Density Functional Theory Study of the Conformational, Electronic, and Antioxidant Properties of Natural Chalcones

Augmenting the effect of solvents on optical nonlinearity by spectroscopic, DFT, solvatochromism and z-scan studies of push-pull chalcone: (2E)-1-(4-ethoxyphenyl)-3-(4-methoxyphenyl)prop-2-en-1-one

In this article, the structural and nonlinear optical behaviour of a chalcone derivative, (2E)-1-(4-ethoxyphenyl)-3-(4-methoxyphenyl)prop-2-en-1-one have been studied. FT-IR, FT-Raman, and NMR spectroscopy were analyzed to validate the molecular structure. To predict the nonlinear optical characteristics of the chalcone, the DFT approach was used and the experimental results were corroborated by the computations. The bathochromic shift is obtained in linear absorbance spectra and is validated using TD-DFT. Also, the broad emission in the blue region demonstrates the blue light emission property of the sample. Using the finite-field method, the dipole moments, polarizability, first-order and second-order hyperpolarizability parameters have been computed. Ground and excited state dipole moments were quantified by solvatochromism. The third-order nonlinear optical characteristics of chalcone in polar and non-polar solvent media were examined using the open/closed-aperture z-scan technique. The chalcone displayed considerable two-photon absorption with a positive nonlinear absorption coefficient and a positive index of refraction due to the self-focussing effect. Furthermore, the optical limiting study manifests that the investigated chalcone might well be favourable for NLO applications.

Hydroxy Chalcones and Analogs with Chemopreventive Properties

The aim of this review is to highlight the chemopreventive properties of hydroxy-substituted natural and synthetic chalcones along with a number of their analogs. These products display various biological activities, and have many applications against various diseases. Antioxidant and anti-inflammatory properties of chalcones bearing hydroxy substituents are underlined. The influence of hydroxy substituents located on ring A, B, or both are systematized according to the exhibited biological properties.

The natural chalcone cardamonin selectively induces apoptosis in human neuroblastoma cells

Neuroblastoma is the most common extracranial malignant tumor in childhood. Approximately 60% of all patients are classified as high-risk and require intensive treatment including non-selective chemotherapeutic agents leading to severe side effects. Recently, phytochemicals like the natural chalcone cardamonin (CD) have gained attention in cancer research. For the first time, we investigated the selective anti-cancer effects of CD in SH-SY5Y human neuroblastoma cells compared to healthy (normal) fibroblasts (NHDF). Our study revealed selective and dose-dependent cytotoxicity of CD in SH-SY5Y. The natural chalcone CD specifically altered the mitochondrial membrane potential (ΔΨm), as an early marker of apoptosis, in human neuroblastoma cells. Caspase activity was also selectively induced and the amount of cleaved caspase substrates such as PARP was thus increased in human neuroblastoma cells. CD-mediated apoptotic cell death was rescued by pan caspase inhibitor Z-VAD-FMK. The natural chalcone CD selectively induced apoptosis, the programmed cell death, in SH-SY5Y human neuroblastoma cells whereas NHDF being a model for normal (healthy) cells were unaffected. Our data indicates a clinical potential of CD in the more selective and less harmful treatment of neuroblastoma.

Protonated Forms of Naringenin and Naringenin Chalcone: Proteiform Bioactive Species Elucidated by IRMPD Spectroscopy, IMS, CID-MS, and Computational Approaches

Naringenin (Nar) and its structural isomer, naringenin chalcone (ChNar), are two natural phytophenols with beneficial health effects belonging to the flavonoids family. A direct discrimination and structural characterization of the protonated forms of Nar and ChNar, delivered into the gas phase by electrospray ionization (ESI), was performed by mass spectrometry-based methods. In this study, we exploit a combination of electrospray ionization coupled to (high-resolution) mass spectrometry (HR-MS), collision-induced dissociation (CID) measurements, IR multiple-photon dissociation (IRMPD) action spectroscopy, density functional theory (DFT) calculations, and ion mobility-mass spectrometry (IMS). While IMS and variable collision-energy CID experiments hardly differentiate the two isomers, IRMPD spectroscopy appears to be an efficient method to distinguish naringenin from its related chalcone. In particular, the spectral range between 1400 and 1700 cm^-1 is highly specific in discriminating between the two protonated isomers. Selected vibrational signatures in the IRMPD spectra have allowed us to identify the nature of the metabolite present in methanolic extracts of commercial tomatoes and grapefruits. Furthermore, comparisons between experimental IRMPD and calculated IR spectra have clarified the geometries adopted by the two protonated isomers, allowing a conformational analysis of the probed species.

