B−Z Conformational Transition of DNA Monitored by Vibrational Circular Dichroism. Ab Initio Interpretation of the Experiment
Bibliographic record
Abstract
The B−Z conformational transition was induced by Mn 2+ ions in a synthetic oligonucleotide (dG-dC) 20 and monitored by the vibrational circular dichroism (VCD). For the first time, the spectra were analyzed on the basis of quantum-mechanical computations. Force field and intensity tensors computed ab initio for smaller DNA fragments were transferred to a d(GCGCGCGC) 2 octamer model including explicit water molecules. The method allowed us to assign and explain most of the frequency and intensity features observed in the absorption and VCD spectra of the B- and Z-forms. Particularly, the computations reproduced the VCD sign flip caused by the transition due to the C O stretching and allowed us to assign most spectral bands in the nitrogen bases vibrational region. Also, known isotopic effects (deuteration and a 18 O substitution) were reproduced correctly. For the sugar−phosphate modes, the assignment of the VCD bands was hindered by a weak experimental signal. The approach based on quantum-mechanical computations was found superior to previous models based on coupled oscillator theory. Water molecules hydrogen-bonded to the DNA skeleton had to be included for reliable interpretation of the VCD and IR spectral patterns, namely, for the sugar−phosphate vibrations.
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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".