Potentiometric study of interaction between dimethyltin(IV)2+ cation and penicillin derivatives in aqueous solution

The co-ordination of dimethyltin(IV)(2+) cation to penicillin derivatives (penicillin G, ampicillin, amoxicillin and methicillin) as ligands was investigated in aqueous solution by means of potentiometric titration. The results showed that if there is no electron withdrawing group on the R substituent (Figure 1) of the penicillin derivative (penicillin G and methicillin) the fast opening of the beta -lactam ring and the time consuming method hinders the investigation of the interaction. In the case of ampicillin and amoxicillin between pH 2 and 6 the ligand coordinates to the metal ion by its carboxylate group forming MLH+ and MLH2+ complexes complexes respectively. In the next step a hydroxide ion builds in the co-ordination sphere or a bonding H2O molecule deprotonates forming mixed hydroxo complexes. Based on the potentiometric results no evidence was found for the existence of other hydroxo complexes or participation of other donor groups of the ligands in the co-ordination at the higher pH ranges.