Theoretical studies of complexes between Hg(II) ions andl-cysteinate amino acids

Abstract

In this study, ab initio and density functional theory methods have been used to understand the structures and thermodynamic stabilities of complexes formed between L-cysteine and mercury (II) ions in neutral aqueous solution. To better understand the interaction between sulfur and mercury (II) ion, the MP2, B3LYP, M06-2X, and TPSS methods have been used to optimize [HgSH x ] 22x , x5 1-4, complexes and compared to benchmark QCISD(T) structures. Furthermore, energies from these same methods are compared to CCSD(T)/CBS(2,3) energies. From these benchmark calculations, the M06-2X method was selected to optimize L-cysteinate-Hg(II) complexes and the MP2 method for estimating complex energies. L-cysteinate-mercury (II) ion complexes are formed primarily by forming a bond between cysteinate sulfur and the mercury ion. Stable complexes of L-cysteinate and mercury can be formed in 1:1, 2:1, 3:1, and 4:1 ratios. Each complex is stabilized further by interaction between carboxylate oxygen and mercury as well as hydrogen bonding among complex cysteinate ligands. The results indicate that at high cysteinate to Hg(II) ratios high-coordinate complexes can be present but at lower ratios the 2:1 complex should be dominant.

Thermodynamic stability of mercury(II) complexes formed with environmentally relevant low-molecular-mass thiols studied by competing ligand exchange and density functional theory

“…By contrast, electron-donating groups, such as the carbonyl and carboxylic groups, can contribute to the stabilization of the Hg II -LMM thiol complexes via additional coordination to Hg II besides the linear S-Hg-S configuration ( Figure 5 and Table S2). 46 The opposing effects between the electron-withdrawing primary amino group and electron-donating oxygens on the stability of Hg(SR)2 complexes can be illustrated by…”

Kinetics of Hg(II) Exchange between Organic Ligands, Goethite, and Natural Organic Matter Studied with an Enriched Stable Isotope Approach

“…[45][46][47] Cysteine forms 1:2-type (Hg(Cys) ) and 1:3-type (Hg(Cys) 3 ) complexes with Hg(II) under the conditions applied in this study. 48,49 Hg(II) is primarily coordinated to the thiol-group and can be further stabilized by the carboxyl-group in the Hg(Cys) 2 complex. 49 ).…”

“…48,49 Hg(II) is primarily coordinated to the thiol-group and can be further stabilized by the carboxyl-group in the Hg(Cys) 2 complex. 49 ). 50 The pH was chosen for experimental considerations due to the high buffer capacity of the carboxyl-resin at pH 4 and represents typical conditions found in organic-rich terrestrial environments.…”

Spectroscopic and Theoretical Studies of Hg(II) Complexation with Some Dicysteinyl Tetrapeptides

“…Others and we have applied the M06-2X method and obtained quality geometries for peptides and Hg(II)-peptide complexes [22,28,29]. As in our previous studies, singlepoint energies calculations were obtained using MP2 (full) with a 6-311G (d, p) basis set on peptide atoms and cc-pVDZ-PP basis set on mercury atom [22].…”