Synthesis, structure, spectroscopic properties and cytotoxic effect of some thiosemicarbazone complexes of palladium

Abstract

Reaction of salicylaldehyde thiosemicarbazone (H2L1), 2-hydroxyacetophenone thiosemicarbazone (H2L2) and 2-hydroxynaphthaldehyde thiosemicarbazone (H2L3) (general abbreviation H2L, where H2 stands for the two dissociable protons, one phenolic proton and one hydrazinic proton) with Na2[PdCl4] affords a family of polymeric complexes of type [{Pd(L)}n]. Reaction of the polymeric species with two monodentate ligands (D), viz. triphenylphosphine (PPh3) and 4-picoline (pic), has yielded complexes of type [Pd(L)(D)]. These mixed-ligand complexes have also been obtained from reaction of the thiosemicarbazones with [Pd(PPh3)2Cl2] and [Pd(pic)2Cl2]. Crystal structures of [Pd(L1)(PPh3)] and [Pd(L2)(pic)] have been determined. The [Pd(L)(D)] complexes show characteristic 1H NMR spectra and intense absorptions in the visible and ultraviolet region. They also fluoresce in the visible region at ambient temperature. In vitro cytotoxicity screenings of the complexes along with four human clinical drugsviz.cisplatin, BCNU, 5-fluorouracil (5-FU) and hydroxyurea have been carried out in two human tumor cell lines, namely promyelocytic leukemia HL-60 and histiocytic lymphoma U-937. [Pd(L2)(PPh3)] shows the lowest IC50 value and is found to be much more cytotoxic than the reference anticancer drugs in both the cell lines. An apoptosis study in HL-60 with [Pd(L2)(PPh3)] confirms that at 10 µM concentration it induces apoptosis to a greater extent than cisplatin and camptothecin.