Substitution of PPh3+ as a lipophilic cation on new water-soluble Co(II) and Zn(II) Schiff base complexes: Effect of central metal and substitutional group of ligand on DNA-complex interaction

Abstract

Abstract New series of water soluble Schiff base complexes by conjugating the lipophilic triphenylphosphonium cation to aromatic moiety of Schiff base ligand, aiming to increase the water solubility and passing through cell membrane were synthesized and characterized. Four new complexes; [N,N′-bis{5-[(triphenylphosphoniumchloride)-methyl]salicylidine}-phenylenediamine] with the formula [Zn(5-CH2PPh3-4-H-1,2-salphen)] (ClO4)2 (1), [Zn(5-CH2PPh3-4-CH3-1,2-salphen)](ClO4)2 (2), [Zn(5-CH2PPh3-4-Cl-1,2-salphen)](ClO4)2 (3), [Co(5-CH2PPh3-4-CH3-1,2-salphen)](ClO4)2 (4) were characterized by elemental analysis, FT-IR, 1H NMR, 13C NMR, 31P NMR and UV–vis spectroscopy. Cobalt(II) complex also characterized by thermal gravimetry analysis (TG). DNA interaction studies were investigated by UV–vis absorption spectroscopy, viscosity measurements, circular dichroism (CD) spectroscopy and fluorescence spectroscopy. The DNA binding affinity (Kb) obtained from absorption spectroscopy had this order: 2 > 3 > 4 > 1 > ligand(L) which revealed that metal complexes had more propensities to interact with DNA. In comparing the metal complexes; Zn(II) complexes revealed DNA binding stronger than the corresponding Co(II) analogue. All the complexes displayed cytotoxicity against Raji, Jurkat and A549 cell lines with potency more than that of cisplatin and thus they are good candidate to act as promising anticancer drug. Finally, docking studies were performed to further investigate the DNA binding interactions.