Indole Adsorption to a Lipid Monolayer Studied by Optical Second Harmonic Generation
Bibliographic record
Abstract
Adsorption of indole from an aqueous subphase to a lipid (DPPC) monolayer at the air/water interface is studied by nonresonant second harmonic generation (SHG) with lambda = 800 nm and by observation of compression isotherms with a Langmuir trough. The nonlinear susceptibilities of the monolayers have been carefully measured, including corrections for the contributions of the lipid monolayer and subphase, calibration of absolute values by comparison with a quartz reference, and measurement of absolute phase by comparison with a clean air/water interface. Details of the calibrations involving z-cut quartz and the clean air/water interface are presented. The number density of adsorbed indole molecules has been estimated by comparison of nonlinear susceptibilities with a reference monolayer of hexadecyl 3-indoleacetate. The extent of adsorption of indole to the lipid monolayer is maximum at low surface pressure, decreasing from an indole/DPPC ratio near 2:1 as the monolayer is compressed. The free energy change for adsorption of indole to the monolayer is estimated as -8.1 kcal/mol, which is similar to a result reported previously for a lipid bilayer. Information on the orientation of adsorbed indole is derived by comparison of observed ratios of nonlinear susceptibilities with calculated ratios for model indole monolayers with assumed orientational distributions. Measurement and analysis procedures are described in detail for effective nonlinear susceptibilities in a s/p polarization basis. The calculations use as input the molecular hyperpolarizability tensor of indole, which is obtained by using several computational approaches including sum-over-states calculations and time-dependent Hartree-Fock and density functional methods. The analysis shows that the pyrrole ring of indole points toward the water subphase, and the tilt angle of the long axis of indole increases from near 50 degrees to near 60 degrees as the monolayer is compressed. The analysis also suggests that the plane of indole lies more nearly parallel than perpendicular to the plane of the interface.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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) | 0.000 | 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".