Observation of vinylidene emission in mixed phosphine/diimine complexes of Ru(II) at room temperature in solution

The mixed ruthenium(II) complexes trans-[RuCl(2)(PPh(3))(2)(bipy)] (1), trans-[RuCl(2)(PPh(3))(2)(Me(2)bipy)](2), cis-[RuCl(2)(dcype)(bipy)](3), cis-[RuCl(2)(dcype)(Me(2)bipy)](4) (PPh(3) = triphenylphosphine, dcype = 1,2-bis(dicyclohexylphosphino)ethane, bipy = 2,2'-bipyridine, Me(2)bipy = 4,4'-dimethyl-2,2'-bipyridine) were used as precursors to synthesize the associated vinylidene complexes. The complexes [RuCl(=C=CHPh)(PPh(3))(2)(bipy)]PF(6) (5), [RuCl(=C=CHPh)(PPh(3))(2)(Me(2)bipy)]PF(6) (6), [RuCl(=C=CHPh)(dcype)(bipy)]PF(6) (7), [RuCl(=C=CHPh)(dcype)(bipy)]PF(6) (8) were characterized and their spectral, electrochemical, photochemical and photophysical properties were examined. The emission assigned to the pi-pi* excited state from the vinylidene ligand is irradiation wavelength (340, 400, 430 nm) and solvent (CH(2)Cl(2), CH(3)CN, EtOH/MeOH) dependent. The cyclic voltammograms of (6) and (7) show a reversible metal oxidation peak and two successive ligand reductions in the +1.5-(-0.64) V range. The reduction of the vinylidene leads to the formation of the acetylide complex, but due the hydrogen abstraction the process is irreversible. The studies described here suggest that for practical applications such as functional materials, nonlinear optics, building blocks and supramolecular photochemistry. (C) 2011 Elsevier B.V. All rights reserved.

Phosphonate ligands in extended inorganic hybrids and as radical units in complexes

Phosphonatliganden in erweiterten anorganischen Hybridmaterialien undrnals Radikalträgern in KomplexenrnrnAnorganisch-organische Hybridmaterialien sind in der Regel extrem vielseitig. Die systematische Darstellung von niederdimensionalen Materialien (eindimensionale Kettenverbindungen oder zweidimensionalen Schichtverbindungen) mit einer Kontrolle über die Art der Verbindung,rnbietet neue Möglichkeiten im Bereich des molekularen Magnetismus. Hier im Fall von Metall-Phosphonat Verbindungen in erweiterten anorganischen Hybriden wurde der pH - Wert während der Reaktion eingestellt, wodurch der Grad der Protonierung des Phosphonatliganden kontrolliert wurde. Aufgrund der Tatsache, dass alle erhaltenen Metall Phosphonatverbindungen neutral waren, konnte das Ligand zu Metallverhältnis erstmals vorhergesagt werden. So wurden mehrere neue Metall–Phosphonat Verbindungen im Bereich von Null-dimensionalen (I0O0, Co-Kristallisation von M(H2O)6 mitrndeprotonierten Phosphonatligand), über eindimensionalen (I1O0, Kettenstrukturen) bis hin zu zweidimensionalen (I2O0, Schichtstrukturen) ausführlich diskutiert in Bezug auf ihr magnetisches Verhalten. Im Allgemeinen sind die erwarteten Austauschwechselwirkungen in einem erweiterten anorganischen Hybridmaterial stark, weil oft ein Superaustausch durch ein einzelnes Sauerstoffatom möglich ist. Hier waren oft mehrere konkurrierende Austauschwechselwirkungen vorhanden, so dass kompliziertere magnetische Verhalten beobachtet wurden.rnrnDarüber hinaus wurden drei neue Beispiele von Nitronyl-Nitroxidradikale dargestellt, in denen eine zusätzliche saure Funktionalität eingeführt war. Die Auswirkungen des sauren Charakters der zusätzlich eingeführten Sulfonsäure oder Phosphonsäure-Gruppe auf das Nitronyl-Nitroxidradikal wurden im Detail zum ersten Mal untersucht. Die mit der Phosphonsäure-Gruppe versehenen Nitronyl-Nitroxidradikale sind perfekte Proben für die Untersuchung einer Spin-Verschiebung in Nitronyl-Nitroxidradikale durch EPR-Spektroskopie, aufgrund des eingeführten Phosphors. Auch der Protonierungsgrad der zusätzlich eingeführten Phosphonsäure-Gruppe wurde berücksichtigt. In dieser Arbeit wurden die ersten Metallkomplexe der neuen substituierten sauren Nitronyl-Nitroxidradikale vorgestellt. Die Koordination von Nickel(II) Metallionen an die saure, zweite funktionelle Gruppe des Nitronyl–Nitroxid Radikal wurde beschrieben. Die magnetische Austauschwechselwirkung der Metallionen untereinander und die Metall-Radikal-Austauschwechselwirkungen wurden untersucht. rnrnIm Allgemeinen können interessante molekulare magnetische Materialien dadurch dargestellt werden, dass die Dimension der Metall-Phosphonat-Verbindungen als Beispiele für die erweiterten anorganischen Hybridmaterialien gesteuert werden kann. Mit Nitronyl-Nitroxidradikale als organische Liganden können in Zukunft noch mehr Spin-Träger in anorganisch-organischen Gerüstmaterialien integriert werden um die magnetischen Eigenschaften zu verbesseren.rn

