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Issue 11, 2004
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New class of potent catalysts of O2˙ dismutation. Mn(III) ortho-methoxyethylpyridyl- and di-ortho-methoxyethylimidazolylporphyrins

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Abstract

Three new Mn(III) porphyrin catalysts of O2˙ dismutation (superoxide dismutase mimics), bearing ether oxygen atoms within their side chains, were synthesized and characterized: Mn(III) 5,10,15,20-tetrakis[N-(2-methoxyethyl)pyridinium-2-yl]porphyrin (MnTMOE-2-PyP5+), Mn(III)5,10,15,20-tetrakis[N-methyl-N′-(2-methoxyethyl)imidazolium-2-yl]porphyrin (MnTM,MOE-2-ImP5+) and Mn(III) 5,10,15,20-tetrakis[N,N′-di(2-methoxyethyl)imidazolium-2-yl]porphyrin (MnTDMOE-2-ImP5+). Their catalytic rate constants for O2˙ dismutation( disproportionation) and the related metal-centered redox potentials vs. NHE are: log kcat = 8.04 (E1/2 = +251 mV) for MnTMOE-2-PyP5+, log kcat = 7.98 (E1/2 = +356 mV) for MnTM,MOE-2-ImP5+ and log kcat = 7.59 (E1/2 = +365 mV) for MnTDMOE-2-ImP5+. The new porphyrins were compared to the previously described SOD mimics Mn(III) 5,10,15,20-tetrakis(N-ethylpyridinium-2-yl)porphyrin (MnTE-2-PyP5+), Mn(III) 5,10,15,20-tetrakis(N-n-butylpyridinium-2-yl)porphyrin (MnTnBu-2-PyP5+) and Mn(III) 5,10,15,20-tetrakis(N,N′-diethylimidazolium-2-yl)porphyrin (MnTDE-2-ImP5+). MnTMOE-2-PyP5+ has side chains of the same length and the same E1/2, as MnTnBu-2-PyP5+ (kcat = 7.25, E1/2 = + 254 mV), yet it is 6-fold more potent a catalyst of O2˙ dismutation, presumably due to the presence of the ether oxygen. The log kcatvs. E1/2 relationship for all Mn porphyrin-based SOD mimics thus far studied is discussed. None of the new compounds were toxic to Escherichia coli in the concentration range studied (up to 30 μM), and protected SOD-deficient E. coli in a concentration-dependent manner. At 3 μM levels, the MnTDMOE-2-ImP5+, bearing an oxygen atom within each of the eight side chains, was the most effective and offered much higher protection than MnTE-2-PyP5+, while MnTDE-2-ImP5+ was of very low efficacy.

Graphical abstract: New class of potent catalysts of O2˙− dismutation. Mn(iii) ortho-methoxyethylpyridyl- and di-ortho-methoxyethylimidazolylporphyrins

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Publication details

The article was received on 19 Jan 2004, accepted on 02 Apr 2004 and first published on 05 May 2004


Article type: Paper
DOI: 10.1039/B400818A
Dalton Trans., 2004, 1696-1702

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    New class of potent catalysts of O2˙ dismutation. Mn(III) ortho-methoxyethylpyridyl- and di-ortho-methoxyethylimidazolylporphyrins

    I. Batinić-Haberle, I. Spasojević, R. D. Stevens, P. Hambright, P. Neta, A. Okado-Matsumoto and I. Fridovich, Dalton Trans., 2004, 1696
    DOI: 10.1039/B400818A

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