Rational design, synthesis, and pharmacological characterisation of dicarbonyl curcuminoid analogues with improved stability against lung cancer via ROS and ER stress mediated cell apoptosis and pyroptosis

Curcumin is a natural medicine with a wide range of anti-tumour activities. However, due to β-diketone moiety, curcumin exhibits poor stability and pharmacokinetics which significantly limits its clinical applications. In this article, two types of dicarbonyl curcumin analogues with improved stability were designed through the calculation of molecular stability by density functional theory. Twenty compounds were synthesised, and their anti-tumour activity was screened. A plurality of analogues had significantly stronger activity than curcumin. In particular, compound B2 ((2E,2'E)-3,3'-(1,4-phenylene)bis(1-(2-chlorophenyl)prop-2-en-1-one)) exhibited excellent anti-lung cancer activity in vivo and in vitro. In addition, B2 could upregulate the level of reactive oxygen species in lung cancer cells, which in turn activated the endoplasmic reticulum stress and led to cell apoptosis and pyroptosis. Taken together, curcumin analogue B2 is expected to be a novel candidate for lung cancer treatment with improved chemical and biological characteristics.

Guaiacol oxidation: theoretical insight into thermochemistry of radical processes involving methoxy group demethylation

Guaiacol (2-methoxyphenol) is naturally occurring phenolic compound essential in various research areas. Oxidative transformation of guaiacol can lead to the formation of various products, including 1,3-benzodioxole or ortho-quinone. Therefore, this study is focused on the investigation of the reaction enthalpies of experimentally observed guaiacol oxidation pathways in gas-phase, as well as in non-polar environment and aqueous solution. Corresponding Density Functional Theory (DFT) calculations were carried out using two hybrid functionals (M06-2X and B3LYP-D3). All reaction enthalpies, as well as Gibbs free energies, were also calculated using composite ab initio G4 method. M06-2X and G4 results show mutual agreement and the best accordance with available experimentally determined reaction enthalpies. Obtained Gibbs free reaction energies indicate that formation of ortho-quinone is thermodynamically preferred to formation of 1,3-benzodioxole at 298 K in studied environments. Moreover, all computational methods confirm that the reaction enthalpy of methoxy group demethylation, i.e. O-C bond dissociation enthalpy (BDE), is substantially lower in comparison to the enthalpy of hydrogen atom transfer from phenolic OH group. In the case of phenoxide anion of guaiacol, which can be formed in ionization supporting solvents, O-C BDE shows further significant decrease, exceeding 50 kJ mol^-1, in comparison to parent molecule.HIGHLIGHTSReaction enthalpies and Gibbs free energies of individual steps of guaiacol transformation to 1,3-benzodioxole or ortho-quinone are studied in three environments.M06-2X functional and composite ab initio G4 methods provide reliable O-H and O-C bond dissociation enthalpies.Dissociation enthalpy of methoxy group O-C bond is lower by ca. 100 kJ mol^-1 in comparison to phenolic O-H bond.Phenoxide anion of guaiacol shows substantially lower O-C BDE than parent molecule.

Antioxidant and Hypoglycemic Activity of Sequentially Extracted Fractions from Pingguoli Pear Fermentation Broth and Identification of Bioactive Compounds

Pear fruits have been reported to contain abundant bioactive compounds and exhibit antidiabetic activity. In this study, Pingguoli pear (Pyrus pyrifolia cv.‘Pingguoli’) fermentation broth was sequentially extracted by five solvents with increasing polarity (petroleum ether, chloroform, ethyl acetate, n-butanol, and water) to evaluate its antioxidant and hypothermic activities, and then the main compounds of the fraction with the highest activity were assessed, which might be responsible for such activities. The results showed that the ethyl acetate fraction (EAF) exhibited the highest antioxidant activity according to DPPH (IC₅₀ = 0.238 mg/mL), ABTS (IC₅₀ = 0.293 mg/mL), and FRAP (IC₅₀ = 0.193 mg/mL) assays. The in vitro hypoglycemic activity assay showed that EAF exhibited the strongest inhibitory effect, with IC₅₀ values of 0.34 and 0.95 mg/mL for α-amylase and α-glucosidase, respectively. The glucose consumption in HepG2 cells treated with EAF was significantly increased to 252%, compare with control group. Liquid chromatography–mass spectrometry analysis implied that the main compounds, 3′-C-glucosylisoliquiritigenin, robustside D, caffeic acid, and chlorogenic acid may be potential candidates for the antioxidant and hypoglycemic activities of the EAF. This study suggested that EAF of Pingguoli pear fermentation broth could be utilized for development of potential functional food and antidiabetic agents.

