PROTON, COPPER(II) AND NICKEL(II) COMPLEXES OF SOME AMADORI REARRANGEMENT PRODUCTS OF D-GLUCOSE AND AMINO-ACIDS

The formation of the copper(II) and nickel(II) complexes of six Amador i rearrangement products of D-glucose with amino acids ('fructose-amin o acids') was investigated by potentiometry, CD and EPR spectroscopy. The - I effect of the fructose residue in the ligands was reflected by the protonation constants of their amino groups. In the complexes ML formed with the copper(II) ion, besides the amino acid-type coordinati on a weak interaction with non-deprotonated alcoholic hydroxy groups w as demonstrated by CD studies. Increase of the pH may lead to transfor mation of the species ML to give complexes ML2 and/or MLH-1. The forme r contains two nitrogen donor atoms in the copper(II) coordination sph ere, while in MLH-1 the ligands are coordinated through their carboxyl , amino and deprotonated alcoholic OH groups, as revealed by equilibri um, CD and EPR studies. Above pH approximately 7, a redox reaction tak es place between copper(II) and the ligand. The nickel(II) ion forms a mino acid-type parent complexes ML and ML2, while deprotonated species predominate in solution above pH-9.