidative addition of CH₃I to [Rh(β-diketone)(P(OPh)₃)₂] complexes was studied in acetone medium at various temperatures. The experimental rate law is R = k[Rh(β-diketone)(P(OPh₃)₂][CH₃I]. The order of the effect of the β-diketone on the reactivity of the complexes is acac >; BA >; DBM >; TFAA >; TFBA >; HFAA indicating that electronegative substituents of the β-diketone decrease the reactivity of the complexes towards oxidative addition reactions. The volume of activation for some of the reactions was determined in various solvents. The large negative values of the volume and entropy of the activation indicated a mechanism which occurs via a polar transition state.     

Synthesis and properties of guanidine-pyridine hybridligands and structural characterisation of their mono- and bis(chelated) cobalt complexes

The synthesis of four guanidine-pyridine hybridligands and their spectroscopic features in MeCN are described. In order to demonstrate their coordinating properties, the corresponding cobalt(II)chloride complexes have been prepared and completely characterised by means of X-ray structure analysis, UV/Vis spectroscopy and mass spectrometry. The neutral complexes {1,1,3,3-tetramethyl-2-(quinolin-8-yl)guanidine}cobalt(II)-dichloride [Co(TMGqu)Cl₂] and {N-(1,3-dimethylimidazolidin-2-yliden)pyridin-8-amine}cobalt(II)-dichloride [Co(DMEGpy)Cl₂] exhibit a tetrahedral coordination of the cobalt atom, whereas in bis[chlorobis{N-(1,3-dimethylimidazolidin-2-yliden)quinolin-8-amine}cobalt(II)]tetrachlorocobaltate [Co(DMEGqu)₂Cl]₂[CoCl₄] and chlorobis{1,1,3,3-tetramethyl-2-((pyridin-2-yl)methyl)guanidine}cobalt(II)chloride [Co(TMGpy)₂Cl]Cl, the cobalt atom is coordinated in a trigonal pyramidal environment. These trigonal pyramidal complex cations represent the first bis(chelated) guanidine cobalt complexes in which the pyridine donor resides on the apical position and the guanidine donor forms with the chlorine atom the base of the pyramid. Besides the structural characterisation, the quenching effect of the cobalt(II) ion (d⁷) on the ligand fluorescence has been studied.     

Reactivity difference between protolytic forms of some macrocyclic chromium(III) complexes in ligand substitution and electron transfer processes

The review provides insight into the mechanism of ligand substitution and electron transfer (from chromium(III) to iron(III)) by comparison of the reactivity of some tetraazamacrocyclic chromium(III) complexes in the conjugate acid-base forms. Use of two geometrical isomers made possible to estimate the influence of geometry and protolytic reactions in trans and cis position towards the leaving group on the rate enhancement. Studies on the reaction rates in different media demonstrated the role played by outer sphere interactions in a monodentate ligand substitution.     

Metal complexes of naphthoquinone based ligand: synthesis,characterization, protein binding,DNA binding/cleavage and cytotoxicity studies

Protein binding, DNA binding/cleavage and in vitro cytotoxicity studies of 2-((3-(dimethylamino)propyl)amino)naphthalene-1,4-dione (L) and its four coordinated M(II) complexes [M(II) = Co(II), Cu(II), Ni(II) and Zn(II)] have been investigated using various spectral techniques. The structure of the ligand was confirmed by spectral and single crystal XRD studies. The geometry of the complexes has been established using analytical and spectral investigations. These complexes show good binding tendency to bovine serum albumin (BSA) exhibiting high binding constant values (10⁵ M^?1) when compared to free ligand. Fluorescence titration studies reveal that these compounds bind strongly with CT-DNA through intercalative mode (K_app 10⁵ M^?1) and follow the order: Cu(II) > Zn(II) > Ni(II) > Co(II) > L. Molecular docking study substantiate the strength and mode of binding of these compounds with DNA. All the complexes efficiently cleaved pUC18-DNA via hydroxyl radical mechanism and the Cu(II) complex degraded the DNA completely by converting supercoiled form to linear form. The complexes demonstrate a comparable in vitro cytotoxic activity against two human cancer cell lines (MCF-7 and A-549), which is comparable with that of cisplatin. AO/EB and DAPI staining studies suggest apoptotic mode of cell death, in these cancer cells, with the compounds under investigation.     

