Formation and Characterization of a High-Spin Heme-Copper Dioxygen (Peroxo) Complex

Abstract

In this report, we describe new dioxygen reactivity of reduced heme-copper complexes employing the tethered tetraarylporphyrinate ligands 5 L and 6 L. 1 Notably, peroxo complex [( 6 L)Fe III -(O 2 2-)-Cu II ](BAr F ) (2a), 5 formed from the reaction of [( 6 L)Fe II -Cu I ](BAr F ) (1a) with O 2 (Scheme 1), has physical properties and reactivity which contrast greatly with those of the few other hemecopper peroxo complexes described in the literature. [6][7][8] These studies are part of our general program aimed at elucidating fundamental aspects of O 2 -interactions with heme-copper centers, 4,8-12 how copper influences (P)Fe II /O 2 chemistry, and how hemes influence copper(I)-dioxygen reactivity patterns. Insights obtained may pertain to heme-copper oxidase (e.g., cytochrome c oxidase) 13,14 active-site O 2 -binding and reduction, or other oxidative processes involving dioxygen.Reduced Fe II ‚‚‚Cu I heme-copper compounds [( 6 L)Fe II Cu I ]-(BAr F ) (1a) and [( 5 L)Fe II Cu I ](BAr F ) (1b) (Scheme 1) were

Homogeneous catalytic O 2 reduction to water by a cytochrome c oxidase model with trapping of intermediates and mechanistic insights

“…Preparation and handling of air-sensitive compounds were performed under MBraun UNilab inert atmosphere (<1 ppm O 2 , <1 ppm H 2 O) glove box filled with nitrogen. The complexes ½ 6 LFe II Cu I þ and 6 LFe II were prepared according to the literature procedure (14,15).…”

“…To help to examine the role of the Cu in this system, a Cu-free version ( 6 LFe) (15) was also subjected to the same catalytic reaction conditions as 6 LFeCu. Even in the absence of Cu the reaction proceeds through the 4e − process (Fig.…”

Superoxo, μ-peroxo, and μ-oxo complexes from heme/O 2 and heme-Cu/O 2 reactivity: Copper ligand influences in cytochrome c oxidase models

“…To unambiguously identify pyrrole resonances, which aid iron oxidation and spin-state assignments (27), complementary 2 H NMR spectroscopic investi-**A minor 2͞O2 reaction is observed in CH2Cl2͞6% EtCN, but it does not affect the 1͞2͞O2 kinetics described in this report. ) S ϭ 2 systems, as previously described (14,15,17,28).…”

The role of copper and protons in heme-copper oxidases: Kinetic study of an engineered heme-copper center in myoglobin

“…Interestingly, peroxy-porphyrin was also observed in synthetic models of HCO (42,43). However, no heme degradation was observed in the model systems.…”

“…The hemecopper center is unique in that it contains not only a heme with a proximal histidine ligand, commonly found in other heme proteins, such as Mb and HO, but also a copper center (called Cu B ) that is coordinated to three histidines and is within Ϸ5 Å of the heme iron center. Understanding the structure and function of this heme-copper center has been the focus of intense biochemical (25)(26)(27)(28), spectroscopic (29)(30)(31)(32)(33)(34)(35)(36)), x-ray crystallographic (20)(21)(22)(23)(24), and biomimetic modeling studies (37)(38)(39)(40)(41)(42)(43)(44)(45).…”