Localization of <sup>23</sup>Na<sup>+</sup> in a DNA Quadruplex by High-Field Solid-State NMR
Bibliographic record
Abstract
Monovalent cations such as Na +, K +, and NH 4 + are known to stabilize DNA quadruplexes formed of guanine-quartets. Such structures readily form from the guanine-rich repeat sequences found in telomeres, the physical ends of eukaryotic chromosomes. We present a solid-state NMR approach for studying ions associated with G-quartets based on the direct NMR observation of 23 Na + ion resonances and report new methods for studying quadrupolar nuclei in biological solids. In the tetraplex forming oligonucleotide d(TG 4 T), high-field (17.6 T) NMR spectra cleanly resolve three distinct classes of sodium ions. A high-resolution 2D-MQMAS spectrum established the assignment of an amorphously broadened signal at −19 ppm (relative to 0.1 M NaCl) to surface-bound Na + ions. Two-dimensional nutation spectroscopy was used to indicate the relative size of the quadrupole coupling for each line, while a standard exchange experiment established a correlation between surface (−19 ppm) and channel-bound (6.8 ppm) Na + ions. Finally, free sodium ions are observed at 0 ppm. This work demonstrates the utility of high field spectroscopy in combination with a suite of 2D solid-state NMR experiments for resolving and assigning multiple Na + sites in [d(TG 4 T)] 4 .
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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 | 0.000 | 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".