Experimental and Theoretical Studies on DNA Binding and Anticancer Activity of Nickel(II) and Zinc(II) Complexes with N- (8-Quinolyl) Salicylaldimine Schiff Base Ligands

Transition metal complexes of nickel(II) with 5-bromo-N-(8-quinolyl)salicylaldimine (HqsalBr, HL1); [Ni(qsalBr)2] (1) and 3,5-dibromo-N-(8-quinolyl)salicylaldimine (HqsalBr2, HL2); [Ni(qsalBr2)2] (3) including zinc(II) complex with HL1, [Zn(qsalBr)2] (2), have been synthesized and successfully characterized using various techniques, namely IR, NMR, mass spectrometry, thermogravimetric analysis (TGA), and single crystal X-ray crystallography. DFT calculations were employed to examine the structural and electronic parameters of the complexes at their optimized geometries. The complexes showed strong DNA-binding activities, assessed by UV-Vis and fluorescence spectroscopy, primarily through intercalation. Molecular docking investigations were carried out to provide profound insights into the interaction mechanisms of these complexes with DNA and lung cancer cells. These computational studies revealed that [Ni(qsalBr2)2] (3) exhibits the most favorable negative binding energies, -9.1 kcal/mol with DNA and -9.3 kcal/mol with cancer cells, facilitated by hydrogen bonding and hydrophobic interactions. Furthermore, the in vitro anticancer activity was evaluated against the A549 human lung adenocarcinoma cell line, with [Zn(qsalBr)2] (2) exhibiting the highest potency against this cancer cell line.