Binding of Ru(terpyridine)(pyridine)dipyridophenazine to DNA studied with polarized spectroscopy and calorimetryElectronic supplementary information (ESI) available. See DOI: 10.1039/c4dt02642j

Linear and circular dichroism (LD and CD) spectroscopy as well as isothermal titration calorimetry (ITC) have been used to investigate the interaction of Ru(tpy)(py)dppz 2+ (tpy = 2,2′:6′,2′′-terpyridyl; py = pyridine; dppz = dipyrido[3,2- a :2′3′- c ]phenazine) with DNA, providing detailed information about the DNA binding thermodynamics and binding geometry of the metal complex. Flow LD, CD and isotropic absorption indicate that Ru(tpy)(py)dppz 2+ bind to DNA from the minor groove with the dppz ligand intercalated between base pairs, very similar to its chiral structural isomers Δ- and Λ-Ru(bpy) 2 dppz 2+ (bpy = 2,2′-bipyridine). A simple cooperative binding model with one binding geometry provide an excellent fit for calorimetric and absorption titration data. The values of the neighbor interaction thermodynamic parameters for Ru(tpy)(py)dppz 2+ suggest that complexes bound contiguously prefer to have their tpy ligands oriented towards the same strand. Achiral Ru(tpy)(py)dppz 2+ intercalated into DNA has similar intermolecular interactions as opposite enantiomers of its structural isomer, the "light-switch" complex Ru(bpy) 2 dppz 2+ .