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Tautomerism in the Guanyl Radical

Chatgilialoglu, Chryssostomos and Caminal, Clara and Altieri, Alessio and Vougioukalakis, Georgios C. and Mulazzani, Quinto G. and Gimisis, Thanasis and Guerra, Maurizio (2006) Tautomerism in the Guanyl Radical. Journal of the American Chemical Society, 128 (42). pp. 13796-13805. ISSN 0002-7863.

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Despite a few decades of intense study, a full description of tautomers of one-electron-oxidized guanine remains to be achieved. Here we show that two of these tautomers are produced by the protonation of an 8-haloguanine electron adduct. The rate constants for the reactions of hydrated electrons (e_(aq)-) with a variety of 8-substituted guanine derivatives have been measured by a pulse radiolysis technique and correlated with both inductive and resonance components of the substituents. The fate of electron adducts was investigated by radiolytic methods coupled with product studies and addressed computationally by means of time-dependent DFT (TD-B3LYP/6-311G**//B1B95/6-31+G**) calculations. The reaction of eaq- with 8-haloguanosine or 8-halo-2‘-deoxyguanosine produces the first observable transient species that decay unimolecularly (k = 1 × 10^5 s^(-1) at 22 °C) to give the one-electron oxidized guanosine or 2‘-deoxyguanosine. Theory suggests that the electron adducts of 8-bromoguanine derivatives protonated at C8 form a π-complex, with the Br atom situated above the molecular plane, that is prompt to eject Br-. The two short-lived intermediates, which show a substantial difference in their absorption spectra, are recognized to be the two purine tautomers (i.e., iminic 7 and aminic 3 forms). The spin density distributions of the two tautomers are quite different at the O6 and N10 positions, whereas they are very similar at the N3, C5, and C8 positions. The resonance structures of the two tautomers are discussed in some detail. B1B95/6-31+G** calculations show also that the tautomerization from the iminic (7) to the aminic (3) arrangement is a water-assisted process.

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Additional Information:© 2006 American Chemical Society. Received May 3, 2006. Publication Date (Web): September 28, 2006. Work supported in part by the European Community's Marie Curie Research Training Network under Contract MRTN-CT-2003-505086 [CLUSTOXDNA]. We thank Professor M. Orfanopoulos (University of Crete) for some helpful discussions and for allowing GCV to visit Bologna during his PhD work. We thank A. Monti and A. Martelli for assistance with pulse radiolysis experiments.
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Marie Curie FellowshipMRTN-CT-2003-505086
Issue or Number:42
Record Number:CaltechAUTHORS:20170510-102021981
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Official Citation:Tautomerism in the Guanyl Radical Chryssostomos Chatgilialoglu, Clara Caminal, Alessio Altieri, Georgios C. Vougioukalakis, Quinto G. Mulazzani, Thanasis Gimisis, and Maurizio Guerra Journal of the American Chemical Society 2006 128 (42), 13796-13805 DOI: 10.1021/ja062636h
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:77339
Deposited By: Tony Diaz
Deposited On:16 May 2017 20:29
Last Modified:03 Oct 2019 17:56

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