Nonheme Iron–Thiolate Complexes as Structural Models of Sulfoxide Synthase Active Sites

Authors

Danushka M. Ekanayake, Marquette University
Anne A. Fischer, Marquette University
Maya E. Elwood, University of St. Thomas
Alexandra M. Guzek, Marquette University
Sergey Lindeman, Marquette UniversityFollow
Cordina V. Popescu, University of St. Thomas
Adam T. Fiedler, Marquette UniversityFollow

Document Type

Article

Language

eng

Publication Date

2020

Publisher

Royal Society of Chemistry

Source Publication

Dalton Transactions

Source ISSN

1477-9226

Abstract

Two mononuclear iron(II)–thiolate complexes have been prepared that represent structural models of the nonheme iron enzymes EgtB and OvoA, which catalyze the O₂-dependent formation of carbon–sulfur bonds in the biosynthesis of thiohistidine compounds. The series of Fe(II) complexes reported here feature tripodal N₄ chelates (L^A and L^B) that contain both pyridyl and imidazolyl donors (L^A = (1H-imidazol-4-yl)-N,N-bis((pyridin-2-yl)methyl)methanamine; L^B = N,N-bis((1-methylimidazol-2-yl)methyl)-2-pyridylmethylamine). Further coordination with monodentate aromatic or aliphatic thiolate ligands yielded the five-coordinate, high-spin Fe(II) complexes [Fe^II(L^A)(SMes)]BPh₄ (1) and [Fe^II(L^B)(SCy)]BPh₄ (2), where SMes = 2,4,6-trimethylthiophenolate and SCy = cyclohexanethiolate. X-ray crystal structures revealed that 1 and 2 possess trigonal bipyramidal geometries formed by the N₄S ligand set. In each case, the thiolate ligand is positioned cis to an imidazole donor, replicating the arrangement of Cys- and His-based substrates in the active site of EgtB. The geometric and electronic structures of 1 and 2 were analyzed with UV-vis absorption and Mössbauer spectroscopies in tandem with density functional theory (DFT) calculations. Exposure of 1 and 2 to nitric oxide (NO) yielded six-coordinate FeNO adducts that were characterized with infrared and electron paramagnetic resonance (EPR) spectroscopies, confirming that these complexes are capable of binding diatomic molecules. Reaction of 1 and 2 with O₂ causes oxidation of the thiolate ligands to disulfide products. The implications of these results for the development of functional models of EgtB and OvoA are discussed.

Comments

Accepted version. Dalton Transactions, Vol. 49, No. 48 (2020): 17745-17757. DOI. © 2020 The Royal Society of Chemistry. Used with permission.

Recommended Citation

Ekanayake, Danushka M.; Fischer, Anne A.; Elwood, Maya E.; Guzek, Alexandra M.; Lindeman, Sergey; Popescu, Cordina V.; and Fiedler, Adam T., "Nonheme Iron–Thiolate Complexes as Structural Models of Sulfoxide Synthase Active Sites" (2020). Chemistry Faculty Research and Publications. 1015.
https://epublications.marquette.edu/chem_fac/1015