Aminyl Radical Generation via Tandem Norrish Type I Photocleavage, β-Fragmentation: Independent Generation and Reactivity of the 2′-Deoxyadenosin- <i>N</i>6-yl Radical
Bibliographic record
Abstract
Formal hydrogen atom abstraction from the nitrogen–hydrogen bonds in purine nucleosides produces reactive intermediates that are important in nucleic acid oxidation. Herein we describe an approach for the independent generation of the purine radical resulting from hydrogen atom abstraction from the N 6-amine of 2′-deoxyadenosine (dA•). The method involves sequential Norrish Type I photocleavage of a ketone ( 7b ) and β-fragmentation of the initially formed alkyl radical ( 8b ) to form dA• and acetone. The formation of dA• was followed by laser flash photolysis, which yields a transient with λ max ≈ 340 nm and a broader weaker absorption centered at ∼560 nm. This transient grows in at ≥2 × 10 5 s –1; however, computations and reactivity data suggest that β-fragmentation occurs much faster, implying the consumption of dA• as it is formed. Continuous photolysis of 7b in the presence of ferrous ion or thiophenol produces good yields of dA, whereas less reactive thiols afford lower yields presumably due to a polarity mismatch. This tandem photochemical, β-fragmentation method promises to be useful for site-specific production of dA• in nucleic acid oligomers and/or polymers and also for the production of aminyl radicals, in general.
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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 | 0.001 |
| 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".