Talanta 71 (2007) 344–352 Soft modelling for the resolution of highly overlapped voltammetric peaks: application to some Pb-phytochelatin systems Ar´ ıstides Alberich, Cristina Ari ˜ no ∗ , Jos´ e Manuel D´ ıaz-Cruz, Miquel Esteban Departament de Qu´ ımica Anal´ ıtica, Universitat de Barcelona, Mart´ ı i Franqu` es 1-11, E–08028 Barcelona, Spain Received 19 December 2005; received in revised form 31 March 2006; accepted 6 April 2006 Available online 26 May 2006 Abstract A differential pulse polarographic (DPP) study of the Pb 2+ /Cys-Gly, Pb 2+ /-Glu-Cys, Pb 2+ /PC 2 and Pb 2+ /PC 3 systems is performed, being PC 2 and PC 3 the phytochelatins of general structure (-Glu-Cys) n -Gly, with n = 2 and 3, respectively. Analysis of DPP data is assisted by multivariate curve resolution with alternating least squares (MCR-ALS) method in order to establish the complexes formation sequence and their final stoichiometries. DPP signals of these systems present, besides overlapping of peaks due to free metal ion and metal complexes, interference of mercury anodic signals. Despite these complications, MCR-ALS allows us to propose a model of complexation for each system, and some tentative structures for the complexes. © 2006 Elsevier B.V. All rights reserved. Keywords: Heavy metals speciation; Lead; Phytochelatins; Voltammetry; Multivariate curve resolution 1. Introduction Heavy metals can cause serious damages – even at very low doses – by replacing essential elements on biological functions. This makes indispensable the heavy metal detoxification of con- taminated soils in order to avoid their entry in the trofic chain. Among the methods to remove/immobilize metals, bioremedia- tion (the process of using organisms to restore damaged areas) presents the advantages of being cheap and non-destructive to ecological systems [1]. In response to an excessive uptake of certain heavy metal ions, plants, algae and many fungi can induce the intracellular synthesis of Cys-rich polypeptides [2,3]. These peptides, named phytochelatins (PC n ), have the general structure (-Glu-Cys) n - Gly, where n can be as high as 11, but is generally in the range of 2–5. In the case of mammalians, heavy metal regulation is through metallothioneins (MT) that are also proteins with high content in thiol groups. The synthesis of PC n in plants and algae has been widely demonstrated both in laboratory cultures and in field studies, and the recent advances in the understanding of PC n biosynthesis and ∗ Corresponding author. Tel.: +34 93 402 15 45; fax: +34 93 402 12 33. E-mail address: cristina@apolo.qui.ub.es (C. Ari ˜ no). its function are derived predominantly from molecular genetic approaches using model organisms [3–6]. However, sequence of formation and final stoichiometry of PC n -metal complexes is still not totally known. By this reason, it is of great interest to study these complexation processes to understand and optimize phytoremediation. Voltammetric techniques have proved to be useful for the study of heavy metal complexation by MT [7,8] and PC n [9,10] because they allow working at the cellular concentration and because the strong dependence of voltammetric signals on the metal speciation. In fact, differential pulse polarography (DPP) provides signals for the different species of the system: free peptide, free metal ion and metal bound in different chemical environments. The application of multivariate curve resolution with alternating least squares (MCR-ALS) to DPP data allows the characterization of involved systems taking profit of its great capability to resolve highly overlapped signals [11–13]. Such approach has been satisfactorily applied in the study of Cd-PC 2 and Cd/Zn-PC 3 systems [14,15], of Cd/Zn with - and -MT domain [16] and of Zn-glutathione-fragment systems [17]. In the present paper, the complexation of PC 2 , PC 3 and two glutathione-fragments with Pb 2+ has been considered. Although Scarano and Morelli [9] induced PC n formation in algae and studied their metal complexes (including lead) by DPP or by combination of size-exclusion chromatography with off-line 0039-9140/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2006.04.006