Interaction of ruthenium(II)[(1,10-phenanthroline) ₂benzodipyrido[3,2-a:2′,3′-c]-phenazine]²⁺ with single stranded poly(dA) and poly(dT): Turning off the light switch

The spectral properties, namely the circular dichroism, electric absorption and luminescence properties, of Λ- and Δ-[Ru(II)(1,10- phenanthroline)₂benzodipyrido[b:3,2-h:2′,3′-j]phenazine] ²⁺ ([Ru(phen)₂BDPPZ]²⁺) in the presence and absence of single stranded poly(dA) and poly(dT) were compared in this work. In the presence of single stranded DNAs, hypochromism in the absorption spectrum and significant changes in the circular dichroism spectrum in the ligand absorption band were apparent, indicating the strong interaction of the [Ru(phen)₂BDPPZ]²⁺ complex with the single stranded DNAs. The luminescence intensity of the Ru(II) complex decreased stoichiometrically with increasing concentrations of the single stranded DNAs. All of these spectral changes were independent of the configuration of the Ru(II) complex and the nature of the DNA bases. Therefore, it is conceivable that both enantiomers of the [Ru(phen)₂BDPPZ]²⁺ complex interact electro-statically with the negatively charged phosphate groups of DNA. However, the spectral properties of [Ru(II)(1,10-phenanthroline)₃] ²⁺ were not altered even in the presence of single stranded DNAs. Therefore, the size of the ligand involved in the interaction of the metal complex with the phosphate group of DNA may play an important role, even when the nature of the interaction is electrostatic.