A combined study on the skeletal vibration of aminopyrine by terahertz time-domain spectroscopy and DFT simulation

Abstract

Aminopyrine is an inexpensive drug that is highly effective on analgesic and anti-inflammatory. However, it is found adulterated to traditional Chinese medicine by unscrupulous merchants though side effects, such as neutropenia, myelosuppression and formation of nitrosamine carcinogens, make it banned in many countries. In this work, terahertz time-domain spectroscopy has been proposed to perform characterization of aminopyrine in the range of 0.2∼2.4 THz. Characteristic absorption peaks of aminopyrine are found at 1.54 THz and 2.15 THz. To gain further insight, DFT studies have been carried out to simulate the THz spectrum and analyze molecular vibration mode of aminopyrine. The spectrum simulated is in good agreement with the experiments and the calcuated absorption peaks at 1.48 THz and 2.29 THz matches with the experimental result of 1.54 THz and 2.15 THz. The main vibrational modes of the characteristic peaks are the skeletal vibrations of the molecule, which is represented by the rotation and the swing of dimethylamino group, pyrazolone and benzene rings. This study shows that terahertz spectroscopy has potential application prospects for the detection of adulteration of aminopyrine in rheumatic Chinese patent medicines and the examination of counterfeit drugs.