Terahertz spectroscopy of short peptides

Absorption spectra of the hydrated and dehydrated alanine short peptides have been studied by the terahertz time-domain spectroscopy in the temperature range of 10-293 K. In the dehydrated alanine tripeptides spectral changes with temperature, which is attributed to the structural changes, have not been observed at the whole temperature range, while the alanine dipeptide has shown the changes of the structure below 100 K. Different temperature dependence between the dipeptide and the tripeptide suggest that conformational stability is related to the neighbor interactions, which are affected by peptide lengths. In the hydrated peptides the inhomogeneous broadening of the absorption bands significantly decreases at 10 K, suggesting that water molecules play an important role for decreasing the disorder.