Low‐frequency vibrational spectra of some homopolypeptides in the solid state

Low‐frequency Raman and far‐infrared spectra of polyglycine, poly‐ L ‐alanine, and poly‐ L ‐valine have been measured. The Raman spectra exhibit an intense band near 100 cm −1 for these homopolypeptides. Lattice calculations of the polyglycines are used to assign the intense Raman band to a rotary lattice mode. For homopolypeptides in the β conformation, an infrared band is observed whose frequency varies inversely with the square root of the mass of the peptide repeating unit. This infrared band is assigned to the hydrogen bond stretching lattice vibration.