The base hydrolysis ofmer-[Co(1,5-diamino-3-azapentane)(amino acidate)X]+ (X = Cl or NO2) complexes and base hydrolysis of complexed peptides in the coordination sphere of the [Co(dien)]3+ moiety

Summary A variety ofmer-Co(dien)(AA)X]⁺ (AA = amino acidate, dien = 1,5-diamino-3-azapentane) andmer-Co(dien)(dipeptideOR)X]²⁺ complexes (X = Cl or NO₂) have been prepared and characterised. Base hydrolysis of the peptide bond in the carbonyl bonded glycyl peptides has been studied at 25°C and I = 0.1 mol dm^–3. The rate constants k_OH for peptide bond hydrolysis fall within the 0.67–0.88 mol dm^–3s^–1 range. Base hydrolysis of the complexed peptide isca. 2×10⁴ times faster than for the uncomplexed peptide ligand at 25 °C. The base hydrolysis of the chloro- and nitro-ligands in these complexes has also been studied. Very rapid hydrolysis occurs if the dien ligand adopts amer-configuration and the reactions are 10²–10⁴ times faster than for analogous complexes where the dien ligand adopts afac-configuration. These results are in agreement with Tobe's criteria for rapid base hydrolysis in cobalt(III) complexes.The following abbreviations are used thoughout this paper; dien 1,5-diamino-3-azapentane - dpt 1,7-diamino-4-azaheptane - glyO glycinate - glyOH glycine - glyOR glycine ester - glyNH₂ glycine amide - glyglyO glycylglycinate - glyglyOR glycylglycine ester - glyglyglyOH triglycine - -alaO -alaninate