Characterization and density functional theory study of the antioxidant activity of quercetin and its sugar-containing analogues

Theoretical studies on the antioxidant activity of potential marine xanthones

In this study, a quantum chemical exploration was conducted to assess the antioxidant activity of xanthones isolated from marine sources, focusing on thermodynamics and kinetics within simulated physiological environments. DFT analysis revealed that xanthones such as 1,4,7-trihydroxy-6-methylxanthone (1), 1,4,5-trihydroxy-2-methylxanthone (2), arthone C (3), 2,3,4,6,8-pentahydroxy-1-methylxanthone (4), sterigmatocystin (5), oxisterigmatocystin C (6), and oxisterigmatocystin D (7) favor the SPLET pathway in water and the FHT pathway in lipid environments. The kinetic study of these xanthones reacting with the hydroperoxyl radical (HOO•) was conducted using the formal hydrogen atom transfer (FHT) mechanism and the single electron transfer (SET) mechanism. The results showed that compounds 1-4 exhibited antioxidant activities in aqueous environments surpassing that of the reference compound Trolox, with rate constants ranging from 2.02 x 105 to 9.44 x 107 M-1·s-1. In lipid environments, compounds 1 and 2 also demonstrated higher rate constants than Trolox. Additionally, molecular docking and molecular dynamics analysis suggested that xanthones 1-7 potentially inhibit the pro-oxidant effect of the Keap1 enzyme, highlighting their promise as both antiradicals and enzyme inhibitors.

Antioxidant activity of an inclusion complex between rutin and β-cyclodextrin: experimental and quantum chemical studies

This study aims to synthesize a guest-host complex derived from rutin (Rut) and β-cyclodextrin (β-CD) (denoted as [Rut⊂β-CD]). The obtained substance was characterized by the FT-IR and DSC methods, signifying the formation of an inclusion complex between Rut and β-CD. Complex formation increased the antioxidant activity of rutin corresponding to the decrease of EC50 values from 1.547 × 10-5 mol L-1 to 1.227 × 10-5 mol L-1 according to the DPPH free radical scavenging test. The rutin-β-CD interaction energies were calculated in the vacuum and various solvents (e.g., water, ethanol, and dimethylsulfoxide) utilizing an accurate and broadly parametrized self-consistent tight-binding quantum chemical method (GFN2-xTB). The calculation results reveal the influence of solvent on the structural formation of the rutin-β-CD complex. In both the vacuum and aqueous solution, rutin can enter into the small-sized empty cavity of β-CD, albeit through different terminals, resulting in distinct preferential structures. The presence of organic solvents appears to reduce the interaction between rutin and β-CD, with the interaction strength following the order: water > ethanol > dimethyl sulfoxide.

Docking and Electronic Structure of Rutin, Myricetin, and Baicalein Targeting 3CLpro

Understanding the role of 3CLpro protease for SARS-CoV-2 replication and knowing the potential of flavonoid molecules like rutin, myricetin, and baicalein against 3CLpro justify an investigation into their inhibition. This study investigates possible bonds and reactivity descriptors of rutin, myricetin, and baicalein through conformational and electronic properties. Density functional theory was used to determine possible interactions. Analyses were carried out through the molecular electrostatic potential, electron localization function, Fukui function descriptors based on frontier orbitals, and non-covalent interactions. A docking study was performed using a resolution of 1.55 Å for 3CLpro to analyze the interactions of rutin, myricetin, and baicalein. Scores of structures showed that rutin is the best ligand, followed by myricetin and baicalein. Docking studies showed that baicalein and rutin can establish effective interactions with residues of the catalytic dyad (Cys145 and His41), but just rutin forms a hydrogen bond. Myricetin, in turn, could not establish an effective interaction with Cys145. Baicalein interaction arose with active residues such as Arg188, Val186, Gln189, and Gln192. Interactions of rutin and myricetin with Arg188 and Gln189 were also found. A critical interaction was observed only for rutin with the hydroxyls of ring A with His41, and also for Cys145 with rings B and C, which is probably related to the highest score of rutin.

