Amide VI band

The amide VI band is associated with C=0 out-of-plane bending, and the amide V band corresponds to the N-H out-of-plane bending. Both modes are associated with the changes in crystal modification as we (11) and others (21) noted by x-ray diffraction in polyamides. For nylon 66 the spectra of the untreated and iodine-potassium iodide desorbed samples are identical although that of the complexed polyamide (12) differs significantly. Evidence from polarized low frequency, particularly of the 140 and 100 cm"1 bands of the ion is also definitive on this point and has... 

The amide IV band is characteristic of secondary amides and appears near 620 cm . It is due mainly to 0=C—N bending. The amide VI band, which appears near 600cm , is due to C=0 out-of-plane bending (Miyazawa et al., 1956, 1958 Miyazawa, 1955, 1956). 

Other characteristic absorptions of secondary amides have been described at lower frequencies, but are of less diagnostic value. These include the out-of-plane NH deformation [79] frequency which occurs near 700 cm and is exceptionally broad in the spectra of solids and concentrated solutions. This has been termed the Amide V absorption by Mizushima et al. [80]. Assignments of Amide IV and Amide VI bands at still lower frequencies have also been made. These are essentially skeletal vibrations, and they have been discussed further by Miyazawa [81]. 

The amide VI band occurs for primary amides in the 1420-1400 cm region. It usually has medium intensity. 

Despite the fact that crude APPL s are totally soluble in DMF, an important residue is obtained at the end of the solvent sequence (0 100, THF DMF) indicating that the protein-rich fractions require association with the polyphenolic part for their solubilization in DMF (Table VI). Because each APPL has a different amino acid composition, its solubility distribution is also different, but in both cases, the THF fraction is the most lignin-like, with only 1% nitrogen. This is confirmed by FTIR analysis (Fig. 7). As the fractionation proceeds with increasing solvent polarity, the lignin characteristic bands at 1515, 1460, 1265, 1095, 1035, and 810 cm-1 disappear, while the amide characteristic bands at 3290 and 3080 cm-1 appear. 

The use of polarized light to generate contrast between bone components provides information on the spatial distribution of bone components and their orientation. Kazanci et al. used Raman polarized imaging to examine the distribution of mineral and matrix constituents around osteons, and showed that the POi Vi and amide I bands are highly orientation-dependent, whereas the amide III and POi V2 and V4 are less orientation-dependent [35]. Orientation effects are nicely illustrated in Figure 4.2 [36]. The POi Vj amide I ratio coincides with the orientation of the lamellae the same lamellae have different contrasts, depending on the polarization of the excitation light and the orientation of the specimen. 

The results of the infrared analysis are presented in Table VI. These results show that carboxylic acids and phenols are found only in the acid concentrates. Carboxylic acids are concentrated in the polar acid subfractions III and IV while phenols are concentrated in subfraction II. Carbazoles, ketones, and amides are found in all three major nonhydrocarbon fractions. The appearance of the same compound type in several fractions may arise from differences in acidity or basicity that are caused by the hydrocarbon portion of the molecule. Multifunctionality could also be a factor in the distribution of compound types among the fractions. The 1695 cm"1 band was assigned to ketones on the basis of work... 

Fig. 14.3. (a) Bone section under polarized light, black line outlines where Raman images were acquired. Polarized Raman images of (b) phosphate V2/amide III, (c) phosphate Vi/amide I, and (d) carbonate/phosphate V2 band ratios at the interface between osteon and interstitial bone, (e and f) Three-dimensional view of phosphate Vi/amide I ratio for different polarization directions. Reprinted with permission from [1]... 

The effect of N-acetyl substitution in methionine on the nature of transients formed after one-electron oxidation was studied as a function of pH and NAM concentration. The observed absorption bands with X = 290 nm, 360 nm, and 490 nm were respectively assigned to a-(alkylthio)alkyl, hydroxysulfuranyl and dimeric radical cations with intermolecular three-electron bond between sulfur atoms. N-acetylmethionine amide (NAMA) (Chart 7) represents a simple chemical model for the methionine residue incorporated in a peptide. Pulse radiolysis studies coupled to time-resolved UV-Vis spectroscopy and conductivity detection of N-acetyl methionine amide delivered the first experimental evidence that a sulfur radical cation can associate with the oxygen of an amide function vide infra). ... 

Table 1 summarizes the analytical results obtained for the thermal reaction of I and of VI. With the exception of the experiment in which methanol was added to VI, the extent of phthalocyanine formation was very small. Moreover, the infrared spectra of these reacted samples exhibited absorptions characteristic of amide or imide carbonyl as well as those for tria-zine. Under these conditions, phthalocyanine formation is not favored. For example, the yield of phthalocyanine ring formation, based on the consumption of starting material, was less than 5% for the model phthalonitrile VI, and less than 10% for the bis-phthalonitrile I. In a separate experiment a thin film of I deposited on a salt plate was allowed to cure while exposed to the atmosphere. Periodic infrared examination of the curing film showed that as the cyano absorbance diminished the absorbance in the carbonyl region increased until the latter was the predominant infrared band. These results demonstrate that... 

---