Seven-coordinate iron and manganese complexes with acyclic and rigid pentadentate chelates and their superoxide dismutase activity

The reactions of seven-coordinate [Fe(III)(dapsox)(H(2)O)(2)]ClO(4).H(2)O (1), [Fe(II)(H(2)dapsox)(H(2)O)(2)](NO(3))(2).H(2)O (2), and [Mn(II)(H(2)dapsox)(CH(3)OH)(H(2)O)](ClO4)2(H2O) (3) complexes of the acyclic and rigid pentadentate H(2)dapsox ligand [H2dapsox = 2,6-diacetylpyridinebis(semioxamazide)] with superoxide have been studied spectrophotometrically, electrochemically, and by a submillisecond mixing UV/vis stopped-flow in dimethyl sulfoxide (DMSO). The same studies were performed on the seven-coordinate [Mn(II)(Me(2)[15]pyridinaneN(5))(H(2)O)(2)]Cl(2).H(2)O (4) complex with the flexible macrocyclic Me(2)[15]pyridinaneN(5) ligand (Me(2)[15]pyridinaneN(5) = trans-2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),14,16-triene), which belongs to the class of proven superoxide dismutase (SOD) mimetics. The X-ray crystal structures of 2-4 were determined. All complexes possess pentagonal-bipyramidal geometry with the pentadentate ligand in the equatorial plane and solvent molecules in the axial positions. The stopped-flow experiments in DMSO (0.06% of water) reveal that all four metal complexes catalyze the fast disproportionation of superoxide under the applied experimental conditions, and the catalytic rate constants are found to be (3.7 +/- 0.5) x 10(6), (3.9 +/- 0.5) x 10(6), (1.2 +/- 0.3) x 10(7), and (5.3 +/- 0.8) x 10(6) M(-1) s(-1) for 1-4, respectively. The cytochrome c McCord-Fridovich (McCF) assay in an aqueous solution at pH = 7.8 resulted in the IC(50) values (and corresponding kMcCF constants) for 3 and 4, 0.013 +/- 0.001 microM (1.9 +/- 0.2 x 10(8) M(-1) s(-1)) and 0.024 +/- 0.001 microM (1.1 +/- 0.3 x 10(8) M(-1) s(-1)), respectively. IC(50) values from a nitroblue tetrazolium assay are found to be 6.45 +/- 0.02 and 1.36 +/- 0.03 microM for 1 and 4, respectively. The data have been compared with those obtained by direct stopped-flow measurements and discussed in terms of the side reactions that occur under the conditions of indirect assays.     

Trivalent chromium,manganese, iron and cobalt chelates of a tetradentate N6 macrocyclie ligand

Summary Trivalent chromium, manganese, iron and cobalt salts reactin situ with 2,6-diaminopyridine and acetylacetone to form complexes of the 16-membered N₆ tetradentate macrocyclic ligand. The chelates are characterised as distorted square-pyramidal of [M(TML)X] type, where M = chromium(III), manganese(III), iron(III) and cobalt(III); X=Cl, Br, NO₃ or NCS for chromium(III) and iron(III) and X=(OAc) for manganese(III) and (OH) for cobalt(III). The ligand coordinates through all the nitrogen atoms through deprotonation of two of them, however, the pyridine nitrogens do not take part in coordination. The chelates incorporate one anion or hydroxyl group in the coordination sphere. The magnetic, electronic and i.r. spectral studies indicate lower symmetries for these chelates. The amount of distortion is calculated in terms of DT/DQ by applying NSH theory. X-ray measurements on powder form of the complexes show their isomorphic nature and also support the proposed structures.     

Mechanism of oxidation of iron(II) chelates by hexavalent chromium and heptavalent manganese in aqueous sulfuric acid and micellar media - a kinetic approach

Summary Oxidation of the Fe^II chelates [FeL] (L = phen or bipy) by Cr^VI and Mn^VII in H₂SO₄ medium was found to proceed through the formation of a bimetallic insertion complex which decomposes in the slow step, followed by electron transfer from [FeL] to the oxidant. The reactions are catalysed by both anionic and non-ionic micelles [SDS and triton-x (Tx), respectively]. A mechanism is suggested involving electrostatic stabilization of the cationic forms of the Fe^II chelates by anionic SDS and the partial anionic character of polyoxyethylene moiety of Tx, respectively. The marginal catalysis of cationic micelles (CTAB) is attributed to co-anion-micellar interactions.     

Reactions of diazoles with manganese and iron carbonyls

The compounds of two types were isolated in the reactions of dimanganese decacarbonyl with diazoles. The compounds with an unaltered oxidation state of the metal were formed as a result of nucleophilic substitution of a carbonyl ligand of Mn₂(CO)₁₀. The compounds with an altered oxidation state of the central atom were produced in redox-transformations of Mn₂(CO)₁₀. The substances were characterized by the data of mass-, IR-, ¹H-NMR-spectra. The EPR-data were obtained for paramagnetic Mn²⁺ salts. The reactions of Mn₂(CO)₁₀ with diazoles are compared with those of iron carbonyls.     

