Oxidation of Metal-Bound Thiolato Sulfur Centers in Fe(III) and Co(III) Complexes with Carboxamido Nitrogens and Thiolato Sulfurs as Donors:  Relevance to the Active Sites of Nitrile Hydratases

Abstract

H2O2 oxidation of [MIII(PyPepS)2]- (M = Fe, Co) complexes with carboxamido nitrogens and thiolato sulfurs as donors affords the corresponding sulfinato [MIII(PyPepSO2)2]- species. The spectral properties of [FeIII(PyPepSO2)2]- resemble those of the iron site of nitrile hydratase.

Evidence of the Participation of Remote Residues in the Catalytic Activity of Co-Type Nitrile Hydratase from Pseudomonas putida

“…The active site of wild type ppNHase (Figure 2) is very similar to previously reported NHase structures where the cobalt is bound in an octahedral conformation, or pyramidal if a sixth ligand is absent, with ligands from the C1-T-L-C2-S-C3 motif: the sulfur atoms from three cysteines, α-Cys112, α-Cys115 and α-Cys117 and the backbone amide nitrogen of a cysteine (α-Cys112) and serine (α-Ser116). In the ptNHase structure, a water molecule is observed as a sixth ligand (27). In other known structures of Co-type NHases, C2 (α-Cys115) is oxidized to a sulfinic acid and C3 (α-Cys117) is oxidized to a sulfenic acid (34, 51–52).…”

“…It has attracted much attention because it is the first example of a biocatalyst used in the large-scale industrial production of commodity chemicals such as acrylamide (27–28). In addition to the use of NHase in the production of acrylamide, it is also used in the production of nicotinamide and 5-cyanovaleramide, the latter being a starting material for the synthesis of the herbicide azafenidin (29).…”

“…There are two types of NHase metalloenzymes; cobalt-dependent and iron-dependent. Cobalt-dependent (Co-type) NHase possesses a noncorrin cobalt center, while iron-containing (Fe-type) NHase possesses a nonheme iron center, and, in each case, the metal center is in the +3 oxidation state (27). The metal coordination spheres for both types involve a C1-S/T-L-C2-S-C3 motif, where cysteines C2 and C3 are typically oxidized to sulfinic and sulfenic acid, respectively (30).…”

Thioether-ligated iron(ii) and iron(iii)-hydroperoxo/alkylperoxo complexes with an H-bond donor in the second coordination sphere

“…1 also include a sulfur donor in the first coordination sphere, but the incorporation of sulfur or other heteroatoms in model complexes is rare. 23,25–41 In addition, little work has been done to determine the effect of secondary sphere interactions, such as hydrogen-bonding networks, on the structures and spectroscopic properties of iron-peroxo complexes, 42,43 despite their roles in many of the corresponding enzyme intermediates. Recently our lab has focused on determining the first and second coordination sphere effects on non-heme iron model complexes, including the incorporation of S donors in the first coordination sphere, and oxidizable substrates or H-bond donors in the second coordination sphere.…”

Addition of Dioxygen to an N4S(thiolate) Iron(II) Cysteine Dioxygenase Model Gives a Structurally Characterized Sulfinato–Iron(II) Complex

“…Thus addition of O 2 to the CDO model 1 leads to the isolation and characterization of an Fe II -sulfinate complex, wherein the thiolate donor has been doubly oxygenated in a manner parallel with the enzymatic chemistry. In addition, although there are a few examples of structurally characterized Fe III -sulfinates, 11f,12 to our knowledge 2 is the first example of a crystallographically characterized mononuclear Fe II -sulfinate complex.…”