Theoretical study on the investigation of antioxidant properties of some hydroxyanthraquinones

A Review on Bioactive Anthraquinone and Derivatives as the Regulators for ROS

Anthraquinones are bioactive natural products, which are often found in medicinal herbs. These compounds exert antioxidant-related pharmacological actions including neuroprotective effects, anti-inflammation, anticancer, hepatoprotective effects and anti-aging, etc. Considering the benefits from their pharmacological use, recently, there was an upsurge in the development and utilization of anthraquinones as reactive oxygen species (ROS) regulators. In this review, a deep discussion was carried out on their antioxidant activities and the structure-activity relationships. The antioxidant mechanisms and the chemistry behind the antioxidant activities of both natural and synthesized compounds were furtherly explored and demonstrated. Due to the specific chemical activity of ROS, antioxidants are essential for human health. Therefore, the development of reagents that regulate the imbalance between ROS formation and elimination should be more extensive and rational, and the exploration of antioxidant mechanisms of anthraquinones may provide new therapeutic tools and ideas for various diseases mediated by ROS.

A Plant Dye for Photocatalytic Methane Conversion

A metal-free natural dye has been developed to selectively convert methane to methyl trifluoroacetate (CH3 TFA) using visible light, probably due to the formation of a chloride-bridged dimer undergoing fast intra-complex charge transfer.

Synthesis and Antioxidant Evaluation of O-Methylated Emodacidamides: Starting from Parietin, a Secondary Metabolite of Lichen Xanthoria parietina

Polyhydroxy-anthraquinones bearing amino acids are found rather seldom in nature. Emodacidamides, isolated from a marine-derived fungus, Penicillium sp. SCSIO sof101 by Luo et al. (2017) are the first natural example of amino acid conjugated anthraquinone. In this study, O-methylated emodacidamides and emodinic acid-anilides were synthesized starting from parietin, extracted from the lichen Xanthoria parietina (L.) Th. Fr. The structural elucidations of prepared compounds were confirmed by 1D and 2D NMR analyses including HSQC and HMBC techniques. In addition, all newly synthesized compounds were evaluated for the antioxidant activities with free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging. The synthesized compounds showed low to moderate antioxidant and DPPH scavenging activities. The antioxidant activities were supported within quantum chemical calculations using the DFT-B3LYP/6-311++G(d,p) level of theory. It is observed that the antioxidant activity of emodacidamides mostly depends on the phenolic groups on anthraquinone ring. The phenolic groups on other substituents help to improve antioxidant activity and also the position of hydroxy group is a decisive factor for antioxidant ability.

A DFT study on OH radical scavenging activities of eriodictyol, Isosakuranetin and pinocembrin

Flavonoids are natural compounds with antioxidant properties that have positive effects on human health, which reduce toxic effects of reactive oxygen species (ROS) and partially oxidative damage. In the work, the density functional theory (DFT/BMK) calculations were performed for antioxidant activity evaluation of pinocembrin (P), isosakuranetin (I) and eriodictyol (E). Four main mechanisms were examined: hydrogen atom transfer (HAT), radical adduct formation (RAF), single electron transfer-proton transfer (SET-PT) and Sequential proton loss electron transfer (SPLET). HAT and SPLET are thermodynamically the most probable process in gas phase and water. The three flavonoids examined + •OH HAT and RAF mechanisms for each possible location were investigated theoretically for the first time. The results were discussed by considering thermodynamic, kinetic and structural data of various reaction paths using IRC approach.Communicated by Ramaswamy H. Sarma.

Ligand-based design of chalcone analogues and thermodynamic analysis of their mechanism of free radical scavenge

