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.
- Research Organization:
- Univ. of Tennessee, Knoxville, TN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Biological and Environmental Research (BER)
- Contributing Organization:
- University of Tennessee
- DOE Contract Number:
- SC0004895
- OSTI ID:
- 1127445
- Report Number(s):
- DOE-TENN-4895
- Country of Publication:
- United States
- Language:
- English
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