Rates of peptide bond hydrolysis by cobalt(III) complexes: observation by rate of amino acid release

The rates of hydrolysis of eleven dipeptides (Gly-Gly; Gly-l-Leu; Gly-d,l-Val; Gly-l-Phe: d,l-Leu-Gly; l-Leu-l-Tyr; l-Pro-l-Tyr; l-Ala-l-Phe; l-Val-Gly; l-Val-l-Ile; l-Ile-l-Val) by cis-β-Co(trien)(OH)(H₂O)²⁺ under pseudo first order conditions (excess Co(III)) are reported. The rates are determined by the rate of amino acid release by liquid chromatography. The range of rates observed for the eleven dipeptides is 10.1. Two of the dipeptides are hydrolyzed more rapidly than Gly-Gly, the remaining six more slowly. Phosphate does not have any significant effect on the rate of peptide hydrolysis. Aquohydroxy-1,8-diamino-3,6-dithiaoctanecobalt(III)²⁺ did not hydrolyze Gly-Gly at 25°, pH8, and aquohydroxy-1,6-bis-(α-pyridyl)-2,5-diazahexanecobalt(III)²⁺ did not hydrolyze Gly-Gly at 65°, pH 8, to any significant extent.