Solid-State <sup>1</sup>H and <sup>13</sup>C Nuclear Magnetic Resonance Spectroscopy of Athabasca Oil Sands Asphaltenes: Evidence for Interlocking π-Stacked Nanoaggregates with Intercalated Alkyl Side Chains
Bibliographic record
Abstract
Solid-state 1 H and 13 C nuclear magnetic resonance (NMR) spectroscopic studies on heptane-extracted Athabasca oil sands asphaltenes show strong support for the “island” or “Yen–Mullins” model. Structural calculations on the deconvolved 13 C direct-polarization magic-angle spinning (DP-MAS) NMR spectrum reveal the existence of large, peri-condensed polycyclic aromatic hydrocarbon (PAH) systems. Further support for this model was obtained from the variable contact time and dipolar dephasing experiments. Variable contact time experiments demonstrated decreased mobility of the alkyl groups with increasing proximity to the aromatic core. Furthermore, it was shown that all of the aromatic groups are highly rigid, with no evidence for mobile aromatic moieties pendant from the main aromatic core. The cross-polarization discrimination induced by variable amplitude minipulses (CP-DIVAM) nutation curves enable discrimination between signals from mobile and rigid components and show that the alicyclic groups are condensed with the main aromatic core. The dipolar and T 2 filter sequences enabled selection of low-level well-resolved signals underlying the mostly broad 1 H NMR spectrum for the first time. These signals provide strong experimental support for aliphatic groups occupying spaces between stacked aromatic sheets in the solid state, which are thought to interfere with the π–π stacking interactions, while promoting stacking via π–σ interactions. The T 2 relaxation behavior of the aliphatic protons suggests clustering of nanoaggregates, forming interlocking structures. All of these observations are consistent with the hierarchical Yen–Mullins model for asphaltenes and provide direct evidence for the existence of the nanoaggregate cluster architecture in a solvent-free environment.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 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".