Chemical Methods To Evaluate Antioxidant Ability

Equipping Uridine with Three Dipeptide Motifs for the Inhibition of Radical-Induced DNA Oxidation

We report the discovery and characterization of antioxidative effects of uridine linked with three dipeptide motifs against DNA oxidation induced by peroxyl radicals. First, the dipeptide motifs are constructed by using the Ugi four-component reaction (Ugi 4CR), in which caffeic, ferulic, sinapic, and syringic acids are used as the carboxylic acid resources, vanillin, benzaldehyde, and p-hydroxybenzaldehyde are used as the aldehyde resources, tyramine- and dopamine-related isocyanides as well as ethyl isocyanoacetate are used as the isocyanide resources, and 2-(p-aminophenyl)ethanol is used as the amine component. We found that the antioxidative effects of the Ugi 4CR products are 1.3-2.8 times higher than those of caffeic, ferulic, sinapic, and syringic acids in the protection of DNA against peroxyl radical-induced oxidation. Moreover, when three Ugi 4CR products are linked with three hydroxyl groups of uridine by using three succinic anhydrides as the linkage, the inhibitory effects of the afforded uridine-dipeptide hybrids against the DNA oxidation increase 4.4-8.9 times (>3 times) compared to that of the Ugi 4CR product. This is due to the hybrid structure consisting of uridine and three motifs of the Ugi 4CR product enabling binding with the DNA strand more efficiently and quenching free radicals more rapidly. Therefore, the hybrid structure constructed by the nucleoside with antioxidative dipeptides offers an additional advantage for protecting DNA against radical-induced oxidation.

Isolation and Characterization of Antioxidant Peptides from Dairy Cow (Bos taurus) Placenta and Their Antioxidant Activities

Our preliminary study identified dairy cow placenta extract (CPE) as a mixture of peptides with potent antioxidant activity both in vivo and in vitro. However, the specific antioxidant peptides (AOPs) responsible for this activity were not yet identified. In the current study, we employed virtual screening and chromatography techniques to isolate two peptides, ANNGKQWAEVF (CP1) and QPGLPGPAG (CP2), from CPE. These peptides were found to be less stable under extreme conditions such as high temperature, strong acid, strong alkali, and simulated digestive conditions. Nevertheless, under normal physiological conditions, both CP1 and CP2 exhibited significant antioxidant properties, including free-radical scavenging, metal chelating, and the inhibition of lipid peroxidation. They also up-regulated the activities of intracellular antioxidant enzymes in response to hydrogen-peroxide-induced oxidative stress, resulting in reduced MDA levels, a decreased expression of the Keap1 gene and protein, and increased levels of the Nrf2 and HO-1 genes and proteins. Furthermore, CP1 demonstrated superior antioxidant activity compared to CP2. These findings suggest that CP1 and CP2 hold potential for mitigating oxidative stress in vitro and highlight the efficacy of virtual screening as a method for isolating AOPs within CPE.

Dicopper Complexes of p-Cresol-2,6-bis(amide-tether-dpa4-X) (X = MeO and Cl): Selective ROS Generation and Cytotoxicity Enhancement Controlled by Electronic and Hydrophobic Effects of the MeO and Cl Groups

Two new p-cresol-2,6-bis(amide-tether-dpa4-X) ligands (HL4-X, X = MeO and Cl) and their dicopper complexes [Cu2(μ-1,1-OAc)(μ-1,3-OAc)(L4-MeO)]Y (Y = PF6 1a, OAc 1b) and [Cu2(μ-1,3-OAc)2(L4-Cl)]Y (Y = ClO4 2a, OAc 2b) were synthesized. The electronic and hydrophobic effects of the MeO and Cl groups were examined compared with nonsubstituted complex [Cu2(μ-1,1-OAc)(μ-1,3-OAc)(L)]+ (3). The electronic effects were found in crystal structures, spectroscopic characterization, and redox potentials of these complexes. 1b and 2b were reduced to Cu(I)Cu(I) with sodium ascorbate and reductively activated O2 to produce H2O2 and HO•. The H2O2 release and HO• generation are promoted by the electronic effects. The hydrophobic effects increased the lipophilicity of 1b and 2b. Cellular ROS generation of 1b, 2b, and 3 was visualized by DCFH-DA. To examine the intracellular behavior, boron dipyrromethene (Bodipy)-modified complexes 4B and 5B corresponding to 1b and 2b were synthesized. These support that 1b and 2b are localized at the ER and Golgi apparatus. The cytotoxicity of 1b and 2b against various cell lines was examined by MTT assay. 1b and 2b were 7- and 41-fold more cytotoxic than 3. 1b generated ROS selectively in cancer cell but 2b nonselectively in cancer and normal cells, causing cancer- and normal-cell-selective cytotoxicity, respectively.

