Secondary structure evident in the far infrared spectra of peptides

Interpretation of the far-infrared spectra of polypeptides is not straightforward. Peptides have peaks between 300-500 cm^-1 that are diagnostic of their secondary structure confirming earlier work with polyamides. The helical peptide had a peak at 380 cm^-1 and the beta-sheet peptide had a peak at 445 cm^-1. The cyclic helical peptide KARAD also had peaks at 385, 402 and 470 cm^-1 which were not present in the linear isomer. Below 300 cm^-1 the spectra are complex and still defy understanding but are evidently data-rich and worthy of further research.