DPPH (= 2,2‐Diphenyl‐1‐picrylhydrazyl = 2,2‐Diphenyl‐1‐(2,4,6‐trinitrophenyl)hydrazyl) Radical‐Scavenging Reaction of Protocatechuic Acid Esters (= 3,4‐Dihydroxybenzoates) in Alcohols: Formation of Bis‐alcohol Adduct

Protocatechuic acid esters (= 3,4‐dihydroxybenzoates) scavenge ca. 5 equiv. of radical in alcoholic solvents, whereas they consume only 2 equiv. of radical in nonalcoholic solvents. While the high radical‐scavenging activity of protocatechuic acid esters in alcoholic solvents as compared to that in nonalcoholic solvents is due to a nucleophilic addition of an alcohol molecule at C(2) of an intermediate o‐quinone structure, thus regenerating a catechol (= benzene‐1,2‐diol) structure, it is still unclear why protocatechuic acid esters scavenge more than 4 equiv. of radical (C(2) refers to the protocatechuic acid numbering). Therefore, to elucidate the oxidation mechanism beyond the formation of the C(2) alcohol adduct, 3,4‐dihydroxy‐2‐methoxybenzoic acid methyl ester ( 4 ), the C(2) MeOH adduct, which is an oxidation product of methyl protocatechuate ( 1 ) in MeOH, was oxidized by the DPPH radical (= 2,2‐diphenyl‐1‐picrylhydrazyl) or o‐chloranil (= 3,4,5,6‐tetrachlorocyclohexa‐3,5‐diene‐1,2‐dione) in CD₃OD/(D₆)acetone 3 : 1). The oxidation mixtures were directly analyzed by NMR. Oxidation with both the DPPH radical and o‐chloranil produced a C(2),C(6) bis‐methanol adduct ( 7 ), which could scavenge additional 2 equiv. of radical. Calculations of LUMO electron densities of o‐quinones corroborated the regioselective nucleophilic addition of alcohol molecules with o‐quinones. Our results strongly suggest that the regeneration of a catechol structure via a nucleophilic addition of an alcohol molecule with a o‐quinone is a key reaction for the high radical‐scavenging activity of protocatechuic acid esters in alcoholic solvents.     

DPPH (= 2,2‐Diphenyl‐1‐picrylhydrazyl) Radical‐Scavenging Reaction of Protocatechuic Acid (= 3,4‐Dihydroxybenzoic Acid): Difference in Reactivity between Acids and Their Esters

Protocatechuic acid (= 3,4‐dihydroxybenzoic acid; 1 ) exhibits a significantly slow DPPH (= 2,2‐diphenyl‐1‐picrylhydrazyl) radical‐scavenging reaction compared to its esters in alcoholic solvents. The present study is aimed at the elucidation of the difference between the radical‐scavenging mechanisms of protocatechuic acid and its esters in alcohol. Both protocatechuic acid ( 1 ) and its methyl ester 2 rapidly scavenged 2 equiv. of radical and were converted to the corresponding o‐quinone structures 1a and 2a , respectively (Scheme). Then, a regeneration of catechol (= benzene‐1,2‐diol) structures occurred via a nucleophilic addition of a MeOH molecule to the o‐quinones to yield alcohol adducts 1f and 2c , respectively, which can scavenge additional 2 equiv. of radical. However, the reaction of protocatechuic acid ( 1 ) beyond the formation of the o‐quinone was much slower than that of its methyl ester 2 . The results suggest that the slower radical‐scavenging reaction of 1 compared to its esters is due to a dissociation of the electron‐withdrawing carboxylic acid function to the electron‐donating carboxylate ion, which decreases the electrophilicity of the o‐quinone, leading to a lower susceptibility towards a nucleophilic attack by an alcohol molecule.     

