Radiation effects on crystalline l-asparagine, revisited: Radical formation by EMR and periodic DFT after X-irradiation at 275K

Knudtsen, Ingerid Skjei; Aalbergsjø, Siv Gundrosen; Hole, Eli O.; Sagstuen, Einar

doi:10.1016/j.radphyschem.2014.07.008

Cited by 5 publications

(10 citation statements)

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“…This can be resolved if the RF domain widths of these components, related to the interaction anisotropy, are examined. In a number of combined experimental and computational studies of different amino acids, − the anisotropy of the amino proton couplings appears to be systematically larger than the anisotropy of the methyl couplings. It can be seen in Figure that the patterns positioned around 57, 66, and 95 MHz are slightly broader than the ones around 58, 86, and 117 MHz.…”

Section: Resultsmentioning

confidence: 99%

“…Fortunately, the principal directions of the HF interactions are known to be reproduced very accurately with DFT for radicals in amino acids. 22,23,37,38 The predictions of the principal values of these tensors, on the other hand, are known to have less absolute precision. It is thus worth performing the simulations of the EPR powder spectrum from before, but with the DFT-predicted tensor eigenframes.…”

Section: Discussionmentioning

confidence: 99%

“…Even though it was not possible to experimentally determine the principal directions of the HF interactions, it is still interesting to illustrate how they influence the EPR spectrum in the present case. Fortunately, the principal directions of the HF interactions are known to be reproduced very accurately with DFT for radicals in amino acids. ,,, The predictions of the principal values of these tensors, on the contrary, are known to have less absolute precision. It is thus worth performing the simulations of the EPR powder spectrum from before but with the DFT-predicted tensor eigenframes.…”

Section: Discussionmentioning

confidence: 99%

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ENDOR-Induced EPR of Disordered Systems: Application to X-Irradiated Alanine

et al. 2018

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The electron paramagnetic resonance (EPR) spectra of radiation-induced radicals in organic solids are generally composed of multiple components that largely overlap due to their similar weak g anisotropy and a large number of hyperfine (HF) interactions. Such properties make these systems difficult to study using standard cw EPR spectroscopy even in single crystals. Electron-nuclear double-resonance (ENDOR) spectroscopy is a powerful and widely used complementary technique. In particular, ENDOR-induced EPR (EIE) experiments are useful for separating the overlapping contributions. In the present work, these techniques were employed to study the EPR spectrum of stable radicals in X-irradiated alanine, which is widely used in dosimetric applications. The principal values of all major proton HF interactions of the dominant radicals were determined by analyzing the magnetic field dependence of the ENDOR spectrum at 50 K, where the rotation of methyl groups is frozen. Accurate simulations of the EPR spectrum were performed after the major components were separated using an EIE analysis. As a result, new evidence in favor of the model of the second dominant radical was obtained.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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ENDOR-Induced EPR of Disordered Systems: Application to X-Irradiated Alanine

et al. 2018

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“…For the reasons mentioned above, there has been a growing interest for understanding the radiation chemistry of amino acids with aminated side chains. In particular, the past decade has seen reports of detailed studies of arginine, , arginine:phosphate, lysine , and asparagine. − Identification of ionic precursors located at the side chains of these amino acids would be of particular interest, as potential electron–hole transfers between DNA and the amino acid most probably are mediated via the H-bonding interaction, in analogy with the cytosine: N -formylglycine complex …”

Section: Introductionmentioning

confidence: 99%

“…Strzelczak and co-workers investigated polycrystalline samples γ-irradiated at 77 K using EPR-only techniques, and suggested the formation of a radical anion, located either at the carboxyl group or at the side-chain amide group . In a recent report from our laboratories, the radical formation after X-irradiation of l -asparagine at room temperature was reinvestigated . In that study, the possibility for a low-temperature successor to a side-chain reduction product was hypothesized.…”

Section: Introductionmentioning

confidence: 99%

Direct Radiation Effects to the Amino Acid Side Chain: EMR and Periodic DFT of X-Irradiated l-Asparagine at 6 K

et al. 2015

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Radical formation in single crystals of L-asparagine monohydrate following X-irradiation at 6 K has been investigated at 6 K and at elevated temperatures using various electron magnetic resonance (EMR) techniques such as electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and ENDOR-induced EPR (EIE) spectroscopy. Molecular structures of the three free radicals stable at 6 K were assessed by detailed analysis of the experimental data and density functional theory (DFT) calculations in a periodic approach. Radical LI is assumed to result from one-electron reduction at the amide functional group in the asparagine side chain followed by protonation at the amide carbonyl oxygen by proton transfer from a neighboring molecule across a hydrogen bond. Radical LII is assigned to a one-electron reduction of the carboxyl group in the amino acid backbone, followed by proton transfer across a hydrogen bond between a carboxylic oxygen and a neighboring asparagine molecule. Radical LIII is suggested to be formed by a net CO2 abstraction from an initial one-electron oxidized amino acid backbone. For the DFT modeling of LIII at 6 K, it was chosen to include the CO2 group stably embedded in the crystalline lattice. The assignments made are discussed in relation to previous work on L-asparagine. The relevance of these results to possible charge transfer processes in protein:DNA complexes is discussed.

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