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97 Study on electron transfer through RNA/DNA duplex using pyrene and 5-bromouracil as an electron donor and acceptor pair

Because of potential applications in nanoscale devices, DNA-mediated charge transfer (CT) has attracted much interest. Through spectroscopic and chemical studies, it has been shown that both positive and negative charges injected into DNA bases can move through DNA over significant distances. The factors affecting to DNA-mediated CT are the nature of the charge donor and acceptor, the structural dynamics of DNA, and the intervening base sequences or the integrity of the base stacks. The last factor led to the electrochemical devices to detect the perturbations of DNA stacks such as a mismatch base pair. The photo-induced charge migration in DNA possessing a donor–acceptor pair has resulted in the long-lived charge separated state. This charge separation offers important insights for the development of photo-energy conversion devices such as solar cells. In contrast to the DNA-mediated CT, little attention has been paid for CT in a RNA duplex. Since RNA duplexes have the base stacking overlaps and dynamics that are significantly different from those of DNA–DNA as well as of DNA–RNA duplexes, they are another choice of attractive medium for CT. We have conducted the research on CT in RNA duplexes consisting of a pendant donor (pyrene) and acceptor (5-bromouracil or nitrobenzene) pair. We have found that long-range excess electron transfer occurs through RNA π-stacks with double exponential distance dependence. This finding should contribute to uncover the mechanism of RNA-mediated electron transfer and open a way for development of RNA-based devices that control electron migrations. By contrast, the pyrene-donor and 5-bromouracil-acceptor system indicates that DNA may not act as an efficient medium for the excess electron transfer.