Synthesis and characterization of an unsymmetrical cobalt(III) active site analogue of nitrile hydratase

J Biol Inorg Chem. 2011 Aug;16(6):937-47. doi: 10.1007/s00775-011-0794-7. Epub 2011 Jun 3.

Abstract

The design, synthesis, and characterization of an unsymmetrical diamidato-dithiol ligand (H(4) 1, where the hydrogen atoms represent deprotonatable amide and thiol protons) and its cobalt(III) complex, a synthetic analogue of the cobalt-containing nitrile hydratase enzyme family, are reported. The ligand was prepared in 24% yield from an overall eight-step synthetic pathway following a modified protocol established in our laboratory that includes two peptide couples using O-(1H-benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate as the coupling agent. The ligand and all precursors were characterized by NMR spectroscopy and elemental analysis. The cobalt nitrile hydratase synthetic analogue complex [NBu(4)][Co(1)] was prepared on deprotonating ligand H(4) 1 to [1](4-) on addition of 5 equiv of NaH in N,N-dimethylformamide and adding 1 equiv of CoCl(2) at -40 °C under a N(2) atmosphere followed by oxidizing the complex by stirring it overnight open to dry air. The complex [NBu(4)][Co(1)] was isolated after counterion exchange with 1 equiv of NBu(4)Cl followed by crystallization from MeCN/Et(2)O in 71% yield. The structure of the complex was confirmed by X-ray diffraction analysis. Cyclic voltammetry studies on [NBu(4)][Co(1)] in a 0.1 M [NBu(4)][PF(6)]/MeCN solution showed a quasi-reversible reduction potential at -1.1 V (vs. Ag/AgCl), and magnetic susceptibility investigations indicated the complex is paramagnetic in both the solid and the solution states as determined from inverse-Gouy and Evans NMR methods, respectively.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Catalytic Domain*
  • Cobalt / chemistry*
  • Crystallography, X-Ray
  • Hydro-Lyases / chemical synthesis*
  • Hydro-Lyases / chemistry*
  • Hydro-Lyases / metabolism
  • Magnetic Resonance Spectroscopy
  • Molecular Sequence Data
  • Molecular Structure

Substances

  • Cobalt
  • Hydro-Lyases
  • nitrile hydratase