THE COBALT(II)-N,N'-DIGLYCYLETHYLENEDIAMINE-DIOXYGEN SYSTEM - A POTENTIAL MODEL FOR METAL-PEPTIDE INTERACTIONS

In order to investigate hitherto undescribed dioxygen interactions in the cobalt(LI)-DGEN system (DGEN: N,N'-diglycylethylenediamine, 1,8-di amino-3,6-diaza-2,7-octanedione) all the equilibria possible under an oxygen-free atmosphere had to be reexamined. Two new equilibria have b een confirmed by potentiometric and spectrophotometric measurements: M + L + H reversible arrow MLH and M i + 2L reversible arrow ML2. Unlik e Co(LI)-dipeptide systems, metal-promoted deprotonation of the amide group has not been observed. The ML2 species may act as an ''active'' complex, able to take up dioxygen in a partially reversible way (rever sibility up to 50%). The reaction mechanism is similar to that known f or diamines. The structure of the bridging unit in the oxygenated mu-p eroxo-mu-hydroxodicobalt(III) complexes has been confirmed by volumetr ic and spectroscopic experiments.