Catalase vs peroxidase activity of a manganese(II) compound: identification of a Mn(III)-(mu-O)(2)-Mn(IV) reaction intermediate by electrospray ionization mass spectrometry and electron paramagnetic resonance spectroscopy.
Herein, we report reactivity studies of the mononuclear water-soluble complex [Mn(II)(HPClNOL)(eta(1)-NO(3))(eta(2)-NO(3))] 1, where HPClNOL = 1-(bis-pyridin-2-ylmethyl-amino)-3-chloropropan-2-ol, toward peroxides (H(2)O(2) and tert-butylhydroperoxide). Both the catalase (in aqueous solution) and peroxidase (in CH(3)CN) activities of 1 were evaluated using a range of techniques including electronic absorption spectroscopy, volumetry (kinetic studies), pH monitoring during H(2)O(2) 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 H(2)O(2). For the reaction of 1 with H(2)O(2), EPR and ESI(+)-MS have led to the identification of the intermediate [Mn(III)Mn(IV)(mu-O)(2)(PClNOL)(2)](+). The peroxidase activity of 1 was also evaluated by monitoring cyclohexane oxidation, using H(2)O(2) or tert-butylhydroperoxide as the terminal oxidants. Low yields (<7%) were obtained for H(2)O(2), 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 O(2) production, the pH variation, and the formation of a Mn(III)-(mu-O)(2)-Mn(IV) intermediate is proposed.
Lessa
Josane A
JA
Laboratorio de Ciencias Quimicas, Universidade Estadual do Norte Fluminense, 28013-602, Campos dos Goytacazes, RJ, Brazil.
Horn
Adolfo
A
Bull
Erika S
ES
Rocha
Michelle R
MR
Benassi
Mario
M
Catharino
Rodrigo R
RR
Eberlin
Marcos N
MN
Casellato
Annelise
A
Noble
Christoper J
CJ
Hanson
Graeme R
GR
Schenk
Gerhard
G
Silva
Giselle C
GC
Antunes
O A C
OA
Fernandes
Christiane
C
D040761:Biomimetic Materials / Q000737:chemistry*; D002374:Catalase; D002384:Catalysis; D004578:Electron Spin Resonance Spectroscopy; D008345:Manganese / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D009195:Peroxidase; D021241:Spectrometry, Mass, Electrospray Ionization
D009942:Organometallic Compounds; D008345:Manganese; D002374:Catalase; D009195:Peroxidase; D010100:Oxygen