Role of Substitution at Terminal Nitrogen of 2-Oxo-1,2dihydroquinoline-3-Carbaldehyde Thiosemicarbazones on the Coordination Behavior and Structure and Biological Properties of Their Palladium(II) Complexes

A series of four new palladium(II) complexes of 2-oxo-1,2-dihydroquinoline-3-carbaldehyde thiosemicarbazones with triphenylphosphine as coligand have been synthesized and characterized by the aid of various spectral techniques. The single-crystal X-ray diffraction studies revealed that the unsubstituted thiosemicarbazone ligand acted as monobasic tridentate (ONS-) in the cationic [Pd(H-Qtsc-H)(PPh3)]Cl complex, whereas the monosubstituted thiosemicarbazone ligands acted as monobasic bidentate (NS-) in their respective complexes, [PdCl(H-Qtsc-R)(PPh3)] (R = Me (2), Et (3), Ph (4)). To ascertain the potentials of the above Pd(II) complexes toward biomolecular interactions, additional experiments involving interaction with calf thymus DNA and bovine serum albumin were carried out. Moreover, all the palladium(II) complexes have been screened for their radical scavenging activity toward DPPH, O-2(-), OH, and NO radicals. The efficiency of the complexes in arresting the growth of human cervical cancer cells (He La), human laryngeal epithelial carcinoma cells (HEp-2), human liver carcinoma cells (Hep G2), and human skin cancer cells (A431) has also been studied along with the cell viability test against the noncancerous NIH 3T3 mouse embryonic fibroblasts cell lines under in vitro conditions. All the in vitro pharmacological evaluation results clearly revealed the relationship between the structure and the activity of the new Pd(II) complexes.