Showing papers by "Jean-Marc Latour published in 2003"

Binuclear manganese compounds of potential biological significance. 1. Syntheses and structural, magnetic, and electrochemical properties of dimanganese(II) and -(II,III) complexes of a bridging unsymmetrical phenolate ligand.

Abstract: Reactions of the unsymmetrical phenol ligand 2-(bis(2-pyridylmethyl)aminomethyl)-6-((2-pyridylmethyl)(benzyl)aminomethyl)-4-methylphenol with Mn(OAc)2·4H2O or Mn(H2O)6(ClO4)2 in the presence of NaOBz affords the dimanganese(II) complexes 1(CH3OH), [Mn2(L)(OAc)2(CH3OH)](ClO4), and 2(H2O), [Mn2(L)(OBz)2(H2O)](ClO4), respectively. On the other hand, reaction of the ligand with hydrated manganese(III) acetate furnishes the mixed-valent derivative 3(H2O), [Mn2(L)(OAc)2(H2O)](ClO4) 2. The three complexes have been characterized by X-ray crystallography. 1(CH3OH) crystallizes in the monoclinic system, space group P21/c, with a = 10.9215(6) A, b = 20.2318(12) A, c = 19.1354(12) A, α = 90°, β = 97.5310(10)°, γ = 90°, V = 4191.7 A3, and Z = 4. 2(H2O) crystallizes in the monoclinic system, space group P21/n, with a = 10.9215(6) A, b = 20.2318(12) A, c = 19.1354(12) A, α = 90°, β = 97.5310(10)°, γ = 90°, V = 4191.7 A3, and Z = 4. 3(H2O) crystallizes in the monoclinic system, space group P21/c, with a = 11.144(6) A, b...

Characterization of chromodulin by X-ray absorption and electron paramagnetic resonance spectroscopies and magnetic susceptibility measurements.

Abstract: The biologically active form of the essential trace element chromium is believed to be the oligopeptide chromodulin. Chromodulin binds four chromic ions before binding at or near the active site of activating insulin receptor and subsequently potentiating the tyrosine kinase activity of the receptor. Charge balance arguments and preliminary spectroscopic studies suggested that the chromic centers might be part of a multinuclear assembly. Using a combination of X-ray absorption and electron paramagnetic resonance spectroscopies and variable-temperature magnetic susceptibility measurements, we found that holochromodulin is shown to possess an antiferromagnetically coupled trinuclear assembly which probably weakly interacts with a fourth chromium center. The chromium centers possess octahedron coordination comprised of oxygen-based ligation, presumably derived primarily from oligopeptide-supplied carboxylate groups. X-ray absorption data cannot be reproduced with the presence of sulfur atom(s), indicating that the cysteine thiolate group does not coordinate to the chromium centers. Thus, chromodulin possesses a unique type of multinuclear assembly, distinct from those known in other bioinorganic systems.

Biologically relevant mono- and di-nuclear manganese II/III/IV complexes of mononegative pentadentate ligands

Abstract: Manganese(II) complexes of mononegative pentadentate N4O ligands [Mn2(mgbpen)2(H2O)2](ClO4)2 (1), (mgbpen− = N-methyl-N′-glycyl-N,N′-bis(2-pyridylmethyl)ethane-1,2-diamine) and [Mn2(bzgbpen)2(H2O)2](ClO4)2 (2), (bzgbpen− = N-benzyl-N′-glycyl-N,N′-bis(2-pyridylmethyl)ethane-1,2-diamine) have been prepared. The crystal structure of the Mn(II)–aqua complex of 1, shows it to be dimeric via (μ-κO)-bridging through one carboxylate oxygen atom of each of the two ligands. The non-coordinated carboxylate oxygen atoms are H-bonded to the water ligands on the adjacent Mn ion. The magnetic coupling interaction is weak and antiferromagnetic, J = −1.3(1) cm−1. The dimeric structures of 1 and 2 are retained in solution and can exist in the gas phase. Complexes 1 and 2 are air stable but can be oxidised by tBuOOH to give unstable mononuclear Mn(III) complexes, or oxo-bridged dimanganese(III) and di-μ-oxo-dimanganese(IV) complexes, depending on solvent. The [Mn(III)–OR]+, R = H or CH3 complexes are generated in water or methanol, respectively, and are potentially useful spectroscopic models for active Mn–lipoxygenases. In acetonitrile, di-μ-oxo-dimanganese(IV) complexes are the highest oxidation state products detected, and these are formed via shorter-lived intermediate μ-oxo-dimanganese(III) compounds. The rate of formation of the various oxidized products is slower in the case of the bzgbpen− systems which contains a bulkier non-coordinating arm. The oxidised complexes were characterised by UV-visible spectroscopy, ESI mass spectrometry and cyclic voltammetry. In addition, III–IV and II–III species were electrochemically generated. Thus the new mononegative pentadentate ligand systems display significant flexibility in the range of Mn oxidation states and species of biological relevance that are accessible: A series of dinuclear compounds with different structures in the five oxidation levels between II–II and IV–IV has been identified. No solid state structures were obtained for high oxidation state species, however it is assumed that in the oxo-bridged compounds the carboxylate groups are terminally ligated in contrast to the starting Mn(II) complexes. Thus the system represents examples of limiting structures in the “carboxylate shift” mechanism proposed to be important in non-heme H2O and O2 activation processes.

Binuclear Manganese Compounds of Potential Biological Significance. Part 2. Mechanistic Study of Hydrogen Peroxide Disproportionation by Dimanganese Complexes: The Two Oxygen Atoms of the Peroxide End up in a Dioxo Intermediate

Abstract: The dimanganese(II,II) complexes 1a [Mn2(L)(OAc)2(CH3OH)](ClO4) and 1b [Mn2(L)(OBz)2(H2O)](ClO4), where HL is the unsymmetrical phenol ligand 2-(bis-(2-pyridylmethyl)aminomethyl)-6-((2-pyridylmethyl)(benzyl)aminomethyl)-4-methylphenol, react with hydrogen peroxide in acetonitrile solution. The disproportionation reaction was monitored by electrospray ionization mass spectrometry (ESI-MS) and EPR and UV−visible spectroscopies. Extensive EPR studies have shown that a species (2) exhibiting a 16-line spectrum at g ∼ 2 persists during catalysis. ESI-MS experiments conducted similarly during catalysis associate 2a with a peak at 729 (791 for 2b) corresponding to the formula [MnIIIMnIV(L)(O)2(OAc)]+ ([MnIIIMnIV(L)(O)2(OBz)]+ for 2b). At the end of the reaction, it is partly replaced by a species (3) possessing a broad unfeatured signal at g ∼ 2. ESI-MS associates 3a with a peak at 713 (775 for 3b) corresponding to the formula [MnIIMnIII(L)(O)(OAc)]+ ([MnIIMnIII(L)(O)(OBz)]+ for 3b). In the presence of H218O, th...