Gus Braun, Stanford University 

Abstract:

High-valent iron species are competent reactive species in the catalytic cycle of mononuclear iron proteins responsible for hydroxylation (cytochrome P450, taurine dioxygenase, tyrosine hydroxylase), halogenation (SyrB2), ring rearrangement (isopenicillin N synthase), and other reactivities. They were found to be a high-spin FeIV=O in the case of α-ketoglutarate-dependent non-heme iron enzymes and low-spin FeIV=O in the case of heme enzymes. Interestingly, synthetic efforts to prepare model complexes yielded 6-coordinate low-spin compounds, even without using a porphyrin ligand, and only the use of tripodal ligands enforcing a 5-coordinate geometry produced high-spin FeIV=O species.

Here, we investigated a model complex family FeIVO(H3buea)-, FeIIIO(H3buea)2- and FeIII(OH)(H3buea)- with a range of X-ray techniques at SSRL (Fe K- and L-edge X-ray absorption spectroscopy (XAS), 1s2p resonant inelastic X-ray scattering (RIXS), and oxygen K-edge XAS) to investigate the impact of the trigonal geometry on the spectral shape and electronic structure of the iron center. Comparison of the spectra simulated using time-dependent density functional theory (TDDFT) with multiplet interaction analysis in the software Quanty revealed that TDDFT is erroneously assigning the pre-edge despite a correct spectral shape.

The key spectral features identified in our study of this well-defined model complex allows us to interpret the Fe K-edge XAS spectra of the biological FeIV=O intermediate of taurine dioxygenase as evidence of its 5-coordinate geometry. This assignment is consistent with the geometric structure determined by nuclear resonant vibrational spectroscopy and these features provide a reliable fingerprint for this kind of coordination mode of FeIV=O intermediates.

Poster Session Link: https://gather.town/invite?token=0pEoq7VP

If you have any questions for the presenter, please contact them via email: gusbraun@stanford.edu