Speciation of dimethyltin(IV) and trimethyltin(IV)- carbocysteinate and glutamate systems in aqueous media

The formation of complex species in the dimethyltin(IV) and trimethyltin(IV)-carboxymethyl-L-cysteinate (carbocysteinate) systems in NaClaq, at different ionic strengths, and in a multicomponent Naþ, Kþ, Ca2þ, Mg2þ, Cl and SO4 2 medium representative of the seawater major composition, is discussed. Experimental results give evidence for the formation of the following species (L¼carbocysteinate): [(CH3)2Sn(L)]0, [(CH3)2Sn(HL)]þ, [(CH3)2Sn(OH)(L)], [(CH3)2Sn(OH)2(L)]2 in the DMT–CCYS system, and [(CH3)3Sn(HL)]0, [(CH3)3Sn(L)] and [(CH3)3Sn(OH)(L)]2 in the TMT-CCYS system. The ionic strength dependence of formation constants was taken into account by an extended Debye Hu¨ ckel type equation and by the SIT (Specific ion Interaction Theory). Measurements were carried out also on the dimethyltin(IV)-glutamate and trimethyltin(IV)-glutamate systems in NaClaq, owing the strict similarity of glutamate and carbocysteinate. Results obtained show the formation of complex species having the same stoichiometry as those formed in the DMT- and TMT-carbocysteinate systems, with very similar stability, confirming that carbocysteinate behaves as a dicarboxylic amino acid without involving the sulfur-bridge potential binding site in metal coordination.