Vibrational analysis of peptides, polypeptides, and proteins. XXXII. α‐Poly( L ‐glutamic acid)

The Raman and ir spectra of α‐helical poly( L ‐glutamic acid) have been assigned on the basis of a normal mode calculation for this structure. The force field was based on our previously refined main‐chain force constants for α‐poly( L ‐alanine) and side‐chain force constants for β‐calcium–poly( L ‐glutamate). Despite the identical backbone α‐helical structures, significantly different frequencies are calculated, and observed, in the amide III and backbone stretch regions of α‐poly( L ‐glutamic acid), as compared with α‐poly( L ‐alanine). This clearly demonstrates the influence of side‐chain structure on mainchain vibrational modes.