Spectrophotometry of iron chelates with 2-hydroxy-5-methylpropiophenone oxime

2-Hydroxy-5-methylpropiophenone oxime (HMP) forms two complexes with ferric iron, the formation of which is pH dependent. Blue colored complex is formed at lower pH values. This complex cannot be extracted into water-immiscible organic solvents. Another complex, brown-red in color, is formed at higher pH values which is extracted into organic solvents. The molar composition of two complexes has been ascertained by using logarithmic and Asmus methods. In the case of blue chelate, the composition is 1:1 (Fe³⁺: oxime) and the composition of brown-red extracted complex is 1:3. The two complexes adhere to Beer's law over a fairly wide range of iron concentration and the sensitivity in terms of Sandell's definition has been calculated. Effect of some foreign ions has been investigated and tentative structures have been assigned to the two complexes.     

DNA cleavage mediated by water-soluble manganese corrole

The DNA nuclease-like activity of a water soluble manganese corrole 5,10,15-tris(N-methyl-4-pyridyl)- corrolatomanganese (Ⅲ)(Mn~ⅢTMPyC) has been investigated.Mn~ⅢTMPyC may bind strongly to DNA via outside groove binding mode as indicated by absorption spectra,viscosity measurements and CD spectra.Mn~ⅢTMPyC exhibited excellent catalytic activity in the DNA oxidative cleavage in the presence of hydroperoxide.     

Preparation and characterization of manganese(IV) in aqueous acetic acid

Mn(IV) acetate was generated in acetic acid solutions and characterized by UV-vis spectroscopy, magnetic susceptibility, and chemical reactivity. All of the data are consistent with a mononuclear manganese(IV) species. Oxidation of several substrates was studied in glacial acetic acid (HOAc) and in 95:5 HOAc-H(2)O. The reaction with excess Mn(OAc)(2) produces Mn(OAc)(3) quantitatively with mixed second-order kinetics, k (25.0 °C) = 110 ± 4 M(-1) s(-1) in glacial acetic acid, and 149 ± 3 M(-1) s(-1) in 95% AcOH, ΔH(?) = 55.0 ± 1.2 kJ mol(-1), ΔS(?) = -18.9 ± 4.1 J mol(-1) K(-1). Sodium bromide is oxidized to bromine with mixed second order kinetics in glacial acetic acid, k = 220 ± 3 M(-1) s(-1) at 25 °C. In 95% HOAc, saturation kinetics were observed.     

Preparation of fructone catalyzed by water-soluble Brφnsted acid ionic liquids

Fructone(2-methyl-2-ethylacetoacetate-1,3-dioxolane),a flavouring material,has been synthesized from ethyl acetoacetate and glycol using five water-soluble Br(?)nsted acid ionic liquids as catalysts for the first time.The used Br(?)nsted acid ionic liquids include [Hmim]Tfa,[Hmim]Tsa,[Hmim]BF_4,[Bmim]HSO4,[Bmim]H_2PO_4,and[Hmim]BF_4 showed the highest catalytic activity for the preparation of fructone.After reaction,the product could be isolated from the reaction system automatically,and the ionic liquid could be directly reused without dehydration.     

Polytetrafluoroethylene surface modification by impregnation with iron and manganese oxides

Polytetrafluoroethylene (PTFE) surfaces can be modified by impregnation with Fe and Mn oxides by procedures based on Fe(CO)₅ sorption in the polymer and followed by oxidation with H₂O₂ or KMnO₄. The effect of some variables (reagent concentrations and temperature) on the amount of oxides deposited was examined. The oxides incorporated in PTFE can be only partly removed by acid cleaning. Water–PTFE contact angles and PTFE surface resistivity are altered. Electron and x-ray diffractograms of the oxides were obtained but unambiguous identification was not achieved. Transmission electron microscopy examination of surface replicas showed that impregnation with oxides which covered most of the PTFE surface was fairly uniform.     

