The hydrolysis of an activated ester by a tris(4,5-di-<i>n-</i>propyl-2-imidazolyl)phosphine-Zn<sup>2+</sup> complex in neutral micellar medium as a model for carbonic anhydrase
Bibliographic record
Abstract
The properties of tris(4,5-di-n-propyl-2-imidazolyl)phosphineM 2+ complexes (3M 2+ , M = Zn, Co) in neutral micellar media of Brij-35 and Triton X-100 have been studied in water with respect to their quantitative potenti metric titration, Co 2+ -visible absorption spectra, and ability of the 3Zn 2+ complex to promote the hydrolysis of the activated ester, p-nitrophenyl acetate (PNPA). Potentiometric titration of the 3M 2+ (CIO 4 ) 2 complexes in 20 mM Brij-35 media yields a steep titration curve indicative of the cooperative consumption of two hydroxides, with computed pK 1 and pK 2 values of 8.75 and 6.25, respectively, and the midpoint of the titration curve (pK app ) being 7.50. A similar titration of the Co 2+ complex also indicates cooperative consumption of two HO , and this is tied to the formation of a 4- or 5-coordinate complex, pK app ~ 7.37.4. The cooperativity is explained in terms of sequential replacement of the two CIO 4 ions associated with the 3M 2+ to eventually yield 3M 2+ HO /(HO (H 2 O) n ) having the first hydroxide ligated to the metal ion and the second associated as an ion pair. The 3Zn 2+ complex catalyzes the hydrolysis of PNPA in 20 mM Brij-35 and 40 mM Triton X-100. Plots of the observed second order rate constant (k 2 ) vs. pH in Brij-35 increase linearly with pH and plateau to a value of k 2 max = 0.86 M 1 s 1 , with a kinetic pK a of 8.7. These data are analyzed by a process wherein the 3Zn 2+ HO is kinetically active in the rate-limiting step of the reaction, while the ion-paired (HO (H 2 O) n ) exists as a spectator to the slow step, possibly promoting rapid breakdown of a tetrahedral intermediate. Analysis of the kinetic data in terms of a model that accounts for the partitioning of PNPA between water and hydrophobic micellar pseudophase indicates that the second-order rate constant of the micelle-bound ester is augmented by 45-fold due to loading of the PNPA substrate into the micelle. Key words: Brij-35, TritonX-100, neutral micelle, carbonic anhydrase model, kinetics, potentiometric titrations, catalysis, p-nitrophenyl acetate hydrolysis.
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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".