Methylmercury(II) Selenolates. Synthesis and Characterization of MeHgSeMe and MeHgSePh, and 1H and 199Hg nmr Studies of Ligand Exchange in MeHg(II) Thiolates and Selenolates, Including Amino Acid Complexes

Selenium has a protective effect in methylmercury poisoning, but possible chemical interactions between MeHg(II) and various chemical forms of selenium occurring in vivo have not been fully elucidated. A possible interaction is that between MeHg(II) and selenohydryl amino acids or selenohydryl groups in proteins, as methylmercury is known to bind to sulfhydryl groups in vivo, e.g. glutathione groups in red blood cells, and seleno-cysteine occurs in some enzymes, e.g. glutathione peroxidase. The complexes MeHgSeMe and MeHgSePh have been prepared and characterized, and the solution chemistry of methylmercury(II) selenolates compared with that of MeHg(II) thiolates by 1H and 199Hg nuclear magnetic resonance studies of exchange equilibria. 1H NMR studies allow determination of lifetimes between exchanges for components of equilibria in dimethylformamide and water. with equivalent concentrations of MeHgCN and MeHgXR. For the amino acid complexes in equilibria, the selenocysteine complex exchanges with a lifetime of about 50 msec at 45°C, approximately one-half that for the slower exchange observed for thiolates. 199Hg nNMR spectra are reported for all of the aforementioned complexes, and for equilibria.