Chiral recognition in bicyclic guanidines

2009 ◽  
Vol 74 (2) ◽  
pp. 299-312 ◽  
Author(s):  
Daniel H. O’ Donovan ◽  
Isabel Rozas ◽  
Fernando Blanco ◽  
Ibon Alkorta ◽  
José Elguero
Keyword(s):  
Gas Phase ◽  
Chiral Recognition ◽  
Theoretical Study ◽  
Benzene Solution ◽  
Bond Distance ◽  
Polarizable Continuum Model ◽  
Hydrogen Bond Distance ◽  
Perturbation Energy ◽  
Polarizable Continuum ◽  
Aim And Nbo

A theoretical study of chiral recognition in bicyclic guanidines has been carried out by means of B3LYP/6-31+G(d,p) DFT calculations. A series of complexes between protonated 4,8-dimethyl-1,5,7-triazabicyclodecene (DTBD) and 2,5-disubtituted chiral cyclopentanones have been evaluated for chiral recognition, both in the gas phase and in benzene solution as per the polarizable continuum model (PCM) and analyzed by AIM and NBO methodologies. An inversion in the sense of chiral recognition has been observed between gas phase and solvated results for cyclopentanone complexes. Among the different correlations found (i.e. between electron density, hydrogen bond distance, second-order perturbation energy), a linear correlation has been established between the chiral recognition energy and different molecular parameters.

Solvent and temperature effects on the tautomerization of a carbonitrile molecule: A conductor-like polarizable continuum model (CPCM) study

2021 ◽  
Vol 20 (1) ◽  
pp. 59-68
Author(s):  
Zohreh Khanjari ◽  
Bita Mohtat ◽  
Reza Ghiasi ◽  
Hoorieh Djahaniani ◽  
Farahnaz Kargar Behbahani
Keyword(s):  
Gas Phase ◽  
Solvent Effects ◽  
Continuum Model ◽  
Solvent Polarity ◽  
Polarizable Continuum Model ◽  
Dielectric Constants ◽  
Frontier Orbitals ◽  
Reaction Field ◽  
Polarizable Continuum ◽  
Homo Lumo

This research examined the effects of solvent polarity and temperature on the tautomerization of a carbonitrile molecule at CAM-B3LYP/6-311G (d,p) level of theory. The selected solvents were n-hexane, diethyl ether, pyridine, ethanol, methanol, and water. The solvent effects were examined by the self-consistent reaction field theory (SCRF) based on conductor-like polarizable continuum model (CPCM). The solvent effects were explored on the energy barrier, frontier orbitals energies, and HOMO-LUMO gap. Dependencies of thermodynamic parameters (ΔG and ΔH) on the dielectric constants of solvents were also tested. Specifically, the temperature dependencies of the thermodynamics parameters were studied within 100–1000 K range. The rate constant of the tautomerism reaction was computed from 300 to 1200 K, in the gas phase.

THEORETICAL CALCULATION OF pKb VALUES FOR ANILINES AND SULFONAMIDE DRUGS IN AQUEOUS SOLUTION

2012 ◽  
Vol 11 (02) ◽  
pp. 283-295 ◽  
Author(s):  
BAHRAM GHALAMI-CHOOBAR ◽  
ALI GHIAMI-SHOMAMI ◽  
PARIA NIKPARSA
Keyword(s):  
Gas Phase ◽  
Continuum Model ◽  
Correlation Equation ◽  
Polarizable Continuum Model ◽  
Free Energies ◽  
Pcm Model ◽  
Solvation Models ◽  
Polarizable Continuum ◽  
Better Than ◽  
Good Agreement

