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Metallothionein-Like Multinuclear Clusters of Mercury(II) and Sulfur in Peat

Abstract : Strong mercury(II)-sulfur (Hg-SR) bonds in natural organic matter, which influence mercury bioavailability, are difficult to characterize. We report evidence for two new Hg-SR structures using X-ray absorption spectroscopy in peats from the Florida Everglades with added Hg. The first, observed at a mole ratio of organic reduced S to Hg (Sred/Hg) between 220 and 1140, is a Hg4Sx type of cluster with each Hg atom bonded to two S atoms at 2.34 Å and one S at 2.53 Å, and all Hg atoms 4.12 Å apart. This model structure matches those of metal-thiolate clusters in metallothioneins, but not those of HgS minerals. The second, with one S atom at 2.34 Å and about six C atoms at 2.97 to 3.28 Å, occurred at Sred/Hg between 0.80 and 4.3 and suggests Hg binding to a thiolated aromatic unit. The multinuclear Hg cluster indicates a strong binding environment to cysteinyl sulfur that might impede methylation. Along with a linear Hg(SR)2 unit with Hg--S bond lengths of 2.34 Å at Sred/Hg of about 10 to 20, the new structures support a continuum in Hg-SR binding strength in natural organic matter.
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Submitted on : Wednesday, March 21, 2012 - 12:11:37 PM
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Kathryn L. Nagy, Alain Manceau, Jarrod D. Gasper, Joseph N. Ryan, G. R. Aiken. Metallothionein-Like Multinuclear Clusters of Mercury(II) and Sulfur in Peat. Environmental Science and Technology, American Chemical Society, 2011, 45 (17), pp.7298-7306. ⟨10.1021/es201025v⟩. ⟨insu-00681353⟩



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