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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 ?((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 ?((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.

SUBMITTER: Leung BO

PROVIDER: S-EPMC3684387 | biostudies-literature | 2013 Apr

REPOSITORIES: biostudies-literature

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Silver(I) complex formation with cysteine, penicillamine, and glutathione.

Leung Bonnie O BO Jalilehvand Farideh F Mah Vicky V Parvez Masood M Wu Qiao Q

Inorganic chemistry 20130404 8

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 ...[more]

PMID: 23556419

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Project description:The complex formation between cadmium(II) and the ligands cysteine (H(2)Cys) and penicillamine (H(2)Pen = 3,3'-dimethylcysteine) in aqueous solutions, having C(Cd(II)) approximately 0.1 mol dm(-3) and C(H(2)L) = 0.2-2 mol dm(-3), was studied at pH = 7.5 and 11.0 by means of (113)Cd NMR and Cd K- and L(3)-edge X-ray absorption spectroscopy. For all cadmium(II)-cysteine molar ratios, the mean Cd-S and Cd-(N/O) bond distances were found in the ranges 2.52-2.54 and 2.27-2.35 A, respectively. The corresponding cadmium(II)-penicillamine complexes showed slightly shorter Cd-S bonds, 2.50-2.53 A, but with the Cd-(N/O) bond distances in a similar wide range, 2.28-2.33 A. For the molar ratio C(H(2)L)/C(Cd(II)) = 2, the (113)Cd chemical shifts, in the range 509-527 ppm at both pH values, indicated complexes with distorted tetrahedral CdS(2)N(N/O) coordination geometry. With a large excess of cysteine (molar ratios C(H(2)Cys)/C(Cd(II)) >or= 10), complexes with CdS(4) coordination geometry dominate, consistent with the (113)Cd NMR chemical shifts, delta approximately 680 ppm at pH 7.5 and 636-658 ppm at pH 11.0, and their mean Cd-S distances were 2.53 +/- 0.02 A. At pH 7.5, the complexes are almost exclusively sulfur-coordinated as [Cd(S-cysteinate)(4)](n-), while at higher pH, the deprotonation of the amine groups promotes chelate formation. At pH 11.0, a minor amount of the [Cd(Cys)(3)](4-) complex with CdS(3)N coordination is formed. For the corresponding penicillamine solutions with molar ratios C(H(2)Pen)/C(Cd(II)) >or= 10, the (113)Cd NMR chemical shifts, delta approximately 600 ppm at pH 7.5 and 578 ppm at pH 11.0, together with the average bond distances, Cd-S 2.53 +/- 0.02 A and Cd-(N/O) 2.30-2.33 A, indicate that [Cd(penicillaminate)(3)](n-) complexes with chelating CdS(3)(N/O) coordination dominate already at pH 7.5 and become mixed with CdS(2)N(N/O) complexes at pH 11.0. The present study reveals differences between cysteine and penicillamine as ligands to the cadmium(II) ion that can explain why cysteine-rich metallothionines are capable of capturing cadmium(II) ions, while penicillamine, clinically useful for treating the toxic effects of mercury(II) and lead(II) exposure, is not efficient against cadmium(II) poisoning.

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Silver(I) complex formation with cysteine, penicillamine, and glutathione.

Publications

Silver(I) complex formation with cysteine, penicillamine, and glutathione.

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