Vibrational circular dichroism (VCD) and infrared absorption spectra in the amide A region of blocked oligopeptides containing proline have been obtained in apolar organic solvents in order to clarify the characteristic VCD for the intramolecularly hydrogen-bonded NH stretching involved in the turn structures of peptide chains as well as the intermolecularly hydrogen-bonded NH stretching in associated molecules. The γ-turn with the intramolecularly hydrogen-bonded C7 conformation exhibits a characteristic positive VCD band at about 3330 cm−1 in dilute solutions of Piv-Pro-NHMe and Ac-Pro-NHMe. The intramolecularly hydrogen-bonded NH stretching in the type II β-turn with C10 conformation gives rise to a positive VCD band at 3345 cm−1 for Piv-Pro-Gly-NHMe. The Gly NH group of Piv-Pro-Gly-OMe and Ac-Pro-Gly-OMe in dilute solutions assumes C7C5 conformation stabilized by a bifurcated three-center intramolecular hydrogen bond and exhibits a positive VCD band near 3300 cm−1 at a lower frequency than the intermolecularly hydrogen-bonded band. All the peptides studied give a characteristic negative—positive bisignate couplet from the high wavenumber side for the intermolecularly hydrogen-bonded NH stretching band at high concentrations.
Competition between inter and intramolecular hydrogen bond evidenced by vibrational circular dichroism spectroscopy: The case of (1
S
,2
R
)‐(−)‐
cis
‐1‐amino‐2‐indanol
