Computational and Experimental Evidence for the Structural Preference of Phenolic C-8 Purine Adducts
Bibliographic record
Abstract
The structural and spectral properties of (ortho and para) C8-aryl-purine adducts formed from carbon attachment by phenolic toxins were investigated through DFT calculations and UV-vis absorbance and emission studies. The global minima of both the deoxyadenosine (dA) and deoxyguanosine (dG) adducts adopted a syn conformation about the glycosidic bond due to the presence of an O5'-H...N3 hydrogen bond, where the anti minima are 20-30 kJ mol-1 higher in energy. While the nucleobase adducts are planar, the presence of the deoxyribose sugar induces a twist about the carbon-carbon bond connecting the phenol and nucleobase rings. ortho-Phenolic adducts are less twisted than the corresponding para adducts due to stabilization provided by an intramolecular O-H...N7 bond. Solvation calculations, in combination with UV-vis studies, demonstrate that the structural preference is solvent dependent, where solvents with hydrogen-bonding abilities disrupt the intramolecular O-H...N7 hydrogen bond such that a greater degree of twist is observed, and less polar solvents stabilize the planar structure. Indeed, the ratio of twisted to planar conformers is estimated to be as large as 50:50 in some aprotic solvents. Thus, the combined experimental and computational approach has provided a greater understanding of the structure of the ortho- and para-dA and dG C-bonded phenoxyl adducts as the first step to understanding the biological consequences of this form of DNA damage.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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) | 0.000 | 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 teacher head, 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".