Selenium’s Role In Mercury’s Toxicity

An analysis of how mercury interacts with sulfur, selenium, and tellurium via a protein mimic compound has provided a better understanding of the mechanism of mercury’s toxicity, according to a study by Columbia University’s Gerard Parkin, Jonathan G. Melnick, and Kevin Yurkerwich (J. Am. Chem. Soc., DOI: 10.1021/ja907523x). Mercury toxicity is typically associated with the element’s high affinity for binding sulfur in cysteine residues of proteins and enzymes. A second toxicity mechanism involves mercury’s interaction with selenium, an important antioxidant element in humans. Mercury is known to reduce the bioavailability of selenium by forming insoluble mercury selenide species and by binding to active sites of selenoenzymes. Parkin and coworkers used a tripodal mercaptoimidazolylborate ligand to study mercury’s affinity for sulfur, selenium, and tellurium. One key finding is that the Hg–Se and Hg–Te bonds are shorter than would be predicted from the covalent radii of the elements. The overall X-ray structure evidence coupled with a competitive mercury-binding study involving sulfur and selenium show that mercury’s “selenophilicity” is greater than its “thiophilicity,” Parkin says. Ligands featuring selenium and possibly tellurium may thus prove to be effective in treating mercury poisoning and prompt the design of new chelating agents, Parkin adds.