Tautomerism in the Guanyl Radical
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- 作者：Chryssostomos Chatgilialoglu ; Clara Caminal ; Alessio Altieri ; Georgios C. Vougioukalakis ; Quinto G. Mulazzani ; Thanasis Gimisis ; Maurizio Guerra
- 刊名：Journal of the American Chemical Society
- 出版年：2006
- 出版时间：October 25, 2006
- 年：2006
- 卷：128
- 期：42
- 页码：13796 - 13805
- 全文大小：338K
- 年卷期：v.128,no.42(October 25, 2006)
- ISSN：1520-5126
文摘
Despite a few decades of intense study, a full description of tautomers of one-electron-oxidizedguanine remains to be achieved. Here we show that two of these tautomers are produced by the protonationof an 8-haloguanine electron adduct. The rate constants for the reactions of hydrated electrons (eaq-) witha variety of 8-substituted guanine derivatives have been measured by a pulse radiolysis technique andcorrelated with both inductive and resonance components of the substituents. The fate of electron adductswas investigated by radiolytic methods coupled with product studies and addressed computationally bymeans 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 thatdecay unimolecularly (k = 1 × 105 s-1 at 22 
C) to give the one-electron oxidized guanosine or2'-deoxyguanosine. Theory suggests that the electron adducts of 8-bromoguanine derivatives protonatedat C8 form a 
chars/pi.gif" BORDER=0 >-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, arerecognized to be the two purine tautomers (i.e., iminic 7 and aminic 3 forms). The spin density distributionsof the two tautomers are quite different at the O6 and N10 positions, whereas they are very similar at theN3, 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.
C) to give the one-electron oxidized guanosine or2'-deoxyguanosine. Theory suggests that the electron adducts of 8-bromoguanine derivatives protonatedat C8 form a chars/pi.gif" BORDER=0 >-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, arerecognized to be the two purine tautomers (i.e., iminic 7 and aminic 3 forms). The spin density distributionsof the two tautomers are quite different at the O6 and N10 positions, whereas they are very similar at theN3, 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.