Theoretical insight into the substituent effects on the antioxidant properties of 8-hydroxyquinoline derivatives in gas phase and in polar solvents

2018 ◽  
Vol 96 (5) ◽  
pp. 453-458
Author(s):  
Anes El-Hadj Saïd ◽  
Sidi Mohamed Mekelleche ◽  
Taki-Eddine Ahmed Ardjani
Keyword(s):  
Electron Transfer ◽  
Gas Phase ◽  
Antioxidant Properties ◽  
Substituent Effects ◽  
Hydrogen Atom Transfer ◽  
Polar Solvents ◽  
Antioxidant Power ◽  
Theoretical Insight ◽  
Insight Into

The objective of this work is to perform a theoretical analysis of the antioxidant properties of a series of 8-hydroxyquinolines (8-HQs) to rationalize the available experimental results and to design new potent 8-HQ derivatives. The study was carried out in gas phase and in methanol at the DFT/B3LYP/ 6-311++G(d,p) computational level. The formation of stable ArO• radicals is discussed on the basis of different mechanisms, namely, hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT), and single proton loss electron transfer (SPLET). The obtained results show that the HAT mechanism is, thermodynamically, more favoured in gas phase, whereas the SPLET pathway is more favoured in polar solvents. The calculated thermochemical descriptors allow classification of the antioxidant power of the studied compounds.

scholarly journals ANTIOXIDANT PROPERTIES OF FOLIC ACID: A DFT STUDY

2018 ◽  
Vol 56 (4A) ◽  
pp. 39 ◽  
Author(s):  
Dao Duy Quang
Keyword(s):  
Free Radicals ◽  
Folic Acid ◽  
Gas Phase ◽  
Antioxidant Properties ◽  
Hydrogen Atom Transfer ◽  
Single Electron Transfer ◽  
To Receive ◽  
Antioxidant Mechanisms ◽  
Insight Into ◽  
Free Radicals Scavenging

Antioxidant activity of folic acid (FA) was investigated via two main antioxidant mechanisms: hydrogen atom transfer (HAT) and single electron transfer (SET) at the DFT/B3LYP/6-311G(d,p) level of theory. The characterizing thermochemical properties such as bond dissociation enthalpies (BDEs), ionization energy (IE) and electron affinity (EA) were calculated in the gas phase. Analyses of HOMOs distribution shows that the postions which easily donate electrons to free radicals are essentially found at C ring, while the positions which easily accept electrons (LUMOs) from radicals are mainly situated at B ring. The lowest BDE values equal to 76.5 and 80.1 kcal/mol are obtained at C19-H and C9–H position, respectively. It is showed that FA represents a potential antioxidant via HAT mechanism. In addition, the IE and EA values calculated in the gas phase are equal to 5.45 eV and 1.87 eV, respectively. This result shows that FA has higher ability to donate electrons into free radicals, while the ability to receive electrons is quite weak. Finally, the HAT reaction between FA and reactive radical like HOO• was also calculated at the same level of theory. This provides more insight into its mechanism on free radicals scavenging.

Theoretical investigation and molecular docking approach on the antioxidant activity of Schiff bases and their tautomers

2017 ◽  
Vol 16 (01) ◽  
pp. 1750001 ◽  
Author(s):  
Ahmed Taki Eddine Ardjani ◽  
Sidi Mohamed Mekelleche
Keyword(s):  
Antioxidant Activity ◽  
Electron Transfer ◽  
Molecular Docking ◽  
Gas Phase ◽  
Great Influence ◽  
Docking Study ◽  
Hydrogen Atom Transfer ◽  
Molecular Docking Study ◽  
Antioxidant Power ◽  
Dissociation Enthalpy

A theoretical study of the antioxidant behavior of N[Formula: see text]-(2-hydroxy-3-methoxy-benzylidene)-4-tert-buty-lenzohydrazide (1), N[Formula: see text]-(5-bromo-2-hydroxy-benzylidene)-4-tert-butyl benzohydrazide (2) and N[Formula: see text]-(2-hydroxy-3-methoxybenzylidene)-4-methyl-benzene-sulfonohydrazide (3) and their tautomers 1 [Formula: see text] –3 [Formula: see text] have been carried out at B3LYP/6-31[Formula: see text]G(2d,2p). The numerical values of descriptors, namely, bond dissociation enthalpy, proton affinity (PA), electron transfer enthalpy (ETE), ionization potential, and proton dissociation enthalpy (PDE) have been calculated in gas phase and media solution (EtOH, DMSO and water). The obtained results show that the hydrogen atom transfer (HAT) mechanism is more favored thermodynamically in gas phase, whereas the sequential proton loss electron transfer (SPLET) mechanism is more preferred in solvents. Moreover, the couple (3,3[Formula: see text]) is found to be the most potent antioxidant as expected experimentally. Furthermore, the BDE values of compound 3 [Formula: see text] is much lower than that of ascorbic acid (AA), indicating that the tautomerization of compounds 1–3 has great influence on the antioxidant activity of these compounds. The antioxidant power of compounds (3.3[Formula: see text]) was also rationalized by the calculation of the atomic spin density. In addition, the molecular docking study of compounds 1–3 and 1[Formula: see text] –3[Formula: see text] on xanthine oxidase (XO) as the protein target revealed important interactions between active compounds and amino acids. Moreover, compound 3 is predicted to be a potential inhibitor with higher activity.