Curcumin-functionalized gold nanoparticles attenuate AAPH-induced acute cardiotoxicity via reduction of lipid peroxidation and modulation of antioxidant parameters in a chicken embryo model

Gold nanoparticles (AuNPs) have gained considerable attention due to their biocompatibility, customizable optical properties and ease of synthesis. In this study, an environmentally friendly method was used for synthesize curcumin-functionalized AuNPs (AuNP-C). AuNP-C exhibited a spherical shape, uniformity, and an average diameter of 6 nm. The in vitro antioxidant activity was analyzed, and cytotoxicity properties of AuNP-C were assessed in fibroblast and macrophage cells. Additionally, the effects of AuNP-C on oxidative stress in chicken embryo liver and hearts were investigated. AuNP-C demonstrated potent free radical scavenging properties without exhibiting cytotoxicity and hepatotoxicity effects. Administration of 300 µg/mL of AuNP-C in chicken embryos, subjected to oxidative damage induced by 2,2'-azobis(2-amidinopropane) dihydrochloride, significantly reduced lipid peroxidation and reactive oxygen species levels in the cardiac tissue. Moreover, the activities of cardiac superoxide dismutase, catalase, and glutathione reductase were restored, accompanied by an increase in overall antioxidant capacity. Furthermore, at higher concentrations, AuNP-C normalized the reduced glutathione content. AuNP-C preserved the normal structure of blood vessels; however, it resulted in an increase in protein carbonylation. This study provides initial evidence for the modulation of antioxidant defense mechanisms by green-synthesized AuNPs and underscores the importance of investigating the in vivo safety of phytoantioxidant-functionalized nanoparticles.

Recent Applications of Melanin-like Nanoparticles as Antioxidant Agents

Nanosized antioxidants are highly advantageous in terms of versatility and pharmacokinetics, with respect to conventional molecular ones. Melanin-like materials, artificial species inspired by natural melanin, combine recognized antioxidant (AOX) activity with a unique versatility of preparation and modification. Due to this versatility and documented biocompatibility, artificial melanin has been incorporated into a variety of nanoparticles (NP) in order to give new platforms for nanomedicine with enhanced AOX activity. In this review article, we first discuss the chemical mechanisms behind the AOX activity of materials in the context of the inhibition of the radical chain reaction responsible for the peroxidation of biomolecules. We also focus briefly on the AOX properties of melanin-like NP, considering the effect of parameters such as size, preparation methods and surface functionalization on them. Then, we consider the most recent and relevant applications of AOX melanin-like NPs that are able to counteract ferroptosis and be involved in the treatment of important diseases that affect, e.g., the cardiovascular and nervous systems, as well as the kidneys, liver and articulations. A specific section will be dedicated to cancer treatment, since the role of melanin in this context is still very debated. Finally, we propose future strategies in AOX development for a better chemical understanding of melanin-like materials. In particular, the composition and structure of these materials are still debated, and they present a high level of variability. Thus, a better understanding of the mechanism behind the interaction of melanin-like nanostructures with different radicals and highly reactive species would be highly advantageous for the design of more effective and specific AOX nano-agents.

Antioxidant and Antidiabetic Properties of Extracts from Three Underutilized Food Plants of North East India

Three underutilized leafy vegetables Sarcochlamys pulcherrima (Roxb.) Gaudich (SP), Ipomoea aquatica Forssk. (IA) and Zanthoxylum rhetsa (Roxb.) DC (ZR) were extracted with different solvents viz. 95 % ethyl alcohol, methanol and hot water. The extracts were evaluated for their antioxidant potential via DPPH, ABTS and FRAP assay along with electroanalytical studies using cyclic voltammetry. The antidiabetic potential was determined by recording their α-amylase and α-glucosidase inhibitory assay. The total phenolic content (TPC), total flavonoid content (TFC) and the liquid chromatography-mass spectrometry (LC/MS) based phytochemical profiles of the extracts were also determined. All three extracts of SP exhibited significant antioxidant capacity. The antidiabetic potential of the IA and ZR extracts was found to be higher than or at par with that of standard acarbose. LC/MS studies reveal the presence of hitherto reported antioxidant and antidiabetic compounds like gamma-aminobutyric acid, cinnamic acid, caffeic acid, α-viniferin, piperlonguminine, niacin, kaempferol, etc., in the extracts.