Antioxidant, antimicrobial, and molecular docking studies of novel chalcones and Schiff bases bearing 1, 4-naphthoquinone moiety

Background:

The 1,4-naphthoquinone ring has attracted prominent interest in the field of medicinal chemistry due to its potent pharmacological activity as antioxidant, antibacterial, antifungal, and anticancer.

Objective:

Herein, a series of new Schiff bases (4-6) and chalcones (8a-c & 9a-d) bearing 1,4-naphthoquinone moiety were synthesized in good yields and were subjected to in-vitro antimicrobial, antioxidant, and molecular docking testing.

Methods:

A facile protocol has been described in this study for the synthesis of new derivatives (4-7, 8a-c, and 9a-d) bearing 1,4-naphthoquinone moiety. The chemical structures of all the synthesized compounds were identified by 1H-NMR, 13C-NMR, MS, and elemental analyses. Moreover, these derivatives were assessed for their in-vitro antimicrobial activity against gram-positive, gram-negative bacteria, and fungal strains. Further studies were conducted to test their antioxidant activity using DPPH (2,2-diphenyl-1-picrylhydrazyl) scavenging assay. Molecular docking studies were realized to identify the most likely interactions of the novel compounds within the protein receptor.

Results:

The antimicrobial results showed that most of the compounds displayed good efficacy against both bacterial and fungal strains. The antioxidant study revealed that compounds 9d, 9a, 9b, 8c, and 6 exhibited the highest radical scavenging activity. Docking studies of the most active antimicrobial compounds within GLN- 6-P, recorded good scores with several binding interactions with the active sites.

Conclusion:

Based on the obtained results, it was found that compounds 8b, 9b, and 9c displayed the highest activity against both bacterial and fungal strains. The obtained findings from the DPPH radical scavenging method revealed that compounds 9d and 9a exhibited the strongest scavenging potential. The molecular docking studies proved that the most active antimicrobial compounds 8b, 9b and 9c displayed the highest energy binding scores within the glucosamine-6-phosphate synthase (GlcN-6-P) active site.

Adsorption and selectivity studies of direct and magnetite-cored molecularly imprinted polymers (MIPs and magMIPs) towards chosen chalcones investigated with various analytical methods

The following article presents a method for obtaining molecularly imprinted polymers (MIPs) dedicated to trans-chalcone (TC) and 2',4'-dihydroxy-3-methoxychalcone (DHMC). The synthetic protocol optimized with a choice of the most suitable functional monomer led to the synthesis of MIPs and their non-imprinted equivalents (NIP) performed via direct polymerization or on the surface of magnetite nanoparticles. The characterized materials were investigated for adsorption isotherms of TC and DHMC, which led to satisfactory values of maximal adsorption capacity, reaching 131.58 and 474.71 mg g^-1, respectively. Moreover, all the polymers were studied for the adsorption kinetics and the selectivity towards four structurally different chalcones, which proved the proper selectiveness towards the template molecules. Also, the kinetic profiles of chalcones' adsorption on the synthesized MIPs showed a quasi-plateau reached already after 2 hours, indicating high sorption effectiveness. The studies involved the use of various analytical techniques, which afforded a comprehensive and reliable description of the materials' adsorption efficacy. It was found that the materials successfully bind the MIP-complementary analytes and also structurally similar chalcones, with slightly lower intensity.

Antioxidant and Signal-Modulating Effects of Brown Seaweed-Derived Compounds against Oxidative Stress-Associated Pathology

The biological and therapeutic properties of seaweeds have already been well known. Several studies showed that among the various natural marine sources of antioxidants, seaweeds have become a potential source of antioxidants because of their bioactive compounds. Most of the metabolic diseases are caused by oxidative stress. It is very well known that antioxidants have a pivotal role in the treatment of those diseases. Recent researches have revealed the potential activity of seaweeds as complementary medicine, which have therapeutic properties for health and disease management. Among the seaweeds, brown seaweeds (Phaeophyta) and their derived bioactive substances showed excellent antioxidant properties than other seaweeds. This review focuses on brown seaweeds and their derived major bioactive compounds such as sulfated polysaccharide, polyphenol, carotenoid, and sterol antioxidant effects and molecular mechanisms in the case of the oxidative stress-originated disease. Antioxidants have a potential role in the modification of stress-induced signaling pathways along with the activation of the oxidative defensive pathways. This review would help to provide the basis for further studies to researchers on the potential antioxidant role in the field of medical health care and future drug development.

