Fragmentations of tautomers of the a-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 a-carbons, and (2) a two-step proton migration involving a 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).
Revised: May 15, 2009 |
Published: June 1, 2009
Citation
Siu C., C. Siu, J. Zhao, J. Zhao, J. Laskin, I.K. Chu, and A.C. Hopkinson, et al. 2009."Kinetics for Tautomerizations and Dissociations of Triglycine Radical Cations."Journal of the American Society for Mass Spectrometry 20, no. 6:996-1005.PNNL-SA-64060.