DPPH and nitric oxide free radical scavenging potential of phenyl quinoline derivatives and their transition metal complexes

In the present study phenyl quinoline (PQ) derivatives and their newly synthesized transition metal (Cu2+, Co2+, Fe3+) complexes were screened for their free radical scavenging potential against DPPH and nitric oxide free radicals. All compounds showed activity against these two free radicals but it was found that coordination of metal ions with ligands increased their antioxidant potential. PQ4Co showed more inhibition potential for DPPH than ascorbic acid with IC50 values 16.30 µg/mL. Among copper(II) complexes PQ5Cu is the most poent antioxidant compounds with IC50 values 8.38 µg/mL while PQ7Fe is the most potent compound among iron(III) complexes with IC50 value 16.00 µg/mL. Similarly formation of metal complexes quinoline derivatives make them much more potent for nitric oxide scavenging. PQ6Cu is the most potent (IC50 = 5.24 µg/mL) among the copper(II) complexes while compounds Q13Fe is the most potent nitric oxide inhibitors with IC50 values 1.90 µg/mL among iron(III) complexes. Job's method was applied to check the ligand metal ratio for the formation of stable complex (ligand and metals with 2:1 ratio). All synthesized complexes were characterized by using different spectroscopic techniques. Iron (III) complexes showed greater thermal stability with melting points higher than 300°C. Comparative FTIR spectra of all synthesized compounds indicated that phenyl quinoline compounds acted as bidentate ligand with CN and NH2 groups as coordination sites. CN stretching peak in the region of 2200-2100 cm−1 in ligands shifted in 2300-2200 cm−1 region while NH2 peaks become weak and non-prominent in FTIR spectra of complexes which confirms the contribution of these two groups in the formation of coordination compounds. Comparative UV-Visible spectra of ligand and complexes also showed different absorption pattern. XRD study of compounds PQ1, PQ1Cu, PQ2 and PQ2Co showed that crystal sizes are 16.11 nm, 14.91 nm, 13.46 nm and 12.68 nm respectively.