Discrimination of Chirality of Glutamic Acid and Threonine by using Coherent Terahertz Light Source

Abstract

Many biomolecular compounds used for medical supplies possess the chiral property of L- and D-form (enantiomers). Different points of chirality are optical activity, bioactivity and circular dichroism. So, there is necessity to discriminate chirality with the objective of application to medical production line. In this study, we discriminate chirality of amino acids as one of the biomolecular compound materials by terahertz vibrational circular dichroism (THz-VCD) spectroscopy for the novel discrimination method.  The inspection target materials of this study were glutamic acid and threonine. THz-VCD spectra were measured with a frequency tunable THz light source based on difference frequency generation from a GaP crystal. These spectra were obtained by right-hand and left-hand circular polarized THz wave which were converted by quarter-wave plate from linear polarized THz light around 2 THz. As a result, there are expected differences in those absorbance between right and left circular polarized light. For both glutamic acid and threonine, the absorption difference of D-form has shown positive value, in contrast that the absorbance of L-form is negative value. These results indicate that it is possible to discriminate chirality by THz-VCD spectroscopy.