Lead(II) Complex Formation with Glutathione

A structural investigation of complexes formed between the Pb2+ ion and glutathione (GSH, denoted AH(3) in its triprotonated form), the most abundant nonprotein thiol in biological systems, was carried out for a series of aqueous solutions at pH 8.5 and CPb2+ = 10 mM and in the solid state. The Pb L-III-edge extended X-ray absorption fine structure (EXAFS) oscillation for a solid compound with the empirical formula [Pb(AH(2))]ClO4 was modeled with one Pb-S and two short Pb-O bond distances at 2.64 +/- 0.04 and 2.28 +/- 0.04 angstrom, respectively. In addition, Pb center dot center dot center dot Pb interactions at 4.15 +/- 0.05 angstrom indicate dimeric species in a network where the thiolate group forms an asymmetrical bridge between two Pb2+ ions. In aqueous solution at the mole ratio GSH/Pb-II = 2.0 (CPb2+ = 10 mM, pH 8.5), lead(II) complexes with two thiolate ligands form, characterized by a ligand-to-metal charge-transfer band (LMCT) S- -> Pb2+ at 317 nm in the UV-vis spectrum and mean Pb-S and Pb-(N/O) bond distances of 2.65 +/- 0.04 and 2.51 +/- 0.04 angstrom, respectively, from a Pb L-III-edge EXAFS spectrum. For solutions with higher mole ratios, GSH/Pb-II >= 3.0, electrospray ionization mass spectroscopy spectra identified a triglutathionyllead(II) complex, for which Pb L-III-edge EXAFS spectroscopy shows a mean Pb-S distance of 2.65 +/- 0.04 angstrom in PbS3 coordination, Pb-207 NMR spectroscopy displays a chemical shift of 2793 ppm, and in the UV-vis spectrum, an S- -> Pb2+ LMCT band appears at 335 nm. The complex persists at high excess of GSH and also at similar to 25 K in frozen glycerol (33%)/water glasses for GSH/Pb-II mole ratios from 4.0 to 10 (CPb2+. = 10 mM) measured by Pb L-III-edge EXAFS spectroscopy.