title: Silver(I) complex formation with cysteine, penicillamine, and glutathione.
abstract: The complex formation between silver(I) and cysteine (H2Cys), penicillamine (H2Pen), and glutathione (H3Glu) in alkaline aqueous solution was examined using extended X-ray absorption fine structure (EXAFS) and (109)Ag NMR spectroscopic techniques. The complexes formed in 0.1 mol dm(-3) Ag(I) solutions with cysteine and penicillamine were investigated for ligand/Ag(I) (L/Ag) mole ratios increasing from 2.0 to 10.0. For the series of cysteine solutions (pH 10-11) a mean Ag-S bond distance of 2.45 ± 0.02 Å consistently emerged, while for penicillamine (pH 9) the average Ag-S bond distance gradually increased from 2.40 to 2.44 ± 0.02 Å. EXAFS and (109)Ag NMR spectra of a concentrated Ag(I)-cysteine solution (C(Ag(I)) = 0.8 mol dm(-3), L/Ag = 2.2) showed a mean Ag-S bond distance of 2.47 ± 0.02 Å and δ((109)Ag) 1103 ppm, consistent with prevailing, partially oligomeric AgS3 coordinated species, while for penicillamine (C(Ag(I)) = 0.5 mol dm(-3), L/Ag = 2.0) the mean Ag-S bond distance of 2.40 ± 0.02 Å and δ((109)Ag) 922 ppm indicate that mononuclear AgS2 coordinated complexes dominate. For Ag(I)-glutathione solutions (C(Ag(I)) = 0.01 mol dm(-3), pH ∼11), mononuclear AgS2 coordinated species with a mean Ag-S bond distance of 2.36 ± 0.02 Å dominate for L/Ag mole ratios from 2.0 to 10.0. The crystal structure of the silver(I)-cysteine compound (NH4)Ag2(HCys)(Cys)·H2O (1) precipitating at pH ∼10 was solved and showed a layer structure with both AgS3 and AgS3N coordination to the cysteinate ligands. A redetermination of the crystal structure of Ag(HPen)·H2O (2) confirmed the proposed digonal AgS2 coordination environment to bridging thiolate sulfur atoms in polymeric intertwining chains forming a double helix. A survey of Ag-S bond distances for crystalline Ag(I) complexes with S-donor ligands in different AgS2, AgS2(O/N), and AgS3 coordination environments was used, together with a survey of (109)Ag NMR chemical shifts, to assist assignments of the Ag(I) coordination in solution.
authors.affiliation: Department of Chemistry, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
authors.forename: Bonnie O
authors.initials: BO
authors.lastname: Leung
authors.forename: Farideh
authors.initials: F
authors.lastname: Jalilehvand
authors.forename: Vicky
authors.initials: V
authors.lastname: Mah
authors.forename: Masood
authors.initials: M
authors.lastname: Parvez
authors.forename: Qiao
authors.initials: Q
authors.lastname: Wu
mesh_terms: D056831:Coordination Complexes / Q000737:chemistry*; D003545:Cysteine / Q000737:chemistry*; D005978:Glutathione / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010396:Penicillamine / Q000737:chemistry*; D012834:Silver / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D056831:Coordination Complexes; D012834:Silver; D005978:Glutathione; D010396:Penicillamine; D003545:Cysteine
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