The isolation of anthocyanin monomers from blueberry pomace and their radical-scavenging mechanisms in DFT study

This study explored the isolation of anthocyanin monomers using a medium- and high-pressure separation technique as a means to increase the added value of a by-product of the blueberry juice industry. Six anthocyanin monomers were isolated with a purity of 95% and identified as mono-galactoside, glucoside, and isomers of delphinidin, malvidin, and even malvidin-3-O-arabinoside, malvidin-3-(6″-acetyl)-O-glucoside by LC-MS and ¹H NMR. Following the conformation search, the computer calculation manifested the active sites of six anthocyanins (C_4'-OH) and their stabilities based on the structural and energy parameters. The DPPH tests demonstrated that delphinidin glycoside's free radical scavenging ability (89.93 ± 2.03 % and 86.50 ± 3.16 %) was significantly higher than that of malvidin (80.39 ± 1.30 % and 81.02 ± 0.45 %), and that malvidin's capacity was improved by conjugation arabinoside (87.48 ± 2.39 %) and acetylated glucoside (88.39 ± 1.37 %), which was compatible with the computer calculation.

Extraction and identification of new flavonoid compounds in dandelion Taraxacum mongolicum Hand.-Mazz. with evaluation of antioxidant activities

Due to the interest in the potential pharmacological application of dandelion, the chemical constituents and activities of Taraxacum mongolicum Hand.-Mazz were studied. Box-Behnken response surface methodology was employed to optimize the protocol for extraction of flavonoid from dandelion. The molecular structures of different flavonoid compounds were acquired and analyzed by liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) spectroscopy. Several major flavonoid compounds were isolated and purified, namely, hesperetin-5'-O-β-rhamnoglucoside, hesperetin-7-glucuronide, kaempferol-3-glucoside, baicalein, hyperseroside, which were extracted for the first time from dandelion. Hesperetin-5'-O-β-rhamnoglucoside was identified as a new type of flavonoid that had never reported in the literature. This new flavonoid has outstanding antioxidant activity, as shown by its IC₅₀ value (8.72 mg/L) for scavenging DPPH free radicals. The determination of the structure-related antioxidant activities could be interpreted based on DFT calculations. As such, we have not only illustrated the rich flavonoid contents in Taraxacum mongolicum Hand.-Mazz, but also revealed new types of flavonoid compounds in dandelion in terms of structure and antioxidant properties.

Processing Stabilization of Polyethylene with Grape Peel Extract: Effect of Extraction Technology and Composition

Dry grape peel powder was extracted by three different techniques, stirred tank reactor, Soxhlet and ultrasound extraction. The composition, physical and chemical structure and inherent stability of the extracts were characterized by various methods. The extracts and reference compounds were added to polyethylene and their stabilization efficiency was determined in multiple extrusion experiments. The composition of the extracts was quite similar. Ten main compounds were identified in the extracts, which contained a considerable number of polyphenols, but only small amounts of quercetin and trans-resveratrol. The extracts proved to be more efficient processing stabilizers than trans-resveratrol and the commercial stabilizer, Irganox 1010, irrespective of the extraction technology used. In spite of their good processing stabilization effect, polymers containing the extracts had poor residual stability. The differences in processing and long-term stabilization must be related to the different structures of the polyphenols contained by the extracts and the reference compounds. The results clearly prove that the IC50 value determined by the DPPH assay is not suitable for the estimation of the efficiency of a compound as a stabilizer for polymers.

Fermentation of Agaricus bisporus for antioxidant activity: response surface optimization, chemical components, and mechanism

Agaricus bisporus is one of the most widely cultivated edible mushrooms in the world. The chemical components of A. bisporus have a wide range of biological activities. In order to deeply understand the antioxidant properties of A. bisporus, this study conducted an investigation on the components of A. bisporus fermentation. Through the single factor experiment and response surface optimization, it was found that when the C/N ratio was 45:1, the inoculum concentration was 10%, and the fermentation time was 7 d, the n-butanol extract of the fermentation product had the strongest scavenging capacity for free radical generated through 2,2'-azino-bis(3-ethylbenzothiazoline)-6-sulphonic acid (ABTS·⁺). The concentration for 50% of the maximal effect (EC₅₀) was 0.33 ± 0.01 mg/mL. Moreover, in order to identify the two main components, the elution-extrusion counter-current chromatography (EECCC) was employed for separation, where 5,5'-oxy-dimethyl-bis(2-furfuraldehyde) and 5-(butoxymethyl) furfural were obtained. The antioxidant activity of 5,5'-oxy-dimethyl-bis(2-furfuraldehyde) (EC₅₀ = 0.26 ± 0.01 mg/mL) was superior to that of 5-butylmethyl furfural (EC₅₀ = 1.52 ± 0.02 mg/mL), indicating that 5,5'-oxy-dimethyl-bis(2-furfuraldehyde) was the main antioxidant in the fermentation products. The thermodynamic parameters and frontier molecular orbitals of 5,5'-oxy-dimethyl-bis (2-furanaldehyde) was evaluated by density functional theory (DFT). The result indicated 5,5'-oxy-dimethyl-bis(2-furanaldehyde) scavenged free radicals in polar media through single electron transfer followed by proton transfer (SET-PT).

