Water-soluble Manganese Porphyrin Research Articles

Homogeneous aqueous oxidation of organic molecules by Oxone ® and catalysis by a water-soluble manganese porphyrin complex

Peroxymonosulfate (KHSO 5) oxidizes a wide variety of water-soluble organic molecules in aqueous solutions, and the reactions are generally more rapid in phosphate buffer (pH 6–7) than in pure water. A water-soluble porphyrin complex, meso-tetrakis(4-N-methylpyridyl)porphyrinatomanganese(III) chloride, catalyzes epoxidation and hydroxylation under neutral pH conditions.

Electrocatalytic reduction of nitric oxide by water-soluble manganese porphyrins

Manganese porphyrins electrochemically catalyze the reduction of nitric oxide to hydroxylamine and ammonia in aqueous media. The reactions occurs via an ECE pathway. Demetallation and porphine ring reduction are the main factors of deactivation.

Selective electrocatalysis of olefins by a water-soluble manganese porphyrin in acidic solution

Stable manganese(IV) tetrakis(N-methyl-2-pyridyl)porphyrin is electrochemically generated in acidic solutions at room temperature to selectively catalyse the oxidation of olefins.

Potassium monopersulfate and a water-soluble manganese porphyrin complex, [Mn(TMPyP)](OAc)5, as an efficient reagent for the oxidative cleavage of DNA.

Reported studies indicate that the association of potassium monopersulfate with [Mn(TMPyP)](OAc)5, a water-soluble manganese porphyrin complex, leads to an efficient reagent for the oxidative cleavage of DNA. Single-strand breaks (SSBs) are observed on double-stranded DNA at manganese porphyrin concentrations as low as 0.5 nM with a short incubation time of 1 min. The number of SSBs linearly varies with the concentration of the manganese complex, and potassium monopersulfate is at least 3 orders of magnitude more efficient as oxygen source than hydrogen peroxide. Cleavage efficiency is optimal in the pH range 7.5-9.0 for a NaCl concentration between 80 and 150 mM or for a MgCl2 concentration of 10 mM. At very low manganese porphyrin concentration and by increasing the incubation time a catalytic cleavage activity of the complex is evidenced: up to 5 SSBs per manganese porphyrin are observed. The high cleavage activity of the monopersulfate-manganese porphyrin system makes it a good candidate for DNA-footprinting experiments.

Chemistry of a high-oxidation-level manganese porphyrin in aqueous solution

Manganese(III) tetrakis(N-methyl-4-pyridiniumyl)porphyrin (Mn/sup III/P/sup +/) (chloride salt) and other water-soluble manganese(III) porphyrins undergo facile one-electron electrochemical or chemical oxidation in alkaline solution. Best available evidence indicates that the final oxidized species is a manganese(IV) /mu/-oxo dimer, PMn/sup IV/-O-Mn/sup IV/P/sup 2+/. This same species is also produced by the reaction of manganese(II) porphyrin and oxygen. The Mn(IV) /mu/-oxo dimer has limited stability in water returning to 90-94% of the original Mn(III) porphyrin. The rate of this reaction is pH dependent with faster rates at lower pH. Oxygen is not produced during this reduction process. Rather, the reaction involves an unusual disproportionation in which a small percentage of the porphyrin macrocycles supply multiple electrons to rescue the remainder of the oxidized dimer. It was also found that the manganese(IV) dimer reacts rapidly with water-soluble olefins as it also does in aprotic solvent. A mechanism for the disproportionation reaction is discussed with a rate-determining step involving rearrangement of charge within the symmetric dimer to one with both oxidation equivalents on one metalloporphyrin unit, viz., PMn/sup IV/-O-Mn/sup III/P/sup +/ or PMn/sup III/-O-Mn/sup III/P/sup 2+/. This species undergoes nucleophilic attach by water or hydroxide, producing an isoporphyrin or bilirubin type molecule that has many olefinicmore » bonds capable of reaction with remaining Mn(IV) /mu/-oxo dimer. Since coordination by OH/sup /minus// to the manganese center favors the higher manganese(IV) oxidation level, the pH dependence of the disproportionation can be explained by rearrangement within the dimer to a porphyrin-centered oxidation site. 24 references, 3 figures.« less

Hydroxylating activity of a water-soluble manganese porphyrin associated with potassium hydrogen persulfate: Formation of 8-hydroxyadenosine-5′-mono-phosphate from AMP.

