Examination of proline, hydroxyproline and pyroglutamic acid with different polar groups by terahertz spectroscopy

Hydroxyproline (HYP) and pyroglutamic acid (PGA), as amino acid derivatives, are highly similar in struc-ture to proline (Pro). However, their low-frequency vibrations show significant differences in the range of 0.25-2.6 THz. Therefore, this study investigated the reasons for the differences combined with terahertz time domain spectroscopy (THz-TDS) and density functional theory (DFT). The results show that HYP and PGA have stronger absorption of terahertz waves due to the existence of polar substituents. Furthermore, the absorption peaks of HYP and PGA are significant red shifted and blue shifted, respectively. We believe that this is caused by the change in the strength of intermolecular hydrogen bonds. Our findings demon-strate that dipole and hydrogen bond effects play a significant role in low-frequency vibrations. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

The research found that hydroxyproline (HYP) and pyroglutamic acid (PGA) have stronger absorption of terahertz waves due to the presence of polar substituents. Additionally, the absorption peaks of HYP and PGA show significant red and blue shifts respectively, which is believed to be caused by changes in the strength of intermolecular hydrogen bonds.