Antioxidative myricetin-enriched nanoparticles towards acute liver injury

Acute liver injury (ALI) could severely destroy the liver function and cause inevitable damage to human health. Studies have demonstrated that excessive reactive oxygen species (ROS) and accompanying inflammatory factors play vital roles in the ALI disease. Herein, we fabricated a kind of nature-inspired myricetin-enriched nanomaterial via Michael addition and Schiff base reaction, which possessed uniform morphology, tunable component ratios, great stabilities, promising free radical scavenging abilities, biocompatibility and protective effects towards cells under oxidative stress. Additionally, the therapeutic effects were demonstrated using an ALI model by down-regulating ROS and inflammatory levels and restoring the liver function. This study could provide a strategy to construct robust and antioxidative nanomaterials using naturally occurring molecules against intractable diseases.

Multiple Bioactivities of Manihot esculenta Leaves: UV Filter, Anti-Oxidation, Anti-Melanogenesis, Collagen Synthesis Enhancement, and Anti-Adipogenesis

The cassava root is an important global agro-industrial crop that yields cassava leaf as a left-over co-product of interest for further development as a sustainable resource of health and cosmeceutical active compounds. This work aimed to investigate the cosmeceutical potential and chemical composition of an ethanolic cassava leaf extract (BM). rutin, apigenin, and kaempferol were found to be major constituents via HPLC-DAD UV analysis. Interestingly, the multiple beneficial bioactivities of BM for cosmeceutical applications were manifested in a dose-dependent manner, including anti-oxidation in a 2,2-diphenyl-1-picrylhydrazyl assay, anti-melanogenesis in B16 melanoma cells, collagen synthesis enhancement in human fibroblasts, and anti-adipogenesis in 3T3-L1 adipocytes. Furthermore, the potential of the collagen synthesis enhancement of BM and rutin was significant when compared to ascorbic acid. Additionally, a UV filter property comparable to BEMT with characteristics of board spectral absorption and constant high absorptivity throughout all UV wavelength ranges was exhibited by UV-visible spectrophotometric analysis. In conclusion, the cassava leaf was found to be a potential natural cosmeceutical active agent with multiple cosmeceutical-related bioactivities with respect to a substantial composition of bioactive flavonols. These obtained data will support and encourage the further study and development of cassava leaves as potential economic and sustainable sources of bioactive agents for health and cosmeceutical applications.

Antioxidant capacity and interaction of endogenous phenolic compounds from tea seed oil

Endogenous phenols play a significant role in delaying oil rancidity. In this study, the profile of 22 endogenous phenols was determined from tea seed oil by UPLC-MS/MS, of which 15 phenols were identified for the first time. Then seven phenols with high content and strong antioxidant capacity were selected to investigate interaction using the DPPH· and Rancimat. It was found that the interaction of combinations was inconsistent in different media. Combined quercetin + esculetin, caffeoyl tartaric acid + esculetin, caffeoyl tartaric acid + gentisic acid and esculetin + gentisic acid showed synergistic antioxidant effects in oil and ethanol systems. Moreover, through the evaluation of the lipid oxidation process, combined esculetin + gentisic acid exhibited the greatest synergistic antioxidant effect. Notably, combined quercetin + esculetin had an inhibitory effect on the formation of volatile compounds. These findings may provide a basis for explaining the oxidation stability of tea seed oil.

