Mercury Complexes with Tripodal Pseudopeptides Derived from D-Penicillamine Favour a HgS3 Coordination

Abstract : The pseudopeptides L-4 and L-5 are built on a nitrilotriacetic scaffold and functionalized with three D-penicillamine (D-Pen) units. D-Pen is an interesting building block and a bulkier analogue of cysteine with the -methylene hydrogen atoms replaced by larger methyl groups. The two sulfur ligands L-4 and L-5 are studied here with the toxic Hg-II ion. The formation of the two mononuclear complexes HgL4 and HgL5 is demonstrated by H-1 NMR spectroscopy and mass spectrometry and the tristhiolato coordination is unambiguously evidenced by the UV absorption signatures. An important feature is the stabilization of the HgS3 coordination mode at the expense of the generally preferred HgS2 linear coordination. It appears that the hindered D-Pen pseudopeptide L-5 is capable of stabilizing the unusual HgS3 coordination over a large pH range in water, pH> 5.5. This water-soluble compound can therefore be considered as a promising chelating agent for mercury detoxification.