Role of trinuclear Zn(II) complexes in promoting the hydrolysis of 4-nitrophenyl acetate
Bibliographic record
Abstract
Potentiometric determination shows that trinuclear Zn(II) complexes of the four tripods 1,3,5-tri(2′,5′-diazahexyl)benzene (L1), 1,3,5-tri(2′,5′-diazaheptyl)benzene (L2), 1,3,5-tri(2′,5′-diazaoctyl)benzene (L3), and 1,3,5-tri(2′,5′-diazanonyl)benzene (L4) could be potential hydrolytic catalysts. CH 3 CN solutions containing [3Zn:L] T (0.5~2 × 10 3 mol·dm 3 ) with I = 0.10 mol·dm 3 of KNO 3 and Good's buffer (10% volume fraction) were studied for the catalyzing hydrolysis of p-nitrophenyl acetate (NA, 0.5~2 × 10 3 mol·dm 3 ), at 298 K, in the 6.58.2 pH range. The observed rate constants, k obs , fit the equilibrium equation k obs = k com [3Zn:L] T + k OH [OH ] + k 0 . The sigmoid pH~k com profiles for NA hydrolysis suggest that either the Zn(II)-bound hydroxyl or the Zn(II)-bound water forms of the catalysts can be the active species. The observed second-order rate constants are 0.0082, 0.011, 0.0059, and 0.0019 mol 1 ·dm 3 ·s 1 for the four Zn 3 LH 2 O complexes (k A ) and 0.342, 0.257, 0.382, and 0.091 mol 1 ·dm 3 ·s 1 for the four Zn 3 LOH - groups (k B ), respectively. However, under the condition that [NA] = 0.5 × 10 3 mol·dm 3 and [3Zn:L1] T = 2~4 × 10 2 mol·dm 3 at pH 7.6, the observed rate constants, k obs , obey the equilibrium k obs = k com [3Zn:L] T /(1/K′ + [3Zn:L] T ). This indicates that the 3:1 complex (or its deprotonated hydroxide form) mediates NA hydrolysis by nucleophilic attack of the carboxyl center with the pre-formation of a coordination bond between the carboxyl oxygen atom and the Zn(II) ion. Comparison with other models was made, and the reasons for the high catalytic efficiency of the tripodal complexes were given.Key words: tripod, Zn(II), catalysis, NA hydrolysis, polynuclear.
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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) | 0.001 | 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 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".