Understanding the Role of Ancillary Ligands in the Interaction of Ru(II) Complexes with Covalent Arylamine-DNA adducts

Abstract The interaction between Ru(II) complexes and covalent DNA-arylamine adduct has been studied by using steady-state fluorescence spectroscopy. Here, we have used 16-mer NarI sequences with variation in next flanking bases i.e., -CG1G2CG3CX- in which X is either C or T and G is unmodified or N-acetylaminofluorene-dG (AAF-dG). To understand the effect of ancillary ligands, we used three Ru(II) complexes [Ru(phen)2(dppz)]2+ (Ru-1), [Ru(TMP)2(dppz)]2+ (Ru-2)and [Ru(DIP)2(dppz)]2+(Ru-3) [where phen: 1,10-phenanthroline; TMP: 3,4,7,8-tetramethyl-1,10-phenanthroline; DIP: 4,7-diphenyl 1,10-phenanthroline; dppz: dipyrido[3,2-a;2’,3’-c]phenazine]. Steady-state luminescence data shows that all the three complexes exhibit strong luminescence when it binds to AAF-dG adducts compared to unmodified control. The addition of sodium iodide to the binary mixture (Ru-oligo) improves the luminescence differential in G1 and G3 AAF adducts while it is minimal with the at G2. Competitive binding studies also show that the ancillary ligand in the complex Ru-2 alters the binding towards the adducted site compared to Ru-1 and Ru-3. Overall, the present study reveals that the probing of adducted site by Ru(II) complexes is dictated not only by the conformational heterogeneity of the AAF-dG adduct but ancillary ligands as well.