Mercury(II) Complexation of Cysteine, Methyl Cysteineate, and S-Methylcysteine in Acidic Media

Abstract

Bis(cysteineato)mercury(II) hydrochloride hemihydrate, (C3H6O2NS),Hg.HCl.-',H2O, was obtained by reaction of ethanolic solutions of L-cysteine hydrochloride with either HgC1, in 95% EtOH, Hg(OAc), in MeOH, Hg(NO,), in HOAc, or by reaction of L-cysteine (free base) with HgCI,. Reaction of L-cysteine (free base) with Hg(OAc), gave a mercury(I1) cysteineate with composition (C3H6O2NS),Hg,. Bis(S-methyl-L-cysteineate)mercury (II),(C4H,02NS)2Hg,wasobtained byreactionof S-methyl-L-cysteinewith Hg(OAc),. 'H-and '3C-n.m.r. spectral data are reported and compared for acidic solutions of cysteine, methyl cysteineate, S-methylcysteine, and their mercury(I1) complexes. The proton spectra for S-methyl-L-cysteine and L-cysteine hydrochloride have been analyzed as ABC systems and relative rotamer populations have been determined. In acidic solution, mercury bonding is localized to sulfur and the complexes appear to have an extended molecular configuration resulting from a trans orientation of the COOH group and the Hg site.

Synthesis, spectroscopic characterization and antimicrobial studies of mercury(II) complexes of thiolates

“…The biological chemistry of mercury is dominated by coordination to cysteine thiolate groups in agreement with the preference of this metal ion for the soft sulfur ligands and a great deal of research has been conducted to understand how the amino acid interacts with metals [11][12][13][14][15]. Several types of cysteine derivatives (e.g., pencillamine and N -actylcysteine) form soluble complexes and have been suggested as possible detoxification agents [16][17][18][19]. Although mercury(II) being a soft Lewis acid forms quit stable complexes with thiol groups [20][21][22][23], many thiolates remain labile and undergo ligand exchange, which is more pronounced in low (two and three)-coordinate compounds [24,25].…”

Mercury Extraction from Contaminated Soils by l-Cysteine: Species Dependency and Transformation Processes

“…During leaching, Hg and L-cysteine form a Hg(II) complex (Neville and Drakenberg 1974). In the literature, there is evidence from polarographic measurements for the formation of at least three mercurial complexes with cysteine (R-SH): Hg(RS) 2 , Hg 2 (RS) 2 and Hg 3 (RS) 2 , whereas Hg(RS) 2 is the predominant complex ( Fig.…”

“…In the literature, there is evidence from polarographic measurements for the formation of at least three mercurial complexes with cysteine (R-SH): Hg(RS) 2 , Hg 2 (RS) 2 and Hg 3 (RS) 2 , whereas Hg(RS) 2 is the predominant complex ( Fig. 2d; Stricks and Kolthoff 1953;Neville and Drakenberg 1974;Bramanti et al 1999). The oxidation process of Hg by cysteine follows the reaction (Kolthoff and Barnum 1940):…”

“…Despite the high thermodynamic stability of Hg-cysteine complexes (pKs=∼40; Stary and Kratzer 1988), it has been observed that these Hg(II) complexes in biological systems are quite labile (Rabenstein and Isab 1982;Cheesman et al 1988) and can be determined by the addition of SnCl 2 and NaBH 4 (Bramanti et al 1999). Neville and Drakenberg (1974) also assumed complex alteration during their experiments. The Hg(II)-cysteine complex thus seems to be a labile complex which can potentially undergo various species transformations probably related to microbial attack of the cysteine complex.…”

N,O- and S,O-bonded Hg(II) complexes with S-substituted amino acids: synthesis and crystal structures of bis(S-methyl-L-cysteinato)mercury(II) and bis(D,L-ethioninato)-mercury(II) diperchlorate

“…Towards mercuric ion (HgZ+) the binding mode is pH dependent. Although early potentiometric work (1) suggested little or no involvement of thioether coordination to HgZ+ for methionine, ethionine, or S-methylcysteine, it later became apparent from lH (2)(3)(4)(5) and 13C nmr (4)(5)(6) studies of Hg2+/ methionine, ethionine, or S-methyl-L-cysteine solutions that under acidic conditions (pD I 2) HgZ+ was bound exclusively to the thioether sulfur atom.…”