Interaction of Inorganic Mercury(II) with Polyamines, Polycarboxylates, and Amino Acids

Abstract

A study on chemical equilibria of different Hg2+−organic ligand systems is reported to establish the sequestration power of N/O donor groups versus metal. Ligand classes considered are: O-donors (succinate, 1,2,3,4-butanetetracarboxylate, 1,2,3,4,5,6-benzenehexacarboxylate, polymethacrylate, and polyacrylates); N-donors (ethylenediamine, diethylenetriamine, spermidine, triethylentetramine, tetraethylenpentamine, poly(allylamine), and poly(ethylenimine)); and amino acids (glycine, histidine, and aspartic acid). Equilibria were studied potentiometrically in NaNO3 at I = 0.1 mol·L−1 and t = 25 °C. For some systems, the dependence on ionic strength in the range (0 ≤ I ≤ 1) mol·L−1 (NaNO3) and the overall enthalpy changes, by calorimetric measurements, were also determined. The sequestering ability of ligands toward Hg2+ was evaluated, defining the amount of ligand necessary to sequester 50 % of the total metal cation concentration, pL50. The dependence on temperature and on ionic strength of pL50 was determined. General trends for the formation parameters for Hg2+−O-donor and −N-donor species depending on the binding sites were found. The free energy of binding for both unprotonated and monoprotonated species of carboxylates (ΔG b = −21.7 ± 3 kJ·mol−1) and for unprotonated species of amines (ΔG b = −35.4 ± 5 kJ·mol−1) was estimated.

Stepwise Reduction Approach Reveals Mercury Competitive Binding and Exchange Reactions within Natural Organic Matter and Mixed Organic Ligands

“…Natural organic matter consists of thousands of heterogeneous organic compounds − and is known to play an important role in controlling the chemical speciation and biogeochemical cycling and toxicity of mercury (Hg) in natural aquatic ecosystems. − This effect is in part due to the formation of strong complexes between mercuric ion (Hg 2+ ) and a suite of organic ligands, particularly the thiol functional groups present in dissolved organic matter (DOM). ,,− Many low-molecular-weight (LMW) organic ligands have been identified in DOM, such as acetate, citrate, cysteine (CYS), glutathione (GSH), phenol, and glutamate, − although their stability constants (log β) for Hg 2+ binding vary by many orders of magnitude. ,,, In general, Hg 2+ forms weaker complexes with carboxylate ligands with log β ranging from 3.7 to 23.2 and much stronger complexes with thiolate ligands with log β ranging from 26 to 53.1 (Supporting Information, Table S1). However, large discrepancies have been reported for the measured log β values for Hg­(II)–DOM species (ranging from 10 to 40), ,,,− and these differences have often been attributed to different origins and properties of DOM (e.g., its sulfur or thiol contents), as well as to methodologies and environmental conditions used in measurements.…”

Quantum Chemical Approach for Calculating Stability Constants of Mercury Complexes

“…The log K value for Hg­(SH) 2 was obtained from a recent report by Drott et al As mentioned earlier, uncertainty in the experimental stability constants can lead to inaccurate predictions of the behavior, fate, and transport of Hg and MeHg in aquatic environments. ,, For some complexes, more than one distinct experimental log K value is available in the literature. For example, at least two distinct values have been reported for glycine [Hg­(Gly)] + : 12.2 (1974) and 13.90 (2009) . Furthermore, for some complexes, such as Hg­(Cys) n , a wide range of log K values have been reported .…”

“…Furthermore, for some complexes, such as Hg­(Cys) n , a wide range of log K values have been reported . Thus, whenever possible we chose the latest refined values, measured under a similar set of rigorous experimental conditions such as temperature and ionic strength, as a reference value. − …”

Simultaneous enrichment, separation and detection of mercury(ii) ions using cloud point extraction and colorimetric sensor based on thermoresponsive hyperbranched polymer–gold nanocomposite

“…S3 †), the degree of substitution of the amino groups of HPEI was calculated to be about 79.4%, indicating that the HPEI-IBAm remains 20.6% unreacted primary and secondary amine groups, which can improve the Hg 2+ binding capacity of the HPEI-IBAm. 41 Fig. 1A shows the inuence of temperature on the light transmittance of HPEI-IBAm-AuNPs solution.…”