Kinetics for tautomerizations and dissociations of triglycine radical cations.

Fragmentations of tautomers of the alpha-centered radical triglycine radical cation, GGG(*), GG(*)G, and G(*)GG, are charge-driven, giving b-type ions; these are processes that are facilitated by a mobile proton, as in the fragmentation of protonated triglycine (Rodriquez, C. F. et al. J. Am. Chem. Soc. 2001, 123, 3006-3012). By contrast, radical centers are less mobile. Two mechanisms have been examined theoretically utilizing density functional theory and Rice-Ramsperger-Kassel-Marcus modeling: (1) a direct hydrogen-atom migration between two alpha-carbons, and (2) a two-step proton migration involving canonical GGG as an intermediate. Predictions employing the latter mechanism are in good agreement with results of recent CID experiments (Chu, I. K. et al. J. Am. Chem. Soc. 2008, 130, 7862-7872).