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Novel mononuclear copper NOx complexes that model interactions of nitrogen oxides with single copper sites in proteins.
COPPER
CO38
199
NOVEL MONONUCLEAR COPPER NO, COMPLEXES THAT MODEL INTERACTIONS OF NITROGEN OXIDES WITH SINGLE COPPER SITES IN PROTEINS.
Susan M. Carrier, Christy E. Ruggiero, and William
Department of Chemistry, University of Minnesota, S.E., Minneapolis, MN 55455, USA
207 Pleasant
St.
Interactions of NO, species with the active sites of copper proteins are of central importance in numerous biological processes, the most significant being global nitrogen cycle transformations. For example, copper-containing enzymes are important in denitrification, a complex set of reactions carried out by several classes of microorganisms that can utilize oxidized nitrogen compounds as terminal electron acceptors in respiration. Copper centers in these enzymes are involved in several steps in the conversion of nitrate (NOg-) and nitrite (N02-) to gaseous products (NO, N20 and/or N2).[1,21 The plausibility of various postulated pathways for this reductive chemistry has not been adequately determined, and a general lack of knowledge of the fundamental chemistry of copper-NxOy species 131 has hindered attempts to better understand how nitrogen oxides bind to and are activated by biological copper centers. As part of our initial efforts to provide such a chemical foundation, several new mononuclear active site model compounds have been prepared by using sterically hindered tris(pyrazolyl)hydroborate (L) and tris(thioethyl)amine (L’) supporting ligands. We have isolated and characterized (X-ray crystallography, IR, UV-vis, EPR) a copper nitrite complex, LCu1’(N02), that models the putative enzyme-substrate adduct of copper nitrite reductase. Preliminary reactivity studies have revealed that the bidentate nitrite ligand is labile, being readily dis laced PI by Cl- and MegSiOTf to yield LC#Cl and the previously unknown LCu OTf, respectively. Formulation of the latter as a rare example of a tetrahedral cupric species was confirmed by X-ray crystallogra hy. Cyclic voltammetry revealed P that reversible reduction of LCu’IOTf to LCu (CH3CN) occurs at high potential (El /2 = +1.17 V vs. NHE, 9:l CH2C12/CH3CN), apparently reflecting thermodynamic instability of the tetrahedral cupric site. A discrete mononuclear copper-nitrosyl complex relevant to postulated NO adducts of copper proteins h;s also been prepared from LCu’fCH3CN) and NO; tentative identification of a Cu NO- moiety in the microcrystalline red adduct currently rests on IR @NO 1711 cm-‘) and EPR evidence. Details of this chemistry, as well as the results of reactions of nitrogen oxides with structurally characterized [L’CuI](ClO& will be presented.
1. 2 3.
Hulse, C.L.; Averill, B.A.; Tiedje, J.M. J. Am. Chem. Sot. 111, 2322-2323
(1989) and references therein. Adman, E.T. personal communication. Paul, PP.; Tyeklar, Z.; Farooq, A.; Karlin, K.D.; Liu, S.; Zubieta, J. J. Am. Gem. Sm. 112, 2430-2432 (1990) and references therein.
CO38
199
NOVEL MONONUCLEAR COPPER NO, COMPLEXES THAT MODEL INTERACTIONS OF NITROGEN OXIDES WITH SINGLE COPPER SITES IN PROTEINS.
Susan M. Carrier, Christy E. Ruggiero, and William
Department of Chemistry, University of Minnesota, S.E., Minneapolis, MN 55455, USA
207 Pleasant
St.
Interactions of NO, species with the active sites of copper proteins are of central importance in numerous biological processes, the most significant being global nitrogen cycle transformations. For example, copper-containing enzymes are important in denitrification, a complex set of reactions carried out by several classes of microorganisms that can utilize oxidized nitrogen compounds as terminal electron acceptors in respiration. Copper centers in these enzymes are involved in several steps in the conversion of nitrate (NOg-) and nitrite (N02-) to gaseous products (NO, N20 and/or N2).[1,21 The plausibility of various postulated pathways for this reductive chemistry has not been adequately determined, and a general lack of knowledge of the fundamental chemistry of copper-NxOy species 131 has hindered attempts to better understand how nitrogen oxides bind to and are activated by biological copper centers. As part of our initial efforts to provide such a chemical foundation, several new mononuclear active site model compounds have been prepared by using sterically hindered tris(pyrazolyl)hydroborate (L) and tris(thioethyl)amine (L’) supporting ligands. We have isolated and characterized (X-ray crystallography, IR, UV-vis, EPR) a copper nitrite complex, LCu1’(N02), that models the putative enzyme-substrate adduct of copper nitrite reductase. Preliminary reactivity studies have revealed that the bidentate nitrite ligand is labile, being readily dis laced PI by Cl- and MegSiOTf to yield LC#Cl and the previously unknown LCu OTf, respectively. Formulation of the latter as a rare example of a tetrahedral cupric species was confirmed by X-ray crystallogra hy. Cyclic voltammetry revealed P that reversible reduction of LCu’IOTf to LCu (CH3CN) occurs at high potential (El /2 = +1.17 V vs. NHE, 9:l CH2C12/CH3CN), apparently reflecting thermodynamic instability of the tetrahedral cupric site. A discrete mononuclear copper-nitrosyl complex relevant to postulated NO adducts of copper proteins h;s also been prepared from LCu’fCH3CN) and NO; tentative identification of a Cu NO- moiety in the microcrystalline red adduct currently rests on IR @NO 1711 cm-‘) and EPR evidence. Details of this chemistry, as well as the results of reactions of nitrogen oxides with structurally characterized [L’CuI](ClO& will be presented.
1. 2 3.
Hulse, C.L.; Averill, B.A.; Tiedje, J.M. J. Am. Chem. Sot. 111, 2322-2323
(1989) and references therein. Adman, E.T. personal communication. Paul, PP.; Tyeklar, Z.; Farooq, A.; Karlin, K.D.; Liu, S.; Zubieta, J. J. Am. Gem. Sm. 112, 2430-2432 (1990) and references therein.