Binding of Cd2+ and Zn2+ with the phytochelatin (γ-Glu-Cys)4-Gly:: a voltammetric study assisted by multivariate curve resolution and electrospray ionization mass spectrometry

The complexation of Cd2+ and Zn2+ with the phytochelatin (gamma-Glu-Cys)(4)-Gly (PC4) is studied by Differential Pulse Polarography (DPP) assisted by Multivariate Curve Resolution with Alternating Least Squares (MCR-ALS) and by Electrospray Ionization Mass Spectrometry (ESI-MS). In the case of Zn2+, voltammetric results show the presence of an inert electroinactive Zn2+-PC4 complex, which is confirmed by ESI-MS. In the case of Cd2+, the unitary DPP peaks and the concentration profiles obtained by MCR-ALS from DPP titrations of PC4 with Cd2+ suggest the formation of two electroactive Cd2+-PC4 complexes. The first complex, with a 1:1 stoichiometry, shows a fixed DPP peak potential characteristic of a kinetically inert behavior. After further Cd2+ additions a second labile complex seems to be formed. This behavior is confirmed by ESI-MS detection of Cd-PC4 and Cd2+-PC4 complexes.