Dioxygen reactivity of copper and heme-copper complexes possessing an imidazole-phenol cross-link

Eunsuk Kim, Kaliappan Kamaraj, Benedikt Galliker, Nick D. Rubie, Pierre Moënne-Loccoz, Susan Kaderli, Andreas D. Zuberbühler, Kenneth D. Karlin

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Abstract

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-phenol moieties 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 to form the 2:1 Cu:O2 adduct, peroxo complex [{CuII(L N4OH)}2(O22-)]2+ (1b). Complex 1b is also short-lived, and a dimer Cu(II)-phenolate complex [Cu II(LN4O-)]22+ (1c) eventually forms as a final product in the later stage of the oxygenation reaction. Dioxygen reactivities of 1 and its anisole analogue [Cu I(LN4OMe)]+ (2) in the presence of a heme complex (F8)FeII (3) (F8 = tetrakis(2,6,- difluorotetraphenyl)-porphyrinate) are also described. Spectroscopic investigations including UV-vis, 1H and 2H NMR, EPR, and resonance Raman spectroscopies along with spectrophotometric titration reveal that low-temperature oxygenation of 1/3 leads to formation of a heme-peroxo-copper species [(F8)FeIII-(O2 2-)-CuII(LN4OH)]+ (4), ν(O-O) = 813 cm-1. Complex 4 is an S = 2 spin system with strong antiferromagnetic coupling between high-spin iron(III) and copper(II) through a bridging peroxide ligand. A very similar complex [(F 8)FeIII-(O22-)-Cu II(LN4OMe)]+ (5) (ν(O-O) = 815 cm-1) can be generated by utilizing the anisole compound 2, which indicates that the cross-linked phenol moiety in 4 does not interact with the bridging peroxo group between heme and copper. This investigation thus reveals that a stable heme-peroxo-copper species can 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 in CcO model compounds.

Original languageEnglish (US)
Pages (from-to)1238-1247
Number of pages10
JournalInorganic Chemistry
Volume44
Issue number5
DOIs
StatePublished - Mar 7 2005

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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    Kim, E., Kamaraj, K., Galliker, B., Rubie, N. D., Moënne-Loccoz, P., Kaderli, S., Zuberbühler, A. D., & Karlin, K. D. (2005). Dioxygen reactivity of copper and heme-copper complexes possessing an imidazole-phenol cross-link. Inorganic Chemistry, 44(5), 1238-1247. https://doi.org/10.1021/ic048907b