不同糖类化合物的太赫兹光谱特性

Terahertz Spectroscopy Characteristics of Sugar Compounds

选取对人体有重要作用的三种糖类化合物,采用高分辨率太赫兹时域光谱系统与傅里叶变换红外光谱系统,在较宽的频谱范围内,对样品进行测谱分析;实验发现无水葡萄糖在1.10,1.30,1.45,1.79,1.88,1.97,2.08,2.40,2.55,2.70,2.84,2.96,3.24,3.64和4.23 THz频率处存在特征吸收,无水果糖在1.09,1.33,1.65,2.14,2.62,2.97,3.24,4.75,6.97,7.35,7.98,8.36,9.16,9.32,9.53和9.73 THz频率处存在特征吸收,无水半乳糖在2.21,2.33,2.70,2.82,3.17,3.42,3.93,4.51,5.07,5.96,6.60,6.91,8.03,8.71和9.01 THz频率处存在特征吸收。对掺杂不同比例葡萄糖、果糖、半乳糖与聚乙烯样品的实验结果做定量分析,发现在测得的上述特征吸收频率处,随化合物样品质量分数的增加,样品的吸收系数或吸光度呈线性递增。实验进一步得到无水葡萄糖与无水果糖在2.96 THz存在共同的特征吸收,无水葡萄糖与无水半乳糖在2.33,2.70和2.82 THz三处存在共同的特征吸收,无水果糖与无水半乳糖在8.00 THz处存在共同的特征吸收,而无水葡萄糖、果糖、半乳糖三者在3.20 THz处存在共同的特征吸收。三种化合物具有相同的分子式,所以三者都具有的3.20 THz特征吸收频率主要源于分子内相互作用,反应同分异构体相同的化学键或者基团。三者特征吸收频率的差异主要源于分子结构以及分子间相互作用的不同,代表同分异构体结构以及分子间振动模式的差异。通过分析三种糖类样品的实验测量结果,预测了葡萄糖在4.70,5.30,5.60,5.98,7.03,7.85,8.26,8.71和9.01 THz处存在特征吸收。基于密度泛函理论,采用CASTEP量子化学计算软件对三种化合物进行理论模拟,对样品在THz波段的特征吸收进行指认,计算得到的结果与实验结果吻合,这表明了CASTEP晶体模拟软件在化合物的THz光谱模拟方面应用的可行性。

Three sugar compounds were selected as the research objects because of their importance to the human body.Their absorption spectra were measured in a wide frequency range by high resolution terahertz time domain spectroscopy and Fourier transformation infrared spectroscopy systems.It has been found that glucose has the characteristic absorption frequencies of 1.10,1.30,1.45,1.79,1.88,1.97,2.08,2.40,2.55,2.70,2.84,2.96,3.24,3.64 and 4.23 THz,fructose has the characteristic absorption frequencies of 1.09,1.33,1.65,2.14,2.62,2.97,3.24,4.75,6.97,7.35,7.98,8.36,9.16,9.32,9.53 and 9.73 THz,as well as galactose has the characteristic absorption frequencies of 2.21,2.33,2.70,2.82,3.17,3.42,3.93,4.51,5.07,5.96,6.60,6.91,8.03,8.71 and 9.01 THz.By analyzing the experimental results of samples mixed from glucose,fructose,galactose and polyethylene quantitatively,it has been known that at the measured characteristic absorption frequencies,absorption increases linearly along with increasing the mass fraction of glucose,fructose and galactose.Furthermore,both the glucose and fructose have a common fingerprint frequency in 2.96 THz,glucose and galactose have a common fingerprint frequencies in 2.33,2.70 and 2.82 THz,fructose and galactose have common fingerprint frequency in 8.00 THz,and all three kinds of compounds have common fingerprint frequency in 3.20 THz.Because the three samples have the same molecular formula,the 3.20 THz characteristic absorption mainly comes from intramolecular interaction,which represents the same chemical bonds or groups of isomers.The difference in characteristic absorption frequency is due to the molecular structure and inter-molecular interaction,which represents the difference between isomer structure and inter-molecular vibration mode.It can be predicted that glucose fingerprint frequencies would be tested in 4.70,5.30,5.60,5.98,7.03,7.85,8.26,8.71 and 9.01 THz in development.Based on Density Functional Theory,CASTEP software was adopted to optimize the structures and calculate the characteristic absorption frequencies of samples.The theoretical simulation results are in agreement with the experimental ones.This result shows that CASTEP is feasible to compound molecules research in the THz range.