Light-Mediated Hydrogen Generation in Photosystem I: Attachment of a Naphthoquinone–Molecular Wire–Pt Nanoparticle to the A<sub>1A</sub> and A<sub>1B</sub> Sites
Bibliographic record
Abstract
The molecular wire-appended naphthoquinone 1-[15-(3-methyl-1,4-naphthoquinone-2-yl)]pentadecyl disulfide [(NQ(CH2)15S)2] has been incorporated into the A1A and A1B sites of Photosystem I (PS I) in the menB variant of Synechocystis sp. PCC 6803. Transient electron paramagnetic resonance studies show that the naphthoquinone headgroup displaces plastoquinone-9 from the A1A (and likely A1B) sites to a large extent. When a Pt nanoparticle is attached to the molecular wire by reductive cleavage of the disulfide and reaction with the resulting thiol, the PS I-NQ(CH2)15S-Pt nanoconstruct evolves dihydrogen at a rate of 67.3 μmol of H2 (mg of Chl)(-1) h(-1) [3.4 e(-) (PS I)(-1) s(-1)] after illumination for 1 h at pH 6.4. No dihydrogen is detected if wild-type PS I, which does not incorporate the quinone, is used or if either (NQ(CH2)15S)2 or the Pt nanoparticle is absent. Time-resolved optical studies of the PS I-NQ(CH2)15S-Pt nanoconstruct show that the lifetimes of the forward electron transfer to and reverse electron transfer from the iron-sulfur clusters are the same as in native PS I. Thus, electrons are not shuttled directly from the quinone to the Pt nanoparticle during either forward or reverse electron transfer. It is found that the rate of dihydrogen evolution in the PS I-NQ(CH2)15S-Pt nanoconstruct depends strongly on the concentration the sacrificial electron donor cytochrome c6. These observations can be explained if the iron-sulfur clusters are involved in stabilizing the electron; the ~50 ms residence time of the electron on FA or FB is sufficiently long to allow cytochrome c6 to reduce P700(+), thereby eliminating the recombination channel. In the absence of P700(+), slow electron transfer through the molecular wire to the Pt catalyst can occur, and hence, H2 evolution is observed.
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How this classification was reachedexpand
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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, 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".