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 1H and 13C-NMR spectroscopy. The equilibrium constants for the trans to cis isomers of captopril bound to Ag+ were measured by 1H 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 13C 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.