Radiation-induced racemization and amplification of chirality: implications for comets and meteorites
Bibliographic record
Abstract
The action of high-energy radiation on prebiotic chiral molecules plays against the preservation of chirality. Chiral molecules incorporated in comets and meteorites are bombarded for billions of years by cosmic rays and by the high-energy radiation due to the decay of naturally occurring radionuclides. The action of cosmic rays on the surface of comets and meteorites causes the complete radiation processing of the surface of these bodies, but at depths of 20 m or so the cosmic rays are completely shielded and the radiation should derive only from the decay of radionuclides. In 4.6×109 yr the radiation dose supplied by the radionuclide decay to the organic molecules present inside the cometary or meteoritic body is equivalent to 14000 kGy. Our studies on the radiolysis of a series of naturally occurring chiral molecules, the terpenes, have shown that although all undergo the radioracemization reaction, the extent of radioracemization is such that a significant fraction of chiral excess and chiral molecules can survive a radiation dose equivalent to 14000 kGy. A unique exception is represented by the terpene β-(−)-pinene which, instead of the expected radioracemization reaction, undergoes a radiation-induced polymerization. The resulting poly-β-pinene, having an highly ordered supramolecular structure, displays an optical activity which is 1.7 times higher than the starting monomer. Thus, in this specific case, the optical activity is not reduced but enhanced by the action of radiation and remains locked into a polymer which displays a considerable radiation resistance and may act as a chiral template and as a chiral surface for prebiotic chemistry.
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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 | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".