Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy ( IF 4.3 ) Pub Date : 2018-05-02 Qiang Cai, Jiadan Xue, Qiqi Wang, Yong Du
The dehydration process of gallic acid monohydrate was carried out by heating method and characterized using Raman spectroscopic technique. Density functional theory calculation with B3LYP function is applied to simulate optimized structures and vibrational frequencies of anhydrous gallic acid and its corresponding monohydrated form. Different vibrational modes are assigned by comparison between experimental and theoretical Raman spectra of above two polymorphs. Raman spectra show that the vibrational modes of the monohydrate are distinctively different from those of anhydrous one. Meanwhile, the dynamic information about dehydration process of gallic acid monohydrate could also be observed and monitored directly with the help of Raman spectral analysis. The decay rate of the characteristic band from gallic acid monohydrate and the growth rate of anhydrous one are pretty consistent with each other. It indicates that there is no intermediate present during the dehydration process of gallic acid monohydrate. The results could offer us benchmark works for identifying both anhydrous and hydrated pharmaceutical compounds, characterizing their corresponding molecular conformation within various crystalline forms, and also providing useful information about the process of dehydration dynamic at the microscopic molecular level.
中文翻译:
没食子酸一水合物的结构和脱水动力学研究:拉曼光谱研究
没食子酸一水合物的脱水过程通过加热方法进行,并利用拉曼光谱技术进行表征。利用B3LYP函数的密度泛函理论计算,模拟了无水没食子酸及其一水合形式的最佳结构和振动频率。通过比较上述两种多晶型物的实验和理论拉曼光谱,可以指定不同的振动模式。拉曼光谱表明,一水合物的振动模式与无水物的振动模式明显不同。同时,借助拉曼光谱分析还可以直接观察和监测有关没食子酸一水合物脱水过程的动态信息。没食子酸一水合物的特征谱带的衰减率与无水酸的生长率非常一致。这表明没食子酸一水合物的脱水过程中不存在中间体。该结果可以为我们鉴定无水和水合药物化合物,表征其在各种结晶形式中的相应分子构象的基准工作,并提供有关微观分子水平上的动态脱水过程的有用信息。