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

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Tongjun Zhang ◽  
Shasha Yan ◽  
Jianjun Hao ◽  
Dehua Li
Keyword(s):  
Solid State ◽  
Density Functional ◽  
State Density ◽  
Hydroxyl Groups ◽  
Hybrid Functional ◽  
Terahertz Time Domain Spectroscopy ◽  
Structural Isomers ◽  
Theoretical Investigations ◽  
Intramolecular Motion ◽  
Normal Mode Calculations

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.

scholarly journals Solid-State and Theoretical Investigations of Some Banister-Type Macrocycles with 2,2’-Aldoxime-1,1’-Biphenyl Units

2021 ◽  
Vol 9 ◽  
Author(s):  
Ioan Stroia ◽  
Ionuţ -Tudor Moraru ◽  
Maria Miclăuş ◽  
Ion Grosu ◽  
Claudia Lar ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Solid State ◽  
Density Functional ◽  
Alkali Metal Ions ◽  
Functional Theory ◽  
State Data ◽  
Supramolecular Associations ◽  
Theoretical Investigations ◽  
The Stability ◽  
Good Agreement

In the context of helical chirality, bridging of biphenyl units leads to banister-type compounds and the stability of the resulted atropisomers may increase dramatically if suitable changes are performed in the linker unit that coils around the biphenyl moiety. A rigorous density functional theory (DFT) study was conducted for macrocycles containing rigid oxime ether segments connected to the biphenyl backbone in order to determine how the rotation barriers are influenced by the presence of either a flexible oligoethyleneoxide or a more rigid m–xylylene component in the macrocycle. The calculated values for the racemization barrier were in good agreement with those obtained experimentally and confirm the benefit of introducing a more rigid unit in the macrocycle on the stability of atropisomers. Solid-state data were obtained and computed data were used to assess the contribution brought by supramolecular associations observed in the lattice to the stabilization of the crystal structure. Beside introducing rigidity in the linker, complexation of flexible macrocycles with alkali metal ions is also contributing to the stability of atropisomers, leading to values for the racemization barrier matching that of the rigid macrocycle. Using diethylammonium cation as guest for the macrocycle, a spectacular increase in the barrier to rotation was observed for the resulted pseudo[2]rotaxane.

scholarly journals Predicting the structures and associated phase transition mechanisms in disordered crystals via a combination of experimental and theoretical methods

2018 ◽  
Vol 211 ◽  
pp. 425-439 ◽  
Author(s):  
Michael T. Ruggiero ◽  
Johanna Kölbel ◽  
Qi Li ◽  
J. Axel Zeitler
Keyword(s):  
Phase Transition ◽  
Solid State ◽  
Time Domain ◽  
Density Functional ◽  
Molecular Crystals ◽  
Terahertz Time Domain Spectroscopy ◽  
Functional Theory ◽  
Theoretical Methods ◽  
Dynamics Simulations ◽  
Transformation Processes

Experimental terahertz time-domain spectroscopy and theoretical solid-state ab initio density functional theory and molecular dynamics simulations are used to elucidate the structures, dynamics, and phase transformation processes of molecular crystals undergoing a solid-state order–disorder transition.

Identifying and explaining vibrational modes of quinacridones via temperature-resolved terahertz spectroscopy: absorption experiments and solid-state density functional theory simulations

2020 ◽  
Vol 22 (35) ◽  
pp. 19672-19679 ◽  
Author(s):  
A. D. Squires ◽  
Adam J. Zaczek ◽  
R. A. Lewis ◽  
Timothy M. Korter
Keyword(s):  
Density Functional Theory ◽  
Solid State ◽  
Density Functional ◽  
Terahertz Spectroscopy ◽  
State Density ◽  
Spectral Features ◽  
Thermal Contraction ◽  
Vibrational Modes ◽  
Functional Theory

New spectral features and anomalous shifting of vibrational modes of beta quinacridone are revealed, unusual thermal contraction the likely origin.

DEVELOPMENT OF COMPUTATIONAL METHODOLOGIES FOR THE PREDICTION AND ANALYSIS OF SOLID-STATE TERAHERTZ SPECTRA

2007 ◽  
Vol 17 (02) ◽  
pp. 193-212 ◽  
Author(s):  
Damian G. Allis ◽  
Timothy M. Korter
Keyword(s):  
Solid State ◽  
Density Functional ◽  
State Density ◽  
Grid Size ◽  
Basis Set ◽  
Detection Methods ◽  
Thz Spectroscopy ◽  
Atomic Charges ◽  
Spectral Features ◽  
Thz Absorption

The analytical applications of terahertz (THz) spectroscopy for the characterization of molecular solids have been limited by the lack of information concerning the assignment of observed spectral features to specific internal (intramolecular) and external (intermolecular) atomic motions. Computational methodologies addressing the assignment of spectral data are the enabling technology for moving THz spectroscopy to the forefront of available detection methods for both imaging and spectroscopic applications. Solid-state density functional theory (DFT) studies have been performed on the high explosives cyclotetramethylenetetranitramine (HMX) and pentaerythritol tetranitrate (PETN) in order to address the dependencies of the predictions of solid-state vibrations in the terahertz (3 to 120 cm−1) region on the choice of basis set and integration grid size, building on previous work that examined this dependency on the choice of density functional. DFT THz simulations reveal that both the choice of basis set and grid size have important influences on the reproduction of spectral features. The sensitivity to basis set choice is most pronounced in the calculation of vibrational intensities, where it is found that THz absorption intensities are most accurately reproduced when derived from basis set-sensitive Mulliken atomic charges as opposed to basis set-insensitive atomic charges generated by the Hirshfeld partitioning method.

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