A dynamic surface prepared by electrochemical triggering of substituted methoxyphenol-terminated self-assembled monolayers for multi-functional purposes

We devised a methoxyphenol thiol derivative with an electron-withdrawing (–CHO) and an electron-donating (–CH₂OH) substituent for the preparation of a dynamic surface that can be used for multi-functional purposes. This molecule was electrochemically activated to an o-quinone form by the oxidative triggering through demethoxylation, followed by hydroxylation on para position upon potential cycling whose rate depended on the nature of substituents. An electron-withdrawing substituent facilitated nucleophilic addition of water, forming a 1,2,5-trihydroxy form, and only para-hydroquinone underwent a redox reaction. An electron-donating substituent, however, was not able to activate this process, leaving behind only an ortho form. The o-quinone showed catalytic activity toward ascorbic acid and NADH oxidation.     

A comparative study of selected vitex species for phenolics estimation along with their antioxidant and herbicidal activities

This study aims to quantitative, qualitative estimation of phenolics, antioxidant (DPPH free radical scavenging, nitric oxide radical scavenging, superoxide anion scavenging, reducing power and metal chelating activity), and herbicidal properties of methanol extract of Vitex species {(Vitex negundo L. collected from Haldwani (VNH), Bhimtal (VNB) and Salari (VNS); Vitex agnus-castus L. collected from Pantnagar (VACP); Vitex trifolia L. collected from Pantnagar (VTP)}, Kumaun region, Uttarakhand, India. Herbicidal activity of methanol extracts of Vitex species was evaluated against Raphanus sativus at various concentrations for 120 h. The results revealed that the phenolic content varies from species to species as well as their location. HPLC profiling of Vitex species was carried out to identify the presence of different phenolic acids viz: vanillic acid, ferulic acid, p-coumaric acid, etc. In methanol extracts of Vitex species. VTP showed the highest DPPH (IC₅₀ = 6.84 μg/mL), nitric oxide (IC₅₀ = 2.86 μg/mL) and superoxide radical scavenging (IC₅₀ = 3.12 μg/mL) activity. The maximum reducing power was observed in VNH (RP₅₀ = 28.22 μg/mL) and the highest ion chelating capacity in VNB (IC₅₀ = 6.80 μg/mL). The effective herbicidal activity was shown by VNS, resulting in complete inhibition of seed germination. Based on the heatmap clustering selected species are divided into two clusters. The first cluster comprises VNB and VTP are there whereas in the second cluster there are two sub-clusters including VNS only in one sub-cluster and VNH and VACP in the second sub-cluster.     

Spectrum–effect relationship study between HPLC fingerprints and antioxidant of honeysuckle extract

Honeysuckle (Lonicera japonica flos) is a well‐known agent of edible and medicinal value in China and its antioxidative activity makes a major contribution to its dual use. However, the compounds responsible for its antioxidative activity are still unknown. In this study, 10 batches of honeysuckle were collected from different origins in China. The fingerprints were established by HPLC technique to investigate the compounds and a 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical scavenging activity assay was carried out to evaluate their antioxidant activity. partial least squares regression analysis was applied to set up the regression equation between DPPH radical scavenging activity and average peak area of common peaks of fingerprints. The results showed that peaks 10 (isochlorogenic acid B), 12 (isochlorogenic acid C), 11 (isochlorogenic acid A) and 9 (cynaroside) in the fingerprints were closely related to the antioxidant activity of 50% methanol extracts of honeysuckle. This study successfully established the spectrum–effect relationship between HPLC fingerprints and DPPH radical scavenging activity and provided a general model for exploring active components with a combination of chromatography and efficacy.     

Radical Chain Breaking Bis(ortho-organoselenium) Substituted Phenolic Antioxidants

