Synthesis, Charcterization and Biological Applications of Some Bis-Schiff Bases and Their Metal Complexes

Abstract

This thesis presents the out comings of research work carried out to study some Schiff bases and their transition metal complexes from their prospect biological perspective. Six Schiff bases and their twenty four new complexes of Co+2, Ni+2, Cu+2 and Zn+ were synthesized, characterized and evaluated for antibacterial, antifungal, antioxidant, α-glucosidase inhibition and urease inhibition potentials. In order to characterize synthesized compounds, various physical and analytical methods were employed including CHN micro analysis, EI Mass spectroscopy, 1H-NMR spectroscopy, AAS, FTIR spectroscopy UVVis., scanning electron microscopy, conductivity measurements and magnetic susceptibility studies. It was determined that complexes of Cu+2 and Zn+2 had tetrahedral and distorted tetrahedral geometries respectively while complexes of Co+2 and Ni+2 acquired octahedral geometries. The complexes were found better antimicrobial agents than their parent Schiff base ligands. The antimicrobial activity of complexes was observed to be dose dependent, as the test concentration was increased the activity was also increased. Similar pattern was found for antifungal activity as well. The mechanism of antimicrobial action of complexes was suggested as the reduced polar metal center increases the lipophilic characteristic which is favorable for antimicrobial inhibition potential. Schiff base ligands were found more potent antioxidant agents than the complexes. The complexes showed less or no antioxidant potential and it was associated with deprotonation of hydroxyl group upon chelation. In the case of α-glucosidase inhibition potency, the metal complexes were noticeably more potent than the corresponding ligands. The ligand SBLC and their complexes were found most potent. The inhibition strength of the ligand SBLC was found to be 51%, best among all ligands while for the complexes of SBLC, the inhibition potential were between 51% and 64%. For urease inhibition, the ligands were found almost inactive against the enzyme. Complexes of all ligands showed however excellent inhibition strength. Complexes of copper for all ligands were particularly better inhibitors among all. The [Cu(SBLN)(OAc)] was found to be the best urease inhibitor with 88% inhibition against the enzyme and was much better than standard. On the bases of results obtained and literature reports, some suggestions are also proposed to produce new potential antibiotic drugs in current global scenario of the "post-antibiotic era".