Gas-Phase Fragmentation Reactions of Protonated Aromatic Amino Acids: Concomitant and Consecutive Neutral Eliminations and Radical Cation Formations
Bibliographic record
Abstract
Gas-phase dissociation reactions of protonated amino acids phenylalanine, tyrosine, tryptophan, and histidine are rich and diverse. Considerable similarities exist among the four amino acids, but there are also significant differences. Facile reactions include the elimination of NH 3, common to all aromatic amino acids except histidine, and the concomitant elimination of H 2 O and CO. Labeling experiments with deuteriums show considerable H/D scrambling prior to dissociation involving N−H, O−H, and C−H (both aliphatic and aromatic hydrogens). Mechanisms of this scrambling are proposed. At higher collision energies, eliminations of H 2 O, CO, CO 2, and CH 2 CO occur after that of NH 3 . Similarly, eliminations of HCN, HCNH 2, and NH 3 occur after that of H 2 O and CO. The elimination of CH 2 CO is preceded by migration of the hydroxyl ion from the carboxylic group to the exocyclic carbon on the side chain. Aromatic amino acids, with the exception of tyrosine, were observed to yield cationic radical fragments by eliminating small radicals, including H •, CH 3 •, and NH CH • .
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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 | 0.001 | 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".