Density Functional Theory Investigation of the Contributions of π–π Stacking and Hydrogen-Bonding Interactions to the Aggregation of Model Asphaltene Compounds
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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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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 source (direct Gemma or distilled Codex), 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".