Fig. 1

Molecular simulation and THz spectrum of L-hydroxyproline. a Molecular model of L-hydroxyproline. b DFT calculated results of L-hydroxyproline. c Absorption spectrum of pure L-hydroxyproline measured experimentally by THz-TDS at room temperature. d to f Several vibration modes corresponding to the absorption peaks of L-hydroxyproline. d 0.76 THz e 1.17 THz f 1.64 THz. White, grey, red, and blue balls represent H, C, O, and N atoms, respectively. Yellow arrows indicate the vibrational direction of the atom. Black dotted and red dashed boxes refer to the dominant functional groups in the vibration modes and the entire molecular vibration of the ring, respectively. g Spectrum of L-hydroxyproline changes with the detection temperature from 290 K to 80 K at 30 K intervals. h Frequency shift of L-hydroxyproline absorption peaks as a function of temperature