title: 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 (S(red)/Hg) between 220 and 1140, is a Hg(4)S(x) 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 S(red)/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 S(red)/Hg of about 10 to 20, the new structures support a continuum in Hg-SR binding strength in natural organic matter.
authors.affiliation: Department of Earth and Environmental Sciences, MC-186, 845 West Taylor Street, University of Illinois at Chicago, Chicago, Illinois 60607, United States. klnagy@uic.edu
authors.forename: Kathryn L
authors.initials: KL
authors.lastname: Nagy
authors.forename: Alain
authors.initials: A
authors.lastname: Manceau
authors.forename: Jarrod D
authors.initials: JD
authors.lastname: Gasper
authors.forename: Joseph N
authors.initials: JN
authors.lastname: Ryan
authors.forename: George R
authors.initials: GR
authors.lastname: Aiken
mesh_terms: D000818:Animals; D005431:Florida; D008628:Mercury / Q000737:chemistry*; D008668:Metallothionein / Q000737:chemistry*; D008958:Models, Molecular; D012987:Soil / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000737:chemistry; D013455:Sulfur / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy / Q000379:methods
chemical_list: D012987:Soil; D013438:Sulfhydryl Compounds; D013455:Sulfur; D008668:Metallothionein; D008628:Mercury