Lignin as a bioactive polymer and heavy metal absorber- an overview

As a pulping and bio-refinery by-product with phenolic chemical structure, lignin indicated high potential as natural antioxidant activity, UV blocker, antibacterial and toxic material absorbent properties. Presence of phenolic hydroxyl groups in lignin structure plays the main role of its antioxidant activity. However, lignin antioxidant power can change depending on its other structural features and functional groups like ortho-methoxy groups, -OCH₃ groups, the α-CH₂ groups, the aliphatic carbonyl groups, and the size of π-conjugated systems. Lignin in mixture with synthetic polymers, improved their thermal stability. Lignin has high UV light absorbing potential in broad-spectrum (UVA, UVB). Adding 1-5% of lignin into hand cream indicated excellent range of sun protection factor (SPF) with more than 95% UV light absorption. Lignin also indicated strong UV light protection when applied in different transparent film and protect paint, oil, and varnish from UV degradation. Lignosulfonate and other modified lignin including chemically modification, nano-particles and lignin hydrogel indicated high potential as heavy metal absorber.

Flavonoids and proanthocyanidins-rich fractions from Eugenia dysenterica fruits and leaves inhibit the formation of advanced glycation end-products and the activities of α-amylase and α-glucosidase

ETHNOPHARMACOLOGICAL RELEVANCE

Different parts of Eugenia dysenterica have been popularly used in Brazil for treating diabetes mellitus and its complications. The present study aimed to screen extracts from E. dysenterica fruit pulp, peel, seed and leaf for carbohydrate digestive enzymes inhibitors with antioxidant and anti-glycation capacities.

MATERIALS AND METHODS

Ethanol extracts of E. dysenterica were subjected to a liquid-liquid fractionation and the fractions were used to evaluate their antioxidant properties and inhibitory potential against the formation of advanced glycation end-products (AGEs) and α-amylase and α-glucosidase.

RESULTS

The ethyl acetate fraction (EtOAcF) from seed and the dichloromethane fraction (CH₂Cl₂F) and EtOAcF from leaf had high antioxidant capacities (ORAC >5500 μmol trolox eq g^-1, FRAP >1500 μmol trolox eq g^-1 and DPPH IC₅₀ < 35 μg mL^-1) and showed exceptional inhibitory activities against AGEs formation (glycation inhibition above 80% at 10 μg mL^-1) and α-amylase and α-glucosidase (inhibition above 50% at 10 μg mL^-1). The gallated B-types proanthocyanidins were the most active ingredients found in the leaf of E. dysenterica (CH₂Cl₂ and EtOAcF), being responsible for the notorious inhibitory effects against glycation and glycoside hydrolases due to their ortho-hydroxyl groups, which play role in scavenge and quench free radicals and glycated products, and may occupy the enzymes' substrate binding pocket. Furthermore, gallic acid, quercetin and its glycoside derivatives were detected by the first time in the E. dysenterica fruit seed (EtOAcF).

CONCLUSIONS

The results strongly contribute to the understanding of the antidiabetic potential of seeds and leaves from E. dysenterica, a species from a global biodiversity hotspot, which appears to be linked to the prevention of oxidative stress, AGEs production and postprandial hyperglycemia.

Biotechnological Applications and Health-Promoting Properties of Flavonols: An Updated View

Flavonols are a subclass of natural flavonoids characterized by a remarkable number of biotechnological applications and health-promoting properties. They attract researchers' attention due to many epidemiological studies supporting their usage. They are phytochemicals commonly present in our diet, being ubiquitous in the plant kingdom and, in particular, relatively very abundant in fruits and vegetables. All these aspects make flavonols candidates of choice for the valorization of products, based on the presence of a remarkable number of different chemical structures, each one characterized by specific chemical features capable of influencing biological targets inside the living organisms in very different manners. In this review, we analyzed the biochemical and physiological characteristics of flavonols focalizing our attention on the most promising compounds to shed some light on their increasing utilization in biotechnological applications in processing industries, as well as their suitable employment to improve the overall wellness of the humankind.

