scholarly journals Calculation of the Proton Affinities of Primary, Secondary, and Tertiary Amines Using Semiempirical and ab initio Methods

2000 ◽  
Vol 55 (8) ◽  
pp. 687-694 ◽  
Author(s):  
Gerhard Raabe ◽  
Yuekui Wang ◽  
Jörg Fleischhauer
Keyword(s):  
Ab Initio ◽  
Preliminary Investigation ◽  
Geometry Optimization ◽  
Dft Method ◽  
Semiempirical Methods ◽  
Tertiary Amines ◽  
Proton Affinities ◽  
Bonding Parameters ◽  
Experimental Values ◽  
The One

The proton affinities of some primary, secondary, and tertiary amines have been calculated with different semiempirical and nonempirical quantum chemical methods. We were particularly interested in the question which of the most popular semiempirical methods yield good overall correlations between calculated and experimental values and, therefore, allow a reliable prediction of hitherto unknown proton affinities. We found that some of the most frequently used semiempirical methods result in good correlations only within the groups of primary, secondary and tertiary amines, while the overall correlation is even worse than the one obtained with the noniterative EHT method. Among the more recent methods which allow geometry optimizations (MINDO/3, MNDO, AMI, PM3, MSINDO) the best results have been calculated with the MSINDO method. Testing for the influence of geometry optimization we surprisingly found that two of these methods (MINDO/3, AMI) perform even better when geometry optimizations are omitted and standard bonding parameters are used instead. Superior results, however, have been obtained with the CNDO/2- and the INDO method. Finally, the best correlations between semiempirically calculated and experimental proton affinities have been achieved with the spectroscopic parametrizations of these methods, CNDO/2S and INDO/2S, respectively. The correlations resulting in these cases are close to those reached at the ZPE+MP2/6-31 l++G**//HF/6-311++G** level of ab initio theory and with a comparable DFT method. A preliminary investigation revealed that an improvement in the semiempirical calculation of proton affinities might be obtained if different Uμμ parameters are used for the nitrogen atoms of primary, secondary, and tertiary amines.

scholarly journals An efficient DFT method of predicting the one-, two- and three-bond indirect spin–spin coupling constants involving a fluorine nucleus in fluoroalkanes

RSC Advances ◽  
2016 ◽  
Vol 6 (86) ◽  
pp. 82783-82792 ◽  
Author(s):  
Adam Gryff-Keller ◽  
Przemysław Szczeciński
Keyword(s):  
Nuclear Spin ◽  
Dft Method ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Fluorine Nucleus ◽  
Spin Coupling Constants ◽  
Experimental Values ◽  
The One ◽  
Spin Spin Coupling

The values of the indirect nuclear spin–spin coupling constants for a series of aliphatic fluorocompounds have been calculated using DFT-based methods and compared with the experimental values of these parameters.

Computational, Experimental Structural Characterization and Molecular Docking Studies of 5,7-Dihydroxy-4-methoxyflavone against Cytochrome P450 Enzymes

2020 ◽  
Vol 5 (3) ◽  
pp. 197-207
Author(s):  
A. Harikrishnan ◽  
R. Madivanane
Keyword(s):  
Cytochrome P450 ◽  
Molecular Docking ◽  
Title Compound ◽  
Density Functional ◽  
Geometry Optimization ◽  
Dft Method ◽  
Cytochrome P450 Enzymes ◽  
Molecular Docking Study ◽  
Experimental Values ◽  
Vibrational Wavenumbers

In this work, the geometry optimization and harmonic vibrational wavenumbers of kaempferide (5,7-dihydroxy-4-methoxyflavone) were computed by density functional theory (DFT) method. Theoretically computed vibrational wavenumbers were compared with experimental values and the interpretation of the vibrational spectra has been studied. Frontier molecular orbitals (FMO) and molecular electrostatic potential (MEP) analysis of the title compound have been carried out. The 1H & 13C NMR, UV visible and electronic properties of the compound were investigated theoretically and compared with the experimental values. Molecular docking study of the compound against cytochrome P450 family enzymes (CYPs 1A1, 1A2, 3A4, 2C8, 2C9 and 2D6) were also studied and the results revealed that the title compound interact with human CYP2C8 enzymes with minimum binding energy of -9.43 kcal/mol. The compound forms hydrogen bond with the residues of Thr302, Thr305, Leu361, Val362, Cys435, Gln356 and Ala297. Thus, these studies assist to understand the inhibitory mechanism of kaempferide with CYP450 enzymes and may facilitate significant clinical implications in the prevention and treatment of various therapeutic diseases.

