Infrared vibrational spectra as a structural probe of gaseous ions formed by caffeine and theophylline
Bibliographic record
Abstract
Ionic hydrogen bond (IHB) interactions, resulting from the association of ammonia and the two protonated methylxanthine derivatives, caffeine and theophylline, have been characterized using infrared multiphoton dissociation (IRMPD) spectroscopy and electronic structure calculations at the MP2/aug-cc-pVTZ//B3LYP/6-311+G(d,p) level of theory. The proton-bound dimer (PBD) of caffeine and ammonia exhibits a low binding energy and was found to be elusive under the experimental conditions due, most probably, to collision-induced dissociation of the complex with helium buffer gas before IRMPD irradiation. The IRMPD spectrum of a PBD of theophylline and ammonia was obtained and revealed bidentate IHB formation within the complex, which greatly increased the binding energy relative to the most stable isomer of the PBD of caffeine and ammonia. The IRMPD spectra of the protonated forms of caffeine and theophylline have also been obtained. The spectrum of protonated caffeine showed dominant protonation at the N(9) site, whereas the spectrum of protonated theophylline showed a mixture of two isomers. The first protonated isomer of theophylline exhibits protonation at the N(9) site and the second isomer demonstrated protonation at the C(6) carbonyl oxygen. The protonated carbonyl isomer of theophylline cannot be produced as a result of direct protonation and is thus suggested to be a consequence of proton-transport catalysis (PTC) initiated by the electrostatic interaction between water and N(9) protonated theophylline. Calculated anharmonic spectra have been simulated at the B3LYP/6-311+G(d,p) level of theory. It is shown that calculated anharmonic frequencies significantly outperform calculated harmonic frequencies in providing simulated IRMPD spectra in all cases.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.000 | 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 teacher head, 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".