DNA binding and cleavage studies of two palladium(II) saccharinate complexes with terpyridine

The aim of the present study is to investigate DNA binding interactions of two highly cytotoxic palladium(II) saccharinate (sac) complexes with 2,2':6',2″-terpyridine (terpy), [Pd(sac)(terpy)](sac)·4H(2)O (1) and [PdCl(terpy)](sac)·2H(2)O (2). UV-Vis spectroscopy, fluorescence spectroscopy, thermal denaturation, viscosity, and gel electrophoresis measurements were employed to study binding properties of the two complexes with Fish Sperm (FS) DNA. The interaction of the palladium(II) complexes with FS-DNA was monitored by hypochromism in the UV-Vis spectra. The binding constants (Kb) obtained from absorption titrations were estimated to be 1.0 (±0.05)×10(5) M(-1) for 1 and 2.0 (±0.22)×10(5) M(-1) for 2. Competitive binding studies with ethidium bromide have shown that both complexes strongly bind to FS-DNA, and the apparent binding constant (Kapp) calculated from emission studies was 2.0×10(6) M(-1) for each complex. Fluorescence Scatchard plots demonstrated that the palladium(II) complexes act as dual-function metallointercalators and bind to FS-DNA by both intercalation and coordination. On addition of the two complexes, significant increases in both viscosity and melting temperature of FS-DNA solutions further support the binding mode of these complexes. Gel electrophoresis assay demonstrates that both complexes efficiently cleavage the supercoiled plasmid 8454: pCMV-VSV-G DNA to its open circular form.