Synthesis, characterization, electrochemical and spectroscopic investigation of cobalt(III) Schiff base complexes with axial amine ligands: The layered crystal structure of [Co(salophen)(4-picoline)2]ClO4 · CH2Cl2

Cobalt(III) complexes with potentially tetradentate salophen (H₂salophen = N,N′-bis(salicylidene)-1,2-phenylenediamine) as equatorial ligand and with different axial amine ligands (NH₃, cyclohexylamine, aniline, 4-picoline and pyridine) were synthesized and characterized by IR, ¹H NMR, elemental analysis. Electronic spectra and electrochemical properties of the complexes were studied in DMF solutions. The lowest energy transitions, which occur between 464.8 and 477 nm, are attributed mainly to the intraligand charge transfer, confirmed by Zindo/S electronic structure calculations. The reduction potentials of Co(III)/Co(II) are more affected than those of Co(II)/Co(I) by the axial amine ligands. The crystal structure of the [Co^III(salophen)(4- picoline)₂]ClO₄ · CH₂Cl₂ was determined, indicating that the cobalt(III) center is six coordinated surrounded by the tetradentate salophen ligand and two 4-picoline ligands. The crystal packing of the complex shows a layered structure, in which the perchlorate counter ions and also the lattice solvent molecules are intercalated between the bc planes of the complex cations.     

Physico-chemical study of first row transition metal ions coordination compounds with N,N′-bis(2-tosylaminobenzylidene)-1,3-diaminopropanol. The crystal structure of bis-azomethine and its cobalt(II) complex

The novel Cu(II), Ni(II), Zn(II), Co(II) coordination compounds with Schiff base ligand - N,N′-bis(2-tosylaminobenzylidene)-1,3-diaminopropanol have been synthesized and studied. The structures of bis-azomethine as well as Co(II) and Zn(II) mononuclear metallochelates have been determined by X-ray analysis. The magnetic properties of all complexes were studied and interpreted in terms of HDVV theory. It was shown that exchange interaction in binuclear copper(II) complexes was affected by tosyl groups.     

Speciation of binary complexes of Co(II), Ni(II) and Cu(II) with L-aspartic acid in propylene glycol–water mixtures

Abstract

Speciation of binary complexes of Co(II), Ni(II) and Cu(II) with L-aspartic acid in (0-60% v/v) propylene glycol-water mixtures was studied pH metrically at 303.0±0.1 K and at an ionic strength of 0.16 mol L^-1. The binary species refined were ML, ML₂, ML₂H₂, ML₂H₃ and ML₂H₄. The stabilities of the complexes followed the Irving-Williams order i.e.Co(II) <Ni(II) < Cu(II). The linear variation of stability constants as a function of dielectric constant of the medium indicated the dominance of electrostatic forces over non-electrostatic forces. Some species were stabilised due to electrostatic interactions and some were destabilised due to the decreased dielectric constant. The order of ingredients influencing the magnitudes of stability constants due to incorporation of errors in their concentrations was alkali > acid > ligand > metal. Equilibria for the formation of binary complexes were proposed based on the forms of the ligand and their existence at different pH values.     

Synthesis,physico-chemical studies of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) complexes with some p-substituted acetophenone benzoylhydrazones and their antimicrobial activity

Complexes of the type [M(pabh)(H₂O)Cl], [M(pcbh)(H₂O)Cl] and [M(Hpabh)(H₂O)₂ (SO₄)] where, M = Mn(II), Co(II), Ni(II), Cu(II) and Zn(II); Hpabh = p-amino acetophenone benzoyl hydrazone and Hpcbh = p-chloro acetophenone benzoyl hydrazone have been synthesized and characterized with the help of elemental analyses, electrical conductance, magnetic susceptibility measurements, electronic, ESR and IR spectra, thermal (TGA & DTA) and X-ray diffraction studies. Co(II), Ni(II) and Cu(II) chloride complexes are square planar, whereas their sulfate complexes have spin-free octahedral geometry. ESR spectra of Cu(II) complexes with Hpabh are axial and suggest as the ground state. The ligand is bidentate bonding through >C = N ? and deprotonated enolate group in all the chloro complexes, whereas, >C = N and >C = O groups in all the sulfato complexes. Thermal studies (TGA & DTA) on [Cu(Hpabh)(H₂O)₂(SO₄)] indicate a multistep decomposition pattern, which are both exothermic and endothermic in nature. X-ray powder diffraction parameters for [Co(pabh)(H₂O)Cl] and [Ni(Hpabh)(H₂O)₂(SO₄)] correspond to tetragonal and orthorhombic crystal lattices, respectively. The ligands as well as their complexes show a significant antifungal and antibacterial activity. The metal complexes are more active than the ligand.     

