Monolayers, microbubble surfactant material

Fig. 7.2 shows a typical H-NMR spectrum obtained with microbubble-surfactant material collected from compressed mono-layers. Comparison of this spectrum with Fig. 7.1 clearly demonstrates that the characteristic family of peaks originating from carbohydrate material (ref. 402,403), between 8 values of 3.4-3.8 ppm, is markedly reduced following monolayer formation and compression. (Note, for example, the relative area and maximum height of the terminal methyl group (8 = 0.9 ppm) versus the carbohydrate family of peaks (8 = 3.4-3.8 ppm) within each of the two spectra (Figs. 7.1 and 7.2).) Contrariwise, the characteristic peaks (cf. Table 7.1) for methylene chains (8 = 1.3 ppm) and terminal methyl groups (8 = 0.9 ppm) of long-chain lipids remain essentially unaltered (Fig. 7.2). 

In the series of microbubble experiments (ref. 394) included in this chapter, the actual film material, contained in compressed microbubble-surfactant monolayers, was collected for structural determinations using H-nuclear magnetic resonance (NMR) spectroscopy. The resulting spectrum is then compared to the H-NMR spectrum which was obtained beforehand from the partially purified, microbubble surfactant mixture prior to monolayer formation and compression. 

For the collection of monolayers, the microbubble surfactant mixture was spread (see above) and compressed to at least 24 dyne/cm. Thereafter, a rectangular piece of stainless steel mesh (4 cm x 1 cm, 30 mesh) was introduced vertically through the surface of the subphase, by means of a small handle, and alternately raised and lowered so that the air/water interface remained within the area of the mesh. This slow, vertical oscillation was coupled with a horizontal movement of the mesh along the surface of the subphase. The procedure resulted in a continual drop in the measured surface pressure (see above) as monolayer material gradually accumulated over the surface of the mesh. The surfactant-coated mesh was then transferred to and shaken in a glass vial containing high-purity ethanol. Once rinsed, the... 

The collected microbubble-surfactant monolayer material was subsequently lyophilized and redissolved in CD3OD. As with the preceding NMR measurements (see Section 7.1), H-NMR spectra at 270 MHz were obtained with the same Bruker Hx-270 NMR spectrometer. In this case, approximately 0.5% solutions (w/v in CD3OD) of the microbubble-surfactant monolayer material were employed in the measurements (all taken at 26°C). Tetra-methylsilane was used as an internal reference standard (ref. 394). 

However, the peaks usually associated (cf. Table 7.1) with CH3 and CH2 attached to olefinic carbon (8 = 1.6 and 2.0, respectively) show a relative reduction in height and area. This finding suggests that compression of the microbubble-surfactant monolayer results in the ejection of some unsaturated lipids, as well as most of the carbohydrate material, from the monolayer. Such a conclusion is consistent with the frequently mentioned... 

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