Palladium(II)-salicylanilide complexes as antibacterial agents: Synthesis, spectroscopic, structural characterization, DFT calculations, biological and in silico studies

Abstract

Palladium(II)-Salicylanilide complexes of the type [Pd(κ2-Saln)2] (1), [Pd(κ2-Saln)2(diphos)] (2-6) (diphos = dppe, dppp, dppb, dppf, and dppmS2) and [Pd(κ2-Saln)2(μ-dppm)] (7) were synthesized and characterized. The salicylanidate ligand (Saln−) was bonded as bidentate chelating through the O atoms of hydroxyl and carbonyl groups in complex (1), whereas coordinated as monodentate through the O atom of hydroxyl group in complexes (2-7), and the all diphosphine ligands except dppm bonded as bidentate chelating to afford a square planner geometry around the Pd(II) ion. The dppm ligand was coordinated as bidentate bridging to afford binuclear complex. The prepared complexes displayed respectable activity against the pathogen bacteria species. Complex (5) showed the highest inhibition value against all types of bacteria, compared to the other complexes and the free ligand. On the other hand, the complex [Pd(Saln)2], showed the lowest inhibition against all types of bacteria. And the inhibition sequence of complexes is as following: (5) > (4) > (2) > (3) > HSaln > (1)Calculations of density function theory (DFT) were performed at the B3LYP/6-311G(d,p) level involved in the Gaussian 09 program to inspect the optimized structures of the chelating agent and its complexes. Docking study of the ligand was performed against the proteins of bacterial strains Pseudomonas aeruginosa (ID: 3P3E), Escherichia coli (ID: 1C14), Staphylococcus aureus (ID: 3BL6), and Salmonella typhimurium (ID: 3V7F) by Auto-Dock tools to portend the best binding mode.