Synthesis, Spectroscopic, and X-Ray Structural Characterization of Methylmercury-D,L-Selenocysteinate Monohydrate, a Key Model for the Methylmercnry(II)-Selenoprotein Interaction

Methylmercury-D.L-selenocysteinate monohydrate complex, a key model for the methylmercury(II)-selenoprotein interaction in vivo, has been prepared via the reaction of seleno-D,L-cysteine (from prior reduction of seleno-D,L-cystine) with methylmercury(II) hydroxide and characterized by single-crystal X-ray diffractometry. The selenoamino acid is coordinated to mercury via a deprotonated selenohydryl group [Hg-Se 2.469(4)A]. A very weak intramolecular Hg...O interaction [2.93(2)A] to a carboxylate group, and a similarly weak intermolecular Hg...Se interaction [3.737(4)A] to the adjacent selenocysteine moiety, are present. Individual molecules of the complex are linked by hydrogen bonds to solvent water molecules. Infrared and Raman spectra are reported; 1H and I99Hg nuclear magnetic resonance data, together with the structural data, support the view that the selenacysteinate group interacts more strongly with CH3Hg+ than the sulfur analogue. Strong Hg-Se bonding to selenocysteinate residues may play an important role in selenium protection in biology.