A new Ru(II) complex of [Ru(bpy)₂(Hpip)]²⁺ {bpy = 2,2′-bipyridine; Hppip = 2-(4-(pyridin-2-yl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline} has been synthesized by grafting of 2-pyridyl to parent complex [Ru(bpy)₂(Hpip)]²⁺ {Hppip = 2-(4-phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline}. The acid-base properties of [Ru(bpy)₂(Hpip)]²⁺ studied by UV-visible and luminescence spectrophotometric pH titrations, revealed off-on-off luminescence switching of [Ru(bpy)₂(Hpip)]²⁺ that was driven by the protonation/deprotonation of the imidazolyl and the pyridyl moieties. The complex was demonstrated to be a DNA intercalator with an intrinsic DNA binding constant of (5.56 ± 0.2) × 105 M-1 in buffered 50 mM NaCl, as evidenced by UV-visible and luminescence titrations, reverse salt effect, DNA competitive binding with ethidium bromide, steady-state emission quenching by [Fe(CN)6]4-, DNA melting experiments and viscosity measurements. The density functional theory method was also used to calculate geometric/electronic structures of the complex in an effort to understand the DNA binding properties. All the studies indicated that the introduction of 2-pyridyl onto Hpip ligand is more favorable for extension of conjugate plane of the main ligand than that of phenyl, and for greatly enhanced ct-DNA binding affinity accordingly.

Key words: Ruthenium; DNA; Bipyridine; Phenanthroline; Density functional theory.

This article can be cited as:

A-G. Zhang, H-X. Yang, K-Z. Wang. The Effects of Grafting of 2-Pyridyl to [Ru(bpy)₂(Hpip)]²⁺ on Acid-Base and DNA-Binding Properties: Experimental and DFT Studies J. Biomol Struct Dyn 28(6), 955-968 (2011).