Lessa, Josane A. and Horn Jr., Adolfo and Bull, Erika S. and Rocha, Michelle R. and Benassi, Mario and Catharino, Rodrigo R. and Eberlin, Marcos N. and Casellato, Annelise and Noble, Christoper J. and Hanson, Graeme R. and Schenk, Gerhard and Silva, Giselle C. and Antunes, O. A. C. and Fernandes, Christiane
Catalase vs Peroxidase Activity of a Manganese(II) Compound:
Identification of a Mn(III)-(μ-O)2-Mn(IV) Reaction Intermediate by
Electrospray Ionization Mass Spectrometry and Electron Paramagnetic
Inorganic Chemistry, 48 (10).
Herein, we report reactivity studies of the mononuclear water-soluble complex [Mn(II)(HPClNOL)(η1-NO3)(η2-NO3)]
1, where HPClNOL ) 1-(bis-pyridin-2-ylmethyl-amino)-3-chloropropan-2-ol, toward peroxides (H2O2 and tertbutylhydroperoxide).
Both the catalase (in aqueous solution) and peroxidase (in CH3CN) activities of 1 were evaluated
using a range of techniques including electronic absorption spectroscopy, volumetry (kinetic studies), pH monitoring
during H2O2 disproportionation, electron paramagnetic resonance (EPR), electrospray ionization mass spectrometry
in the positive ion mode [ESI(+)-MS], and gas chromatography (GC). Electrochemical studies showed that 1 can
be oxidized to Mn(III) and Mn(IV). The catalase-like activity of 1 was evaluated with and without pH control. The
results show that the pH decreases when the reaction is performed in unbuffered media. Furthermore, the activity
of 1 is greater in buffered than in unbuffered media, demonstrating that pH influences the activity of 1 toward H2O2.
For the reaction of 1 with H2O2, EPR and ESI(+)-MS have led to the identification of the intermediate [Mn(III)Mn(IV)(μ-
O)2(PClNOL)2]+. The peroxidase activity of 1 was also evaluated by monitoring cyclohexane oxidation, using H2O2
or tert-butylhydroperoxide as the terminal oxidants. Low yields (<7%) were obtained for H2O2, probably because it
competes with 1 for the catalase-like activity. In contrast, using tert-butylhydroperoxide, up to 29% of cyclohexane
conversion was obtained. A mechanistic model for the catalase activity of 1 that incorporates the observed lag
phase in O2 production, the pH variation, and the formation of a Mn(III)-(μ-O)2-Mn(IV) intermediate is proposed.
||The definitive version of this article was published in Inorganic Chemistry Vol.48 No.10(2009), pp.4569-4579 and is available at DOI: 10.1021/ic801969c . Copyright © 2009 American Chemical Society
||Catalase; Peroxidase; Activity; Manganese Compound; Reaction;
Electrospray Ionization; Mass Spectrometry; Electron Paramagnetic
Resonance Spectroscopy; volumetry; kinetic studies; electron paramagnetic resonance (EPR);
||Science & Engineering > Chemistry
||29 May 2012 15:33
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