DNA/protein interaction and cytotoxicity of palladium(II) complexes of thiocarboxamide ligands

Four planar palladium(II) complexes with general formula [Pd(Cl)(L)(PPh3)] (HL = N-substituted pyridine-2-thiocarboxamide) have been synthesized and characterized by analytical, spectral (IR, UV–Vis and 1H, 13C and 31P NMR) and single crystal X-ray methods. Crystal structure of all the complexes indicated a mono negative bidentate coordination of thiocarboxamide ligands to the palladium center via pyridine nitrogen and thiol sulfur and reveals a square planar geometry. The interaction of palladium(II) thiocarboxamide complexes with calf thymus DNA (CT-DNA) studied by absorption and emission spectroscopic methods revealed that complexes 5–8 could interact with CT-DNA through intercalation. Further, the interaction of the palladium complexes with bovine serum albumin (BSA) was investigated using UV–Vis, fluorescence and synchronous fluorescence methods. The tryptophan and tyrosine residues in BSA as model protein was quenched by the complexes in a static quenching process. The radical scavenging ability of all the complexes was accessed by in vitro antioxidant assays involving DPPH radical, hydroxyl radical, nitric oxide radical and ABTS radicals and was found to be excellent. Further, the anti-cancer activity of complexes 5–8 against HeLa, MCF-7 and NIH-3T3 cell line has been studied. Though the complexes 5, 6 and 8 showed more potent anticancer activity than cisplatin, complex 5 was found to be superior.