skip to main content

DOE PAGESDOE PAGES

Title: Formation of Hg(II) tetrathiolate complexes with cysteine at neutral pH

Mercury(II) ions precipitate from aqueous cysteine (H 2Cys) solutions containing H 2Cys/Hg(II) mole ratio ≥ 2.0 as Hg( S-HCys) 2. In absence of additional cysteine, the precipitate dissolves at pH ~12 with the [Hg( S, N-Cys) 2] 2- complex dominating. With excess cysteine (H 2Cys/Hg(II) mole ratio ≥ 4.0), higher complexes form and the precipitate dissolves at lower pH values. Previously, we found that tetrathiolate [Hg( S-Cys) 4] 6- complexes form at pH = 11.0; in this work we extend the investigation to pH values of physiological interest. We examined two series of Hg(II)-cysteine solutions in which C Hg(II) varied between 8 – 9 mM and 80 – 100 mM, respectively, with H 2Cys/Hg(II) mole ratios from 4 to ~20. The solutions were prepared in the pH range 7.1 – 8.8, at the pH at which the initial Hg( S-HCys) 2 precipitate dissolved. The variations in the Hg(II) speciation were followed by 199Hg NMR, X-ray absorption and Raman spectroscopic techniques. Our results show that in the dilute solutions (C Hg(II) = 8 – 9 mM), mixtures of di-, tri- (major) and tetrathiolate complexes exist at moderate cysteine excess (C H2Cys ~ 0.16 M) at pH 7.1. In the more concentratedmore » solutions (C Hg(II) = 80 – 100 mM) with high cysteine excess (C H2Cys > 0.9 M), tetrathiolate [Hg( S-cysteinate) 4] m-6 ( m = 0 – 4) complexes dominate in the pH range 7.3 – 7.8, with lower charge than for the [Hg( S-Cys) 4] 6- complex due to protonation of some ( m) of the amino groups of the coordinated cysteine ligands. In conclusion, the results of this investigation could provide a key to the mechanism of biosorption and accumulation of Hg(II) ions in biological / environmental systems.« less
Authors:
 [1] ;  [1]
  1. Univ. of Calgary, Calgary, AB (Canada). Dept. of Chemistry
Publication Date:
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
Canadian Journal of Chemistry
Additional Journal Information:
Journal Volume: 94; Journal Issue: 4; Journal ID: ISSN 0008-4042
Publisher:
NRC Research Press
Research Org:
Univ. of Calgary, Calgary, AB (Canada)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); National Institutes of Health (NIH); Natural Sciences and Engineering Council (NSERC) of Canada
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Mercury(II); Cysteine; EXAFS; 199Hg NMR; Raman
OSTI Identifier:
1345215

Warner, Thomas, and Jalilehvand, Farideh. Formation of Hg(II) tetrathiolate complexes with cysteine at neutral pH. United States: N. p., Web. doi:10.1139/cjc-2015-0375.
Warner, Thomas, & Jalilehvand, Farideh. Formation of Hg(II) tetrathiolate complexes with cysteine at neutral pH. United States. doi:10.1139/cjc-2015-0375.
Warner, Thomas, and Jalilehvand, Farideh. 2016. "Formation of Hg(II) tetrathiolate complexes with cysteine at neutral pH". United States. doi:10.1139/cjc-2015-0375. https://www.osti.gov/servlets/purl/1345215.
@article{osti_1345215,
title = {Formation of Hg(II) tetrathiolate complexes with cysteine at neutral pH},
author = {Warner, Thomas and Jalilehvand, Farideh},
abstractNote = {Mercury(II) ions precipitate from aqueous cysteine (H2Cys) solutions containing H2Cys/Hg(II) mole ratio ≥ 2.0 as Hg(S-HCys)2. In absence of additional cysteine, the precipitate dissolves at pH ~12 with the [Hg(S,N-Cys)2]2- complex dominating. With excess cysteine (H2Cys/Hg(II) mole ratio ≥ 4.0), higher complexes form and the precipitate dissolves at lower pH values. Previously, we found that tetrathiolate [Hg(S-Cys)4]6- complexes form at pH = 11.0; in this work we extend the investigation to pH values of physiological interest. We examined two series of Hg(II)-cysteine solutions in which CHg(II) varied between 8 – 9 mM and 80 – 100 mM, respectively, with H2Cys/Hg(II) mole ratios from 4 to ~20. The solutions were prepared in the pH range 7.1 – 8.8, at the pH at which the initial Hg(S-HCys)2 precipitate dissolved. The variations in the Hg(II) speciation were followed by 199Hg NMR, X-ray absorption and Raman spectroscopic techniques. Our results show that in the dilute solutions (CHg(II) = 8 – 9 mM), mixtures of di-, tri- (major) and tetrathiolate complexes exist at moderate cysteine excess (CH2Cys ~ 0.16 M) at pH 7.1. In the more concentrated solutions (CHg(II) = 80 – 100 mM) with high cysteine excess (CH2Cys > 0.9 M), tetrathiolate [Hg(S-cysteinate)4]m-6 (m = 0 – 4) complexes dominate in the pH range 7.3 – 7.8, with lower charge than for the [Hg(S-Cys)4]6- complex due to protonation of some (m) of the amino groups of the coordinated cysteine ligands. In conclusion, the results of this investigation could provide a key to the mechanism of biosorption and accumulation of Hg(II) ions in biological / environmental systems.},
doi = {10.1139/cjc-2015-0375},
journal = {Canadian Journal of Chemistry},
number = 4,
volume = 94,
place = {United States},
year = {2016},
month = {1}
}