Temperature Dependence Of Terahertz Spectra Of Amino Acid

Terahertz wave is a kind of electromagnetic wave,which is between microwave and infrared.Its frequency is ranging from 0.1 to 10 THz.Because of its strong penetrates and low energy,terahertz pulse does not cause damage to biomolecule.So it is an effective nondestructive testing methods,and being gradually used in the identification of biological molecules and detection.Amino acids are organic compounds containing both amino groups(-NH2)and carboxyl groups(-COOH).It plays an important role in the construction of cells,which constitute the basic constituent units of protein.Amino acids have a sensitive spectral response in the terahertz band,manifested in a significant characteristic absorption peak,it can reflect the amino acid molecular structure in the terahertz band and has a rich vibration and rotation mode.In this paper,a mixture of 20 ?-amino acids and PE was studied by using Terahertz timedomain spectrometer(THz-TDS)and Fourier transform infrared spectroscopy(FTIR).We found that the absorption of the terahertz spectrum is stronger when amino acid is in high concentration.The absorption spectra of these 20 amino acids show that there is a strong correlation between the molecular structure and the absorption spectrum.It also provides a reference for the improvement of 0-6THz broadband amino acid terahertz absorption spectroscopy database,which provides a scientific basis for the identification of amino acids.L-Asparagine,L-Cysteine acid,L-alanine and aromatic amino acids were selected from aliphatic amino acids by using an adjustable temperature terahertz time-domain spectrometer.Its spectral characteristics shows temperature correlation in the range of 0.5-2.0THz band,it was found that the absorption peaks of aliphatic L-Asparagine and L-Cysteine were decreased and Blue-shifts when the temperature goes down.The absorption peak at low temperature is narrower,stronger,easier to identify.When the temperature decreased to a certain extent,we observed that a new absorption peak of aromatic L-tyrosine was found when the temperature is low enough.We also observed that there is a phenomenonof blue shift when lower the temperature,but the absorption intensity and line width basically did not change.The single molecule and unit cell structure of aliphatic L-alanine,L-asparagine,L-cysteine and aromatic L-tyrosine were calculated by Gaussian 09 software package.The results were compared with the experimental.In contrast,it is speculated that the interaction between the benzene ring and the intermolecular molecules in the single molecule are the main reason for the absorption of the terahertz spectrum of the amino acid molecules.