<scp>MNDO</scp> calculations for compounds containing aluminum and boron

Davis, Larry P.; Guidry, R. Martin; Williams, James R.; Dewar, Michael J. S.; Rzepa, Henry

doi:10.1002/jcc.540020412

Cited by 91 publications

(23 citation statements)

References 10 publications

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“…For low level calculation using semiempirical methods [27] AM1 [28,29], PM3 [30], and PM6 [31], molecular mechanical methods UFF [32] (UFF uses charges calculated by the method of charge equilibration [33]), and Dreiding [34], the Gaussian 09 program [25] was used while for the MM+ method [35] the Hyperchem program [36] and for the MM3 the Tinker Program [22] were used instead.…”

Section: Journal Of Theoretical Chemistrymentioning

confidence: 99%

An Assessment of Alternative Low Level Calculation Methods for the Initial Selection of Conformers of Diastereomeric Esters

Metsala

Tamp

Danilas

et al. 2014

Journal of Theoretical Chemistry

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Critical assessment of performance of alternative molecular modeling methods depending on a specific object and goal of the investigation is a question of continuous interest. This prompted us to demonstrate the origin of the guidelines we have used for a rational choice and use of a proper low level calculation method (LLM) for an initial geometry optimization of generated conformers, with the aim of selecting a set for further optimization. What was performed herein was a comparison of LLMs: MM3, MM+, UFF, Dreiding, AM1, PM3, and PM6 on the optimization of conformers' geometry of -methoxyphenylacetic acid (MPA) 2-butyl esters as a set of typical diastereomeric esters of a chiral derivatizing agent. This set of esters calculated represents only compounds of this certain type in the current work. The LLM conformer energies were correlated with benchmark energies found by using higher level reference method B3LYP/6-311++G * * on the geometries gained previously by optimization with LLMs. In an alternative treatment, the energy range to be covered and corresponding number of LLM optimized conformers obligatory for submitting to further optimization using a high level optimization cascade were considered on the basis of determination of the cut-off conformer (COFC).

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Section: Journal Of Theoretical Chemistrymentioning

confidence: 99%

An Assessment of Alternative Low Level Calculation Methods for the Initial Selection of Conformers of Diastereomeric Esters

Metsala

Tamp

Danilas

et al. 2014

Journal of Theoretical Chemistry

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“…7 The IP(E R ) was calculated as the difference between the total energies of the optimized neutral and ionic E R molecules. These calculations were performed by the modified neglecting differential overlap (MNDO) semiempirical method, 8 with a set convergence fixed at 0.04 KJ/mol. The geometry optimization was computed using the Polak-Ribierre (conjugated gradient) algorithm in which the convergence threshold was 0.04 KJ/ mol.…”

Section: Computational Detailsmentioning

confidence: 99%

R2PI Study of intermolecular hydrogen bond in solvent‐free chiral complexes

et al. 2001

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One- and two-color, mass selected R2PI spectra of the S(1)<--S(0) transitions in the bare (+)-(R)-1-phenyl-1-ethanol (E(R)) and its complexes with different solvent molecules (solv) (-)-(R)-2-butanol (B(R)) or (+)-(S)-2-butanol (B(S)) and (-)-(R)-2-butylamine (A(R)) or (+)-(S)-2-butylamine (A(S)), have been recorded after a supersonic molecular beam expansion. The one-color R2PI excitation spectra of the diastereomeric complexes are characterized by significant shifts of their band origin relative to that of bare E(R). The extent and the direction of these spectral shifts are found to depend on the structure and the configuration of solv and are attributed to different short-range interactions in the ground and excited states of the complexes. In analogy with other diastereomeric complexes, the phenomenological binding energy of the homochiral cluster is found to be greater than that of the heterochiral one.

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“…To study the different stable conformations obtained for each isomer (see Fig. 1), three potential energy surfaces obtained through the independent rotation of dihedral angles ω 1 (C6′‐C1′‐C2‐O), ω 2 (O‐C11*‐C8‐C8a), and ω 3 (O‐C2‐C1‐C6′) were calculated in vacuo with a semiempirical calculation using the AM1 Hamiltonian 32–34 as implemented in the Gaussian 03 package 35. All minima for each dihedral were combined together to generate tentative whole‐molecule minima.…”

Section: Methodsmentioning

confidence: 99%

Conformational study of two diasteroisomers of vinylcatechin dimers in a methanol solution

Brás

Cruz

Fernandes

et al. 2011

Int J of Quantum Chemistry

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Red wine possess anthocyanins (red colored pigments) and flavan-3-ol compounds (associated to the flavor). In an acidic environment, these compounds have higher reactivity due to the acidic character of the phenolic groups. Vinylcatechin adducts play a crucial role as intermediates in the formation mechanism of some anthocyanin-derived pigments (e.g., pyranoanthocyanins) during wine aging. They have gained increasing attention because of the large number of compounds detected in wines and their unusual spectroscopic properties. However, vinylcatechins are very unstable molecules in acidic solutions and their occurrence in wines has never been detected, probably due to their high reactivity. Using computational methods, we have characterized and identified the different conformations of two stable diasteroisomers (9S,11R)-and (9R,11S)-vinylcatechin dimers, which were obtained in model wine solutions from acid-catalyzed dimerization of vinylcatechin. To identify the different conformations for both isomers, first potential energy surface calculation around the most relevant dihedral angles of each isomer were performed using the density functional theory (DFT) approach with the B3LYP hybrid density functional. Molecular Dynamics (MD) simulations starting from the previous minima were subsequently performed to investigate the possible conformations acquired by the two different compounds in a methanol solution. Six and five different conformations were obtained during the MD simulations for (9S,11R) and (9R,11S) isomers, respectively. Ten nanoseconds of MD simulations were enough to obtain the most favored conformations of these molecules. DFT calculations were used for the optimizations of all structures in vacuum as well as in a methanol environment. Gibbs free energy values were calculated for all structures, and these values show that similar quantities of both (9S,11R) and (9R,11S) diasteroisomers are obtained in a methanol solution, and that their formation is thermodynamically favored.

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MNDO calculations for compounds containing aluminum and boron

Cited by 91 publications

References 10 publications

An Assessment of Alternative Low Level Calculation Methods for the Initial Selection of Conformers of Diastereomeric Esters

An Assessment of Alternative Low Level Calculation Methods for the Initial Selection of Conformers of Diastereomeric Esters

R2PI Study of intermolecular hydrogen bond in solvent‐free chiral complexes

Conformational study of two diasteroisomers of vinylcatechin dimers in a methanol solution

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