| Terahertz(THz) wave belongs to the far infrared wave band, between the microwave and the infrared wave on the electromagnetic spectrum, which sometimes also called the far infrared wave. It is refers to the frequency within 0.1~10THz electromagnetic wave(1THz=1012Hz). THz radiation has low energy, it won’t cause damage biological molecules of structure and activity genererlly. Moreover it also has characteristic of the penetrability and the fingerprint, makes the THz technology widely used in nondestructive testing field. Fourier Transform Infrared Spectroscopy(FTIR) is a common terahertz wide-band measurement method, which is used to measure the optical properties of all kinds of materials and biological molecules. And it has been confirmed a similar sensitivity compare with terahertz time-domain Spectroscopy(TDS) in low frequency. Molecules of THz spectrum reflects the intramolecular and intermolecular interaction,the former including translation and rotation of the groups and molecules and non covalent bonding effection, the latter including the weak hydrogen bonding, electrostatic force and van der Waals force, etc. And it also influenced by the molecular interaction with the environment at the same time. Studies have shown that in addition to the terahertz spectrum, study the vibration and rotation characteristic of the biological molecules in high far infrared spectrum, infrared and near infrared band spectrum also have important guiding significance.This paper by using Fourier transform infrared spectroscopy to study the THz spectrum of several vitamin samples. At the same time, try to use the density functional theory(DFT) in the Gaussian software to explain the formation mechanism of the fingerprint spectrum with the result of the experiment. This work of the research content mainly includes two aspects of experimental measurement and theoretical analytic, the main contents include:Firstly, through the Fourier transform infrared spectroscopy system, studing the terahertz spectrum characteristics of biotin, pyridoxine, riboflavin, folic acid, vitamin K2 this several common vitamins of broadband segment. A detailed analysis about vitamin samples and polyethylene powder mixing with different ratio of absorption spectra. We compare the spectra obtained, and finally determine the detailed and reliable spectra. Results show that there have very big differences within the effective band spectrum. It performance for the difference of the number and position of absorption peak, etc. Experimental results can be used to establish a vitamin terahertz spectrum fingerprint database, as well as vitamin terahertz spectrum provides basis for the theory section.Secondly, using density functional theory(DFT) to calculate folic acid and vitamin K2 this single molecule models, and the vibration modes were identified. Studies show that for the most solid vitamin, their single molecule model to simulate the absorption peak position exist certain differences with the experiment, it is considered to be the differences between single molecular model of the theory simulation and the actual in crystal samples. And riboflavin single molecule compared with unit cell molecular theory simulation, test results good consistency with theexperiment, prove that riboflavin absorption peaks are mostly from the vibration of the groups in molecules.Thirdly, in order to overcome the limitation about using single molecule model to simulate the crystal vitamin, we respectively for biotin and pyridoxine crystal simulated, and focus on analysising the terahertz spectrum about biotin and pyridoxine of single molecule, two molecules,three molecules, as well as the cell molecular. And we clarify the intramolecular and intermolecular forces of vibration and rotation mechanism, and identify the spectrum of vibration modes. |
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