Doubly Charged Small Organic Fragments Derived from [Ce(tripeptide)(CH<sub>3</sub>CN)<i><sub>m</sub></i>]<sup>3+</sup> Complexes: Observation of the Elusive [b<i><sub>n</sub></i> + H]<sup>2+</sup> Ions
Bibliographic record
Abstract
[a 3 + H] 2+ ions generated from Ln 3+ /tripeptide complexes, where Ln = La or Ce, have similar structures to the linear [a n ] + ions but with protonation at both the terminal NH 2 and N═CH 2 groups. Ion stability is favored by having the basic secondary amine of the proline residue at the N-terminus and by an amino acid residue accommodating one of the protons on the side chain. Dissociation of [a 3 + H] 2+ ions derived from peptides containing only aliphatic residues is by cleavage of the second amide bond to give [b 2 ] + or [a 2 ] + ions along with internal [a 1 ] + ions. For [a 3 + H] 2+ ions containing a tryptophan residue in the central location, in addition to cleavage of the amide bond, losses of neutrals NH 3, HN═CHR, (NH 3 + CO), and HNCO were observed. Dissociations of some unsolvated Ln 3+ /tripeptide complexes gave [b 3 + H] 2+ ions in low abundance; formation of these [b 3 + H] 2+ ions was favored by the presence of a proline residue at the N-terminus and by either a histidine or tryptophan residue in the central position. Dissociation of these [b 3 + H] 2+ ions was by the loss of (H 2 O + CO) and not only CO, indicating that these ions did not have the same type of oxazolone structure as found for [b n ] + ions. Density functional theory calculations suggest that the observed [b 3 + H] 2+ ions of ProGlyGly were formed from [Ce(ProGlyGly)] 3+ complexes in which the peptide was bound to the metal ion as an enolate. Dissociation of the slightly lower-energy complex, where the peptide is bound in the keto form, would produce an oxazolone but the high barrier required to create this isomer of the [b 3 + H] 2+ ion would be sufficient to result in further dissociation. Two isomers of the [b 3 + H] 2+ ion of ProHisGly have been created, one from the [Ce(ProHisGly)] 3+ complex that characteristically dissociates by the combined loss of (H 2 O + CO) and the other by the loss of glycine from [ProHisGlyGly + 2H] 2+ . The [b 3 + H] 2+ ion derived from [ProHisGlyGly + 2H] 2+ dissociated by the loss of only CO.
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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 | 0.000 | 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".