Raman bands corresponding to peptide backbone vibrations were identified by comparing the low-frequency spectra of the fibrils to those of β-poly-gly, which lacks side chains. In contrast, peaks associated with methyl group vibrations of aliphatic amino acids (e.g., Ala, Leu, Ile, Val, Met) were identified by comparing the spectra in Figure to those of β-poly-ala and model polymer systems such as polypropylene. Based on these comparisons and our TB calculations, we could unambiguously assign some of the bands in the ∼ 200 -420 cm -1 region (Table ). Specifically, we assign the bands between ∼ 400 -420 cm -1 region to methyl and methylene umbrella modes (Figure ). In addition, we assign the bands between ∼ 235 -250 cm -1 , observed in all fibril spectra, to torsional rotation motions of methyl and methylene groups (Figure ). This assignment is supported by inelastic neutron scattering data of β-poly-ala, which shows a strong peak at around 230 cm -1 .