ESR spectral change of radicals produced in L-alanine-3,3,3-d3 and L-alanine-d4. -A new pathway to produce the de-hydrogen radical and the hydrogen exchange reactions of the de-amino radical-

Publication date: Available online 20 July 2019Source: Radiation Physics and ChemistryAuthor(s): Seiko NakagawaAbstractRadicals produced in L-alanine-3,3,3-d3 and L-alanine-d4 by X-irradiation and their spectral change were investigated using X-band ESR. Apparently, two major radicals appeared. One is the radical formed by deamination from a protonated anion and the other is produced by the loss of an alpha hydrogen. Before the appearance of the de-hydrogen radical, the precursor radical with a singlet feature was observed at 148–158 K. The signal of the precursor decreased and that of the de-hydrogen radical increased with temperature. Because the feature of the precursor radical was a singlet, it will be produced by deprotonation of the alpha hydrogen from the deprotonated cation radical observed at 77–80 K. Protonation to the amine moiety of the deprotonated radical will be a new pathway to produce the de-hydrogen radical.In L-alanine-3,3,3-d3, the hydrogen exchange reaction between the alpha hydrogen in the de-amino radical and the beta deuterium in a neighboring molecule occurred at the first-order rate of 7 × 10−4 s−1 at 294 K. The activation energy was 25 kcal/mol. By annealing at 393 K, the spectral features have obviously changed by the hydrogen exchange reactions in the de-amino radicals. Finally, all the de-amino radicals changed to •CHCH3COOH(D) and the methyl deuterium in the de-hydrogen radicals changed to hydrogen by a hydrogen exch...
Source: Radiation Physics and Chemistry - Category: Physics Source Type: research
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