Charge-separation reactions of doubly-protonated peptides: Effect of peptide chain length
Bibliographic record
Abstract
The collision induced dissociation of doubly-protonated (Ala)(x)His (x = 5, 6, 7, 8, 10) peptides have been studied. The major fragmentation reactions observed are symmetrical amide bond cleavages to give the complementary b(m) and y(N-m) ions, where N is the total number of residues in the peptide. Minor asymmetric cleavage to give doubly-protonated y ions also is observed, involving cleavage near the N-terminus. The shorter peptides (x = 5, 6, 7) show major cleavage of the second amide bond to yield b2 and y(N-2) ions, while (Ala)10His shows major symmetrical cleavage at the fourth and fifth amide bonds. (Ala)8His appears to be a transitional peptide in showing substantial symmetrical cleavage at the second, fourth, and fifth amide bonds. The results are in general agreement with the bifurcating nature of charge separation noted by Zubarev (J. Am. Soc. Mass Spectrom.2008, 19, 1755-1763) from a statistical analysis of a large body of doubly-protonated tryptic peptide CID mass spectra. It is shown that the b2 ion derived from doubly-protonated (Ala)5His has a protonated oxazolone structure.
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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 | 0.001 |
| 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 | 0.001 |
| Open science | 0.000 | 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 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".