A Guide to Elucidate the Hidden Multicomponent Layered Structure of Plant Cuticles by Raman Imaging

The cuticle covers almost all plant organs as the outermost layer and serves as a transpiration barrier, sunscreen, and first line of defense against pathogens. Waxes, fatty acids, and aromatic components build chemically and structurally diverse layers with different functionality. So far, electron microscopy has elucidated structure, while isolation, extraction, and analysis procedures have revealed chemistry. With this method paper, we close the missing link by demonstrating how Raman microscopy gives detailed information about chemistry and structure of the native cuticle on the microscale. We introduce an optimized experimental workflow, covering the whole process of sample preparation, Raman imaging experiment, data analysis, and interpretation and show the versatility of the approach on cuticles of a spruce needle, a tomato peel, and an Arabidopsis stem. We include laser polarization experiments to deduce the orientation of molecules and multivariate data analysis to separate cuticle layers and verify their molecular composition. Based on the three investigated cuticles, we discuss the chemical and structural diversity and validate our findings by comparing models based on our spectroscopic data with the current view of the cuticle. We amend the model by adding the distribution of cinnamic acids and flavonoids within the cuticle layers and their transition to the epidermal layer. Raman imaging proves as a non-destructive and fast approach to assess the chemical and structural variability in space and time. It might become a valuable tool to tackle knowledge gaps in plant cuticle research.

Benzofuran–stilbene hybrid compounds: an antioxidant assessment – a DFT study

The kinetic reaction of the benzofuran–stilbene hybrid compound 5-(2-(2-(4-hydroxyphenyl)benzofuran-5-yl)vinyl)benzene-1,3-diol captures the HOO˙ free radical.

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.

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.

Antioxidation of 2-phenylbenzofuran derivatives: structural-electronic effects and mechanisms

Stilbenoid-type 2-phenylbenzofuran derivatives, which are widely distributed in nature, are now promising antioxidant agents. In the present study, a quantum computational approach principally based on the DFT/B3LYP method with the 6-311++G(d,p) basis set was used to shed light on free radical scavenging for the isolated compounds stemofurans A-K and S-W. On the basis of the findings and from a thermodynamic perspective, the antioxidant activity of all studied compounds in the gaseous phase was mostly controlled by the O-H bond dissociation enthalpy (BDE), consistent with the hydrogen atom transfer (HAT) mechanism. The solvent effect was investigated, and the hydroxyl radicals of these studied compounds possessed the lowest proton affinity (PA) enthalpy and the sequential proton loss electron transfer (SPLET) pathway occurred in water, methanol and acetone. The studied compounds interacted with DPPH radicals, which is kinetic evidence of the involvement of two intermediates and one transition state. From both thermodynamics and kinetics perspectives, it can be proposed that stemofuran U is likely to be a leader compound in antioxidant drug development due to the presence of a 4'-OH moiety. Regarding the structure-bioactivity relationship, methylation can lead to a decrease in BDE.

Functionalization and antioxidant activity of polyaniline–fullerene hybrid nanomaterials: a theoretical investigation

Functionalized fullerene is one of the most advantageous nanotechnologies to develop novel materials for potential biomedical applications. In this study, we applied the ONIOM-GD3 approach to explore the nucleophilic addition reaction mechanism between polyaniline (emeraldine and leucoemeraldine forms) and fullerene. Potential energy surfaces were also analyzed to predict the predominantly formed products of the functionalized reaction. The themoparameters, such as bond dissociation enthalpy (BDE), ionization energy (IE), and electron affinity (EA), characterized by two mechanisms HAT and SET, were used to evaluate the antioxidant activities of the selected compounds. Moreover, the calculated HOMO, LUMO, and DOS results indicate that the electronic structures of polyaniline–fullerene were significantly affected by the presence of fullerene. The computational results show that C60-L1 seems to be the best antioxidant following the SET mechanism.

Functionalized fullerene is one of the most advantageous nanotechnologies to develop novel materials for potential biomedical applications.

