@article{7613,
  author = {S. Osburn and G. Berden and J. Oomens and R. A. J. O'Hair and V. Ryzhov},
  title = {S-to-alpha C Radical Migration in the Radical Cations of Gly-Cys and Cys-Gly},
  abstract = {The radical cations of Cys-Gly and Gly-Cys were studied using ion-molecule reactions (IMR), infrared multiple-photon dissociation (IRMPD) spectroscopy, and density functional theory (DFT) calculations. Homolytic cleavage of the S-NO bond of nitrosylated precursors generated radical cations with the radical site initially located on the sulfur atom. Time-resolved ion-molecule reactions showed that radical site migration via hydrogen atom transfer (HAT) occurred much more quickly in Gly-Cys(aEuro cent+) than in Cys-Gly(aEuro cent+). IRMPD and DFT calculations indicated that for Gly-Cys, the radical migrated from the sulfur atom to the alpha-carbon of glycine, which is lower in energy than the sulfur radical (-53.5 kJ/mol). This migration does not occur for Cys-Gly because the glycine alpha-carbon is higher in energy than the sulfur radical (10.3 kJ/mol). DFT calculations showed that the highest energy barriers for rearrangement are 68.2 kJ/mol for Gly-Cys and 133.8 kJ/mol for Cys-Gly, which is in agreement with both the IMR and IRMPD data and explains the HAT in Gly-Cys.
},
  year = {2012},
  journal = {Journal of the American Society for Mass Spectrometry},
  volume = {23},
  pages = {1019-1023},
  month = {Jun},
  isbn = {1044-0305},
  doi = {10.1007/s13361-012-0356-4},
  language = {English},
}