Dioxygen activation at enzyme metal active sites often involves one-electron reduction of O2 to form a metal-superoxide Mn+1(O2-.) species. While often thought of as a pass-through point to give a highly reactive high-valent metal-oxo species, recent proposed mechanisms suggest the direct reactivity of Mn+1(O2-.) species as oxidants, including mechanisms proposed for the heme dioxygenases (tryptophan-2,3-dioxygenase (TDO), indoleamine-2,3-dioxygenase (IDO)). Due to their metastable nature, direct spectroscopic characterization of metal-superoxide intermediates is often difficult, and there is limited information about the substrate oxidation reactivity of these species. In this presentation, metal-superoxide species in different porphyrinoid frameworks (e.g. porphyrin, corrolazine) will be described. Efforts will be detailed regarding their generation from dioxygen, spectroscopic characterization, and their reactivity toward different substrates. These species were characterized using a combination of techniques, including UV-Vis, NMR, EPR, Mössbauer and resonance Raman spectroscopies. Their reactivity toward O–H and N–H H-atom transfer substrates, and indole derivatives for dioxygenation, will be described, including product and kinetic analyses.

Iron and cobalt porphyrinoid superoxides: Synthesis, characterization and reactivity

ACS Fall 2021

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