Truncation of the class II beta-chain cytoplasmic domain influences the level of class II/invariant chain-derived peptide complexes.

Previous studies have established that antigen presenting cells (APC) expressing major histocompatibility complex class II beta chains with truncated cytoplasmic domains are impaired in their capacity to activate T cells. While it had been widely accepted that this impairment is due to a defect in class II cytoplasmic domain-dependent signal transduction, we recently generated transgenic mice expressing only truncated class II beta chains, and functional analyses of APC from these mice revealed signaling-independent defects in antigen presentation. Here, we demonstrate that T cells primed on such transgenic APC respond better to stimulation by APC expressing truncated beta chains than by wild-type APC. This finding suggests that APC expressing truncated class II beta chains are not inherently defective in their antigen presenting capacity but, rather, may differ from wild-type APC in the peptide antigens that they present. Indeed, analysis of the peptides bound to class II molecules isolated from normal and transgenic spleen cells revealed clear differences. Most notably, the level of class II-associated invariant chain-derived peptides (CLIP) is significantly reduced in cells expressing only truncated beta chains. Prior studies have established that CLIP and antigenic peptides compete for binding to class II molecules. Thus, our results suggest that the cytoplasmic domain of the class II beta chain affects antigen presentation by influencing the level of CLIP/class II complexes.

Palladium(II) pincer complexes of α-amino acids: towards the synthesis of catalytically active artificial peptides

NCN palladium(II) complexes have been covalently attached to the N- and C-terminus of the dipeptide L-Phe-L-Va-OMe. Remarkably, the hydrolysis of the NCN-Pd(II) L-Val-OMe afforded the corresponding, palladated free amino acid without affecting the metal site. This deprotected amino acid could be coupled to any protein, enzyme or peptidic chain by simple peptide chemistry. This bioorganometallic systems were active as catalysts in the aldol reaction between methyl isocianate and benzaldehyde.

New hybrid materials based on the grafting of Pd(II)-amino complexes on the graphitic surface of AC: preparation, structures and catalytic properties