Overproduction of free radicals in the body may result in oxidative stress, which plays an active role in the development of various health disorders. Consequently, the development of efficient free radical scavengers and evaluation of their antioxidant properties is a research area of interest. In the present research, computational quantum chemical approach based on the density functional theory (DFT) method was employed to elucidate the free radical scavenge of chalcone derivatives via thermodynamic studies. New set of chalcone antioxidants were designed. Their reactivity towards hydroperoxyl (HOO·) and methyl peroxyl (CH₃OO·) radicals were investigated through systematic study of their mechanism of free radical scavenge. Various reaction enthalpies and Gibbs free energy that characterize the various steps in these mechanisms were computed in the gas phase and aqueous solution, in order to identify the main channels of reaction. Results in the gas phase indicate that hydrogen atom transfer (HAT) and sequential proton loss electron transfer (SPLET) mechanisms represent the most plausible reaction pathways, while single electron transfer followed by proton transfer (SET-PT) mechanism was thermodynamically unfeasible. However, these mechanisms were thermodynamically favoured in aqueous solution. Also, these chalcone derivatives were observed to be more effective in scavenging HOO· than CH₃OO· radicals in both phases. Based on the exergonicity of the obtained results, the molecule MCHM 17 ((E)-1-(3-bromo-5-hydroxyphenyl)-3-(2,5-dihydroxyphenyl)prop-2-en-1-one) at the 5-OH site was found to exhibit the greatest potential to scavenge HOO· and CH₃OO· radicals in both phases. This research is a gateway to the efficient exploitation of these compounds in pharmacy and food chemistry.

The significance of long-range correction to the hydroperoxyl radical-scavenging reaction of trans-resveratrol and gnetin C

Density functional theory has been gaining popularity for studying the radical scavenging activity of antioxidants. However, only a few studies investigate the importance of calculation methods on the radical-scavenging reactions. In this study, we examined the significance of (i) the long-range correction on the coulombic interaction and (ii) the London dispersion correction to the hydroperoxyl radical-scavenging reaction of trans-resveratrol and gnetin C. We employed B3LYP, CAM-B3LYP, M06-2X exchange-correlation functionals and B3LYP with the D3 version of Grimme's dispersion in the calculations. The results showed that long-range correction on the coulombic interaction had a significant effect on the increase of reaction and activation energies. The increase was in line with the change of hydroperoxyl radical's orientation in the transition state structure. Meanwhile, the London dispersion correction only had a minor effect on the transition state structure, reaction energy and activation energy. Overall, long-range correction on the coulombic interaction had a significant impact on the radical-scavenging reaction.

DFT Studies of Distinct Anilines with p-Hydroxycinnamic Acids for Antioxidant Profile

BACKGROUND

Life style and jobs in current situations have generated increased free radicals such as hydroxyl (OH•) and superoxide (O2•) radicals, thereby increasing stress in humans. Interest in search of antioxidants that trap these free radicals has increased to relieve stress. β-carotene (provitamin A), ascorbic acid (vitamin C), tocopherol or vitamin E, Trolox; butyl hydroxy toluene and phenolic compounds are the well-known antioxidants. Several methods evaluate the antioxidant property existing in natural substances (medicinal plants and agri-food products) and synthetic compounds (2-methyl-3- (pyrrolidin-2-ylideneamino) quinazolin-4 (3H) -one and 3,3'- (1,4- phenylenebis (methanylylidene)) bis (azanylylidene) (2-methyl-quinazolin-4 (3H) -one).

OBJECTIVE

The objective of this study is to focus on complexes with p-hydroxycinnamic acids to trap free radicals in a greener way.

METHODS

Spectroscopic shifts and structural studies were employed to attribute electronic properties responsible for antioxidant profile. Spectroscopic shifts in wavenumbers were attributed with Fourier Transform Infrared Spectra (FTIR) and Fourier Transform Raman spectra (FT Raman Spectra). Structural studies were performed with Gaussian package, electron density method the B3LYP method, basis set 6-31(d) for attributing electronic properties responsible for antioxidant profile.

RESULTS

Interpretation of FTIR spectra revealed spectroscopic shifts in wavenumbers in all the complexes responsible for bonding. Further, studies confirmed the formation of complex with reduced intensities in Raman spectra. Computational studies revealed enhancement in molecular and electronic properties responsible for antioxidant power.

CONCLUSION

Studies revealed that complex with p-nitroaniline contribute to greater acceptor and donor power responsible for antioxidant power. These higher powers suggest the best antiradicals to trap free radicals.