Antioxidant Activity and Mechanism of Avenanthramides: Double H+/e- Processes and Role of the Catechol, Guaiacyl, and Carboxyl Groups

Avenanthramides (AVAs), unique phenolic compounds in oats, have attracted increasing interest due to their health benefits. Eight representative AVAs were studied using the density functional theory (DFT) method to elucidate their antioxidant activity and mechanism. Preference of different mechanisms was evaluated based on thermodynamic descriptors involved in double (2H⁺/2e^-) free radical scavenging reactions. It was found that the hydrogen atom transfer (HAT) mechanism is more favorable in the gas and benzene phases, while sequential proton loss electron transfer (SPLET) is preferred in polar media. The results suggest the feasibility of the double HAT and double SPLET mechanisms for 2s and c-series AVAs. The sequential triple proton loss double electron transfer (StPLdET) mechanism represents the dominant pathway in aqueous solution at physiological pH. In addition, the sequential proton loss hydrogen atom transfer (SPLHAT) mechanism provides an alternative pathway to trap free radicals. Results also revealed the important role of the catechol, guaiacyl, and carboxyl moieties.

Synthesis of Biobased Phloretin Analogues: An Access to Antioxidant and Anti-Tyrosinase Compounds for Cosmetic Applications

The current cosmetic and nutraceutical markets are characterized by a strong consumer demand for a return to natural products that are less harmful to both the consumers and the environment than current petrosourced products. Phloretin, a natural dihydrochalcone (DHC) found in apple, has been widely studied for many years and identified as a strong antioxidant and anti-tyrosinase ingredient for cosmetic formulations. Its low concentration in apples does not allow it to be obtained by direct extraction from biomass in large quantities to meet market volumes and prices. Moreover, its remarkable structure prevents its synthesis through a green process. To overcome these issues, the synthesis of phloretin analogs appears as an alternative to access valuable compounds that are potentially more active than phloretin itself. Under such considerations, 12 chalcones (CHs) and 12 dihydrochalcones (DHCs) were synthesized through a green Claisen-Schmidt condensation using bio-based reagents. In order to evaluate the potential of these molecules, radical scavenging DPPH and anti-tyrosinase tests have been conducted. Moreover, the UV filtering properties and the stability of these analogs towards UV-radiations have been evaluated. Some molecules showed competitive antioxidant and anti-tyrosinase activities regarding phloretin. Two compounds in particular showed EC₅₀ lower than phloretin, one chalcone and one dihydrochalcone.

Hydroxylated Chalcones as Aryl Hydrocarbon Receptor Agonists: Structure-Activity Effects

Hydroxylated chalcones are phytochemicals which are biosynthetic precursors of flavonoids and their 1,3-diaryl-prop-2-en-1-one structure is used as a scaffold for drug development. In this study, the structure-dependent activation of aryl hydrocarbon receptor (AhR)-responsive CYP1A1, CYP1B1, and UGT1A1 genes was investigated in Caco2 colon cancer cells and in non-transformed young adult mouse colonocytes (YAMC) cells. The effects of a series of di- and trihydroxychalcones as AhR agonists was structure dependent with maximal induction of CYP1A1, CYP1B1, and UGT1A1 in Caco2 cells observed for compounds containing 2,2'-dihydroxy substituents and this included 2,2'-dihydroxy-, 2,2',4'-trihydroxy-, and 2,2',5'-trihydroxychalcones. In contrast, 2',4,5'-, 2'3',4'-, 2',4,4'-trihydroxy, and 2',3-, 2',4-, 2',4'-, and 2',5-dihydroxychalcones exhibited low to non-detectable AhR activity in Caco2 cells. In addition, all of the hydroxychalcones exhibited minimal to non-detectable activity in YAMC cells, whereas 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced CYP1A1, CYP1B1, and UGT1A1 in Caco2 and YAMC cells. The activity of AhR-active chalcones was confirmed by determining their effects in AhR-deficient Caco2 cells. In addition, 2,2'-dihydroxychalcone induced CYP1A1 protein and formation of an AhR-DNA complex in an in vitro assay. Simulation and modeling studies of hydroxylated chalcones confirmed their interactions with the AhR ligand-binding domain and were consistent with their structure-dependent activity as AhR ligands. Thus, this study identifies hydroxylated chalcones as AhR agonists with potential for these phytochemicals to impact AhR-mediated colonic pathways.

