scholarly journals New theoretical insights on tautomerism of hyperforin—a prenylated phloroglucinol derivative which may be responsible for St. John’s wort ( Hypericum perforatum ) antidepressant activity

2019 ◽  
Vol 31 (2) ◽  
pp. 657-666
Author(s):  
Wojciech P. Oziminski ◽  
Agata Wójtowicz
Keyword(s):  
Density Functional ◽  
Parent Compound ◽  
Antidepressant Activity ◽  
Functional Theory ◽  
Tautomeric Forms ◽  
Stability Order ◽  
Enol Tautomer ◽  
Intramolecular Hydrogen ◽  
Gradual Transformation ◽  
Tautomeric Mixture

AbstractThe thermodynamic aspects of keto-enol tautomerism of hyperforin were investigated theoretically using density functional theory methods. At the B3LYP/aug-cc-pVTZ//B3LYP/aug-cc-pVDZ level of theory the enol tautomer dominates the tautomeric mixture and the second enol tautomer 1OH-HB has Gibbs free energy higher by 1.2 kcal/mol, despite possessing an intramolecular hydrogen bond. The purely keto tautomer is less stable by 3.3 kcal/mol compared with the 1OH tautomer, which means that the percentage of the keto tautomer in the tautomeric mixture is only about 0.4%. This is a different picture than in the parent compound of hyperforin—the phloroglucinol, where the keto tautomer is more stable than corresponding enol 1OH tautomer by 0.6 kcal/mol. To explain this difference, several in-between model molecules reflecting gradual transformation from phloroglucinol to hyperforin were build, and all the tautomeric forms were optimized for each molecule. It turned out that the addition of an aliphatic three-carbon bridge to phloroglucinol ring is crucial for the reversal of the tautomer stability order to that for hyperforin. The probable reason is the unfavorable strain in the keto tautomer introduced by the carbon bridge, which forces a specific geometric configuration which destabilizes in consequence the keto tautomer. This picture of hyperforin tautomerism underlines the dominance of enol tautomers, which can be important when studying the antidepressant activity of hyperforin—its interactions with neurotransmitters receptors.

scholarly journals Using Chou’s 5-Step Rule to Evaluate the Stability of Tautomers: Susceptibility of 2-[(Phenylimino)-methyl]-cyclohexane-1,3-diones to Tautomerization Based on the Calculated Gibbs Free Energies

Energies ◽  
2020 ◽  
Vol 13 (1) ◽  
pp. 183
Author(s):  
Robert Dobosz ◽  
Jan Mućko ◽  
Ryszard Gawinecki
Keyword(s):  
Benzene Ring ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Free Energies ◽  
Functional Theory ◽  
1H And 13C Nmr ◽  
Tautomeric Forms ◽  
Methyl Cyclohexane ◽  
The Stability ◽  
Intramolecular Hydrogen

Gibbs free energies, based on DFT (Density Functional Theory) calculations, prove that enaminone (2-(anilinemethylidene)cyclohexane-1,3-dione) and ketamine (2-[(phenylimino)-methyl]cyclohexane-1,3-dione) are the most and least stable tautomeric forms of the studied systems, respectively. 1H and 13C NMR spectra prove that 2-(anilinemethylidene)cyclohexane-1,3-diones are the only tautomeric species present in dimethylsulfoxide solution (a very weak signal can be seen only for the p-methoxy derivatives). The zwitterionic character of these enaminones is strengthened by naphthoannulation and by the insertion of the electron-withdrawing substituent into the benzene ring (the latter weakens the intramolecular hydrogen bond in the compound). Substituent and naphtoannulation have no effect on the stability of the studied tautomers. Slight twisting of the benzene ring, with respect to the CArNC plane (seen in the crystalline state), was proven to also take place in vacuum and in solution.

