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| - Glycosidic Bond Cleavage of Pyrimidine Nucleosides byLow-Energy Electrons: A Theoretical Rationale
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| - DNA damage by attachment of low-energy secondary electrons is a very interesting and importantmechanism. Electron capture and subsequent base release are thought to be the elementary steps of thismechanism. The process of the N1-glycosidic bond breaking of anion radicals of pyrimidine nucleosides,specifically the 2‘-deoxyribothymidine (dT) and 2‘-deoxyribocytidine (dC) anions, has been investigatedtheoretically at the B3LYP/DZP++ level of theory. The release of nucleobases by the attachment of low-energy electrons depends on the formation of a stable anion radical of the nucleoside. The lower bond-breaking activation energy and the higher vertical electron detachment energy for dT enables the heterolyticcleavage of the N1-glycosidic bond. However, with the higher bond-breaking activation energy and thelower vertical electron detachment energy for dC, the release of cytosine might be impractical when theincident electrons have high kinetic energy. Furthermore, the release of cytosine would have a quantumyield much lower than that of dT when the incident electrons have lower kinetic energy. This study alsodemonstrates the importance of the proton at O5‘ of 2‘-deoxyribose in the base release process. Extendingthis investigation from dT to dC advances the insight into the mechanism of the N1-glycosidic bond-breakingprocess. The information from this extensive investigation should be valuable for further experimental studiesof cytosine release in irradiated DNA.
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