In this work, calculations of p K b values have been performed for aniline and its substituted derivatives and sulfonamide drugs by using Gaussian 98 software package. Gas-phase energies were calculated with HF /6-31 G ** and B3LYP /6-31 G ** levels of theory. Free energies of solvation have been computed using the polarizable continuum model (PCM), conductor-like polarizable continuum model (CPCM) and the integral equation formalism-polarizable continuum model (IEFPCM) at the same levels which have been used for geometry determination in the gas-phase. The results show that the calculated p K b values using the B3LYP /6-31 G ** are better than those using the corresponding HF /6-31 G **. At first, the correlation equation was found to determine the p K b values of the investigated anilines. Then, this correlation equation was used to calculate the p K b values of the sulfonamide drugs. The results obtained indicate that the PCM model is a suitable solvation model for calculating p K b values in comparison to the other solvation models. For the investigated compounds a good agreement between the experimental and the calculated p K b values was also observed.

scholarly journals Calculated Molecular Structures Of Anion Ubiquinone In The Gas Phase, In Solvents And In The Qa Binding Site Of Purple Bacteria Reaction Centers

2012 ◽  
Vol 3 ◽  
pp. 18-23
Author(s):  
Hari Prasad Lamichhane
Keyword(s):  
Binding Site ◽  
Gas Phase ◽  
Anion Radical ◽  
Purple Bacteria ◽  
Polarizable Continuum Model ◽  
Reaction Centers ◽  
Molecular Structures ◽  
Carbonyl Groups ◽  
Methoxy Groups ◽  
Polarizable Continuum

Structural properties of ubiquinone one anion radical (UQ1-) are studied in the gas phase and in QA binding site of purple bacteria reaction center using Gaussian 03. Polarizable continuum model (PCM) and Our own N-layered quantum mechanics + molecular mechanics (ONIOM) methods have been used to optimize the UQ1- molecule in solvent and in the QA binding site of purple bacteria Rhodobactor sphaeroides reaction centers. The UQ1- molecule exist four equivalent conformations of methoxy groups in the gas phase and solvents. However, all four conformations reduce to one in the QA binding site of the purple bacteria reaction centers. Both carbonyl (C=O) bond lengths are similar in all four conformations in the gas phase and in solvents. However, C4=O bond is slightly longer than C1=O bond in the QA binding site. This result infers that QA binding site impacts asymmetric interaction on the carbonyl groups of the quinone molecule.The Himalayan PhysicsVol. 3, No. 32012Page : 18-23

scholarly journals Theoretical Study about the Effect of Halogen Substitution on the Reactivity of Antitumor 3-Formylchromones and Their Free Radicals

2017 ◽  
Vol 2017 ◽  
pp. 1-5
Author(s):  
Maximiliano Martínez-Cifuentes ◽  
Boris Weiss-López ◽  
Ramiro Araya-Maturana
Keyword(s):  
Free Radicals ◽  
Hydrogen Atom ◽  
Gas Phase ◽  
Theoretical Study ◽  
Computational Study ◽  
Bond Dissociation Enthalpy ◽  
Radical Species ◽  
Anticancer Compounds ◽  
Dissociation Enthalpy ◽  
Polarizable Continuum

The mandatory presence of a chlorine atom on the aromatic ring of 6-hydroxy-3-formyl angular chromones, on the respiration inhibition of mammary carcinoma mouse, is explained through a computational study of these compounds. This study analyzes the reactivity of the neutral molecules and their free radicals, in gas phase and with water solvation, incorporated by the polarizable continuum medium (PCM) approach. Electrophilic reactivities were evaluated using Fukui (f+) and Parr (P+) functions. The stabilities of radical species formed by the abstraction of a hydrogen atom from the O-H bond were evaluated by bond dissociation enthalpy (BDE) and spin density (SD) calculations. This study has potential implications for the design of chromone analogues as anticancer compounds.

scholarly journals Quantum Chemistry for Molecules at Extreme Pressure on Graphical Processing Units: Implementation of Extreme Pressure Polarizable Continuum Model

2021 ◽  
Author(s):  
Ariel Gale ◽  
Eugen Hruska ◽  
Fang Liu
Keyword(s):  
High Pressure ◽  
Quantum Chemistry ◽  
Gas Phase ◽  
Continuum Model ◽  
Polarizable Continuum Model ◽  
Medium Size ◽  
Extreme Pressure ◽  
Graphical Processing Units ◽  
Graphical Processing ◽  
Polarizable Continuum

