Amide group coordination to the Hg2+ ion. Potentiometric, H-1 NMR and structural study on Hg2+-N-protected amino acid systems

The binary complexes of Hg2+ formed by N-carbonyl and N-sulfonyl amino acid s, which are ligands containing peptide and sulfonamide groups respectively , are investigated in aqueous solution by H-1 NMR, UV spectroscopy and pote ntiometry. The corresponding ternary systems with 2,2'-bipyridine are studi ed in aqueous solution by potentiometry and in DMSO solutions by H-1-NMR. A ll the amino acids behave as simple carboxylate ligands at acid pH, while, around neutrality, N-p-tolylsulfonylglycine (tsglyH(2)), N-p-tolylsulfonyl- beta -alanine (ts-beta -alaH(2)) and N-2-nitrophenylsulfonylglycine (NO(2)p sglyH(2)) switch to dianionic N,O-bidentate chelating ligands due to the in volvement of the deprotonated amide nitrogen as an additional donor site. T he Hg2+ ion is ineffective in promoting peptide nitrogen deprotonation in N -benzoylglycine (bzglyH). The binary and ternary species formed in aqueous solution and their stability constants are determined and compared with tho se of the homologous complexes of Pd2+, Cu2+, Cd2+ and Pb2+. The molecular structure of [Hg(bpy)(2)(NO2-psgly-N,O)].0.5H(2)O is determined by X-ray cr ystallography. It represents a rare example of Hg2+ N,O coordination by an amino acid molecule. In the complex Hg2+ shows a distorted octahedral envir onment with a N5O donor set. Four nitrogen atoms are derived from the two b py ligands, while the oxygen and the fifth nitrogen are from the NO2-psgly dianion. New information on the solution and solid state chemistry of Hg2with ligands of biological interest is provided which may be of great relev ance in understanding the mechanism of metal toxicity.