Novel palladium(II) complexes containing a sulfur ligand: structure and biological activity on HeLa cells

Two novel palladium(II) complexes with a thiosalicylic acid (HSC(6)H(4)CO(2)H) ligand, with the formulas [Pd(TSA)(L)]·mH(2)O (TSA is thiosalicylic acid; in complex 1, L is 1,10-phenanthroline and m = 1; in complex 2, L is 2,2'-bipyridine and m = 2), have been synthesized and characterized. The coordination geometry of both palladium atoms is square planar; they are four-coordinated and each is coordinated in an N,N,O(-),S(-) mode. There is a sigmoid oxygen chain in complex 1, but an oxygen ring in complex 2. The competitive binding of the complexes to HeLa cell DNA (HL-DNA) has been investigated by fluorescence spectroscopy. The results show that the two complexes have the ability to bind with HL-DNA. Viscosity studies suggest that the complexes bind to DNA by intercalation. Gel electrophoresis assay demonstrated the ability of the complexes to cleave the HL-DNA. The two complexes exhibit cytotoxic specificity and a significant cancer cell inhibitory rate. The apoptosis tests indicated that the complexes have an apoptotic effect. Furthermore, complex 1 exhibits more biological activity than complex 2, which is mainly because the area of the aromatic ring of 1,10-phenanthroline is larger than that of 2,2'-bipyridine.