Trans-dioxo manganese(V) porphyrins.
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ABSTRACT:
SUBMITTER: Jin N
PROVIDER: S-EPMC2773832 | biostudies-literature | 2007 Oct
REPOSITORIES: biostudies-literature
Publications
Trans-dioxo manganese(V) porphyrins.
Jin Ning N Ibrahim Mohammed M Spiro Thomas G TG Groves John T JT
Journal of the American Chemical Society 20070921 41
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Project description:Manganese porphyrins (MnPs), MnTE-2-PyP5+, MnTnHex-2-PyP5+ and MnTnBuOE-2-PyP5+, are superoxide dismutase (SOD) mimetics and form a redox cycle between O2 and reductants, including ascorbic acid, ultimately producing hydrogen peroxide (H2O2). We previously found that MnPs oxidize hydrogen sulfide (H2S) to polysulfides (PS; H2Sn, n = 2-6) in buffer. Here, we examine the effects of MnPs for 24 h on H2S metabolism and PS production in HEK293, A549, HT29 and bone marrow derived stem cells (BMDSC) using H2S (AzMC, MeRho-AZ) and PS (SSP4) fluorophores. All MnPs decreased intracellular H2S production and increased intracellular PS. H2S metabolism and PS production were unaffected by cellular O2 (5% versus 21% O2), H2O2 or ascorbic acid. We observed with confocal microscopy that mitochondria are a major site of H2S production in HEK293 cells and that MnPs decrease mitochondrial H2S production and increase PS in what appeared to be nucleoli and cytosolic fibrillary elements. This supports a role for MnPs in the metabolism of H2S to PS, the latter serving as both short- and long-term antioxidants, and suggests that some of the biological effects of MnPs may be attributable to sulfur metabolism.
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Project description:Photocatalytic oxygenation of 10-methyl-9,10-dihydroacridine (AcrH2) by dioxygen (O2) with a manganese porphyrin [(P)Mn(III): 5,10,15,20-tetrakis-(2,4,6-trimethylphenyl)porphinatomanganese(III) hydroxide [(TMP)Mn(III)(OH)] (1) or 5,10,15,20-tetrakis(pentafluorophenyl)porphyrinatomanganese(III) acetate [(TPFPP)Mn(III)(CH3COO)] (2)] occurred to yield 10-methyl-(9,10H)-acridone (Acr═O) in an oxygen-saturated benzonitrile (PhCN) solution under visible light irradiation. The photocatalytic reactivity of (P)Mn(III) in the presence of O2 is in proportion to concentrations of AcrH2 or O2 with the maximum turnover numbers of 17 and 6 for 1 and 2, respectively. The quantum yield with 1 was determined to be 0.14%. Deuterium kinetic isotope effects (KIEs) were observed with KIE = 22 for 1 and KIE = 6 for 2, indicating that hydrogen-atom transfer from AcrH2 is involved in the rate-determining step of the photocatalytic reaction. Femtosecond transient absorption measurements are consistent with photoexcitation of (P)Mn(III), resulting in intersystem crossing from a tripquintet excited state to a tripseptet excited state. A mechanism is proposed where the tripseptet excited state reacts with O2 to produce a putative (P)Mn(IV) superoxo complex. Hydrogen-atom transfer from AcrH2 to (P)Mn(IV)(O2(•-)) generating a hydroperoxo complex (P)Mn(IV)(OOH) and AcrH(•) is likely the rate-determining step, in competition with back electron transfer to regenerate the ground state (P)Mn(III) and O2. The subsequent reductive O-O bond cleavage by AcrH(•) may occur rapidly inside of the reaction cage to produce (P)Mn(V)(O) and AcrH(OH), followed by the oxidation of AcrH(OH) by (P)Mn(V)(O) to yield Acr═O with regeneration of (P)Mn(III).
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Project description:We show that peripheral nitro groups enhance the maximum two-photon absorption cross-section of trans-A(2)B(2)-porphyrins bearing two phenylethynyl substituents by more than one order of magnitude. Maximum values as high as 1000 GM result from realization of suitable conditions for effective resonance enhancement along with a lowering of the energy and intensification of the two-photon allowed transitions in the Soret region.
