A new end-on low-spin ferric heme peroxide, [(P )Fe -(O )] (P -P), and subsequently formed hydroperoxide species, [(P )Fe -(OOH)] (P -HP) are generated utilizing the iron-porphyrinate P with its tethered axial base imidazolyl group. Measured thermodynamic parameters, the ferric heme superoxide [(P )Fe -(O )] (P -S) reduction potential (E°') and the P -HP pK value, lead to the finding of the OO-H bond-dissociation free energy (BDFE) of P -HP as 69.5 kcal mol using a thermodynamic square scheme and Bordwell relationship. The results are validated by the observed oxidizing ability of P -S via hydrogen-atom transfer (HAT) compared to that of the F superoxide complex, [(F )Fe -(O )] (S) (F =tetrakis(2,6-difluorophenyl)porphyrinate, without an internally appended axial base imidazolyl), as determined from reactivity comparison of superoxide complexes P -S and S with the hydroxylamine (O-H) substrates TEMPO-H and ABNO-H.
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| http://dx.doi.org/10.1002/anie.202013791 | DOI Listing |
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