The presence of a chalcogen atom at the ortho-position of phenols enhances their radical chain-breaking activity. Here, a copper(I)-catalyzed reaction of 2,6-dibromo- and 2,6-diiodophenols with diorganodiselenides has been studied for the introduction of two organoselenium substituents at both ortho-positions of the phenolic radical chain-breaking antioxidants, which afforded 2,6-diorganoseleno-substituted phenols in 80–92% yields having electron-donating CH₃, and electron-withdrawing CN and CHO functionalities. Additionally, 2,6-diiodophenols with electron-withdrawing CHO and CN groups also afforded novel 5,5′-selenobis(4-hydroxy-3-(phenylselanyl)benzaldehyde) and 5,5′-selenobis(4-hydroxy-3-(phenylselanyl)benzonitrile) consisting of three selenium and two phenolic moieties along with 2,6-diorganoseleno-substituted phenols has been synthesized. The electron-withdrawing CHO group has been reduced by sodium borohydride to the electron-donating alcohol CH₂OH group, which is desirable for efficient radical quenching activity of phenols. The developed copper-catalyzed reaction conditions enable the installation of two-arylselenium group ortho to phenolic radical chain-breaking antioxidants, which may not be possible by conventional organolithium-bromine exchange methods due to the sluggish reactivity of trianions (dicarba and phenoxide anion), which are generated by the reaction of organolithium with 2,6-dibromophenols, with diorganodiselenides. The antioxidant activities of the synthesized bis and tris selenophenols have been accessed by DPPH, thiol peroxides, and singlet oxygen quenching assay. The radical quenching antioxidant activity has been studied for the synthesized compounds by 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. The bis-selenophenols show comparable radical deactivating activity, while tris seleno-bisphenols show higher radical deactivating activity than α-tocopherol. Furthermore, the tris seleno-bisphenol shows comparable peroxide decomposing activity with ebselen molecules.     

Synthesis and biological evaluations of some Schiff-base esters of ferrocenyl aniline and simple aniline

The synthesis and biological studies of some long chain esters containing Schiff bases and their ferrocenyl analogues were carried out. The 4-amino ferrocene was prepared by the reported method. Long chain esters were synthesized by the condensation of different aliphatic acids with the corresponding aldehyde. The esters were then reacted with aniline as well as with 4-aminophenyl ferrocene to give corresponding Schiff bases. All the synthesized compounds were analyzed by elemental, FTIR and proton NMR studies, were also investigated for a range of biological activities. Determined by crown gall tumor inhibition assay. Antioxidant and DNA protective activities were determined by DPPH free radical scavenging assay and OH radical induced oxidative DNA damage assay, respectively. Among all test compounds, o-hydroxy-p-n-octadecanoyloxy-benzylidine-p-ferrocenyl aniline (FA2.1: a ferrocene containing Schiff base) showed highest antitumor, DPPH free radical scavenging and DNA protective activities.     

Novel 1,3,4-thiadiazole conjugates derived from protocatechuic acid: Synthesis,antioxidant activity,and computational and electrochemical studies

A series of 15 novel 1,3,4-thiadiazole amide derivatives containing a protocatechuic acid moiety were synthesized and structurally characterized. In addition, the corresponding imino (4) and amino (5) analogues of a phenyl-substituted 1,3,4-thiadiazole amide derivative 3a were prepared to compare the effects of the structural changes on the radical-scavenging activity. The obtained compounds were examined for their antioxidative potential by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays. In addition, selected compounds were studied by density functional theory (DFT) and cyclic voltammetry experiments. The tested compounds showed high potential to scavenging DPPH radical and ABTS radical cation compared with the referent antioxidants ascorbic acid and nordihydroguaiaretic acid (NDGA). On the basis of the calculated thermodynamic parameters, it can be concluded that the sequential proton loss electron transfer (SPLET) mechanism represents the most probable reaction path in a polar solvent for DPPH radical–scavenging activity. On the other hand, the single electron transfer followed by proton transfer (SET-PT) can be a likely mechanistic pathway in the case of an ABTS radical cation.     

Radiolysis study of genistein in methanolic solution

The aim of the present work was to identify products obtained from genistein by ionizing radiation and to enhance the antioxidant properties of genistein through radiation-induced transformation. Genistein dissolved in methanol was irradiated γ-rays at a dose of 100 kGy. NMR and (HR) EI-MS spectroscopy were used to identify radiolysis products (GM1 and GM2). We proposed that CH₂OH may be implicated in the formation GM1 and GM2 during radiolysis of genistein in methanol. The genistein in methanol solution showed higher DPPH radical scavenging activity after γ-irradiation. Then, the antioxidant activities of radiolysis products were evaluated and compared to those of genistein.     

