A multinuclear NMR study of the complexation of W(VI) with meso-2,3-dimercaptosuccinic acid (DMSA)

Abstract

Meso-2,3-dimercaptosuccinic acid (DMSA), which is used as an antidote for heavy metal poisoning and in complexes of 99mTc for diagnostic purposes, forms several complexes with tungsten(VI) in aqueous solutions, as found by 1H, 13C, 17O and 183W NMR spectroscopy. In the pH range ~4-7, there are four complexes in which the acid acts as a bidentate ligand through one carboxyl group and the adjacent sulfhydryl group (a dominant 2:2 species and three 1:2 metal-ligand isomers are proposed) and 2:1 complexes in which the ligand is twisted in order to use the four binding groups. It is proposed that in both the 2:2 and 2:1 cases the S atoms bridge the two W atoms. At lower pH, the acid is again predominantly a tetradentate ligand in m:n associations with the metal (m>n).