Complexes of 3,4-dihydroxyphenyl derivatives. I. Copper(II) complexes of DL-3,4-dihydroxyphenylalanine

Abstract

Abstract pH-metric, visible, UV and ESR spectral studies of the copper(II)-DL-3,4-dihydroxyphenylalanine (DL-DOPA) and the copper(II)-aminoacid-pyrocatechol systems were used to draw conclusions on the complexes formed in the copper(II)-DOPA system. The stability constants of these complexes were determined from the pH-metric data. It was found that at lower pH( 2 A and Cu(H 2 A) 2 are formed, while at higher pH values (>9) the pyrocatechol type complex Cu(HA) 2 and its deprotonated species are formed. In the intermediate pH range cyclic and open-chain dimeric species are produced, together with a complex containing both N,O and O,O bonds. The existence of this complex is also supported by the fact that formation of the mixed ligand complex is favoured in the copper(II)-pyrocatechol-alanine and copper(II)-pyrocatechol-phenylalanine systems.