Synthesis and Spectroscopic Characterization of Copper (I) and Copper (II) Nitrosyl Complexes with Tris(2-pyridylmethyl)amine Ligand

Abstract

Copper nitrite reductase (CuNIR) is a metalloprotein found in bacteria that reduces nitrite to nitric oxide (NO). The binding mode of NO to CuNIR has high significance for the understanding of the catalytic mechanism of CuNIR and in particular, the role of the amino acids that are located within the active site. An X-ray crystal structure of NO bound to copper in CuNIR was found to be side-on while all model complexes of Cu-NO have been reported to have end-on geometries. The coordination chemistry of NO with cooper(I) and copper (II) complexes were investigated with the tetradentate ligand tris(2- pyridylmethyl)amine (TPA). The complex [CuI(TPA)(CH3CN)]PF6 was synthesized followed by the reactions with NO and NOBF4 in attempt to produce [CuI(TPA)(NO)]+ and [CuII(TPA)(NO)]2+. The progression of the reactions were monitored via dip-probe UV-Vis spectroscopy, which showed the formation of Cu(II) complexes with NO reaction; the spectra of the NOBF4 reaction indicated the nitrosylation of the amine backbone prior interacting with the copper center . The EPR spectra also showed the formation of Cu(II) complexes with the NO reaction and a mixture of Cu(II) complexes with the NOBF4 reaction. The results provided valuable insights to the understanding of the NO species with Cu-TPA complex.