Electron spin polarization transfer induced by triplet–radical interactions in the weakly coupled regime
Bibliographic record
Abstract
We report the observation of electron spin polarization transfer from the triplet state of a porphyrin to a weakly coupled nitroxide radical in a mutant of human neuroglobin (NGB). The native iron-containing heme substrate of NGB has been substituted with Zn(ii) protoporphyrin IX and the nitroxide has been attached via site-directed spin labeling to the Cys120 residue. A reference synthetic polypeptide with free base tetraphenylporphyrin and a nitroxide bound to it is also studied. In both systems the nitroxide and the porphyrin are held at a fixed distance of approximately 2.4 nm. The transient EPR data of the NGB sample show that the triplet state of Zn(ii) protoporphyrin acquires significant net polarization, which is attributed to the dynamic Jahn-Teller effect. As the spin polarization of the protoporphyrin triplet state decays, a polarized EPR signal of the nitroxide arises. In contrast, the free base porphyrin in the reference polypeptide does not acquire net polarization and no polarization of the nitroxide label is observed. This is likely a result of the fact that the porphyrin is not Jahn-Teller active because of its lower symmetry. A perturbation theory treatment suggests that in the NGB sample, the polarization of the radical occurs by the transfer of net polarization from the triplet state. This process is also enhanced by the spectral broadening caused by the back and forth transitions associated with the dynamic Jahn-Teller effect. We propose that the novel transfer of polarization to the radical could be exploited to enhance the sensitivity of light-induced dipolar spectroscopy experiments.
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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".