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A Structural and Functional Model for the Tris‐Histidine Motif in Cysteine Dioxygenase
Author(s) -
Anandababu Karunanithi,
Ramasubramanian Ramamoorthy,
Wadepohl Hubert,
Comba Peter,
Johnee Britto Neethinathan,
Jaccob Madhavan,
Mayilmurugan Ramasamy
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201901005
Subject(s) - chemistry , acetonitrile , crystallography , redox , octahedral molecular geometry , tris , cysteine , alkyl , octahedron , ligand (biochemistry) , stereochemistry , medicinal chemistry , crystal structure , inorganic chemistry , enzyme , organic chemistry , biochemistry , receptor
The iron(II) complexes [Fe(L)(MeCN) 3 ](SO 3 CF 3 ) 2 (L are two derivatives of tris(2‐pyridyl)‐based ligands) have been synthesized as models for cysteine dioxygenase (CDO). The molecular structure of one of the complexes exhibits octahedral coordination geometry and the Fe−N py bond lengths [1.953(4)–1.972(4) Å] are similar to those in the Cys‐bound Fe II ‐CDO; Fe−N His : 1.893–2.199 Å. The iron(II) centers of the model complexes exhibit relatively high Fe III/II redox potentials ( E 1/2 =0.988–1.380 V vs. ferrocene/ferrocenium electrode, Fc/Fc + ), within the range for O 2 activation and typical for the corresponding nonheme iron enzymes. The reaction of in situ generated [Fe(L)(MeCN)(SPh)] + with excess O 2 in acetonitrile (MeCN) yields selectively the doubly oxygenated phenylsulfinic acid product. Isotopic labeling studies using 18 O 2 confirm the incorporation of both oxygen atoms of O 2 into the product. Kinetic and preliminary DFT studies reveal the involvement of an Fe III peroxido intermediate with a rhombic S = 1 / 2 Fe III center (687–696 nm; g ≈2.46–2.48, 2.13–2.15, 1.92–1.94), similar to the spectroscopic signature of the low‐spin Cys‐bound Fe III CDO (650 nm, g ≈2.47, 2.29, 1.90). The proposed Fe III peroxido intermediates have been trapped, and the O−O stretching frequencies are in the expected range (approximately 920 and 820 cm −1 for the alkyl‐ and hydroperoxido species, respectively). The model complexes have a structure similar to that of the enzyme and structural aspects as well as the reactivity are discussed.