On the interaction of N-acetylcysteine with Pb2 +, Zn2 +, Cd2 + and Hg2 +

The binding ability of N-acetylcysteine (NAC) towards Pb2 +, Zn2 +, Cd2 + and Hg2 + metal cations was studied by potentiometry, UV spectrophotometry and 1H NMR spectroscopy. For all the systems, very similar speciation models were obtained, with the formation of ML0, ML22 − and ML(OH)− species. Their stability was found to be quite different: as an example, at I = 0.1 mol·L− 1 and t = 25 °C, logβ (ML0) = 32.11, 7.21, 6.53 and 5.52 for Hg2 +, Pb2 +, Cd2 + and Zn2 +, respectively. The speciation models and the coordination mode of the complexes formed were discussed on the basis of spectroscopic results. The sequestering ability of NAC towards metal cations was evaluated by determining the concentration of the ligand able to complex half of the metal ion fraction (pL0.5). The values such obtained were very different, ranging from a maximum of 12.4 for Hg2 + to a minimum of 3.7 for Zn2 + (at pH = 7.4 and I = 0.15 mol·L− 1), following the order: Hg2 + ≫ Pb2 + > Cd2 + > Zn2 +.