Tuning the Geometric and Electronic Structure of Synthetic High-Valent Heme Iron(IV)-Oxo Models in the Presence of a Lewis Acid and Various Axial Ligands
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- Johns Hopkins Univ., Baltimore, MD (United States)
- Stanford Univ., Stanford, CA (United States)
- Oregon Health & Science Univ., Portland, OR (United States)
- Stanford Univ., Menlo Park, CA (United States)
- Stanford Univ., Stanford, CA (United States); Stanford Univ., Menlo Park, CA (United States)
High-valent ferryl species (e.g., (Por)FeIV=O, Cmpd-II) are observed or proposed key oxidizing intermediates in the catalytic cycles of heme-containing enzymes (P-450s, peroxidases, catalases, and cytochrome c oxidase) involved in biological respiration and oxidative metabolism. Herein, various axially ligated iron(IV)-oxo complexes were prepared to examine the influence of the identity of the base. These were generated by addition of various axial ligands (1,5-dicyclohexylimidazole (DCHIm), a tethered-imidazole system, and sodium derivatives of 3,5-dimethoxyphenolate and imidazolate). Characterization was carried out via UV–vis, electron paramagnetic resonance (EPR), 57Fe Mössbauer, Fe X-ray absorption (XAS), and 54/57Fe resonance Raman (rR) spectroscopies to confirm their formation and compare the axial ligand perturbation on the electronic and geometric structures of these heme iron(IV)-oxo species. Mössbauer studies confirmed that the axially ligated derivatives were iron(IV) and six-coordinate complexes. XAS and 54/57Fe rR data correlated with slight elongation of the iron-oxo bond with increasing donation from the axial ligands. The first reported synthetic H-bonded iron(IV)-oxo heme systems were made in the presence of the protic Lewis acid, 2,6-lutidinium triflate (LutH+), with (or without) DCHIm. Mössbauer, rR, and XAS spectroscopic data indicated the formation of molecular Lewis acid ferryl adducts (rather than full protonation). Here, the reduction potentials of these novel Lewis acid adducts were bracketed through addition of outer-sphere reductants. The oxidizing capabilities of the ferryl species with or without Lewis acid vary drastically; addition of LutH+ to F8Cmpd-II (F8 = tetrakis(2,6-difluorophenyl)porphyrinate) increased its reduction potential by more than 890 mV, experimentally confirming that H-bonding interactions can increase the reactivity of ferryl species.
- Research Organization:
- SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
- Sponsoring Organization:
- USDOE Office of Science (SC), Biological and Environmental Research (BER)
- Grant/Contract Number:
- AC02-76SF00515; R01GM074785; F32GM122194; GM60353; P41GM103393; R01GM040392; AC02-05CH11231
- OSTI ID:
- 1529246
- Alternate ID(s):
- OSTI ID: 1542892
- Journal Information:
- Journal of the American Chemical Society, Vol. 141, Issue 14; ISSN 0002-7863
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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