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Published September 13, 2007 | Supplemental Material
Journal Article Open

DFT Study on the Nucleophilic Addition Reaction of Water and Ammonia to the Thymine Radical Cation

Abstract

The nucleophilic addition reactions of water and ammonia molecules toward the C5−C6 double bond of thymine radical cations were investigated using density functional theory. We predicted that the nucleophilic addition favored the C5-site of thymine radical cations, in contrast to the previous experimental observations in bulk solution where the addition product to the C6-site was dominant. Considering the molecular orbital factors, we estimated the relative reactivity of the C5- and C6-sites of thymine radical cations for the nucleophilic addition of ammonia. We found that the C5 was more reactive than the C6 for the small-size clusters of Thy_1(NH_3)_n+, n = 0−2, in the gas phase and even in aqueous solution, though the difference in the reactivity between the two sites became smaller as the number of ammonia molecules increased. This variation of the reactivity was attributed to the electron density redistribution within the thymine radical cations induced by the ammonia molecules as a nucleophile. We suggest that the dominance of the C6-addition product in bulk solution is mainly due to the higher stability of the C6-addition product by solvation, rather than to the higher reactivity of the C6-site for the nucleophilic addition.

Additional Information

© 2007 American Chemical Society. Received: May 4, 2007; In Final Form: June 18, 2007. Publication Date (Web): August 21, 2007. This work was supported by the research grant of the Chungbuk National University in 2006. N.J.K. thanks Professor Young Kee Kang for helpful discussions.

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