DFT Investigation of Dehalogenation of Adenine−Halouracil Base Pairs upon Low-Energy Electron Attachment
Bibliographic record
Abstract
The energetics of the dehalogenation of adenine-halouracil base pairs (A5XU), upon attachment of low-energy electrons, was investigated by use of density functional theory. These results are compared to those of single halouracils reported previously [J. Phys. Chem. A 2002, 106, 11248-11253]. Using the B3LYP functionals it was found that the gas phase adiabatic electron affinities (EA) of halogenated base pairs (A5BrU 0.59, A5ClU 0.56, A5FU 0.47 eV) are higher than that of AU (0.32 eV) and are slightly higher or comparable to the other DNA abundant base pair, guanine-cytosine (0.49 eV). Base pairing with adenine slightly decreases the EA of the halouracils, in contrast to the substantial increase in EA on base pairing of natural bases; as a result, the probability of electron capture by halouracils when in double-stranded DNA is suggested to be substantially reduced relative to that in single-stranded DNA. Even though the activation barriers for dehalogenation are small for both BrU-A and ClU-A, only the former has negative values of both DeltaH (-0.95 kcal/mol) and DeltaG (-1.52), while the latter has negative DeltaG (-0.28) but positive DeltaH (1.27). Infinite separations into halogen anions plus the remaining A-U-5-yl neutral radical are energetically unfavorable owing to sizable halide ion, radical interactions as reported earlier for non base paired halouracils. It is found that base pairing does not change the reactive nature of the uracil-5-yl radical. The results suggest that the radiosensitization properties of halouracils should be less effective in double-stranded DNA than in single-stranded DNA.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.004 | 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".