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Issue 48, 2020

Nonheme iron–thiolate complexes as structural models of sulfoxide synthase active sites

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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 (LA and LB) that contain both pyridyl and imidazolyl donors (LA = (1H-imidazol-4-yl)-N,N-bis((pyridin-2-yl)methyl)methanamine; LB = 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 [FeII(LA)(SMes)]BPh4 (1) and [FeII(LB)(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.

Graphical abstract: Nonheme iron–thiolate complexes as structural models of sulfoxide synthase active sites

Supplementary files

Article information


Submitted
01 Oct 2020
Accepted
09 Nov 2020
First published
26 Nov 2020

Dalton Trans., 2020,49, 17745-17757
Article type
Paper

Nonheme iron–thiolate complexes as structural models of sulfoxide synthase active sites

D. M. Ekanayake, A. A. Fischer, M. E. Elwood, A. M. Guzek, S. V. Lindeman, C. V. Popescu and A. T. Fiedler, Dalton Trans., 2020, 49, 17745 DOI: 10.1039/D0DT03403G

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