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, Christopher J. and Hanson, Graeme R. and Schenk, Gerhard and Silva, Giselle C. and Antunes, O. A. C. and Fernandes, Christiane (2009) 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 Resonance Spectroscopy. Inorganic Chemistry, 48 (10). pp. 4569-4579. ISSN 0020-1669

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Abstract

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.

Item Type:	Article
Additional Information:	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
Keywords:	Catalase; Peroxidase; Activity; Manganese Compound; Reaction; Electrospray Ionization; Mass Spectrometry; Electron Paramagnetic Resonance Spectroscopy; volumetry; kinetic studies; electron paramagnetic resonance (EPR);
Academic Unit:	Faculty of Science and Engineering > Chemistry
Item ID:	3697
Depositing User:	Gary Schenk
Date Deposited:	29 May 2012 15:33
Journal or Publication Title:	Inorganic Chemistry
Publisher:	American Chemical Society
Refereed:	Yes
URI:
Use Licence:	This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available here

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