Formation of Hg(II) tetrathiolate complexes with cysteine at neutral pH
Bibliographic record
Abstract
Mercury(II) ions precipitate from aqueous cysteine (H 2 Cys) solutions containing H 2 Cys/Hg(II) mole ratio ≥ 2.0 as Hg(S-HCys) 2 . In the absence of additional cysteine, the precipitate dissolves at pH ∼12 with the [Hg(S,N-Cys) 2 ] 2– complex dominating. With excess cysteine (H 2 Cys/Hg(II) mole ratio ≥ 4.0), higher complexes form and the precipitate dissolves at lower pH values. Previously, we found that tetrathiolate [Hg(S-Cys) 4 ] 6– complexes form at pH = 11.0; in this work, we extend the investigation to pH values of physiological interest. We examined two series of Hg(II)–cysteine solutions in which C Hg(II) varied between 8 and 9 mmol/L and 80 and 100 mmol/L, respectively, with H 2 Cys/Hg(II) mole ratios from 4 to ∼20. The solutions were prepared in the pH range 7.1–8.8 at the pH at which the initial Hg(S-HCys) 2 precipitate dissolved. The variations in the Hg(II) speciation were followed by 199 Hg NMR, X-ray absorption, and Raman spectroscopic techniques. Our results show that in the dilute solutions (C Hg(II) = 8–9 mmol/L), mixtures of di-, tri- (major), and tetrathiolate complexes exist at moderate cysteine excess (C H2Cys ∼0.16 mol/L) at pH 7.1. In the more concentrated solutions (C Hg(II) = 80–100 mmol/L) with high cysteine excess (C H2Cys > 0.9 mol/L), tetrathiolate [Hg(S-cysteinate) 4 ] m − 6 (m = 0–4) complexes dominate in the pH range 7.3–7.8, with lower charge than for the [Hg(S-Cys) 4 ] 6– complex due to protonation of some (m) of the amino groups of the coordinated cysteine ligands. The results of this investigation could provide a key to the mechanism of biosorption and accumulation of Hg(II) ions in biological/environmental systems.
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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".