Solid and solution NMR studies of the complexation of Ag+ with the trans isomer of captopril: biological activities of this high blood pressure drug along with its Ag+ complex

Complexation of Ag(+) with captopril, 1-[(2S)-3-mercapto-2-methylpropionyl]-L-proline, has been studied by (1)H and (13)C-NMR spectroscopy. The equilibrium constants for the trans to cis isomers of captopril bound to Ag(+) were measured by (1)H NMR spectroscopy. It is observed that the trans isomer of the drug binds more strongly to Ag(+) between pH 5 and 8, as shown by the broadening of the trans isomer's resonances in (13)C NMR spectra on complexation. A monodentate complexation of the trans captopril with Ag(+) via the thiol site is proposed based on the solid-state NMR and IR data. A superior antimicrobial activity is exhibited by the Cap-Ag(I) complex compared to captopril ligand itself against Heterotrotropic Plate Counts (HPC), Pseudomonas aeruginosa and Fecal streptococcus bacteria.