Thermodynamic and structural study of phenanthroline derivative ruthenium complex/DNA interactions: Probing partial intercalation and binding properties

The binding of [Ru(PDTA-H2)(phen)]Cl (PDTA = propylene-1,2-diaminetetra-acetic acid; phen = 1,10 phenanthroline) with ctDNA (=calf thymus DNA) has been investigated through intrinsic and induced circular dichroism, UV–visible absorption and fluorescence spectroscopies, steady-state fluorescence, thermal denaturation technique, viscosity and electrochemical measurements. The latter indicate that the cathodic and anodic peak potentials of the ruthenium complex shift to more positive values on increasing the DNA concentration, this behavior being a direct consequence of the interaction of both the reduced and oxidized form with DNA binding. From spectrophotometric titration experiments, the equilibrium binding constant and the number of monomer units of the polymer involved in the binding of one ruthenium molecule (site size) have been quantified. The intrinsic circular dichroism (CD) spectra show an unwinding and a conformational change of the DNA helix upon interaction of the ruthenium complex. Quenching process, thermal denaturation experiments and induced circular dichroism (ICD) are consistent with a partial intercalative binding mode.

The [Ru(PDTA-H2)(phen)]+ complex binds to the ctDNA in a partial intercalative mode. Considering the positive ICD observed, the aromatic phenanthroline ring is perpendicular to the DNA axis with its long direction parallel to the base-pairs long axis.Figure optionsDownload as PowerPoint slide