Stabilization of the base-off forms of vitamin B12 and coenzyme B12 by encapsulation of the α-axial 5,6-dimethylbenzimidazole ligand with cucurbit[7]uril
Bibliographic record
Abstract
Cucurbit[7]uril (CB[7]) forms very stable complexes with the alpha-axial 5,6-dimethylbenzimidazole (alpha-DMB) nucleotide base when dissociated from the Co(III) center in vitamin B(12) (CNCbl, K(CB[7]) = (7.5 +/- 0.5) x 10(4) dm(3) mol(-1)) and coenzyme B(12) (AdoCbl, K(CB[7]) = (3.02 +/- 0.35) x 10(6) dm(3) mol(-1)). The inclusion of alpha-DMB ligand facilitates its release from the metal center and its subsequent protonation, with significantly higher pK(base-off) values of 3.77 and 6.61, than determined for the free CNCbl (0.11) and AdoCbl (2.67), respectively. Addition of CB[7] to the base-on form of CNCbl at pH 2 provides for a direct measurement of the rate constant for the dissociation of the alpha-DMB ligand from the Co center (k = (4.6 +/- 0.2) x 10(-2) s(-1), DeltaH = 93 +/- 2 kJ mol(-1), DeltaS = +41 +/- 6 J K(-1) mol(-1)). The beta-axial 5'-deoxyadenosyl ligand (beta-Ado) on coenzyme B(12) is bound more weakly by a second CB[7] host (K(CB[7]) = (1.1 +/- 0.2) x 10(3) dm(3) mol(-1)), however inclusion of the beta-Ado ligand has no effect on the kinetics of its heterolytic photodissociation from the Co(III) center.
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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 | 0.001 | 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".