Cisplatin-DNA Adducts by Vibrational Circular Dichroism Spectroscopy: Structure and Isomerization of d(CCTG*G*TCC)·d(GGACCAGG) Intrastrand Cross-Linked by Cisplatin
Bibliographic record
Abstract
The intrastrand cisplatin adduct of the duplex d(CCTG*G*TCC)·d(GGACCAGG), where the asterisks denote the 1,2-intrastrand crosslink, was synthesized and studied in solution in D 2 O by vibrational circular dichroism (VCD) and infrared absorption spectroscopy. Comparison of the spectra of the platinated and unmodified complexes confirmed that the entire structure is considerably distorted, as a result of the platinum coordination to the octamer duplex. The major changes in the VCD spectra were detected in the fourth base step, where the cisplatin cross-links the adjacent guanine bases G4 and G5. Platinum coordination shifts the G4−C13 and G5−C12 base pairs apart, with a concomitant disruption of the stacking between the neighboring bases T3−G4 and G5−T6. The resultant new VCD couplets were assigned to stacking interactions between A11 and A14, which implies a substantially distorted structure. Slow isomerization is indicated by diagnostic changes in VCD, converting the intra strand adduct to other adducts. The corresponding absorption spectra remain essentially unchanged. This DNA octamer was previously studied by NMR in great detail when the isomerization was first detected after one day. Our measurements show that the conversion began soon after both strands were annealed and the first signs were detected in 2 h. This investigation again demonstrated convincingly that VCD is very sensitive to DNA structure modified by complex formation with cisplatin and may become more widely applicable for other similar applications.
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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 | 0.001 |
| 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".