L-阿拉伯糖指纹区太赫兹光谱和拉曼光谱的研究

Investigations on Spectra of Terahertz and Raman of L-Alabinose at Fingerprint Region

为了解生物体内L-阿拉伯糖在代谢过程中的合成与降解机制,采用太赫兹和拉曼光谱系统,对其指纹区的振动进行检测。结果表明,L-阿拉伯糖太赫兹图谱在频率49.5和72.2cm^(-1)分别检测出了振动吸收,其中72.2cm^(-1)的振动为首次检出。该振动频率与其折射率图谱反常色散的频率基本一致,故这两个振动吸收可以作为L-阿拉伯糖的特征吸收。最为重要的是,在该频域内,检测得到图谱的波型与三种异构体理论值简单叠加后波型极为相似,故可以初步判定样品含有三种构象异构体(α-型、β-型和l-型结构),非单一组分,而是混合组分;对于拉曼图谱而言,其特点简洁而明晰,一般将指纹区的振动,从高到低分为四个区域:吡喃环结构的伸缩振动、亚甲基的摇摆振动、环上羟基的扭曲振动及环骨架扭曲和畸变振动。同时也根据密度泛函理论B3LYP/6-311G**基组,分别对L-阿拉伯糖的三种构象异构体的振动进行模拟计算,利用势能分布对这些振动进行归属和指认。与理论值相比,振动频率检测值有不同程度的红移,即振动频率向低频发生了偏移,其原因是样品内不同分子间相互影响所致。

In order to further understand the synthesis and biodegradation mechanism of L-arabinose during the course of metabolism,terahertz time-domain spectroscopyand laser Raman spectrometer were used to measure the vibrations of their groupsin this paper.The results shows that:in the frequency range of 5~85 cm^-1 frequencyrange,The 49.5and 72.2 cm^-1 vibrational peaks were detected and the two vibrations were in agreement with the frequencies of anomalous dispersion in the curve of refraction index,the second peak was detected for the first time.Therefore,thetwo vibration peaks could be as characteristic absorption peaks of L-arabinosebecause of their strong absorption.To the most,the wave type of terahertz spectra in this range was very similar to the theoretical wave type of the simple combinations of the three isomers,and the sample was not a single component,but a mixture of three isomers.Raman spectra showed that vibrations of L-arabinose were concise and clear and that vibrations in fingerprint frequency ranges were divided into four characteristic vribrational regions(from high to low):stretching vibrations of bonds in pyran cycle,rocking of methylene,twisting of H-O in cycle and torsions and deformations of cycle skeleton,including puckering.The vibrations ofα-,β-and open chain isomers were calculated byB3LYP/6-311G**according to DFT,respectively.The vibrations of the three isomer were assigned by potential energy distribution.Comparisons betweenobserved and theoretical curves were that frequencies of theoretical curves showed red shift for vibrations of L-arabinose and the exact causes must be confirmed by further tests.