Dioxygen Reactivity of Copper and Heme-Copper Complexes Possessing an Imidazole-Phenol Cross-Link
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- 作者：Eunsuk Kim ; Kaliappan Kamaraj ; Benedikt Galliker ; Nick D. Rubie ; Pierre Moë ; nne-Loccoz ; Susan Kaderli ; Andreas D. Zuberbü ; hler ; and Kenneth D. Karlin
- 刊名：Inorganic Chemistry
- 出版年：2005
- 出版时间：March 7, 2005
- 年：2005
- 卷：44
- 期：5
- 页码：1238 - 1247
- 全文大小：264K
- 年卷期：v.44,no.5(March 7, 2005)
- ISSN：1520-510X
文摘
Recent spectroscopic, kinetics, and structural studies on cytochrome c oxidases (CcOs) suggest that the histidine-tyrosine cross-link at the heme a3-CuB binuclear active site plays a key role in the reductive O2-cleavage process.In this report, we describe dioxygen reactivity of copper and heme/Cu assemblies in which the imidazole-phenolmoieties are employed as a part of copper ligand LN4OH (2-{4-[2-(bis-pyridin-2-ylmethyl-amino)-ethyl]-imidazol-1-yl}-4,6-di -tert-butyl-phenol). Stopped-flow kinetic studies reveal that low-temperature oxygenation of [CuI(LN4OH)]+(1) leads to rapid formation of a copper-superoxo species [CuII(LN4OH)(O2-)]+ (1a), which further reacts with 1 toform the 2:1 Cu:O2 adduct, peroxo complex [{CuII(LN4OH)}2(O22-)]2+ (1b). Complex 1b is also short-lived, and adimer Cu(II)-phenolate complex [CuII(LN4O-)]22+ (1c) eventually forms as a final product in the later stage of theoxygenation reaction. Dioxygen reactivities of 1 and its anisole analogue [CuI(LN4OMe)]+ (2) in the presence of aheme complex (F8)FeII (3) (F8 = tetrakis(2,6,-difluorotetraphenyl)-porphyrinate) are also described. Spectroscopicinvestigations including UV-vis, 1H and 2H NMR, EPR, and resonance Raman spectroscopies along withspectrophotometric titration reveal that low-temperature oxygenation of 1/3 leads to formation of a heme-peroxo-copper species [(F8)FeIII-(O22-)-CuII(LN4OH)]+ (4), 
(O-O) = 813 cm-1. Complex 4 is an S = 2 spin system withstrong antiferromagnetic coupling between high-spin iron(III) and copper(II) through a bridging peroxide ligand. Avery similar complex [(F8)FeIII-(O22-)-CuII(LN4OMe)]+ (5) ((O-O) = 815 cm-1) can be generated by utilizing theanisole compound 2, which indicates that the cross-linked phenol moiety in 4 does not interact with the bridgingperoxo group between heme and copper. This investigation thus reveals that a stable heme-peroxo-copper speciescan be generated even in the presence of an imidazole-phenol group (i.e., possible electron/proton donor source)in close proximity. Future studies are needed to probe key factors that can trigger the reductive O-O cleavage inCcO model compounds.
(O-O) = 813 cm-1. Complex 4 is an S = 2 spin system withstrong antiferromagnetic coupling between high-spin iron(III) and copper(II) through a bridging peroxide ligand. Avery similar complex [(F8)FeIII-(O22-)-CuII(LN4OMe)]+ (5) ((O-O) = 815 cm-1) can be generated by utilizing theanisole compound 2, which indicates that the cross-linked phenol moiety in 4 does not interact with the bridgingperoxo group between heme and copper. This investigation thus reveals that a stable heme-peroxo-copper speciescan be generated even in the presence of an imidazole-phenol group (i.e., possible electron/proton donor source)in close proximity. Future studies are needed to probe key factors that can trigger the reductive O-O cleavage inCcO model compounds.