Binding ability of glutathione towards alkyltin(IV) compounds in aqueous solution

The interactions between glutathione (H3GSH) and (CH3)2Sn(2+), (CH3)3Sn(+), (C2H5)3Sn(+) and (C3H7)3Sn(+) cations were studied by potentiometry, UV spectrophotometry, (1)H NMR spectroscopy and electrospray mass spectrometry (ESI MS). Potentiometric measurements evidenced speciation models very similar for all the alkyltin(IV) cation-GSH(3-) systems, with the formation of M(GSH)(z-3), M(GSH)H(z-2) and M(GSH)H2(z-1) species [M(z+)=(CH3)2Sn(2+), (CH3)3Sn(+), (C2H5)3Sn(+), or (C3H7)3Sn(+)] and, for dimethyltin(IV) cation, also the mixed hydrolytic M(GSH)(OH)(2-) one. The equilibrium behavior in NaCl aqueous solution, at different ionic strengths and temperatures, is discussed. The stability of the species for the dimethyl and trialkyl cations is quite different. As an example, for M(GSH)(z-3), logβ=13.33, 6.55, 6.44 and 5.84, for (CH3)2Sn(2+), (C3H7)3Sn(+), (C2H5)3Sn(+) and (CH3)3Sn(+), respectively (at I=0.1M and t=25°C). The speciation models and the possible structures of the complexes formed are discussed on the basis of spectroscopic and spectrometric results. The sequestering ability of glutathione towards alkyltin(IV) cations was evaluated by determining the concentration of the ligand able to complex half of the metal ion fraction (pL0.5). Glutathione shows a fairly good sequestering ability towards alkyltin(IV) cations, in 10(-3)-10(-5)M range.