Similarities between N-Acetylcysteine and Glutathione in Binding to Lead(II) Ions

N-Acetylcysteine is a natural thiol-containing antioxidant, a precursor for cysteine and glutathione, and a potential detoxifying agent for heavy metal ions. However, previous accounts of the efficiency of N-acetylcysteine (H2NAC) in excretion of lead are few and contradicting. Here, we report results on the nature of lead(II) complexes formed with N-acetylcysteine in aqueous solution, which were obtained by combining information from several spectroscopic methods, including (207)Pb, (13)C, and (1)H NMR, Pb LIII-edge X-ray absorption, ultraviolet-visible (UV-vis) spectroscopy, and electro-spray ionization mass spectrometry (ESI-MS). Two series of solutions were used containing CPb(II) = 10 and 100 mM, respectively, varying the H2NAC/Pb(II) mole ratios from 2.1 to 10.0 at pH 9.1-9.4. The coordination environments obtained resemble those previously found for the Pb(II) glutathione system: at a ligand-to-lead mole ratio of 2.1, dimeric or oligomeric Pb(II) N-acetylcysteine complexes are formed, while a trithiolate [Pb(NAC)3](4-) complex dominates in solutions with H2NAC/Pb(II) mole ratios >3.0.