Methylmercury(II) complexes with tryptophan and its <i>N</i>-acetyl derivative

Abstract

CH 3 HgOH reacts with tryptophan in aqueous ethanol to form a 2:1 neutral complex in which CH 3 Hg groups are bound to the terminal amino group and to the deprotonated indole nitrogen. When this complex is dissolved in water, 1 H and 13 C nuclear magnetic resonance show that the indole CH 3 Hg group hydrolyzes, leading to an amino-bound 1:1 species. Under the same conditions, N-acetyltryptophan forms a neutral 1:1 compound where the metal is bound to a carboxylate oxygen, and a neutral 2:1 complex in which an extra CH 3 Hg group is fixed to the deprotonated indole ring. It is shown by 1 H and 13 C nuclear magnetic resonance that the 1:1 species is stable in DMSO-d 6 , but that the 2:1 compound is readily hydrolyzed to the 1:1 compound by traces of water. The solid-state infrared and Raman spectra are discussed. In the crystal structure of the 2:1 tryptophan complex, the ligand adopts a conformation favoring a short intramolecular π interaction between Hg and the indole ring. No such π interaction is found in the crystal structure of the 1:1 carboxylate-bonded complex with acetyltryptophan.