The final spectral region considered spans ∼ 15 -40 cm -1 . This region contains a broad band that is observed as a shoulder feature in most of the fibril spectra (Figures and). Assigning this band is challenging. One hypothesis is that this band can be attributed to breathing motions in proteins. Therefore, based on Chou's work, the bands that are observed in this region for fibrils may arise from accordion-like motions that occur along the growth axis of their β-sheets.