Amide II band

The amide II band is a group frequency found for primary amides (RCONH2) secondary amides (RCONHR). The band occurs in the region from 1600 to 1500 cm Apparently the amide II band is due to the vibration of several structural units such as NH and CN. An extensive study of this band in N-methylacetamide has led to the suggestion that the band is 60% NH bend and 40% CN stretch 

The position of the band depends on the physical state and on the degree of association of the molecules, since hydrogen bonding can occur for amides. 

In a polyamide such as nylon the band is at 1545 cm An extensive study has shown that the conformation of polypeptides determines the position of the band [ ]. In polyacrylamide the amide II band coincides with the carbonyl vibration 

In methylthiourea complexes with metals such as platinum, palladium, copper, zinc, and cadmium the amide band appears in a range from 1565 to 1580 cm S which is shifted from its normal position at 1550 cm in methylthiourea In thiourea complexes of platinum, palladium, zinc, and nickel the band appears between 1625 and 1615 cm compared to 1610 cm in thiourea [ ]. In boron halide complexes of acetamides the band appears in the 1555-1525 cm range [ ]. In trifluoroacetamides the band appears in almost the same positions as in the corresponding acetamides, near 1580 cm  

The amide III band is a vibration near 1290 cm for secondary amides. For N-methylacetamide it has been shown that the band is made up of 40 % CN, 30 % NH, and 20 % CH3 -C vibrations [ ]. 

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Urethanes R—O—CO—N 1740-1690 Also shows amide II band when nonsubsti-tuted on N... 

The polyamides and polyureas exhibited broad, intense N-H stretches around 3300 cm- , a very strong carbonyl stretching vibration was present at 1630 cm- . The amide II band was evident near 1540 cm- . jn addition, sp C-H stretches occurred around 3100 cm- an(j asymmetric and symmetric sp3 c-H stretches at 2950 and 2860 cm- , respectively. The polyurethane showed the carbonyl absorption near 1700 cm-1 and C-0 stretches in the vicinity of... 

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 ... 

Primary amides and secondary amides, and a few lactams, display a band or bands in the region of 1650-1515 cm-1 caused primarily by NH2 or NH bending the amide II band. This absorption involves coupling be-... 

All primary amides show a sharp absorption band in dilute solution (amide II band) resulting from NH2 bending at a somewhat lower frequency than the C=0 band. This band has an intensity of one-half to one-third of the C=0 absorption band. In mulls and pellets the band occurs near 1655-1620 cm-1 and is usually under the envelope of the amide I band. In dilute solutions, the band appears at lower frequency, 1620-1590 cm-1, and normally is separated from the amide I band. Multiple bands may appear in the spectra of concentrated solutions, arising from the free and associated states. The nature of the R group... 

Secondary acyclic amides in the solid state display an amide II band in the region of 1570-1515 cm-1. In dilute solution, the band occurs in the 1550-1510 cm-1 region. This band results from interaction between the N—H bending and the C—N stretching of the C—N—H group. A second, weaker band near 1250 cm-1 also results from interaction between the N—H bending and C—N stretching. 

The usefulness of infrared spectroscopy of proteins and membranes is increased when spectra of dry films are compared with those taken in deuterium oxide. Exchange of protons for deuterons can affect both the amide I and amide II bands. For randomly coiled proteins in D20 the amide I band is shifted down by about 10 cm."1 but for many proteins D20 does not affect the frequency of the carbonyl stretch of either the ft structure or the a-helix. In addition, upon complete exchange the amide... 

II band in the neighborhood of 1540 cm. 1 disappears and is replaced by a band at about 1450 cm. 1. The extent of diminution of the amide II band is, at least in principle, a measure of the extent of proton exchange. Little effect is observed in ordinary water since, of course, proton exchange does not occur. Table II summarizes some of the characteristic frequencies observed with proteins (83). 

The observation by Maddy and Malcolm (53) that the amide I band of bovine erythrocyte ghosts in D20 is not shifted is remarkable because it implies that all of the membrane protein is either deeply buried in an environment of hydrophobic lipids or exists in a tightly folded a-helical conformation. We have examined extensively the infrared spectra of bovine erythrocyte ghosts, both as dry films and as intact ghosts in D20 and H20 (73). The results for dry films essentially agree with those of other workers and show no evidence of f3 structure. Little change occurs in water. In D20, however, we consistently obtained a shift in the amide I band and a considerable decrease in absorption of the amide II band. 

The spectra of dry films of intact ghosts prepared by lysis in 20 millios-molal phosphate buffer (21) and of ghost protein prepared by cold butyl alcohol extraction (51) are shown in Figure 6. In both cases the amide I band occurs at 1651 cm. 1 and shows no shoulder near 1630 cm. 1, characteristic of fl structure. The amide II band is also unaffected by removal of lipid and occurs at 1540 cm."1. As expected, extraction of lipid results in removal of the band at 1737 cm. 1 assigned to lipid ester carbonyl stretch and a decrease of the band at about 1455 cm."1 arising from methylene and methyl bending. 

Formation of an amide is also indicated in the reaction of PCTFE with Cr(CO)6 and the primary amine, benzylamine. The infrared absorption spectrum shows an N-H stretch centered at 3400 cm, aromatic C-H stretches at 3063 and 3030 cm1, aliphatic C-H stretches at 2933 and 2876 cm1, a broad amide I/amide II band ranging from 1680-1580 cm1, and a C-N stretch at 1454 cm1. The C-Cl stretch at 970 cm1 also shows a significant decrease in... 

In charring rabbit hair, some compositional features of the infrared spectra were lost (Figure 11). It should be noted that the 35 and 45 minute charred samples were still black and fibrous, yet their IR spectra were considerably different from the materials charred for a lesser period of time. This means that some charred protein fibers might not provide much infrared information. The 1650 cm-1 was reduced and shifted a bit to 1664 cm-1, a new C=0 band occurs at 1716 cm-1, the N-H amide II band was completely gone after 35 minutes of charring, but was still present in the 10 and 20 minute samples. 

Amides have a very strong tendency to self-associate by hydrogen bonding, and the appearance of the spectrum is very much dependent on the physical state of the sample. Considerable shifts in band positions can occur on passing from a dilute solution to a solid, thus N—H and C=0 stretching bands show a marked shift to lower frequency while the N—H bending (amide II) band moves to higher frequency. 

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