Antioxidant compounds of Kielmeyera coriacea Mart. with α-amylase, lipase and advanced glycation end-product inhibitory activities

Chronic hyperglycemia and hyperlipidemia are associated with excessive formation of reactive oxygen species and advanced glycation end-products. The present study aimed to evaluate the potential in vitro antidiabetic properties of Kielmeyera coriacea inner bark. The main phytochemical compounds were identified by UHPLC-ESI/MSⁿ and the ethanol extract and its fractions were used to evaluate their antioxidant and anti-glycation capacities, as well as their inhibitory potential against glycoside and lipid hydrolases activities. The polar fractions, especially the n-butanol fraction, had free radical scavenging and quenching properties (ORAC and FRAP values>1800 and 1000 µmol trolox eq/g, respectively, and DPPH IC₅₀<4 µg/mL), and inhibited ROS production (p < 0.01), lipid peroxidation (p < 0.001), glycation (IC₅₀ ~ 10 µg/mL in the BSA-fructose assay; IC₅₀ ~ 200 µg/mL in the BSA-methylglyoxal and arginine-methylglyoxal assays), α-amylase (IC₅₀<0.1 µg/mL) and lipase (IC₅₀<5 µg/mL), with no cytotoxicity. Biomolecules well-known as potent antioxidants were identified for the first time in the inner bark of K. coriacea, such as protocatechuic acid, epicatechin and procyanidins A, B and C. Together, our results support the antioxidant, anti-glycation and glycoside and lipid hydrolases inhibitory properties of the inner bark of K. coriacea, a species found in the Brazilian savanna, which makes it especially useful to combat oxidative stress and hyperglycemia and hyperlipidemia.

Attaching a Dipeptide to Fullerene as an Antioxidant Hybrid against DNA Oxidation

Emerging evidence has revealed that oxidative damages of DNA correlate with the pathogenesis of some diseases, and numerous investigations have also suggested that supplementation of antioxidants is beneficial for keeping health by rectifying in vivo redox status. Here, we construct antioxidative dipeptides with the Ugi four-component reaction (comprising p-aminobenzyl alcohol, benzaldehyde, or vanillin, a series of antioxidative carboxylic acids and isocyanides as reagents) and then attempt to attach the dipeptides to [60]fullerene by the Bingel reaction. However, this endeavor does not lead to the amelioration of the radical-scavenging property because abilities of fullerenyl dipeptides to trap 2,2'-diphenyl-1-picrylhydrazyl and galvinoxyl radicals are still dependent upon the phenolic hydroxyl group in the dipeptide scaffold rather than upon the fullerenyl group. Alternatively, when the obtained fullerenyl dipeptides are evaluated in a peroxyl radical-induced oxidation of DNA, it is found that introducing a fullerene moiety into dipeptide enables antioxidative effect to be enhanced 20-30% because the fullerene moiety facilitates the corresponding dipeptide to intercalate with DNA strands, and thus, to increase the antioxidative efficacy. Our results suggest that connecting an antioxidative skeleton with the hydrophobic fullerene moiety might lead to a series of novel antioxidant hybrids applied for the inhibition of DNA oxidation.

Development of novel anti-infective and antioxidant azole hybrids using a wet and dry approach

Background: Considering emerging drug resistance in microbes, this work is focused on the synthesis of azole hybrids as novel antimicrobials. Materials & methods: The triazole derivatives were prepared using azide alkyne cycloaddition reaction. The antimicrobial potential of these compounds was evaluated by serial dilution method. Results: A series of azole hybrids containing benzimidazole-1,2,3-triazole skeleton was designed and synthesized via click reaction. Compound 4s showed notable antimicrobial activity against Staphylococcus aureus and Candida albicans (MIC 0.0165 μmol/ml), and 4q gives remarkable radical scavenging activity (IC₅₀ 0.0092 μmol/ml). The compounds 4a, 4k, 4o, 4s, 4x. 4m, 4n, 4s, 4t and 4x are commendable antibacterial and antifungal molecules, even better than established drugs. Molecular docking reveals that compound 4s binds with tyrosyl-tRNA synthetase residues through two H-bonds. Conclusion: Compounds 4s and 4k may be considered valuable lead compounds for further optimization as antimicrobial drugs.

