Amides infrared absorption band positions

Figure 4. Optical image and two infrared images of a dividing cell (35 pm x 20 pm) obtained from IR spectromicroscopy. These chemical maps are derived from the strength of absorption bands from approximately 100 infrared transmittance spectra collected over the area of the dividing cell. The maximum in the color scale (yellow) represents the position of the maximum absorption by the cell, while the minimum (blue) represents no absorption by the cell. Strikingly, the intensity map of the amide II absorption band shows two peaks in the center of the two halves of the cell, representing the position of two separate nuclei before the cell division is complete. The intensity map of the C-H stretch absorption bands shows that lipids are concentrated at the contractil ring, where the cleavage furrow is located. [Used by permission of the National Academy of Sciences, U.S.A., from Jamin et al. (1998), Proc Natl Acad Sci, Vol. 95, Fig. 3, p. 4839.]...

A rapid FTIR method for the direct determination of the casein/whey ratio in milk has also been developed [26]. This method is unique because it does not require any physical separation of the casein and whey fractions, but rather makes use of the information contained in the whole spectrum to differentiate between these proteins. Proteins exhibit three characteristic absorption bands in the mid-infrared spectrum, designated as the amide I (1695-1600 cm-i), amide II (1560-1520 cm-i) and amide III (1300-1230 cm >) bands, and the positions of these bands are sensitive to protein secondary structure. From a structural viewpoint, caseins and whey proteins differ substantially, as the whey proteins are globular proteins whereas the caseins have little secondary structure. These structural differences make it possible to differentiate these proteins by FTIR spectroscopy. In addition to their different conformations, other differences between caseins and whey proteins, such as their differences in amino acid compositions and the presence of phosphate ester linkages in caseins but not whey proteins, are also reflected in their FTIR spectra. These spectroscopic differences are illustrated in Figure 15, which shows the so-called fingerprint region in the FTIR spectra of sodium caseinate and whey protein concentrate. Thus, FTIR spectroscopy can provide a means for quantitative determination of casein and whey proteins in the presence of each other. 

The infrared spectrum of one of the first synthetic polypeptides made by Woodward and Schramm (1947) was investigated by Darmon and Sutherland (1947) and found to exhibit intense absorption bands at the positions expected for the peptide link from work on the amides viz., 3330 cm. i, 1670 cm. and 1560 cm. i About twenty synthetic polypeptides since investigated by the same workers all show these same three characteristic absorption bands, which may be regarded as well established key bands for the identification of a polypeptide structure (c/. Fig. 8 in Katchalski, 1951). 

Many amines were employed in the course of this extensive investigation. Since most of the diamines selected are solids at room temperature they were reacted in solution or in the melt state (working at 75°C). The results can be summarized as follows (1) Aromatic diamines are the most reactive, and the reactivity of aliphatic diamines decreases with increasing molecular weight (2) diamines are more reactive than monoamines, especially if the amine group is in an aromatic para position. The formation of copolymer was proved by infrared analysis. The spectra show absorption bands at 1470, 1640, 2990, and 3100 cm characteristic of amide groups, and at 3300 and 920 cm" for primary amine groups. From the viewpoint of chemical composition, the reaction products are composed of a fraction insoluble in water (and in other common solvents) and a second soluble... 

The structure of nucleohistone appears to be rather different from that of nucleoprotamine, since its X-ray diffraction pattern is different (Wilkins and Zubay, 1959 Zubay and Wilkins, 1962 Pardon et al., 1967), also the position of the amide II band in the infrared absorption spectrum and the rate of deuteration [Bradbury etal., 1962 (2)j. 

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