Kinetics of the Electron Self-Exchange and Electron-Transfer Reactions of the (Trimethylammonio)methylferrocene Host−Guest Complex with Cucurbit[7]uril in Aqueous Solution
Bibliographic record
Abstract
The electron self-exchange rate constants for the (trimethylammonio)methylferrocene(+/2+) couple (FcTMA+/2+) have been measured in the absence and presence of the cucurbit[7]uril (CB[7]) host molecule in aqueous solution, using 1H NMR line-broadening experiments. The very strong binding of the ferrocene to CB[7] results in slow exchange of the guest on the NMR time scale, such that resonances for both the free and bound forms of the reduced ferrocene can be observed. The extents of line broadening in the resonances of the two forms of the guest in the presence of the FcTMA2+ species can be monitored independently, allowing for the determination of the rate constants for the possible self-exchange pathways involving the bound and free forms of both the oxidized and reduced members of the redox couple. The encapsulation of both the reduced and oxidized forms of the ferrocene increases the rate constant (25 degrees C) from (2.1+/-0.1)x10(6) M-1 s-1 (for FcTMA+/2+) to (6.7+/-0.7)x10(6) M(-1) s(-1) (for {FcTMA.CB[7]}+/2+), whereas inclusion of the reduced form only decreases the rate constant to (6+/-1)x10(5) M(-1) s(-1). The changes in the exchange rate constants upon inclusion of the reactants are related to the effects of CB[7] acting as an outer, second-coordination sphere and are compared to those observed previously for the electron-exchange process in the presence of beta-cyclodextrin and p-sulfonated calix[6]arene hosts. The binding of FcTMA+ and hydroxymethylferrocene to CB[7] significantly reduces the rate constants for their oxidations by the bis(2,6-pyridinedicarboxylato)cobaltate(III) ion (which does not bind to CB[7]) as a result of reduced thermodynamic driving forces and steric hindrance to close approach of the oxidant to the encapsulated ferrocenes.
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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 | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".