A novel procedure for the preparation of solid Pd(II)-based catalysts consisting of the anchorage of designed Pd(II)-complexes on an activated carbon (AC) surface is reported. Two molecules of the Ar–S–F type (where Ar is a plane-pyrimidine moiety, F a Pd(II)-ligand and S an aliphatic linker) differing in F, were grafted on AC by π–π stacking of the Ar moiety and the graphene planes of the AC, thus favouring the retaining of the metal-complexing ability of F. Adsorption of Pd(II) by the AC/Ar–S–F hybrids occurs via Pd(II)-complexation by F. After deep characterization, the catalytic activities of the AC/Ar–S–F/Pd(II) hybrids on the hydrogenation of 1-octene in methanol as a catalytic test were evaluated. 100% conversion to n-octane at T = 323.1 K and P = 15 bar, was obtained with both catalysts and most of Pd(II) was reduced to Pd(0) nanoparticles, which remained on the AC surface. Reusing the catalysts in three additional cycles reveals that the catalyst bearing the F ligand with a larger Pd-complexing ability showed no loss of activity (100% conversion to n-octane) which is assigned to its larger structural stability. The catalyst with the weaker F ligand underwent a progressive loss of activity (from 100% to 79% in four cycles), due to the constant aggregation of the Pd(0) nanoparticles. Milder conditions, T = 303.1 K and P = 1.5 bar, prevent the aggregation of the Pd(0) nanoparticles in this catalyst allowing the retention of the high catalytic efficiency (100% conversion) in four reaction cycles.

Réaction d’amination intramoléculaire de liens C-H à partir de N-mésyloxycarbamates catalysée par des complexes de rhodium et d’autres métaux de transition : s ynthèse verte d’oxazolidinones

La réaction d’amination de liens C-H, impliquant la transformation directe d’un lien C-H en lien C-N constitue une approche synthétique d’avenir pour la préparation de composés azotés. L’application de cette stratégie de manière intramoléculaire apparaît comme une approche puissante pour la synthèse de composés hétérocycliques. En particulier, les oxazolidinones, carbamates cycliques à cinq chaînons, constituant une nouvelle classe d’antibiotiques très prometteuse, pourraient être synthétisées par cette méthode. Il y a moins d’une dizaine d’années, notre groupe de recherche a travaillé sur le développement de méthodologies utilisant des espèces nitrènes métalliques pour l’amination intra et intermoléculaire. Les N-tosyloxycarbamates, en présence d’une base et d’un catalyseur dimère de rhodium (II) tétracarboxylate sont les précurseurs de ces espèces nitrènes métalliques, capables de faire l’insertion de liens C(sp3)-H. Dans ces travaux de thèse, nous avons travaillé sur le développement d’une méthode plus « verte » d’amination intramoléculaire. Les N-mésyloxycarbamates, plus légers que leurs homologues N-tosyloxycarbamates, ont été identifiés comme d’excellents précurseurs de nitrènes. La méthodologie développée ne nécessite que 3 mol % de dimère de rhodium Rh2(tpa)4 et de 1,5 équivalents de solution aqueuse saturée de K2CO3, le tout dans l’acétate d’éthyle et donne de bons rendements de cyclisation. Une étude de l’étendue réactionnelle a été effectuée, montrant la tolérance et les limitations de notre système catalytique : les hétéroatomes ne posent pas de problèmes hormis l’atome d’azote, qui doit être protégé afin de garantir la transformation. En outre, nous avons constaté que les liens C-H aliphatiques secondaires sont moins réactifs que les liens tertiaires. Après avoir tenté de développer des conditions réactionnelles spécifiques aux liens C-H non activés, nous avons montré la possibilité d’aminer des liens C-H propargyliques de manière chimiosélective ; la triple liaison C-C peut ensuite être dérivatisée efficacement, donnant accès à la formule saturée correspondante ainsi qu’à d’autres motifs. Dans un désir de substituer les complexes de rhodium par d’autres complexes de métaux plus abondants et moins dispendieux, nous nous sommes tournés, dans un premier temps, vers les complexes de fer et par la suite, vers les pinceurs de nickel. Les phtalocyanines de fer ont été identifiées comme étant de bons catalyseurs de l’amination intramoléculaire de N-mésyloxycarbamates. Le chlorure de phtalocyanine de fer (III), en présence d’un sel de AgBF4 et de K2CO3, dans le 1,1,2,2-tétrachloroéthane anhydre, permet l’obtention de la 4-phenyloxazolidin-2-one avec 63% de rendement. En outre, il est possible d’atteindre un rendement de 49% à partir du même substrat N-mésyloxycarbamate, par catalyse avec un pinceur de nickel de type POCN, en présence d’un sel de mésylate. Des indices sur le mécanisme des ces deux transformations ont pu être recueillis lors de la courte étude de ces systèmes.

