The unimolecular chemistry of [Zn(amino acid)2-H]+ in the gas phase: H2 elimination when the amino acid is a secondary amine
Bibliographic record
Abstract
The unimolecular chemistry of the [Zn(Pro-H)(Pro)](+) complex following collisional or infrared multiple photon activation was studied, and interestingly was found to lose H2 as one of the main dissociation pathways. Furthermore a second dehydrogenation step, forming [Zn(Pro-H)(Pro)-2H2](+), was also observed. When proline was substituted for sarcosine, also a secondary amine, a single dehydrogenation was observed. In contrast, [Zn(Gly-H)(Gly)](+) and [Zn(Ala-H)(Ala)](+) were found to lose H2O as their primary fragmentation route with no dehydrogenation observed. Tandem mass spectrometry, deuterium substitution, and infrared spectroscopy were used to determine the origin of the H atoms in the losses of H2, as well as for other fragmentation routes, including the loss of H2O. The hydrogen atoms for H2 loss from [Zn(Pro-H)(Pro)](+) was found to originate on the amine group and primarily from C5 on the non-deprotonated proline, with a smaller contribution from the C2 hydrogen. Both hydrogens for H2O loss were determined to be from labile hydrogens. Potential energy surfaces were computed for the H2 loss and H2O loss routes for both [Zn(Pro-H)(Pro)](+) and [Zn(Gly-H)(Gly)](+) and were compared. For [Zn(Pro-H)(Pro)](+), H2 loss was found to be the pathway with the lower energy requirement than for H2O loss, and the opposite was found for [Zn(Gly-H)(Gly)](+). The greater basicities of proline and sarcosine are most likely responsible for stabilizing the 3 coordinate Zn(2+) transition states en route to H2 loss, compared to those complexes formed with the much less basic glycine or alanine.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 | 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".