COMPLEXATION OF LISINOPRIL DRUG WITH ALKALINE EARTH AND TRANSITION METAL IONS IN MIXED SOLVENT MEDIA

Objective: To investigate the stability constant of Lisinopril hydrochloride drug with alkaline earth metal ions Mg(II), Ca(II) and transition metal ions Fe(III), Cu(II) using potentiometric titration technique in 20%(v/v) ethanol-water mixture at 27 °C temperature and at an ionic strength of 0.1M NaClO4. Materials and Methods: The ligand Lisinopril hydrochloride is soluble in 20% (v/v) ethanol-water mixture. NaOH, NaClO4, HClO4 and metal salts were of AR grade. The solutions used in the pH metric titration were prepared in double distilled water. All the measurements were made at 27 0Cin 20%(V/V) ethanol-water mixture at constant ionic strength of 0.1M NaClO4. The pH measurement were made using a digital pH meter. Results: The method of Calvin and Bjerrum as adopted by Irving and Rossotti has been employed to determine proton ligand (pKa) and metal-ligand stability constant (logK) values. It is observed that alkaline earth metal & transition metal ion forms 1:1 and 1:2 complexes. The order of stability constants for these metal complexes was as: Fe3+ > Cu2+ > Mg2+ > Ca2+ Conclusion: The stability constants of trivalent Fe show maximum stability whereas divalent Ca shows minimum stability