中文摘要：

采用混合密度泛函理论中的B3LYP方法,并结合6-31G（d）、6-31G（df,p）、6-31＋G（d）和6-311＋G（2d,2p）四种基组,首次系统地计算了蛋氨酸在空气、四氯化碳、四氢呋喃、水和模拟蛋白质环境中的几何结构、电离能和红外光谱。研究结果表明,在不同的基组和介质环境下,蛋氨酸的几何参数与晶体结构实验参数相比,其键长和键角的差值分别小于0.0271（？）和5.32°;但二面角相差12.04°～122.11°;在同一计算方法下,介质的介电常数越高,分子的单点能越低,电离能也越小,对应的主要振动频率随之减小,强度增大;蛋氨酸的电离能比组氨酸的计算结果高0.33eV～0.56eV。所有数据均显示,较高基组下的计算结果更接近实验值。该研究为深入探索叶绿素与蛋氨酸配位后在光反应中心中的功能与作用提供了理论参考依据。

英文摘要：

In combination with four basis sets：6-31G（d）,6-31G（df,p）,6-31＋G（d） and 6- 311＋G（2d,2p）,a B3LYP method of the hybrid density functional theory is used to calculate the geometry, ionization energy and infrared spectra of methionine in air,CC14,THF,water and simulated protein environment systematically for the first time.The research result shows that for different basis sets and media,the changes in bond length and bond angle of methionine are less than 0.027l（？）and 5.322°respectively compared with those of the crystal structure.But their changes in dihedral angle are in the range 12.04°to 122.11°.With a same calculation method,the higher the dielectric constant of the medium is,the lower the single point energy is and the lower the ionization energy is.Thus, the prominent corresponding vibration frequencies decrease and the intensity increases.The ionization energy of methionine is 0.33eV to 0.56eV higher than the calculation result of the histidine.All calculations show that the results calculated by using the higher basis sets with diffusion functions are closer to the experimental data.This study is helpful to the further understanding of functional and vibrational properties of chlorophyll-a ligated to methionine in photosynthetic reaction center.