A Nonheme Iron(III) Superoxide Complex Leads to Sulfur Oxygenation

Abstract

A new alkylthiolate-ligated nonheme iron complex, Fe II (BNPA Me2 S)Br (1), is reported. Reaction of 1 with O 2 at −40 °C, or reaction of the ferric form with O 2 •− at −80 °C, gives a rare iron(III)-superoxide intermediate, [Fe III (O 2 )(BNPA Me2 S)] + (2), characterized by UV−vis, 57 Fe Mossbauer, ATR-FTIR, EPR, and CSIMS. Metastable 2 then converts to an S-oxygenated Fe II (sulfinate) product via a sequential O atom transfer mechanism involving an iron-sulfenate intermediate. These results provide evidence for the feasibility of proposed intermediates in thiol dioxygenases.

An Unusual Ferryl Intermediate and Its Implications for the Mechanism of Oxacyclization by the Loline-Producing Iron(II)- and 2-Oxoglutarate-Dependent Oxygenase, LolO

“… ,, In most of the complete reactant complexes that have been crystallographically characterized, this open site is trans to the C-terminal histidine ligand (His C ). ,, This site is considered to be “in-line” because it projects toward the target site of the prime substrate. Some structures have shown the carboxylate of 2OG shifted toward or fully into this in-line position, rendering the site trans to the N-terminal histidine ligand (His N ), the “off-line” site, apparently more open for O 2 addition. ,, In either case, capture of O 2 is presumed to yield a superoxoiron­(III) complex that has not yet been directly characterized in any Fe/2OG oxygenase but has been trapped in other mononuclear nonheme iron enzymes and model complexes. − Decarboxylation of 2OG and coupling of its C2 to the distal oxygen of the O 2 ligand then yield a Fe­(II)–peroxysuccinate complex that has been crystallographically characterized in the l -arginine 3-hydroxylase, VioC . Heterolysis of the peroxide bond of this complex produces the marquee intermediate of the class, the oxoiron­(IV) (ferryl) complex (Scheme ), which has been characterized by Mössbauer spectroscopy in more than 10 different enzymes. ,,,,,,− These intermediates all have S = 2 electron-spin ground states that result in isomer shifts (δ) of 0.22–0.32 mm/s and quadrupole splitting parameters (|Δ E Q |) of ∼ 1.0 mm/s. ,, …”

Cobalt(II)-Substituted Cysteamine Dioxygenase Oxygenation Proceeds through a Cobalt(III)-Superoxo Complex

“…Two proposed mechanistic pathways emerge from the extensive characterization of the founding member of the thiol dioxygenase superfamily, cysteine dioxygenase (CDO), and the synthetic non-heme Fe model complexes. − O 2 , a diradical molecule, ligates to the substrate-bound Fe­(II) center, forming an Fe­(III)-bound single radical in the form of superoxo, marking the divergence of the two pathways (Scheme ). The pathway illustrated at the top involves non-ferryl-dependent concurrent dioxygen transfer to the thiolate group of the bound l -cysteine substrate.…”