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Nucleic Acids Research 2005 33(17):5553-5564; doi:10.1093/nar/gki857
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Published online 4 October 2005

© The Author 2005. Published by Oxford University Press. All rights reserved
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Article

UVA-visible photo-excitation of guanine radical cations produces sugar radicals in DNA and model structures

Amitava Adhikary, Aramice Y. S. Malkhasian, Sean Collins, Jessica Koppen, David Becker and Michael D. Sevilla*

Department of Chemistry, Oakland University Rochester, MI 38309, USA

*To whom correspondence should be addressed. Tel: +1 248 370 2328; Fax: +1 248 370 2321; Email: sevilla{at}oakland.edu

Received August 17, 2005. Revised September 6, 2005. Accepted September 6, 2005.

This work presents evidence that photo-excitation of guanine radical cations results in high yields of deoxyribose sugar radicals in DNA, guanine deoxyribonucleosides and deoxyribonucleotides. In dsDNA at low temperatures, formation of C1'• is observed from photo-excitation of G•+ in the 310–480 nm range with no C1'• formation observed ≥520 nm. Illumination of guanine radical cations in 2'dG, 3'-dGMP and 5'-dGMP in aqueous LiCl glasses at 143 K is found to result in remarkably high yields (~85–95%) of sugar radicals, namely C1'•, C3'• and C5'•. The amount of each of the sugar radicals formed varies dramatically with compound structure and temperature of illumination. Radical assignments were confirmed using selective deuteration at C5' or C3' in 2'-dG and at C8 in all the guanine nucleosides/tides. Studies of the effect of temperature, pH, and wavelength of excitation provide important information about the mechanism of formation of these sugar radicals. Time-dependent density functional theory calculations verify that specific excited states in G•+ show considerable hole delocalization into the sugar structure, in accord with our proposed mechanism of action, namely deprotonation from the sugar moiety of the excited molecular radical cation.


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A. Adhikary, D. Becker, S. Collins, J. Koppen, and M. D. Sevilla
C5'- and C3'-sugar radicals produced via photo-excitation of one-electron oxidized adenine in 2'-deoxyadenosine and its derivatives
Nucleic Acids Res., March 14, 2006; 34(5): 1501 - 1511.
[Abstract] [Full Text] [PDF]


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