pH metric studies on the mixed ligand complex systems involving an amino penicillin drug, ampicillin (amp), as ligand (A) and ligands containing imidazole moieties such as Imidazole (him), Benzimidazole (bim), Histamine (hist), and Histidine (his) as ligands (B) at 37oC and I = 0.15 M (NaClO4) reveal the presence of ZnABH, ZnAB, ZnAH-1B and ZnAB2. The proton in the ZnABH species is attached to ligand A. In the mixed ligand complexes, the ligand, amp (A), binds the metal ion through the oxygen atom of the carbonyl group and amino nitrogen. In the ZnAB/ZnAB2 species the binding of the ligands A and B is similar to their binding in their respective binary complexes. In the deprotonated species ZnAH-1B, deprotonation occurs in the ligand amp (A). The ZnAB (B = hist/his)/ZnAB2 (B = him/bim) species in all these systems were isolated, and the analytical data confirm its formation. Non-electrolytic behavior and monomeric types of chelates have been assessed from their low conductance values. The vibrational spectral data were interpreted to find the mode of binding of ligands to metal. The thermal behavior of complexes was studied by TG/DTA. The antimicrobial activity and CT DNA cleavage of the complexes show higher activity for mixed ligand complexes.
Regupathy et al. (Wed,) studied this question.