Speciation of dimethyltin(IV) and trimethyltin(IV) cations with some biologically important ligands in aqueous medium: A potentiometric investigation

Abstract

The coordination of Me₂Sn(IV)²⁺ and Me₃Sn(IV)⁺ to uracil, thymine, 5-fluorouracil, thymidine and L-ascorbic acid in aqueous solution has been investigated by means of potentiometric titration. The concentration distribution of the various complex species in solution has been evaluated as a function of <i>p</i>H. It has been found that the ligands (L) with potential oxygen donor groups

such as thymidine and L-ascorbic acid interact more strongly Me₂Sn(IV)²⁺ and Me₃Sn(IV)⁺ as compared to those with potential nitrogen donor groups, viz. uracil, thymine and 5-fluorouracil at <i>p</i>H 7. The complexes are water soluble in the <i>p</i>H range 2-11. Thymidine forms ~28% of Me2SnL and ~60% of Me₃SnLH, whereas, L-ascorbic acid forms ~ 60% Me₂SnL(OH) and ~60%

Me₃SnL with Me₂Sn(IV)²⁺ and Me₃Sn(IV)⁺ respectively, At physiological <i>p</i>H. On the other hand, the nucleic acid bases, viz ., uracil, thymine and 5-fluorouracil have been found to form only small amount of Me₂SnL(OH ) (~10-20%) and Me₃SnL (~10-15%) under similar conditions. Significant amounts of hydroxo species, viz. Me₃SnOH and Me₂Sn(OH)₂, are also formed at <i>p</i>H 7.