Experimental and Theoretical Investigations of Terahertz Spectra of the Structural Isomers: Mannose and Galactose

Tongjun Zhang,Jianjun Hao,Dehua Li,Shasha Yan,Vincenza Crupi

doi:10.1155/2021/3469262

Abstract

The high-resolution terahertz spectra of the two structural isomers, mannose and galactose, have been measured by terahertz time-domain spectroscopy (THz-TDS) in the range of 0.5–4.0 THz at room temperature. Significant differences between these similar molecules have been found in their THz characteristic spectra, implying that THz-TDS is a powerful tool for identifying isomers. Structural analyses and normal mode calculations of the two systems were performed using solid-state density functional theory (DFT) with the PBE and PW91 density functionals as well as using gas-state DFT with B3LYP hybrid functional. Among these calculations, the solid-state simulated results obtained from the PBE method exhibit a good agreement with the experimentally measured spectra. According to the calculated results of PBE, the observed spectral features were assigned as primarily external lattice translations, deformations, and rotations with lesser contributions due to intramolecular motion of pyranose ring, CH2OH group, and hydroxyl groups.

Highlights

Due to the nondestructive and fingerprint properties, terahertz time-domain spectroscopy (THz-TDS) has been established as a promising technique for the study of molecules in the solid state
Recent studies have shown that solid-state density functional theory (DFT) is an excellent means for the complete assignment of the calculated modes to their corresponding experimental THz spectral features [14]. e inclusion of a crystal packing arrangement in solid-state DFT simulations has led to the accurate reproduction of the external crystal lattice vibrations in addition to the internal molecular motions typically seen in the THz region [15]
Structural Analysis. e DFT calculated values and X-ray experimental structural data for mannose and galactose are presented in Table 1(length), 2, and 3 (HB length). e structural data were obtained from the c O3

Summary

Introduction

Due to the nondestructive and fingerprint properties, terahertz time-domain spectroscopy (THz-TDS) has been established as a promising technique for the study of molecules in the solid state. Recent studies have shown that solid-state density functional theory (DFT) is an excellent means for the complete assignment of the calculated modes to their corresponding experimental THz spectral features [14]. E inclusion of a crystal packing arrangement in solid-state DFT simulations has led to the accurate reproduction of the external crystal lattice vibrations in addition to the internal molecular motions typically seen in the THz region [15]. The experimental THz absorption spectra from 0.5 to 4.0 THz for mannose and galactose are presented along with a complete computational analysis by using solid- and gas-state DFT. E study shows that the solid-state DFT calculations can provide good reproduction of the structures and spectra of substances and can accurately explain the subtle differences in the terahertz spectra of the isomers studied here

Materials and Methods

Results and Discussion

35 Experiment 30

Conclusions