Investigations on the structural, vibrational, computational, and molecular docking studies on potential antidiabetic chemical agent Diosmetin

In the present study, the harmonic vibrational frequencies of Diosmetin(5, 7 dihydroxy-2(3-hydroxy-4 methoxyphenyl) chromen-4-one) have been investigated by both experimental (FTIR and FT-Raman) and theoretical (HF and DFT/B3LYP) method. The calculated harmonic vibrational frequencies were compared with experimental data. A detailed interpretation of the vibrational spectra of the compound has been made on the basis of the calculated potential energy distribution (PED). The ¹ H, ¹³ C NMR chemical shifts and TD-DFT calculations of the molecule were calculated and compared with the available experimental observations. A study on the molecular electrostatic potential surface (MEP) of the compound was performed, and the electrophilic and nucleophilic reactive sites were identified. Furthermore, the inhibition effect of compound against aldose reductase enzyme has been analyzed by molecular docking method, and the results were compared with the standard drug. The docking study indicates that the investigated compound shows better inhibitory activity toward aldose reductase enzyme than the standard drug, and hence this study may be supportive in the field of drug discovery to design more potential antidiabetic agents.

The antioxidant activity and active sites of delphinidin and petunidin measured by DFT, in vitro chemical-based and cell-based assays

A computational DFT B3LYP method with 6-311G (d,p) basis set, the in vitro chemical-based and cellular antioxidant activity (CAA) assays were applied in this study to explain the structure-antioxidant activity relationships of delphinidin and petunidin. The compound molecular structures, spectral properties, frontier orbital energy, and transition state of delphinidin and petunidin were compared. In transition state, the result of the active site (O21-H32 and O22-H33) was consistent with the result of bond length. The frontier orbital theory results indicated that the probable antioxidant activity order was petunidin (0.09126 a.u.) > delphinidin (0.09175 a.u.), which agreed well with the cell-based antioxidant activity determined by CAA. However, the order of ABTS^•+ and DPPH radical scavenging activity was delphinidin > petunidin. Our study could help to provide a rational approach for the investigation of antioxidant activity of phytochemicals. PRACTICAL APPLICATIONS: As anthocyanins, delphinidin and petunidin with great antioxidant activity are widely found in various fruits and vegetables. However, there are many kinds of methods used to measure their antioxidant activity and the antioxidant mechanism which are not concrete and clear. Therefore, it is crucial to study the antioxidant actvity of anthocyanins utilizing the DFT method combined with in vitro chemical-based and cell-based assays. Our study could contribute not only to the elucidation of chemical mechanism of antioxidants and exploration the structural features in essence, but also to promote the further development of phytochemicals in the field of food chemistry and pharmacy.

Fabrication of hesperidin nanoparticles loaded by poly lactic co-Glycolic acid for improved therapeutic efficiency and cytotoxicity

Hesperidin, as a flavonone, is recognized as promising anti-inflammatory, antioxidant, and anticancer agent. Its poor bioavailability is crucial bottleneck for therapeutic efficacy. To enhance the stability and bioactive potentials, hesperidin -PLGA-Poloxamer 407 was successfully prepared to minimize or overcome problems associated with hesperidin absorption. The characteristics of nanohesperidin were testing by in vitro dissolution study, XRD, FTIR, PSA and SEM. Antioxidant effects of nanohesperidin were studied. The structure-activity relationship analysis with antioxidant pharmacophore has been performed by using density functional theory method and quantum chemical calculations. The structural properties were investigated using Becke three-parameter hybrid exchange and the Lee-Yang-Parr correction functional methods. Nanohesperidin was found to decrease the H₂O₂ activity-induced DNA instability. Blood compatibility on human erythrocytes was confirmed by haemolytic and in vitro toxicity assessments. The in vitro anticancer activity of nanohesperidin towards MCF-7 cells using various parameters was carried out. The nanohesperidin was found to exert cell growth arrest, activated DNA fragmentation and induced apoptotic cell death through caspase-3 and p53-dependent pathways. These findings showed that nanohesperidin play an important role in its anticancer effects, suggesting might be used for clinical trials and can represent driving formulation for novel chemotherapeutic agents.

