Introducing new nuclei in solid state NMR of gas hydrates
Bibliographic record
Abstract
Extensive developments in experimental techniques in recent years have opened new exciting opportunities for application of solid state nuclear magnetic resonance (SS NMR) in studies of gas hydrates and inclusion compounds in general. Perhaps the most important advance of the last ten years was the extension into very high magnetic fields beyond 20T. This progress is especially significant in studies concerned with low-γ, low natural abundance and quadrupolar nuclei. This work reports our recent exploration of hydrates with SS NMR of nuclei that were not so long ago completely out of reach for NMR, but can be very useful in hydrate research. Although 129Xe is a widely used NMR probe, the applications of low-γ isotope 131Xe were very scarce. Being a quadrupolar spin 3/2 nucleus, 131Xe provides an additional probe for sampling the electric field gradients in inclusion compounds. Another nucleus that has been seriously under-explored is 83Kr, with its very low-γ being the main obstacle. Here we report our attempts to utilize this nucleus in studies of gas hydrates and some other inclusion compounds such as β-quinol and tert-Bu-Calix[4]. In most cases the spectra are affected by the quadrupolar interactions, providing information on the symmetry of the environment of the guest molecules. The next nucleus to be discussed is 33S, which is notoriously difficult due to its low-γ, low natural abundance, and relatively large quadrupolar moment. Nevertheless, working at the field of 21.1T we succeeded in acquiring, in a reasonable time, natural abundance 33S SS NMR spectra of various H2 S and SO2 gas hydrates and inclusion compounds. The spectra are dominated by the quadrupolar interactions and reflect very well the symmetry of the cages encapsulating the guest molecules. The impact of the introduction of new NMR nuclei on hydrate research will be discussed.
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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 | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
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".