Modeling deoxyribose radicals by neutralization-reionization mass spectrometry. Part 2. Preparation, dissociations, and energetics of 3-hydroxyoxolan-3-yl radical and cation

Abstract

The title radical (1) is generated in the gas-phase by collisional neutralization of carbonylprotonated oxolan-3-one. A 1.5% fraction of 1 does not dissociate and is detected following reionization as survivor ions. The major dissociation of 1 (ϳ56%) occurs as loss of the hydroxyl H atom forming oxolan-3-one (2). The competing ring cleavages by O™C-2 and C-4™C-5 bond dissociations combined account for ϳ42% of dissociation and result in the formation of formaldehyde and 2-hydroxyallyl radical. Additional ring-cleavage dissociations of 1 resulting in the formation of C 2 H 3 O and C 2 H 4 O cannot be explained as occurring competitively on the doublet ground (X) electronic state of 1, but are energetically accessible from the A and higher electronic states accessed by vertical electron transfer. Exothermic protonation of 2 also produces 3-oxo-(1H)-oxolanium cation (3 ؉ ) which upon collisional neutralization gives hypervalent 3-oxo-(1H)-oxolanium radical (3). The latter dissociates spontaneously by ring opening and expulsion of hydroxy radical. Experiment and calculations suggest that carbohydrate radicals incorporating the 3-hydroxyoxolan-3-yl motif will prefer ring-cleavage dissociations at low internal energies or upon photoexcitation by absorbing light at ϳ590 and

Dissecting the Proline Effect: Dissociations of Proline Radicals Formed by Electron Transfer to Protonated Pro-Gly and Gly-Pro Dipeptides in the Gas Phase

“…Another fragment anion was observed at m / z 59, which likely corresponded to - CH 2 COOH or an isomer. The - CH 2 COOH anion is known to be stable under collisional reionization, and it can be formed by reionization of a • CH 2 COOH radical that represents a z -type fragment from an N−C α bond dissociation in the neutral intermediate 1a • . The complementary c -type fragment appeared as a small peak at m / z 112.…”

Treatment of Ribonucleoside Solution With Atmospheric‐Pressure Plasma

“…Thus, the dimer should be a C8–C8 bridged dimer . Deoxyribose is dissolved in water and decomposed into compounds with low molecular weight . For this reason, the m/z value of deoxyribose is not shown in Figure .…”

3 Mass spectrometry of free radicals: a methodological overview

“…Similar experiments have been conducted on 3-hydroxyoxolan-3-yl radical for the modelling of radical intermediates initiating strand breaks in DNA. 49 In all of these studies, the control of internal energy intervenes obviously as a major parameter which determinates the rates of observed unimolecular dissociations. In the particular case of gas-phase experiments, this parameter cannot be related only to the ''bulk parameter'' governed by the distribution of energy states following a Maxwell-Boltzman distribution and characterized by the temperature of the experiment.…”