Far‐infrared spectra of poly(‐α‐amino acids) with basic alkyl group side chains

Far‐infrared spectra in the region from 700 to 60 cm −1 have been measured for the α‐helix structures of poly( L ‐α‐amino‐ n ‐butyric acid), poly‐ L ‐norvaline, poly‐ L ‐norleucine, and poly‐ L ‐leucine and for the β‐form structures of poly( L ‐α‐amino‐ n ‐butyric acid), poly‐ L ‐valine, poly( DL ‐amino‐ n ‐butyric acid), poly‐ DL ‐norvaline, and poly‐ DL ‐norleucine. The changes of the spectra on N ‐deuteration have been measured in the region between 700 and 400 cm −1 . It is concluded that, the α‐helix has characteristic bauds near 690, 650, 610, 380, 150, and 100 cm −1 , and that the β‐form has characteristic bands near 700, 240, and 120 cm −1 . The main‐chain vibrations in the region from 600 to 200 cm −1 are strongly coupled with the side‐chain deformation vibrations.