氟虫氰表面增强拉曼光谱的密度泛函理论研究（英文）

Study of Density Functional Theory on Surface Enhanced Raman Spectroscopy of Fipronil

2017年8月初,荷兰发现大范围鸡蛋受杀虫剂氟虫腈污染。用拉曼光谱检测的方法对解决氟虫腈检测问题做了一定的探索。为了获得氟虫腈分子的分子结构振动信息,根据密度泛函理论中的B3LYP杂化泛函和6-311G++(d,p)基组,对氟虫腈分子进行了几何结构优化和频率计算,得到了该分子的稳定构型和全部振动模式,计算了氟虫腈分子稳定构型的拉曼散射光谱。利用HORIBA公司的T64000型光栅共聚焦显微拉曼光谱仪采集了FP的拉曼光谱并配合使用Ag/Cu纳米基底采集了表面增强拉曼光谱,较强峰出现在211,308,350,867,1323和1432 cm-1处,次强峰出现在254,407,443,463,511,607,646,712,800,1065和1639 cm-1处。结果表明,理论计算得到的振动频率与实验测量值在全部较强峰处和部分次强峰处吻合的较好。并对FP分子200~2000 cm-1区间内各频率谱线对应的振动模式进行了归属指认,6个较强峰依由小到大的次序分别指认为21H-22H蜷曲振动,10F-11F变形振动和21H-22H面外摇摆振动,15N-22H蜷曲振动,6C伸缩振动和21H面内弯曲振动,苯环呼吸振动和9C伸缩振动,7H-8H面内弯曲振动。发现表面增强拉曼光谱相对于拉曼光谱整体有微小的频移,两者整体吻合较好,表面增强拉曼光谱中211,867,1400和1432 cm-1处的峰得到了选择性增强,根据表面增强拉曼光谱的选择定则,解释为相关振动峰的原子与银衬底表面或许为接近垂直的状态,并可能与银表面吸附。下一步计划将氟虫腈混入鸡蛋中,对氟虫腈在鸡蛋中不同浓度情况下进行指认研究。研究结果可为氟虫腈的拉曼光谱分析提供理论依据,将促进食品和农产品中氟虫腈残留的快速检测和在线检测研究。将拉曼光谱作为对传统化学检测方法的补充。

At the beginning of August 2017,Netherlands reported that a wide range of eggs were contaminated with the insecticide fipronil.In this study,the Raman spectroscopy was used to solve the problem of fipronil detection.The stable configuration and all vibration modes of the molecule were obtained after the geometrical structure optimization and frequency calculation,and the theoretical Raman Scattering spectroscopy of the stable configuration of fipronil was also calculated.Normal Raman spectroscopy and surface enhanced Raman spectroscopy of fipronil were collected by HORIBA’s T64000 grating confocal micro-Raman spectroscopy and Ag/Cu nano-substrate.The strong peaks appeared at 211,308,350,867,1323,1432 cm-1,and the sub-strong peak appeared at 254,407,443,463,511,607,646,712,800,1065,1639 cm-1.The results show that the theoretically calculated vibration frequency agrees well with the experimental measurements at all strong peaks and most sub-strong peaks.The vibration modes corresponding to the frequencies of the fipronil molecule in the range of 200~2000 cm-1 were assigned.The six strong peaks arranged from small to large were judged to be 21 H-22 H torsional vibration,10 F-11 F deformation vibration,21 H-22 H out-of-plane torsional vibration,15 N-22 H twisting vibration,6 C stretching vibration and 21 H in-plane torsional vibration,benzene ring breathing vibration and stretching vibration of 9 C,7 H-8 H in-plane torsional vibration.It was found that the surface-enhanced Raman spectrum has a slight frequency shift with respect to the Raman spectrum.The peaks at 211,867,1400,and 1432 cm-1 in the surface-enhanced Raman spectroscopy were selectively enhanced.According to the selection rule of surface-enhanced Raman spectroscopy,it is interpreted as the atom corresponding to the relevant vibration peak and the surface of the silver substrate may be in a nearly vertical state and may be stick to the silver surface.In the next step,fipronil will be planned to be mixed into eggs,and the identification of fipronil in different concentrations in eggs will be carried out.The results of the study can provide a theoretical basis for the Raman spectroscopy of fipronil,which will promote the rapid detection and on-line detection of fipronil residues in food and agricultural products.Raman spectroscopy will be used as a supplement to conventional chemical detection methods.