Theoretical Interpretation of the Fragments Generated from a Glycine Radical Cation

Abstract

By applying the CCSD(T)//B3LYP method with 6-31+G(d,p) basis sets, this work presents possible mechanisms of various fragmentation products found in the glycine mass spectrum. Imposing the criterion of low fragmentation energy enabled the m/z 17, 28,29,30,31, 39, 41, 44, 45, and 74 fragments to be identified as NH 3 + , HNCH + , H 2 NCH + , H 2 NCH 2 + , H 3 NCH 2 + , NCCH + , H 2 NCCH + , NH 2 CO + , COOH + , and CH 2 CO 2 H + , respectively. This result indicates that the dominant fragmentation process arises from a C R -C cleavage by abstracting COOH, which corresponds to the m/z 30 peak (NH 2 CH 2 + ). This interpretation is consistent with experimental observations. The neutral species ofthe m/z 28 (HCNH + ) peak is CH(OH) 2 rather than [CHO + H 2 O] because the corresponding critical energy of the latter is higher than that of the former. The intermediates in the reaction pathway by which NCCH + and HNCH + fragments are formed reveal that water may participate in the reaction and stabilize the intermediates.

Furthering the Diverse Hydrogen Atom Transfer and Carbon Bond Dissociation of Amino Acids under Vacuum Ultraviolet

“…This is consistent with the previous finding that C–COO bond is readily split in glycine and the mass channel for m/z 30 corresponds to CH 2 NH 2 + as verified by deuterium generation experiment . Besides, the observation of a weak peak at m/z 17 indicates the existence of HAT enabling to produce a stable NH 3 molecule . There is also a weak peak at m/z 114 likely due to a glycine dimer with a loss of two H 2 O molecules, for which the intermolecular dehydration of such amino acids was also noted in previous studies …”

“…For example, an early experimental study of glycine anions (H 2 NCH 2 CO 2 − ) in aqueous found the fast fragmentation into CO 2 and • NH 2 CH 2 , where the • OH‐induced mechanism was demonstrated to be initiated by oxidation of the amino group . Also theoretical studies have interpreted the low‐fragmentation energy criterion enabling varied fragment peaks to be identified in mass spectra, with a dominant fragment NH 2 CH 2 + (m/z 30) due to C α ‐C 1 cleavage . The production of m/z 30 has also been noted in a few other amino acids, allowing the C α ‐C 1 bond of glycine to be a model to understand complex amino acids and even polycarboxylic acids.…”

Ионизация молекул глицина alpha-частицами keV-энергий

“…Идентификация ионов-фрагментов основана на результатах расчетов, выполненных в работе [6], и на исследованиях фотоионизации глицина, в том числе с использованием дейтерированных молекул [7,8]. Одно-кратная ионизация молекулы глицина, как и большинства аминокислот, сопровождается фрагментацией [4][5][6][7][8][9]. Основной по величине сечения Письма в ЖТФ, 2017, том 43, вып.…”

“…канал процесса фрагментации иона Gly + обусловлен простым разры-вом C α −C-связи (вставка на рисунке) и осуществляется при энергии возбуждения молекулярного иона E ex = 0.36 eV [6][7][8]. Незначительная вероятность появления двухзарядных фрагментов с массой m = 28.5 a.m.u.…”

Reactions between neutral molecules and cation-radicals in the gas-phase: Can protonation occur without proton transfer?

“…Another question that requires explanation is whether self-protonation processes occur via hydrogen or proton abstraction. Several theoretical questions regarding the fragmentation of amino acids' cation-radicals [13][14][15][16] and intramolecular proton transfer in amino acids [17][18][19][20] have been examined in the literature. One should note, however, that while mass spectrometrically observed protonated amino acids might be products of intramolecular reactions, these reactions cannot occur in a single amino acid, but rather proceed within their higher mass charged complexes or as an intermolecular particle transfer during two-body collisions between charged and neutral amino acids [5].…”