Voltammetric Studies of Cadmium‐ and Zinc‐Containing Metallothioneins at Nafion‐Coated Mercury Thin Film Electrodes

Abstract

AbstractVoltammetric studies of rabbit liver metallothioneins (MTs, containing both Zn and Cd ions) and Zn7‐MT were carried out at Nafion‐coated mercury film electrodes (NCMFEs). The accumulation of MT molecules into the NCMFEs enhances the voltammetric signals and the electrostatic interaction between the Nafion membrane and MT facilitates facile electron transfer reactions. Two well‐defined redox waves, with reduction potential (Epc) values at −0.740 and −1.173 V, respectively, were observed. The peak at Epc =−0.740 V is attributable to the reduction of the Cd‐MT complex, whereas that at Epc=−1.173 V was assigned to the reduction of the Zn‐MT complex. Zn7‐MT exhibits only one redox wave with Epc=−1.198 V. The NCMFE was found to be more advantageous than thin mercury film electrode (MFE), because the pristine metal ions in MTs (e.g., Cd2+ and/or Zn2+) are not significantly replaced by Hg2+. The NCMFE is also complementary to Nafion‐coated bismuth film electrode in that it has a greater hydrogen overpotential, which allows the reduction of the Zn‐MT complex to be clearly observed. Moreover, intermetallic compound formation between Cd and Zn appears to be less serious at NCMFEs. Consequently, the amounts of Cd and Zn deposited into the electrode upon the reduction reactions can be quantified more accurately.