Interaction of a new Pd(II)-piperidine complex with CT-DNA usingfluorescence spectroscopy

While the platinum-based anticancer agents have great therapeutic utilities [۱], the types ofcancer that can be cured with these agents are limited and the drugs exhibit side effects andresistance phenomena. Thus, bioinorganic synthetic chemists are continually trying to prepare nonplatinum-based complexes bearing more effective, less toxic, target-specific and interact noncovalentlywith DNA as a target molecule in the cancer cells [۲]. Recently, numerous Pd(II)complexes having higher anticancer activity and lower toxic side effects have been reported [۳].In this study, a new Pd(II) complex with the formula cis-[Pd(pip)۲Cl۲], in which pip is thepiperidine ligand, was synthesized and characterized. The interaction of the complex with doublestranded calf thymus DNA (CT-DNA) was studied by a competitive binding fluorescenceexperiment using ethidium bromide (EB) as a probe. This study was done at three differenttemperatures of ۲۹۸, ۳۰۵ and ۳۱۰ K. In these experiments, the fluorescence intensity of EB boundto DNA was quenched considerably on addition of the Pd(II) complex. This indicates that theintercalated EB molecules on ds-DNA could be replaced partially by the Pd(II) [۴]. The bindingconstant (Kb) values in the interaction of the studied complex with CT-DNA were calculated to be۴.۵ × ۱۰۴, ۱.۷ × ۱۰۵ and ۶.۱ × ۱۰۵ M‒۱ at ۲۹۸, ۳۰۵ and ۳۱۰ K, respectively. The number of bindingsites (n) on DNA for this complex was found to be about ۱. The obtained results indicate amoderately strong interaction between the Pd(II) complex and CT-DNA, which is probably occurvia groove binding. The thermodynamic parameters ΔH°, ΔS° and ΔG° in the interaction of themetal complex with CT-DNA were also determined using the results obtained from thefluorescence spectroscopy, which indicate a spontaneous hydrophobic interaction between thePd(II) complex and DNA.