scholarly journals Free Radical Scavenging Activity of Five Benzoic Acid Derivatives: A Theoretical M06-2X Study

2022 ◽  
Author(s):  
Bienfait Kabuyaya Isamura ◽  
Issofa Patouossa ◽  
Isaac Kaba Elaka ◽  
Aristote Matondo ◽  
Pius Tshimankinda Mpiana
Keyword(s):  
Electron Transfer ◽  
Free Radical ◽  
Benzoic Acid ◽  
Gas Phase ◽  
Antioxidant Properties ◽  
Radical Scavenging ◽  
Free Radical Scavenging ◽  
Basis Set ◽  
Antioxidant Power ◽  
Benzoic Acid Derivatives

The meta hybrid M06-2X functional combined with the 6-311++G(d,p) basis set are used to investigate the antioxidant activity of five benzoic acid derivatives naturally occurring in several plant food: gallic acid, para-hydroxybenzoic acid, protocatechuic acid, syringic acid and vanillic acid. To assess the antioxidant properties of these compounds, three mechanisms of free radicals scavenging are considered, namely the hydrogen atom transfer (HAT), stepwise electron transfer proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET) models. The effect of polar environments on the antioxidant power of these compounds is mimicked in water and methanol using the IEF-PCM solvation method. Our findings suggest that HAT is the preferred mechanistic pathway in gas phase, while SPLET is favoured in polar mediums. Protocatechuic and gallic acids are the most active in gas and polar solutions respectively, whereas PHBA is the least active in all the environments considered. The O-H group in para position of the carboxylic group (O3-H for GA and O2-H for the rest) is confirmed to be the most reactive site in gas phase, while in solution it is either of the O1-H site (for PHBA, PCA, SA and VA) or O4-H groups (for GA). The “HOMO-rule” of free radical scavenging ability does not seem to account properly for the antioxidant properties of this set of chemicals.

scholarly journals Evaluation of the Radical-Scavenging Properties of Various Flavonols in Ethanol Environment: an ab initio Study

2019 ◽  
Vol 92 (3) ◽  
pp. 337-346
Author(s):  
Raluca Pop
Keyword(s):  
Electron Transfer ◽  
Antioxidant Properties ◽  
Radical Scavenging ◽  
Hydrogen Atom Transfer ◽  
Hydroxyl Groups ◽  
Spin Distribution ◽  
Parent Molecule ◽  
Oh Groups ◽  
Fukui Functions ◽  
Reactivity Descriptors

The antioxidant properties of six flavonols -fisetin, galangin, gossipetin, kaempferol, morin and myricetin- have been investigated at HF/6-311G+(d,p) level of theory, using ethanol as solvent. Three known antioxidant mechanisms, namely HAT (hydrogen atom transfer), SET-PT (single electron transfer followed by proton transfer) and SPLET (sequential proton loss electron transfer) have been employed in order to evaluate the radical scavenging abilities of the investigated compounds. Thermodynamic parameters like bond dissociation energy (BDE), proton affinity (PA), electron transfer enthalpy (ETE), ionization potential (IP) and proton dissociation enthalpy (PDE) were calculated and the results were associated with the number and the positions of the hydroxyl groups, the geometry of the parent molecule and of the corresponding radicals, as well as with the electron spin distribution. Also, computations of global reactivity descriptors like HOMO-LUMO gap showed that an increased reactivity is related to the presence of the catechol moiety (gossipetin, myricetin, fisetin). The influence of the catecholic OH groups is also outlined by the HOMO energies, highest electron-donor ability being obtained for gossipetin, the flavonol with two catecholic moieties on rings A and B. According to the HAT mechanism, it has been outlined an enhanced antioxidant character of the 3-OH groups, followed by the hydroxyl groups attached to the phenyl ring B. The calculated values of the condensed Fukui functions, computed for a radical attack, are in good agreement with the above-mentioned results.

