Formation of [M − <i>n</i>H + <i>m</i>Na]<sup>(m−n)+</sup> and [M − <i>n</i>H + <i>m</i>K]<sup>(m−n)+</sup> ions in electrospray mass spectrometry of peptides and proteins
Bibliographic record
Abstract
The [M - nH + mNa](m-n)+ and [M - nH + mK](m-n)+ ions are common in the electrospray mass spectra of proteins and peptides. The feasibility of forming these ions in the gas phase via collision activation and/or ion-molecule reaction is investigated. Sodium and potassium affinities of the N-methylacetamide anion, the acetate anion, and the 1-propanamide anion have been calculated using density functional theory at the B3LYP/6-311+ +G(d,p) level of theory. These anions were chosen as models for the functional groups on a protein or peptide. These affinity values are then used to calculate reaction enthalpies of alkali hydroxides, chlorides, and hydrates with N-methylacetamide, acetic acid, the acetate anion, and 1-propanamine, model reactions that may lead to formation of the [M - nH + mNa](m-n) and [M - nH + mK](m-n)+ ions. It is found that a number of these reactions are exothermic or slightly endothermic (deltaH(o) < + 20 kcal/mol) and are accessible after collision activation in the lens region. The potential energy hypersurfaces of model reactions between NaOH and formamide as well as NaCl and formamide show relatively flat surfaces devoid of significant barriers.
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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 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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".