Absolute Rate Constants and Yields of Transients from Hydroxyl Radical and H Atom Attack on Glycine and Methyl-Substituted Glycine Anions
Bibliographic record
Abstract
The reaction of the amino acid anions, R 2 N−CR 2 −CO 2 - (R = H or methyl), with • OH radicals and H • atoms was quantified with respect to the site of attack, the respective absolute rate constants, and the yields of the primary transients generated in these processes. The method applied was pulse radiolysis with time-resolved optical detection. Specifically investigated amino acids were glycine, alanine, α-methylalanine and N, N -dimethylglycine. Absolute overall rate constants, as determined from the growth of UV absorptions and competition with carbonate, ranged from (1.7−3.6) × 10 9 M -1 s -1 for the reaction of • OH with the anions of these amino acids, and (0.1−1) × 10 8 M -1 s -1 for the corresponding reaction with the respective zwitterions. H • atoms react with amino acid anions containing C α −H bonds with a rate constant of 1.4 × 10 8 M -1 s -1, whereas k < 10 7 M -1 s -1 was estimated for the reaction with α-methylalanine. The primary transient radicals from these reactions include aminyl radicals (RN • -CR 2 −CO 2 - ), α-amino-α-carboxyalkyl radicals, R 2 N−C • R−CO 2 -, α-aminoalkyl radicals, R 2 N−C • R 2, and ( • CH 2 −) type side-chain radicals (for R = CH 3 compounds). The yields of the reducing species (all but aminyl) were determined via titration with electron acceptors of different and thus distinguishing reduction potentials, namely, 4-carboxybenzophenone, methyl viologen, and hexacyanoferrate-III. On the basis of the overall rate constants and the yields of the various transients, partial rate constants were evaluated for the attack of • OH at C α −H, at the lone electron pair at nitrogen, and at the more remote methyl groups. The results substantiate earlier conclusions that the amino nitrogen is indeed the preferred site of oxidative attack, but also that substantial amounts of R 2 N−C • R−CO 2 - type radicals are formed via direct abstraction of hydrogen from the C α −H bond. Trends and individual data are discussed in the light of structure and substitution pattern of the amino acids investigated.
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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 | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
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".