One-Electron Oxidation of Methionine in Peptide Environments: The Effect of Three-Electron Bonding on the Reduction Potential of the Radical Cation
Bibliographic record
Abstract
The complexes between the radical cation of dimethyl sulfide 2 and models for eight biologically available electron pair donors,:X (:X = H 2 O ( 2a ), H 2 CO ( 2b ), HC(O)NH 2 ( 2c ), HC(O)NHCH 3 ( 2d ), HCO 2 - ( 2e ), HCO 3 - ( 2f ), H 2 PO 4 - ( 2g ), and CH 3 NH 2 ( 2h )), were optimized at the B3LYP/6-31G(d) level of theory. S∴X bond dissociation enthalpies (BDEs) were determined by single point calculations at the CBS−RAD level, a method designed for quantitative thermochemistry of free radicals. The effect of solvation was determined by application of a polarizable continuum model. Only the amine complex is predicted to be stable in water. H 2 O and H 2 PO 4 - make transient complexes, and the remaining complexes are predicted to dissociate spontaneously. The dissociation is driven by entropy and conformationally constrained complexes are predicted to be stable in water. Reduction potentials, E °, accurate to ±0.1 V were calculated for the complexes with dimethyl sulfide and for the amino acid, methionine, both as an isolated amino acid and incorporated into a polypeptide at the N- and C-terminals and midchain. Stabilization of the radical cation of Met by three-electron bonding is predicted if an S∴N bond can be formed to a free amino group, as in N-terminal Met or a nearby Lys. Likewise, Met oxidation is facilitated by phosphodiesters, but not by carboxylate groups or amide groups. No lowering of E ° is predicted for C-terminal Met or for midchain Met. The implications of the results for the redox chemistry associated with Alzheimer's disease are discussed.
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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 | 0.001 | 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 | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".