The Application Research Of Terahertz Spectra In The Nitrogen Heterocyclic Molecular Structures

Terahertz (THz) science and technology is developed in recent years. Compounds in THz wave band contain physical and chemical information that is helpful for people to understand the structures and properties in far infrared wave band. THz wave that is sensitive to the weak forces (eg, hydrogen bonding, van der Waals force) has important application prospect in molecular recognition and drug testing. However, analysis and summaries of vibrational modes of characteristic absorption peaks has always been the problem and challenge that exist in the THz spectral application. In this paper, terahertz time-domain spectroscopy (THz-TDS) technology was used for different series of pharmacal molecules containing heterocyclic structure and exploring the relationships between molecular structures and spectra. The density functional theory was employed to simulation of molecular structures to help understand the vibrational modes of characteristic peaks and reveal the relationships between molecular structures and the weak forces.THz-TDS was used to study the THz spectra and molecular structures of pyridine mono-and di-carboxylic acids (2-,3-,4-pyridine carboxylic acids and 2,3-,2,4-,2,5-,2,6-,3,4-,3,5-pyridine dicarboxylic acids). With the help of simulated calculation, the vibrational modes at characterisitic peaks of 3-,4-pyridine carboxylic acids and 2,3-,3,4-,3,5-pyridine dicarboxylic acids were analyzed. Considered that the calculation was conducted at 0 K, the experiments verified the accuracy of the simulation results at low temperature. In addition, the quantitative analysis of binary and ternary mixtures were done. The results show that similar peaks may come from vibrational modes that nitrogen atoms and oxygen atoms participate in the hydrogen bond. THz-TDS can be used for quantitative analysis of multicomponent mixture, such as testing of the active ingredients of drug.THz-TDS was used to study the spectra and molecular structures of indole and its derivatives (indole, indole-3-carboxylic acid, indole-3-acetic acid, indole-3-propionic acid, gramine, tryptamine and L-tryptophan). In order to explore the sources of the absorption peaks, indole-3-carboxylic acid, indole-3-propionic acid and tryptamine had carried on the simulated calculation. The reliability of the calculation was verified by the experiments at low temperature. The quantitative analysis and THz imaging of mixtures were done. The results clearly identify the vibrational modes of absorption peaks. THz-TDS is good to be applied to the analysis of the effective components of drugs.In addition, THz-TDS was used to study the THz spectra and molecular structures of L-tryptophan and its copper complex. The quantitative calculation was used to explore the sources of similar peaks. The studies show that THz spectra of complexes contains L-tryptophan and L-tryptophan have similarity that exsist twisting vibration of indole ring and branched chain.