Structure/function correlations over binuclear non-heme iron active sites.

ABSTRACT: Binuclear non-heme iron enzymes activate O2 to perform diverse chemistries. Three different structural mechanisms of O2 binding to a coupled binuclear iron site have been identified utilizing variable-temperature, variable-field magnetic circular dichroism spectroscopy (VTVH MCD). For the ?-OH-bridged Fe(II)2 site in hemerythrin, O2 binds terminally to a five-coordinate Fe(II) center as hydroperoxide with the proton deriving from the ?-OH bridge and the second electron transferring through the resulting ?-oxo superexchange pathway from the second coordinatively saturated Fe(II) center in a proton-coupled electron transfer process. For carboxylate-only-bridged Fe(II)2 sites, O2 binding as a bridged peroxide requires both Fe(II) centers to be coordinatively unsaturated and has good frontier orbital overlap with the two orthogonal O2 ?* orbitals to form peroxo-bridged Fe(III)2 intermediates. Alternatively, carboxylate-only-bridged Fe(II)2 sites with only a single open coordination position on an Fe(II) enable the one-electron formation of Fe(III)-O2 (-) or Fe(III)-NO(-) species. Finally, for the peroxo-bridged Fe(III)2 intermediates, further activation is necessary for their reactivities in one-electron reduction and electrophilic aromatic substitution, and a strategy consistent with existing spectral data is discussed.

SUBMITTER: Solomon EI 

PROVIDER: S-EPMC5010389 | biostudies-literature | 2016 Sep

REPOSITORIES: biostudies-literature