A. Manceau J. D. Gasper J. N. Ryan G. R. Aiken K. L. Nagy 2011 <div class="article_abstract"><div class="container container_scaled-down"><div class="row"><div class="col-xs-12"><div id="abstractBox" class="article_abstract-content hlFld-Abstract"><p class="articleBody_abstractText">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 Hg₄S_<i>x</i><span>&nbsp;</span>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<span>&nbsp;</span>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.</p></div></div></div></div></div> application/pdf 10.1021/es201025v en American Chemical Society Metallothionein-like multinuclear clusters of mercury(II) and sulfur in peat article