Bezzina, J.P., Prendergast, M.B., Blanksby, S.J. et al. (1 more author) (2018) Gas-phase oxidation of the protonated uracil-5-Yl radical cation. Journal of Physical Chemistry A, 122 (4). pp. 890-896. ISSN 1089-5639
Abstract
This study targets the kinetics and product detection of the gas-phase oxidation reaction of protonated 5-dehydrouracil (uracil-5-yl) distonic radical cation using iontrap mass spectrometry. Protonated 5-dehydrouracil radical ion (5-dehydrouracilH+ radical ion, m/z 112) is produced within an ion trap by laser photolysis of protonated 5-iodouracil. Storage of the 5-dehydrouracilH+ radical ion in the presence of controlled concentration of O2 reveals two main products. The major reaction product pathway is assigned as the formation of protonated 2-hydroxypyrimidine-4,5-dione (m/z 127) + OH. A second product ion (m/z 99), putatively assigned as a 5-member-ring ketone structure, is tentatively explained as arising from the decarbonylation (- CO) of protonated 2-hydroxypyrimidine-4,5-dione. Because protonation of the 5-dehydrouracil radical likely forms a di-enol structure, the O2 reaction at the 5 position is ortho to an-OH group. Following this addition of O2, the peroxyl radical intermediate isomerises by H atom transfer from the -OH group. The ensuing hydroperoxide then decomposes to eliminate OH radical. It is shown that this elimination of OH radical (-17 Da) is evidence for the presence of an -OH group ortho to the initial phenyl-radical site, in good accord with calculations. The subsequent CO loss mechanism, to form the aforementioned 5-member-ring structure, is unclear but some pathways are discussed. By following the kinetics of the reaction, the room temperature second order rate coefficient of the 5-dehydrouracilH+ distonic radical cation with molecular oxygen is measured at 7.2 × 10-11 cm3 molecul-1s-1, Φ = 12% (with ±50% total accuracy). For aryl radical reactions with O2, the presence of OH elimination product pathway, following the peroxyl radical formation, is a indicator of an -OH group ortho to the radical site.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2018 American Chemical Society. This is an author produced version of a paper subsequently published in Journal of Physical Chemistry A. Uploaded in accordance with the publisher's self-archiving policy. |
Dates: |
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Institution: | The University of Sheffield |
Academic Units: | The University of Sheffield > Faculty of Engineering (Sheffield) > Department of Chemical and Biological Engineering (Sheffield) |
Depositing User: | Symplectic Sheffield |
Date Deposited: | 08 Jan 2018 14:06 |
Last Modified: | 28 Jul 2020 14:52 |
Status: | Published |
Publisher: | American Chemical Society |
Refereed: | Yes |
Identification Number: | 10.1021/acs.jpca.7b09411 |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:125962 |