Stereochemistry-60 : Kinetic control of asymmetric induction during oxazolidine formation from (-)-ephedrine and aromatic aldehydes

Kinetically controlled oxazolidine formation was observed with aromatic aldehydes substituted by electron-withdrawing groups. The stereoselectivity is solvent dependent: non-stereoselective ring closure occurred in chloroform while a high diastereodifferentiation was observed in methanol. The first oxazolidine showing an unambiguous 2R configuration was synthesized from p-bromobenzaldehyde and (-)-ephedrine in alcohol medium. A mechanism involving a nucleophilic assistance by alcoholic solvents is suggested in order to clarify the differences in stereoselectivity.     

Synthesis of vicinal diols from various arenes with a heterocyclic, amino or carboxyl group by using recombinant Escherichia coli cells expressing evolved biphenyl dioxygenase and dihydrodiol dehydrogenase genes

Various aromatic molecules, in which heterocycles are linked with a phenyl or benzyl group, were converted to their respective 2,3-diols (catechols) in the benzene ring by growing cell reactions using recombinant Escherichia coli, which expressed the evolved biphenyl dioxygenase [bphA (2072)] genes and the subsequent bacterial dihydrodiol dehydrogenase (bphB) gene. These vicinal diol products showed strong in vitro inhibitory activity against the lipid peroxidation induced by free radicals and strong scavenging activity towards DPPH radicals. The vicinal diols were also synthesized from ionized monocyclic aromatics incorporating an amino or carboxyl group.     

Syntheses,characterization, in vitro antiglycation and DPPH radical scavenging activities of isatin salicylhydrazidehydrazone and its Mn (II), Co (II), Ni (II), Cu (II), and Zn (II) metal complexes

2-Hydroxy salicylhydrazide isatin hydrazone (L) and its Mn (II), Co (II), Ni (II), Cu (II), and Zn (II), metal complexes were synthesized. ¹H NMR, UV–Vis, IR spectroscopy and elemental (CHN/S) analysis techniques were applied for characterization. TG/DTA techniques revealed that all the synthetic compounds are thermally stable up to 300 °C. They were found non-electrolytes in nature. Furthermore, all these complexes were evaluated for antiglycation and DPPH radical scavenging activities. They showed varying degree of activity with IC₅₀ values between 168.23 and 269.0 μM in antiglycation and 29.63–57.71 μM in DPPH radical scavenging activity. Mn (II), Co (II), Ni (II), Cu (II), and Zn (II), metal complexes showed good antiglycation as well as DPPH radical scavenging activity. The IC₅₀ values for antiglycation activity are 168.23 ± 2.37, 234.27 ± 4.33, 257.1 ± 6.43, 267.7 ± 8.43, 269.0 ± 8.56 Ni for Co, Zn, Mn, Cu, and Ni complexes, respectively, while IC₅₀ value were found to be 29.63 ± 2.76, 31.13 ± 1.41, 35.16 ± 2.45, 43.53 ± 3.12, 57.71 ± 2.61 μM for Cu, Zn, Mn, Co and Ni complexes, respectively, for DPPH radical scavenging activity. These synthesized metal complexes were found to be better active than standards Rutin (IC₅₀ = 294.46 μM) for anti-glycation, and tert-butyl-4-hydroxyanisole (IC₅₀ = 44.7 μM) for DPPH radical scavenging activity.     

LC-MS/MS Screening,Total Phenolic,Flavonoid and Antioxidant Contents of Crude Extracts from Three Asclepiadaceae Species Growing in Jordan

This study aimed to evaluate the antioxidant activity and total phenolic content (TPC) and total flavonoid content (TFC) of crude extracts obtained from three Asclepiadaceae species, namely, Calotropis procera L., Peruglaria tomentosa L., and Pentatropis spiralis (Forsk.) Decne. Both butanol and aq. methanol extracts of the three species showed the highest amount of phenol and flavonoid contents, which exhibited the greatest antioxidant activity in the scavenging of 2,2-diphenyl-2-picrylhydrazyl free radical (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt radical cation (ABTS), ferrous chelating effect (FIC), and hydroxyl radical (HDR) assays. Phytochemical screening of the extracts revealed the presence of alkaloids, tannins, sponins, flavonoids, terpenoids, and glycosides. LC-MS analysis was carried out to identify the major compounds from each crude extract. A total of 12 phenolic compounds in the extracts of the 3 species were identified and quantified, including 9 flavonoids, 2 hydroxybenzoic acids, and 3 hydroxycinnamic acids. The current study also revealed a good correlation between total phenolic contents and the observed antioxidant activity of the crude extracts.     

