Centre for THz Research, China Jiliang University, Hangzhou 310018, China.
Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, China.
Spectrochim Acta A Mol Biomol Spectrosc. 2018 Nov 5;204:99-104. doi: 10.1016/j.saa.2018.06.034. Epub 2018 Jun 11.
Vibrational modes of 2-thiobarbituric acid (TBA) tautomeric polymorphs (form I, II and IV) were characterized by terahertz time-domain spectroscopy (THz-TDS) and Raman spectral techniques. The experimental results indicate that both vibrational spectroscopy techniques could be used to recognize the above TBA three tautomeric forms clearly. Experimental THz spectral results show that each of TBA tautomeric polymorphs has distinctive fingerprint peaks in the terahertz region. Raman spectra also show similar results about differences of TBA tautomeric polymorphs, but not significant as that of terahertz spectra since Raman-active vibrational modes are mostly from intra-molecular interaction of various functional groups within the specific molecule while that of terahertz region is more sensitive to inter-molecular interaction within crystalline unit cells. In addition, density functional theory (DFT) was used to simulate the optimized structures and vibrational modes of these three TBA tautomeric forms above. The characteristic vibrational modes of TBA polymorphs are assigned comparing the simulated DFT results with experimental vibrational spectra. The results provide fundamental benchmark for the study of pharmaceutical polymorphism based on both Raman and terahertz vibrational spectroscopic techniques combined with theoretical simulations.
2-硫代巴比妥酸（TBA）互变异构体（形式 I、II 和 IV）的振动模式通过太赫兹时域光谱（THz-TDS）和拉曼光谱技术进行了表征。实验结果表明，两种振动光谱技术都可用于清晰地识别上述 TBA 三种互变异构形式。太赫兹光谱实验结果表明，TBA 互变异构体的每种形式在太赫兹区域都具有独特的指纹峰。拉曼光谱也显示了 TBA 互变异构体之间差异的类似结果，但不如太赫兹光谱明显，因为拉曼活性振动模式主要来自特定分子内各种官能团的分子内相互作用，而太赫兹区域对晶胞内的分子间相互作用更敏感。此外，还使用密度泛函理论（DFT）模拟了上述三种 TBA 互变异构形式的优化结构和振动模式。通过将模拟的 DFT 结果与实验振动光谱进行比较，对 TBA 多晶型物的特征振动模式进行了归属。这些结果为基于拉曼和太赫兹振动光谱技术结合理论模拟研究药物多晶型提供了基本的基准。
