RNA碱基的太赫兹光谱和拉曼光谱特征研究

应用傅里叶红外光谱仪和激光拉曼光谱仪测试了RNA碱基在太赫兹波段(1～10 THz)的红外和拉曼光谱，同时结合Guassian09软件和周期性边界条件下基于能量的分块方法(PBC—GEBF)，分析了RNA碱基晶体的红外和拉曼光谱特征，得到了所有特征峰位置及其对应的振动模式，且计算光谱与测试光谱一致吻合，表明碱基粉末样品为无定形晶体结构。通过对红外光谱的分析可知，在太赫兹波段，腺嘌呤和鸟嘌呤都有6个红外活性振动模式，胞嘧啶和尿嘧啶分别为6个和3个红外活性振动模式，与实验结果相比，除了鸟嘌呤6.35 THz处的弱吸收峰没能重现，4.83和5.39 THz处的吸收峰简并;胞嘧啶4.3和4.79 THz处吸收峰简并;尿嘧啶3.32和3.82 THz处的吸收峰简并外，其他吸收峰的位置和强度均被准确地模拟重现。通过对拉曼光谱的分析可知，理论和实验光谱基本一致，除了尿嘧啶3.52和4.48 THz处特征峰简并;鸟嘌呤7.26和8.03 THz，3.57，4.02，4.49，4.89和5.98 THz处特征峰简并外，其他特征峰的位置和强度均被准确的模拟重现。通过对特征峰的分析和辨认，可知在1～10 THz，RNA碱基的振动模式均来源于晶格内分子的集体振动，分子间的氢键和弱相互作用力对振动模式的贡献很大，进一步分析可知，在1～5.5 THz，其振动模式来自所有原子参与的集体振动，在5.5～10 THz，振动模式来自于部分原子参与的集体振动。此项研究对揭示RNA碱基在构成生物大分子结构、生物大分子鉴定以及太赫兹波段光谱的形成机制等方面，具有重要的理论和实际参考价值。

Research on THz and Raman Spectra of RNA Nucleobases

The Infrared and Raman spectra of RNA nucleobases in terahertz (THz)band (1~10 THz)were detected with Fourier transform infrared spectroscopy (FTIR)and Raman spectroscopy.The position of all the characteristic peaks and corresponding vibration modes of RNA nucleobase crystals were obtained with Guassian09 software and energy-based fragmenta-tion approach under periodic boundary conditions (PBC-GEBF)method.The computational results were verified to be in accord-ance with experimental data,which indicated that the powder of RNA nucleobases is amorphous crystal structure.The infrared spectra demonstrated that adenine,guanine and cytosine all have 6 infrared active vibrational modes,while uracil only has 3. Comparing to experimental results,the position and intensity of the absorption peaks were nicely corroborated by the predicted spectrum,except that one weak vibrational frequency at 6.35 THz is missing and two peaks (4.83 and 5.39 THz)merge in the predicted spectrum of guanine;two peaks in 4.3 and 4.79 THz merge into a single one in the calculated spectrum of cytosine;the peaks of thymine in 3.32 and 3.82 THz merged.The computational results of Raman spectra were also verified to be in line with the experimental data.The position and intensity of the characteristics peaks were exactly simulated except that two peaks of guanine in 3.52 and 4.48 THz merged;two peaks in 7.26 and 8.03 THz merge and five peaks (3.57,4.02,4.49,4.89, 5.98 THz)merge in the calculated spectrum of guanine.Through the analysis and identification of the characteristic peaks,it is indicated that the vibration modes of DNA nucleobases in 1~10 THz were derived from collective vibration of molecules in the lattice.The intermolecular hydrogen bond and the weak interaction force contribute greatly to the vibration modes.In addition, as the frequency increases to over 5.5 THz,the vibration modes will change from the atoms collective vibration to some atoms vibration.This research has important theoretical and practical reference value to reveal the effect of RNA nucleobases in the are-as of RNA molecular structure constitution,biological macromolecules identification and terahertz spectra formation mechanism and biological inheritance.