Total phenolic content,ferric reducing and DPPH scavenging activity of Arum dioscoridis

Arum dioscoridis, locally called ‘Gavur pancari’, is a wild plant the leaves of which have been used as vegetable and for preparing special soup which has a sour taste. This study was set up to determine in vitro antioxidant activities and total phenolic and flavonoid contents of different extracts of A. dioscoridis. Free radical scavenging activity was evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing activity with different concentrations of ethanol, methanol, acetone and water extracts of the plant leaves. Total phenolic and flavonoid contents were widely variable depending on solvents. Ethanol and methanol extractions of the plant material showed better performances with respect to both phenolic and flavonoid contents, respectively. The highest phenolic and flavonoid contents of ethanol and methanol extracts were 100.890 mg/g GAE and 72.643 mg/g QE, respectively. The lower DPPH scavenging and ferric reducing activities were determined in comparison with previous reports and standard synthetic chemicals.     

Effect of acid and base catalyzed hydrolysis on the yield of phenolics and antioxidant activity of extracts from germinated brown rice (GBR)

The influence of both acidic and basic hydrolysis on the yield, total phenolic content and antioxidative capacity of methanolic extract of germinated brown rice (GBR) was studied. Total phenolic content (TPC), total flavonoid content (TFC), 2,2'-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS) radical cation scavenging, and ferric reducing antioxidant power (FRAP) tests were used for the measurement of antioxidant ability. There was a significant difference p < 0.05) in the TPC and DPPH radical scavenging assay results when comparing neutral with acidic and basic catalysed hydrolysis. The yield of the crude extract was slightly higher in acidic hydrolysis than in basic hydrolysis p > 0.05). The TPC and TFC were highest in acidic hydrolysis. A significant correlation was observed between ABTS radical cation scavenging and FRAP. The antioxidant activity measured using DPPH radical scavenging assay showed high activity in acidic hydrolysis, while the ABTS radical cationscavenging activity and FRAP showed the highest values in basic hydrolysis. The samples were further evaluated using HPLC to determine the individual phenolic concentrations in different hydrolytic media contributing to the antioxidant effects. This study revealed that acidic and basic hydrolysis can improve the yield, phenolic content, and antioxidant activity of germinated brown rice.     

Antibacterial and antioxidant constituents of Acalypha wilkesiana

This study was aimed at characterising the secondary metabolites responsible for antibacterial and antioxidant activities of Acalypha wilkesiana. Purification of the defatted methanol leaves extract was guided by the DPPH free radical scavenging assay as well as by evaluation of the antibacterial activity against four bacterial strains. As a result, geraniin, corilagin, quadrangularic acid M and shikimic acid were purified and isolated. Shikimic acid, reported for the first time from this plant, proved to be the major metabolite of the extract. All the four isolated compounds showed bactericidal activity against extended spectrum beta-lactamase-producing Klebsiella pneumoniae (700603), while corilagin was the single compound to exhibit antioxidant activity (IC₅₀ 53 μg/mL).     

Anti-photoaging activity and inhibition of matrix metalloproteinase (MMP) by marine red alga,Corallina pilulifera methanol extract

Matrix metalloproteinases (MMPs), a key component in photoaging of the skin due to exposure to ultraviolet A, appear to be increased by UV-irradiation-associated generation of reactive oxygen species (ROS). In this study, the alga Corallina pilulifera methanol (CPM) extract has been shown to exert a potent antioxidant activity and protective effect on UVA-induced oxidative stress of human dermal fibroblast (HDF) cell. Antioxidant evaluated by various antioxidant assays. These include reducing power, total antioxidant, DPPH radical scavenging, hydroxyl radical scavenging and protective effect on DNA damage caused by hydroxyl radicals generated. Further, the ROS level was detected using a fluorescence probe, 2′,7′-dichlorofluorescein diacetate (DCFH-DA), which could be converted to highly fluorescent dichlorofluorescein (DCF) with the presence of intracellular ROS on HT-1080 cells. Those various antioxidant activities were compared to standard antioxidants such as α-tocopherol. In addition, the in vitro activities of MMP-2 and MMP-9 in HDF cell were inhibited by C. pilulifera methanol extract dose dependently by using gelatin zymography method. The results obtained in the present study suggested that the C. pilulifera methanol extract may be a potential source of natural anti-photoaging.     

