Hydrocarbon chain absorption

The quoted frequencies are for typical open-chain saturated hydrocarbon chains (R). Conjugation and cyclic structures will influence the absorption frequency. 

Figure 6.3 Effects of hydrocarbon chain modifications on melting points of similar-sized cuticular lipids. When lipids melt, the absorption frequency of C-H symmetric stretching vibrations increases from -2849 cm1 to -2854 cm4. From right to left, compounds are (chemical change relative to n-alkane, molecular mass in daltons) filled circles, n-dotnacontane (no change, 450) open circles, palmitic acid myristyl ester (wax ester, 452) filled triangles, 13-methylhentriacontane (methyl-branched alkane, 450) open triangles, (Z)-13-tritriacontene (double bond, 462) filled squares, 9,13-dimethylhentriacontane (2 methyl branches, 464) open squares, oleic acid oleyl ester (2 double bonds and an ester link, 532). Data from Gibbs and Pomonis (1995) and Patel el al. (2001).

To elucidate the role ofhydrophobic bonding, a detailed study on the kinetics ofin-testinal absorption has been performed on sulfonamides. It was concluded that transport across the microvillus membrane occurs via kinks in the membrane which are pictured as mobile structural defects representing mobile free volumes in the hydrocarbon phase of the membrane and whose diffusion coefficient is fairly fast ( 10-5 cm2/s) [1]. The thermal motion of the hydrocarbon chain leads to the formation of kinks. It was also postulated that a transient association of the drug molecules with proteins on the surface of the microvillus membrane is involved in the formation of the activated complex in the absorption process [1]. 

Furthermore, the conformation and orientation of the hydrocarbon chains of MS in the MS-C20 binary and MS-C2o-AL18 ternary systems were investigated by using infrared absorption spectroscopy. In this respect, deuterated arachidic acid (C2o-d) and deuterated n-octadecane AL %-d) were utilized to separate infrared bands due to the hydrocarbon chains of MS from those arising from C2o and AL18. Fig. 26 shows polarized infrared spectra A of 10-layer LB films of pure cadmium arachidate (CdC20), MS-C20- binary and MS-C20-t/-AL18-t/... 

Fig. 28(b) depicts polarized infrared absorption spectra of 10-layer LB films of pure CdC2()-r/, and the MS-C2o binary and MS-C20-AL18-r/ ternary systems [80,82]. In the case of CdC20-r/ LB film, peaks at 2193 and 2089 cm-1 are assigned to the CD2 antisymmetric and symmetric stretching modes of the hydrocarbon chain, respectively, and their peak positions are characteristic of the stW-trans conformation of the hydrocarbon chain. The LB film of the MS-C20 binary system does not show the peak, as a matter of course. The film of the MS-C20-AL18 ternary system yields the peaks at 2194 and 2089 cm suggesting the presence of AL 18-d with the all-/ra//,v conformation. 

CHj - CHj - CHj - 0 ) - The hydrophobic moiely can be a linear hydrocarbon chain (abbreviated where n Is the number of carbons) there can be a phenyl group (( i) in the chain (which may assist in the binding when the adsorbent is hydrophobic, and which makes analytical detection straightforward using ultraviolet absorption), some polypropylene segments, etc. Generally the composition can be abbreviated as Cj ())Ejj, etc. This code has been proposed by... 

The results of this study show that ultrasonic absorption techniques, when used in conjunction with other aggregate properties, provide important kinetic information about the partitioning process of alcohols tetween ionic micelles and the bulk phase. The effect of hydrocarbon chain length of the alcohol on the exit rates of monomer surfactant and alcohol components from the mixed micelles, aggregate size distribution, and the electrostatic stabilization of the head group region of the micelles will be considered. As well, previously unreported data for water- 1-butoxyethanol-DTAB will be used to extend conclusions based on previous work [2,3]. 

Information on the conformational state of the hydrocarbon chains and their orientation has been obtained from external infrared reflection absorption spectroscopy (IRRAS). The first systematic IRRAS studies on phospholipid Langmuir monolayers were reported by Dluhy et al ) (see, for instance fig. 3.62). For DPPC monolayers in the LE phase the positions of the conformation-sensitive symmetric and anti-symmetric C-H stretching bands in the IRRAS spectra were found to be at the same positions as for bilayer systems of DPPC above the Kralft temperature. In the LC phase the frequencies of these bands indicate that the hydrocarbon chains of the lipid molecules are in the all-trans ) conformation (i.e. zig-zag) and analysis of polarized IRRAS spectra show that their average tilt is ca 35° relative to the monolayer normal. This is in reasonable agreement with the tilt angle of 30° obtciined from X-ray diffraction on DPPC monolayers (30°). 

Conformational changes in hydrocarbon chains can be related to shifts in the CH2 vibrations near 3000 cm L In a typical measurement, 4096 scans at a resolution of 8 cm are summed, and absorption maxima can be located with a precision of 0.1 cm . 

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