Density Functional Theory Investigation of the Contributions of π–π Stacking and Hydrogen-Bonding Interactions to the Aggregation of Model Asphaltene Compounds
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Bibliographic record
Abstract
We performed density functional theory (DFT) calculations using the WB97Xd functional with a dispersion correction term and the 6-31G(d,p) basis set to study the contributions of π–π stacking and hydrogen-bonding interactions to the aggregation of asphaltene model compounds containing a 2,2′-bipyridine moiety covalently bonded to one (monosubstituted) and two (disubstituted) aromatic hydrocarbon moieties (phenyl, naphthyl, anthracyl, phenanthryl, and pyrenyl) through ethylene tethers. In these compounds, the N atoms of the 2,2′-bipyridine moiety provide lone pairs for hydrogen bonding to water molecules present in solution. The aggregation strength of the homodimers of these model compounds is evaluated in terms of the aggregation energies, enthalpies, and Δ G 298, as well as the π–π interaction distances. Geometry optimization and thermochemistry analysis results show that the homodimers of both mono- and disubstituted compounds are stable and have a negative Δ G 298 of aggregation because of π–π stacking interactions. Two water bridges containing one, two, or three water molecules per bridge span between two monomers and provide additional stabilization of the homodimers because of hydrogen bonding. The stabilization of the monosubstituted homodimers is the largest with two water molecules per bridge, whereas the stabilization of the disubstituted homodimers is the largest with three water molecules per bridge. The calculated 1 H nuclear magnetic resonance chemical shifts for the monomers and dimers of the three model compounds of this series synthesized to date are in excellent agreement with experimental results for dilute and concentrated solutions in chloroform, respectively ( Tan, X.; Fenniri, H.; Gray, M. R. Water enhances the aggregation of model asphaltenes in solution via hydrogen bonding. Energy Fuels 2009, 23, 3687). The Δ H and Δ G 298 results show that hydrogen bonding is as important as π–π interactions for asphaltene aggregation.
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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)
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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 it