外电场下L-茶氨酸分子的结构特征与光谱性质

L-茶氨酸(N-乙基-L-谷氨酰胺)是一类具有降压、抗氧化的非蛋白氨基酸,研究外场下它的结构和光谱特征有助于人们更好地认识L-茶氨酸分子的性质.基于密度泛函理论,利用B3LYP方法,在6-311g(d,p)基组水平上对L-茶氨酸分子进行几何构型优化,在此基础上计算L-茶氨酸分子在不同外电场下(0～0.0125 a.u.)的分子各键长与振动频率,得到对应的红外光谱.同时,在相同的基组下采用含时密度泛函方法(TD-DFT)计算外电场对分子的激发态、前线轨道和能隙的影响.结果表明:分子结构及其紫外、红外光谱都随外电场强度发生变化.随外电场的增加,伸缩振动频率红移,弯曲振动频率蓝移;最高占据轨道的能量(E_(HOMO))与最低空轨道的能量(E_(LUMO))发生改变,前线轨道能隙先小幅增加后随电场减小,分子活性先减小后增强;紫外吸收光谱先蓝移后红移.本研究对L-茶氨酸分子的检测、合成及其生物活性的研究可提供理论依据.

Molecular structure and spectral properties of l-theanine under external field

L-theanine(N-ethyl-L-glutamine) is a class of non-protein amino acid with hypotension and antioxidation. It is helpful to understand the properties of L-theanine molecules by studying its structure and spectral characteristics under external field. The B3LYP method is used to optimize the geometric configuration of L-theanine molecules at the base ground level of 6-311g(d, p) based on the density functional theory in Gaussian 09W-D01 software. On this basis, the bond lengths and vibrational frequencies of L-theanine molecule are calculated under different external electric fields (0 / 0.0125 a.u.). The corresponding infrared spectra are obtained from above calculation. At the same time, the time-dependent density functional method (TD-DFT) is used to calculate the influence of external electric field on the excited states, frontier orbital and energy gaps of molecules under the same basis set. The results show that the molecular structure and its ultraviolet and infrared spectra change with the external electric field intensity. With the increase of external electric field, the frequency of stretching vibration is red-shift, and the frequency of bending vibration is blue-shift. The energy gap increases slightly at first and then increases with the decrease of electric field, and the UV absorption spectrum shifts blue-shift and then red-shift. This study can provide a theoretical basis for the detection, synthesis and biological activity of L-theanine.