Structures and reactivity of gaseous glycine and its derivatives

Balta, Bülent; Basma, Maral; Avi̇yente, Vi̇ktorya; Zhu, Chen; Lifshitzb, Chava

doi:10.1016/s1387-3806(00)00218-9

Cited by 51 publications

(54 citation statements)

References 38 publications

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“…Previous calculations on the fragmentation of protonated monoglycine have yielded satisfactory results using this functional [29]. The 6-31 ϩ G** basis set has been used in conjunction with the B3LYP method.…”

Section: Methodsmentioning

confidence: 99%

“…The 6-31 ϩ G** basis set has been used in conjunction with the B3LYP method. This basis set is similar to the one we have used in the study of the fragmentation of protonated monoglycine (6-31 ϩ G**) [29] except that diffuse functions on hydrogens are omitted in the present work. As the B3LYP method may be inadequate for proton transfer barriers, the global minimum, the highest energy transition state and the separated products in the lowest energy reaction channel, have been reoptimized at the MP2/6-31 ϩ G** level of theory in order to confirm the B3LYP/6-31 ϩ G** results.…”

Section: Methodsmentioning

confidence: 99%

“….H-O4. Interestingly, the O-protonated monoglycines have been found to be 15.8 -30.8 kcal/mol less stable than the most stable N-protonated isomer at the B3LYP/6-31ϩϩG** level of theory [29]. The transition state 1_3 has an extremely low free energy.…”

Section: Formation Of the N-protonated Oxazolonementioning

confidence: 99%

“…This high barrier suggests that such a fragmentation channel may be open only at high collision energies in CID experiments. It is also interesting to note that in protonated monoglycine, the barrier for proton transfer in the geminal diol group is much higher (⌬E elϩZPE ‡ ϭ 71.6 kcal/mol) [29].…”

Section: Formation Of the N-protonated Oxazolonementioning

confidence: 99%

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Elimination of water from the carboxyl group of GlyGlyH⁺

Balta

Avi̇yente

Lifshitz

2003

J. Am. Soc. Mass Spectrom.

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The elimination of water from the carboxyl group of protonated diglycine has been investigated by density functional theory calculations. The resulting structure is identical to the b 2 ion formed in the mass spectrometric fragmentation of protonated peptides (therefore named "b 2 " in this study). The most stable geometry of the fragment ion ("b 2 ") is an O-protonated diketopiperazine. However, its formation is kinetically disfavored as it requires a free energy of 58.2 kcal/mol. The experimentally observed N-protonated oxazolone is 3.0 kcal/mol less stable. The lowest energy pathway for the formation of the "b 2 " ion requires a free energy of 37.5 kcal/mol and involves the proton transfer from the amide oxygen of protonated diglycine to the hydroxyl oxygen. Fragmentation initiated by proton transfer from the terminal nitrogen has also a comparable free energy of activation (39.4 kcal/mol). Proton transfer initiating the fragmentation, from the highly basic terminal nitrogen or amide oxygen to the less basic hydroxyl oxygen is feasible at energies reached in usual mass spectrometric experiments. Amide N-protonated diglycine structures are precursors of mainly y 1 ions rather than "b 2 " ions. In the lowest energy fragmentation channels, proton transfer to the hydroxylic oxygen, bond breaking and formation of an oxazolone ring occur concertedly but asynchronously. Proton transfer to hydroxyl oxygen and cleavage of the corresponding C™O bond take place at the early stages of the fragmentation step, while ring closure to form an oxazolone geometry occurs at the later stages of the transition. The experimentally observed low kinetic energy release is expected to be due to the existence of a strongly hydrogen bonded protonated oxazolone-water complex in the exit channel. Whereas the threshold energy for "b 2 " ion formation (37.1 kcal/mol) is lower than for the y 1 ion (38.4 kcal/mol), the former requires a tight transition state with an activation entropy, ⌬S ‡ ϭ Ϫ1.2 cal/mol.K and the latter has a loose transition state with ⌬S ‡ ϭ ϩ8.8 cal/mol.K. This leads to y 1 being the major fragment ion over a wide energy range. (J

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Formation Of the N-protonated Oxazolonementioning

confidence: 99%

Section: Formation Of the N-protonated Oxazolonementioning

confidence: 99%

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Elimination of water from the carboxyl group of GlyGlyH⁺

Balta

Avi̇yente

Lifshitz

2003

J. Am. Soc. Mass Spectrom.

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“…Although gas-phase H/D exchange reactions are widely used , only the reaction mechanism with ND 3 as the deuterating agent has been studied in detail [24]. Several studies discussed simplified mechanisms of H/D exchange reactions with CH 3 OD and D 2 O as deuterium donors.…”

mentioning

confidence: 99%

The gas-phase H/D exchange mechanism of protonated amino acids

Rožman

2005

J. Am. Soc. Mass Spectrom.

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A mass spectrometry and Density Functional Theory study of gas-phase H/D exchange in protonated Ala, Cys, Ile, Leu, Met, and Val is reported. Site-specific rate constants were determined and results identify the ␣-amino group as the protonation site. Lack of exchange on the Cys thiol group is explained by the absence of strong intramolecular hydrogen bonding within the reaction complex. In aliphatic amino acids the presence of a methyl group at the ␤-C atom was found to lower the site-specific H/D exchange rate for amino hydrogens. Study of the exchange mechanism showed that isotopic exchange occurs in two independent reactions: in one, only the carboxylic hydrogen is exchanged and in the other, both carboxylic and amino group hydrogens exchange. The proposed reaction mechanisms, calculated structures of various species, and a number of structural findings are consistent with experimental data. (J Am Soc Mass Spectrom 2005, 16, 1846 -1852

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Current Awareness

2000

J. Mass Spectrom.

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In order to keep subscribers up‐to‐date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of mass spectrometry. Each bibliography is divided into 11 sections: 1 Books, Reviews & Symposia; 2 Instrumental Techniques & Methods; 3 Gas Phase Ion Chemistry; 4 Biology/Biochemistry: Amino Acids, Peptides & Proteins; Carbohydrates; Lipids; Nucleic Acids; 5 Pharmacology/Toxicology; 6 Natural Products; 7 Analysis of Organic Compounds; 8 Analysis of Inorganics/Organometallics; 9 Surface Analysis; 10 Environmental Analysis; 11 Elemental Analysis. Within each section, articles are listed in alphabetical order with respect to author (4 Weeks journals ‐ Search completed at 4th. Oct. 2000)

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Structures and reactivity of gaseous glycine and its derivatives

Cited by 51 publications

References 38 publications

Elimination of water from the carboxyl group of GlyGlyH⁺

Elimination of water from the carboxyl group of GlyGlyH⁺

The gas-phase H/D exchange mechanism of protonated amino acids

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Structures and reactivity of gaseous glycine and its derivatives

Cited by 51 publications

References 38 publications

Elimination of water from the carboxyl group of GlyGlyH+

Elimination of water from the carboxyl group of GlyGlyH+

The gas-phase H/D exchange mechanism of protonated amino acids

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Elimination of water from the carboxyl group of GlyGlyH⁺

Elimination of water from the carboxyl group of GlyGlyH⁺