Choice of a spin singlet or triplet: electronic properties of Bis-Co(II), Bis-Ni(II), Bis-Cu(II) and Bis-Zn(II) oxygen doubly N-confused hexaphyrin (1.1.1.1.1.1)

Fused hexaphyrins have many physical and chemical properties and can coordinate transition metal ions. In this study, we investigated the geometric structure, charge decomposition analysis (CDA), spin density, frontier molecular orbital (FMO) compositions and absorption spectra of four oxygen doubly N-confused hexaphyrin (1.1.1.1.1.1) (ONCP) complexes with the metal ions Co(II), Ni(II), Cu(II) and Zn(II) (designated ONCP-d-Co, ONCP-d-Ni, ONCP-d-Cu and ONCP-d-Zn). Based on their energies, geometric structures, FMO characteristics and comparison to experiments, ONCP-d-Co and ONCP-d-Cu have the mix-states of the triplet state and broken-symmetry state (antiferromagnetic state) rather than the spin singlet of a closed shell as previously reported. Moreover, based on analyses of the spin density and spin population of the spin triplet ONCP-d-Co and ONCP-d-Cu complexes, the charge transfer in ONCP-d-Cu is greater than that in ONCP-d-Co because the spin density in ONCP-d-Cu is concentrated not only on the Cu ion but also on the ONCP ligand. Thus, the CDA value for ONCP-d-Cu is larger. Finally, through comparative analysis of the FMO compositions and absorption spectra, the complexes and ligand are shown to have very similar absorption spectra with characteristics that arise mainly from π?→?π* transitions both in the B-band and the Q-band, which is due to the FMO compositions being dominated by the highly delocalized conjugated system, rather than by the metal ions. The absorption maxima of the Q-band are ONCP-d-Co (1020 nm)?>?ONCP-d-Zn (1012 nm)?>?ONCP-d-Ni (997 nm)?>?ONCP-d-Cu (988 nm), which is inversely proportional to the energy gap in their FMOs.

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Graphical Abstract The present work investigates the geometric structure, charge decomposition analysis (CDA), spin density, frontier molecular orbital (FMO) compositions and absorption spectra of four oxygen doubly N-confused hexaphyrin (1.1.1.1.1.1) (ONCP) complexes with the metal ions Co(II), Ni(II), Cu(II) and Zn(II) (designated ONCP-d-Co, ONCP-d-Ni, ONCP-d-Cu and ONCP-d-Zn). Based on their energies, geometric structures, FMO characteristics and comparison to experiments, ONCP-d-Co and ONCP-d-Cu have the mix-state of the triplet state and broken-symmetry state (antiferromagnetic state) rather than the spin singlet of a close shell as were previously reported. Meanwhile, ONCP-d-Ni and ONCP-d-Zn show spin singlet structure. The calculated CDA shows the following order: ONCP-d-Cu (1.487)?>?ONCP-d-Ni (1.255)?>?ONCP-d-Co (1.211)?>?ONCP-d-Zn (1.201). Through comparisons of spin density and spin populations of ONCP-d-Co and ONCP-d-Cu, charge transfer between Cu and ligand ONCP is greater than that of Co and ONCP, which makes the CDA value of ONCP-d-Cu obviously larger than that of the other complexes

     

Synthesis, spectroscopic, structural and complexation studies of a new tetra-naphthylmethylene pendant-armed macrocyclic ligand

A novel emissive tetra-naphthylmethylene pendant-armed macrocyclic ligand and a series of complexes with monovalent and divalent metal ions have been synthesized. Solid compounds have been isolated as mononuclear (Co(II), Cu(II) and Zn(II)) or dinuclear (Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Ag(I)), complexes, depending on the counterions used. The chemical and photophysical properties of the free ligand, the protonation behavior and its metal complexes have been investigated in solution. UV-Vis spectroscopy has revealed a 1:1 binding stoichiometry for Cu(II), Zn(II), Cd(II), Ni(II) and Co(II), and 2:1 molar ratio for Ag(I). In chloroform, the free ligand presents two emission bands related to the monomer naphthalene emission and a red-shifted band attibutable to an exciplex due to a charge transfer from the nitrogen lone electron pair to the excited chromophore. Upon protonation of the free amines or due to metal complexation, the exciplex band disappears. The crystal structure of [Ag₂L(NO₃)₂] is also reported. The structure reveals that both metal ions are into the macrocyclic cavity in a distorted square plane {AgN₃O} environment. Each Ag(I) atom interacts with two neighbouring amine nitrogen atoms, one pyridine nitrogen and one oxygen atom from a monodentate nitrate ion.