Du Yong, Cai Qiang, Xue Jiadan, Zhang Qi, Qin Dan
Centre for THz Research, China Jiliang University, Hangzhou 310018, China.
Centre for THz Research, China Jiliang University, Hangzhou 310018, China.
Spectrochim Acta A Mol Biomol Spectrosc. 2017 May 5;178:251-257. doi: 10.1016/j.saa.2017.02.004. Epub 2017 Feb 7.
The vibrational spectra of 5-fluorocytosine, fumaric acid and their cocrystal were measured using terahertz time-domain spectroscopy (THz-TDS) and Raman spectroscopy at room temperature. Experimental THz results show that the cocrystal has distinct fingerprint spectra in terahertz region. The absorption peaks observed in the terahertz spectra of the cocrystal were at 0.61 and 0.91THz. These are quite different from corresponding raw starting materials. Raman spectra also show similar results about differences between the cocrystal and corresponding raw starting materials. Density functional theory (DFT) was used to simulate the structure of the possible salt form and the cocrystal form between 5-fluorocytosine and fumaric acid. The theoretical terahertz result shows that the cocrystal form has absorption at 0.62 and 0.87THz, which is in agreement with the experimental result. The theoretical Raman result also indicates that the cocrystal form has more possibilities than the salt form. So, it is more reasonable that the structure between 5-fluorocytosine and fumaric acid could be the corresponding cocrystal form. The characteristic bands of the cocrystal between 5-fluorocytosine and fumaric acid are also assigned based on the simulation results from the DFT calculation.
在室温下，使用太赫兹时域光谱（THz - TDS）和拉曼光谱对5 - 氟胞嘧啶、富马酸及其共晶体的振动光谱进行了测量。实验太赫兹结果表明，该共晶体在太赫兹区域具有独特的指纹光谱。在共晶体的太赫兹光谱中观察到的吸收峰位于0.61和0.91THz。这些与相应的原料有很大不同。拉曼光谱也显示了共晶体与相应原料之间差异的类似结果。采用密度泛函理论（DFT）模拟了5 - 氟胞嘧啶和富马酸之间可能的盐形式和共晶体形式的结构。理论太赫兹结果表明，共晶体形式在0.62和0.87THz处有吸收，这与实验结果一致。理论拉曼结果也表明，共晶体形式比盐形式具有更多可能性。因此，5 - 氟胞嘧啶和富马酸之间的结构为相应的共晶体形式更为合理。基于DFT计算的模拟结果，还对5 - 氟胞嘧啶和富马酸共晶体的特征谱带进行了归属。
