Kinetics and intermediates in the autoxidation of (cyclidene)iron(II) dioxygen carriers in a variety of solvent systems

Sauer-Masarwa, Alexandra; Dickerson, Lyndel D.; Herron, Norman; Busch, Daryle H.

doi:10.1016/0010-8545(93)80026-2

Cited by 13 publications

(8 citation statements)

References 37 publications

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“…For instance, Busch observed complicated parabolic dependence of the rate constant with temperature for O 2 with myoglobin, hemoglobin, and cyclidene complexes. 40 Busch's interpretation of the temperature dependence relied on competing inner and outer sphere O 2 reduction pathways in addition to competitive ligand binding – all of which are possible in the system studied here.…”

Section: Resultsmentioning

confidence: 95%

Deciphering the mechanism of O₂ reduction with electronically tunable non-heme iron enzyme model complexes

et al. 2018

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Section: Resultsmentioning

confidence: 95%

Deciphering the mechanism of O₂ reduction with electronically tunable non-heme iron enzyme model complexes

et al. 2018

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“…This point is important, for it implies inner-sphere coordination prior to, or concomitant with, the rate-determining step in the oxidation to form peroxide adducts. For a series of capped cyclidene iron(II) complexes, complicated kinetic changes accompanied the O 2 binding process when the cavity was constricted to a size which prevented O 2 access. , It was proposed that, under such conditions, autoxidation proceeded by an outer-sphere electron transfer mechanism. Compound 1a is unreactive with dioxygen over a period of hours below −77 °C in propionitrile.…”

Section: Discussionmentioning

confidence: 99%

Mechanistic Studies of the Formation and Decay of Diiron(III) Peroxo Complexes in the Reaction of Diiron(II) Precursors with Dioxygen

et al. 1996

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Mechanistic studies of the reactions of three analogous alkoxo-bridged diiron(II) complexes with O(2) have been carried out. The compounds, which differ primarily in the steric accessibility of dioxygen to the diiron(II) center, form metastable &mgr;-peroxo intermediates when studied at low temperature. At ambient temperatures, these intermediates decay to form (&mgr;-oxo)polyiron(III) products. The effect of ligand steric constraints on the O(2) reactivity was investigated. When access to the diiron center was unimpeded, the reaction was first-order with respect to both [Fe(II)(2)] and [O(2)] and the activation parameters for O(2) addition were similar to those for O(2) reacting with the dioxygen transport protein hemerythrin. When the binding site was occluded, however, reduced order with respect to [O(2)] was observed and a two-step mechanism was required to explain the kinetic results. Decay of all three peroxide intermediates involves a bimolecular event, implying the formation of tetranuclear species in the transition state.

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“…In contrast, the EPR spectrum generated by cryoreduction of oxy-2 dissolved in the protic solvent, MeOH/1-MeIm, Figure 5, is that of the [FeO 2 ] 7 peroxo/hydroperoxo-ferri-2 center prepared directly by Busch and co-workers. 34,[39][40][41] By analogy to the cryoreduced centers typically generated from oxy-hemes, the low-spin ferric center generated by cryoreduction of oxy-2 in MeOH could be either the peroxoferric or the hydroperoxo-ferric form. Either assignment would require the presence of ENDOR signals from the in-plane 14 N ligands and from an exchangeable proton interacting with the O-O ligand.…”

Section: Methodsmentioning

confidence: 99%

A Superoxo-Ferrous State in a Reduced Oxy-Ferrous Hemoprotein and Model Compounds

et al. 2003

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Cryoreduction of the [FeO2]6 (n = 6 is the number of electrons in 3d orbitals on Fe and pi* orbitals on O2) dioxygen-bound ferroheme through irradiation at 77 K generates an [FeO2]7 reduced oxy-heme. Numerous investigations have examined [FeO2]7 centers that have been characterized as peroxo-ferric centers, denoted [FeO2]per7, in which a ferriheme binds a dianionic peroxo-ligand. The generation of such an intermediate can be understood heuristically if the [FeO2]6 parent is viewed as a superoxo-ferric center and the injected electron localizes on the O-O moiety. We here report EPR/ENDOR experiments which show quite different properties for the [FeO2]7 centers produced by cryoreduction of monomeric oxy-hemoglobin (oxy-GMH3) from Glycera dibranchiata, which is unlike mammalian "globins" in having a leucine in place of the distal histidine; of frozen aprotic solutions of oxy-ferrous octaethyl porphyrin; and of the oxy-ferrous complex of the heme model, cyclidene. These [FeO2]7 centers are characterized as "superoxo-ferrous" centers ([FeO2]sup7), with nearly unit spin density localized on a superoxo moiety which is end-on coordinated to a low-spin ferrous ion. This assignment is based on their g tensors and 17O hyperfine couplings, which are characteristic of the superoxide ion coordinated to a diamagnetic metal ion, and on the absence of detectable ENDOR signals either from the in-plane 14N ligands or from an exchangeable H-bond proton. Such a center would arise if the electron that adds to the [FeO2]6 superoxo-ferric parent localizes on the Fe ion, to make a superoxo-ferrous moiety. Upon annealing to T > 150 K, the [FeO2]sup7 species converts to peroxo/hydroperoxo-ferric ([FeO2H]7) intermediates. These experiments suggest that the primary reduction product is [FeO2]sup7 and that the internal redox transition to [FeO2]per7/[FeO2H]7 states is driven at least in part by H-bonding/proton donation by the environment.

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Kinetics and intermediates in the autoxidation of (cyclidene)iron(II) dioxygen carriers in a variety of solvent systems

Cited by 13 publications

References 37 publications

Deciphering the mechanism of O₂ reduction with electronically tunable non-heme iron enzyme model complexes

Deciphering the mechanism of O₂ reduction with electronically tunable non-heme iron enzyme model complexes

Mechanistic Studies of the Formation and Decay of Diiron(III) Peroxo Complexes in the Reaction of Diiron(II) Precursors with Dioxygen

A Superoxo-Ferrous State in a Reduced Oxy-Ferrous Hemoprotein and Model Compounds

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Kinetics and intermediates in the autoxidation of (cyclidene)iron(II) dioxygen carriers in a variety of solvent systems

Cited by 13 publications

References 37 publications

Deciphering the mechanism of O2 reduction with electronically tunable non-heme iron enzyme model complexes

Deciphering the mechanism of O2 reduction with electronically tunable non-heme iron enzyme model complexes

Mechanistic Studies of the Formation and Decay of Diiron(III) Peroxo Complexes in the Reaction of Diiron(II) Precursors with Dioxygen

A Superoxo-Ferrous State in a Reduced Oxy-Ferrous Hemoprotein and Model Compounds

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Deciphering the mechanism of O₂ reduction with electronically tunable non-heme iron enzyme model complexes

Deciphering the mechanism of O₂ reduction with electronically tunable non-heme iron enzyme model complexes