Molecular structure and spectral characteristics of hyperoside and analysis of its molecular imprinting adsorption properties based on density functional theory

The structure of hyperoside was optimized according to the skeletal types of different galactopyranosides in hyperoside at the DFT/B3LYP/6-31++G(d,p) level, and the frequencies were calculated. The accuracy of the theoretical calculations of the ¹H and ¹³C NMR signals was evaluated by linear correlation. The excited state was calculated via time-dependent density functional theory (TD-DFT). The stable conformation, NMR, UV-vis, natural bond orbital (NBO), molecular electrostatic potential (MEP) and thermodynamic information were obtained. In the most stable conformation of hyperoside, seven intramolecular hydrogen bonds are formed, which affect the imprinting efficiency. The theoretical ¹H and ¹³C NMR results are in good agreement with the experimental results. The B3PW91 function is more suitable than B3LYP for TD-DFT calculations. Combining the UV-vis and NBO analyses, the HOMO→LUMO transition mainly results from the n→π^∗ transition of the phenolic hydroxyl groups and the π→π^∗ transition of the benzene ring on the B ring in ethanol. The HOMO-1→LUMO+1 transition mainly results from the n→π^∗ and π→π^∗ transition on the A ring. The MEP and NBO calculations indicate that the imprinted active sites are mainly located on the carbonyl oxygen atom and the hydroxyl hydrogen atoms. As the temperature increases, the molecular heat capacity, entropy, enthalpy, and activity of the imprinting sites increase. The obtained results provide strong theoretical guidance for hyperoside in the synthesis of molecularly imprinted polymers and separation techniques.

Synthesis, Antioxidant Activity and Cytotoxicity of N-Functionalized Organotellurides

The use of antioxidants is the most effective means to protect the organism against cellular damage caused by oxidative stress. In this context, organotellurides have been described as promising antioxidant agents for decades. Herein, a series of N-functionalized organotellurium compounds has been tested as antioxidant and presented remarkable activities by three different in vitro chemical assays. They were able to reduce DPPH radical with IC₅₀ values ranging from 5.08 to 19.20 µg mL^-1, and some of them also reduced ABTS⁺ radical and TPTZ-Fe³⁺ complex in ABTS⁺ and FRAP assays, respectively. Initial structure-activity relationship discloses that the nature of N-substituent strongly influenced both activity and cytotoxicity of the studied compounds. Furthermore, radical scavenging activities of N-functionalized organotellurides have been compared with those of their selenilated congeners, demonstrating that the presence of tellurium atom has an essential role in antioxidant activity.

Effects of nitro- and amino-group on the antioxidant activity of genistein: A theoretical study

Five novel compounds (Gen-NO₂, Gen-2NO₂, Gen-NH₂, Gen-2NH₂ and Gen-6NH₂) have been designed via introducing an electron-withdrawing group -NO₂ and an electron-donating group -NH₂ into the structure of genistein. The effects of -NO₂ and -NH₂ groups on the antioxidant ability of genistein were investigated via quantum chemistry method in gas and methanol phases. The crucial parameters related to three antioxidant mechanisms were calculated. Moreover, the frontier molecular orbital, natural bond orbital and global descriptive parameters were calculated to evaluate the reactivity of genistein and its derivatives. Calculated results indicate the antioxidant process of genistein and its derivatives inclines to the hydrogen atom transfer (HAT) and sequential proton loss electron transfer (SPLET) mechanisms in gas and methanol phases, respectively. Moreover, introducing -NH₂ group into genistein can improve its antioxidant activity owing to the outstanding activities of amino-substituents of genistein, which will provide valuable guidance for the synthesis of new antioxidants experimentally.

Calculated antioxidant activity of selected phenolic compounds

Determination of the corresponding bond dissociation enthalpy, ionization potential and proton affinity, dipole moment values, highest occupied molecular orbital eigenvalues, and spin density along with the bioactivity score is central to the antioxidant activity evaluation in this paper. Molecular geometries were optimized with DFT using B3LYP and UB3LYP for parent, ionic, and radical species and 6-311+G(d,p) basis set. Bioactivity, drug likeness, and drug scores were calculated using freely available cheminformatics programs for data visualization and analysis. Overall, the values revealed two structures as promising molecules because of good reaction enthalpies (ΔHr). Lipinski rules were fully satisfied for all molecules.

