Spectroscopic characterization, DFT calculations, in vitro pharmacological potentials, and molecular docking studies of N, N, O-Schiff base and its trivalent metal complexes

Abstract

In this study, trivalent metal complexes of the category: [M(L)(H2O)nCly] obtained from the interaction of metal3+ ion salts with organic N, N, O-Schiff base (HL) (where: HL = 4-{(Z)-((2-{(E)-((2-hydroxyphenyl)methylidene)amino}ethyl)imino)methyl}-2-methoxyphenol; n, y = 1 or 2 and M = Ti(III), Fe(III), Ru(III), Cr(III) and Al(III)) were synthesized and characterized viz molar conductance, FT-IR, and UV–Vis spectroscopies, elemental analyses, thermal analyses (TGA and DTA), and UV–Vis spectroscopy, theoretical calculations. A distorted octahedral structure around the metal ions was proposed based on the obtained experimental and calculated data. Thermal examination of the complexes signposts the step-by-step disintegration to give the final decomposition product as metal oxides. Moreover, DFT calculations were executed utilizing the B3LYP/LANL2DZ theory level, which revealed that the synthesized metal (III) complexes were more stable than the free ligand (HL). The value of ΔE for HL is 4.60 eV while the related values for the complexes of Cr(III) (C1), Ru(III) (C2), Fe(III) (C3), Al(III) (C4), and Ti(III) (C5) are respectively 2.59, 3.68, 3.15, 1.64, and 2.75 eV. Scavenging abilities of DPPH and ABTS radicals by the test compounds revealed promising antioxidant behavior. It was observed that the compounds are proficient DPPH radical scavengers in a dose-dependent configuration. Ru(III); IC50 = 1.69 ± 2.68 µM for DPPH and Ti(III); IC50 = 8.70 ± 2.78 µM for ABTS performed best. Similarly, the complexes demonstrated higher antimicrobial activities compared to HL against the designated strains, while ciprofloxacin acted as a standard antibiotic. Furthermore, the ligand and its most effective complexes C2 and C5 were docked against the targets S. aureus DNA gyrase (2XCT), S. pneumoniae DNA gyrase (5BOD), and E. coli DNA gyrase (5L3J). The binding sites were evaluated and the docking results showed that the studied molecules bind to the targets through classical O—H…O and/or N—H…O hydrogen bonds, as well as via hydrophobic contacts.