Sequestering ability of some chelating agents towards methylmercury(II)

Area of Science:

• Environmental Chemistry
• Coordination Chemistry
• Toxicology

Background:

• Methylmercury (CH(3)Hg(+)) is a potent neurotoxin with significant environmental and health implications.
• Understanding its complexation behavior with various ligands is crucial for assessing its environmental fate and developing remediation strategies.
• Ligand speciation and complex formation influence methylmercury's bioavailability and toxicity.

Purpose of the Study:

• To investigate the speciation and complex formation of methylmercury(II) cation with a diverse set of sulfur, nitrogen, and oxygen donor ligands.
• To evaluate the sequestering ability of these ligands towards methylmercury in aqueous solutions.
• To elucidate the structural aspects and stability of the formed methylmercury-ligand complexes.

Main Methods:

• Potentiometric, calorimetric, and UV spectrophotometric measurements were employed to study complex formation.
• Electrospray mass spectrometry was used to identify complex species in solution.
• Speciation models were developed to describe the interactions under varying conditions (ionic strength, temperature, pH).

Main Results:

• Sulfur donor ligands (thiolactic acid, 3-mercaptopropanoic acid, thiomalic acid, D,L-penicillamine, L-cysteine, glutathione) demonstrated significant methylmercury sequestering power (10(-11) mol L(-1) range).
• The sequestering ability of sulfur ligands followed the trend: MPA(2-) < PSH(2-) < GSH(3-) < TLA(2-) < CYS(2-) < TMA(3-).
• Nitrogen and oxygen donor ligands (mellitic acid, spermine, EDTA) exhibited substantially lower sequestering abilities (10(-3)-10(-5) mol L(-1) range).

Conclusions:

• Sulfur-containing ligands are highly effective in sequestering methylmercury(II) cation in aqueous environments.
• The speciation and stability of methylmercury complexes are highly dependent on the nature of the donor atoms and ligand structure.
• These findings provide valuable insights for predicting methylmercury's environmental behavior and designing effective chelating agents for remediation.