scholarly journals Spectra–Structure Correlations in Isotopomers of Ethanol (CX3CX2OX; X = H, D): Combined Near-Infrared and Anharmonic Computational Study

Molecules ◽  
2019 ◽  
Vol 24 (11) ◽  
pp. 2189 ◽  
Author(s):  
Krzysztof B. Beć ◽  
Justyna Grabska ◽  
Christian W. Huck ◽  
Mirosław A. Czarnecki
Keyword(s):  
Recent Progress ◽  
Near Infrared ◽  
Computational Study ◽  
Basis Sets ◽  
Quantum Mechanical ◽  
Isotopic Substitution ◽  
Quantum Mechanical Calculations ◽  
Spectral Changes ◽  
Structure Correlations ◽  
Second Order Perturbation Theory

The effect of isotopic substitution on near-infrared (NIR) spectra has not been studied in detail. With an exception of few major bands, it is difficult to follow the spectral changes due to complexity of NIR spectra. Recent progress in anharmonic quantum mechanical calculations allows for accurate reconstruction of NIR spectra. Taking this opportunity, we carried out a systematic study of NIR spectra of six isotopomers of ethanol (CX3CX2OX; X = H, D). Besides, we calculated the theoretical spectra of two other isotopomers (CH3CD2OD and CD3CH2OD) for which the experimental spectra are not available. The anharmonic calculations were based on generalized vibrational second-order perturbation theory (GVPT2) at DFT and MP2 levels with several basis sets. We compared the accuracy and efficiency of various computational methods. It appears that the best results were obtained with B2PLYP-GD3BJ/def2-TZVP//CPCM approach. Our simulations included the first and second overtones, as well as binary and ternary combinations bands. This way, we reliably reproduced even minor bands in the spectra of diluted samples (0.1 M in CCl4). On this basis, the effect of isotopic substitution on NIR spectra of ethanol was accurately reproduced and comprehensively explained.

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.

Unconventional basis sets in quantum mechanical calculations

1972 ◽  
Vol 24 (5) ◽  
pp. 979-992 ◽  
Author(s):  
David M. Bishop ◽  
J.-C. Leclerc
Keyword(s):  
Basis Sets ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations

scholarly journals KCs molecular bands in the visible region-=SUP=-*-=/SUP=-

2020 ◽  
Vol 128 (11) ◽  
pp. 1613
Author(s):  
Robert Beuc ◽  
Goran Pichler ◽  
David Sarkisyan
Keyword(s):  
Light Absorption ◽  
Spectral Region ◽  
Near Infrared ◽  
Visible Region ◽  
Visible Spectral Region ◽  
Electronic Transitions ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Infrared Spectral ◽  
Potential Curves

We measured light absorption of potassium and cesium mixed vapors at temperatures 360-660o in the visible spectral region 380-780 nm. By comparison with the absorption of pure potassium or cesium vapors, we concluded that the spectral phenomena observed in the mixture peaking at 539 nm, 562 nm (and 700 nm) are new KCs molecular bands. Quantum mechanical calculations of the KCs molecular bands in the visible and near-infrared spectral region were performed using available theoretical potential curves for the KCs molecule. Using these calculations, we identified the three observed molecular bands as 31-X, 41Sigma+-X and 11- X electronic transitions of KCs molecule respectively. Key words: potassium and cesium mixed vapors, absorption spectra, KCs molecular bands, quantum mechanical calculations.

A computational study on heterodimerization of charged porphyrins

2001 ◽  
Vol 05 (06) ◽  
pp. 512-522 ◽  
Author(s):  
SAFİYE SAǦ ERDEM
Keyword(s):  
Computational Methods ◽  
Ground State ◽  
Computational Study ◽  
Electrostatic Attraction ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Face To Face ◽  
Ground State Structures ◽  
Semi Empirical ◽  
Porphyrin Rings

The structures of the charged porphyrins and their dimers have been investigated with computational methods. Dimers have been formed based on electrostatic attraction of the opposite charges on two different porphyrin monomers, tetra ammonium porphyrin (TAP) and tetra carboxy porphyrin (TCP). Semi-empirical quantum mechanical calculations have been employed to explore the most stable ground-state structures of TCP, TAP and their hetero-dimers. Dimeric structures analyzed are all in face-to-face fashion indicating the strong electrostatic attraction between the two porphyrin rings. Calculations have also predicted that the protons transfer from [Formula: see text]; groups to -COO- groups when the interplanar separation is shorter than 3.7 Å.

Scaled Quantum Mechanical (SQM) Force Field Calculations of the Hexathiometadiphosphate Anion P2S2-6

1992 ◽  
Vol 47 (4) ◽  
pp. 614-618 ◽  
Author(s):  
Martin Ystenes ◽  
Wolfgang Brockner ◽  
Frank Menzel
Keyword(s):  
Force Field ◽  
Ab Initio ◽  
Good Description ◽  
Basis Sets ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Force Field Calculations ◽  
Scaling Factors ◽  
Calculated Frequency ◽  
Polarization Functions

AbstractBy ab initio quantum mechanical calculations on P2S2-6 its equilibrium energy, geometry and vibrational frequencies along with their PED values have been obtained. The basis sets STO-5G, 6-31G, STO-5G* and 6-31G* were employed, and force field calculations were carried out at the STO-5G and the STO-5G* levels. The calculations show that the assignment for some bands between 180 and 260 cm -1 should be corrected. Two scaling factors were needed to fit the calculated frequencies with the observed frequencies within a deviation of less then 20 cm -1 for all vibrations, with the exception of v6(B1g). The calculated frequency of this vibration is very dependent on the polarization functions, and use of STO-2G for the 3d-orbitals corrects most of the deviation. STO-5G* and 6-31G* both give a good description of the geometry of the title ion, although STO-5G* yields a 0.04 Å too short terminal P - S distance.

Bonded Force Constant Derivation of Lysine-Arginine Cross-linked Advanced Glycation End-Products

2018 ◽  
Author(s):  
Anthony Nash ◽  
Nora H de Leeuw ◽  
Helen L Birch
Keyword(s):  
Molecular Dynamics ◽  
Force Constant ◽  
Computational Study ◽  
Force Constants ◽  
Quantum Mechanical ◽  
Advanced Glycation ◽  
Partial Charges ◽  
Cross Links ◽  
Complete Set ◽  
Dynamics Simulations

<div> <div> <div> <p>The computational study of advanced glycation end-product cross- links remains largely unexplored given the limited availability of bonded force constants and equilibrium values for molecular dynamics force fields. In this article, we present the bonded force constants, atomic partial charges and equilibrium values of the arginine-lysine cross-links DOGDIC, GODIC and MODIC. The Hessian was derived from a series of <i>ab initio</i> quantum mechanical electronic structure calculations and from which a complete set of force constant and equilibrium values were generated using our publicly available software, ForceGen. Short <i>in vacuo</i> molecular dynamics simulations were performed to validate their implementation against quantum mechanical frequency calculations. </p> </div> </div> </div>

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.

Computational study of the binding mode, action mechanism and potency of pregabalin through molecular docking and quantum mechanical descriptors

2021 ◽  
Vol 1199 ◽  
pp. 113200
Author(s):  
Lorena Meneses ◽  
Sebastian Cuesta Hoyos ◽  
Guillermo Salgado Morán ◽  
Patricio Muñoz C. ◽  
Lorena Gerli Candia ◽  
...  
Keyword(s):  
Molecular Docking ◽  
Computational Study ◽  
Binding Mode ◽  
Quantum Mechanical ◽  
Action Mechanism
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