Ab initio MO study of protonation of carbamic acid, methyl carbamate and methyl N-methylcarbamate

1988 ◽  
Vol 53 (6) ◽  
pp. 1141-1148 ◽  
Author(s):  
Milan Remko
Keyword(s):  
Ab Initio ◽  
Gas Phase ◽  
Correlation Energy ◽  
Geometry Optimization ◽  
Carbamic Acid ◽  
Proton Affinities ◽  
Acid Methyl ◽  
Methyl Derivatives ◽  
Moller Plesset ◽  
Complete Geometry Optimization

The ab initio SCF method was applied to the protonation of the carbonyl group in carbamic acid and its methyl derivatives, viz. methyl carbamate and methyl N-methylcarbamate. Complete geometry optimization was accomplished for these compounds and their protonated species using the MINI-1, 3-21 G, and 6-31 G* bases and the proton affinities were calculated at the MINI-1, 3-21 G, 6-31 G*, and 6-31 G** levels. 2nd and 3rd order Moller-Plesset perturbation calculations were also performed for examining the effect of the correlation energy on the calculated protonation energies. The carbonyl protonation energies were found to increase in order carbamic acid < methyl carbamate < methyl N-methylcarbamate. The absolute values of calculated gas phase proton affinities depend on the basis used and way of evaluating the correlation energy. The results are discussed with respect to the theoretical proton affinities of structurally related amides and to related available theoretical gas phase proton affinities.

Ion solvation by dipolar aprotic solvents. An ab initio study

1987 ◽  
Vol 52 (1) ◽  
pp. 6-13 ◽  
Author(s):  
Petr Kyselka ◽  
Zdeněk Havlas ◽  
Ivo Sláma
Keyword(s):  
Ab Initio ◽  
Geometry Optimization ◽  
Molecular Structures ◽  
Dimethyl Sulphoxide ◽  
Ion Solvation ◽  
Interaction Energies ◽  
Ab Initio Study ◽  
Solvation Energies ◽  
Dipolar Aprotic Solvents ◽  
Complete Geometry Optimization

The paper deals with the solvation of Li+, Be2+, Na+, Mg2+, and Al3+ ions in dimethyl sulphoxide, dimethylformamide, acetonitrile, and water. The ab initio quantum chemical method was used to calculate the solvation energies, molecular structures, and charge distributions for the complexes water···ion, acetonitrile···ion, dimethyl sulphoxide···ion, and dimethylformamide···ion. The interaction energies were corrected for the superposition error. Complete geometry optimization was performed for the complex water···ion. Some generalizations are made on the basis of the results obtained.

scholarly journals Parametric study of hyperfine structure of Zr II even-parity levels

2016 ◽  
Vol 94 (12) ◽  
pp. 1310-1313 ◽  
Author(s):  
Safa Bouazza
Keyword(s):  
Hyperfine Structure ◽  
Ion Beam ◽  
Model Space ◽  
Laser Fluorescence ◽  
Beam Laser ◽  
Extended Space ◽  
Experimental Values ◽  
The One ◽  
Fast Ion ◽  
Laser Fluorescence Spectroscopy

Until now experimental hyperfine structure (hfs) data of 12 even-parity Zr II levels were given in the literature. Recently new hyperfine splitting measurements of 11 other Zr II levels, of the same parity are achieved, applying fast-ion-beam laser-fluorescence spectroscopy. The hfs of these 23 gathered levels has been analysed by simultaneous parametrisation of the one- and two-body interactions, first in model space (4d + 5s)3 and secondly in extended space. For the three lowest configurations, radial parameters of the magnetic dipole A and quadrupole electric B factors are deduced in their entirety for 91Zr II, compared and discussed with calculated values, available in the literature, and also with ours, computed by means of the ab initio method. For instance we give the main experimental values of the extracted single-electron hfs parameters of 4d25s: [Formula: see text] = –2701 MHz, [Formula: see text] = –122.4 MHz, and [Formula: see text] = –113.5 MHz.

First Principles Investigation of the Stability and the Chemical Behavior of Hydrogen in ThCoH4

2011 ◽  
Vol 66 (3) ◽  
pp. 269-274
Author(s):  
Samir F. Matar
Keyword(s):  
Negative Charge ◽  
Geometry Optimization ◽  
Full Geometry Optimization ◽  
Intermetallic Matrix ◽  
Charge Analysis ◽  
The Stability ◽  
The One ◽  
Site Selective ◽  
Bader Charge Analysis ◽  
Positively Charged

We address the changes in the electronic structure brought by the insertion of hydrogen into ThCo leading to the experimentally observed ThCoH4. Full geometry optimization positions the hydrogen in three sites stabilized in the expanded intermetallic matrix. From a Bader charge analysis, hydrogen is found to be in a narrow iono-covalent (~−0.6) to covalent (~−0.3) bonding which should enable site-selective desorption. The overall chemical picture shows a positively charged Thδ+ with the negative charge redistributed over a complex anion {CoH4}δ− with δ~1.8. Nevertheless this charge transfer remains far from the one in the more ionic hydridocobaltate anion CoH54− in Mg2CoH5, due to the largely electropositive character of Mg.

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