Lead(II) binding to the chelating agent D-penicillamine in aqueous solution.
A spectroscopic investigation of the complexes formed between the Pb(II) ion and D-penicillamine (H2Pen), a chelating agent used in the treatment of lead poisoning, was carried out on two sets of alkaline aqueous solutions with CPb(II) ≈ 10 and 100 mM, varying the H2Pen/Pb(II) molar ratio (2.0, 3.0, 4.0, 10.0). Ultraviolet-visible (UV-vis) spectra of the 10 mM Pb(II) solutions consistently showed an absorption peak at 298 nm for S(-) → Pb(II) ligand-to-metal charge-transfer. The downfield (13)C NMR chemical shift for the penicillamine COO(-) group confirmed Pb(II) coordination. The (207)Pb NMR chemical shifts were confined to a narrow range between 1806 ppm and 1873 ppm for all Pb(II)-penicillamine solutions, indicating only small variations in the speciation, even in large penicillamine excess. Those chemical shifts are considerably deshielded, relative to the solid-state (207)Pb NMR isotropic chemical shift of 909 ppm obtained for crystalline penicillaminatolead(II) with Pb(S,N,O-Pen) coordination. The Pb LIII-edge extended X-ray absorption fine structure (EXAFS) spectra obtained for these solutions were well-modeled with two Pb-S and two Pb-(N/O) bonds with mean distances 2.64 ± 0.04 Å and 2.45 ± 0.04 Å, respectively. The combined spectroscopic results, reporting δ((207)Pb) ≈ 1870 ppm and λmax ≈ 298 nm for a Pb(II)S2NO site, are consistent with a dominating 1:2 lead(II):penicillamine complex with [Pb(S,N,O-Pen)(S-HnPen)](2-n) (n = 0-1) coordination in alkaline solutions, and provide useful structural information on how penicillamine can function as an antidote against lead toxicity in vivo.
Department of Chemistry, University of Calgary , 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada.
Natalie S
NS
Sisombath
Farideh
F
Jalilehvand
Adam C
AC
Schell
Qiao
Q
Wu
D002614:Chelating Agents / Q000737:chemistry*; D007854:Lead / Q000737:chemistry*; D015394:Molecular Structure; D010396:Penicillamine / Q000737:chemistry*; D012996:Solutions; D021241:Spectrometry, Mass, Electrospray Ionization; D013054:Spectrophotometry, Atomic; D014867:Water / Q000737:chemistry*
D002614:Chelating Agents; D012996:Solutions; D014867:Water; D007854:Lead; D010396:Penicillamine