| Abstract
| - We have examined the structural and electronic effects of the one-electron oxidation of the C·G*G triplex, where G is located in a quite different environment from the G of duplex DNA. Uponphotoirradiation of an external photosensitizer (riboflavin) with the C·G*G triplex, oxidative DNA cleavageoccurred exclusively at guanine repeat sequences in the third strand of triple helix DNA. Hole transportthrough the C·G*G triplex also occurred, resulting in selective cleavage at G in the third strand. Thus, thehole generated in the duplex can migrate to GGG in the third strand and is trapped exclusively at Gs in thethird strand. These experimental results, together with molecular orbital calculations, suggest that the originof the selective strand cleavage can be explained as follows: (i) guanine repeat sequences in the thirdstrand are more easily oxidized than in duplex DNA and (ii) in their radical cation states, G of the thirdstrand rapidly deprotonates and reacts with oxygen and/or water, leading to strand cleavage. These resultsindicate that the oxidative damage preferentially occurred at Gs of the third strand owing to thermodynamicand kinetic features of the one-electron oxidation of the C·G*G triplex.
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