Studies on synthesis, characterization, and G-quadruplex binding of Ru(II) complexes containing two dppz ligands

Abstract

In this work, the interaction between the guanine-rich single-strand oligomer AG3(T2AG3)3 quadruplex and two Ru(II) complexes, [Ru(L1)(dppz)2](PF6)4 (1) and [Ru(L2)(dppz)2](PF6)4 (2) (L1=5,5′-di(1-(trimethylammonio)methyl)-2,2′-dipyridyl cation, L2=5,5′-di(1-(triethylammonio)methyl)-2,2′-dipyridyl cation, dppz=dipyrido[3,2-a:2′,3′-c] phenazine), has been studied by UV–Visible, fluorescence, DNA melting, and circular dichroism in K+ buffer. The two complexes after binding to G-quadruplex have shown different DNA stability and fluorescence enhancement. The results show that both complexes can induce the stabilization of quadruplex DNA. ΔTm values of complexes 1 and 2 at [Ru]/[DNA] ratio of 1:1 were 9.4 and 7.0, respectively. Binding stoichiometry along with the quadruplex was investigated through a luminescence-based Job plot. The major inflection points for complexes 1 and 2 were 0.49 and 0.46, respectively. The data were consistent with the binding mode at a [quadruplex]/[complex] ratio of 1:1. In addition, the conformation of G-quadruplex was not changed by the complexes at the high ionic strength of K+ buffer.