Vibrational analysis of peptides, polypeptides, and proteins. XXIV. Conformation of poly(α‐aminoisobutyric acid)

Raman and polarized ir spectra have been obtained on built‐up monomolecular films of poly(α‐aminoisobutyric acid), and analyzed in the context of normal mode calculations on 3 10 ‐, α‐, and α′‐helix conformations of this molecule. The average discrepancy between observed and calculated frequencies is significantly smaller for the 3 10 ‐helix than for the other structures. This, together with the more satisfactory explanation of several special features of the spectra, indicates that this polypeptide adopts a 3 10 ‐helix conformation in such thin films.