Proton- and lanthanide-coordinating properties of the tetraaza macrocycle (EDDA-KA)<sub>2</sub> in aqueous solution
Bibliographic record
Abstract
The new potentially multidentate ligand (EDDA-KA) 2 has been prepared and its acid-base properties determined. Its coordination properties with three lanthanide ions (La 3+ , Gd 3+ , and Lu 3+ ) and Fe 3+ have been studied in aqueous solution (I = 0.16 M NaCl, 25°C) by potentiometric pH, spectrophotometric, and 1 H NMR titrations. In total, eight pK a values could be determined by these diverse methods. From the 1 H NMR titrations, all the deprotonation steps could be determined and assigned (in groups). Strong hydrogen bonding among two nitrogen atoms and one oxygen atom on the pyrone ring was observed, and the corresponding pK a values were estimated to be 13.2 and 14.0. By comparison with similar systems, an equilibrium constant for the formation of the hydrogen bond was estimated, K I = 10 4.4 . Eight stability constants in total were determined for various protonation states of the La 3+ and Gd 3+ complexes, but for Lu 3+ only the last four constants were obtained. The species distribution diagram showed that [M(EDDA-KA) 2 -4H] 2- predominated in the range 5 [Formula: see text] pH [Formula: see text] 9 and [M(EDDA-KA) 2 -6H] 4- predominated in the region 9 [Formula: see text] pH [Formula: see text] 11. In the former complex, two strong hydrogen bonds anchored the macrocycle and Ln 3+ was coordinated with the four carboxylate groups; in the latter, the two hydrogen bonding protons were absent and the metal ion might also bind to the nitrogens on the macrocycle. The stability of Gd 3+ -(EDDA-KA) 2 is lower than the analogous Gd 3+ complexes of DOTA, DTPA, and DTPA-BMA.Key words: acidity constants, stability constants, La 3+ , Gd 3+ , Lu 3+ , Fe 3+ , amino carboxylate chelator.
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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".