Effects of Tris and Hepes buffers on the interaction of palladium-diaminopropane complexes with DNA

The Pd(II) complexes, [PdCl2(1,2-pn)] and [PdCl2(1,3-pn)] (pn is diaminopropane), were synthesized and characterized by analytical and spectroscopic (FT-IR, 1H NMR and 13C NMR) techniques. UV difference spectral study performed on Pd-pn/DNA systems, indicate a pronounced interaction of palladium complexes with DNA in cell-free media; comparison of λmax, Absmax and %H values observed for the two compounds might be attributed to structural differences of the chelated ligand rings. Results obtained from electrophoretic analysis of Pd complexes in presence of pBR322 plasmid DNA show a clear decreasing of the supercoiled (SC) DNA form mobility, that could be attributed to unwinding of the double helix; a parallel increasing of the open-circular (OC) DNA form mobility is also noted, this fact implying that the binding of complexes either shortens or condenses the DNA helix. Interaction studies of Pd complexes with plasmid DNA in different buffer systems indicate that DNA binding efficiency capable of modifying the tertiary structure of pBR322 decreased from NaClO4 to Hepes 2, Hepes 1 [Hepes = 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid], and Tris [(hydroxymethyl)aminomethane] buffers, in this order. Moreover, the level of DNA modifications produced by palladium complexes in 10 mM NaClO4 remains unchanged after transferring the samples into the medium required for subsequent biophysical or biochemical analyses.