Terahertz Spectral Simulation And Analytical Study Of Caffeic Acid And Its Structural-similar Substances

Caffeic acid is a kind of natural phenolic compound,which has strong antioxidant activity and has good application prospect in the field of medicine.Substances similar to its structure,such as ferulic acid,hydroxycinnamic acid,etc.,also have important medical value.For such substances with similar structure,studying their structural properties is an important prerequisite for the application and performance optimization of such substances.Terahertz spectroscopy detection technology has the characteristics of strong penetration,high spectral resolution,and low photon energy,which can effectively identify such substances.This paper combines terahertz spectroscopy and quantum chemistry-related analysis methods,takes similar structures of caffeic acid,ferulic acid,2-hydroxycinnamic acid and 4-hydroxycinnamic acid as research objects,and analyzes the terahertz spectral characteristics and molecular interaction characteristics of these substances by experimental measurement and theoretical calculation.The main research contents and results of this paper are as follows:(1)Experimental study of caffeic acid and its structural-similar substances by terahertz spectroscopy.Terahertz Time-Domain Spectroscopy(THz-TDS)was used to measure the terahertz spectroscopy of four drugs,caffeic acid,ferulic acid,2-hydroxycinnamic acid and 4-hydroxycinnamic acid,and enrich the characteristics of low terahertz spectrum of these drugs.Experiments have found that there are differences in the terahertz characteristic absorption peaks of such materials with similar structures,this detection technology provides a reference method for the detection and identification of these structural-similar substances.Based on Density Functional Theory(DFT)and added dispersion correction(D3),the terahertz theoretical spectra of four substances were calculated,and the differences between the theoretical spectra and the experimental spectra were analyzed.The theoretical calculation spectrum of caffeic acid and its structural-similar substances are basically consistent with the measured spectra,which provides a theoretical basis for the subsequent vibration analysis and weak interaction analysis.(2)Study on terahertz spectral vibration characteristics of caffeic acid and its structural-similar substances.The Potential Energy Distribution(PED)method was used to identify the vibration modes corresponding to the characteristic absorption peaks in the terahertz spectra of four substances: caffeic acid,ferulic acid,2-hydroxycinnamic acid and 4-hydroxycinnamic acid.The main vibration mode corresponding to the terahertz spectral absorption peak of caffeic acid is dihedral torsion;For ferulic acid,in addition to dihedral torsion,bond angle bending contributes to the formation of absorption peaks.The main vibration mode of each absorption peak of 2-hydroxycinnamic acid is dihedral torsion,while the vibration mode of 4-hydroxycinnamic acid is relatively rich,including dihedral torsion,bond angle bending,and bond length stretching.The difference in the molecular structure of the material makes its spatial arrangement different,and the main vibration mode corresponding to the terahertz absorption peaks of each substance are therefore different.Through the vibration mode diagram,it can be found that driven by the atomic group that constitutes the main vibration mode,each molecule and characteristic group in the system participate in the overall vibration,which jointly promotes the formation of the characteristic absorption peaks.(3)Study on weak intermolecular interaction between caffeic acid and its structural-similar substances.To explore the relationship between the formation of terahertz absorption peaks and the internal structure and interaction of four substances,caffeic acid,ferulic acid,2-hydroxycinnamic acid and 4-hydroxycinnamic acid,using the Interaction Region Indicator(IRI)and Energy Decomposition Analysis based on Forcefield(EDA-FF)method shows the weak intermolecular interaction.The analysis found that the carboxyl group and hydroxyl group in the structure of the material are involved in the formation of hydrogen bonds,and some hydrogen bonds directly participate in the formation of the main vibration modes of terahertz absorption peaks.Meanwhile,the overall vibration of the system requires van der Waals actionto maintain.Combining these two methods,the genesis of terahertz absorption peaks of substances is explained from the perspective of internal molecular structural differences and weak interactions,which provides a new perspective for understanding the spectral characteristics of substances and further exploring their properties.