Copper-Mediated Peptide Radical Ions in the Gas Phase
Why this work is in the frame
A frame that forgets how it found something cannot be audited. These are the routes that admitted this work.
Bibliographic record
Abstract
Molecular radical cations, M •+, of amino acids and oligopeptides are produced by collision-induced dissociation of mixed complex ions, [Cu II (dien)M] •2+, that contain Cu II, an amine, typically diethylenetriamine (dien), and the oligopeptide, M. With dien as the amine ligand, abundant M •+ formation is observed only for the amino acids tryptophan and tyrosine, and oligopeptides that contain either the tryptophanyl or tyrosyl residue. Dissociation of the M •+ ion is rich and differs considerably from that of protonated amino acids and peptides. Facile fragmentation occurs around the α-carbon of the tryptophanyl residue. Cleavage of the N−C α bond and proton transfer from the exocyclic methylene group in the side chain to the N-terminal residue results in formation of the [z n − H] •+ ion and elimination of the N-terminal fragment as ammonia or an amide, depending on the position of the tryptophanyl residue. Cleavage of the C α −C bond of an oligopeptide containing a C-terminal tryptophan residue and proton transfer from the carboxylic group to the N-terminal fragment (a carbonyl oxygen atom) results in formation of the [a n + H] •+ ion and elimination of carbon dioxide. Both types of fragmentation have no analogous reactions in protonated peptides. For the M •+ of tryptophanylglycylglycine, WGG, elimination of the tryptophanyl side chain results in GGG •+ . This radical cation fragments by eliminating its C-terminal glycine to give the [b 2 − H] •+ ion, which is an oxazolone and shares much of the structure and reactivity of the b 2 + ion from protonated triglycine. Density functional theory shows the mechanism of forming the [b 2 − H] •+ ion is similar to that of the b 2 + ion, although the free-energy barrier at 29.4 kcal/mol is lower. The [b 2 − H] •+ ion eliminates CO readily to give the [a 2 − H] •+ ion, which is an iminium radical ion.
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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 | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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 it