Formation of Liquid Ordered Lamellar Phases in the Palmitic Acid/Cholesterol System
Bibliographic record
Abstract
The phase behavior of the palmitic acid (PA)−cholesterol system in aqueous buffer at pH 5.5 has been investigated using infrared spectroscopy and 2 H NMR spectroscopy of both chain deuterated PA and partially deuterated cholesterol. The results indicate that at temperatures below 50 °C, both lipids exist in a crystalline phase and are not miscible. However, we report the formation of a lamellar liquid ordered (lo) phase upon heating. In this phase, the acid and cholesterol molecules experience an axial symmetric motion while the acid acyl chains are conformationally ordered. Despite this unusual composition, the lo phase formed by PA−cholesterol exhibits similar properties to the phospholipid−cholesterol lo phases. The acyl chain order, the thermal expansivity of the bilayer, and the orientation and the dynamics of cholesterol are similar to those previously measured on phospholipidic lo phases. A temperature−composition diagram is proposed for the PA−cholesterol system. This diagram includes the presence of a eutectic with a PA/cholesterol molar composition of 30:70. It is proposed that melted palmitic acid provides a nonpolar environment for the solubilization of cholesterol and the latter induces a straightening of the fatty acid chains, promoting a molecular order compatible with bilayer formation. The implications of these findings in the understanding of the structure of the stratum corneum and in the development of non-phospholipidic liposomes are discussed.
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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 | 0.000 | 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)
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".