Proton Transfer via π-Interactions from Pyridine Provides a Facilitated Route for Transfer of CO<sub>2</sub> in Its Complex with a Carbanion
Bibliographic record
Abstract
Aromatic π-interactions have been recognized as enhancing enzymatic catalytic processes, providing an efficient route to overcome entropic barriers. A nonenzymic analogue, a complex of protonated pyridine and a phenyl substituent in a thiamin conjugate, facilitates the departure of CO 2 by protonation of a vicinal carbanion in a reactive complex. To evaluate the efficiency of the catalytic pathway from the π-associated proton donor, a system was assessed that produced measurable competition through the rates of formation of alternative products resulting from the same thiamin-derived carbanion. The barriers to competing pathways from the decarboxylation of p -(bromomethyl)-mandelylthiamin in the presence and absence of protonated pyridine were determined, establishing the efficiency of the vicinal proton transfer between π-associated species. The formation of the complex of CO 2 and the co-formed carbanion also addresses the mechanism of the uncatalyzed exchange of 13 CO 2 into carboxyl groups discovered by Lundgren. Finally, microscopic reversibility implicates pyridine as a vicinal Brønsted base in thiamin-aldehyde adducts, producing carbanions that could incorporate dissolved CO 2 into carboxyl groups.
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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) | 0.002 | 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".