Structure modification of maltol (3-hydroxy-2-methyl-4H-pyran-4-one) upon cation and anion formation studied by vibrational spectroscopy and quantum-mechanical calculations

2007 ◽  
Vol 43 (2) ◽  
pp. 344-350 ◽  
Author(s):  
Krzysztof Zborowski ◽  
Ryszard Grybos ◽  
Leonard M. Proniewicz
Keyword(s):  
Vibrational Spectroscopy ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Structure Modification ◽  
Anion Formation

scholarly journals Distinct Difference in Sensitivity of NIR vs. IR Bands of Melamine to Inter-Molecular Interactions with Impact on Analytical Spectroscopy Explained by Anharmonic Quantum Mechanical Study

Molecules ◽  
2019 ◽  
Vol 24 (7) ◽  
pp. 1402 ◽  
Author(s):  
Justyna Grabska ◽  
Krzysztof B. Beć ◽  
Christian G. Kirchler ◽  
Yukihiro Ozaki ◽  
Christian W. Huck
Keyword(s):  
Vibrational Spectroscopy ◽  
Molecular Interactions ◽  
Near Infrared ◽  
Three Dimensions ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Spectral Simulation ◽  
Analytical Spectroscopy ◽  
Quality Control Tool ◽  
Out Of Plane

Melamine (IUPAC: 1,3,5-Triazine-2,4,6-triamine) attracts high attention in analytical vibrational spectroscopy due to its misuse as a food adulterant. Vibrational spectroscopy [infrared (IR) and Raman and near-infrared (NIR) spectroscopy] is a major quality control tool in the detection and quantification of melamine content. The physical background for the measured spectra is not interpreted in analytical spectroscopy using chemometrics. In contrast, quantum mechanical calculations are capable of providing deep and independent insights therein. So far, the NIR region of crystalline melamine has not been studied by quantum mechanical calculations, while the investigations of its IR spectra have remained limited. In the present work, we employed fully anharmonic calculation of the NIR spectrum of melamine based on finite models, and also performed IR spectral simulation by using an infinite crystal model—periodic in three dimensions. This yielded detailed and unambiguous NIR band assignments and revised the previously known IR band assignments. We found that the out-of-plane fundamental transitions, which are essential in the IR region, are markedly more sensitive to out-of-plane inter-molecular interactions of melamine than NIR transitions. Proper description of the chemical surrounding of the molecule of melamine is more important than the anharmonicity of its vibrations. In contrast, the NIR bands mostly arise from in-plane vibrations, and remain surprisingly insensitive to the chemical environment. These findings explain previous observations that were reported in IR and NIR analytical studies of melamine.

Crystal Forms of Semisynthetic Ergot Alkaloid Terguride

2002 ◽  
Vol 67 (4) ◽  
pp. 479-489 ◽  
Author(s):  
Michal Hušák ◽  
Bohumil Kratochvíl ◽  
Ivana Císařová ◽  
Ladislav Cvak ◽  
Alexandr Jegorov ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Ergot Alkaloid ◽  
Simplified Model ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
X Ray Diffraction ◽  
Torsion Angles ◽  
Crystal Forms ◽  
X Ray ◽  
Independent Molecules

Two new structures of semisynthetic ergot alkaloid terguride created by unusual number of symmetry-independent molecules were determined by X-ray diffraction methods at 150 K. Form A (monoclinic, P212121, Z = 12) contains three symmetry-independent terguride molecules and two molecules of water in the asymmetric part of the unit cell. The form CA (monoclinic, P21, Z = 8) is an anhydrate remarkable by the presence of four symmetry-independent molecules in the crystal structure. Conformations of twelve symmetry-independent molecules that were found in four already described terguride structures are compared with torsion angles obtained by ab initio quantum-mechanical calculations for the simplified model of N-cyclohexyl-N'-diethylurea.

Chemical accuracy from ‘Coulomb hole’ extrapolated molecular quantum-mechanical calculations

2001 ◽  
Vol 567-568 ◽  
pp. 375-384 ◽  
Author(s):  
K.L Bak ◽  
A Halkier ◽  
P Jørgensen ◽  
J Olsen ◽  
T Helgaker ◽  
...  
Keyword(s):  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Coulomb Hole
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