Réaction d’amination intramoléculaire de liens C-H à partir de N-mésyloxycarbamates catalysée par des complexes de rhodium et d’autres métaux de transition : s ynthèse verte d’oxazolidinones

La réaction d’amination de liens C-H, impliquant la transformation directe d’un lien C-H en lien C-N constitue une approche synthétique d’avenir pour la préparation de composés azotés. L’application de cette stratégie de manière intramoléculaire apparaît comme une approche puissante pour la synthèse de composés hétérocycliques. En particulier, les oxazolidinones, carbamates cycliques à cinq chaînons, constituant une nouvelle classe d’antibiotiques très prometteuse, pourraient être synthétisées par cette méthode. Il y a moins d’une dizaine d’années, notre groupe de recherche a travaillé sur le développement de méthodologies utilisant des espèces nitrènes métalliques pour l’amination intra et intermoléculaire. Les N-tosyloxycarbamates, en présence d’une base et d’un catalyseur dimère de rhodium (II) tétracarboxylate sont les précurseurs de ces espèces nitrènes métalliques, capables de faire l’insertion de liens C(sp3)-H. Dans ces travaux de thèse, nous avons travaillé sur le développement d’une méthode plus « verte » d’amination intramoléculaire. Les N-mésyloxycarbamates, plus légers que leurs homologues N-tosyloxycarbamates, ont été identifiés comme d’excellents précurseurs de nitrènes. La méthodologie développée ne nécessite que 3 mol % de dimère de rhodium Rh2(tpa)4 et de 1,5 équivalents de solution aqueuse saturée de K2CO3, le tout dans l’acétate d’éthyle et donne de bons rendements de cyclisation. Une étude de l’étendue réactionnelle a été effectuée, montrant la tolérance et les limitations de notre système catalytique : les hétéroatomes ne posent pas de problèmes hormis l’atome d’azote, qui doit être protégé afin de garantir la transformation. En outre, nous avons constaté que les liens C-H aliphatiques secondaires sont moins réactifs que les liens tertiaires. Après avoir tenté de développer des conditions réactionnelles spécifiques aux liens C-H non activés, nous avons montré la possibilité d’aminer des liens C-H propargyliques de manière chimiosélective ; la triple liaison C-C peut ensuite être dérivatisée efficacement, donnant accès à la formule saturée correspondante ainsi qu’à d’autres motifs. Dans un désir de substituer les complexes de rhodium par d’autres complexes de métaux plus abondants et moins dispendieux, nous nous sommes tournés, dans un premier temps, vers les complexes de fer et par la suite, vers les pinceurs de nickel. Les phtalocyanines de fer ont été identifiées comme étant de bons catalyseurs de l’amination intramoléculaire de N-mésyloxycarbamates. Le chlorure de phtalocyanine de fer (III), en présence d’un sel de AgBF4 et de K2CO3, dans le 1,1,2,2-tétrachloroéthane anhydre, permet l’obtention de la 4-phenyloxazolidin-2-one avec 63% de rendement. En outre, il est possible d’atteindre un rendement de 49% à partir du même substrat N-mésyloxycarbamate, par catalyse avec un pinceur de nickel de type POCN, en présence d’un sel de mésylate. Des indices sur le mécanisme des ces deux transformations ont pu être recueillis lors de la courte étude de ces systèmes.

Synthetic, spectroscopic and X-ray crystallographic structural study of the monomeric [Cu(pysme)(sac)(MeOH)] and dimeric [Cu(6mptsc)(sac)](2) complexes [pysme = anion of the pyridine-2-carboxaldehyde Schiff base of S-methyldithiocarbazate, 6mptsc=the anio