Quantum chemical investigation of the antiradical property of avenanthramides, oat phenolics

Avenanthramides (AVs) are polyphenolic components found in oats. The present work is devoted to the exploration of structure-based radical scavenging activity of nine AVs; 2p, 2f, 2c, 1p, 1c, 1f, 1s, 2s, and 3f, using M06-2X functional level of density functional theory with basis set 6-31+G(d, p) both in gas and ethanol medium. The act of compounds towards the electron transfer mechanism was analyzed with the help of a Donor-acceptor map (DAM) and classified as antioxidants and anti-reductants. The main mechanism of radical action, HAT, SET-PT, and SPLET were examined and found to be the preference of HAT and SPLET respectively in the gas phase and ethanol medium. The computed quantum mechanical atom in molecule (QTAIM) parameters; the intramolecular H-bonding, Noncovalent interactions, aromaticity also acted as pillars to supports the activity of compounds. The activity was found to be increasing with the stabilizing group ortho to the reactive phenolic OH group.

Chalcones as Scavengers of HOCl and Inhibitors of Oxidative Burst: Structure-Activity Relationship Studies

AIMS

Evaluate the ability of chalcones to scavenge hypochlorous acid (HOCl) and modulate oxidative burst.

BACKGROUND

The chemistry of chalcones has long been a matter of interest to the scientific community due to the phenolic groups often present and to the various replaceable hydrogens that allow the formation of a broad number of derivatives. Due to this chemical diversity, several biological activities have been attributed to chalcones, namely anti-diabetic, anti-inflammatory and antioxidant.

OBJECTIVES

Evaluate the ability of a panel of 34 structurally related chalcones to scavenge HOCl and/or suppress its produc-tion through the inhibition of human neutrophils' oxidative burst, followed by the establishment of the respective structure-activity relationships.

METHODS

The ability of chalcones to scavenge HOCl was evaluated by fluorimetric detection of the inhibition of dihydro-rhodamine 123 oxidation. The ability of chalcones to inhibit neutrophils' oxidative burst was evaluated by chemiluminomet-ric detection of the inhibition of luminol oxidation.

RESULTS

It was observed that the ability to scavenge HOCl depends on the position and number of hydroxy groups on both aromatic rings. Chalcone 5b was the most active with an IC50 value of 1.0 ± 0.1 μM. The ability to inhibit neutrophils' oxi-dative burst depends on the presence of a 2'-hydroxy group on A-ring and on other substituents groups, e.g. methoxy, hy-droxy, nitro and/or chlorine atom(s) at C-2, C-3 and/or C-4 on B-ring, as in chalcones 2d, 2f, 2j, 2i, 4b, 2n and 1d, which were the most actives with IC50 values ranging from 0.61 ± 0.02 μM to 1.7 ± 0.2 μM.

CONCLUSION

The studied chalcones showed high activity at a low micromolar range, indicating their potential as antioxidant agents and to be used as a molecular structural scaffold for the design of new anti-inflammatory compounds.

Antioxidant activity and mechanism of dihydrochalcone C-glycosides: Effects of C-glycosylation and hydroxyl groups

Dihydrochalcones (DHCs), an important subgroup of flavonoids, have recently received much attention due to their diverse biological activities. In contrast to their O-glycosides, understanding of the antioxidant property and mechanism of DHC C-glycosides remains limited. Herein, the free radical scavenging activity and mechanism of two representative C-glycosyl DHCs, aspalathin (ASP) and nothofagin (NOT) as well as their aglycones, 3-hydroxyphloretin (HPHL) and phloretin (PHL) were evaluated using the density functional theory (DFT) calculations. The results revealed the crucial role of sugar moiety on the conformation and the activity. The o-dihydroxyl in the B-ring and the 2',6'-dihydroxyacetophenone moiety were found significant in determining the activity. Our results showed that hydrogen atom transfer (HAT) is the dominant mechanism for radical-trapping in the gas and benzene phases, while the sequential proton loss electron transfer (SPLET) is more preferable in the polar environments. Also, the results revealed the feasibility of the double HAT and double SPLET as well as the SPLHAT mechanisms, which provide alternative pathways to trap radical for the studied DHCs. These results could deepen the understanding of the antiradical activity and mechanism of DHCs, which will facilitate the design of novel efficient antioxidants.

Density Functional Theory Studies on the Antioxidant Mechanism and Electronic Properties of Some Bioactive Marine Meroterpenoids: Sargahydroquionic Acid and Sargachromanol

Certain meroterpenoids isolated from brown alga of the genus Sargassum are known to be antioxidant agents. Herein, density functional theory has been performed to analyze the preferred antioxidant mechanism of the two reactive antioxidant compounds derived from the Sargassum genus, that is, Sargahydroquinoic acid and Sargachromanol and some of their derivatives. Their global reactivity descriptors have been calculated to reveal their reactivity as an antioxidant. Molecule 1 is the most reactive antioxidant according to calculated descriptors. The results of molecule 1 are comparable to that of Trolox, suggesting their similar activity. The calculated descriptors are closely matched with experimental pieces of evidence. It has been found that hydrogen atom transfer (HAT) is more favored in gas media. Also, the effect of solvent polarity on the antioxidant activity has been explored for molecule 1. The results disclose that the polarity of the solvent increases the contribution of two other mechanisms, that is, single-electron transfer, followed by proton transfer and sequential proton loss electron transfer.

