Degradation mechanism of methyl mercury selenoamino acid complexes

A computational study

Abu Asaduzzaman, Georg Schreckenbach

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

Density functional theory (DFT) calculations have been carried out on the possible degradation/demethylation mechanism of methyl mercury (CH 3Hg+) complexes with free cysteine and seleonocysteine. The binding of CH3Hg+ ions with one (seleno)amino acid is thermodynamically favorable. However, the binding with another acid molecule is a highly unfavorable process. The CH3Hg-(seleno)cysteinate then degrades to bis(methylmercuric)sulphide (selenide for the Se-containing complex) which in turn forms dimethyl mercury and HgS/HgSe, the latter being precipitated out as nanoparticles. The dimethyl mercury interacts with water molecules and regenerates the CH3HgOH precursor. The calculated free energies of formation confirm the thermodynamic feasibility of every intermediate step of the degradation cycle and fully support earlier experimental results. In completing the cycle, one unit of mercury precipitates out from two units of sources, and thereby Se antagonizes the Hg toxicity. The degradation of CH3Hg-L-cysteinate is thermodynamically more favorable than the formation of CH3Hg-L-cysteinate. The preferred degradation of the CH3Hg-L-cysteinate suggests that another mechanism for CH 3Hg to cross the blood-brain barrier should exist.

Original languageEnglish (US)
Pages (from-to)2366-2372
Number of pages7
JournalInorganic Chemistry
Volume50
Issue number6
DOIs
StatePublished - Mar 21 2011

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Mercury
degradation
Degradation
acids
Acids
methylidyne
blood-brain barrier
cycles
Molecules
selenides
cysteine
Sulfides
energy of formation
toxicity
Free energy
Density functional theory
Cysteine
amino acids
Toxicity
sulfides

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

Cite this

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abstract = "Density functional theory (DFT) calculations have been carried out on the possible degradation/demethylation mechanism of methyl mercury (CH 3Hg+) complexes with free cysteine and seleonocysteine. The binding of CH3Hg+ ions with one (seleno)amino acid is thermodynamically favorable. However, the binding with another acid molecule is a highly unfavorable process. The CH3Hg-(seleno)cysteinate then degrades to bis(methylmercuric)sulphide (selenide for the Se-containing complex) which in turn forms dimethyl mercury and HgS/HgSe, the latter being precipitated out as nanoparticles. The dimethyl mercury interacts with water molecules and regenerates the CH3HgOH precursor. The calculated free energies of formation confirm the thermodynamic feasibility of every intermediate step of the degradation cycle and fully support earlier experimental results. In completing the cycle, one unit of mercury precipitates out from two units of sources, and thereby Se antagonizes the Hg toxicity. The degradation of CH3Hg-L-cysteinate is thermodynamically more favorable than the formation of CH3Hg-L-cysteinate. The preferred degradation of the CH3Hg-L-cysteinate suggests that another mechanism for CH 3Hg to cross the blood-brain barrier should exist.",
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Degradation mechanism of methyl mercury selenoamino acid complexes : A computational study. / Asaduzzaman, Abu; Schreckenbach, Georg.

In: Inorganic Chemistry, Vol. 50, No. 6, 21.03.2011, p. 2366-2372.

Research output: Contribution to journalArticle

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AB - Density functional theory (DFT) calculations have been carried out on the possible degradation/demethylation mechanism of methyl mercury (CH 3Hg+) complexes with free cysteine and seleonocysteine. The binding of CH3Hg+ ions with one (seleno)amino acid is thermodynamically favorable. However, the binding with another acid molecule is a highly unfavorable process. The CH3Hg-(seleno)cysteinate then degrades to bis(methylmercuric)sulphide (selenide for the Se-containing complex) which in turn forms dimethyl mercury and HgS/HgSe, the latter being precipitated out as nanoparticles. The dimethyl mercury interacts with water molecules and regenerates the CH3HgOH precursor. The calculated free energies of formation confirm the thermodynamic feasibility of every intermediate step of the degradation cycle and fully support earlier experimental results. In completing the cycle, one unit of mercury precipitates out from two units of sources, and thereby Se antagonizes the Hg toxicity. The degradation of CH3Hg-L-cysteinate is thermodynamically more favorable than the formation of CH3Hg-L-cysteinate. The preferred degradation of the CH3Hg-L-cysteinate suggests that another mechanism for CH 3Hg to cross the blood-brain barrier should exist.

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