New mixed-ligand copper(II) complexes of empirical formulas [Cu(pysme)(sac) (CH3OH)] and [Cu(6mptsc)(sac)](2) have been synthesized and characterized by conductance, magnetic, IR and electronic spectroscopic techniques. X-ray crystallographic structure analyses of these complexes indicate that in both complexes the copper(II) ions adopt a five-coordinate distorted square-pyramidal geometry with an N3SO donor environment. The Schiff bases are coordinated to the copper(II) ions as tridentate NNS chelates via the pyridine nitrogen atom, the azomethine nitrogen atom and the thiolate sulfur atom. In the monomeric [Cu(pysme)(sac)(MeOH)] complex, the saccharinate anion acts as a monodentate ligand coordinating the copper(II) ion via the imino nitrogen atom whereas in the dimeric [Cu(6mptsc)(sac)](2) complex, the sac anion behaves as a bridging bidentate ligand providing the imino nitrogen donor atom to one of the copper(II) ions and the carbonyl oxygen as a weakly coordinated axial ligand atom to the other Cu(II) ion. In both complexes, the copper(II) ions have distorted square-pyramidal environments. The distortion from an ideal square-pyramidal geometry is attributed to the restricted bite angles of the planar tridentate ligand. (C) 2004 Elsevier Ltd. All rights reserved.

Stereocontrol in complexes of cyclam-like macrocycles - influences of chirality

Enforcement of chirality upon a macrocyclic tetramine ligand structure by the introduction of an asymmetric pendent arm which does not significantly modify the macrocycle conformation has no significant effect upon the geometry of the coordination sphere of a bound metal. Where substitution engendering chirality does cause a change in the ligand conformation, in particular for a ligand of restricted stereochemistry, these effects can be much greater. Thus, conversion of 3,7-diazacycloheptane to a macrocycle via attachment of chiral sidearms and ring closure through a template reaction leads to cyclam derivatives with unusual coordination properties. (C) 2004 Elsevier Ltd. All rights reserved.

Disturbed microtubule function and induction of micronuclei by chelate complexes of mercury(II)

Interactions of mercury(II) with the microtubule network of cells may lead to genotoxicity. Complexation of mercury(II) with EDTA is currently being discussed for its employment in detoxification processes of polluted sites. This prompted us to re-evaluate the effects of such complexing agents on certain aspects of mercury toxicity, by examining the influences of mercury(H) complexes on tubulin assembly and kinesin-driven motility of microtubules. The genotoxic effects were studied using the micronucleus assay in V79 Chinese hamster fibroblasts. Mercury(II) complexes with EDTA and related chelators interfered dose-dependently with tubulin assembly and microtubule motility in vitro. The no-effect-concentration for assembly inhibition was 1muM of complexed Hg(II), and for inhibition of motility it was 0.05 muM, respectively. These findings are supported on the genotoxicity level by the results of the micronucleus assay, with micronuclei being induced dose-dependently starting at concentrations of about 0.05 muM of complexed Hg(II). Generally, the no-effect-concentrations for complexed mercury(II) found in the cell-free systems and in cellular assays (including the micronucleus test) were identical with or similar to results for mercury tested in the absence of chelators. This indicates that mercury(II) has a much higher affinity to sulfhydryls of cytoskeletal proteins than to this type of complexing agents. Therefore, the suitability of EDTA and related compounds for remediation of environmental mercury contamination or for other detoxification purposes involving mercury has to be questioned. (C) 2004 Elsevier B.V. All rights reserved.

Studies on the thermal decomposition behaviour, kinetics and electrical conductivity of the non-isothermal decomposition of pyridine mono carboxylic acids and some of their transition metal complexes

