Synthesis, spectral characterization and antioxidant activity studies of new pyridine-carboxamide schiff base and its NI(II), CU(II) and cCD(II) complexes

Schiff base complexes are a class of molecules of great interest due to their interesting chemical and physical properties as well as their diverse applicability in various scientific fields. Schiff bases and the pyridine-3-carboxamide (nicotinamide) structure system are widely used and continuously investigated as drugs and bioactive compounds. However, there is still a need to synthesize new ligand and complex compounds with better properties. In the present thesis, it was aimed to prepare a new Schiff base ligand and metal complexes, characterize the obtained compounds and determine their antioxidant activities using various methods. In the first step, 2-amino-6-methyl-4,5,6,7-tetrahydrothieno[2,3-c]pyridine-3-carboxamide was synthesized as starting material and then reacted with 5-bromo-2-hydroxybenzaldehyde to obtain Schiff base (H2L). The metal salts NiCl2∙6H2O, Cu(NO3)2∙3H2O, and Cd(NO3)2∙4H2O were used to prepare the complexes. The structures of all synthesized compounds were determined using elemental analysis, FT-IR, 1H-NMR, 13C-NMR, LC-MS, UV-Vis, magnetic susceptibility, thermogravimetric analysis techniques. Finally, the antioxidant activities of the ligand and complexes were investigated in vitro using DPPH free radical scavenging activity, ABTS+ cation radical scavenging activity and CUPRAC reducing power assay methods. Octahedral structure is proposed for Ni+2 and Cd+2 complexes and square plane structure for Cu+2 complex. When the antioxidant activity results were evaluated, it was found that some of the complex compounds showed better antioxidant effect than the Schiff base ligand.