title: Radical formation in X-irradiated single crystals of guanine hydrochloride monohydrate. III. Secondary radicals and reaction mechanisms.
abstract: This work involves an ESR and ENDOR study of the reactions of the three primary radicals observed in X-irradiated single crystals of guanine hydrochloride monohydrate. Radical I, the O6-protonated anion, decays at 250 K yielding a stable room temperature radical (Radical V). The experimental evidence indicates that Radical V results from H-abstraction at N9 of a neighboring molecule. Radical II, the N7-deprotonated cation, decays at 60 K with no detectable successor. Radical IV, a C8 H-addition radical, is formed when an imidazole ring-opened radical (Radical III) decays at 150 K. The added H-atom was found to be from an easily exchangeable source. It is proposed that Radical III decays by the formation of a diamagnetic formamido molecule and an H-atom. It is important to note that Radical IV, the purine H-addition radical, is the result of basic oxidation events. Previous assumptions have been that purine H-addition radicals result either from reduction, i.e., protonation of a pristine anion, or from the "excitation pathway," by addition of H-atoms dissociated from superexcited purine bases.
authors.affiliation: Department of Physics, East Tennessee State University, Johnson City 37614.
authors.forename: D M
authors.initials: DM
authors.lastname: Close
authors.forename: E
authors.initials: E
authors.lastname: Sagstuen
authors.forename: W H
authors.initials: WH
authors.lastname: Nelson
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D006147:Guanine / Q000528:radiation effects*; D009686:Nuclear Physics; D011854:Radiochemistry
chemical_list: D006147:Guanine