Antioxidant Activity/Capacity Measurement. 1. Classification, Physicochemical Principles, Mechanisms, and Electron Transfer (ET)-Based Assays

Compounds from the plant world that possess antioxidant abilities are of special importance for the food and pharmaceutical industry. Coumarins are a large, widely distributed group of natural compounds, usually found in plants, often with good antioxidant capacity. The coumarin-hydroxybenzohydrazide derivatives were synthesized using a green, one-pot protocol. This procedure includes the use of an environmentally benign mixture (vinegar and ethanol) as a catalyst and solvent, as well as very easy isolation of the desired products. The obtained compounds were structurally characterized by IR and NMR spectroscopy. The purity of all compounds was determined by HPLC and by elemental microanalysis. In addition, these compounds were evaluated for their in vitro antioxidant activity. Mechanisms of antioxidative activity were theoretically investigated by the density functional theory approach and the calculated values of various thermodynamic parameters, such as bond dissociation enthalpy, proton affinity, frontier molecular orbitals, and ionization potential. In silico calculations indicated that hydrogen atom transfer and sequential proton loss–electron transfer reaction mechanisms are probable, in non-polar and polar solvents respectively. Additionally, it was found that the single-electron transfer followed by proton transfer was not an operative mechanism in either solvent. The conducted tests indicate the excellent antioxidant activity, as well as the low potential toxicity, of the investigated compounds, which makes them good candidates for potential use in food chemistry.

Download Full-text

Effect of Molecular Interactions on Electron-Transfer and Antioxidant Activity of Bis(alkanol)selenides: A Radiation Chemical Study

Chemistry - A European Journal ◽

10.1002/chem.201601918 ◽

2016 ◽

Vol 22 (34) ◽

pp. 12189-12198 ◽

Cited By ~ 5

Author(s):

Pavitra V. Kumar ◽

Beena G. Singh ◽

Prasad P. Phadnis ◽

Vimal K. Jain ◽

K. Indira Priyadarsini

Keyword(s):

Antioxidant Activity ◽

Electron Transfer ◽

Molecular Interactions ◽

Chemical Study ◽

Radiation Chemical

Download Full-text

Theoretical Study of the Iron Complexes with Lipoic and Dihydrolipoic Acids: Exploring Secondary Antioxidant Activity

Antioxidants ◽

10.3390/antiox9080674 ◽

2020 ◽

Vol 9 (8) ◽

pp. 674

Author(s):

Roger Monreal-Corona ◽

Jesse Biddlecombe ◽

Angela Ippolito ◽

Nelaine Mora-Diez

Keyword(s):

Antioxidant Activity ◽

Electron Transfer ◽

Rate Constant ◽

Thermodynamic Stability ◽

Rate Constants ◽

Theoretical Study ◽

Oh Radicals ◽

Single Electron Transfer ◽

Coordination Numbers ◽

Ph Conditions

The thermodynamic stability of twenty-nine Fe(III) complexes with various deprotonated forms of lipoic (LA) and dihydrolipoic (DHLA) acids, with coordination numbers 4, 5 and 6, is studied at the M06(SMD)/6-31++G(d,p) level of theory in water under physiological pH conditions at 298.15 K. Even though the complexes with LA- are more stable than those with DHLA−, the most thermodynamically stable Fe(III) complexes involve DHLA2−. The twenty-four exergonic complexes are used to evaluate the secondary antioxidant activity of DHLA and LA relative to the Fe(III)/Fe(II) reduction by O2•− and ascorbate. Rate constants for the single-electron transfer (SET) reactions are calculated. The thermodynamic stability of the Fe(III) complexes does not fully correlate with the rate constant of their SET reactions, but more exergonic complexes usually exhibit smaller SET rate constants. Some Cu(II) complexes and their reduction to Cu(I) are also studied at the same level of theory for comparison. The Fe(III) complexes appear to be more stable than their Cu(II) counterparts. Relative to the Fe(III)/Fe(II) reduction with ascorbate, DHLA can fully inhibit the formation of •OH radicals, but not by reaction with O2•−. Relative to the Cu(II)/Cu(I) reduction with ascorbate, the effects of DHLA are moderate/high, and with O2•− they are minor. LA has minor to negligible inhibition effects in all the cases considered.

Download Full-text

COMPARATIVE ANTIRADICAL ACTIVITY AND MOLECULAR DOCKING STUDY OF BERGAPTOL AND XANTHOTOXOL

Journal of the Serbian Society for Computational Mechanics ◽

10.24874/jsscm.2020.01.07 ◽

2020 ◽

pp. 71-84

Author(s):

Žiko Milanović ◽

Marko Antonijević ◽

Jelena Đorović ◽

Dejan Milenković

Keyword(s):

