# Effects of Temperature on the FT NIR Raman Spectra of Fish Skin Collagen
## 3 Results and Discussion
### Raman Spectra of FS and BAT Collagen Measured at Room Temperature
As was discussed in the earlier papers [42; 43], the lines related to C-C stretching vibrations in the range 890 to 1060 cm\({}^{-1}\) may also characterize the secondary structure of collagen. The lines at 918 and 936 cm\({}^{-1}\) are characteristic of \(\alpha\)-helices and the lines in the range from 1020 to 1060 cm\({}^{-1}\) are related to \(\beta\)-sheet structure. A gradual loss of these structures leads to a broadening and weakening in the intensity of the bands which are assigned to these vibrations [43]. The Raman band positions of these vibrations are similar for FS and BAT types of collagen. There are, however, some differences in the ratio of the band intensities. The band at 918 cm\({}^{-1}\) for FS exhibits higher intensity compared to the same line for BAT. It could also be related to a higher content of the \(\alpha\)-chain conformation in FS. Another difference between the Raman spectra of BAT and FS collagen appears for the line at 1171 cm\({}^{-1}\), which is assigned to v(CCC) out-of-phase vibration related to the vibrations of tyrosine residue. The line, which is sharp and intense for FS collagen, has very low intensity for BAT. The vibrations of amide I and amide III are most sensitive to changes in the conformation of the secondary structures of collagen. The vibrations related to these molecular groups appear in the spectral range from 1200-1750 cm\({}^{-1}\). The bands between 1200 and 1350 cm\({}^{-1}\) are assigned to the vibrations of amide III, where the modes related to C-N stretching and N-H in-plane bending vibrations of the peptide bond as well as contributions from C-C stretching and C=O in-plane bending vibrations exist. The bands located in the range around 1260-1300 cm\({}^{-1}\) may be responsible for the \(\alpha\)-helix conformation, whereas the bands between 1240 and 1250 cm\({}^{-1}\) could be related to both random coil and \(\beta\)-sheet structures [43]. The bands revealed in the range \(\sim\)1600-1680 cm\({}^{-1}\) are mainly assigned to the stretching vibrations C=O of the peptide bond and the bending vibrations of the N-H group. The bands of amide I can characterize the hydrogen bonds of diverse structures. These diverse hydrogen bonds in the polypeptide chain are responsible for the type of the secondary structure of the protein that is an \(\alpha\)-helix arranged in a spiral which is stabilized by hydrogen bonds between the oxygen of the C=O group of one amino acid and nitrogen of a second amino acid located four positions away. The \(\beta\)-sheet is conformation which should contain a minimum of two strands and is stabilized by hydrogen bonds between the C=O group of one strand and the NH group of the another strand as well as disordered structures. The Raman band assigned to amide I of FS collagen consists of a narrow line at \(\sim\)1666 cm\({}^{-1}\) and a shoulder at \(\sim\)1633 cm\({}^{-1}\). On the basis of the previous Raman studies on collagen [37; 57], this band can be attributed to a significant content of \(\alpha\)-helix structures. In the case of BAT collagen, a wide band of amide I having the local maximum at \(\sim\)1655 cm\({}^{-1}\), along with extra shoulders at \(\sim\)1671 cm\({}^{-1}\) and \(\sim\)1680 cm\({}^{-1}\), was observed. Such a wide, complex band related to amide I of BAT collagen can suggest that it contains \(\alpha\)-helix structures as well as \(\beta\)-sheet and other disordered structures. The most intense bands presented in the range 2800-3200 cm\({}^{-1}\) belong to the stretching vibrations of the CH\({}_{2}\) group and are similar for both FS and BAT types of collagen.