Kinetics of Metal−Fulvic Acid Complexation Using a Stopped-Flow Technique and Three-Dimensional Excitation Emission Fluorescence Spectrophotometer
Bibliographic record
Abstract
A stopped-flow technique and three-dimensional excitation emission (Ex/Em) fluorescence spectrophotometer were used to detect the full fluorescence spectral kinetic changes that occurred during the complexation between fulvic acid (FA) and several metals [Cu(II), Ni(II), Co(II), Cd(II) and Ca(II)]. The study was carried out with a fulvic acid isolated from Cavan Bog, Canada. At pH 7, the FA reacted rapidly with all metals studied. Two major kinetically distinguishable binding sites on FA (“fast” and “slow”), having reaction half-lives of 1.3−3.9 and 34.7−69.3 s, respectively, were identified using pseudo-first-order kinetic plots. Kinetic changes of Ex and Em wavelengths of the fluorescence maximums also indicate two major binding sites. For the fast-reacting binding site, the rate constant and the site relative contribution were as follows, Cu 2+ > Ni 2+ > Co 2+ > Cd 2+ > Ca 2+, which agrees with the Irving−Williams series, indicating that complexation kinetics are affinity dependent. Within each kinetic phase, both Ex and Em wavelengths of fluorescence maximums increased with time, indicating the occurrence of structural changes during the binding process. Based on the results obtained, the use of full fluorescence spectra appears to be a promising tool for further understanding metal−FA complexation mechanisms.
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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".