ANTIOXIDANT ACTIVITY OF AMINOTHIAZOL HYDROXYCOUMARIN DERIVATIVES

2013 ◽  
Vol 12 (06) ◽  
pp. 1350058 ◽  
Author(s):  
DAVOOD FARMANZADEH ◽  
MEYSAM NAJAFI
Keyword(s):  
Antioxidant Activity ◽  
Gas Phase ◽  
Antioxidant Activities ◽  
Antioxidant Properties ◽  
Experimental Studies ◽  
Structure Parameters ◽  
Coumarin Derivatives ◽  
Polar Solvents ◽  
B3lyp Method ◽  
High Antioxidant Activity

In this work, the antioxidant properties of the series of 10 aminothiazol hydroxyl coumarin derivatives have been investigated with DFT/B3LYP method. For these antioxidants all reaction enthalpies related to HAT, SPLET, SET-PT mechanisms were calculated in the gas phase and polar solvents. Based on calculated reaction enthalpies (BDE, IP and PA values) the derivations 2, 3 and 4 have the highest antioxidant activity among the studied compounds. Calculated results show that derivations 7, 5 and 6 have the lowest antioxidant activity. The observed theoretical trends for antioxidant activities of studied compounds were similar to trends of previous experimental studies that OH50, TAC50, IC50, CE50 values have been used as a benchmark for measuring the antioxidant properties of these compounds. These results can be useful in synthesis of novel aminothiazol hydroxycoumarin derivatives with high antioxidant activity. Calculated results show that BDE, PA and IP values of studied derivations have linear dependence with structure parameters such as R( O – H ), q( O ) and E HOMO . These observed linear dependences can be useful in synthesis of novel aminothiazol hydroxyl coumarin derivatives with high antioxidant activity. For studied compounds, results indicated that the SPLET and HAT mechanisms represent the thermodynamically preferred mechanism both, in solvent and the gas phase.

Substituent effects on homolytic versus heterolytic photocleavage of (1-naphthylmethyl)trimethylammonium chlorides

1987 ◽  
Vol 65 (7) ◽  
pp. 1599-1607 ◽  
Author(s):  
B. Foster ◽  
B. Gaillard ◽  
N. Mathur ◽  
A. L. Pincock ◽  
J. A. Pincock ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Hydrogen Atom ◽  
Charge Distribution ◽  
Rate Constants ◽  
Bond Cleavage ◽  
Substituent Effects ◽  
Hydrogen Atom Transfer ◽  
Singlet Excited State ◽  
State Rate

Singlet excited state rate constants have been measured for both the heterolytic and homolytic photocleavage of 3- and 4-methoxy and 3- and 4-cyano (1-naphthylmethyl)trimethylammonium chlorides, 6–10. The results are interpreted in terms of the meta effect or changes in charge distribution upon excitation and the competition between bond cleavage, electron transfer, and hydrogen atom transfer in the contact pairs resulting from the two types of cleavage.

Gas-phase reactions of anions with halogenated methanes at 297 ± 2 K

1976 ◽  
Vol 54 (10) ◽  
pp. 1643-1659 ◽  
Author(s):  
K. Tanaka ◽  
G. I. Mackay ◽  
J. D. Payzant ◽  
D. K. Bohme
Keyword(s):  
Gas Phase ◽  
Rate Constants ◽  
Hydrogen Atom Transfer ◽  
Gas Phase Reactions ◽  
Phase Measurements ◽  
Displacement Reactions ◽  
Nucleophilic Reactivity ◽  
Apparent Activation Energies

The rate constants for a number of exothermic displacement (SN2) reactions of the type X− + CH3Y → Y− + CH3X where X− = H−, O−, C−, F−, S−, Cl−, OH−, C2−, CN−, SH−, S2−, C2H−, NH2−, NO2−, CHF−, CH2Cl−, CH2Br−, CH3O−, CH3S−, and CH3NH− and Y = F, Cl, and Br, have been measured in the gas phase at 297 ± 2 K using the flowing after-glow technique. These gas-phase measurements provided an opportunity to determine the intrinsic nucleophilic reactivity of 'nude' anions and hence to assess the role of solvation in the kinetics of SN2 reactions proceeding in solution. Comparisons of the experimental rate constants with rate constants calculated using classical theories of capture indicate that several displacement reactions may possess large intrinsic energies of activation, [Formula: see text]. Correlations were found between apparent activation energies and the heats of reaction. These correlations provided a convenient classification of the various anion nucleophiles. Displacement was observed to compete with proton transfer in reactions involving nucleophiles of high intrinsic basicity and with hydrogen atom transfer and H2+ transfer in the reactions of the O− radical anion.

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