A spectroscopic investigation of captopril and the Cu(II)-captopril system

A Raman and IR study of captopril (CpSH), a synthetic derivative of l-proline, and the Cu(II)±CpSH system at different pHs and metal/ligand ratios was carried out. The vibrational spectra suggested disulphide formation (CpSSCp) by the reduction of Cu(II) to Cu(I) and allowed the identi®cation of the sites involved in metal coordination. Various complexes can be formed and the nature of the predominant species depends mainly on the pH. At pH 10 CpSH gives rise to two monomeric complexes with different structures depending on the metal/ligand ratio, whereas at acid pH a water-insoluble polymeric species predominates.