Alignment Layer of Liquid Crystal Using Plant-Based Isoeugenol-Substituted Polystyrene

We synthesized a series of renewable and plant-based isoeugenol-substituted polystyrenes (PIEU#, # = 100, 80, 60, 40, and 20, where # is the molar percent content of isoeugenol moiety), using polymer modification reactions to study their liquid crystal (LC) alignment behavior. In general, the LC cells fabricated using polymer film with a higher molar content of isoeugenol side groups showed vertical LC alignment behavior. This alignment behavior was well related to the surface energy value of the polymer layer. For example, vertical alignments were observed when the polar surface energy value of the polymer was smaller than approximately 3.59 mJ/m2, generated by the nonpolar isoeugenol moiety with long and bulky carbon groups. Good alignment stability at 100 °C and under ultraviolet (UV) irradiation of 15 J/cm2 was observed for the LC cells fabricated using PIEU100 as a LC alignment layer. Therefore, renewable isoeugenol-based materials can be used to produce an eco-friendly vertical LC alignment system.

Multicomponent Reactions for Integrating Multiple Functional Groups into an Antioxidant

A large number of convincing evidences has revealed the correlation of the pathogeny of diseases with the oxidative damages of DNA, protein, biomembrane, and other biological species, while supplementation of antioxidants is demonstrated to be a promising way to avoid, at least, rectify the unbalance redox status in vivo. Although many endeavors have focused on synthesis of antioxidants, a main hurdle still hinders the wide usages of synthetic antioxidants because of low bioavailability and potential cytotoxicity. The search for antioxidants with multiple functional groups being recognized by different receptors becomes a much sought by researchers, and multicomponent reactions (MCRs) provide with powerful tools for the construction of multifunctional antioxidants. Presented herein is a personal account on the application of MCRs for the synthesis of multifunctional antioxidants, while radical-induced oxidation of DNA acts as the experimental system for evaluating antioxidative effect. Concretely, the Biginelli three-component reaction (3CR) affords such a dihydropyrimidine scaffold that the tautomerization between C=S and C-SH leads to antioxidative effect. The Povarov 3CR is able to integrate multiple antioxidative groups, i. e., ferrocenyl and -N(CH₃ )₂ , into a quinoline scaffold, while the Groebke 3CR provides with imidazo[1,2-a]pyridine skeleton for inhibiting DNA oxidation. Additionally, the Knoevenagel-related MCRs also become efficient strategies for achieving radical-scavengers. On the other hand, the Ugi 4CR and Passerini 3CR result in the dipeptide and α-acyloxycarboxamide, respectively, with the benefit for the integration of antioxidative features by aliphatic chains. Therefore, MCRs have emerged as efficient tools for integrating multiple antioxidative features into one molecule in order to meet with complicated requirements from various biological surroundings.

Bridging free radical chemistry with drug discovery: A promising way for finding novel drugs efficiently

Many diseases have been regarded to correlate with the in vivo oxidative damages, which are caused by overproduced free radicals from metabolic process or reactive oxygen species (ROS). This background motivates chemists to explore free radical reactions and to design a number of antioxidants, but whether free radical chemistry can be applied to accelerate the efficacy of the drug discovery is still underrepresented. Herein, in light of recent findings as well as kinetics on free radical reaction, the discipline of free radical chemistry is introduced to be a novel tool for finding potential drugs from antioxidant libraries accumulated during the study on free radical chemistry. These antioxidants provide with such abundant types of structural skeleton that might be employed to inhibit oxidations in different biological microenvironments. Although the in vitro characterization on the antioxidative property exerts a potential role of an antioxidant as a prodrug, the in vivo investigation on the property for quenching free radicals will make a final decision for the antioxidant whether it is worthy to be further explored pharmacologically. Therefore, it is reasonable to expect that bridging free radical chemistry with the pharmacological research will provide with a succinct way for finding novel drugs efficiently.

