Synthesis, DFT calculation, DNA-binding, antimicrobial, cytotoxic and molecular docking studies on new complexes VO(II), Fe(III), Co(II), Ni(II) and Cu(II) of pyridine Schiff base ligand

A new H2L ligand (6, 6 '-(pyridine-2, 6-diylbis(azan-1-yl-1-ylidene))bis(methan-1-yl-1-ylidene)bis(2-ethoxyphenol) was obtained from the reaction of 2, 6- diamino pyridine and 3- ethoxy salicyaldehyde in 1:2 molar ratio and fully characterized using elemental analyses and spectroscopic tools. The reaction of a ligand with the different metal salts yields five new complexes CuL, CoL, NiL, FeL, and VOL. The new complexes were identified according to the results of elemental analyses, IR and UV-vis spectra, magnetic moment, molar conductance and thermal analyses (TGA). From the conductivity data, it is deduced that all complexes are non-electrolytes. FT-IR spectra displayed that the Schiff base ligand coordinated to the metal ions in a manner with ONNO donor sites, the nitrogen atom of the pyridine ring, the nitrogen of one azomethine group and two oxygen atoms of the two phenolic OH groups. The results of electronic spectra and magnetic susceptibility confirmed octahedral geometry of FeL complex and square pyramidal geometry for CoL, CuL and VOL and square planar for NiL. The electronic structure of H2L ligand and its complexes were investigated theoretically at the DFT-B3LYP-311 G** level of the theory. FT-IR spectra established the involvement of pyridine nitrogen in the coordination process. The presence of coordinated water molecules inside the coordination sphere of the complexes CoL, CuL and FeL are supported by TGA studies. The antimicrobial activities of the ligand and its complexes were determined against two Gram-positive bacteria (B. subtitles and S. aureus) and two Gram-negative (E. coli and P. vulgaris) and two fungus (Candida albicans and Aspergilla's fumigates). The results showed that the complexes behaved as better antimicrobial agents than the ligand, VOL complex shows exceptional antimicrobial efficacy. The order of increasing the antibacterial and antifungal potency is H2L < NiL < CuL < CoL < FeL < VOL. The binding of the complexes with CT-DNA was followed using electronic absorption, viscosity and gel-electrophoresis measurements. These studies confirmed that the complexes bind to CT-DNA through a groove binding mode with certain affinities (Kb = 6.25 x 10(5), 5.50 x 10(5), 3.20 x 10(5), 2.50 x 10(5) and 1.52 x 10(5) for CuL, FeL, VOL, NiL, and CoL respectively). Moreover, cytotoxic effect against hepatocellular carcinoma cell line (HEP-G2) was screened. The IC50 values of the ligand and complexes suggest that the compounds possess very good cytotoxic activity and follow the order: CuL >FeL>VOL>NiL>CoL > H2L. These results strongly agree with results of binding constant of CT-DNA with different metal complexes.