Binding of Hg2+ with Phytochelatins: Study by Differential Pulse Voltammetry on Rotating Au-Disk Electrode, Electrospray Ionization Mass-Spectrometry, and Isothermal Titration Calorimetry

The binding of Hg2+ with synthetic phytochelatins ((gamma-Glu-Cys)(n)-Gly, PCn, n = 2, 3, 4) was investigated by a recently proposed electroanalytical method, using differential pulse voltammetry on the rotating Au-disk electrode, Electrospray ionization mass-spectrometry (ESI-MS) and isothermal titration calorimetry (ITC). ESI-MS experiments provided the exact stoichiometries of the complexes formed at different PCn/Hg2+ ratios. Voltammetry provided more detailed information on the complexation processes through the use of multivariate curve resolution by alternating least squares of the data matrix obtained from titrations with fine increments of metal or ligand. The system Hg2+-GSH-PC2 Was investigated by voltammetry in order to obtain an estimation of the Hg2+ behavior in the presence of two related ligands. The additional assessment of the stability of Hg2+-PCn complexes was achieved through ITC by using the therapeutic chelator sodium 2,3-dimercaptopropanesulfate (DMPS) over Hg2+-PCn systems. The stability of various Hg2+-PCn complexes and the ability of DMPS to replace PCn from these complexes were examined.