Photoactivated cleavage of pBR 322 DNA by a series of ruthenium(II) polypyridyl complexes has been studied. The experimental results were compared with our previous observations using spectroscopic methods and viscosity measurements. The experimental results suggest that the capacity of ruthenium(II) polypyridyl complex to photocleavage DNA depends on not only the mode and strength of the complex binding to DNA, but also the electron structure of the complex, and that ruthenium(II) polypyridyl complex can photocleavage DNA enantioselectively. The mechanism of DNA cleavage of these complexes was also discussed and proposed as follows: the excited state of Ru(II) polypyridyl complex transfers its energy to the oxygen in solution, producing singlet molecular oxygen as the active oxygen species in the scission reactions, which oxidizes guanine of DNA and leads to cleavage of DNA. These studies are very important to the design of chemical nucleases and DNA-targeting drugs.

Key words: ruthenium(II) polypyridyl complex, DNA, photocleavage, chemical nuclease