A theoretical evaluation on free radical scavenging activity of 3-styrylchromone derivatives: the DFT study

Chromone (4H-chromen-4-one, 4H-1-benzopyran-4-one) and related compounds are important pharmacophores and privileged structures in medicinal chemistry because of their important biological activities such as anti-tumor, anti-HIV, and antioxidant. In the study, the density functional theory (DFT) calculations were performed for radical scavenging activity evaluation of a series of 3-styrylchromone derivatives. The reaction enthalpies related to the steps in the radical scavenging action mechanisms and several physicochemical descriptors such as global hardness, softness, and electronegativity were computed in gas phase and in water. The solvation effect of water on the antioxidant activity was taken into account by using the conductor-like polarizable continuum model. The calculated results were discussed by considering all physicochemical properties of molecules: thermodynamic, orbital, and structural. The results obtained were consistent with the experimental results.

Free radical scavenging mechanism of 1,3,4-oxadiazole derivatives: thermodynamics of O-H and N-H bond cleavage

The thermodynamics of free radical scavenge of 1,3,4-oxadiazole derivatives towards oxygen-centred free radicals were investigated by the density functional theory (DFT) method in the gas phase and aqueous solution. Three mechanisms of free radical scavenge namely, hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET) were considered. The antioxidant descriptors that characterize these mechanisms such as, bond dissociation enthalpy (BDE), adiabatic ionization potential (AIP), proton dissociation enthalpy (PDE), proton affinity (PA) and electron transfer enthalpy (ETE) were evaluated. The sequence of electron donation as predicted by the HOMO results were in good agreement with the sequence of ETE for the considered molecules at their favoured sites of free radical scavenge. The reaction Gibbs free energy for inactivation of the selected peroxyl radicals, show that 1,3,4-oxadiazole antioxidants are more efficient radical scavengers by HAT and SPLET mechanisms than SET-PT mechanism in vacuum. In aqueous solution, the SET-PT mechanism was observed to be the dominant reaction pathway.

In silico design of hydrazone antioxidants and analysis of their free radical-scavenging mechanism by thermodynamic studies

Background

Antioxidants are very crucial in maintaining the normal function of body cells, as they scavenge excess free radical in the body. A set of hydrazone antioxidants was designed by in silico screening. The density functional theory (DFT) method was employed to explore the reaction energetics of their free radical-scavenging mechanism. With the aid of the developed quantitative structure-activity relationship (QSAR) model for hydrazone antioxidants, the structure and antioxidant activity of these compounds were predicted. Three potential reaction mechanisms were investigated, namely, hydrogen atom transfer (HAT), single-electron transfer followed by proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET). Bond dissociation enthalpy (BDE), adiabatic ionization potential (AIP), proton dissociation enthalpy (PDE), proton affinity (PA), electron transfer enthalpy (ETE) and Gibbs free energy that characterize the various steps in these mechanisms were calculated in the gas phase.

Results

A total of 25 hydrazone antioxidants were designed, in which the molecule MHD 017 gave the best antioxidant activity. Among the tested molecules, MHD 017 at the 10-OH site gave the best results for the various thermodynamic parameters calculated. The reaction Gibbs free energy results also indicate that this is the most favoured site for free radical scavenge.

Conclusion

The obtained results show that HAT and SPLET mechanisms are the thermodynamically plausible reaction pathways of free radical scavenge by hydrazone antioxidants. The reactivity of these compounds towards the hydroperoxyl radical (HOO·) was greater than that towards the methyl peroxyl radical (CH3OO·) based on the exergonicity of the calculated reaction Gibbs free energy.

Graphical abstract

A DFT mechanistic, thermodynamic and kinetic study on the reaction of 1, 3, 5-trihydroxybenzene and 2, 4, 6-trihydroxyacetophenone with •OOH in different media

