Energetics of the cyclo(Pro-Gly) cation fragmentation: a mass spectrometric study and theoretical calculations
✍ Scribed by Ling, Yun; Lifshitz, Chava
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 472 KB
- Volume
- 33
- Category
- Article
- ISSN
- 1076-5174
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✦ Synopsis
The energetics of HNCO elimination from the cyclo(Pro-Gly) radical cation was studied by electron ionization tandem mass spectrometry, photoionization mass spectrometry and RRKM/QET modeling. The heat of formation and vibrational frequencies of the reactant were calculated by density functional theory (DFT). Homodesmotic reactions involving cyclo(Pro-Gly) were used to derive its heat of formation at 0 K as Ô72.0 » 3.0 kcal mol-1 (1 kcal = 4.184 kJ). Vibrational frequencies were calculated at the B3LYP/6-31G(d) level. The critical energy for HNCO loss was determined from the experiment, by modeling, to be 1.2 » 0.1 eV. The heat of formation of the cyclo(Pro-Gly) radical cation and of the product ion at 0 K were determined to be 130.9 » 3.0 and C 6 H 9 NO'Õ 182.8 » 5.0 kcal mol-1, respectively. The salient features of the potential energy proÐle along the reaction coordinate were probed by DFT calculations. 1998