The observation of terahertz spectra of all-trans beta-carotene molecule

The carotenoid molecules associated with the proteins perform the important physiological functions of harvesting, transferring and dissipating light energy in the light-harvesting process. Especially, these functions originate from changes in the electronic and molecular configurations of the carotenoid molecules under the influence of intermolecular or intramolecular interactions with the apo-protein. Terahertz spectroscopy is a power tool for the prediction of the configuration or conformation of the carotenoid and non-covalent interactions. All-trans beta-carotene molecule has eleven conjugated double bonds in the polyene chain with all-trans configuration. In this paper, the low-frequency vibrations of all-trans beta carotene molecule were firstly observed. One hand, the vibrational modes of 0-3 THz were obtained by terahertz time-domain spectroscopy (THz-TDS) and Fourier transform far-infrared (FT-FIR) spectrometer, respectively. The absorption spectrum of all-trans beta-carotene molecules were also presented in this frequency region. On the other hand, the other vibrational modes in the range of 3-20 THz were only obtained through FT-FIR spectrometer. There exhibit a lot of rich and distinct vibrational peaks. The terahertz spectra of all-trans beta-carotene molecules represent unique fingerprints of the molecular geometries structures of both beta-ionone and long conjugated double bonds. And the environment of the molecule leads us to the conclusion that THz technique can be used for the recognition of the organic molecules and their conformations.