Reactions of One-Electron-Oxidized Methionine with Oxygen: An ab Initio Study
Bibliographic record
Abstract
A one-electron oxidation of a methionine residue is thought to be a key step in the neurotoxicity of the beta amyloid peptide of Alzheimer's disease. The chemistry of the radical cation of N -formylmethioninamide ( 11 • + ) and two model systems, dimethyl sulfide ( 1 • + ) and ethyl methyl sulfide ( 6 • + ), in the presence of oxygen have been studied by B3LYP/6-31G(d) and CBS-RAD calculations. The stable form of 11 • + has a three-electron bond between the sulfur radical cation and the carbonyl oxygen atom of the i − 1 residue. The radical cation may lose a proton from the methyl or methylene groups flanking the oxidized sulfur. Both 11 • + and the resultant C-centered radicals may add oxygen to form peroxy radicals. The calculations indicate that unlike C-centered radicals the sulfur radical cation does not form a covalent bond to oxygen but rather forms a loose ion-induced dipole complex with an S−O separation of about 2.7 Å, and is bound by about 13 kJ mol -1 (on the basis of 1 • + + O 2 ). Direct intramolecular abstraction of an H atom from the α C site is unlikely. It is endothermic by more than 20 kJ mol -1 and involves a high barrier (Δ G = 79 kJ mol -1 ). The α-to-S C-centered radicals will add oxygen to form peroxy radicals. The OH BDEs of the parent hydroperoxides are in the range of 352−355 kJ mol -1, similar to SH BDEs (360 kJ mol -1 ) and α C−H BDEs (345−350 kJ mol -1 ). Thus, the peroxy radicals are oxidizing species comparable in strength to thiyl radicals and peptide backbone α C-centered radicals. Each peroxy radical can abstract a hydrogen atom from the backbone α C site of the Met residue to yield the corresponding α C-centered radical/hydroperoxide in a weakly exothermic process with modest barriers in the range of 64−92 kJ mol -1 .
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.000 | 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 | 0.001 |
| 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".