The interaction of metal ions with some dipeptides

Abstract

The dissociation constants of five dipeptides (glycylglycine, glycyl-D-asparagine, glycyl-L-leucine, DL-alanyl-DL-alanine, DL-alanyl-DL-phenylalanine) and the formation constants of some of their complexes with nickel(II) and copper(II) were determined potentiometrically. The visible spectra of the 1:1 copper(II) dipeptide systems were studied as a function of pH and an attempt was made to relate the spectra to the structures of the complexes present in solution. Nuclear magnetic resonance spectroscopy was used to follow the titration of glycylglycine with acid and base. This technique was also used to obtain information concerning the structures of the complexes of the dipeptides with copper(II) , nickel(II), and zinc(II), and, in the case of glycylasparagine, the possible conformation of the compound in aqueous solution. Finally, the hydrolysis of glycylglycine was studied as a function of alkali concentration by both U.V. and n.m.r. spectroscopy.