Direct evidence of singlet molecular oxygen [O <sub>2</sub> ( <scp> <sup>1</sup> Δg </scp> )] production from <scp>UVA</scp> excited 6‐thioguanine
Bibliographic record
Abstract
Abstract 6‐Thioguanine (6‐TGua) is one of the thiopurines used as a cytostatic drug. When internalized by cells, 6‐TGua is metabolized through the purine salvage pathway and readily incorporated into DNA. Patients treated with these thiopurines are more prone to develop squamous cell carcinoma of the skin. The absorbance spectrum of 6‐TGua, in contrast to guanine (Gua) or any other canonical base, has a maximum absorbance at 342 nm. Therefore, 6‐TGua undergoes photoexcitation upon exposure to UVA radiation, with maximum absorption at 340 nm. In this study, the used approach unequivocally demonstrates the generation and quenching of 1 O 2 by 6‐TGua via the direct spectroscopic detection of 1 O 2 monomol light emission at 1270 nm. Chemiluminescence‐based methods were employed for the determination of the 1 O 2 generation quantum yield (Φ 1 O 2 ) and the total 1 O 2 quenching rate constant (k t ). For the 1 O 2 quantum yield, we found values of 0.22 ± 0.03 for 6‐TGua and 0.12 ± 0.03 for 2′‐deoxy‐6‐thioguanosine (6‐TdGuo). These compounds presented k t values of 1.5 × 10 7 L mol −1 s −1 and 1.1 × 10 7 L mol −1 s −1 , respectively. Through the comparison of these values with the ones obtained for 2′‐deoxyguanosine (dGuo) and its oxidation product 8‐oxo‐7,8‐dihydro‐2′‐deoxyguanosine (8‐oxodGuo), we aim to provide new insights into the 6‐TGua‐containing DNA (DNA‐6‐TGua) reactivity towards 1 O 2 in a biological context.
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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) | 0.003 | 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".