Researchers from Sweden and Vietnam developed a sensitive and selective method for the speciation of methylmercury-thiol complexes found in the extracellular milieu of methylating bacteria.
Methylmercury (MeHg) is one of the most potent neurotoxins. Humans are exposed to MeHg mainly via seafood and rice consumption. Mercury speciation in environmental and biological systems is dominated by complexes with sulfide, and low or high molecular mass thiols. Low molecular mass (LMM) thiols are important for biological processes due to their ability to form metal complexes and subsequent biotransformation through redox reactions mediated by enzymatic activities. Significant increases in the Hg(II) biomethylation rates and subsequent cellular export have been observed in the presence of specific LMM thiols. Despite the evidence of the important role of LMM thiols for the mercury cycling, their specific interaction in the environment and biological systems remains poorly investigated. In such systems, many different LMM thiol compounds are present, calling for a highly selective and sensitive method for the determination of MeHg-thiol complexes. The new study:
Researchers from Sweden and Vietnam developed a speciation method based on liquid chromatography (LC) coupled with electrospray ionization (ESI) triple quadrupole tandem mass spectrometry (ESI-MS/MS). For obtaining limits of detection (LODs) at the pM level, the method was combined with online preconcentration by solid-phase extraction (SPE) under optimized conditions. Among three different SPE materials, a weak cation exchange phase (Oasis WCX) showed the best efficiency at a low pH of 2.5, improving the LODs by a factor of 70.
The different MeHg-thiol complexes found in bacteria cell cultures were identified by their accurate mass and typical fragmentation patterns. The selected reaction monitoring (SRM) mode was applied for quantification. Using the developed method, the researchers report the presence of MeHg-cysteine, MeHg-cysteamine, MeHg-penicillamine, MeHg-cysteinylglycine, and MeHgglutamylcysteine as the predominant MeHg–thiol complexes in the extracellular milieu of an important HgII methylating bacterium, Geobacter sulfurreducens PCA, exposed to 100 nM of HgII.
The authors also investigated the stability of the complexes and found that all investigated complexes were stable for at least 2 weeks at room temperature.
The original publication:
Van Liem-Nguyen, Hoang-Tung Nguyen-Ngoc, Gbotemi A. Adediran, Erik Björn, Determination of picomolar levels of methylmercury complexes with low molecular mass thiols by liquid chromatography tandem mass spectrometry and online preconcentration
, Anal. Bioanal. Chem., 412 (2020) 1619–1628. DOI: 10.1007/s00216-020-02389-y
Used techniques and instrumentation:
Van Liem-Nguyen, Ulf Skyllberg, Erik Björn, Thermodynamic Modeling of the Solubility and Chemical Speciation of Mercury and Methylmercury Driven by Organic Thiols and Micromolar Sulfide Concentrations in Boreal Wetland Soils
, Environ. Sci. Technol., 51/7 (2017) 3678-3686. DOI: 10.1021/acs.est.6b04622
Van Liem-Nguyen, Ulf Skyllberg, Erik Björn, Thermodynamic stability of mercury (II) complexes formed with environmentally relevant low-molecular-mass thiols studied by competing ligand exchange and density functional theory
. Environ. Chem., 14/4 (2017) 243–53. DOI: 10.1071/EN17062
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last time modified: March 23, 2020