Multi-edge X-ray Absorption Spectroscopic Evidence for Sulphur-based Redox in [4Fe-4S] Molecular Clusters
Bibliographic record
Abstract
Central to the dogma of Fe–S World Hypothesis for the Emergence of Biosphere is the transition from non-living Fe–S geochemistry to the molecular Fe–S biochemistry. While often assumed this being a trivial and spontaneous process; however, the chemical reality is a critical discontinuity of oxidation states of ferrous iron-based minerals and nanoparticles in low temperature hydrothermal environments and ferric iron-based prosthetic groups in metalloproteins. A recent ingenious synthetic effort enabled the access of the first four-electron transfer-series in [4Fe-4S] molecular cluster with the same aromatic thiolate ligand environment. This discovery opened up the possibility to probe a range of [4Fe-4S] cubanes from the geological all ferrous to the hypothetical all ferric cluster along with each intermediate oxidation state. Multi-edge X-ray absorption spectroscopic (meXAS) approach provided us with the insights to put forward the exclusive sulphur-based redox chemistry with only minor perturbations to the Fe centres. The meXAS results unambiguously prove that the Fe ions in the molecular cubanes remain essentially the same as in the mackinawite-like nanoparticles (n(FeS)(aq), 𝑛 <150) formed in the precipitation reaction of Fe2+(aq) and HS–(aq) ions under ambient aqueous conditions. Furthermore, the non- innocent redox chemistry of [4Fe-4S] clusters underscores the intimate relationship between the Fe and S ions that give rise to the concept of chimera of chemical elements - as the building block of Fe–S clusters and nanoparticles - with tantalizing chemical properties that neither of its components can manifest.
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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".