Interconversion between 4-Imidazolone Ions; Isomers of [b<sub>4</sub>]<sup>+</sup> Derived from Protonated Tetraglycine
Bibliographic record
Abstract
Collision-induced dissociations of isotopically labeled protonated tetraglycines establish that the [b 4 ] + ion formed by loss of water from the second amide bond (structure II ) rearranges to form N 1 -protonated 3,5-dihydro-4 H -imidazol-4-one (structure I ), the product of water loss from the first amide bond. Structure II is slightly higher in energy than I (Δ H at 0 K is 5.1 kJ mol –1, as calculated at M06-2X/6-311++G-(d,p)), and the barrier to interconversion is 139.8 kJ mol –1 above I . The dominant dissociation pathway is the loss of methanimine (HN=CH 2 ) from ion I with a barrier of 167.1 kJ mol –1, giving [GlyGlyGlyGly + H – H 2 O – HN=CH 2 ] +, ion III; a minor channel, loss of NH 3, has a slightly higher barrier (181.5 kJ mol –1 ). Using labeled glycine ( 13 C α ) it was determined that loss of the imine is from the same residue as that from which water was initially lost. The collision-induced dissociation spectra of ion III derived from both I and II were identical, and their energy-resolved curves were also very similar. Ion III fragments by losses of a glycine molecule (the dominant channel), a water molecule, and a glycine residue (57 Da), giving ions IV, V, and VII, respectively. Isotopic labeling established the origins of each of the neutral molecules that are lost. Using glycine (2,2 D 2 ), rapid deuterium exchange was observed for both ions I and II for the α-hydrogens that are from the same residue as that from which the water had been eliminated.
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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 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".