Binding Ability of Sodium Catechol Disulfonate (Tiron) toward Hg²⁺, CH₃Hg⁺, (CH₃)₃Sn⁺, and (CH₃)₂Sn²⁺ Cations

Abstract

A potentiometric study on the interactions between catechol disulfonate (disodium 4,5-dihydroxybenzene-1,3-disulfonate, tiron) and Hg 2+ , CH 3 Hg + , (CH 3 ) 2 Sn 2+ , and (CH 3 ) 3 Sn + cations is reported in aqueous NaCl solution with ionic strength in the range (0 ≤ I ≤ 1) mol•L −1 and at a temperature of 298.15 K. In the presence of tiron, CH 3 Hg + and (CH 3 ) 3 Sn + form only the two species ML and MLH; Hg 2+ forms ML, MLH, and ML(OH) species; and (CH 3 ) 2 Sn 2+ forms ML, MLH, and ML 2 species. The interactions of tiron with Hg 2+ and (CH 3 ) 2 Sn 2+ are stronger than those with CH 3 Hg + and (CH 3 ) 3 Sn + . As an example, at the ionic strength I = 0.1 mol•L −1 , equilibrium constants for the formation of ML species are log β = 18.87, 17.076, 10.39, and 7.55, for M = Hg 2+ , (CH 3 ) 2 Sn 2+ , CH 3 Hg + , and (CH 3 ) 3 Sn + , respectively. On the basis of the speciation models proposed, the sequestering ability of tiron toward Hg 2+ , CH 3 Hg + , (CH 3 ) 2 Sn 2+ , and (CH 3 ) 3 Sn + was quantitatively evaluated by determining the concentration of the ligand able to complex half of the metal ion fraction. In the range 5 ≤ pH ≤ 8, the sequestering ability is high toward Hg 2+ and (CH 3 ) 2 Sn 2+ (at the (10 −11 to 10 −6 ) mol•L −1 level), fairly low toward CH 3 Hg + (at the 10 −3 mol•L −1 level), and very low toward (CH 3 ) 3 Sn + (at the 10 −1 mol•L −1 level).

Thermodynamic data for Pb2+and Zn2+sequestration by biologically important S-donor ligands, at different temperatures and ionic strengths

“…In many papers we evidenced the dependence of the empirical parameter C on the charges involved in the formation reaction (z*), and some ligand classes showed constant values of C/z*. 10,13,37 Data reported in Table 4 show a significant dispersion, but it was possible to derive a linear dependence on z* with C = 0.72(AE0.04) À 0.11(AE0.02) z* for Pb 2+ systems and C = À1.7(AE0.3) + 0.14(AE0.02) z* for Zn 2+ . These equations can be used to calculate fairly good predictive values for other ligands of this class.…”

Complexation of Hg2+, CH3Hg+, Sn2+ and (CH3)2Sn2+ with phosphonic NTA derivatives

“…Some examples are represented by ref. [41][42][43][44][45][46][47] for Hg 2+ and CH 3 Hg + , while ref. 7, 18 and 48-51 may be considered for Sn 2+ and (CH 3 ) 2 Sn 2+ .…”