B procyanidins of Annona crassiflora fruit peel inhibited glycation, lipid peroxidation and protein-bound carbonyls, with protective effects on glycated catalase

Advanced glycation end-products (AGEs) have been reported as results of increased oxidative stress. Consequently, the search for new antioxidant and anti-glycating agents is under intense investigation. Plant-derived procyanidins have previously demonstrated anti-glycation properties. Thus, this study aimed to isolate procyanidins from Annona crassiflora fruit peel, a species from the Brazilian Savanna, and investigate their antioxidant and anti-glycation effects. Free radical scavenging and quenching properties, formation of reactive oxygen species (ROS), AGEs, protein carbonyl and thiol groups, lipid peroxidation, crosslinked AGEs, as well as glycated catalase activity, were analyzed. In addition, in silico assessment of absorption, distribution, metabolism, excretion and toxicity was carried out. The procyanidins-enriched fraction, named here as F7, showed high antioxidant and anti-glycation capacities, with inhibitory activities against lipid peroxidation, and AGEs and ROS formation. In addition, there were reductions in AGEs-induced crosslinks and protein carbonyls and protective effects against oxidation of thiol groups and glycated-catalase. ADMET predictions of F7 showed favorable absorption and distribution, with no hepatotoxicity or mutagenicity. Together, our results support the anti-glycation activities of the procyanidins-enriched fraction from A. crassiflora, and suggest that these effects are triggered, at least in part, by scavenging free radical and dicarbonyls intermediates.

Chain Breaking Antioxidant Activity of Heavy (S, Se, Te) Chalcogens Substituted Polyphenols

Polyphenols are probably the most important family of natural and synthetic chain-breaking antioxidants. Since long ago, chemists have studied how structural (bioinspired) modifications can improve the antioxidant activity of these compounds in terms of reaction rate with radical reactive oxygen species (ROS), catalytic character, multi-defence action, hydrophilicity/lipophilicity, biodistribution etc. In this framework, we will discuss the effect played on the overall antioxidant profile by the insertion of heavy chalcogens (S, Se and Te) in the phenolic skeleton.

Anti-Oxidant in China: A Thirty-Year Journey

Anti-oxidant refers to such a kind of endogenous or exogenous compound that is able to retard or even prohibit in vivo or in vitro oxidation with only small amount being used. The study of anti-oxidants starts nearly 30 years ago, and the research on this topic in China almost begins simultaneously with that in the world. Gratifyingly, contributions on anti-oxidants from China researchers have rapidly increased in the recent decade as anti-oxidants have become a hot topic in biochemistry, pharmacology, food science, chemistry as well as other related disciplines. Anti-oxidants provide a specific viewpoint for clarifying pharmacological effects of Chinese medicinal herbs. For example, as a traditional Chinese medicinal herb, Panax ginseng C. A. Meyer is found to be a natural anti-oxidant resource. Meanwhile, some signaling pathways such as nuclear factor-[Formula: see text]B (NF-[Formula: see text]B), nuclear factor erythroid 2 related factor 2 (Nrf2), and Kelch-like ECH associated protein 1 (Keap1) are regarded to play an important role in anti-oxidant responses. These findings provide a substantial basis for understanding the pharmacological behaviors of Chinese medicinal herbs in view of regulating the aforementioned signaling pathways. Moreover, inhibition of reactive oxygen species (ROS) by supplementation of anti-oxidant becomes a popularly accepted idea in keeping health and treating diseases. Isolations of antio-xidative ingredients from medicinal herbs and foods lead to set up a large range of anti-oxidative compound libraries, and intake of anti-oxidants from foods may be the most efficient way for supplementing exogenous anti-oxidants. On the other hand, designing anti-oxidants with novel structures motivates organic and medicinal chemists to explore the structure–activity relationship, and then, to find novel structural features with anti-oxidative properties. Therefore, it is reasonable to believe that China researchers will donate more endeavors to obtain more achievements on anti-oxidants in the future.

A Comprehensive Review on the Chemical Constituents and Functional Uses of Walnut (Juglans spp.) Husk

The walnut (Juglans spp.) is an appreciated nut that belongs to the Juglandaceae family. The fruit includes four main parts: the kernel, the skin, the shell, and the green husk. It is widely cultivated due to its edible kernel. In walnut production centers, high amounts of the husk as an agro-forest waste product are produced and discarded away. Recently, it has been demonstrated that the walnut green husk could be valued as a source of different natural bioactive compounds with excellent antioxidant and antimicrobial properties. Regarding this respect, in this contribution, the current scientific knowledge on the antioxidant and antiradical activities, various identified and isolated individual chemical constituents, as well as the functional applications of the walnut husk with more emphasis on the Persian walnut (Juglans regia L.) are reviewed.

