Abstract
The infrared spectra of proline rich proteins display a strong band in the 1450 cm-1 region. In the literature, this band was assigned either to the deformation modes of the CH2 and CH3 groups or to the CN stretching mode of proline residues. In order to establish the correct assignment of this band, the impact of proline vibrations in a polypeptide chain is studied and ab-initio calculations are performed for a model molecule (I) containing a repeat unit of polyproline. A strong band is effectively calculated in the 1450 cm-1 region and mostly assigned to CN stretching whereas, due to the absence of N-H bond, there is no amide II band. These results are in good agreement with the spectral features observed in the FTIR spectra of gliadins. Moreover, the spectral shifts calculated when a water molecule is complexed with (I) are consistent with the hydration effect observed in the experimental data.