EQUILIBRIUM AND STRUCTURAL STUDIES ON PROTON AND COPPER(II) COMPLEXES OF N-D-GLUCONYLGLYCINE

N-D-Gluconylglycine, a pseudopeptide derivative of glucono-1,5-lactone and glycine, was prepared and the equilibrium constants of its protonation and copper(II) co-ordination and the structures of the copper complexes formed were studied in aqueous solution by potentiometry, spectrophotometry, CD, EPR and C-13 NMR relaxation. The parent complexes formed in an acidic medium have low stabilities, characteristic of carboxylate co-ordination. In the range pH 5-9 the amide group and the 2-OH group of the ligand undergo deprotonation. In parallel with these processes, one ligand is replaced from the copper(II) coordination sphere. For the species MLH-2, 3O,1 N co-ordination in the equatorial plane is proposed. The EPR measurements indicate that dimeric species are also formed. At pH > 9, further base-consuming processes start as an indication of the deprotonation of other alcoholic hydroxy groups of the sugar moiety or the formation of mixed hydroxo complexes.