Reaction of Hydrated Electrons with Guanine Derivatives: Tautomerism of Intermediate Species

Abstract

Here, we show that two tautomers are produced by the protonation of the guanine-electron adduct. The fate of electron adducts of a variety of substituted guanosines was investigated by radiolytic methods and addressed computationally by means of time-dependent DFT (TD-B3LYP/6-311G**//B1B95/6-31+G**) calculations. The reaction of e(aq-) with guanosine and 1-methylguanosine produces two transient species, whereas the reaction with N2-ethylguanosine and N2,N2-diethylguanosine produces only one. The two short-lived intermediates, which show a substantial difference in their UV-visible spectra, are recognized to be two purine tautomers (i.e., iminic 18 and aminic 19 forms). The tautomerization 18 --> 19 occurs with a rate constant of ca. 1.5 x 106 s(-1) , and theory suggests that it is a water-assisted process.

Radiosensitization of DNA by Cisplatin Adducts Results from an Increase in the Rate Constant for the Reaction with Hydrated Electrons and Formation of PtI

“…The latter species may undergo further reactions with H 2 O or radicals in the reaction mixture. 32 Figure 5 shows our proposed mechanism of d(GpTpG) release from a GTG-cisPt complex following reaction with a single e − aq , by a two-step process. Adam et al have shown using transient absorption measurements at 310 nm that Pt II can be reduced by e − aq and also by H • radicals (k = 1.2 × 10 10 mol −1 L s −1 ).…”

New Insights into the Reaction Paths of Hydroxyl Radicals with 2′-Deoxyguanosine

“…Rate constants of 6 Â 10 9 and 7.9 Â 10 9 M À1 s À1 were obtained for the reaction of HO • radical with N 2 -ethyl-2 0 -deoxyguanosine (21) and N 2 ,N 2 -diethyl-2 0 -deoxyguanosine (24), respectively (Scheme 8). Figure 6 shows the spectral changes obtained from the pulsed irradiation of N 2 O saturated aqueous solution (unbuffered) of 1 mM 21.…”

Converging Fate of the Oxidation and Reduction of 8-Thioguanosine

“…This pathway could explain the absence of further consumption of 8-TG in the predominant presence of HO • radicals. Additionally, the intermediate E could be directly formed by Br 2 •− and N 3 • and provide regeneration of 1 in the same fashion, explaining the comparable results in the presence of these two radical species [31,51,52].…”

“…In fact, in all the reactions we could observe similar results to the ones obtained in the previous experiments in terms of G values, while no further consumption of the substrate was achieved via side product formation. On the basis of our strong background of radical chemistry of guanosine derivatives [31,47,48,49,50,51,52], it was established that HO • radicals could perform hydrogen abstraction predominantly on the exocyclic NH 2 group [48,49,50], leading to the radical intermediate D (Scheme 5). This species could undergo tautomerization to the more stable radical E .…”