光谱学与光谱分析, 2020, 40 (8): 2447, 网络出版: 2020-12-03  

基于密度泛函的吲哚美辛外场下的解离特性

Theoretical Study on the Molecular Structure and Infrared Spectroscopy of Indometacin in External Electric Field
作者单位
1 桂林电子科技大学电子工程与自动化学院, 广西 桂林 541004
2 广西光电信息处理重点实验室, 广西 桂林 541004
3 清华大学物理系, 北京 100084
摘要
废弃的药物化合物处理不当最终会进入环境成为污染物, 存在于天然水饮用水和城市废水中。 医院污水中含有低浓度的药物, 当这些药物进入环境会成为污染物, 进而严重污染自然生态系统。 吲哚美辛一种广泛使用的非甾体抗炎药, 其不易溶于水, 使得污水中的药物降解成为一项挑战。 为研究在外电场(EEF)作用下, 吲哚美辛分子结构和光谱的变化, 选用密度泛函理论(DFT)以及6-31+G(d, p)基组, 沿Y轴(N15-C16)方向施以EEF(0~0.025 a.u.)并优化吲哚美辛分子的基态几何构型, 探究了分子总能量、 键长、 红外光谱(IR)、 偶极矩(DM)和HOMO-LUMO能隙。 结果显示, 无EEF时, 吲哚美辛分子中C2与C17间的单键优化成了苯环间的双键, 就使得C16与C17的π电子还有N15的孤立电子与苯环形成牢固的共轭体系, 使吲哚美辛分子能量降到最低, 形成最稳定的构型。 DM随着EEF的增强缓慢增加, 当F≥0.015a.u.时增速变大, 基态总能量的变化则与此相反。 随着EEF的增强, 各个键长的伸缩变化不同。 C3-C4, C3-N15, C5-C6, O10-C11和N15-C16的键被拉长, 尤其是O10-C11, C3-N15和N15-C16键长变化剧烈, 最易断裂进而使吲哚美辛分解。 当EEF变大, 能隙不断降低, 表明在EEF下吲哚美辛分子的电子易过渡到高能级, 使分子处于激发态。 吲哚美辛分子中不同化学键的振动产生的IR, 相应地出现了不同的频谱移动, 这主要与能级有关, 能级差减小, 频率减小, 导致红移(RS), 反之则产生蓝移(BS); C16-C18与N15-C40键长变化ΔR与频移变化Δf的对应关系表明频谱移动还与分子轨道配置和偶极矩的变化等因素有关。 较强的4, 5, 6, 7吸收峰发生RS且振动强度增强, 说明对应的化学键变得脆弱进而断裂。 这些现象皆说明吲哚美辛分子随着EEF的增强, 变得不稳定, 易发生解离。 分析EEF下物质的分子结构和IR, 可以电场解离方法研究降解吲哚美辛, 以便为污水中的顽固药物降解提供理论指导。
Abstract
Waste drug compounds can end up in the environment as pollutants in natural drinking water and municipal wastewater if not properly treated. Hospital sewage will contain low concentrations of drugs, and when these drugs enter the environment, they will become pollutants, which will seriously pollute the natural ecosystem. Indomethacin is a widely used non-steroidal anti-inflammatory drug, but it is not easily soluble in water, and refractory degradation makes drug degradation in sewage a challenge. In order to study the changes of the molecular structure and spectrum of indomethacin under the action of the external electric field (EEF), the density functional theory (DFT) and the 6-31+G(d, p) basis set are used along the Y-axis (N15-C16). The EEF (0~0.025 a.u.) was applied and the ground state geometry of the indomethacin molecule was optimized. The total energy, bond length, infrared spectrum (IR), dipole moment and HOMO-LUMO energy gap were investigated. The results show that in the absence of EEF, the single bond between C2 and C17 in the indomethacin molecule is optimized to become a double bond between the benzene rings, which makes the electrons of C16 and C17 and the isolated electrons of N15 form a strong bond with the benzene ring. The conjugated system minimizes the energy of indomethacin and forms the most stable configuration. The total energy of the ground state decreases slowly with the increase of EEF. When F≥0.015 a. u., it decreases significantly, and the change of dipole moment is opposite. As the EEF is enhanced, the expansion and contraction of each key length vary. The bond lengths of C3-C4, C3-N15, C5-C6, O10-C11 and N15-C16 are elongated, especially the bond lengths of O10-C11, C3-N15 and N15-C16 are drastically changed, and the easiest to break and then Indomethacin decomposition. When the EEF becomes larger, the energy gap is continuously reduced, indicating that the electrons of the indomethacin in the EEF are easily transitioned to a high energy level, and the molecules are excited to an excited state. The IR generated by the vibration of different chemical bonds in the indomethacin molecule, corresponding to different spectral shifts, is mainly related to the energy level, the energy level difference is reduced, the frequency is reduced, resulting in red shift (RS), and vice versa. Shift (BS); but the correspondence between N15-C40, C16-C18 bond length change ΔR and frequency shift change Δf indicates that the spectrum shift is also related to factors such as molecular orbital configuration and dipole moment change. Stronger 4, 5, 6, and 7 absorption peaks occur RS and the vibration intensity increases, indicating that the corresponding chemical bonds become weak and cause a fracture. All these phenomena indicate that indomethacin molecules become unstable and prone to dissociation with the enhancement of EEF. Analysis of the molecular structure and IR under EEF can be used to study the degradation of indomethacin by electric field dissociation method, in order to provide theoretical guidance for the degradation of stubborn drugs in sewage.

葛浩然, 王方原, 李桂琴, 叶松, 汪杰君, 李树, 王新强. 基于密度泛函的吲哚美辛外场下的解离特性[J]. 光谱学与光谱分析, 2020, 40(8): 2447. GE Hao-ran, WANG Fang-yuan, LI Gui-qin, YE Song, WANG Jie-jun, LI Shu, WANG Xin-qiang. Theoretical Study on the Molecular Structure and Infrared Spectroscopy of Indometacin in External Electric Field[J]. Spectroscopy and Spectral Analysis, 2020, 40(8): 2447.

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