The Amide I and II bands

The amide II band is essentially normal and falls in the range 1570—1500 cm for the twenty-five compounds studied by the two main groups of workers [17, 18]. The shifts on solution are 

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In order to test whether our CIRcle cell spectra were dominated by adsorbed protein or protein in solution, we ran spectra of a series of lysozyme solutions ranging in concentration from 0.12 to 102. The IR response of the amide I and II bands at 1653 and 1543 cm-1 is nearly linear with concentration between 5 and 102 lysozyme. However, the IR intensities change very little between 0.1 and 12, strongly suggesting that most of the signal we observe at 0.12 concentration is due to adsorbed lysozyme. Since our study of subtilisin BPN was done at 0.012, we are almost certainly observing only adsorbed species in our ATR spectra. 

Table 10.3. Observed and Calculated Frequencies, in cm of the Amide I and II Bands of Polypeptides in Various Conformations" (Schellman and Schellman, 1964)... 

FTIR measures the wavelength and intensity of the absorption of IR radiation energy by the protein sample. The polypeptide and protein repeat units give rise to nine characteristic IR absorption bands amides A, B, and I-VII. Among these bands, the amide I and II bands are the two most prominent vibrational bands of the protein backbone (Snsi and Byler 1986 Surewicz and Mantsch, 1988). The amide... 

N-acyl substitution results in compounds which combine some of the characteristic features of amino-acids and of amides. Their spectra show a number of distinctive features, some of which are similar to those of amino-acids, so that they are more conveniently considered here than under amides. In common with amides, however, the positions of key bands in these compounds are prone to alteration following changes of state, and it is important that comparisons should be made only between materials examined in comparable states. The differences associated with the spectra of solid and Uquid esters have been employed by Randall et al. [17] for their identification. These compounds do not exist as zwitterions, and therefore show NH and CO frequencies and the amide I and II bands, like the amino-acids, they also show absorptions in the 3000—2000 cm" region. Dipeptides and similar products also containing the NHa group are dealt with separately in Chapter 12. 

Because of the complexity of biological polymers, their IR spectra are generally more difficult to analyze than the IR spectra of synthetic polymers. At present, IR spectra have been used basically as an analytic tool to identify certain functional groups of biological polymers. For proteins, the amide I and II bands appear in the region 1700-1500 cm and are localized in the —CO—NH— group. The frequencies of these bands are not dependent on the neighboring amino acid residue side... 

Cryopreservation Overall reduction in intensity, shifts in the Amide I and II bands Reduction in the intensity of 1002 1447 and 1637 cm- bands ... 

Table 12.2 Typical vibrational wavenumbers for the amide I and II bands in polypeptides...

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