The thesis is divided into four chapters. They are: introduction, experimental, results and discussion about the free ligands and results and discussion about the complexes. The First Chapter, the introductory chapter, is a general introduction to the study of solid state reactions. The Second Chapter is devoted to the materials and experimental methods that have been used for carrying out tile experiments. TIle Third Chapter is concerned with the characterisations of free ligands (Picolinic acid, nicotinic acid, and isonicotinic acid) by using elemental analysis, IR spectra, X-ray diffraction, and mass spectra. Additionally, the thermal behaviour of free ligands in air has been studied by means of thermogravimetry (TG), derivative thermogravimetry (DTG), and differential scanning calorimetry (DSC) measurements. The behaviour of thermal decomposition of the three free ligands was not identical Finally, a computer program has been used for kinetic evaluation of non-isothermal differential scanning calorimetry data according to a composite and single heating rate methods in comparison with the methods due to Ozawa and Kissinger methods. The most probable reaction mechanism for the free ligands was the Avrami-Erofeev equation (A) that described the solid-state nucleation-growth mechanism. The activation parameters of the decomposition reaction for free ligands were calculated and the results of different methods of data analysis were compared and discussed. The Fourth Chapter, the final chapter, deals with the preparation of cobalt, nickel, and copper with mono-pyridine carboxylic acids in aqueous solution. The prepared complexes have been characterised by analyses, IR spectra, X-ray diffraction, magnetic moments, and electronic spectra. The stoichiometry of these compounds was ML2x(H20), (where M = metal ion, L = organic ligand and x = water molecule). The environments of cobalt, nickel, and copper nicotinates and the environments of cobalt and nickel picolinates were octahedral, whereas the environment of copper picolinate [Cu(PA)2] was tetragonal. However, the environments of cobalt, nickel, and copper isonicotinates were polymeric octahedral structures. The morphological changes that occurred throughout the decomposition were followed by SEM observation. TG, DTG, and DSC measurements have studied the thermal behaviour of the prepared complexes in air. During the degradation processes of the hydrated complexes, the crystallisation water molecules were lost in one or two steps. This was also followed by loss of organic ligands and the metal oxides remained. Comparison between the DTG temperatures of the first and second steps of the dehydration suggested that the water of crystallisation was more strongly bonded with anion in Ni(II) complexes than in the complexes of Co(II) and Cu(II). The intermediate products of decomposition were not identified. The most probable reaction mechanism for the prepared complexes was also Avrami-Erofeev equation (A) characteristic of solid-state nucleation-growth mechanism. The tempemture dependence of conductivity using direct current was determined for cobalt, nickel, Cl.nd copper isonicotinates. An activation energy (ΔΕ), the activation energy (ΔΕ ) were calculated.The ternperature and frequency dependence of conductivity, the frequency dependence of dielectric constant, and the dielectric loss for nickel isonicotinate were determined by using altemating current. The value of s paralneter and the value of'density of state [N(Ef)] were calculated. Keyword Thermal decomposition, kinetic, electrical conduclion, pyridine rnono~ carboxylic acid, cOlnplex, transition metal compJex.

Synthesis and characterization of some Mn(II) and Mn(III) complexes of N,N′-o-phenylenebis(salicylideneimine)(LH2) and N,N′-o-phenylenebis(5-bromosalicylideneimine)(L′H2). Crystal structures of [Mn(L)(H2O)(ClO4)], [Mn(L)(NCS)] and an infinite linear chain of [Mn(L)(OAc)]

A series of manganese(II) [Mn(L)] and manganese(III) [Mn(L)(X)] (X = ClO4, OAc, NCS, N3, Cl, Br and I) complexes have been synthesized from Schiff base ligands N,N′-o- phenylenebis(salicylideneimine)(LH2) and N,N′-o-phenylenebis(5- bromosalicylideneimine)(L′H2) obtained by condensation of salicylaldehyde or 5-Br salicylaldehyde with o-phenylene-diamine. The complexes have been characterized by the combination of IR, UV-Vis spectroscopy, magnetic measurements and electrochemical studies. Three manganese(III) complexes 3 [Mn(L)(ClO4)(H2O)], 5 [Mn(L)(OAc)] and 13 [Mn(L)(NCS)] have been characterized by X-ray crystallography. The X-ray structures show that the manganese(III) is hexa-coordinated in 3, it is penta-coordinated in 13, while in 5 there is an infinite chain where the MnL moieties are connected by acetate ions acting as bridging bidentate ligand. The cyclic voltammograms of all the manganese(III) complexes exhibit two reversible/quasi-reversible/ irreversible responses assignable to Mn(III)/Mn(II) and Mn(IV)/Mn(III) couples. It was observed that the ligand L′H2 containing the 5-bromosal moiety always stabilizes the lower oxidation states compared to the corresponding unsubstituted LH2. Cyclic voltammograms of the manganese(II) complexes (1 and 2) exhibit a quasi-reversible Mn(III)/Mn(II) couple at E1/2 -0.08 V for 1 and 0.054 V for 2. © 2005 Elsevier B.V. All rights reserved.

