On the thermal stability β-peptides: A two-dimensional vibrational spectroscopy study

A temperature-dependent 2D-IR study of the amide-I band of a β-peptide forming a 12/10/12/10 helix is presented. Cross-relaxation of a spectrally separated marker amide-I mode, which could be assigned with the help of the NMR structure of the molecule, can be used as measure of conformational flexibility of the molecule. We find that the conformational flexibility of the N-terminal part of the helix increases slightly upon increasing the temperature from 0° to 80°. The cross-peaks in the 2D-IR spectrum, and hence the connectivity of the corresponding peptide units, do not change, suggesting that the N-terminal part of the helix remains essentially intact at 80°. This conclusion is in agreement with previous NMR and CD measurements.