Publication: Are the Radical Centers in Peptide Radical Cations Mobile? The Generation, Tautomerism, and Dissociation of Isomeric α-Carbon-Centered Triglycine Radical Cations in the Gas Phase
All || By Area || By Year| Title | Are the Radical Centers in Peptide Radical Cations Mobile? The Generation, Tautomerism, and Dissociation of Isomeric α-Carbon-Centered Triglycine Radical Cations in the Gas Phase | Authors/Editors* | Ivan K. Chu, Junfang Zhao, Minjie Xu, Shiu On Siu, Alan C. Hopkinson, K. W. Michael Siu |
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| Where published* | Journal of the American Chemical Society |
| How published* | Journal |
| Year* | 2008 |
| Volume | 130 |
| Number | 25 |
| Pages | 7862-7872 |
| Publisher | |
| Keywords | |
| Link | http://dx.doi.org/10.1021%2Fja801108j |
| Abstract |
The mobility of the radical center in three isomeric triglycine radical cationsâ[Gâ¢GG]+, [GGâ¢G]+, and [GGGâ¢]+âhas been investigated theoretically via density functional theory (DFT) and experimentally via tandem mass spectrometry. These radical cations were generated by collision-induced dissociations (CIDs) of Cu(II)-containing ternary complexes that contain the tripeptides YGG, GYG, and GGY, respectively (G and Y are the glycine and tyrosine residues, respectively). Dissociative electron transfer within the complexes led to observation of [Yâ¢GG]+, [GYâ¢G]+, and [GGYâ¢]+; CID resulted in cleavage of the tyrosine side chain as p-quinomethide, yielding [Gâ¢GG]+, [GGâ¢G]+, and [GGGâ¢]+, respectively. Interconversions between these isomeric triglycine radical cations have relatively high barriers (â¥44.7 kcal/mol), in support of the thesis that isomerically pure [Gâ¢GG]+, [GGâ¢G]+, and [GGGâ¢]+ can be experimentally produced. This is to be contrasted with barriers < 17 kcal/mol that were encountered in the tautomerism of protonated triglycine [Rodriquez C. F. et al. J. Am. Chem. Soc. 2001, 123, 3006â3012]. The CID spectra of [Gâ¢GG]+, [GGâ¢G]+, and [GGGâ¢]+ were substantially different, providing experimental proof that initially these ions have distinct structures. DFT calculations showed that direct dissociations are competitive with interconversions followed by dissociation. |
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