Molecular Investigations of the Newly Synthesized Azomethines as Antioxidants: Theoretical and Experimental Studies

2019 ◽  
Vol 19 (6) ◽  
pp. 419-433 ◽  
Author(s):  
Siyamak Shahab ◽  
Masoome Sheikhi ◽  
Liudmila Filippovich ◽  
Evgenij Dikusar ◽  
Anhelina Pazniak ◽  
...  
Keyword(s):  
Density Functional ◽  
Energy Gap ◽  
Experimental Studies ◽  
Antioxidant Property ◽  
Nbo Analysis ◽  
Antioxidant Potential ◽  
Functional Theory ◽  
Homo And Lumo ◽  
Intramolecular Hydrogen ◽  
Activity Mechanism

: In this study, the antioxidant property of new synthesized azomethins has been investigated as theoretical and experimental. Methods and Results: Density functional theory (DFT) was employed to investigate the Bond Dissociation Enthalpy (BDE), Mulliken Charges, NBO analysis, Ionization Potential (IP), Electron Affinities (EA), HOMO and LUMO energies, Hardness (η), Softness (S), Electronegativity (µ), Electrophilic Index (ω), Electron Donating Power (ω-), Electron Accepting Power (ω+) and Energy Gap (Eg) in order to deduce scavenging action of the two new synthesized azomethines (FD-1 and FD-2). Spin density calculations and NBO analysis were also carried out to understand the antioxidant activity mechanism. Comparison of BDE of FD-1 and FD-2 indicate the weal antioxidant potential of these structures. Conclusion: FD-1 and FD-2 have very high antioxidant potential due to the planarity and formation of intramolecular hydrogen bonds.

scholarly journals 8-(Pyridin-2-yl)quinolin-7-ol as a Platform for Conjugated Proton Cranes: A DFT Structural Design

Micromachines ◽  
2020 ◽  
Vol 11 (10) ◽  
pp. 901 ◽  
Author(s):  
Anton Georgiev ◽  
Liudmil Antonov
Keyword(s):  
Excited State ◽  
Structural Design ◽  
Density Functional ◽  
Intramolecular Proton Transfer ◽  
State Density ◽  
Strong Electron ◽  
Functional Theory ◽  
Substituted Pyridines ◽  
Donor Acceptor ◽  
Enol Tautomer

Theoretical design of conjugated proton cranes, based on 7-hydroxyquinoline as a tautomeric sub-unit, has been attempted by using ground and excited state density functional theory (DFT) calculations in various environments. The proton crane action request existence of a single enol tautomer in ground state, which under excitation goes to the excited keto tautomer through a series of consecutive excited-state intramolecular proton transfer (ESIPT) steps with the participation of the crane sub-unit. A series of substituted pyridines was used as crane sub-units and the corresponding donor-acceptor interactions were evaluated. The results suggest that the introduction of strong electron donor substituents in the pyridine ring creates optimal conditions for 8-(pyridin-2-yl)quinolin-7-ols to act as proton cranes.

An analogy study on ESIPT reaction for 3BHC sensor between polar DMF and nonpolar toluene

2017 ◽  
Vol 95 (12) ◽  
pp. 1303-1307
Author(s):  
Dapeng Yang ◽  
Min Jia ◽  
Jingyuan Wu ◽  
Xiaoyan Song ◽  
Qiaoli Zhang
Keyword(s):  
Excited State ◽  
Density Functional ◽  
Emission Spectra ◽  
Dft Method ◽  
Intramolecular Proton Transfer ◽  
Nonpolar Solvent ◽  
State Behavior ◽  
Functional Theory ◽  
Td Dft ◽  
Intramolecular Hydrogen

A comparison about excited state intramolecular proton transfer (ESIPT) mechanism of a new sensor 3-(1,3-benzothiazol-2-yl)-2-hydroxynaphthalene-1-carbaldehyde (3BHC) in polar solvent dimethylformamide (DMF) and nonpolar solvent toluene have been investigated within the framework of the time-dependent density functional theory (TD-DFT) method. The reproduced previous experimental absorption and emission spectra via our calculations reveals the reasonability of the DFT and TD-DFT theoretical level. The staple bond lengths, bond angles, and corresponding infrared vibrational spectra demonstrate that the intramolecular hydrogen bond of 3BHC should be strengthened in both polar DMF and nonpolar toluene. Two kinds of ESIPT mechanisms for different solvents have been put forward; there is a low potential barrier in the ESIPT process in the DMF solvent, whereas there is almost a nonbarrier for the ESIPT process in the toluene solvent. Hence, we could conclude that the ESIPT process of 3BHC sensor is more likely to occur in the nonpolar solvent upon the photoexcitation, based on which, the excited state behavior of 3BHC could be controlled.

