IRMPD Spectroscopic Study of Microsolvated [Na(GlyAla)]<sup>+</sup> and [Ca(GlyAla–H)]<sup>+</sup> and the Blue Shifting of the Hydrogen-Bonded Amide Stretch with Each Water Addition
Bibliographic record
Abstract
In this study, the structures of [Na(GlyAla)(H2O)](+) and [Ca(GlyAla-H)(H2O)n](+), (n = 1-3) solvated ion-molecule complexes (as well as the AlaGly isomers) were investigated using infrared multiple photon dissociation (IRMPD) spectroscopy and with computational methods. Calculations showed that in the calcium clusters, the lowest-energy complex is the one in which the peptide is deprotonated at the carboxylic acid end and that Ca(2+) binds to both carboxylate oxygen atoms as well as the amide carbonyl oxygen. For the microsolvated structures, all three water molecules also bind directly to Ca(2+). For the singly, doubly, and triply solvated complexes, these structures are supported by experimental IRMPD spectra. For the [Na(GlyAla)(H2O)](+) complex, both carbonyl oxygen atoms, one from the intact carboxylic acid and one from the amide group, as well as the water molecule were found to be bound to the Na(+). In all of the spectra, a strong band is observed between 3300 and 3400 cm(-1) and is assigned to the amide N-H stretch, which is red-shifted due to hydrogen bonding with the amine nitrogen. The position of the hydrogen-bonded amide N-H stretch is experimentally and theoretically found to be sensitive to the number of water molecules; it is shown to blue shift upon successive hydrations.
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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 | 0.001 | 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".