One-electron oxidation of methionine peptides — Stability of the three-electron S—N(amide) bond
Bibliographic record
Abstract
The possibility of sulfur–nitrogen (S—N) three-electron bond formation in a one-electron oxidized methionine peptide model was investigated computationally following the detection of such species in pulse radiolysis experiments (C. Schöneich, D. Pogocki, G.L. Hug, and K. Bobrowski. J. Am. Chem. Soc. 125, 13700 (2003)). Geometry optimiza tions were carried out at the B3LYP/6-31G(d) level of theory. Relative free energies in aqueous solution at pH 7 were predicted for all intermediates with enthalpy evaluations at the CCSD(T)/6-31+G(d′) level and free energies of solvation predicted using a continuum model (CPCM). Both the initial oxidation product and the intermediate formed at higher pH were identified as cyclic S—N bonded species in which the intramolecular three-electron interaction is between the S atom and the π orbital of the amide group. TD-B3LYP calculations of the UV spectra support the assignments. A mechanism for the conversion to the most stable α-C-centered radical is proposed. The mechanism involves a novel deprotonation–reprotonation via an intermediate backbone-delocalized radical anion.Key words: methionine oxidation, three-electron bonding, S—N bonding, B3LYP.
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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".