Fragmentation of short single DNA strands by 1-30 eV electrons: dependence on base identity and sequence
Bibliographic record
Abstract
PURPOSE: To investigate the dependence of base identity and sequence on the damage induced by low-energy (1-30 eV) electron impact on a short single strand of DNA. MATERIALS AND METHODS: Monolayers of homogeneous nonamers of deoxycytidine and thymidine (dCy9 and T9) and heterogeneous nonamers of thymidine substituted with 33 and 66% of deoxycytidine (dCy3-T6 and dCy6-T3) were chemisorbed onto a gold substrate. They were bombarded under ultrahigh vacuum conditions by a 1-30 eV electron beam. Neutral fragments desorbed from the films were detected by a mass spectrometer. From partial pressure measurements, the effective cross-section (ECS) per base for desorption of various fragments was estimated. RESULTS: CN, OCN and/or H2NCN were the major neutral species observed to desorb in the present experiments. A small contribution of 55 amu neutral species, tentatively attributed to CH3CCO, were only detected from fragmentation of oligonucleotides containing thymine. The total ECS per base estimated for the CN, OCN and CH3CCO species production from fragmentation of dCy9, dCy6-T3, dCy3-T6 and T9 at 12 eV incident electron energy were (3.4, 2.0, 2.9 and 2.3) x 10(-17) cm(2), respectively. The incident electron energy dependence of ECS for desorption of these fragments exhibited structures <20 eV, which are characteristic of transient anion formation. CONCLUSIONS: At incident electron energies <20 eV, neutral fragment desorption arise from dissociation of the DNA bases, principally via dissociative electron attachment and/or decay of the transient anion into a dissociative electronic excited state of the base. Non-resonant mechanisms (e.g. direct dipolar dissociation) mostly control the fragmentation processes >20 eV. From comparison of the electron energy dependence of the ECS for base fragmentation in the homo- and heteronucleotides, it is concluded that damage to a short DNA strand is dependent on base identity, sequence and electron energy.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
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".