Studies on the relative stabilities of Mn(II) and Mn(III) in complexes with N4O2 donor environments:crystal structures of [Mn(pybzhz)2] and [Mn(Ophsal)(imzH)2] ClO4 (pybzhz = N-(benzoyl)-N-(picolinylidene) hydrazine, Ophsal = N,N-o-phenylenebis(salicylideneimine), imzH = imidazole)

Five manganese complexes in an N 4O 2 donor environment have been prepared. Four of the compounds involve aroyl hydrazone as ligands and manganese is in a +2 oxidation state. The fifth compound was prepared using N,Nprime-o-phenylenebis(salicylideneimine) and imidazole as ligands where manganese is present in +3 oxidation state. X-ray crystal structure of one Mn +2 compound and the Mn +3 compound was determined. The relative stabilities of the Mn +2 and Mn +3 oxidation states were analyzed using the structural data and MO calculations. Manganese(II) complexes of four aroyl hydrazone ligands were prepared and characterized by different physicochemical techniques. The complexes are of the type Mn(L) 2, where L stands for the deprotonated hydrazone ligand. One of the compounds, Mn(pybzhz) 2, was also characterized by single crystal structure determination. In all these complexes, the Mn(II) is in an N 4O 2 donor environment and the Mn(II) center cannot be oxidized either chemically or electrochemically. However, when another ligand Ophsal is used to give the compound [Mn(Ophsal)(imzH) 2]ClO 4, which was also characterized by X-ray crystal structure determination, manganese can easily avail the +3 oxidation state. The relative stabilities of the +2 and +3 oxidation states of manganese were analyzed and it was concluded that the extent of distortion from the perfect octahedral geometry is the main controlling factor in these cases. © 2004 Elsevier B.V. All rights reserved.

Spectroscopic characterization of schiff base-copper complexes immobilized in smectite clays

Herein, the immobilization of some Schiff base-copper(II) complexes in smectite clays is described as a strategy for the heterogenization of homogeneous catalysts. The obtained materials were characterized by spectroscopic techniques, mostly UV/Vis, EPR, XANES and luminescence spectroscopy. SWy-2 and synthetic Laponite clays were used for the immobilization of two different complexes that have previously shown catalytic activity in the dismutation of superoxide radicals, and disproportionation of hydrogen peroxide. The obtained results indicated the occurrence of an intriguing intramolecular redox process involving copper and the imine ligand at the surface of the clays. These studies are supported by computational calculations.

DNA damage by sulfite autoxidation catalyzed by cobalt complexes

DNA damage was investigated in the presence of sulfite, dissolved oxygen and cobalt(II) complexes with glycylglycylhistidine, glycylhistidyllysine, glycylglycyltyrosylarginine and tetraglycine. These studies indicated that only Co(II) complexed with glycylglycylhistidine (GGH) induced DNA strand breaks at low sulfite concentrations (1-80 mu M) via strong oxidants formed in the reaction. In the presence of the other complexes, some damage occurred only in the presence of high sulfite concentrations (0.1-2.0 mM) after incubation for 4 h. In the presence of GGH, Co(II) and dissolved O(2), DNA damage must involve a reactive high-valent cobalt complex. The damaging effect was increased by adding S(IV), due to the oxysulfur radicals formed as intermediates in S(IV) autoxidation catalyzed by the complex. SO(3)(center dot)-S-, HO(center dot) and H(center dot) radicals were detected by EPR-spin trapping experiments with DMPO (5,5-dimethyl-1-pyrroline N-oxide). The results indicate that Co(II) binds O2 in the presence of GGH, and leads to the formation of a DMPO-HO(center dot) adduct without first forming free superoxide or hydroxyl radical, supporting the participation of a reactive high-valent cobalt complex.