Molecular Characterization and Theoretical Calculation of Plant Growth Regulators Based on Terahertz Time-Domain Spectroscopy

Abstract

Terahertz (THz), as an advanced spectral technology, has unique absorption characteristics for most biological macromolecules. In this work, the theoretical fundamentals for the application of THz time-domain spectroscopy (THz-TDS) to molecular characterization and fingerprint peak detection of three plant growth regulators (PGRs), including 2,4-Dichlorophenoxyacetic acid (2,4-D), forchlorfenuron (CPPU) and indole-3-acetic acid (IAA) were researched. Meanwhile, the effects of eight types of window functions on THz spectra were studied when converting time-domain spectra into frequency-domain spectra by Fourier transform. Based on the optimal window function, the THz absorption coefficient and refractive index of PGRs in frequencies of 0.2-3 THz were extracted. The molecule structure and vibration mode of three PGR samples were simulated by using density functional theory (DFT). The results showed that the three PGRs had different fingerprint peaks. Characteristic absorption and anomalous dispersion of 2,4-D were found at 1.35, 1.57 and 2.67 THz, those of CPPU were found at 1.77 and 2.44 THz, and the absorption peak of IAA was located at 2.5 THz. The absorption peaks obtained from THz spectra were identified according to the theoretical calculation results of DFT. These fingerprint peaks in THz spectra were generated by the interior stretching vibration and external deformation vibration of molecular groups. The experimental results revealed the feasibility of identifying PGRs species and detecting residues using THz-TDS.

Study of 2,4-D Spectral Characteristics and Its Detection in Zizania Latifolia Using Terahertz Time-Domain Spectroscopy

“…Also, there were three positions with absorption characteristics in the frequency-domain spectrum of 2,4-D at 1.36, 1.60, and 2.38 THz, respectively, among which, the position at 1.36 THz had the most obvious absorption effect. In a previous experiment, the third peak of 2,4-D was detected at 2.67 THz [35], which was different from the results obtained in this work. A THz time-domain spectrometer (Teraview, UK) was used in the previous experiment.…”

State-of-the-art in terahertz sensing for food and water security – A comprehensive review

“…As an effective means of detecting material spectra information in the THz region by employing ultrafast laser technology, THz-TDS has comparatively high signal-tonoiseratio due to the wider frequency band, and can be used to detect material composition and subtle structure changes [137]- [140]. F. F. Qu et al [142] detected the molecular characterization and fingerprint peak of three plant growth regulators including 2,4-Dichlorophenoxyacetic acid, forchlorfenuron and indole-3-acetic acid. Baek et al [118]investigated the feasibility of detecting melamine in foodstuffs and found the characteristic absorption peaks of melamine at 2, 2.26, and 2.6 TH.…”

Exploring the Reliability of DFT Calculations of the Infrared and Terahertz Spectra of Sodium Peroxodisulfate

“…Choice of basis set or pseudo-potential [15,16], density functional [17], DFT package [16] and convergence criteria can all have a dramatic affect on any calculated spectral parameter. This accessibility has a downside and can lead to unsuitable calculations being compared with experiment, for instance it is still commonplace to compare single molecule DFT calculations to THz measurements of crystalline material [18][19][20][21][22][23] which has often been shown to be unsuitable [24].…”