| Abstract
| - Density functional calculations at the B3LYP/6-311+G(2d,p)//pBP/DN* level predict all cationicadducts combining guanine, at either its N2, O6, N7, or C8 positions, with phenylnitrenium ion, ateither its N, 2, or 4 positions, to be lower in energy than the separated reactants. This relativestability of all adducts is preserved after addition of aqueous solvation free energies computed atthe SM2 level, although some leveling of the adduct relative energies one to another is predicted.Cations having the lowest relative energies in solution correspond structurally to those adductsmost commonly found when guanine reacts with larger, biologically relevant nitrenium ions invitro and in vivo. One of these, the N−C8 adduct, is stabilized both by a rearomatized phenyl ringand by the operation of an anomeric effect not found in any of the others. On the basis of energeticanalysis, direct conversion of an N−N7 cation to an N−C8 cation according to a previously proposedmechanism is unlikely; however, an alternative rearrangement converting a 2-N7 cation to an N−C8cation via the intermediacy of a five-membered ring may be operative in nitrenium ions witharomatic frameworks better able than phenyl to stabilize endocyclic cationic charge.
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