Theoretical Study of the Formation of Mercury (Hg²⁺) Complexes in Solution Using an Explicit Solvation Shell in Implicit Solvent Calculations

Abstract

The structures and harmonic vibrational frequencies of water clusters (H2O)n, n = 1-10, have been computed using the M06-L/, B3LYP/, and CAM-BLYP/cc-pVTZ levels of theories. On the basis of the literature and our results, we use three hexamer structures of the water molecules to calculate an estimated "experimental" average solvation free energy of [Hg(H2O)6](2+). Aqueous formation constants (log K) for Hg(2+) complexes, [Hg(L)m(H2O)n](2-mq), L = Cl(-), HO(-), HS(-), and S(2-), are calculated using a combination of experimental (solvation free energies of ligands and Hg(2+)) and calculated gas- and liquid-phase free energies. A combined approach has been used that involves attaching n explicit water molecules to the Hg(2+) complexes such that the first coordination sphere is complete, then surrounding the resulting (Hg(2+)-Lm)-(OH2)n cluster by a dielectric continuum, and using suitable thermodynamic cycles. This procedure significantly improves the agreement between the calculated log K values and experiment. Thus, for some neutral and anionic Hg(II) complexes, particularly Hg(II) metal ion surrounded with homo- or heteroatoms, augmenting implicit solvent calculations with sufficient explicit water molecules to complete the first coordination sphere is required-and adequate-to account for strong short-range hydrogen bonding interactions between the anion and the solvent. Calculated values for formation constants of Hg(2+) complexes with S(2-) and SH(-) are proposed. Experimental measurements of these log K values have been lacking or controversial.

A coumarin derivative-Cu2+ complex-based fluorescent chemosensor for detection of biothiols

“…The stability constant of the complex, also known as the complexation equilibrium constant in aqueous solutions, was calculated using the Gibbs free energy of the ligand-exchange reaction determined by a solvation model based on density (SMD), a density functional theory (DFT) method, and thermodynamic cycles. 26,27 The calculated results are in good agreement with the experimental data obtained by a nonlinear curve-tting method. 28,29 From the value of the stability constant, the applicability of the complex as a uorescent sensor for the detection of biothiols based on the complex exchange reaction was predicted.…”

“…The stability constant of the complex, also known as the complexation equilibrium constant in aqueous solutions (log b), is calculated by the Gibbs free energies of ligand-exchange reactions determined using thermodynamic cycles, the DFT theory method, and the SMD solvent model (Scheme 1). [23][24][25][26][27] Accordingly, the complexation equilibrium constant in aqueous solutions (log b) is calculated by the following equation: , which was used as a reference complex for calculation. DG aq is the Gibbs free energy of the ligandexchange reaction in the aqueous solution, which was determined by Scheme 1 and calculated using eqn (2):…”

Nucleation of mercury sulfide by dealkylation

“…Better estimates of the free energy are obtained when explicit water molecules are added to Hg(II) complexes to account for strong short-range hydrogen bonding interactions between the anion (here CH 3 S − ) and the solvent26. The length of the S d …H hydrogen bonds effectively decreased from 2.37 Å in the free reactants to 2.24 Å in the transition-state structure when two water molecules were placed near the S d atom, thus confirming the importance of solute-solvent covalent interactions2627 (see Supplementary Materials). Overall, the activation energy decreased to 36.2 kcal mol −1 with two explicit water molecules, 34.7 kcal mol −1 with four, and 31.9 kcal mol −1 with seven (Fig.…”

Modeling of Hg (II) Adsorption onto Ca-bentonite

“…[3] Different computational tools have been used to model metal adsorption on clay minerals. Quantum, molecular mechanics, and molecular dynamics methods, and also Monte Carlo simulation techniques have been successfully applied to the behavior of clay materials as well as various hydrated cations during adsorption [4][5][6][7][8][9][10][11][12][13][14][15][16].…”