Low Energy Electron Interactions with Uracil: The Energetics Predicted by Theory
Bibliographic record
Abstract
Low energy electrons (LEEs) induce strand breaks and base damage in DNA and RNA via fragmentation of molecular bonding. This includes the formation of hydrogen atoms from N−H and C−H bond dissociations in the bases thymine, cytosine and uracil, respectively. To better understand the dissociation of uracil induced by LEEs, we theoretically characterized the potential energy surfaces (PESs) along the N−H and C−H bonds of the uracil anion, as well as the energetics involved. The PESs show that an activation barrier of less than 1 eV exists for the N 1 −H dissociation with rather flat PES beyond N−H = ∼1.5 Å. The PESs for C 5 −H and C 6 −H show larger barriers, which increase monotonically with bond stretching. All the N−H and C−H bond dissociations are endothermic; the adiabatic PESs suggest the energy threshold for formation of hydrogen from N−H and C−H bonds are in the order: 0.78 (N 1 −H) < 1.3 (N 3 −H) < 2.2 (C 6 −H) < 2.7 eV (C 5 −H). The H-deleted uracil radicals (U-yl radical family) are found to have exceptionally high adiabatic electron affinities, namely, 3.46 (N 1 ), 3.8 (N 3 ), 2.35 (C 5 ), and 2.67 eV (C 6 ). During the H bond breaking process of an uracil transient anion, these electron affinities compensate the extra energy needed to break the N−H or C−H bonds. This process may therefore explain the large hydrogen yield found experimentally from uracil upon attachment of LEEs. Potential applications of this process for the synthesis of uracil analogues using LEE irradiation are suggested.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.002 |
| Scholarly communication | 0.002 | 0.002 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".