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Analysis of the structure, fragmentation and proton exchange mechanisms of glycine and diglycine

Glisin ve diglisinin yapıları, parçalanma ve proton değişimi tepkimelerinin incelenmesi

  1. Tez No: 139489
  2. Yazar: BÜLENT BALTA
  3. Danışmanlar: PROF. DR. VİKTORYA AVİYENTE
  4. Tez Türü: Doktora
  5. Konular: Kimya, Chemistry
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 2003
  8. Dil: İngilizce
  9. Üniversite: Boğaziçi Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Kimya Ana Bilim Dalı
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 163

Özet

IV ÖZET * _,._

Özet (Çeviri)

in ABSTRACT ANALYSIS OF THE STRUCTURE, FRAGMENTATION AND PROTON EXCHANGE MECHANISMS OF GLYCINE AND DIGLYCINE B3LYP (Becke-3 -parameters-Lee- Yang-Pair functional) calculations have been used to model the gas phase conformers of glycine and protonated glycine, progressive solvation of the zwitterionic and neutral glycine tautomers, mass spectrometric fragmentation reactions and H/D exchange reactions of protonated glycine and diglycine. Seven gas phase glycine conformers have been located with relative stabilities in agreement with experiment and higher level calculations. An intramolecular proton transfer and a water assisted mechanism can be visualized for tautomerization. In the intramolecular mechanism, only the neutral tautomer exists in mono- and dihydrated clusters and in gas phase. In the smaller clusters, zwitterions are mainly stabilized by conformational effects, whereas in larger clusters, in particular when glycine is solvated on both sides, polarization effects dominate the stability of a given tautomer. Generally, the strength of the solute-solvent interactions is governed by the intermolecular charge transfer interactions. The neutral isomer does not exist for some solvent arrangements with five water molecules. In the water assisted mechanism, the free energy of reaction is close to the experimental value however, the free energy of activation is higher then in the intramolecular mechanism and experiment. In protonated glycine, 30.80 kcal/mol is needed for intramolecular proton migration. Threshold energies of 71.61 kcal/mol for sequential elimination of water and carbon monoxide and 85.50 kcal/mol for elimination of hydrogen molecule have been computed. The lowest energy pathway for water elimination from protonated diglycine requires a free energy of 37.54 kcal/mol. Oniom and salt bridge mechanisms are considered for H/D exchange reactions.

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