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|Type:||Artigo de periódico|
|Title:||Catalase Vs Peroxidase Activity Of A Manganese(ll) Compound: Identification Of A Mn(iii)-(μ-o)2-mn(iv) Reaction Intermediate By Electrospray Ionization Mass Spectrometry And Electron Paramagnetic Resonance Spectroscopy|
Horn Jr. A.
|Abstract:||Herein, we report reactivity studies of the mononuclear water-soluble complex [Mn(II)(HPCINOL)(η1-NO3)(η2- NO3)] 1, where HPCINOL = 1-(bis-pyridin-2-ylmethyl-amino)-3- chloropropan-2-ol, toward peroxides (H2O2 and tenbutylhydroperoxide). 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 H 2O2 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)(w-O)2(PCINOL) 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. © 2009 American Chemical Society.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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