A combined computational and experimental study on DNA-photocleavage of Ru(ii) polypyridyl complexes [Ru(bpy)2(L)]2+ (L = pip, o-mopip and p-mopip)

Abstract

A combined computational and experimental study on DNA-photocleavage by Ru(II) polypyridyl complexes [Ru(bpy)₂(L)]²⁺1–3 (bpy = 2,2-bipyridine; L: pip = 2-phenylimidazo[4,5-f]1,10-phenanthroline, o-mopip = 2-(2-methoxyphenyl)imidazo[4,5-f]1,10-phenanthroline and p-mopip = 2-(4-methoxyphenyl)imidazo[4,5-f]1,10-phenanthroline) has been carried out. The DNA-photocleavage behavior of these complexes was comparably measured by the gel electrophoresis experiments. The experimental results show that they can induce considerable DNA-photocleavage, and have different DNA-photocleavage efficiencies (φ) following the order φ (1) < φ (2) < φ (3). In order to understand their DNA-photocleavage mechanism and trend, the theoretical studies on the geometric and electronic structures of these complexes in the ground state (S₀), the first singlet excited state (S₁) and triplet excited states (T₁), have been carried out using the density functional theory (DFT/TD-DFT), Hartree–Fock (HF) and configuration interaction singles (CIS) methods. In particular, the reduction potentials (E*_red) of the excited complexes in aqueous solution, which seem to be closely responsible for the DNA-photocleavage behavior, were calculated to be 0.966 V (vs. SCE) for complex 1, 1.024 V (vs. SCE) for complex 2 and 1.030 V (vs. SCE) for complex 3, respectively. Such computational results show that the reduction potentials of the excited complexes reach the theoretical range for oxidizing some DNA-bases, and follow the order E*_red (1) < E*_red (2) < E*_red (3). Therefore, here, in addition to the general theoretical explanation of their DNA-photocleavage mechanism according to our recent report, a further explanation on the trend of their DNA-photocleavage efficiencies, i.e., φ (1) < φ (2) < φ (3), was reasonably carried out, on the basis of the calculated electrochemical properties in the excited states as well as general photochemical insights.