Lesslie Michael, Lau Justin Kai-Chi, Lawler John T, Siu K W Michael, Oomens Jos, Berden Giel, Hopkinson Alan C, Ryzhov Victor
Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL, 60115, USA.
Department of Chemistry and Centre for Research in Mass Spectrometry, York University, Toronto, Ontario, M3J 1P3, Canada.
Chemistry. 2016 Feb 12;22(7):2243-6. doi: 10.1002/chem.201504631. Epub 2016 Jan 12.
Intramolecular hydrogen atom transfer (HAT) was examined in homocysteine (Hcy) thiyl radical/alkali metal ion complexes in the gas phase by combination of experimental techniques (ion-molecule reactions and infrared multiple photon dissociation spectroscopy) and theoretical calculations. The experimental results unequivocally show that metal ion complexation (as opposed to protonation) of the regiospecifically generated Hcy thiyl radical promotes its rapid isomerisation into an α-carbon radical via HAT. Theoretical calculations were employed to calculate the most probable HAT pathway and found that in alkali metal ion complexes the activation barrier is significantly lower, in full agreement with the experimental data. This is, to our knowledge, the first example of a gas-phase thiyl radical thermal rearrangement into an α-carbon species within the same amino acid residue and is consistent with the solution phase behaviour of Hcy radical.
