Qualitative Analysis Of Amino Acids By Terahertz Spectroscopy Based On Quantum Chemistry

Terahertz wave is an electromagnetic wave with a wavelength of 30 microns to 3 mm.Its energy is between photons and electrons.It can penetrate non-metallic and non-polar materials,making terahertz time-domain spectroscopy possible as a new non-destructive testing technology.The vibration-rotation modes of some biological macromolecules are located in the terahertz band,which makes the biological molecules have fingerprints in the terahertz band.After obtaining the Terahertz Absorption Spectra of the substances to be measured,the qualitative identification of the substances to be measured can be realized by comparing with the standard spectra.On this basis,combined with data processing techniques such as least squares method and support vector machine,terahertz time-domain spectroscopy can also be used to quantitatively analyze the substances to be measured.The intramolecular atomic vibration,intermolecular hydrogen bonding and low-frequency vibration of crystal lattices of amino acids are all in terahertz band,which makes them have obvious absorption peaks in terahertz band,and different amino acid molecules have different Terahertz Absorption peaks.Therefore,the qualitative analysis of amino acids can be realized by using this "fingerprint characteristic" of amino acids in terahertz band.Quantum chemical analysis can apply the basic principles and methods of quantum mechanics to study the structure,properties and relationship of stable and unstable molecules.It can also study the interaction,collision and reaction between molecules.The Terahertz Absorption Spectrum of amino acid molecule can be simulated and calculated by quantum chemical calculation method,which can match the molecular vibration mode of the terahertz absorption peak of amino acid molecule,have certain reference and directivity for the qualitative analysis of amino acid,and provide theoretical support for the terahertz time-domain spectrum of sample obtained by experiment.Quantum Chemometer is carried out on the basis of the Terahertz Absorption spectrum obtained by experiment.It can also be used to verify the experimental results.In this paper,Terahertz Absorption Spectra of threonine were obtained by terahertz timedomain spectroscopy.The monomolecular,dimer and cell configurations of threonine samples in the form of amphoteric ions were constructed.The Terahertz Absorption spectra weresimulated by quantum chemical calculation method after completing the structural optimization.The calculated results show that the Terahertz Absorption Spectra of monomer and dimer configurations are quite different from the experimental results,but the absorption peaks at high frequencies are basically in agreement with the experimental results,while the more comprehensive calculation results of hydrogen bond and van der Waals force among reaction molecules are in good agreement with the experimental results.The results show that terahertz time-domain spectroscopy can realize the qualitative identification of amino acids.To some extent,quantum chemical calculation can provide theoretical support for the absorption spectrum library of amino acids.At the same time,the experimental method indicates that stoichiometric analysis and calculation should select the cell configuration which is more fully consistent with the actual sample structure as the minimum research structure.