Preparation and some properties of cobalt(III) complexes with a dipeptide containing L-methionine residue

Abstract Cobalt(III) complexes with a dipeptide containing L -methionine residue, [Co(dipeptidato- N,N,O ) 2 ] − , [Co(dipeptidato)(diamine)] + and cis -[Co(dipeptidato)(NH 3 ) 2 ] + , have been prepared, where dipeptidate is L -methionyl-glycinate, glycyl- L -methioninate, L -methionyl- L -alaninate or L -alanyl- L -methioninate, and diamine is 1,2-ethanediamine or 1,3-propanediamine. All the complexes were characterized by electronic absorption, 1 H NMR and 13 C NMR and circular dichroism (CD) spectra. In the diamine and diammine complexes, the dipeptide coordinates to the cobalt(III) ion as the quadridentate through the nitrogen atoms of NH 2 and peptide N, the oxygen atom of COO − and the sulfur atom of SCH 3 . The 500 MHz 1 H NMR spectra indicate that the NS chelate rings of the L -met residue take the chair conformation and the S-methyl groups take the S ( S ) configuration for the C-terminal L -met., The CD spectra of the complexes were discussed with respect to their configurations.