Voltammetric Analysis of Phytochelatin Complexation in Ternary Metal Mixtures Supported by Multivariate Analysis and ESI‐MS

The competitive binding of Cu²⁺, Cd²⁺ and Pb²⁺ in ternary mixtures by the phytochelatins PC₂ and PC₅ (PC_n; (γGlu‐Cys)_n‐Gly, n=2 and 5) are examined by voltammetry, which allows one to follow the displacements of the voltammetric signals induced by the competitive binding among the metal ions towards PC₂ or PC₅ complexation, and direct injection positive‐mode Electrospray Ionization Mass Spectrometry (ESI‐MS), in order to obtain the stoichiometries of the complexes. Voltammetric data are analyzed by Gaussian Peak Adjustment (GPA), which is a recently developed multivariate analysis method for nonlinear electrochemical data. Different complexes have been detected or deduced their presence, depending on the experimental conditions. Ternary complexes CuCdPC_n and CdPbPC_n were detected for both PC₂ and PC₅, while the ternary CuPbPC_n complex was only detected for PC₂. Some of the complexes have been only detected by ESI‐MS because in some cases voltammetry data could not be totally resolved, even by using GPA. The quaternary CdPbCuPC_n complex has been detected for PC₅, but for PC₂ data are not so conclusive. In summary, the signal evolution for mixed CdCuPC_n complexes is quite different. These observations could be a reflection of an antagonistic effect for the case of PC₂ and a synergetic one for PC₅.