Antioxidative potential of ferulic acid phenoxyl radical

The vast majority of previous studies dealing with antioxidant potency of (poly)phenols does not investigate the fate of phenoxyl radical obtained after single free radical scavenging. We investigated possible pathways of inactivation of ferulic acid phenoxyl radical (FAPR) using DFT method. Direct coupling with a set of 10 physiologically important free radicals, H-atom donation and dimerization were analysed by estimation of Gibbs free energy changes related to these processes. The former two processes are thermodynamically feasible to inactivate more dangerous free radicals such as hydroxyl, alkoxyl and carbon-centered radicals. Among dimerization reactions, the least energy demanding is formation of C-5-C-5 dimer of ferulic acid (FA), which has higher antiradical potency than FA itself. Obtained results reveal that FAPR, a priori considered as stable and unreactive, may contribute to the overall antioxidant activity of FA. This is a beneficial behavior, which makes FA a particularly valuable protector against oxidative stress. Hence, the contribution of phenoxyl radicals to the antioxidant activity of (poly)phenolic compounds should be taken into account, what has been scarcely considered until now.

Synthesis, biological activity and molecular modeling of a new series of condensed 1,2,4-triazoles

A ring transformation of 6-methyl-7H[1,2,4]triazolo [4,3-b][1,2,4] triazepine-8(9H)-ones (thiones) in the presence of acetic anhydride give rise to a new series of 17 condensed 1,2,4-triazole derivatives (1-17). Plausible mechanisms are proposed and show the formation of a beta fused β-lactam moiety. The compounds were tested for their (i) inhibitory potential on digestive enzymes (α-amylase and α-glucosidase), and (ii) antioxidant activity using radical scavenging (DPPH and ABTS radicals) and ferric reducing power assays. The compounds showed interesting and promising antidiabetic activities compared to the reference drug Acarbose. Molecular docking study has been carried out to determine the binding mode interactions between these derivatives and the targeted enzymes. The results showed the strength of intermolecular hydrogen bonding in ligand-receptor complexes as an important descriptor in rationalizing the observed inhibition results. Moreover, molecular dynamics simulations are also performed for the best protein-ligand complex to understand the stability of small molecule in a protein environment. To shed light on the antioxidant activity of the synthesized compounds and the mechanism involved in DPPH free radical, DFT calculations were performed at the B3P86/6-311++G(d,p) level using the polarizable continuum model. The effect of aprotic solvent on bond dissociation enthalpies (BDEs) is investigated by calculating and comparing BDEs of 1 in methanol and dimethylsulfoxide as solvents using PCM. The obtained results show that the mechanism of action depends on the basic skeleton and the presence of substituted functional groups in these derivatives. BDEs are found to be slightly influenced by the aprotic solvent of less than 0.01 kcal/mol compared with those obtained in methanol.

Lignin Modification Supported by DFT-Based Theoretical Study as a Way to Produce Competitive Natural Antioxidants

The valorization of lignins as renewable aromatic feedstock is of utmost importance in terms of the use of sustainable resources. This study provides a deductive approach towards market-oriented lignin-derived antioxidants by ascertaining the direct effect of different structural features of lignin on the reactivity of its phenolic OH groups in the radical scavenging reactions. The antioxidant activity of a series of compounds, modeling lignin structural units, was experimentally characterized and rationalized, using thermodynamic descriptors. The calculated O–H bond dissociation enthalpies (BDE) of characteristic lignin subunits were used to predict the modification pathways of technical lignins. The last ones were isolated by soda delignification from different biomass sources and their oligomeric fractions were studied as a raw material for modification and production of optimized antioxidants. These were characterized in terms of chemical structure, molecular weight distribution, content of the functional groups, and the antioxidant activity. The developed approach for the targeted modification of lignins allowed the products competitive with two commercial synthetic phenolic antioxidants in both free radical scavenging and stabilization of thermooxidative destruction of polyurethane films.

