Copper(II)-promoted hydrolysis of ethyl glycylglycinate, ethyl glycyl-β-alaninate, and ethyl glycyl-L-leucinate

Abstract

Copper(II)-promoted hydrolysis of the ethyl esters of glycylglycine, glycyl-β-alanine, and glycyl-L-leucine has been studied at 25 °C, I= 0·01M, and pH values >7·6. Under these conditions, and at a 1 : 1 metal to ligand ratio, the peptide esters act as tridentate ligands, donation occurring from the terminal amino·group and the deprotonated amide nitrogen atom, with a weak interaction between the metal ion and the carbonyl group of the ester. An aqua ⇌ hydroxo equilibrium occurs in these complexes, and rate constants are reported for base hydrolysis of the aqua- and hydroxo-complexes. Rate accelerations of the order of 10³(compared with the unprotonated ligands) have been observed.