Amides characteristic frequencies

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). 

Amide I vibrations - characteristic amide I frequencies in H20 and 2H20 solvents... 

IR, Raman characteristic bands of monosubstituted amides, low frequencies. 

The large observed splittings in the amide I modes are very well accounted for by the TDC interactions. Since without TDC the normalmode calculation gives a maximum splitting of 10 cm" (Ag, 1684 Au, 1677 Bg, 1676 Bu, 1674 cm ), whereas the observed splitting is about 50 cm , it is evident that this interaction is of major importance in accounting for the observations (see Section II,D,2,c). The same is even more true of the amide II modes without TDC we find Ag, 1534 Au, 1535 Bg, 1559 Bu, 1559 cm . The relatively low observed amide II frequencies (1517 and 1515 cm ) seem to be characteristic of the APRS structure of (Gly) I. 

Amino acid side chains, particularly those with aromatic groups, exhibit characteristic frequencies that often are very useful in probing the local environment of the group in the protein (Spiro and Gaber, 1977). From our present point of view, however, we are interested in characterizing spectral features of backbone chain conformation. It is therefore important to know the locations of such bands so that their contribution to the spectrum is not confused with amide and backbone vibrations. We discuss below some features (in the nonstretching region) of such side-chain modes these are summarized in Table XL. 

III spectral region (1330-1230 cm" ). Note the most intense band in this region is near 1300 cm l with a weaker component seen at about 1245 cm . Thus the spectra of a-helix proteins are dominated by characteristic a-Amide I (1655 cm" ) and Amide III (1300 cm"l) bands. There is a characteristic Amide II frequency... 

NSRS bands in the characteristic frequency range of 500 to 600 cm The amide I vibration is obscured by the water band at 1650 cm and the amide III vibration shows only a shoulder at 1280 cm and a broad 1250 cmband. 

Susi et al. (1967) have observed spectra of poly-L-lysine, poly-L-glutamic acid, )S-lactoglobulin, myoglobin, and a -casein in the region of absorption of the amide I band in HjO and DjO solutions, and in the solid state. Their results indicated that characteristic frequencies exhibited by specific conformations of the synthetic polypeptides studied are not transferable to corresponding conformations of globular proteins. 

The frequencies obtained for different conformations of globular proteins in HjO and DjO solution are internally consistent, in general agreement with corresponding values of fibrous proteins and with the limited data available in the literature concerning deuterated proteins in D2O solution. Dissolution in aqueous environment by itself does not noticeably alter the amide I frequencies. A tentative set of characteristic frequencies and interaction constants was obtained for the amide I modes of N-deuterated proteins. These modes were easily observed in DjO solution and showed sufficient variations in frequency to permit a distinction between the a-helical, the antiparallel-chain pleated sheet, and the solvated random configurations of globular proteins (Table 10.10). 

The characteristic frequencies of N-deuterated secondary amides, polypeptides, and proteins are conventionally labeled amide I, amide IF, etc. (Miyazawa, 1962). 

In symmetrical dialkyl ureas the 1575 cm" band vanishes whereas those at 1656 and 1610 cm" remain. In contrast, in unsymmetrical dialkyl ureas, it is the 1656 cm" band which vanishes whilst the others remain. Other symmetrical dialkyl ureas have been studied by Mido [165] with similar results. He quotes pqo in the 1640—1625 cm" range with little deuterium sensitivity, and the D-sensitive amide II band at 1580 cm". Kutepov [166] et al. have studied symmetrical diaryl ureas where the carbonyl band appears close to 1640 cm" Gompper et al. [115] have discussed the characteristic frequencies of the NH—CO—N— grouping in cyclic systems. 

Recently, a vibrational analysis was reported that assigns the characteristic amide bands of p turns (Bandekar and Krimm, 1979). An interesting conclusion is that amide I bands observed in proteins near 1690 cm can be correlated with p turns as well as structures. The amide II frequencies correlated with P turn type I are expected near 1550-1555 cm and 1567 cm" S those for type II near 1545,1555, and 1560 cm" The turns are characterized by amide II modes with frequencies higher than those of p structures and a helices. 

Spectral Characteristics. The iafrared stretching frequency of the penicillin P-lactam carbonyl group normally occurs at relatively high frequencies (1770 1815 cm ) as compared to the absorptions for the secondary amide (1504-1695 cm ) and ester (1720-1780 cm ) carbonyl groups. 

The random coil amide I VCD pattern is exacdy the same shape, but smaller in amplitude and shifted in frequency from the pattern characteristic of poly-L-proline II (PLP II) which is a left-handed 3ihelix of trans peptides (Kobrinskaya et al., 1988 Dukor and Keiderling, 1991 Dukor et al., 1991 Dukor and Keiderling, 1996 Keiderling et al., 1999b). This... 

---