Research ArticleChemistry

Reactivity of prehydrated electrons toward nucleobases and nucleotides in aqueous solution

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Science Advances  15 Dec 2017:
Vol. 3, no. 12, e1701669
DOI: 10.1126/sciadv.1701669

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DNA damage induced via dissociative attachment by low-energy electrons (0 to 20 eV) is well studied in both gas and condensed phases. However, the reactivity of ultrashort-lived prehydrated electrons (Embedded Image) with DNA components in a biologically relevant environment has not been fully explored to date. The electron transfer processes of Embedded Image to the DNA nucleobases G, A, C, and T and to nucleosides/nucleotides were investigated by using 7-ps electron pulse radiolysis coupled with pump-probe transient absorption spectroscopy in aqueous solutions. In contrast to previous results, obtained by using femtosecond laser pump-probe spectroscopy, we show that G and A cannot scavenge Embedded Image at concentrations of ≤50 mM. Observation of a substantial decrease of the initial yield of hydrated electrons (Embedded Image) and formation of nucleobase/nucleotide anion radicals at increasing nucleobase/nucleotide concentrations present direct evidence for the earliest step in reductive DNA damage by ionizing radiation. Our results show that Embedded Image is more reactive with pyrimidine than purine nucleobases/nucleotides with a reactivity order of T > C > A > G. In addition, analyses of transient signals show that the signal due to formation of the resulting anion radical directly correlates with the loss of the initial Embedded Image signal. Therefore, our results do not agree with the previously proposed dissociation of transient negative ions in nucleobase/nucleotide solutions within the timescale of these experiments. Moreover, in a molecularly crowded medium (for example, in the presence of 6 M phosphate), the scavenging efficiency of Embedded Image by G is significantly enhanced. This finding implies that reductive DNA damage by ionizing radiation depends on the microenvironment around Embedded Image.

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