DFT and QTAIM based investigation on the structure and antioxidant behavior of lichen substances Atranorin, Evernic acid and Diffractaic acid

In this study, the structural and antioxidant behavior of the three lichen-derived natural compounds such as atranorin (AT), evernic acid (EV) and diffractaic acid (DF) has been investigated in the gas and water phase using both B3LYP and M06-2X functional level of density functional theory (DFT) with two different basis sets 6-31+G (d, p) and 6-311++G (d, p). The intramolecular H-bonds (IHB) strength, aromaticity and noncovalent interactions (NCI) have been computed with the help of the quantum theory of atoms in molecules (QTAIM). This calculation gives major structural characteristics that indirectly influence the antioxidant behavior of the investigated compounds. The spin density (SD) delocalization of the unpaired electron is found to be the main stabilizing factor of neutral and cationic radical species. The main mechanisms, recommended in the literature, for the antioxidant action of polyphenols as radical scavengers such as hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET), were examined. The result shows that the HAT and SPLET mechanism are the most conceivable one for the antioxidant action of this class of compounds in gas and water phase respectively. Preference of SPLET over HAT in water phase is due to the significantly lower value of proton affinity (PA) compared to the bond dissociation enthalpy (BDE) value. This study reveals that O₂-H₃, O₉-H₂₆ and O₄-H₄₅ respectively are the most favored site of AT, EV and DF for homolytic as well as heterolytic OH bond breaking.

Design, synthesis and biological evaluation of chalcone analogues with novel dual antioxidant mechanisms as potential anti-ischemic stroke agents

Scavenging reactive oxygen species (ROS) by antioxidants is the important therapy to cerebral ischemia-reperfusion injury (CIRI) in stroke. The antioxidant with novel dual-antioxidant mechanism of directly scavenging ROS and indirectly through antioxidant pathway activation may be a promising CIRI therapeutic strategy. In our study, a series of chalcone analogues were designed and synthesized, and multiple potential chalcone analogues with dual antioxidant mechanisms were screened. Among these compounds, the most active 33 not only conferred cytoprotection of H2O2-induced oxidative damage in PC12 cells through scavenging free radicals directly and activating NRF2/ARE antioxidant pathway at the same time, but also played an important role against ischemia/reperfusion-related brain injury in animals. More importantly, in comparison with mono-antioxidant mechanism compounds, 33 exhibited higher cytoprotective and neuroprotective potential in vitro and in vivo. Overall, our findings showed compound 33 could emerge as a promising anti-ischemic stroke drug candidate and provided novel dual-antioxidant mechanism strategies and concepts for oxidative stress-related diseases treatment.

Crystal structure and optical spectroscopic analyses of (E)-3-(1H-indol-2-yl)-1-(4-nitro-phen-yl)prop-2-en-1-one hemihydrate

The asymmetric unit of the title compound, 2C17H12N2O3·H2O comprises two mol-ecules of (E)-3-(1H-indol-2-yl)-1-(4-nitro-phen-yl)prop-2-en-1-one and a water mol-ecule. The main mol-ecule adopts an s-cis configuration with respect to the C=O and C=C bonds. The dihedral angle between the indole ring system and the nitro-substituted benzene ring is 37.64 (16)°. In the crystal, mol-ecules are linked by O--H⋯O and N-H⋯O hydrogen bonds, forming chains along [010]. In addition, weak C-H⋯O, C-H⋯π and π-π inter-actions further link the structure into a three-dimensional network. The optimized structure was generated theoretically via a density functional theory (DFT) approach at the B3LYP/6-311 G++(d,p) basis level and the HOMO-LUMO behaviour was elucidated to determine the energy gap. The obtained values of 2.70 eV (experimental) and 2.80 eV (DFT) are desirable for optoelectronic applications. The inter-molecular inter-actions were qu-anti-fied and analysed using Hirshfeld surface analysis.

4- O -Caffeoylquinic acid as an antioxidant marker for mulberry leaves rich in phenolic compounds

Mulberry (Morus alba L.) leaves are widely used as herbal tea to prevent heat stroke. Potential chemical markers of the antioxidant properties and its correlation with harvesting times and leaf location were explored in this study. A 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging assay guided isolation of mulberry leaves extract provided five phenolic compounds: 5-O-caffeoylquinic acid (1), 4-O-caffeoylquinic acid (2), gastrodin (3), isoquercetin (4) and rutin (5). The 50% radical-scavenging concentrations (SC₅₀) of these compounds were 32.76 ± 0.27, 11.41 ± 0.48, 404.30 ± 4.92, 10.63 ± 0.96, and 10.57 ± 0.61 μg/mL, respectively. Chromatographic fingerprinting allowed content analysis of 1–5 in samples over a 12-month period. Compounds 1–5 were abundance in apical leaves (0–10 cm) in January and February at temperatures < 20 °C. Contents of 2 and 5 were highest in these months and were strongly correlated to the antioxidant property. Therefore, we suggested that the mulberry leaves harvested during January and February have high yield of 4-O-caffeoylquinic acid and this compound can be used as antioxidative marker in mulberry leaves.