Design, synthesis, and biological activity evaluation of BACE1 inhibitors with antioxidant activity

The proteolytic enzyme β-secretase (BACE1) plays a central role in the synthesis of the pathogenic β-amyloid peptides (Aβ) in Alzheimer's disease (AD), antioxidants could attenuate the AD syndrome and prevent the disease progression. In this study, BACE1 inhibitors (D1-D18) with free radical-scavenging activities were synthesized by molecular hybridization of 2-aminopyridine with natural antioxidants. The biological activity evaluation showed that D1 had obvious inhibitory activity against BACE1, and strong antioxidant activity in 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS^+• ) assay, which could be used as a lead compound for further study.

Comparative Analysis of Radical Adduct Formation (RAF) Products and Antioxidant Pathways between Myricetin-3-O-Galactoside and Myricetin Aglycone

The biological process, 3-O-galactosylation, is important in plant cells. To understand the mechanism of the reduction of flavonol antioxidative activity by 3-O-galactosylation, myricetin-3-O-galactoside (M3OGa) and myricetin aglycone were each incubated with 2 mol α,α-diphenyl-β-picrylhydrazyl radical (DPPH^•) and subsequently comparatively analyzed for radical adduct formation (RAF) products using ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UPLC-ESI-Q-TOF-MS) technology. The analyses revealed that M3OGa afforded an M3OGa–DPPH adduct (m/z 873.1573) and an M3OGa–M3OGa dimer (m/z 958.1620). Similarly, myricetin yielded a myricetin–DPPH adduct (m/z 711.1039) and a myricetin–myricetin dimer (m/z 634.0544). Subsequently, M3OGa and myricetin were compared using three redox-dependent antioxidant analyses, including DPPH^•-trapping analysis, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide radical (PTIO^•)-trapping analysis, and ^•O₂ inhibition analysis. In the three analyses, M3OGa always possessed higher IC₅₀ values than those of myricetin. Conclusively, M3OGa and its myricetin aglycone could trap the free radical via a chain reaction comprising of a propagation step and a termination step. At the propagation step, both M3OGa and myricetin could trap radicals through redox-dependent antioxidant pathways. The 3-O-galactosylation process, however, could limit these pathways; thus, M3OGa is an inferior antioxidant compared to its myricetin aglycone. Nevertheless, 3-O-galactosylation has a negligible effect on the termination step. This 3-O-galactosylation effect has provided novel evidence that the difference in the antioxidative activities of phytophenols exists at the propagation step rather than the termination step.

Enhancing Antioxidant Effect against Peroxyl Radical-Induced Oxidation of DNA: Linking with Ferrocene Moiety!

As a major member in the family of reactive oxygen species, peroxyl radical is able to abstract hydrogen atom from 4-position of ribose, leading to the collapse of DNA strand. Thus, inhibiting oxidative stress with exogenous antioxidants acts as a promising strategy to protect the integrity of DNA structure and is thereby suggested to be a pathway against developments of related diseases. Ferrocene as an organometallic scaffold is widely applied in the design of organometallic drugs, and redox of Fe(II)/Fe(III) in ferrocene offers advantage for providing electron to radicals. Presented herein are our ongoing studies on ferrocene-appended antioxidants, including McMurry reaction applied to construct ferrocifen; Aldol condensation used to prepare ferrocenyl curcumin; Povarov reaction employed to prepare ferrocenyl quinoline; Biginelli reaction used to construct ferrocenyl dihydropyrimidine; Groebke reaction used to synthesize ferrocenyl imidazo[1,2-a]pyridine; and Passerini three-component reaction as well as Ugi four-component reaction applied to synthesize α-acyloxycarboxamide and bisamide, respectively. It is found that ferrocene moiety is able to enhance antioxidative effect of the aforementioned scaffolds even without the aid of phenolic hydroxyl group. The role of ferrocene in enhancing antioxidative effect can be attributable to trapping radicals, decreasing oxidative potential, and increasing the affinity toward DNA strand. Therefore, ferrocene is worthy to be taken into consideration in the design of drugs in relation to DNA oxidation.

Facile template synthesis of water-soluble triazine-based Schiff base ligand bridged-coordination polymers of Co(ii), Ni(ii), and Cu(ii): structure, biomolecular interactions, and cytotoxic activity

For the first time, a new hydrazone Schiff base ligand and its Co(ii), Ni(ii), and Cu(ii) complexes were synthesised and characterised. Their antioxidant and binding activities towards CT-DNA and BSA were evaluated.

