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Title: Molecular Mechanisms of Bacterial Mercury Transformation

Mercury (Hg) is a major global pollutant arising from both natural and anthropogenic sources. Defining the factors that determine the relative affinities of different ligands for the mercuric ion, Hg2+, is critical to understanding its speciation, transformation, and bioaccumulation in the environment. Here, we used quantum chemistry to dissect the relative binding free energies for a series of inorganic anion complexes of Hg2+. The results show that, whereas in the gas phase the binding affinity of two identical anionic ligands (forming HgL2) increases with ligand (L–) hardness, in contrast, in the aqueous phase the affinity increases with ligand softness. This switch in affinity upon hydration is shown to result mostly from interactions with only a small number (e.g. one or two) of water molecules. The results yield a clear, robust periodic trend within the chalcogenide and halide groups and are in agreement with the well-known experimentally observed preference of Hg2+ for soft ligands. By comparing the Hg2+ binding of one with two anions, the gas phase preferences are found to arise from the enhancement of reactivity of the cationic complex (HgL+) with the hardness of L–. The approach establishes a theoretical basis for understanding Hg speciation in the biosphere.
Authors:
Publication Date:
OSTI Identifier:
1127445
Report Number(s):
DOE-TENN-4895
DOE Contract Number:
SC0004895
Resource Type:
Technical Report
Research Org:
University of Tennessee
Sponsoring Org:
USDOE; USDOE Office of Science (SC); USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Contributing Orgs:
University of Tennessee
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES mercury, computational science