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, 1H NMR and 13C 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 1H 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.