Combined use of the potential shift correction and the simultaneous treatment of spectroscopic and electrochemical data by multivariate curve resolution:: analysis of a Pb(II)-phytochelatin system

The combined use of differential pulse polarography (DPP), circular dichroism (CD) and multivariate curve resolution by alternating least squares (MCR-ALS), with potential shift correction for data analysis, provides valuable information on the complexation of Pb(II) by the phytochelatin (gamma-Glu-Cys)(3)-Gly (PC3). All data confirm the formation of the predominant 1 : 1 Pb-PC3 complex. However, in the presence of an excess of Pb(II), the same complex seems to be present but with some modi. cation in its structure. This is suggested by the shift towards more negative potentials of the DPP signal, and by a dramatic change in CD spectra. This evolution seems to be more related to a conformational change of the complex than with a modi. cation of the electrochemical process kinetics.