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Title: Quantum Chemical Approach for Calculating Stability Constants of Mercury Complexes

Abstract

Stability constants are central to the multi-scale modeling of the thermodynamic speciation, cycling, and transport of mercury (Hg) and other contaminants in aquatic environments. However, for Hg, experimental values for many relevant complexes are not available, and for others can span ranges in excess of 10 log units. The missing data and large uncertainties mean there are significant knowledge gaps in predictions of thermodynamic speciation. As an alternative to experimental measurements, thermodynamic quantities can be calculated with quantum chemical methods. Among these, density functional theory (DFT) with a polarizable continuum solvent combines accuracy with practicability. In this paper, we present an accurate and quick approach in which we use DFT with continuum solvation to calculate stability constants of Hg complexes with inorganic and low molecular-weight organic ligands in aqueous solution. Specifically, we use the M06/[SDD]6-31+G(d,p) level of theory in combination with a modified version of the SMD solvent model in which the solute radii are re-optimized with a scaled solvent-accessible surface (sSAS) approach. For the set of 37 Hg complexes used for optimization, which contain environmentally relevant functional groups and have reliable experimental stability constants, we obtain a mean unsigned error of 1.4 log units. Testing the method on anmore » independent set of 12 Hg complexes reproduces the experimental stability constants to a mean unsigned error of 1.6 log units. Finally, this approach is a substantial step toward generally applicable rapid stability constant derivation for a wide range of Hg complexes, including those present in dissolved organic matter.« less

Authors:
 [1];  [2];  [3];  [2];  [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). UT/ORNL Center for Molecular Biophysics. Biosciences Division; Univ. of Tennessee, Knoxville, TN (United States). Dept. of Biochemistry and Cellular and Molecular Biology
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). UT/ORNL Center for Molecular Biophysics. Biosciences Division
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Environmental Sciences Division
Publication Date:
Research Org.:
Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
OSTI Identifier:
1475452
Alternate Identifier(s):
OSTI ID: 1504015
Grant/Contract Number:  
SC0016478; AC05-00OR22725
Resource Type:
Accepted Manuscript
Journal Name:
ACS Earth and Space Chemistry
Additional Journal Information:
Journal Volume: 2; Journal Issue: 11; Journal ID: ISSN 2472-3452
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; stability constants; mercury; DFT; continuum models; functional groups of dissolved organic matter

Citation Formats

Devarajan, Deepa, Lian, Peng, Brooks, Scott C., Parks, Jerry M., and Smith, Jeremy C. Quantum Chemical Approach for Calculating Stability Constants of Mercury Complexes. United States: N. p., 2018. Web. doi:10.1021/acsearthspacechem.8b00102.
Devarajan, Deepa, Lian, Peng, Brooks, Scott C., Parks, Jerry M., & Smith, Jeremy C. Quantum Chemical Approach for Calculating Stability Constants of Mercury Complexes. United States. doi:10.1021/acsearthspacechem.8b00102.
Devarajan, Deepa, Lian, Peng, Brooks, Scott C., Parks, Jerry M., and Smith, Jeremy C. Fri . "Quantum Chemical Approach for Calculating Stability Constants of Mercury Complexes". United States. doi:10.1021/acsearthspacechem.8b00102. https://www.osti.gov/servlets/purl/1475452.
@article{osti_1475452,
title = {Quantum Chemical Approach for Calculating Stability Constants of Mercury Complexes},
author = {Devarajan, Deepa and Lian, Peng and Brooks, Scott C. and Parks, Jerry M. and Smith, Jeremy C.},
abstractNote = {Stability constants are central to the multi-scale modeling of the thermodynamic speciation, cycling, and transport of mercury (Hg) and other contaminants in aquatic environments. However, for Hg, experimental values for many relevant complexes are not available, and for others can span ranges in excess of 10 log units. The missing data and large uncertainties mean there are significant knowledge gaps in predictions of thermodynamic speciation. As an alternative to experimental measurements, thermodynamic quantities can be calculated with quantum chemical methods. Among these, density functional theory (DFT) with a polarizable continuum solvent combines accuracy with practicability. In this paper, we present an accurate and quick approach in which we use DFT with continuum solvation to calculate stability constants of Hg complexes with inorganic and low molecular-weight organic ligands in aqueous solution. Specifically, we use the M06/[SDD]6-31+G(d,p) level of theory in combination with a modified version of the SMD solvent model in which the solute radii are re-optimized with a scaled solvent-accessible surface (sSAS) approach. For the set of 37 Hg complexes used for optimization, which contain environmentally relevant functional groups and have reliable experimental stability constants, we obtain a mean unsigned error of 1.4 log units. Testing the method on an independent set of 12 Hg complexes reproduces the experimental stability constants to a mean unsigned error of 1.6 log units. Finally, this approach is a substantial step toward generally applicable rapid stability constant derivation for a wide range of Hg complexes, including those present in dissolved organic matter.},
doi = {10.1021/acsearthspacechem.8b00102},
journal = {ACS Earth and Space Chemistry},
number = 11,
volume = 2,
place = {United States},
year = {2018},
month = {9}
}

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