SOLUTION STUDIES OF COPPER(II) COMPLEXES AS MODELS FOR THE ACTIVE-SITE IN GALACTOSE-OXIDASE

The complexation of copper(II) (from the perchlorate) by two tripodal ligands H(2)L bearing one pyridine and two phenolic arms has been stud ied in co-ordinating solvents. One of the ligands bears a MeS group at the para position of one of the phenolic moieties. In the presence of triethylamine, only brown dimeric neutral complexes [(CuL)(2)] have b een obtained. In the absence of base, green [Cu(HL)](+) complexes were identified, in which one of the phenolic ligands remains protonated. The brown and the green complexes are reversibly interconverted upon a ddition of acid or base. Some evidence is given supporting the hypothe sis of protonation of the axial tyrosine ligand in the form of galacto se oxidase which has been isolated with an exogenous ligand bound to C u. Electrochemical studies have been performed for the free pro-ligand s and for the copper complexes.