Far‐infrared spectra of polyalanines with α‐helical and β‐form structures

Far‐infrared spectra of poly‐ L ‐alanines having the α‐helical conformation and the β‐form structure were measured. The spectra of glycine– L ‐alanine copolymer, silk fibroin, and copoly‐ D , L ‐alanines with different D : L compositions were also measured. In addition to the bands so far reported, four bands at 190, 107, 120, and 90 cm −1 were found for the α‐helix conformation and the two bands at 442 and 247 cm −1 were found for the β form. The 442 cm −1 band consists of the parallel 432 cm −1 and perpendicular 445 cm −1 bands. The 247 cm −1 band is well defined and has strong dichroism parallel to the direction of stretching. These two bands appear also for silk fibroin and glycine– L ‐alanine copolymer. All the far‐infrared bands of copoly‐ D , L ‐alanines can be interpreted as α‐helix bands, the three peaks at 580, 478, and 420 cm −1 being ascribed to the D ‐residue incorporated into the right‐handed α‐helix or to the L ‐residue in the left‐handed α‐helix.