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Mercury‐Sequestering Pseudopeptides with a Tris(cysteine) Environment in Water
Author(s) -
Pujol Anaïs M.,
Lebrun Colette,
Gateau Christelle,
Manceau Alain,
Delangle Pascale
Publication year - 2012
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201200484
Subject(s) - chemistry , nitrilotriacetic acid , protonation , carboxylate , sulfur , extended x ray absorption fine structure , amide , inorganic chemistry , titration , chelation , nuclear magnetic resonance spectroscopy , cysteine , proton nmr , crystallography , stereochemistry , absorption spectroscopy , organic chemistry , ion , physics , quantum mechanics , enzyme
The three pseudopeptides L 1 – 3 having three converging cysteine arms anchored on a nitrilotriacetic acid scaffold, are demonstrated to be efficient sulfur‐based Hg II chelating agents. The three ligands differ by the nature of the carbonyl group of the cysteine moieties, ester, amide, and carboxylate for L 1 , L 2 , and L 3 , respectively. The coordination chemistry of the mercury thiolate complexes was characterized in water by acid–base titration and several spectroscopic methods, including UV, 1 H, and 199 Hg NMR spectroscopy and Hg‐L III EXAFS. At alkaline pH, they form monometallic complexes with typical signatures of a trigonal HgS 3 coordination site, which is uncommon, as Hg II usually prefers a coordination number of two. The digonal HgS 2 structure is formed at acidic pH, where one cysteine group is protonated (Hg L H complex). EXAFS spectra at liquid He temperature and alkaline pH are nearly identical for the three Hg L complexes. Their analysis reveals an asymmetrical HgS 3 binding environment with three S atoms at 2.38, 2.51, and 2.67 Å. This suggests that the C 3 ‐symmetrical species detected by 1 H NMR spectroscopic analysis at 298 K are averages of nonsymmetrical complexes that rapidly equilibrate on the NMR time‐scale at ambient temperature. At acidic pH, Hg II is coordinated in a linear configuration to the two sulfur atoms from the thiolate groups at a distance of 2.36 Å, and in a T‐shaped geometry to the third sulfur atoms from the protonated cysteine at 3.07 Å. The three pseudopeptides have high affinities for Hg II and are interesting alternatives for the design of efficient water‐soluble mercury‐sequestering agents that favor an uncommon tris(thiolato)mercury environment.