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摘要
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 (phi) following the order phi(1)<phi(2)<phi( 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 (S-0), the first singlet excited state (S-1) and triplet excited states (T-1), 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., phi(1)<phi(2)<phi(3), was reasonably carried out, on the basis of the calculated electrochemical properties in the excited states as well as general photochemical insights.
