The interaction of native calf thymus DNA with the Pd(II) complex, PdCl2(LL) (LL = chelating diamine ligand: N,N-dimethyltrimethylenediamine), in 10 mM Hepes aqueous solutions at neutral pH has been monitored as a function of metal complex/DNA molar ratio by UV absorption spectrophotometry, circular dichroism (CD), viscosimetry, and fluorescence spectroscopy. The results support two modes of interaction. In particular, this complex showed absorption hypochromism and then hyperchromism, increase in melting temperature, and some structural changes in specific viscosity when bound to calf thymus DNA. The binding constant determined using absorption measurement is 2.69.10(3) M(-1). As evidenced by the increasing fluorescence of methylene blue-DNA solutions in the presence of increasing amounts of metal complex, PdCl(2)(LL) is able to displace the methylene blue intercalated into DNA, but not so completely, as indicated by partial intercalation. CD spectral changes in two steps and viscosity decrease confirm our conclusions.

The [PtCl(2)(LL)] complex, as a cisplatin derivative, which LL is diamine chelate ligand (N,N-dimethyltrimethylendiamine), was synthesized and characterized by elemental analysis (CHN) mass, (1)H, and (13)C nuclear magnetic resonance techniques. Then the binding of this complex to calf thymus DNA was investigated by various physicochemical methods such as spectrophotometric, circular dichroism, spectrofluorometric, melting temperature, and viscosimetric techniques. Upon addition of the complex, important changes were observed in the characteristic UV-Vis bands (hypochromism) of calf thymus DNA, increase in melting temperature and some changes in specific viscosity. Also, the fluorescence spectral characteristics showed an increase in the fluorescence intensity of methylene blue-DNA solutions in the presence of increasing amounts of metal complex, indicating PtCl(2)(LL) is able to displace the methylene blue bound to DNA but not as complete as intercalative molecules. The experimental results showed that the platinum complex is bound to DNA non-intercalatively, and an outside binding is the preferred mode of interaction.