Our data and TB calculations challenge these assignments and conclusions. All our fibril samples exhibit parallel βsheet structures, yet we observe a peak near ∼60 cm -1 for amylin 20-29 fibrils and no peak near ∼120 cm -1 for amylin sample 1 fibrils. This suggests that the peaks at 60 cm -1 and 120 cm -1 identified by Hiramatsu and coworkers are not specific to antiparallel and parallel β-sheets. Instead, our TB calculations indicate that bands in the 60-140 cm -1 region originate primarily from inter-strand lattice-like vibrations that mainly involve C--O• • •H-N hydrogen bond deformations and stretching motions (Figure ). This aligns with earlier work on β-poly-ala by Moore and Krimm, as well as Fanconi, who described these vibrations as inter-strand hydrogen bond rotatory and translatory lattice modes (Table ).