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 studied 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 been 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 addition of acid or base. Some evidence is given supporting the hypothesis of protonation of the axial tyrosine ligand in the form of galactose oxidase which has been isolated with an exogenous ligand bound to Cu. Electrochemical studies have been performed for the free pro-ligands and for the copper complexes.