New pH-Metric method for determination of some angiotensin converting enzyme inhibitors through their complex formation with some transition metal ions

ABSTRACT

Study of mixed ligand complexes of Co[2+] and Zn[2+] with three Angiotensin converting enzyme inhibitors [ACE] was conducted in aqueous solution by pH metric titration. These are Enalapril maleate [I], Perindopril [II] and Moexipril [III] and one of the amino acid family [glycine]. Protonation constants of the three drugs and stability constants of the binary and ternary complexes were determined at [25 +/- 1] [degree sign] C and ionic strength 0.1M NaCl. The stability constants of the binary complexes of I, II and III with Co[2+] and Zn[2+] were performed and the results indicate the presence of one formation constant for the complexes of Co[2+] and Zn[2+] ions with II and III and two formation constants for I. By introducing glycine in the above binary complexes, ternary complexes were formed. The formation constant of the ternary complexes of I, II and III with Co[2+] and Zn[2+] ions with glycine was also calculated at the same temperature and ionic strength. This potentiometric technique was utilized also for the determination of the cited drugs