Issue Date: March 19, 2007
Electronically excited DNA
For more than a half-century, chemists have debated what happens immediately after genomic DNA is exposed to damaging ultraviolet radiation. Is the resulting UV-induced electronic excitation localized on a single nucleotide base or does it spread over neighboring bases in the helical DNA stack? Boston College chemists now have demonstrated experimentally that the electronic excitation delocalizes in single- and double-stranded polyadenine (Proc. Natl. Acad. Sci. USA 2007, 104, 4794). Torsten Fiebig's team used femtosecond time-resolved broadband spectroscopy to show that this delocalization in polyadenine spreads over three to four stacked bases. Some scientists have suggested that, because delocalized excited states tend to stick around longer than those centered on single bases, delocalization might prolong the window during which the excited bases are susceptible to chemical damage. But Fiebig suspects that delocalization is inhibited in vivo because bases in random genetic sequences are not as neatly stacked as they are in extended strings of adenine or guanine.
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