胆酸和脱氧胆酸分子的远红外与THz吸收光谱研究

胆酸和脱氧胆酸是胆汁酸中的主要成分, 是人体中重要的生物表面活性剂. 两种分子只相差一个羟基, 在远红外和太赫兹波段有不同的吸收光谱. 胆酸分子的太赫兹(THz)吸收光谱有1.26 THz(42 cm-1)和2.02 THz(67 cm-1)两个吸收峰, 脱氧胆酸分子的THz吸收光谱有1.13, 1.26, 1.69和2.17 THz(即38, 42, 56, 72 cm-1)等几个吸收峰. 两个分子的THz吸收光谱都包含有1.26 THz(42 cm-1) 峰, 反映出二者结构的相似性. 它们的远红外光谱都有部分频率相近的谱带, 但对比之下可以观察到峰位位移和相对峰强的改变. 指认了两种物质的某些可能与羧基振动有关的特征吸收峰. 为找出THz光谱隐含的信息, 利用Omnic程序采用二阶导数方法来处理THz光谱数据, 观察到多个子峰, 说明分子结构中可能存在更复杂的氢键状态. 实验结果表明, 远红外和THz吸收光谱是研究生物分子及鉴别生物分子结构的很好方法.

Far-IR and THz Absorption Spectra Studies of Cholic Acid and Deoxycholic Acid

Cholic acid(HC) and deoxycholic acid(HDC) are main components of bile and have an important biological function in human body. In this paper the two polycrystalline molecules were studied via far-IR and THz absorption spectroscopy. Their characteristic bands in far-IR and THz region were observed. Some similar bands appear in the far-IR region for the two molecules because they have similar structures. There are two bands at 1.26 and 2.02(e.g. 42 and 67 cm-1) in the THz spectrum of cholic acid molecule,and 1.13,1.26,1.69 and 2.17 THz(e.g. 38,42,56,72 cm-1) in the THz spectrum of deoxycholic acid. The results indicate that far-IR and THz results are consistent in some extent. The bands related to COOH were considered in the far-IR and THz region. Omnic 5.0 program was adopted to treat the data and the bands with a low signal-noise ratio were emphasized via this method. And many sub bands were observed,which indicate that complicated hydrogen bond networks exist. The difference in the structures of the two molecules is only one hydroxyl group,but their far-IR and THz absorption spectra have many differences,which may be caused by the differences of their molecule structures,for example,different hydrogen bonding networks and the various packing of CH chain,etc.. The results indicate that far-IR and THz absorption spectra are effective methods for investigating biomolecules and distinguishing their structures.