ELECTROCHEMICAL OXIDATION OF THE NI(II) COMPLEX OF 2-AMINO CYCLOPENTENE-1-DITHIOCARBOXYLATE AT A PT ELECTRODE

The electrochemical oxidation of 2-amino dithiocarboxylic acid (ACDA) and its nickel(II) complex has been studied in DMF at a platinum elect rode. The oxidation of the ligand shows two oxidation peaks (+0.8 V an d +1.1 V). The first oxidation peak is related to ring formation betwe en two dithio groups with the elimination of one sulphur atom via two electron processes. The second peak is due to a two-electron transfer process by releasing a proton. The oxidation of the Ni(II) complex of ACDA, Ni(ACD)(2), is usually irreversible and metal-based on a short t ime scale while on a long time scale a ligand-based oxidation predomin ates. Although the formally nickel(III) species could not be prepared and isolated chemically, they are readily formed from Ni(ACD)(2) and t he electrochemically generated ACD radical. It was found that the redo x potential of the Ni(IT) complex studied is substantially reduced rel ative to those of most synthetic complexes and is in the region of Ni( III)/Ni(II) potentials in the native proteins (-390 to -640 mV vs. SCE ). (C) 1997 Elsevier Science S.A.