橙皮素电场作用的分子结构和红外光谱理论研究

橙皮素(HES)是一种二氢黄酮药物, 为研究在外电场(EEF)作用下, HES的分子结构和光谱的变化，利用密度泛函理论(DFT)以及6-311G(d,p)基组，在C2-C1方向施加EEF(-0.005～0.010 a.u.)并优化HES分子的基态几何构型, 研究了分子总能量、键长、红外光谱(IR)、偶极矩(DM)和HOMO-LUMO能隙。在优化结构的基础上，采用含时密度泛函理论(TDDFT)，探究不同EEF对紫外可见吸收光谱(UV-Vis)、激发态(ES)的影响。结果显示，无EEF时，HES分子中C1-O18和C2-C26间的单键都优化成了双键，转变为烯醇式结构，这样分子中更多的基团构成一个共轭体系，形成最稳定的结构。随着EEF的增强，分子总能量先升后降，DM则先降后增，键长的变化复杂。当正向负向EEF都增强时，由于HES分子中不同化学键的振动产生的IR吸收峰(AP)，相应地出现了不同的频谱移动，各个AP的强度也有不同的变化。无EEF时, UV-Vis在223.6和262 nm处有2个AP，分别处于E₂带、K带。223.6 nm处的AP随着EEF的增大出现了蓝移(BS)，当EEF大于0.002 5 a.u.谱峰消失；262 nm处的AP在正向EEF下出现红移(RS)，吸收强度随EEF的增强呈现衰弱趋势，当EEF为0.01 a.u.时, 谱峰RS至283 nm，强度达到最小值5 889.64 L·mol-1·cm-1；在负向EEF下出现BS，且吸收强度均增强，在EEF为-0.002 5 a.u.时, 谱峰BS至261 nm，强度增至最大值为12 500.36 L·mol-1·cm-1。当正向负向EEF都增强时，分子的能隙和激发态能量(EE)均呈现减小趋势，说明HES分子易被激发而处于活跃状态。在无EEF时, OS均大于零, 表明能够被激发。当不断加强正向EEF时, ES的OS均先升高再降低; 在负向EEF下OS有复杂的变化。分析EEF下物质的分子结构和光谱, 将为探究橙皮素的药效对其进行电场解离提供理论参考。

Theoretical Study on the Molecular Structure and Infrared Spectroscopy of Hesperidin in External Electric Field

In order to investigate the molecular structure and spectrum of Hesperetin (HES), a kind of dihydroflavone drug. Density Functional theory (DFT) and basis set 6-311G(d,p) are combined to optimize the ground state’s geometry of HES molecules under an external electric field (EEF) ranging from -0.005 to 0.010 a. u. in C2-C1 direction. Total molecular energy, infrared spectrum (IR), dipole moment (DM), and HOMO-LUMO Energy Gap are investigated at the same time. Based on the optimized configuration, time-dependent density functional (TDDFT) is applied to study the influence of different EEF on excited states and UV-Vis spectrum of HES. The results show that when there is no external EEF, the single bonds between C1-O18 and C2-C26 are optimized as double bonds, and the enol structure is converted to a more conjugated system, forming the most stable structure. With the increase of EEF, the total energy of molecule rises at first and then falls, DM decreases at first and then increases. The change of bond length is complicated. When the negative EEF increases, due to the IR absorption peak (AP) generated by the vibration of different chemical bonds in HES molecule, different spectrum shifts occur, and the intensity of each AP also varies according to its relative chemical bond. In the absence of EEF, there are two APs at 223.6 and 262 nm in UV-Vis, related to in the E₂ band and the K band respectively. AP at 223.6 nm appears blue-shift (BS) with the increase of EEF. When EEF is greater than 0.002 5 a. u., peak 223.6 nm disappear. AP at 262 nm shows a red-shift (RS), and the absorption intensity shows a declining trend with the increase of EEF. When EEF is 0.01 a. u., peak 262 nm shifts to 283 nm, and it’s intensity reaches 5 898.64 L·mol-1·cm-1. BS occurs under negative EEF and the absorption intensity increases. When EEF is -0.002 5 a. u., peak 262 nm shifts to 261 nm and the intensity increases to 12 500.36 L·mol-1·cm-1. When positive EEF increases, both energy gap and excited energy (EE) show a decreasing trend, indicating that the HES molecule is easily excited and is in an active state. In the absence of EEF, oscillator strength (OS) is greater than zero, indicating that it can be stimulated. When EEF is continuously enhanced toward the positive direction, OS of ES increases at first and then decreases; OS has complex changes under negative EEF. Investigating the molecular structure and spectrum of HES under EEF will provide a theoretical reference for its electric field dissociation.