The association of potassium monopersulfate, KHSO 5, with a water-soluble manganese porphyrin complex has been recently reported as being a very efficient system for the oxidative cleavage of DNA (Fouquet et al., J. Chem. Soc., Chem. Commun., 1987, 1169); similar results are observed with RNA. As puzzle piece of the mechanism of this oxidative degradation of nucleic acids, we report in the present communication the identification of 8-hydroxyadenosine-5′-monophosphate as oxidation product of adenosine-5′-monophosphate (AMP) by KHSO 5/[Mn(Mepy) 4P](OAc) 5. In the absence of manganese catalyst, the only detectable compound is the adenosine-N 1-oxide- 5′-monophosphate.

Nuclease activity of a water-soluble manganese porphyrin associated with potassium hydrogen persulphate: oxidative cleavage of DNA

Oxidative cleavage of DNA is observed when the oxygen donor potassium hydrogen persulphate is associated with a water-soluble managanese porphyrin; the nuclease activity is obtained for low concentrations of both the manganese porphyrin (2–200 nM) and potassium hydrogen persulphate (1–25 µM), and the latter is more efficient than hydrogen peroxide in this metalloporphyrin-mediated cleavage of DNA.

Photoinduced oxidation of a water-soluble manganese(III) porphyrin

The photoinduced oxidation of tetra(N-methyl-4-pyridyl)porphyrinmanganese(III) has been achieved in homogeneous solution. The manganese porphyrin was used as an electron donor in a three-component system with tris-(2,2'-bipyridine)ruthenium(II) as the photosensitizer and chloropentaamminecobalt(III) as the electron acceptor. The photooxidized manganese porphyrin is unstable in aqueous solution, reverting to the starting manganese(III) porphyrin. The oxidation of manganese(III) porphyrin and the subsequent reduction of the oxidized porphyrin can be cycled repeatedly.

CATALYTIC ELECTROREDUCTION OF MOLECULAR OXYGEN USING [5,10,15,20-TETRAKIS-(1-METHYLPYRIDINIUM-4-YL)PORPHINATO]MANGANESE

Abstract The water-soluble manganese porphyrin in the title was found to catalyze electroreduction of oxygen. The reaction could be explained by an electrochemical (EC) catalytic regeneration mechanism, and at the porphyrin concentrations of more than ca. 5×10−5 mol dm−3 two-electron reduction was attained. Electronic absorption and magnetic circular dichroism (MCD) spectroscopies have suggested that the active species of the porphyrin is in a high-spin divalent state.

ChemInform Abstract: PHOTOCHEMISTRY OF MANGANESE PORPHYRINS. PART 8. ELECTROCHEMISTRY

AbstractCyclisch voltammetrische Messungen zeigen, daß die wasserlöslichen Mn‐Porphyrin‐Komplexe (I) einer Ein‐Elektron‐Reduktion zu den entsprechenden Mn(ll)‐Derivaten mit hoher Reversibilität unterliegen.

Photochemistry of manganese porphyrins. Part 8. Electrochemistry

Water-soluble manganese(III) porphyrins undergo a well defined, one-electron reduction to the corresponding manganese(II) derivative for which the overall reversibility is very high. The intrinsic electrochemical rate constant (k0) was (1.2 ± 0.4)× 10–3 cm s–1 and it remained essentially independent of pH. The nature of the porphyrin ligand affected the magnitude of E½ but caused no significant differences in electrode behaviour. One-electron oxidations were observed for which both E½ and k0 depended markedly upon pH. At pH > 13, oxidation approached the fully reversible case but as the pH was decreased oxidation became progressively more difficult and less reversible. These differences are associated with acid–base equilibria of axially co-ordinated water molecules.

Photochemistry of manganese porphyrins. Part 6. Oxidation–reduction equilibria of manganese(III) porphyrins in aqueous solution

Water-soluble manganese(III) porphyrins are oxidised in alkaline aqueous solution to the corresponding manganese(IV) porphyrins which, from magnetic moment measurements, appear to exist in solution as µ-oxo-dimers. Midpoint potentials and rate constants for oxidation of the manganese(III) porphyrins have been measured for a series of oxidants and throughout the range 9 < pH < 14, but the overall electronic charge on the metalloporphyrin had little effect upon either parameter. The midpoint potentials for the MnIII/IV couple are strongly dependent upon pH and increase with decreasing pH. Although manganese(IV) porphyrins are mild oxidants at pH 14, they should be capable of oxidising water to molecular oxygen in neutral solution. With hypochlorite as oxidant, a second oxidation step is possible and the final product is believed to be a manganese(V) oxo-porphyrin.