Amide IV band

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). 

In general, acyclic imides exhibit two amide I bands and weak amide IV bands have also been observed near 610cm (16.39pm) and 560cm (17.86 pm). 

Urethanes 1265-1200 7.90-8.33 m m-s Amide IV band (coupled C-N and C-O stretching vibrations)... 

In addition, for solid samples or peptides in nonaqueous solvents, the amide II (primarily in-plane NH deformation mixed with C—N stretch, -1500-1530 cm-1) and the amide A (NH stretch, -3300 cm-1 but quite broad) bands are also useful added diagnostics of secondary structure 5,15-17 Due to their relatively broader profiles and complicated by their somewhat weaker intensities, the frequency shifts of these two bands with change in secondary structure are less dramatic than for the amide I yet for oriented samples their polarization properties remain useful 18 Additionally, the amide A and amide II bands are highly sensitive to deuteration effects. Thus, they can be diagnostic of the degree of exchange for a peptide and consequently act as a measure of protected or buried residues as compared to those fully exposed to solvent 9,19,20 Amide A measurements are not useful in aqueous solution due to overlap with very intense water transitions, but amide II measurements can usefully be measured under such conditions 5,19,20 The amide III (opposite-phase NH deformation plus C—N stretch combination) is very weak in the IR and is mixed with other local modes, but has nonetheless been the focus of a few protein-based studies 5,21-26 Finally, other amide modes (IV-VII) have been identified at lower frequencies, but have been the subject of relatively few studies in peptides 5-8,18,27,28 ... 

IV. STRUCTURE AND DYNAMICS OF THE AMIDE I BAND OF SMALL PEPTIDES... 

Homogeneous 1 2 and 1 4 molar mixtures of aliphatic Urethanes III or IV with polypropylene glycol (2000 MW) are similar to the aromatic Urethane I or II mixtures in the Amide I and II regions. However, the Amide III band absorbs at 1245 cm-1, with a weaker 1260-cm 1 shoulder. The 1210-cm 1 shoulder due to vibrations of the aromatic ring is missing. Also, the 1320-cm 1 shoulder present in the aromatic mixtures is absent in the aliphatic mixtures. 

A number of 1°, 2° and 3° amides were studied extensively. It was found that all the three types showed a characteristic band close to 1670 em which may be attributed to the earbonyl group but in the case of the primary amides there was an additional band at 1613 cm and with the seeondaiy amides the band was found to be close to 1515 cm These findings reveal that the penieillins possess the secondary amide structure (IV), because the secondary amide band at 1670 em was almost equal to 1684 and 1681 cm besides the band at 1515 cm was equivalent to 1506 and 1515 em . Thus, in all, four out of five bands have been accounted for duly. 

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 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... 

The absence of Bohlmann bands in the infrared (IR) spectrum indicates that the nitrogen lone pairs of the di-iV-nitroso-l,4-diazepines 23 are delocalized <1995JOC7461>. While the absence of an amide moiety in the ring confers torsional freedom, the m-2,7-di-Ph groups reduce ring flexibility and the 111 NMR data are consistent with major and minor families of four twist chair conformers that project the C-7 Ph and C-6 R -substituents equatorially These interconvert by a pseudorotation that allows the C-2 phenyl and C-3 R substituents to adopt a pseudoaxial orientation in the preferred conformer family. 

Other mixed vibration bands known as the amide III, IV and V bands have been identified in various regions of the spectrum but they are of limited diagnostic value. 

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