Comparative study of palladium(II) complexes bearing tridentate ONS and NNS Schiff base ligands: Synthesis, characterization, DFT calculation, DNA binding, bioactivities, catalytic activity, and molecular docking

Abstract

Two palladium (II) Schiff base complexes were prepared by using equivalent molar of Schiff base ligand [L1= (E)-2-(((2-(benzylthio)phenyl)imino)methyl)naphthalen-1-ol and L2= (E)-N-(2-(benzylthio)phenyl)-1-phenyl-1-(pyridin-2-yl)methanimine] and sodium tetrachloropalladate. The structure of ligands and complexes were characterized by physicochemical and spectroscopic analyses. The results suggested that the Pd(II) complexes have a distorted square planar geometry when coordinated to the tridentate ONS from L1 and the NNS donor ligand from L2. Electronic absorption and spectrofluorometric measurements were employed to investigate the DNA binding of ligands and their associated complexes with CT-DNA. DFT calculations were used to optimize the geometric structures and calculate the electronic and structural properties of the synthesized compounds. NBO analysis was also performed in combination with the TD-DFT method. Moreover, to study the reactivity and bioactivity, the synthesized compounds were tested for in-vitro antioxidant activity by utilizing the DPPH method, in-vitro anti-inflammatory activity using protein denaturation method, and in-vitro anti-diabetic activity employing α-glucosidase and α-amylase enzymes. The results reflect that PdL1 is more biologically potent than PdL2 or other related palladium complexes, as discussed in the literature. The binding mechanism of the synthesized compounds with CT-DNA, α-glucosidase, and α-amylase, was investigated using molecular docking experiments. In addition to these, the catalytic activity of palladium metal complexes (PdL1 and PdL2) was evaluated for the Suzuki-Miyaura reaction for comparisons.