腺嘌呤与富马酸共晶体的太赫兹光谱分析

Terahertz Spectroscopic Analysis of Adenine and Fumaric Acid Cocrystals

利用太赫兹时域光谱(THz-TDS)技术在室温下对腺嘌呤、富马酸及两者的共晶体进行测量,实验结果显示腺嘌呤与富马酸共晶体在0.92、1.24、1.52 THz处有明显的吸收峰,与腺嘌呤和富马酸不同,表明共晶体物相结构不同于原料.根据腺嘌呤分子氢键供体与受体的结构特点,使用密度泛函理论(DFT)对腺嘌呤与富马酸三种可能的共晶体结构进行模拟.结果显示其中一种可能的共晶体结构在0.89、1.16、1.41 THz处存在特征吸收峰,与实验结果较好吻合.由此判断腺嘌呤与富马酸共晶体氢键形成位置为腺嘌呤的氨基与富马酸其中一个羧酸的碳氧双键形成氢键,而此羧酸的羟基与腺嘌呤六元环上的邻位氮原子形成第二处氢键.本文还结合理论模拟的结果对腺嘌呤与富马酸共晶体的特征吸收峰对应的相关振动模式进行了归属.

The absorption spectra of adenine, fumaric acid, and their cocrystal were measured using terahertz time-domain spectroscopy （THz-TDS） at room temperature. Experimental results show that they al have distinct fingerprint spectra in the terahertz region. The absorption peaks observed in the terahertz spectra of the cocrystal were at 0.92, 1.24, and 1.52 THz. These are very different from the corresponding reagents. Based on the characteristic hydrogen donor and/or acceptor behavior of adenine, density functional theory （DFT） was used to simulate three possible theoretical cocrystal structures with a focus on hydrogen bond formation between adenine and fumaric acid. The theoretical result shows that one of three possible simulated cocrystal structures had absorption peaks at 0.89, 1.16, and 1.41 THz, which is in agreement with the terahertz experimental result. Therefore, the structure of the cocrystal was confirmed wherein the first hydrogen bond is formed between the amino group of adenine and the hydroxyl group of fumaric acid. The second hydrogen bond is formed between the nitrogen atom of the nitrogen ring in adenine and the carbonyl group of fumaric acid. The characteristic absorption bands of the cocrystal between adenine and fumaric acid are also assigned based on the simulation results from the DFT calculation.