Coordination properties of the ACE inhibitor captopril towards Me2Sn(IV)2+ in aqueous solution, and biological aspects of some dialkyltin(IV) derivatives of this ligand

Abstract The coordination of Me 2 Sn(IV) 2+ (M) to captopril { N -[( S )-3-mercapto-2-methylpropionyl]- l -proline, H 2 (cap), H 2 L} in aqueous solution was studied by means of potentiometric titration, electrospray mass spectrometry, 1 H-NMR spectroscopy and Mossbauer spectroscopy in the pH range 2–11 ( I =0.1 mol dm −3 NaClO 4 , 298 K). The results obtained with these methods proved that only monomeric complexes are formed in solution. In the acidic pH range, species with a metal-to-ligand ratio of 1:1 exist. The neutral complex ML, similarly to the complex Me 2 Sn(cap) crystallized in the same pH range, adopts a tbp structure with eq S − and ax COO − , while, instead of the coordination of the amide CO, observed in the solid state, the other ax position is occupied by a H 2 O molecule. With increasing pH, in the neutral and weakly basic pH range the complexes MLH −1 and ML 2 are formed, in which the COO − group is displaced from the coordination sphere by an OH − and an S − of another ligand, respectively. Biological activity tests on Me 2 Sn(cap) and three further R 2 Sn(IV) captopril complexes showed that n- Bu 2 Sn(cap) and t- Bu 2 Sn(cap) exert toxic activity towards the embryos of Ciona intestinalis , while the ligand itself does not affect the development of the embryos to any significant extent; Me 2 Sn(cap) and Et 2 Sn(cap) produced normal swimming larvae.