INFRARED AND RAMAN STUDY IN THE SOLID-STATE OF FULLY PROTECTED, MONODISPERSED HOMO-OLIGOPEPTIDES OF L-VALINE, L-ISOLEUCINE, AND L-PHENYLALANINE

An ir‐absorption and Raman‐scattering study, in the solid state, has been carried out on monodispersed, N‐ and C‐protected homooligopeptides (number of residues, n, from 2 to 7) of L‐valine, L‐isoleucine, and L‐phenylalanine. The amide I, II, III, V, and vNH regions have been examined. Some deuterated (ND) samples have been examined to complete the assignments. L‐Phenylalanine dipeptide displays spectral characteristics compatible with the parallel β‐structure; L‐isoleucine and L‐valine dipeptides are probably in a distorted structure. A mixture of parallel and antiparallel extended chains cannot be excluded for the peptides with n = 3. In the amide I region the spectra of peptides with n ≥ 4 show the existence of the β‐conformation. The problem of chain orientation within the pleated‐sheet structure is discussed on the basis of a recent theoretical treatment of vibrational interactions of the amide I mode. Copyright © 1979 John Wiley & Sons, Inc.