Nuclear magnetic resonance and potentiometric studies of the complexation of methylmercury(II) by dithiols

Abstract

. Can. J. Chem. 63, 2430Chem. 63, (1985. Complexation of methylmercury, CH3Hg(II), by 2,3-dimercaptosuccinic acid (DMSA), 2,3-dimercaptopropanesulfonate (DMPS, Unithiol), dithioerythritol (DTE), and 2,3-dimercaptopropanol (British AntiLewisite, BAL) has been studied by 'H nuclear magnetic resonance spectroscopy and by potentiometric titration. In the nmr study, the equilibrium constants for displacement of mercaptoacetate from its CH3Hg(II) complex by the dithiols were determined over a wide pH range, from mercaptoacetate chemical shift data. Similar competition reactions between the dithiols and mercaptoethanol were used in the potentiometric study. Using previously determined CH3Hg(II) formation constants for the competing ligands, equilibrium constants for the formation of mono-and bis-CH3Hg(II) complexes with the dithiols have been determined. The formation constants for the mono-CH3Hg(II) complexes with the vicinal dithiols BAL and DMPS are significantly higher than expected by consideration of the basicity of the sulfhydryl donors, in comparison with those for DMSA, non-vicinal DTE, and monothiols. We interpret this to indicate chelation of CH3Hg(II) by BAL and DMPS but not by DMSA. The conditional formation constants at physiological pH are discussed with reference to the effectiveness of BAL, DMPS, and DMSA as antidotes for methylmercury poisoning. In particular, the constants obtained indicate that, for dithiol antidotes at concentrations greater than that of methylmercury(II), methylmercury(I1) complexes formed at physiological pH are of 1 : 1 stoichiometry. For BAL, a substantial proportion of the complex will be in the neutral form, in contrast to DMPS and DMSA which form anionic species only. Faisant appel 21 la rmn du 'H et i des titrages potentiomCtriques, on a CtudiC la complexation du mCthylmercure, CH3Hg(II), par les composCs suivantes: I'acide dimercaptosuccinique (ADMS), le dimercapto-2,3 propanesulfonate (DMPS, Unithiol), le dithioCrythritol (DTE) et le dimercapto-2,3 propanol (British AntiLewisite, BAL). A partir des donntes de dkplacement chimique du mercaptoacetate en rmn du 'H, on a determine, sur un large intervalle de pH, les constantes d'Cquilibre des rkactions de dCplacement, par les dithiols, du mercaptoacCtate de son complexe de CH3Hg(II). On a Cgalement utilisC des rkactions de compCtitions du mCme type entre des dithiols et le mercaptoCthanol, lors de 1'Ctude potentiomktrique. Faisant appel a des constantes de formation du CH3Hg(II) qui ont Ct C dCterminCes anterieurement pour les ligands entrant en competition, on a dCterminC les constantes dlCquilibre de formation des complexes mono-et bis-CH3Hg avec les dithiols. Si on les compare avec les constantes de I'ADMS, du DTE (qui sont des dithiols qui ne sont pas vicinaux) ou avec celles des monothiols, les constantes de formation des complexes de mono-CH3Hg(II) avec les dithiols vicinaux BAL et DMPS sont nettement plus ClevCes que celles prCvues en tenant compte de la basicit6 des sulfhydryles donneurs. Pour interprkter ces rCsult...

Evaluation of Protonation Constants of Mercaptosuccinic Acid in Aqueous Solutions of Propylene Glycol and Dioxan

“…The result is in agreement with those reported in the literature for the media containing pure water as solvent [26][27][28][29] but the small differences are possibly due to the different experimental procedures, temperature and different background …”

Use of a laboratory robot for repetitive solution NMR sample preparation

“…4 for details). Using the nonlinear least-squares routine Sigmaplot, the value of Ka was refined to obtain the 3~trictly speaking, activity, but we will neglect consideration of activity coefficients here for simplicity, since it [2], [3], and [4]. See text for further details.…”

“…We have found a combination of both of these techniques to be a potent method for elucidation of a variety of multiequilibrium systems (3)(4)(5)(6)(7). Details of implementation have been discussed therein; a simple example of the application of NMR studies is given later in this paper (see Performance evaluation).…”

Coordination complexes of 2‐thienyl‐ and 2‐furyl‐mercurials

“…5,6 For example, the effectiveness of 2,3-dimercaptopropan-1-ol (British anti-Lewisite; BAL) in treating organomercury poisoning is dependent upon the acceptor properties of the mercury compounds and upon their ability to react with the available sulfur atom of BAL. 7,8 The ability of 2-coordinate mercury(II) to form complexes is very dependent upon the nature of the groups attached to mercury. Thus, whereas mercury(II) halides form a wide range of adducts with monodentate and polydentate ligands, 9,10 no complexes have been isolated for mercury dialkyls.…”