Intramolecular H-atom transfer reactions in rigid peptides — Correlated solvent and structural effects
Bibliographic record
Abstract
The rates and the mechanism of intramolecular hydrogen-atom transfer across the rigid diketopiperazine spacer in two epimeric benzophenone–tyrosine dyads were studied by nanosecond laser flash photolysis in 12 non-protic and protic solvents. Effects of the stereochemistry on the ground-state structures and conformational equilibria and dynamics have been addressed by means of NMR-based population analysis and long-term molecular-dynamics simulations. The excited triplet state of the benzophenone is found to be quenched intramolecularly by the remote phenol moiety with rates that are highly dependent on the solvent and on the relative benzophenone–phenol orientation. In agreement with previous studies, the kinetic diversity, with rates ranging from <105 s−1 to 2 × 107 s−1, can be attributed to retarding effects of the bulk viscosity and to effects of specific solvation, which can be both rate retarding and rate accelerating. As an extension of the previous knowledge, however, the phenomenology of the kinetic solvent effects, that is, the nature of the predominating solvent parameter and its absolute impact on the reactivity, is found to be highly correlated with structural effects.
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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 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".