基于密度泛函理论的氯氰菊酯振动光谱研究

Study on Vibrational Spectra of Cypermethrin Based on DensityFunctional Theory

氯氰菊酯作为一种广谱杀虫剂被广泛用于多种农产品,由于其用量大、降解速度慢,导致在水果、蔬菜及家畜等农产品中存在药物残留,危害人体健康。为避免人体摄入,对农产品中的氯氰菊酯残留检测非常重要。目前的检测方法中振动光谱技术具有无损快速的优点,因此采用密度泛函理论方法结合振动光谱技术为氯氰菊酯的振动光谱检测和鉴定提供理论依据,为农药残留检测应用领域提供参考。研究中首先采用Gaussian view6.0软件构建氯氰菊酯分子的空间构型,基于密度泛函理论DFT中的B3LYP方法,先用3-21G基组进行初始结构粗优化,在粗优化结构的基础上用6-311++G基组进行结构的再优化,得到分子的最稳定构象及前线轨道分布。然后在优化结构的基础上计算了氯氰菊酯的理论红外光谱和拉曼光谱。理论计算结果可见氯氰菊酯分子在3 300~3 000与1 700~500 cm^(-1)范围两个区域有明显的红外活性,前者主要是官能团的振动,后者则为指纹区的振动;从计算结果还可以明显看出,拉曼光谱中3 044和1 459 cm^(-1)处的环丙基上亚甲基碳氢的伸缩振动、剪式振动,1 196 cm^(-1)处的环丙基中次甲基的摇摆振动,1 153 cm^(-1)处的苯环中碳氢的面内摇摆振动等明显的振动峰,在红外光谱中没有活性;在拉曼光谱中显示为强谱带的氰基在红外光谱中也没有活性;在红外光谱中为弱吸收的苯环骨架振动,在拉曼光谱中显示为强谱带,这些都体现了红外光谱和拉曼光谱互补的优越性,两种光谱相结合,更有利于化合物结构的鉴定与检测。然后通过实验方法测定了氯氰菊酯粉末的自然拉曼光谱,将理论计算结果误差由频率校正因子0.973进行修正,将实验结果与理论计算结果进行比较分析,峰值频率波数相差大多在4~10 cm^(-1)范围内,理论与实验结果基本一致。该研究为氯氰菊酯的振动光谱检测与结构鉴定提供了理论基础,为其在农药检测领域的应用提供了理论参考。

As a broad-spectrum insecticide,Cypermethrin is widely used in various agricultural products,such as fruits,vegetables and poultry and so on.Because of its large dosage and slow degradation rate,drug residues in fruits,vegetables,livestock and other agricultural products are harmful to human health.In order to avoid human intake,it is very important to detect cypermethrin residues in agricultural products.Among the current detection methods,the vibration spectrum technology has the advantages of being non-destructive and fast.Therefore,this paper uses the density functional theory method combined with the vibration spectrum technology to provide a theoretical basis for the vibration spectrum detection and identification of Cypermethrin,and provide a reference for the application field of pesticide residue detection.The specific research contents and results are as follows:the first step is to construct the molecular space configuration of Cypermethrin by using Gaussian view software.Based on the DFT/B3LYP method of density functional theory,the structure is roughly optimized with a 3-21G basis set and then reoptimized with 6-311++G basis set based on coarse structure to obtain the stable configuration and frontier orbital distribution of the molecule.Then,based on the optimized structure,the theoretical infrared and Raman spectra of Cypermethrin were calculated.The theoretical results show that Cypermethrin has obvious infrared activity in the range of 3300~3000 and 1700~500 cm^(-1).The former is mainly the vibration of functional groups,and the latter is the vibration of the fingerprint region.It can also be seen from the calculation results that the stretching vibration and scissor vibration of methylene hydrocarbon on cyclopropyl at 3044 and 1459 cm^(-1),the wagging vibration of methyne on cyclopropyl at 1196 cm^(-1) and the rocking vibration of hydrocarbon in benzene ring at 1153 cm^(-1) in Raman spectrum have no activity in the infrared spectrum.The cyano group without infrared activity shows a strong band in the Raman spectrum.The benzene ring skeleton vibration is weakly absorbed in the infrared spectrum but shows a strong band in the Raman spectrum.These reflect the complementary advantages of infrared spectroscopy and Raman spectroscopy.The combination of the two spectra is more conducive to the identification and detection of compound structure.In the second step,the natural Raman spectrum of Cypermethrin powder was measured by experimental method.The theoretical calculation error was corrected by the frequency correction factor of 0.973.The experimental results were compared with the theoretical calculation results.The difference in the peak frequency wavenumber was mostly in the range of 4~10 cm^(-1),and the theoretical data were consistent with the experimental results.This study provides a theoretical basis for the vibration spectrum detection and structure identification of Cypermethrin,and provides a theoretical reference for its application in pesticide detection.