Pressure plays essential roles in chemistry by altering structures and controlling chemical reactions. The extreme-pressure polarizable continuum model (XP-PCM) is an emerging method with an efficient quantum mechanical description of small and medium-size molecules at high pressure (on the order of GPa). However, its application to large molecular systems was previously hampered by CPU computation bottleneck: the Pauli repulsion potential unique to XP-PCM requires the evaluation of a large number of electric field integrals, resulting in significant computational overhead compared to the gas-phase or standard-pressure polarizable continuum model calculations. Here, we exploit advances in Graphical Processing Units (GPUs) to accelerate the XP-PCM integral evaluations. This enables high-pressure quantum chemistry simulation of proteins that used to be computationally intractable. We benchmarked the performance using 18 small proteins in aqueous solutions. Using a single GPU, our method evaluates the XP-PCM free energy of a protein with over 500 atoms and 4000 basis functions within half an hour. The time taken by the XP-PCM-integral evaluation is typically 1\% of the time taken for a gas-phase density functional theory (DFT) on the same system. The overall XP-PCM calculations require less computational effort than that for their gas-phase counterpart due to the improved convergence of self-consistent field iterations. Therefore, the description of the high-pressure effects with our GPU accelerated XP-PCM is feasible for any molecule tractable for gas-phase DFT calculation. We have also validated the accuracy of our method on small molecules whose properties under high pressure are known from experiments or previous theoretical studies.

scholarly journals Theoretical Study of a New Diarylic Ligand for M2+ Cations Detection

Proceedings ◽  
2018 ◽  
Vol 9 (1) ◽  
pp. 45
Author(s):  
Carla M. Ormachea ◽  
Cristián A. Ferretti ◽  
Pablo Noriega ◽  
Leandro Gutierrez ◽  
Pedro M. E. Mancini ◽  
...  
Keyword(s):  
Density Functional ◽  
Theoretical Study ◽  
Polarizable Continuum Model ◽  
Ligand Complex ◽  
Hydrazone Ligand ◽  
Molecular Systems ◽  
The Density Functional Theory ◽  
Td Dft ◽  
Structural Electronics ◽  
Polarizable Continuum

A novel byphenyl hydrazone ligand developed as a chemosensor for the detection of Cu2+ was studied using a theoretical analysis based on the density functional theory (DFT) and time-dependent DFT (TD-DFT). The geometries of the ligand (L) and the Cu2+-ligand complex were optimized at the CAM-B3LYP/631+G(d,p) level of theory in dimethyl sulfoxide, using the conductor-like polarizable continuum model. The adsorption spectra of these molecular systems were analyzed and compared with the experimental data. Theoretical study of the structural, electronics and optical properties allowed us to understand the chemical changes that the ligand undergoes in the complexation process with the Cu+2 ion.

scholarly journals Favipiravir Tautomerism: A Short Theoretical Report

2020 ◽  
Author(s):  
Liudmil Antonov
Keyword(s):  
Experimental Data ◽  
Gas Phase ◽  
Continuum Model ◽  
Density Functional ◽  
Polarizable Continuum Model ◽  
Enol Form ◽  
Functional Theory ◽  
Theoretical Predictions ◽  
Polarizable Continuum ◽  
Good Agreement

There is no experimental data about the tautomerism of Favipiravir (T-705). Therefore its tautomeric state was predicted by using density functional theory in gas phase and in solution (toluene, acetonitrile and water). The solvent effect was described by means of the Polarizable Continuum Model. The results have shown that the enol form is strongly dominating in both gas phase and solution. In order to validate the theoretical predictions, 2-hydroxy pyridine and 2-hydroxy pyrazine were also included in the set of studied compounds. The available experimental data for their tautomerism are in very good agreement with the theoretical predictions, which validate the conclusions made for T-705.

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