Solid-State <sup>23</sup>Na Nuclear Magnetic Resonance of Sodium Complexes with Crown Ethers, Cryptands, and Naturally Occurring Antibiotic Ionophores: A Direct Probe to the Sodium-Binding Sites
Bibliographic record
Abstract
We report a systematic solid-state 23 Na nuclear magnetic resonance study of sodium complexes with crown ethers, cryptands, and naturally occurring antibiotic ionophores. Precise information about 23 Na quadrupole coupling constants and chemical shifts was determined from analysis of 23 Na magic-angle spinning (MAS) NMR spectra. We found that the experimental 23 Na chemical shifts can be related to an empirical parameter that is a function of the atomic valence of the donor ligand, the Na + −ligand distance, and the coordination number (CN) around the Na + ion of interest. A reasonably good correlation was also observed between the 23 Na quadrupole parameters measured in CDCl 3 solution and those measured in the solid state, indicating that the cation exchange is slow in CDCl 3 . In MeOH solution, however, neither 23 Na quadrupole parameters nor chemical shifts of the Na−ionophore complexes show correlation with the corresponding solid-state data. Finally, we report the 23 Na chemical shift tensor in Na(12C4) 2 ClO 4: δ 11 = δ 22 = −1 ppm and δ 33 = −15 ppm.
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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 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 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".