Mechanism of Peroxynitrite Oxidation of Aliphatic CH Bonds in Saturated and Unsaturated Hydrocarbons. A Theoretical Model for the CH Oxidation of Lipids
Bibliographic record
Abstract
The oxidation of aliphatic CH bonds in methane, propane, isobutane, propene, and 1,4-pentadiene with peroxynitrous acid and peroxynitrite anion has been studied computationally with the B3LYP, MP2, and QCISD(T) levels of theory. The CCD, CISD, and CCSD(T) methods were also used for the parent systems, methane−ONOOH and methane−ONOO - . Three pathways were considered: path a, direct oxygen insertion into a C−H bond (two-electron oxidation); path b, H atom abstraction leading to alkyl radicals (one-electron oxidation); and path c, O−O bond homolysis of ONOOH (initial oxidation by hydroxyl radicals). Transition structures were located for path a which correspond to a concerted electrophilic oxygen insertion into the CH leading to the corresponding alcohols. At the QCISD(T)/6-31+G*//B3LYP/6-31+G* level, the activation barriers for the path a oxidation of methane, propane, isobutane, propene, and 1,4-pentadiene with ONOOH are 30.8, 18.1, 17.0, 21.1, and 17.8 kcal mol - 1 and with ONOO - they are 35.8, 29.4, 26.3, 25.0, and 14.0 kcal mol - 1, respectively. The direct abstraction of the hydrogen atom from the hydrocarbons by these oxidants (path b) yielding alkyl radicals is thermodynamically much less favorable than the two-electron oxidation even for 1,4-pentadiene (model for lipids). The calculated lower limit for the free energy of activation for the two-electron CH oxidation of 1,4-pentadiene with ONOOH (Δ G ≠ 298 = 20.5 kcal mol - 1 ) is higher than the free energy of homolysis of the O−O bond (path c) in ONOOH (Δ G 298 = 12.2−17.4 kcal mol - 1, theoretical and experimental estimates). This supports the hypothesis that the reactive species in hydrocarbon oxidations by peroxynitrous acid, and in lipid peroxidation induced by peroxynitrous acid in the presence of air, is the discrete hydroxyl radical formed in the homolysis of this acid.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.004 | 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".