A theoretical investigation on the reactions of 1, 3, 5-trihydroxybenzene (PG) and 2, 4, 6-trihydroxyacetophenone (ACPG) with •OOH has been performed with the aim of elucidating the peroxyl radical scavenging properties of PG and its acylated derivative. The study has considered the hydrogen atom transfer (HAT), the single electron transfer-proton transfer and the sequential proton loss-electron transfer mechanisms and determined the geometric, energetic and electronic properties of the reaction species as well as the kinetic parameters for the HAT mechanism. DFT/M06-2X, DFT/MPW1K and DFT/BHHLYP calculation methods have been utilized in combination with the 6-311++G(3df, 2p) basis set. The DFT methods were benchmarked using the CBS-QB3 method. Thermodynamic parameters such as bond dissociation enthalpy (BDE) and ionization energy suggest that the thermodynamically preferred mechanism is the HAT mechanism. The geometric, electronic and energetic parameters suggest that the preferred site for the abstraction of the free phenolic H atom in ACPG is the ortho position. Spin density and branching ratio values indicate that the most stable and preferable product formed is for the reaction of ACPG [Formula: see text] •OOH at the ortho position. The estimated rate constants obtained indicate that the reaction of ACPG [Formula: see text] •OOH is kinetically preferred to the reaction of PG [Formula: see text] •OOH, which is in agreement with experimental findings.

A DFT Analysis on Antioxidant and Antiradical Activities from Anthraquinones Isolated from the Cameroonian Flora

The present work is devoted to the exploration antioxidant and antiradical activity of twenty anthraquinones isolated from the Cameroonian flora at B3LYP/6-311++G(d,p) level of theory using the B3LYP/6-31 + G(d,p) geometrical data as geometry optimization starting points. The single electron transfer mechanism has been adopted to examine both biological activities. The classification of the antiradical profile to integrate the electrodonating power (ω−), electroaccepting power (ω+), donor index (Rd) and acceptor index (Ra) has been performed using the donor-acceptor map (DAM). The antioxidant and radical powers of compounds analyzed have been compared to that of two classical vitamins (vitamin C and gallic acid). The stability of each anthraquinone derivative of the molecular library has been developed according to thermodynamic and kinetic concepts. The global reactivity descriptors (GRDs; electrophilicity index (ω), electronegativity (χ), global softness (S), and global hardness (η)) have been used to analyze the reactivity. The topological analysis of optimized structures indicates that the strength of the hydrogen bonds formed is situated between 44.205 and 52.001 kJ/mol. Our B3LYP results reveal that 3-methoxy-1-vismiaquinone (in a configuration without hydrogen bond) exhibits the best antioxidant capacity in gas phase. A comparison between antioxidant performance of molecules examined and that of classical vitamins (gallic acid, caffeic acid, ferulic acid, and ascorbic acid (vitamin C)) displayed the fact that the single electron transfer (SET) mechanism is more prominent for compounds of the molecular library analyzed. In the same vein, the antiradical behaviors of anthraquinone derivatives have shown to be higher than that of gallic acid and vitamin C in gas phase and water. The 5,8-dihydroxy-2-methylantraquinone structure in a configuration bearing one hydrogen bond has been found to be the best antiradical of the series in aqueous solution.

Structure-Antioxidative and Anti-Inflammatory Activity Relationships of Purpurin and Related Anthraquinones in Chemical and Cell Assays

Anthraquinone (9,10-anthraquinone) and several hydroxy derivatives, including purpurin (1,2,4-trihydroxyanthraquinone), anthrarufin (1,5-dihydroxyanthraquinone), and chrysazin (1,8-dihydroxyanthraquinone), were evaluated for antioxidative and anti-inflammatory activities in chemical assays and mammalian cells (murine macrophage RAW 264.7 cells). Several tests were used to assess their activities: 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical; ABTS radical cation; hydrogen peroxide scavenging; reduction of potassium ferricyanide; chelation of ferrous ions; inhibition of lipid peroxidation; inhibition of nitric oxide generation; scavenging of the intracellular hydroxyl radical; expression of NLRP3 polypeptide for inflammasome assembly; and quantitation of proinflammatory cytokine interleukin 1β (IL-1β) for inflammasome activation. The results show that purpurin, from the root of the madder plant (Rubia tinctorum L.), exhibited the highest antioxidative activity in both chemical and cultured cell antioxidant assays. The antioxidative activities of the other three anthraquinones were lower than that of purpurin. In addition, purpurin could down-regulate NLRP3 inflammasome assembly and activation, suggesting that it might protect foods against oxidative damage and prevent in vivo oxidative stress and inflammation. Structure-activity relationships and the significance of the results for food quality and human health are discussed.