A DFT-D study on the stability and intramolecular interactions of the salts of 1,2,3- and 1,2,4-triazoles

2014 ◽  
Vol 92 (11) ◽  
pp. 1111-1117
Author(s):  
Xueli Zhang ◽  
Xuedong Gong
Keyword(s):  
Hydrogen Bonds ◽  
Density Functional ◽  
Energy Gap ◽  
Lattice Energy ◽  
Intramolecular Interactions ◽  
Dispersion Energy ◽  
Functional Theory ◽  
Formation Reaction ◽  
The Stability ◽  
Intramolecular Hydrogen

Nitrogen-rich 1,2,4-triazole (1) and 1,2,3-triazole (2) react as bases with the oxygen-rich acids HNO3 (a), HN(NO2)2 (b), and HClO4 (c) to produce energetic salts (1a, 1b, and 1c and 2a, 2b, and 2c, respectively) potentially applicable to composite explosives and propellants. In this study, these salts were studied with the dispersion-corrected density functional theory. For the isomers such as 1a and 2a, the more negative ΔrGm of the formation reaction leads to a higher thermally stable salt. The ability to form intramolecular hydrogen bonds predicted with the quantum theory of atoms in molecules has the order of 2 > 1. Different hydrogen bonds result in different second-order perturbation energies, redshifts in IR, and electron density differences. The charge transfer, binding energy, dispersion energy, lattice energy, and energy gap between frontier orbits in the salts of 1 are larger than those of 2, which is helpful for stabilizing the former, and 1 is more obviously stabilized than 2 by formation of salts. Different conformations of 1 and 2 hardly affect the frontier orbital distributions. Base 1 is a more preferred base than 2 to form salts.

Solvent effects on the tautomeric equilibrium of 2,4-pentanedione

1982 ◽  
Vol 60 (10) ◽  
pp. 1178-1182 ◽  
Author(s):  
J. N. Spencer ◽  
Eric S. Holmboe ◽  
Mindy R. Kirshenbaum ◽  
Daniel W. Firth ◽  
Patricia B. Pinto
Keyword(s):  
Hydrogen Bond ◽  
Solvent Effects ◽  
Tautomeric Equilibrium ◽  
Spectroscopic Techniques ◽  
Hydrogen Bond Formation ◽  
Entropy Changes ◽  
Tautomeric Forms ◽  
Self Association ◽  
Enol Tautomer ◽  
Intramolecular Hydrogen

The influence of solvent on the equilibrium position of the tautomeric forms of 2,4-pentanedione was studied by calorimetric and nmr spectroscopic techniques. For solvents such as CCl4 and cyclohexane the intramolecular bond of the enol form persists and bulk solvent effects account for the equilibrium enol–keto content. In solvents such as DMSO, disruption of the intramolecular bond occurs and the percentage of enol falls due to unfavorable entropy changes. The enol intramolecular bond is disrupted by the solvents water and methanol. Enol hydrogen bond formation through self-association and with the solvent accounts for the entropy changes upon enolization in these solvents. The thermodynamic parameters for enolization in neat 2,4-pentanedione are rationalized by the disruption of the enol intramolecular hydrogen bond through consequent polymerization of the enol tautomer.

scholarly journals Influence of catecholic ring torsion on hydroxyflavones

2020 ◽  
Vol 13 (1) ◽  
pp. 49-55
Author(s):  
Martin Michalík ◽  
Monika Biela ◽  
Denisa Cagardová ◽  
Vladimír Lukeš
Keyword(s):  
Gas Phase ◽  
Phenyl Ring ◽  
Density Functional ◽  
Hydroxyl Group ◽  
Torsional Deformation ◽  
Functional Theory ◽  
Electron Transitions ◽  
The Density Functional Theory ◽  
Intramolecular Hydrogen ◽  
Theoretical Results

AbstractSystematic quantum chemical investigation of quercetin and selected eight mono- and bihydroxyflavonols is presented. Structural analysis based on the Density Functional Theory showed that the energetically preferred conformation of flavonols substituted at the C5 and C3 atoms by a hydroxyl group is stabilised via intramolecular hydrogen bonds occurring between the (C4)O···HO(3 or 5) atomic pairs. Depending on the hydroxyl group positions, energetically preferred torsional orientation of the phenyl ring with respect to the planar benzo-γ-pyrone moiety changed from 0 to 180 degrees. Gas-phase electron transitions were investigated using the time-dependent DFT treatment. The dependence of maximal wavelengths on the torsional deformation of the phenyl ring is of a similar shape, i.e. minima observed for the perpendicular orientation and maxima for the planar one. Shape and energies of the Highest Occupied (HOMO) and Lowest Unoccupied (LUMO) Molecular Orbitals were compared. The obtained theoretical results were compared with available experimental data.

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