Hydrogen atom abstraction by synthetic heme ferric superoxide and hydroperoxide species

Abstract

To date, artificial dioxygen adducts of heme have not been demonstrated to be able to oxidize organic substrates in sharp contrast to their non-heme analogues and naturally occurring enzymes like heme dioxygenases.

Ferric Heme Superoxide Reductive Transformations to Ferric Heme (Hydro)Peroxide Species: Spectroscopic Characterization and Thermodynamic Implications for H‐Atom Transfer (HAT)

“…EPR spectra of P Im ‐ HP confirm an end‐on low‐spin ferric heme hydroperoxide structure ( g= 2.25, 2.14, and 1.95) as shown in Figure 3 B. These values correspond closely to those already known for synthetically derived end‐on low‐spin hydroperoxide complexes [3, 6f,g,i,j, 7a,b] as well as for ferric heme hydroperoxides generated within hemoglobin and myoglobin [10a,b] . A high yield of H 2 O 2 (90.1 %) is also obtained when P Im ‐ HP is acidified using HOTf (see Figure S1).…”

“…Synthetic bioinorganic groups have been interested in the characterization of model compounds for the superoxide, peroxide, or hydroperoxide intermediates, as relevant to O 2 or H 2 O 2 activating heme enzymes. There are many known ferric heme superoxide [6] and hydroperoxide synthetic compounds [3, 6g,i,j, 7] . Valentine and co‐workers [8] originally synthesized and characterized a series of ferric heme peroxides possessing a side‐on bound O 2 2− ligand (η 2 , with both peroxide O‐atoms equivalently bound to Fe III ).…”

Quinol-containing ligands enable high superoxide dismutase activity by modulating coordination number, charge, oxidation states and stability of manganese complexes throughout redox cycling

“…Similar reactivity was recently reported for an iron porphyrin complex with a pendant quinol group; in this work, an Fe( iii )-superoxo reacts to form a ferryl species (Fe( iv )-oxo) with an oxidized para -quinone moiety. 76 The reaction goes through an Fe( iii )-semiquinone (quinoxyl radical) species as an intermediate. 76 This path (upper orange arrow in Scheme 4 ) might contribute to our detection of a quinoxyl-radical by the UV/vis spectroscopy ( vide infra ) during the catalytic degradation of O 2 ˙ − by 3 .…”

“… 76 The reaction goes through an Fe( iii )-semiquinone (quinoxyl radical) species as an intermediate. 76 This path (upper orange arrow in Scheme 4 ) might contribute to our detection of a quinoxyl-radical by the UV/vis spectroscopy ( vide infra ) during the catalytic degradation of O 2 ˙ − by 3 .…”

Proton-coupled electron transfer reactivities of electronically divergent heme superoxide intermediates: a kinetic, thermodynamic, and theoretical study

“…, electrons(e − )), and/or H˙ donors are only a handful. 23 Intriguingly, Naruta, 24 Dey, 25 and their coworkers have presented unique examples of heme superoxide intermediates that react with intramolecular H + or H˙ donors, ultimately giving rise to the corresponding heme hydroperoxo (Fe III –OOH) adduct. To the best of our knowledge, recent work by Karlin and coworkers is the only instance where proton-coupled electron transfer reactivities of heme superoxide intermediates have been shown, where H˙ abstraction from an exogenous, weak O–H bond substrate generates the corresponding heme hydroperoxo species in a single kinetic step.…”