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Project description:A series of asymmetrically substituted free-base di- and tetra-phenylporphyrins and the associated Zn-phenylporphyrins were synthesized and studied by X-ray diffraction, NMR, infrared, electronic absorption spectra, as well as fluorescence emission spectroscopy, along with theoretical simulations of the electronic and vibration structures. The synthesis selectively afforded trans-A₂B₂ porphyrins, without scrambling observed, where the AA and BB were taken as donor- and acceptor-substituted phenyl groups. The combined results point to similar properties to symmetrically substituted porphyrins reported in the literature. The differences in FTIR and fluorescence were analyzed by means of detailed density functional theory (DFT) calculations. The X-ray diffraction analysis for single crystals of zinc-containing porphyrins revealed small deviations from planarity for the porphyrin core in perfect agreement with the DFT optimized structures. All calculated vibrational modes (2162 modes for all six compounds studied) were found and fully characterized and assigned to the observed FTIR spectra. The most intense IR bands are discussed in connection with the generic similarity and differences of calculated normal modes. Absorption spectra of all compounds in the UV and visible regions show the typical ethio type feature of meso-tetraarylporphyrins with a very intense Soret band and weak Q bands of decreasing intensity. In diphenyl derivatives, the presence of only two phenyl rings causes a pronounced hypsochromic shift of all bands in the absorption spectra. Time-dependent DFT calculations revealed some peculiarities in the electronic excited states structure and connected them with vibronic bands in the absorption and fluorescence spectra from associated vibrational sublevels.
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Project description:Thirteen new manganese porphyrins and two porphodimethenes bearing one to three different substituents at the meso positions in a variety of architectures have been synthesized. The substituents employed generally are (i) electron-withdrawing to tune the reduction potential to the desirable range (near +0.3V vs NHE), and/or (ii) lipophilic to target the interior of lipid bilayer membranes and/or the blood-brain barrier. The influence of the substituents on the Mn(III)/Mn(II) reduction potentials has been characterized, and the superoxide dismutase activity of the compounds has been examined.
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Project description:Virus-like particles are powerful platforms for the development of functional hybrid materials. Here, we have grown a cross-linked polymer (cross-linked aminoethyl methacrylate) within the confines of the bacteriophage P22 capsid (P22-xAEMA) and functionalized the polymer with various loadings of paramagnetic manganese(III) protoporphyrin IX (MnPP) complexes for evaluation as a macromolecular magnetic resonance imaging contrast agent. The resulting construct (P22-xAEMA-MnPP) has r1,particle = 7,098 mM(-1) s(-1) at 298 K and 2.1 T (90 MHz) for a loading of 3,646 MnPP molecules per capsid. The Solomon-Bloembergen-Morgan theory for paramagnetic relaxivity predicts conjugating MnPP to P22, a supramolecular structure, would result in an enhancement in ionic relaxivity; however, all loadings experienced low ionic relaxivities, r 1,ionic, ranging from 1.45 to 3.66 mM(-1) s(-1), similar to the ionic relaxivity of free MnPP. We hypothesize that intermolecular interactions between neighboring MnPP molecules block access of water to the metal site, resulting in low r 1,ionic relaxivities. We investigated the effect of MnPP interactions on relaxivity further by either blocking or exposing water binding sites on MnPP. On the basis of these results, future design strategies for enhanced r 1,ionic relaxivity are suggested. The measured r 2,ionic relaxivities demonstrated an inverse relationship between loading and relaxivity. This results in a loading-dependent r 2/r 1 behavior of these materials indicating synthetic control over the relaxivity properties, making them interesting alternatives to current magnetic resonance imaging contrast agents.
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Project description:The title complex, {[Mn(C(14)H(6)O(8)S(2))(C(12)H(8)N(2))(2)]·4H(2)O}(n), exhibits a chain-like polymeric structure with 9,10-dioxo-anthracene-1,5-disulfonate anions bridging Mn(II) atoms in a bis-monodentate mode. The unique Mn(II) atom is located on a crystallographic centre of inversion. Four N atoms from two chelating 1,10-phenanthroline ligands and two sulfonate O atoms from two symmetry-related 9,10-dioxoanthracene-1,5-disulfonate anions give rise to a slightly distorted octa-hedral coordination environment around the Mn(II) centre. The centroid of the central ring of the anthraquinone ligand represents another crystallographic centre of inversion. In the crystal structure, inter-ligand π-π stacking [centroid-to-centroid distances 3.532 (1) and 3.497 (3) Å] and inter-molecular O-H⋯O hydrogen-bonding inter-actions assemble the chains into a three-dimensional supra-molecular network.
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Project description:In the title manganese(III) complex, [MnCl(2)(C(10)H(24)N(4))]BF(4) or trans-[MnCl(2)(cyclam)]BF(4) (cyclam is the tetra-dentate amine ligand 1,4,8,11-tetra-azacyclo-tetra-deca-ne), the Mn(III) ions occupy the center of a distorted octa-hedron coordinated by all four ligand nitro-gen donors in the macrobicyclic cavity and two chloride ions occupy the axial positions. Intra-molecular hydrogen bonding involving the coordinated chloride ions and the hydrogen atoms of the cyclam ligand is observed. Inter-molecular hydrogen bonding involving the tetrafluoridoborate anion and hydrogen atoms of the cyclam ligand leads to an infinite one-dimensional chain along the a axis. The tetra-fluoridoborate and inorganic units are linked by N-H⋯F hydrogen bonds. The structure may be compared with those of analogous compounds [MnCl(2)(cyclam)]ClO(4) and [Mn(CN)(2)(cyclam)]ClO(4).
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