Quantitative Functional Group Orientation in Langmuir Films by Infrared Reflection−Absorption Spectroscopy: CO Groups in Behenic Acid Methyl Ester and <i>sn</i>2-<sup>13</sup>C-DSPC
Bibliographic record
Abstract
IR reflection−absorption spectroscopy (IRRAS) is used to determine the orientation of carbonyl groups in behenic acid methyl ester (BME) and in sn 2- 13 C 1,2 distearoylphosphatidylcholine ( sn 2- 13 C-DSPC) in aqueous monolayer films. The C O stretching contour of BME consists of three overlapped peaks arising from unhydrated, monohydrated, and doubly hydrated forms at 1737, 1721, and 1702 cm -1, respectively. Dichroic ratios constructed from the p- and s-polarized IRRAS intensities of the resolved components of the contour were simulated with the optical theory of V. L. Kuzmin. 1,2 On the basis of valence bond and molecular modeling considerations, the carbonyl group is essentially perpendicular to the chain axes. The transition moment is determined by IRRAS to indeed lie along the C O bond for the unhydrated groups (thus providing good support for the theory) but changes direction for hydrated groups. A satisfactory fit between simulation and experiment could not be obtained by assuming a uniaxial distribution of the zigzag all-trans methylene chain to which the carbonyl group is rigidly attached. A slight preferential orientation of the chain planes in the direction perpendicular to that of the trough barrier movement is found for both BME and sn 2- 13 C DSPC. In addition, spectral quality in the 1000−1300 cm -1 region for BME was sufficient to determine that the orientation of the single-bond C−O stretch of the ester moiety was within 20° of the vertical. For sn 2- 13 C-DSPC, each C O bond stretching contour was split into a doublet arising from hydrated and unhydrated forms. The best fit to the IRRAS data for the unhydrated C O mode in each chain led to a suggested chain tilt of 30°. This value, in good accord with X-ray diffraction measurements, 3 was confirmed through analysis of the CH 2 stretching vibrations. The transition moments of the hydrated C O bonds in sn 2- 13 C-DSPC were again found to not lie along the bond direction. The current analysis provides a new method for determining functional group orientation in monolayers. The approach, when coupled with X-ray and neutron reflectivity measurements, will provide unique information about the structures and interactions of film constituents.
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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) | 0.000 | 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 | 0.001 |
| 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".