红景天苷分子结构与光谱的密度泛函理论分析

随着科学技术不断发展，中药质量控制和质量评价出现了越来越多的新技术。在中药标准化过程中，现代药学研究已经取得了许多令人瞩目的成果，检测方法和技术取得了很大的进展，由过去单一指标检测发展到多指标检测，但由于中草药成分复杂，作用机制不明等因素制约了中药的发展。红景天是一种少数民族药，是中医药发展不可或缺的组成部分。红景天苷是红景天中的主要有效成分之一，其提取、分离和纯化等方法报道甚多，但其分子键长键角二面角、前线轨道分布、表面静电势等分子参数却鲜有报道，这些都是决定其化学性质和反应机理的重要因素。采用Gaussian09W化学计算软件的密度泛函理论DFT/B3LYP方法和6-31(d)基组优化红景天苷分子，得到其稳定结构的键长、键角和二面角参数。在此稳定构型的基础上，计算其表面静电势（ESP）、最低空轨道（LUMO）、最高占据轨道（HOMO）、红外光谱（IR）和核磁共振波谱数据（NMR）。分别对IR和NMR峰位置进行了归属并与文献报道数据进行了对比，结果表明：计算结果的红外吸收频率没有出现虚频说明该优化结果是合理可靠的，最高占据轨道能量E=-5.82 eV，最低空轨道能量E=-0.000 42 eV，二者差值为5.81 eV。通过绘制了轨道的电子云分布图可以看出HOMO轨道主要分布于苯环，为π电子的成键轨道有一个节面；LUMO轨道也主要分布在苯环上，为π电子的反键轨道有两个节面。表面静电势的绘制可以直观地反映出分子中哪部分易发生亲核取代、哪部分易发生亲电取代反应。通过绘制第一激发态和基态电子差值，可以直观地得到电子的迁移方向。对红景天苷分子计算理论研究可以为进一步探索其化学反应机理、结构修饰和活性位点的确认等提供重要的参考依据和新思路。

Density Functional Theory Studies on Structure and Spectra of Salidroside Molecule

At present, with the continuous development of science and technology, more and more new techniques emerge in quality control quality evaluation of Traditional Chinese Medicines (TCMs). In the standardization process of TCMs, modern pharmaceutical research has made many remarkable achievements. Detection methods and technologies have made great progress from single-index detection to multi-index detection. Rhodiola Rosea is a kind of minority nationality medicine that is an indispensable part of the development of traditional Chinese medicine. Salidroside is one of the main components of Rhodiola Rosea. There are many reports on its extraction, separation and purification. However, far few reports have been reported up to now on its molecular parameters, such as bond length, bond angle, dihedral angle, frontier orbital distribution and surface electrostatic charge Distributions, which are critical factors determining its chemical properties and reaction mechanism. The parameters of bond length, bond angle and dihedral angle of salidroside were obtained by DFT / B3LYP method and 6-31 (d) basis set from Gaussian09W software. As the result of optimization, the surface electrostatic charge (ESP), the lowest occupied orbit (LUMO), the highest occupied orbit (HOMO). Infrared (IR) and nuclear magnetic resonance (NMR) data were calculated, and their peak positions were assigned and compared with the reported data. The results reveal that there is no imaginary frequency in the infrared absorption frequency, which indicates that the optimization result is reasonable and reliable; the highest occupied orbit energy E=-5.82 eV, the lowest orbit energy E=-0.000 42 eV, and the difference is 5.81 eV. By drawing the electron cloud distribution map of the orbit, we can see that the HOMO orbit is the π bonding orbital of electron mainly distributing on the benzene ring with a node; the LUMO orbit is the π antibonding orbital of electron mainly distributing on the benzene ring with two nodes. The drawing of surface electrostatic charge can directly determine which part of the molecule is prone to nucleophilic substitution reaction and which is prone to electrophilic reaction. The electron migration direction can be obtained directly by drawing the electron difference between the first excited state and the ground state. The theoretical study of salidroside molecular calculation in this dissertation can provide important references and new ideas for further exploring the chemical reaction mechanism, structural modification and identification of active sites.