Journal
INORGANIC CHEMISTRY
Volume 52, Issue 8, Pages 4593-4602Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ic400192c
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Funding
- National Institutes of Health, National Center for Research Resources, Biomedical Technology Program
- Department of Energy, Office of Biological and Environmental Research [2848]
- Natural Sciences and Engineering Council (NSERC) of Canada
- Canadian Foundation for Innovation (CFI)
- Alberta Science and Research Investment Program (ASRIP)
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The complex formation between silver(I) and cysteine (H(2)Cys), penicillamine (H(2)Pen), and glutathione (H(3)Glu) in alkaline aqueous solution was examined using extended Xray absorption fine structure (EXAFS) and Ag-109 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 angstrom consistently emerged, while for penicillamine (pH 9) the average Ag-S bond distance gradually increased from 2.40 to 2.44 +/- 0.02 angstrom. EXAFS and Ag-109 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 A and delta(Ag-109) 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 angstrom and delta(Ag-109) 922 ppm indicate that mononuclear AgS2 coordinated complexes dominate. For Ag(I)-glutathione solutions (C-Ag(I) = 0.01 mol dm(-3), pH similar to 11), mononuclear AgS2 coordinated species with a mean Ag-S bond distance of 2.36 +/- 0.02 angstrom dominate for L/Ag mole ratios from 2.0 to 10.0. The crystal structure of the silver(I)-cysteine compound (NH4)Ag-2(HCys)(Cys)center dot G(2)O (1) precipitating at pH similar to 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)center dot 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 Ag-109 NMR chemical shifts, to assist assignments of the Ag(I) coordination in solution.
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