Phytochemical analysis and antioxidant activity of the seed of Telfairia occidentalis Hook (Cucurbitaceae)

The 2,2-diphenyl-1-picryl hydrazyl (DPPH) radical, nitric oxide, reducing power, hydrogen peroxide scavenging, and total antioxidant activities of the methanol extract, n-hexane, dichloromethane, ethyl acetate, butanol and aqueous fractions of the seed of Telfairia occidentalis were evaluated. Total phenolic content was determined using the Folin–Ciocalteu method. The dichloromethane fraction exhibited the highest DPPH radical scavenging, reducing power and total antioxidant activities. Two pure compounds which were identified by FTIR, H-and 2D NMR and Mass spectroscopy as 9-octadecenoic acid (TOS B) and 10-hydroxyoctadecanoic acid (TOS C) and four oily isolates, TOS A, TOS D, TOS E and TOS F were obtained from the dichloromethane fraction. TOS E had the highest DPPH radical scavening activity comparable to that of ascorbic acid. GC-MS analysis revealed the major compounds in TOS E as 4-(2,2-Dimethyl-6-methylene cyclohexylidene)-2-butanol; 3-(3-hydroxybutyl)-2,4,4-trimethyl-2-cyclohexene-1-one and 1,2-Benzenedicarboxylic acid disooctyl ester. Thus, the seed of T. occidentalis can be consumed for its antioxidant property.     

Tertiary aminomethylphenols and methylene bisphenols with isobornyl substituents in the reaction with diphenylpicrylhydrazyl and peroxy radicals in ethylbenzene

The effect of the structure of aminomethylphenols and methylene bisphenols with isobornyl substituents on their reactivity in interactions with peroxy radicals in ethylbenzene and with 1,1-diphenyl-2-picrylhydrazyl (DPPH) is studied. Isobornylphenols with o-aminomethyl substituents, as opposed to p-aminomethyl derivatives, were found to possess rather low activity in the initiated oxidation of ethylbenzene, due to the formation of intramolecular hydrogen bonds between the hydrogen atom of the OH group and the nitrogen atom of the aminomethyl substituent. An increase in activity of o-aminomethyl-substituted phenols with increasing polarity of the medium is observed in the reaction with DPPH. The reaction rate constants for the interaction between two isomeric 2,2′- and 4,4′-methylene-bisphenols having isobornyl moieties and ethylbenzene peroxy radicals are measured. The ratio between activities of the first and second OH groups in 2,2-methylene-bisphenol is shown to be close to 50.     

Thidiazuron-Induced Changes in Biomass Parameters,Total Phenolic Content,and Antioxidant Activity in Callus Cultures of Artemisia absinthium L.

Callus culture of Artemisia absinthium L. was established for enhanced production of phenolics and higher antioxidant activity. Callus was induced from seed-derived leaf explants, incubated on to MS media supplemented with thidiazuron (TDZ; 0.5–5.0 mg/l) either alone or in combination with α-naphthalene acetic acid (NAA; 1.0 mg/l). These callus cultures were investigated for their growth kinetics, total phenolic content, and antioxidant activity on weekly basis for a period of 49 days. Maximum dry biomass accumulation of 8.73 g/l was observed on day 42 in response to 1.0 mg/l TDZ and 1.0 mg/l NAA. Furthermore, maximum level of total phenolic content of 8.53 mg GAE/g DW and highest 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity of 72.6 % were observed in calli formed in response to 1.0 mg/l TDZ on day 42. The results showed a positive correlation of total phenolic content and DPPH radical scavenging activity in most of the callus cultures of A. absinthium L.