Synthesis of the some novel N-heterocyclic schiff bases and their metal complexes: Investigation of their antioksidant properties against the oxidative radical species

Schiff bases were first synthesised in 1864 by Hugo Schiff and these compounds have been used in various research areas. In the literature, they have been observed in epoxidation reactions as a catalyst; in the synthesis of conductor polymers as a monomer; in biological applications as an antifungal, antibacterial and antimicrobial; and against some oxidative radical species as an antioxidant. Synthesis of Schiff bases continues to this day. A significant number of Schiff bases have been used in the organic synthesis and design of novel compounds. In the current work, novel N-heterocyclic Schiff bases (L1, L2, L3, HL4 and L5), which have antioxidant potential, and their Cu(II), Mn(II), Co(II) and Ni(II) complexes were synthesised. The characterisation of those compounds was successfully carried out by Elemental, FT-IR, NMR (1H, 13C), LC-MS and UV-Vis spectral analysis and magnetic moment measurements. The molecular structures of L1 and L2, which were obtained as singlet crystal forms, were elucidated by means of X-ray analysis. The antioxidant properties of ligands and their metal complexes were carefully investigated using UV-Vis and electron paramagnetic resonance spectral methods toward DPPH, Rhodamine TEMPO and hydroxyl radical species. In this study, quercetin and vitamin C were used as controls. Consequently, it was found that N-heterocyclic ligands and their metal complexes exhibited antioxidant activity, as did the control group. Key Words: Schiff bases, complexes, characterisation, radical, antioxidant activity