Aqueous speciation and electrochemical properties of a water-soluble manganese phthalocyanine complex

The speciation behavior of a water-soluble manganese(III) tetrasulfonated phthalocyanine complex was investigated with UV-visible and electron paramagnetic resonance (EPR) spectroscopies, as well as cyclic voltammetry. Parallel-mode EPR (in dimethylformamide?:?pyridine solvent mix) reveals a six-line hyperfine signal, centered at a g-value of 8.8, for the manganese(III) monomer, characteristic of the d(4)S = 2 system. The color of an aqueous solution containing the complex is dependent upon the pH of the solution; the phthalocyanine complex can exist as a water-bound monomer, a hydroxide-bound monomer, or an oxo-bridged dimer. Addition of coordinating bases such as borate or pyridine changes the speciation behavior by coordinating the manganese center. From the UV-visible spectra, complete speciation diagrams are plotted by global analysis of the pH-dependent UV-visible spectra, and a complete set of pK(a) values is obtained by fitting the data to a standard pK(a) model. Electrochemical studies reveal a pH-independent quasi-reversible oxidation event for the monomeric species, which likely involves oxidation of the organic ligand to the radical cation species. Adsorption of the phthalocyanine complex on the carbon working electrode was sometimes observed. The pK(a) values and electrochemistry data are discussed in the context of the development of mononuclear water-oxidation catalysts.     

Thermochemistry of iron manganese oxide spinels

Oxide melt solution calorimetry has been performed on iron manganese oxide spinels prepared at high temperature. The enthalpy of formation of (Mn_xFe_1−x)₃O₄ at 298 K from the oxides, tetragonal Mn₃O₄ (hausmannite) and cubic Fe₃O₄ (magnetite), is negative from x=0 to x=0.67 and becomes slightly positive for 0.67<x<1.0. Relative to cubic Mn₃O₄ (stable at high temperature) and cubic Fe₃O₄ (magnetite), the enthalpy of formation is negative for all compositions. The enthalpy of formation is most negative near x=0.2. There is no significant difference in the trend of enthalpy of formation versus composition for cubic (x<0.6) and tetragonal (x>0.6) spinels of intermediate compositions. The enthalpies of formation are discussed in terms of three factors: oxidation-reduction relative to the end-members, cation distribution, and tetragonality. A combination of measured enthalpies and Gibbs free energies of formation in the literature provides entropies of mixing. ΔS_mix, consistent with a cation distribution in which all trivalent manganese is octahedral and all other ions are randomly distributed for x>0.5, but the entropy of mixing appears to be smaller than these predicted values for x<0.4.     

Metal chelates of phosphonate-containing ligands-II: stability constants of some beta-styrylphosphonic acid metal chelates

The synthesis and properties of beta-styrylphosphonic acid (SPA) are reported. The values of the protonation constants of the ligand were determined potentiometrically at different ionic strengths and in the temperature range 0-65 degrees. The enthalpy and entropy of protonation have been calculated by using the van't Hoff isochore. The protonation process is endothermic and is stabilized by a relatively large positive entropy change. The stability constants of the complexes formed between SPA and the bivalent Mg, Ca, Ba, Co, Ni and Pd ions at 25 degrees and ionic strength of 0.12M KNO(3) were also determined. All measurements were carried out in 18% dimethylformamide-water mixture.     

Chromatographic methods for the separation of biocompatible iron chelators from their synthetic precursors and iron chelates

Chromatographic methods have been developed for the separation of the three novel biocompatible iron chelators pyridoxal isonicotinoyl hydrazone (PIH), salicylaldehyde isonicotinoyl hydrazone (SIH), and pyridoxal 2-chlorobenzoyl hydrazone (o-108) from their synthetic precursors and iron chelates. The chromatographic analyses were achieved using analytical columns packed with 5 microm Nucleosil 120-5 C18. For the evaluation of all chelators in the presence of the synthetic precursors, EDTA was added to the mobile phase at a concentration of 2 mM. The best separation of PIH and its synthetic precursors was achieved using a mixture of phosphate buffer (0.01 M NaH2PO4, 5 mM 1-heptanesulfonic acid sodium salt; pH 3.0) and methanol (55:45, v/v). For separation of SIH and its synthetic precursors, the mobile phase was composed of 0.01 M phosphate buffer (pH 6.0) and methanol (60:40, v/v). o-108 was analyzed employing a mixture of 0.01 M phosphate buffer (pH 7.0), methanol, and acetonitrile (60:20:20, v/v/v). These mobile phases were slightly modified to separate each chelator from its iron chelate. Furthermore, a RP-TLC method has also been developed for fast separation of all compounds. The chromatographic methods described herein could be applied in the evaluation of purity and stability of these drug candidates.     

Uranyl chelates of phthalic acid and its substituted derivatives

The interactions of uranyl ion with phthalic acid and 3-chloro, 3-bromo, 3-iodo, 3-nitro, 4-nitro and 3 : 6-dichloro phthalic acids have been investigated by the Calvin-Bjerrum titration technique. The stability constants of these complexes have been determined at 30°C at 0.1 M (NaClO₄) ionic strength. Uranyl ion forms 1 : 1 complexes with all the ligands, while a 1 : 2 complex is formed only with phthalic acid. All the 1 : 1 uranyl complexes except those of 3 : 6-dichloro and 3-iodo phthalic acids follow the relationship log K = apk + b. The deviation of the two chelates from the linear relationship is explained on the basis of steric effects and L → M π-bonding.