Bidentate acylthiourea ligand anchored Pd-PPh₃ complexes with biomolecular binding, cytotoxic, antioxidant and antihemolytic properties

Acylthiourea-based Pd(II) complexes (1–5) with a PPh₃ moiety bearing the general formula [PdCl(PPh₃)(L-R)] [L-R = monoanionic bidentate acylthiourea ligand, where R = C₆H₅ (L1), C₆H₄CH₃(o) (L2), C₆H₄OCH₂CH₃(p) (L3), C₁₀H₇ (L4) or C₆H₄Cl (L5)] have been synthesized and characterized by spectroscopic and analytical tools. The single crystal X-ray structures (1–3) revealed that the acylthiourea ligands coordinated to Pd(II) ion in an uncommon bidentate fashion through S and N atoms, forming a four-member ring. The Pd(II) ion exhibited a square planar geometry fulfilled by the ligand (N, S), one Cl^‐ and one triphenylphosphine (PPh₃). Calf thymus (CT) DNA and bovine serum albumin (BSA) binding of the complexes have been analyzed by spectroscopic and molecular docking studies. The complexes were tested for their in vitro cytotoxicity on three cancer (cervical, breast and lung) and one normal (human embryo) cell lines. Complex 4 bearing the naphthalene substitution exhibited the highest activity against three cancer cells with the half-maximal inhibitory concentration (IC₅₀) values of 8.6 (cervical), 8.8 (breast) and 9.4 μM (lung). The acridine orange/ethidium bromide (AO/EB) and 4′,6-diamidino-2-phenylindole (DAPI) staining assays indicated that 4 induced cancer cell death through apoptosis. Among the complexes, 4 exhibited the highest 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity of 86.19%. All the complexes were subjected to the hemolysis assay which revealed their biocompatibility with red blood cells (RBCs) with a lysis rate of less than 5 %.