Impacts of hydroxylation on the photophysics of chalcones: insights into the relation between the chemical composition and the electronic structure

A combined theoretical/experimental study of the photoreactivity of two flavylium-derived chalcones, 2,4,4'-trihydroxychalcone and 2,4'-dihydroxychalcone, at the multiconfigurational wavefunction level of theory (CASSCF//CASPT2) in vacuo and in an implicit solvent (water, treated as a polarisable continuum) and by means of linear absorption spectroscopy is presented. The photosensitivity of flavium salts is expressed in the ability of their chalcone form to undergo a cis-trans isomerisation which has found application in logical networks. Despite a considerable amount of experimental data documenting the dependence of the isomerisation on solvent, pH and temperature, the knowledge of how chalcones process energy under various conditions at the molecular level is still scarce. On the example of 2,4,4'-trihydroxychalcone we unravel the complex excited state deactivation mechanism in vacuo involving ultrafast decay through conical intersections, formation of twisted intramolecular charge transfer species, intramolecular proton transfer and inter system crossings. Furthermore, we rationalise the observed discrepancies in the linear absorption spectra of 2,4,4'-trihydroxychalcone and 2,4'-dihydroxychalcone, thereby establishing a link between the functionalisation pattern and the observed spectral properties.

Absence of genotoxic effects of the chalcone (E)-1-(2-hydroxyphenyl)-3-(4-methylphenyl)-prop-2-en-1-one) and its potential chemoprevention against DNA damage using in vitro and in vivo assays

The chalcone (E)-1-(2-hydroxyphenyl)-3-(4-methylphenyl)-prop-2-en-1-one), or 2HMC, displays antileishmanial, antimalarial, and antioxidant activities. The aim of this study was to investigate the cytotoxic, genotoxic, mutagenic, and protective effects of 2HMC using the Ames mutagenicity test, the mouse bone marrow micronucleus test, and the comet assay in mice. In the assessment using the Ames test, 2HMC did not increase the number of His⁺ revertants in Salmonella typhimurium strains, demonstrating lack of mutagenicity. 2HMC showed no significant increase in micronucleated polychromatic erythrocyte frequency (MNPCE) in the micronucleus test, or in DNA strand breaks using the comet assay, evidencing absence of genotoxicity. Regarding cytotoxicity, 2HMC exhibited moderate cytotoxicity in mouse bone marrow cells by micronucleus test. 2HMC showed antimutagenic action in co-administration with the positive controls, sodium azide (SA) and 4-nitroquinoline-1-oxide (4NQO), in the Ames test. Co-administered and mainly pre-administered with cyclophosphamide (CPA), 2HMC caused a decrease in the frequency of MNPCE using the micronucleus test and in DNA strand breaks using the comet assay. Thus, 2HMC exhibited antimutagenic and antigenotoxic effects, displaying a DNA-protective effect against CPA, SA, and 4NQO carcinogens. In conclusion, 2HMC presented antimutagenic, antigenotoxic and moderate cytotoxic effects; therefore it is a promising molecule for cancer prevention.

Benchmarking the DFT methodology for assessing antioxidant-related properties: quercetin and edaravone as case studies

The overall objective was to identify an accurate computational electronic method to virtually screen phenolic compounds through their antioxidant and free-radical scavenging activity. The impact of a key parameter of the density functional theory (DFT) approach was studied. Performances of the 21 most commonly used exchange-correlation functionals are thus detailed in the evaluation of the main energetic parameters related to the activities of two prototype antioxidants, namely quercetin and edaravone, is reported. These functionals have been chosen among those belonging to three different families of hybrid functionals, namely global, range separated, and double hybrids. Other computational parameters have also been considered, such as basis set and solvent effects. The selected parameters, namely bond dissociation enthalpy (BDE), ionization potential (IP), and proton dissociation enthalpy (PDE) allow a mechanistic evaluation of the antioxidant activities of free radical scavengers. Our results show that all the selected functionals provide a coherent picture of these properties, predicting the same order of BDEs and PDEs. However, with respect to the reference values, the errors found at CBS-Q3 level significantly vary with the functional. Although it is difficult to evidence a global trend from the reported data, it clearly appears that LC-ωPBE, M05-2X, and M06-2X are the most suitable approaches for the considered properties, giving the lowest cumulative mean absolute errors. These methods are therefore suggested for an accurate and fast evaluation of energetic parameters related to an antioxidant activity via free radical scavenging.