title: Comparison of isoelectronic 8-HO-G and 8-NH2-G derivatives in redox processes.
abstract: 8-Oxo-7,8-dihydroguanine (8-oxo-G) is the major lesion of oxidatively generated DNA damage. Despite two decades of intense study, several fundamental properties remain to be defined. Its isoelectronic 8-aminoguanine (8-NH(2)-G) has also received considerable attention from a biological point of view, although its chemistry involving redox processes remains to be discovered. We investigated the one-electron oxidation and one-electron reduction reactions of 8-oxo-G and 8-NH(2)-G derivatives. The reactions of hydrated electrons (e(aq)(-)) and azide radicals (N(3)(*)) with both derivatives were studied by pulse radiolysis techniques, and the transient absorption spectra were assigned to specific tautomers computationally by means of time-dependent DFT (TD-B3LYP/6-311G**//B1B95/6-31+G**) calculations. The protonated electron adducts of 8-NH(2)-G and 8-oxo-G showed a substantial difference in their absorption spectra, the unpaired electron being mainly delocalized in the imidazolyl ring and in the six-membered ring, respectively. On the other hand, the deprotonated forms of one-electron oxidation of 8-NH(2)-G and 8-oxo-G showed quite similar spectral characteristics. In a parallel study, the one-electron reduction of 8-azidoguanine (8-N(3)-G) afforded the same transient of one-electron oxidation of 8-NH(2)-G, which represents another example of generation of one-electron oxidized guanine derivatives under reducing conditions. Moreover, the fate of transient species was investigated by radiolytic methods coupled with product studies and allowed self- and cross-termination rate constants associated with these reactions to be estimated.
authors.affiliation: ISOF, Consiglio Nazionale delle Ricerche, Via P. Gobetti 101, 40129 Bologna, Italy.
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Kaloudis
authors.forename: Mila
authors.initials: M
authors.lastname: D'Angelantonio
authors.forename: Maurizio
authors.initials: M
authors.lastname: Guerra
authors.forename: Marie
authors.initials: M
authors.lastname: Spadafora
authors.forename: Crina
authors.initials: C
authors.lastname: Cismaş
authors.forename: Thanasis
authors.initials: T
authors.lastname: Gimisis
authors.forename: Quinto G
authors.initials: QG
authors.lastname: Mulazzani
authors.forename: Chryssostomos
authors.initials: C
authors.lastname: Chatgilialoglu
mesh_terms: D004583:Electrons; D006147:Guanine / Q000031:analogs & derivatives* / Q000737:chemistry; D008958:Models, Molecular; D010084:Oxidation-Reduction
chemical_list: C546379:8-azidoguanine; C024829:8-hydroxyguanine; D006147:Guanine