O₂ Reduction Reaction by Biologically Relevant Anionic Ligand Bound Iron Porphyrin Complexes

Abstract

Iron porphyrin complex with a covalently attached thiolate ligand and another with a covalently attached phenolate ligand has been synthesized. The thiolate bound complex shows spectroscopic features characteristic of P450, including the hallmark absorption spectrum of the CO adduct. Electrocatalytic O2 reduction by this complex, which bears a terminal alkyne group, is investigated by both physiabsorbing on graphite surfaces (fast electron transfer rates) and covalent attachment to azide terminated self-assembled monolayer (physiologically relevant electron transfer rates) using the terminal alkyne group. Analysis of the steady state electrochemical kinetics reveals that this catalyst can selectively reduce O2 to H2O with a second-order k(cat.) ~10(7) M(-1 )s(-1) at pH 7. The analogous phenolate bound iron porphyrin complex reduces O2 with a second-order rate constant of 10(5) M(-1) s(-1) under the same conditions. The anionic ligand bound iron porphyrin complexes catalyze oxygen reduction reactions faster than any known synthetic heme porphyrin analogues. The kinetic parameters of O2 reduction of the synthetic thiolate bound complex, which is devoid of any second sphere effects present in protein active sites, provide fundamental insight into the role of the protein environment in tuning the reactivity of thiolate bound iron porphyrin containing metalloenzymes.

Valence tautomerism in synthetic models of cytochrome P450

“…S12A). These features are quite different from the ferrous CO complex, which features a Soret band at 445 nm and a Q band at 567 nm (30). The rR data of this CO adduct show a major species with ν 4 and ν 2 bands at 1,366 and 1,564 cm −1 and two new bands at 522 and 1,953 cm −1 (SI Appendix, Fig.…”

“…rR data of the bulky aliphatic and benzylic complexes when attached to self-assembled monolayers of thiols on Ag surfaces (SI Appendix, Fig. S14 A and B, blue) and dipped in aqueous solution show the presence of only ferric thiolate species (30,31). In contrast to the data observed in organic solution (SI Appendix, Fig.…”

Electrochemistry-mass spectrometry to study reactive drug metabolites and CYP450 simulations

“…The use of a synthetic model of CYP450 with a terminal alkyne chain and a thiol-ligated iron porphyrin complex has been reported for studying the electrocatalytic oxygen-reduction reaction [74]. The kinetic study of dioxygen reduction using the resulting model CYP450 provided relevant insight into the role of the apoprotein in tuning the reactivity of thiolate-bound iron porphyrin.…”

Graphene‐Supported Pyrene‐Modified Cobalt Corrole with Axial Triphenylphosphine for Enhanced Hydrogen Evolution in pH 0–14 Aqueous Solutions

“…A Co‐bound pyridine (py) group is located at the trans axial position, and the trans effect is, therefore, anticipated. Although the trans effect has been studied extensively in several kinds of reactions, which include atom‐transfer reactions, oxygen reduction reactions, and oxygen evolution reactions, it has been demonstrated rarely for the HER. Porphyrin and corrole ligands can provide the metal center with a square‐planar coordination environment, in which the two axial positions are trans to each other.…”

“…Porphyrin and corrole ligands can provide the metal center with a square‐planar coordination environment, in which the two axial positions are trans to each other. Therefore, this geometry is ideal to study the trans effect . In nature, heme proteins are excellent examples that show the trans effect of Fe porphyrins .…”