- Email: [email protected]
Dioxygen activation by copper complexes supported by 2-(2-pyridyl)ethylamine ligands. Mechanistic insights into copper monooxygenases and copper oxidases
20
Journal of Inorganic Biochemistry 96 (2003)
Dioxygen Activation by Copper Complexes Supported by 2-(2-PyridyQethylamine Ligands. Mechanistic Insights into Copper Monooxygenases and Copper Oxidases Shinobu Itoh, Osaka City University, Japan Reactions of copper(I) complexes with molecular oxygen have been examined using a series of N-alkyl-bis[2-(2pyridyl)ethyl]amine tridentate ligands (KPy2R)and N,N-dialkyl-2-(2-pyridyl)ethylamine didentate ligands (XPylR1,RZ) at low temperature (Chart 1). The tridentate ligands predominantly provide side-on type peroxo dicopper(I1) complex (A), while the didentate ligands enhance O-O bond homolysis of the peroxo speciesto produce bis(p-oxo)dicopper(III) complex (B) (Figure 1). With the u-peroxo dicopper(I1) complex (A) supported by the tridentate ligand, efficient oxygenation of phenolates to the corresponding catechols has been accomplished to provide a good model reaction oftyrosinase. The bis(p-oxo)dicopper(III) complex (B), on the other hand, undergo aliphatic ligand hydroxylation as well as oxygen atom transfer to sulfides to give the corresponding sulfoxides. In the reaction of bis(y-oxo)dicopper(III) complex (B) with IO-methyl-9,10-dihydroacridine (AcrH,) and 1,4-cyclohexadiene (CHD), a new active oxygen intermediate such as a (p-0x0)@-oxyl radical)dicopper(IJI) or a tetranuclear copper-oxygen complex has been suggested to be involved as the real active oxygen species for the C-H bond activation of the external substrates.A mixed valence -, FigurPr R’ I bis(y,-oxo) trinuclear copper(II,II,III) complex (C) has also Nv been assessedusing the didentate ligand with the smallest N, +/-+p “‘a+ nJJ, I &Q alkyl substituent (methyl). Mechanistic details of the above R’ tiR’ .wpylR1,R2 Ml (61 PI %yzR reactions as well as ligand effects on the copper(I)-dioxygen reactivity are discussed systematically.
Understanding the Mechanism of Superoxide Reduction by the Non-Heme Iron Enzyme Superoxide Reductase (SOR) using a Synthetic Analogue Approach Julie A Kovacs, University of Washington, United States Sarah Fitch, Universib of Washington, United States Roslyn Theisen, University of Washington, United States Jason Shearer, University of Washington, United States Terry Kitagawa, Universiv of Washington, United States Robert Scarrow, Haverford College, United States Superoxide reductases (SORs) belong to a new classof metalloenzymes that degrade superoxide by reducing it to hydrogen peroxide. These enzymes contain a cysteinate-ligated non-heme iron site that cycles between the Fe” and Fe”’ states during catalysis. A key step in the reduction of superoxide has been suggested to involve superoxide binding to Fe”, followed by inner-sphere electron transfer to afford an Ferrr-OO(H) intermediate. Oxygen does not appear to react readily with the Fe11 form of SOR. Cyanide inhibits superoxide reduction. Synthetic models prepared in our group have been shown to reduce superoxide at rates similar to the enzyme, and form an S= l/2 Fe”*-OOH intermediate that displays a vomOstretch at 784 cm-’ in the vibrational stretch shifts to 753 cm-’ in the I*O; labeled compound. Upon binding .60 spectrum. This vgmO r! cyanide, the redox potential of our Fe”’ model shifts significantly, suggesting that cyanide eM inhibits SOR by preventing the ferrous form from being regenerated, and thus preventing the enzyme from turning over. Although oxygen reacts with our SOR model to afford a WJO 790780no 7601%740 730 a p-0x0 dimer, slight modification of our ligand results in a complex that is unreactive am-’ towards oxygen.
Journal of Inorganic Biochemistry 96 (2003)
Dioxygen Activation by Copper Complexes Supported by 2-(2-PyridyQethylamine Ligands. Mechanistic Insights into Copper Monooxygenases and Copper Oxidases Shinobu Itoh, Osaka City University, Japan Reactions of copper(I) complexes with molecular oxygen have been examined using a series of N-alkyl-bis[2-(2pyridyl)ethyl]amine tridentate ligands (KPy2R)and N,N-dialkyl-2-(2-pyridyl)ethylamine didentate ligands (XPylR1,RZ) at low temperature (Chart 1). The tridentate ligands predominantly provide side-on type peroxo dicopper(I1) complex (A), while the didentate ligands enhance O-O bond homolysis of the peroxo speciesto produce bis(p-oxo)dicopper(III) complex (B) (Figure 1). With the u-peroxo dicopper(I1) complex (A) supported by the tridentate ligand, efficient oxygenation of phenolates to the corresponding catechols has been accomplished to provide a good model reaction oftyrosinase. The bis(p-oxo)dicopper(III) complex (B), on the other hand, undergo aliphatic ligand hydroxylation as well as oxygen atom transfer to sulfides to give the corresponding sulfoxides. In the reaction of bis(y-oxo)dicopper(III) complex (B) with IO-methyl-9,10-dihydroacridine (AcrH,) and 1,4-cyclohexadiene (CHD), a new active oxygen intermediate such as a (p-0x0)@-oxyl radical)dicopper(IJI) or a tetranuclear copper-oxygen complex has been suggested to be involved as the real active oxygen species for the C-H bond activation of the external substrates.A mixed valence -, FigurPr R’ I bis(y,-oxo) trinuclear copper(II,II,III) complex (C) has also Nv been assessedusing the didentate ligand with the smallest N, +/-+p “‘a+ nJJ, I &Q alkyl substituent (methyl). Mechanistic details of the above R’ tiR’ .wpylR1,R2 Ml (61 PI %yzR reactions as well as ligand effects on the copper(I)-dioxygen reactivity are discussed systematically.
Understanding the Mechanism of Superoxide Reduction by the Non-Heme Iron Enzyme Superoxide Reductase (SOR) using a Synthetic Analogue Approach Julie A Kovacs, University of Washington, United States Sarah Fitch, Universib of Washington, United States Roslyn Theisen, University of Washington, United States Jason Shearer, University of Washington, United States Terry Kitagawa, Universiv of Washington, United States Robert Scarrow, Haverford College, United States Superoxide reductases (SORs) belong to a new classof metalloenzymes that degrade superoxide by reducing it to hydrogen peroxide. These enzymes contain a cysteinate-ligated non-heme iron site that cycles between the Fe” and Fe”’ states during catalysis. A key step in the reduction of superoxide has been suggested to involve superoxide binding to Fe”, followed by inner-sphere electron transfer to afford an Ferrr-OO(H) intermediate. Oxygen does not appear to react readily with the Fe11 form of SOR. Cyanide inhibits superoxide reduction. Synthetic models prepared in our group have been shown to reduce superoxide at rates similar to the enzyme, and form an S= l/2 Fe”*-OOH intermediate that displays a vomOstretch at 784 cm-’ in the vibrational stretch shifts to 753 cm-’ in the I*O; labeled compound. Upon binding .60 spectrum. This vgmO r! cyanide, the redox potential of our Fe”’ model shifts significantly, suggesting that cyanide eM inhibits SOR by preventing the ferrous form from being regenerated, and thus preventing the enzyme from turning over. Although oxygen reacts with our SOR model to afford a WJO 790780no 7601%740 730 a p-0x0 dimer, slight modification of our ligand results in a complex that is unreactive am-’ towards oxygen.