Structure-function relationships of hydroxyl radical scavenging and chromium-VI reducing cysteine-tripeptides derived from rye secalin

The aim of the study was to determine the activity of four rye peptides and molecular descriptors responsible for the detected biological function. The activity was determined using hydroxyl radical scavenging and chromium-VI (Cr(VI) reducing assays while the density functional theory (DFT) was used for molecular descriptors (i.e. structure-activity relationships). It was found that at pH 7.4, peptide CQV had the highest Cr(VI) reducing activity (76%) followed by QCA (30.8%) while other peptides had less than 25% reduction. All tested peptides were less active at pH 3.0 and this was due to poor spatial proximity of thiol and amine on the glutamine side chain. In the hydroxyl radical scavenging assay, CQV had the highest activity with 28.9 ± 1.3% inhibition of the formation of HO radicals compared to 19.0-13.6% for other peptides. Cysteine at the N-terminal was important for both the reduction of chromium (pH 7.4) and the HO activity because S-H bond energies at that position were lower based on DFT calculations.

The small molecule luteolin inhibits N-acetyl-α-galactosaminyltransferases and reduces mucin-type O-glycosylation of amyloid precursor protein

Mucin-type O-glycosylation is the most abundant type of O-glycosylation. It is initiated by the members of the polypeptide N-acetyl-α-galactosaminyltransferase (ppGalNAc-T) family and closely associated with both physiological and pathological conditions, such as coronary artery disease or Alzheimer's disease. The lack of direct and selective inhibitors of ppGalNAc-Ts has largely impeded research progress in understanding the molecular events in mucin-type O-glycosylation. Here, we report that a small molecule, the plant flavonoid luteolin, selectively inhibits ppGalNAc-Ts in vitro and in cells. We found that luteolin inhibits ppGalNAc-T2 in a peptide/protein-competitive manner but not promiscuously (e.g. via aggregation-based activity). X-ray structural analysis revealed that luteolin binds to the PXP motif-binding site found in most protein substrates, which was further validated by comparing the interactions of luteolin with wild-type enzyme and with mutants using 1H NMR-based binding experiments. Functional studies disclosed that luteolin at least partially reduced production of β-amyloid protein by selectively inhibiting the activity of ppGalNAc-T isoforms. In conclusion, our study provides key structural and functional details on luteolin inhibiting ppGalNAc-T activity, opening up the way for further optimization of more potent and specific ppGalNAc-T inhibitors. Moreover, our findings may inform future investigations into site-specific O-GalNAc glycosylation and into the molecular mechanism of luteolin-mediated ppGalNAc-T inhibition.

Olive (Olea europaea L.) Biophenols: A Nutriceutical against Oxidative Stress in SH-SY5Y Cells

Plant biophenols have been shown to be effective in the modulation of Alzheimer’s disease (AD) pathology resulting from free radical-induced oxidative stress and imbalance of the redox chemistry of transition metal ions (e.g., iron and copper). On the basis of earlier reported pharmacological activities, olive biophenols would also be expected to have anti-Alzheimer’s activity. In the present study, the antioxidant activity of individual olive biophenols (viz. caffeic acid, hydroxytyrosol, oleuropein, verbascoside, quercetin, rutin and luteolin) were evaluated using superoxide radical scavenging activity (SOR), hydrogen peroxide (H₂O₂) scavenging activity, and ferric reducing ability of plasma (FRAP) assays. The identification and antioxidant activities in four commercial olive extracts—Olive leaf extract^TM (OLE), Olive fruit extract^TM (OFE), Hydroxytyrosol Extreme^TM (HTE), and Olivenol plus^TM (OLP)—were evaluated using an on-line HPLC-ABTS^•+ assay, and HPLC-DAD-MS analysis. Oleuropein and hydroxytyrosol were the predominant biophenols in all the extracts. Among the single compounds examined, quercetin (EC₅₀: 93.97 μM) and verbascoside (EC₅₀: 0.66 mM) were the most potent SOR and H₂O₂ scavengers respectively. However, OLE and HTE were the highest SOR (EC₅₀: 1.89 μg/mL) and H₂O₂ (EC₅₀: 115.8 μg/mL) scavengers among the biophenol extracts. The neuroprotection of the biophenols was evaluated against H₂O₂-induced oxidative stress and copper (Cu)-induced toxicity in neuroblastoma (SH-SY5Y) cells. The highest neuroprotection values (98% and 92%) against H₂O₂-induced and Cu-induced toxicities were shown by the commercial extract HTE^TM. These were followed by the individual biophenols, caffeic acid (77% and 64%) and verbascoside (71% and 72%). Our results suggest that olive biophenols potentially serve as agents for the prevention of neurodegenerative diseases such as AD, and other neurodegenerative ailments that are caused by oxidative stress.