Exploring Atypical Fluorine–Hydrogen Bonds and Their Effects on Nucleoside Conformations
Bibliographic record
Abstract
Abstract The ability of fluorine to serve as a hydrogen‐bond acceptor has been debated for many years. Short fluorine–hydrogen contacts are thought to play a key role in stabilizing some complex supramolecular systems. To directly probe the existence of fluorine–hydrogen bonds, we have performed NMR spectroscopy and computational modeling on a series of C2′‐fluorinated nucleosides. Specifically, quantum mechanics/molecular mechanics (QM/MM) analysis and [19F,1H] HMBC NMR experiments provided direct evidence for a C−H⋅⋅⋅F hydrogen bond in a 2′‐F,4′‐C‐α‐alkyl‐ribonucleoside analogue. This interaction was also supported by QTAIM and NBO analyses, which confirmed a bond critical point for the C−H⋅⋅⋅F interaction (0.74 kcal mol−1). In contrast, although conformational analysis and NMR experiments of 2′‐deoxy‐2′‐fluoro‐arabinonucleosides indicated a close proximity between the 2′‐fluorine and the H6/8 protons of the nucleobase, molecular simulations did not provide evidence for a C−H⋅⋅⋅F hydrogen bond.
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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 | 0.001 |
| 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".