An understanding of the mechanisms by which Nature employs mononuclear nonheme
iron centers and dioxygen to carry out biological oxidative transformations of substantial
biological and environmental relevance is of great fundamental and practical interest.
Direct biochemical studies of nonheme iron oxygenases themselves can be
complemented by spectroscopic studies of small model complexes to afford significant
mechanistic insight, and this work employs a combination of these approaches.
Substitution of Fe(II) into the active center of a Mn(II)-dependent extradiol
dioxygenase under aerobic expression conditions leads to in vivo formation of a selfhydroxylated
form of the enzyme that is not observed for the native Mn(II) form, and we
suggest that this reflects a significantly lowered redox potential for the Fe(II) form. We
have also found that Co(II) substitution into an Fe(II)-dependent extradiol dioxygenase
affords active enzyme, with X-ray absorption spectroscopy (XAS) providing metrical
parameters for the resting state of this enzyme and its complexes with substrates. XAS studies were carried out for an assortment of high-valent nonheme iron
complexes of relevance to the oxoiron(IV) intermediates proposed in the catalytic cycles
of mononuclear nonheme iron oxygenases. Studies of a series of pseudo-octahedral lowspin
oxoiron(IV) complexes employing pentadentate ligands with a pendant axial ligand
trans to the oxo moiety demonstrated that the properties of the oxoiron unit were not
significantly affected by the identity of the trans ligand, in agreement with earlier
observations on chemically similar systems. We also characterized the products of oxo transfer to a thiolate-ligated nonheme iron(II) complex, providing structural evidence for
conversion of the thiolate to an O-bound sulfinate. We structurally characterized the first
example of a high-spin oxoiron(IV) complex in a trigonal bipyramidal (TBP) geometry,
and also examined the XAS properties of a series of TBP iron complexes with different
axial ligands as part of efforts to provide a basis for interpretation of the spectroscopic
properties of TBP iron centers. Finally, in studies of a diiron(IV) complex of relevance
to intermediate Q in methane monooxygenase, we demonstrated that the μ-oxo bridge of
its diiron(III) precursor is retained upon oxidation.
University of Minnesota Ph.D. dissertation. July 2010. Major: Chemistry. Advisor: Professor Lawrence Que, Jr. 1 computer file (PDF); xxiii, 300 pages, appendix p. 276-300.
Farquhar, Erik Rejman.
Metal substitution studies of an extradiol dioxygenase and X-Ray absorption studies of high-valent nonheme iron complexes..
Retrieved from the University of Minnesota Digital Conservancy,
Content distributed via the University of Minnesota's Digital Conservancy may be subject to additional license and use restrictions applied by the depositor.