Perylene Diimide as a Precise Graphene-like Superoxide Dismutase Mimetic

Here we show that the active portion of a graphitic nanoparticle can be mimicked by a perylene diimide (PDI) to explain the otherwise elusive biological and electrocatalytic activity of the nanoparticle construct. Development of molecular analogues that mimic the antioxidant properties of oxidized graphenes, in this case the poly(ethylene glycolated) hydrophilic carbon clusters (PEG-HCCs), will afford important insights into the highly efficient activity of PEG-HCCs and their graphitic analogues. PEGylated perylene diimides (PEG_n-PDI) serve as well-defined molecular analogues of PEG-HCCs and oxidized graphenes in general, and their antioxidant and superoxide dismutase-like (SOD-like) properties were studied. PEG_n-PDIs have two reversible reduction peaks, which are more positive than the oxidation peak of superoxide (O₂^•-). This is similar to the reduction peak of the HCCs. Thus, as with PEG-HCCs, PEG_n-PDIs are also strong single-electron oxidants of O₂^•-. Furthermore, reduced PEG_n-PDI, PEG_n-PDI^•-, in the presence of protons, was shown to reduce O₂^•- to H₂O₂ to complete the catalytic cycle in this SOD analogue. The kinetics of the conversion of O₂^•- to O₂ and H₂O₂ by PEG₈-PDI was measured using freeze-trap EPR experiments to provide a turnover number of 133 s^-1; the similarity in kinetics further supports that PEG₈-PDI is a true SOD mimetic. Finally, PDIs can be used as catalysts in the electrochemical oxygen reduction reaction in water, which proceeds by a two-electron process with the production of H₂O₂, mimicking graphene oxide nanoparticles that are otherwise difficult to study spectroscopically.

Scavenging ability of dendritic PAMAM bridged hindered phenolic antioxidants towards DPPH˙ and ROO˙ free radicals

The intramolecular synergistic effects of two dendritic antioxidants between hindered phenol groups and tertiary amine groups were investigated using the DPPH˙ method and the oxygen uptake method.

Mechanistic Study of the Conversion of Superoxide to Oxygen and Hydrogen Peroxide in Carbon Nanoparticles

Hydrophilic carbon clusters (HCCs) are oxidized carbon nanoparticles with a high affinity for electrons. The electron accepting strength of HCCs, employing the efficient conversion of superoxide (O2(•-)) to molecular oxygen (O2) via single-electron oxidation, was monitored using cyclic voltammetry and electron paramagnetic resonance spectroscopy. We found that HCCs possess O2 reduction reaction (ORR) capabilities through a two-electron process with the formation of H2O2. By comparing results from aprotic solvents to those obtained from ORR activity in aqueous media, we propose a mechanism for the origin of the antioxidant and superoxide dismutase mimetic properties of poly(ethylene glycolated) hydrophilic carbon clusters (PEG-HCCs).

Quantification of Phenolic Antioxidant Moieties in Dissolved Organic Matter by Flow-Injection Analysis with Electrochemical Detection

Phenolic moieties in dissolved organic matter (DOM) play important roles as antioxidants in oxidation processes in natural and engineered systems. This work presents an automated and highly sensitive flow injection analysis (FIA) system coupled to both spectrophotometric and electrochemical detection to quantify electron-donating phenolic moieties in DOM by determining the number of electrons that these moieties transfer to an added chemical oxidant, the radical cation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS(•+)). The FIA system was successfully validated using Trolox as a redox standard. Highest method sensitivity was attained when combining the FIA with chronoamperometric detection, resulting in limits of quantification of picomolar amounts of Trolox and nanogram amounts of DOM (corresponding to solutions with <1 mg carbon per liter). The analysis of DOM isolates showed a strong linear correlation between the number of electrons donated and their titrated phenol contents, supporting oxidation of phenols by ABTS(•+). The broad application spectrum of the FIA system to dilute natural DOM samples was illustrated by analyzing water samples collected from northern peatlands and by monitoring the oxidation of phenols in one peat sample upon incubation with a phenol oxidase. The superior analytical capability of the FIA system allows quantifying phenols and monitoring phenol dynamics in dilute DOM samples.