Investigation of the temperature dependence of THz spectra of amino acids based on THz spectroscopy and density functional theory

In this paper, we employed a temperature-tuned terahertz time domain spectroscopy (THz-TDS) to measure THz spectroscopic features of four amino acids, i.e., L-alanine, L-asparagine, L-cysteine and L-tyrosine in the temperature range of 4.5-300K. The THz spectra of four amino acids were found to be sensitive to temperature change. All of the amino acids have blue-shift phenomenon with about 0.10 THz during the temperature cooling process, and a common new absorption peak at 0.20 THz appears with temperature below 100 K for the L-asparagine and L-cysteine. The measured transmission spectra were compared with the results simulated by density function theory (DFT) using hybrid functional B3LYP with basis set of 6-31 G (d). We calculate the transmission features for the L-alanine and L-cysteine at different temperatures. The calculated results display the blue shift trend with decreasing temperature.