Abstract：Terahertz time-domain spectroscopy (THz-TDS), Fourier transform infrared (FTIR) and Fourier transform Raman (FT-Raman) spectroscopic techniques were utilized for the characterization and analysis of γ-aminobutyric acid (GABA), benzoic acid (BA), and their solvent/grinding co-crystals. All experimental results demonstrated that GABA-BA co-crystal possessed unique spectroscopical characteristic compared with that of starting materials in THz-TDS, FTIR, FT-Raman spectra. THz-TDS results showed that similar absorption peaks of solvent and grinding co-crystals which formed between GABA and BA at 0.93, 1.33 and 1.57 THz can be observed. The result demonstrated that THz-TDS technique could effectively identify and characterize GABA, BA and its co-crystal, which was also a presentation of various substance that had different fingerprint characteristic features in THz range. To identify and affirm the crystal structure of GABA-BA co-crystal, FT-Raman and FTIR spectroscopic techniques were also employed by spectral assignment. Through the assignment of FTIR spectrum, it was confirmed that the first hydrogen bond of GABA-BA co-crystal was formed at place between amino H23 of GABA and carbonyl O1 of BA, while the second one was constituted by amino group N18 of GABA and hydroxyl group H15 of BA. Some Raman scattered peaked, such as 576, 886, 1 250, 1 283, 1 337, 1 423 and 1 470 cm-1 which belonged to bending vibrations of —CH2, —NH2 in GABA, disappeared upon the formation of GABA-BA co-crystal, demonstrating the atom nitrogen (N18) in GABA can be served as hydrogen bond acceptor. So the Raman result verified the validity of above FTIR deduction, which confirmed the crystal structure of GABA-BA co-crystal, Furthermore, formation of co-crystal was impacted by pH value of solvent. With the solvent condition of 2.00≤pH≤7.20, the GABA-BA co-crystal can be stably formed. This work provides experimental and theoretical benchmark to discriminate and identify the crystal structure of co-crystal formed between active ingredients and co-crystal formers and crystalline formation conditions in the solid state with THz-TDS and FT-Raman techniques.
张 琪，方虹霞，张慧丽，秦 丹，洪 治，杜 勇. γ-氨基丁酸和苯甲酸共晶体及其形成条件的振动光谱分析[J]. 光谱学与光谱分析, 2017, 37(12): 3786-3792.
ZHANG Qi, FANG Hong-xia, ZHANG Hui-li, QIN Dan, HONG Zhi, DU Yong. Vibrational Spectroscopic Characterization of the Co-Crystal and the Forming Condition between γ-Aminobutyric Acid and Benzoic Acid. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2017, 37(12): 3786-3792.
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