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Talk- Deepa Devarajan

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  • cmb seminar
When Nov 27, 2017
from 11:00 AM to 12:30 PM
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Density Functional Theory Calculations of Thermodynamic Constants for Mercury Complexes: Toward a Multiscale Environmental Mercury Speciation Model


Mercury (Hg) contamination is a global challenge. Hg is present in many forms that are transported throughout in the environment. The oxidized Hg(II) form is prevalent in aquatic environments where it forms complexes with inorganic nucleophiles, low molecular weight organic compounds (LMWOC), and high molecular weight dissolved organic matter (DOM). The methylated form, methylmercury, is a neurotoxin that accumulates in living organisms throughout the food web. To fully understand Hg speciation, cycling, and transport in the environment, it is essential to understand Hg interactions at the molecular scale. Hg speciation can be characterized by the Hg-ligand thermodynamic formation constant (log K). Even with recent progress in the quantitative measurement of thermodynamic parameters, uncertainties in the experimental log K values and mechanistic models are still large for some Hg-ligand species. In this work, the uncertainties in the experimental log K values are addressed by applying state-of-the-art quantum mechanical density functional theory (DFT) calculations to compute highly accurate log K values. To benchmark our DFT method, solvation model, and thermodynamic schemes, calculations are performed for Hg-ligand complexes with definitive, high-quality, experimentally determined thermodynamic constants. The benchmarked method and scheme will then be applied to the accurate calculation of thermodynamic constants for Hg and other environmentally relevant molecular species and complexes for which no reliable experimental values exist. The long-term goal of this project is to use thermodynamic constants computed from first principles as input for larger scale speciation and reactive transport models.




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