Antioxidant Activity ◽

Electron Transfer ◽

Molecular Docking ◽

Free Radical ◽

Hydrogen Atom ◽

Antiradical Activity ◽

Docking Study ◽

Hydrogen Atom Transfer ◽

Molecular Docking Study ◽

Anionic Species

The antioxidant activity of bergaptol (4-hydroxyfuro[3,2-g]chromen-7-one, BER) and xanthotoxol (9-hydroxyfuro[3,2-g]chromen-7-one, XAN) was investigated in water and benzene, as solvents. For this purpose, the density functional theory (DFT) was used. The free radical scavenging potency of investigated compounds towards different reactive oxygen species (ROS) was performed. Antioxidative mechanism of investigated compounds – hydrogen atom transfer (HAT), single-electron transfer–proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET) were examined using M06-2X/6-311++G(d,p) theoretical model. The important thermodynamic parameters (BDE, IP, PDE, PA, ETE) and Gibbs free energies of reactions, were used to determine the most probable antioxidant mechanism of action. The obtained thermodynamic parameters suggested that Hydrogen Atom Transfer (HAT) is the most probable reaction pathway in benzene, while Sequential Proton Loss Electron Transfer (SPLET) was favorized in water. The obtained results indicate that the favorable mechanism of antiradical activity depends on the polarity of medium and the nature of free radical species. By comparing the antioxidant activity of investigated compounds, it can be concluded that bergaptol exhibits better antioxidant properties. Molecular docking study of neutral and anionic species of investigated compounds was performed according to Estrogen receptor alpha (ERα). In both cases, bergaptol showed better inhibitory potency. All the anionic species showed a higher inhibition constant, indicating lower inhibition potency than corresponding parent molecules.

Download Full-text

The Flow of the Redox Energy in Quercetin during Its Antioxidant Activity in Water

International Journal of Molecular Sciences ◽

10.3390/ijms21176015 ◽

2020 ◽

Vol 21 (17) ◽

pp. 6015

Author(s):

Zhengwen Li ◽

Mohamed Moalin ◽

Ming Zhang ◽

Lily Vervoort ◽

Erik Hursel ◽

...

Keyword(s):

Antioxidant Activity ◽

Electron Transfer ◽

Hydroxyl Radicals ◽

Hydrogen Transfer ◽

Energy Content ◽

Quantum Calculations ◽

Carbonyl Groups ◽

Oh Groups ◽

Energy Flows ◽

Intramolecular Hydrogen

Most studies on the antioxidant activity of flavonoids like Quercetin (Q) do not consider that it comprises a series of sequential reactions. Therefore, the present study examines how the redox energy flows through the molecule during Q’s antioxidant activity, by combining experimental data with quantum calculations. It appears that several main pathways are possible. Pivotal are subsequently: deprotonation of the 7-OH group; intramolecular hydrogen transfer from the 3-OH group to the 4-Oxygen atom; electron transfer leading to two conformers of the Q radical; deprotonation of the OH groups in the B-ring, leading to three different deprotonated Q radicals; and finally electron transfer of each deprotonated Q radical to form the corresponding quercetin quinones. The quinone in which the carbonyl groups are the most separated has the lowest energy content, and is the most abundant quinone. The pathways are also intertwined. The calculations show that Q can pick up redox energy at various sites of the molecule which explains Q’s ability to scavenge all sorts of reactive oxidizing species. In the described pathways, Q picked up, e.g., two hydroxyl radicals, which can be processed and softened by forming quercetin quinone.

Download Full-text

Defining a standardized methodology for the determination of the antioxidant capacity: case study of Pistacia atlantica leaves

The Analyst ◽

10.1039/c9an01643k ◽

2020 ◽

Vol 145 (2) ◽

pp. 557-571 ◽

Cited By ~ 2

Author(s):

Ziyad Ben Ahmed ◽

Yousfi Mohamed ◽

Viaene Johan ◽

Bieke Dejaegher ◽

Kristiaan Demeyer ◽

...

Keyword(s):

Antioxidant Activity ◽

Electron Transfer ◽

Hydrogen Atom ◽

Antioxidant Capacity ◽

Hydrogen Atom Transfer ◽

Single Electron ◽

Single Electron Transfer ◽

Pistacia Atlantica

Antioxidant activity can be measured by a variety of methods, that include hydrogen atom transfer (HAT) and single electron transfer (ET) methods.

Download Full-text

DFT Study of Structure and Radical Scavenging Activity of Natural Pigment Delphinidin and Derivatives

10.5772/intechopen.98647 ◽

2021 ◽

Author(s):

Sumayya Pottachola ◽

Arifa Kaniyantavida ◽

Muraleedharan Karuvanthodiyil

Keyword(s):

Antioxidant Activity ◽

Electron Transfer ◽

Gas Phase ◽

Radical Scavenging Activity ◽

Radical Scavenging ◽

Scavenging Activity ◽

Natural Pigment ◽

Physiochemical Parameters ◽

Dissociation Enthalpy ◽

Spin Density Calculation

A theoretical evaluation of the antioxidant activity of natural pigment delphinidin (1a) and derivatives 1b, 1c, 1d & 1e was performed using the DFT-B3LYP/6–311 + G (d, p) level of theory. Three potential working mechanisms, hydrogen atom transfer (HAT), stepwise electron transfer proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET), have been investigated. The physiochemical parameters, including O–H bond dissociation enthalpy (BDE), ionization potential (IP), proton dissociation enthalpy (PDE), proton affinity (PA), and electron transfer enthalpy (ETE), have been calculated in the gas phase and aqueous phase. The study found that the most suitable mechanism for explaining antioxidant activity is HAT in the gas phase and SPLET in the aqueous medium in this level of theory. Spin density calculation and delocalization index of studied molecules also support the radical scavenging activity. When incorporated into natural pigment delphinidin, the gallate moiety can enhance the activity and stability of the compounds.

Download Full-text

Antioxidant Activity and Capacity Measurement

Plant Antioxidants and Health - Reference Series in Phytochemistry ◽

10.1007/978-3-030-45299-5_22-1 ◽

2021 ◽

pp. 1-66

Author(s):

Esra Capanoglu ◽

Senem Kamiloglu ◽

Sema Demirci Cekic ◽

Kevser Sozgen Baskan ◽

Asli Neslihan Avan ◽

...

Keyword(s):

Antioxidant Activity ◽

Capacity Measurement

Download Full-text