Co^III Complexes with Square‐Planar N₂S₂‐ and N₂(SO₂)₂‐Type Ligands as An Active Site Structural Model for Nitrile Hydratase – Biological Implications of an Amidate Coordination

Abstract

}(tBuNC) 2 ] (3) were synthesized and characterized on the basis of electronic absorption spectroscopy, IR spectroscopy, cyclic voltammetry, and X-ray structural analysis. Both of the crystal structures of complexes 1-Na and 1-PPh 4 revealed a square planar structure with N 2 S 2 donating atoms, and 2 exhibited an octahedral structure coordinated with two tert-butylisocyanide (tBuNC) molecules at the axial sites of complex 1-PPh 4 . Complex 3, which showed an octahedral structure with sulfinate sulfur atoms equatorially coordinated to the center, was synthesized by the treatment of 2 with a suitable oxidant. The reduction potential values from Co III to Co II for complex 3 in solution demonstrated a larger positive shift when compared with those of complexes 1-PPh 4 and 2, which indicates that the oxygenation of the sulfur atoms increased the Lewis acidity of the Co III center. Interestingly, the coordination equilib-

Use of Metallopeptide Based Mimics Demonstrates That the Metalloprotein Nitrile Hydratase Requires Two Oxidized Cysteinates for Catalytic Activity

“…Other support for this supposition comes from additional computational and synthetic work on NHase-like metal centers. 15,39,115 We note that it remains to be seen, both on the basis of this study and others, if the SO(H) ligand plays a more intimate role in the NHase catalytic-cycle (such as proton shuttling to the substrate) 115,116 beyond the tuning of the metal-center electronics.…”

Synthesis and Characterization of Cobalt(III) Complexes with High Selectivity for NO Sensing

“…Structures of 1 and 2 in solution Complex 1 showed a square planar structure with trivalent cobalt ion to which two deprotonated amine nitrogens and two thiolate sulfurs were provided as previously reported (15). An X-ray structural analysis for a single crystal clarified that 1 had a square planar geometry with large vacant sites at the axial positions to which small molecules including NO can coordinate.…”

“…Ligand L1 (N,N'-bis(2-percapto-2-methylpropioyl)propyldiamine) and 1 were prepared according to the method previously reported (15). Preparation of ligand L2 (4,4'-dithio-bis[(N-(2-mercapto-2-methyl)propyl)-2-(2-mercapto-2-methylpropionyl amino)-butaneamide]), which is a dimer and has a similar but an unsymmetric structure as compared with L1, was also carried out according to the similar method of L1 with some modifications.…”

Structure of Thiocyanate Hydrolase: A New Nitrile Hydratase Family Protein with a Novel Five-coordinate Cobalt(III) Center

“…In fact, the coordination number of Co(III) complexes with square-planar N 2 S 2 type ligand mimicking NHase active site was influenced by electrophilicities of solvents as well as the oxidations of sulfur ligands to sulfinate. 29 …”