Vibrational CD (VCD) and atomic force microscopy (AFM) study of DNA interaction with Cr<sup>3+</sup> ions: VCD and AFM evidence of DNA condensation
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Bibliographic record
Abstract
The interaction of natural calf thymus DNA with Cr(3+) ions was studied at room temperature by means of vibrational CD (VCD) and infrared absorption (ir) spectroscopy, and atomic force microscopy (AFM). Cr(3+) ion binding mainly to N(7) (G) and to phosphate groups was demonstrated. Psi-type VCD spectra resembling electronic CD (ECD) spectra, which appear during psi-type DNA condensation, were observed. These spectra are characterized mainly by an anomalous, severalfold increase of VCD intensity. Such anomalous VCD spectra were assigned to DNA condensation with formation of large and dense particles of a size comparable to the wavelength of the probing ir beam and possessing large-scale helicity. Atomic force microscopy confirmed DNA condensation by Cr(3+) ions and the formation of tight DNA particles responsible for the psi-type VCD spectra. Upon increasing the Cr(3+) ion concentration the shape of the condensates changed from loose flower-like structures to highly packed dense spheres. No DNA denaturation was seen even at the highest concentration of Cr(3+) ions studied. The secondary structure of DNA remained in a B-form before and after the condensation. VCD and ir as well as AFM proved to be an effective combination for investigating DNA condensation. In addition to the ability of VCD to determine DNA condensation, VCD and ir can in the same experiment provide unambiguous information about the secondary structure of DNA contained in the condensed particles.
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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 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 it