Anodic stripping voltammetry in the complexation study of the peptide Lys-Cys-Thr-Cys-Cys-Ala [56-61] MT I and cadmium: application in determination of the complexing capacity and stability constant

摘要

A study of Cd complexation with the peptide Lys-Cys-Thr-Cys-Cys-Ala thionein fragment [56—61] MT I (FT) was performed in the differential pulse anodic stripping voltammetric (DPASV) mode. Amperometric titrations of FT with cadmium standard dis4 solution were performed in 0.59 mol dm ~(-3) NaCi at pH 7.9, and at a constant temperature of 25.0deg C. The signal of FT without a i cadmium has the peak potential at E_(p(FT)=-0.52 V (vs. an Ag AgCI electrode). As the titration with CdCl2 proceeds, a signal red related to CdFT complex appears at the potential E_(P(cdFT))-0.67 V. When the available complexing sites on FT are saturated fra the signal of ionic Cd appears. From the amperometric titration data the capacity of FT to complex Cd (CL) and the apparentstability constant of the CdFT complex (K’) using amodified van den Berg-Ruzic-Lee method were determined. The mean value vol of the stability constant corrected for the partition of the hydrated Cd~(2+) ion within the ionic cadmium concentration is 5.3 X 10~(10) ate dm~3 mol~(-1) In addition, titration of the constant Cd~(2+) concentration with FT was performed. Due to the excess of cadmium over str the FT and vice versa the existence of complexes of different stoichiometry are proposed to cause the poorly resolved signal.