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Molecules 2018, 23(7), 1607; https://doi.org/10.3390/molecules23071607

Spectral Characterization and Molecular Dynamics Simulation of Pesticides Based on Terahertz Time-Domain Spectra Analyses and Density Functional Theory (DFT) Calculations

1,2,†
,
1,2,†
,
1,2
,
1,2,3,*
,
1,2
,
1,2
,
4
,
5
and
5
1
College of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou 310058, China
2
Key Laboratory of Spectroscopy Sensing, Ministry of Agriculture, Hangzhou 310058, China
3
State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou 310027, China
4
Laser Information Technology Research Center, Harbin Institute of Technology Shenzhen Graduate School, Guangdong 518055, China
5
College of Automation, Zhongkai University of Agriculture and Engineering, Guangzhou 510225, China
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work
Received: 25 May 2018 / Revised: 27 June 2018 / Accepted: 28 June 2018 / Published: 2 July 2018
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Abstract

This work provides the experimental and theoretical fundamentals for detecting the molecular fingerprints of six kinds of pesticides by using terahertz (THz) time-domain spectroscopy (THz-TDS). The spectra of absorption coefficient and refractive index of the pesticides, chlorpyrifos, fipronil, carbofuran, dimethoate, methomyl, and thidiazuron are obtained in frequencies of 0.1–3.5 THz. To accurately describe the THz spectral characteristics of pesticides, the wavelet threshold de-noising (WTD) method with db 5 wavelet fucntion, 5-layer decomposition, and soft-threshold de-noising was used to eliminate the spectral noise. The spectral baseline correction (SBC) method based on asymmetric least squares smoothing was used to remove the baseline drift. Spectral results show that chlorpyrifo had three characteristic absorption peaks at 1.47, 1.93, and 2.73 THz. Fipronil showed three peaks at 0.76, 1.23, and 2.31 THz. Carbofuran showed two peaks at 2.72 and 3.06 THz. Dimethoate showed three peaks at 1.05, 1.89, and 2.92 THz. Methomyl showed five peaks at 1.01, 1.65, 1.91, 2.72, and 3.20 THz. Thidiazuron showed four peaks at 0.99, 1.57, 2.17, and 2.66 THz. The density functional theory (DFT) of B3LYP/6-31G+(d,p) was applied to simulate the molecular dynamics for peak analyzing of the pesticides based on isolated molecules. The theoretical spectra are in good agreement with the experimental spectra processed by WTD + SBC, which implies the validity of WTD + SBC spectral processing methods and the accuracy of DFT spectral peak analysis. These results support that the combination of THz-TDS and DFT is an effective tool for pesticide fingerprint analysis and the molecular dynamics simulations. View Full-Text
Keywords: terahertz time-domain spectroscopy; wavelet threshold de-noising; spectral baseline correction; density functional theory; pesticides; molecular dynamics simulations terahertz time-domain spectroscopy; wavelet threshold de-noising; spectral baseline correction; density functional theory; pesticides; molecular dynamics simulations
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Qu, F.; Lin, L.; He, Y.; Nie, P.; Cai, C.; Dong, T.; Pan, Y.; Tang, Y.; Luo, S. Spectral Characterization and Molecular Dynamics Simulation of Pesticides Based on Terahertz Time-Domain Spectra Analyses and Density Functional Theory (DFT) Calculations. Molecules 2018, 23, 1607.

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