Vibrational analysis of peptides, polypeptides, and proteins. II. β‐Poly(<scp>L</scp>‐alanine) and β‐poly(<scp>L</scp>‐alanylglycine)

Abstract

Abstract The normal vibration frequencies of poly( L ‐alanine) and poly( L ‐alanylglycine) in the antiparallel chain‐pleated sheet structure have been calculated, using the force field for polyglycine I from the previous paper ( Biopolymers 15 , 2439–2464) plus additional force constants for the methyl group. The agreement with observed ir and Raman bands is very good. This substantiates the excellent transferability of the force field, since polyglycine I was shown to have a rippled‐sheet structure. The amide I and amide II mode splittings are very well accounted for by transition dipole coupling, showing that subtle structural differences are sensitively manifested through this mechanism.