Composition and properties of the reaction products of p-cresol with camphene

Russian Chemical Bulletin - The products of the reaction between p-cresol and camphene were isolated and characterized. Their antiradical activity and toxicity were studied. The pharmacological...     

Antioxidant activity of uracil derivatives

The antiradical properties of a number of uracil derivatives are studied in initiated 1,4-dioxane oxidation as a model reaction. The antioxidant activity of the uracil derivatives as inhibitors is estimated. The antiradical activity of the compounds is quantitatively characterized in terms of the effective rate constant of inhibition, fk _In.     

New examples of the involvement of air oxygen in chemical reactions in solution

Two different processes, oxidation of the simplest alkylarenes in aqueous solutions and assessment of antiradical activity of natural antioxidants in blood serum by the rate of formation of fluorescing products from fluorescein dibutyrate, are characterized from a common viewpoint of the involvement in the reactions of air oxygen dissolved in the reaction medium.     

Natural phenolic compounds in the reaction with a nitrogen-centered radical in an aprotic solvent

Kinetics and mechanism of the reaction of vegetable phenols (PhOH) with 2,2′-diphenyl-1-picrylhydrazyl radical (DPPH?) in a polar aprotic solvent, dimethyl sulfoxide, were studied. The reaction of natural phenols with DPPH? in dimethyl sulfoxide occurs in two stages. In the first stage, a proton-coupled electron transfer (PCET) occurs from a PhOH molecule to DPPH? to give primary transformation products, phenoxyl radicals (PhO?) and diphenyl hydrazine (DPPH–H), and in the second, the hydrazyl radical is consumed in the reaction with PhO? transformation products, enolized dimers, which is confirmed by NMR spectroscopy. A relationship was revealed between the antiradical activity of phenols in the reaction with DPPH? (ln k) and the ionization potential of the phenolates being formed.     

Factor Analysis of the Relationship of the Chemical Structure and Anti-Radical Activity of Natural Phenols

Russian Journal of Applied Chemistry - Using multiple linear regression analysis, a relationship has been established between the antiradical activity of various classes of natural phenols and...     

Electrochemical transformations and antiradical activity of asymmetrical RS-substituted pyrocatechols

Redox transformations of sulfides 1–8 combining a fragment of sterically hindered pyrocatechol with alkyl, cycloalkyl, and aromatic substituents were studied. The first step of electrooxidation of thioethers affords o-benzoquinones. The introduction of the redox-active thioether group extends the range of redox properties of pyrocatechols. In the second step, the thioether fragment is involved in the quasi-reversible anodic process, and the number of electrons participating in the electrode reaction depends on the structure of the hydrocarbon group bonded to the sulfur atom. The reactivity of compounds 1–8 toward O₂^?– was evaluated on the basis of the electrochemical data. Cyclopentyl, phenyl, or benzyl substituents in the thioether group exert a greater effect on the antiradical activity than the alkyl moieties. The formation of an o-semiquinolate radical anion in the reaction of pyrocatechol thioethers with KO₂ was detected by the ESR method. It was shown using the reaction with the stable 2,2-diphenyl-1-picrylhydrazyl radical as an example that RS-functionalized pyrocatechols show a higher antiradical activity compared to 3,5-di-tert-butylpyrocatechol.     

Macromolecular antioxidants based on polysaccharides and 2,6-diisobornyl-4-methylphenol derivatives

New macromolecular antioxidants that were conjugates of dextran or hydroxyethylated starch with functionalized derivatives synthesized from 2,6-diisobornyl-4-methylphenol were prepared. Their antiradical activity compared with derivatives of 2,6-di-tert-butyl-4-methylphenol was studied in a model reaction with 2,2-diphenyl-1-picrylhydrazyl. The studied conjugates exhibited greater activity than sterically hindered phenols not bonded to a polymer chain. The synthesized isobornyl derivatives were more active than previously studied tert-butyl analogs.     

Effect of UV radiation and hydrogen peroxide on the antiradical and antioxidant activities of DOPA-melanin and melanosomes from retinal pigment epithelial cells

The effect of continuous UV radiation and hydrogen peroxide on destruction and antioxidant properties of synthetic DOPA-melanin (prepared by oxidation of 3,4-dihydroxyphenylalanine (DOPA)) and melanosomes isolated from cells of the retinal pigment epithelium (RPE) was investigated. The kinetics of melanin destruction was recorded based on the accumulation of fluorescent low-molecular-weight reaction products, the antiradical activity of melanin was determined by chemiluminescence method, the concentration of free radical products was measured by electron paramagnetic resonance, and the antioxidant activity of melanins was estimated by their inhibitory effect on lipid peroxidation. It was shown that UVC—UVA irradiation (up to 5 hours) of DOPA-melanin and melanosomes of retinal pigment epithelium decreased neither the latency period of luminol chemiluminescence nor the inhibitory action of pigments on Fe²⁺- and UV-induced peroxidation of cardiolipin liposomes. However, very long UV irradiation gave rise to fluorescent destruction products, decreased the concentration of paramagnetic centers in the pigment (especially light-dependent ones), and decreased the antiradical and antioxidant activities. For example, UV irradiation of DOPA-melanin during 52 h resulted in approximately a 2-fold decrease in the concentration of paramagnetic centers and decline of antiradical and antioxidant activities. However, even with such a hard irradiation the pigment retained significant inhibitory activity against lipid peroxidation. The oxidative destruction of DOPA-melanin in the presence of hydrogen peroxide in the dark resulted in complete destruction of the polymer and loss of its protective properties. It is assumed that destruction of RPE cell melanin is caused mainly by oxidative processes.     

Phenolic composition and antioxidant activity of propolis from various regions of Poland

The aim of this work was to determine phenolic acid and flavonoid contents, as well as antioxidant properties of propolis from different regions of Poland. Total phenolic content of propolis samples ranged from 150.05 to 197.14 mg/g GAE, while total flavonoid content was 35.64–62.04 mg/g QE. The dominant phenolic acid was p-coumaric acid, the content of which was from 37.54 to 116.95 mg/g. The samples also contained much ferulic acid. Among the flavonoids, chrysine and galangine were dominant, and for two samples, naringine was dominant. The propolis samples exhibited various antiradical activity measured towards DPPH^√ (1.92–2.69 mM TE/g) and ABTS^√+ (3.96–4.98 mM TE/g) and reducing power was determined by the ferric reducing antioxidant power method (6.23–9.19 mM Fe(II)/g). The significant linear correlations between total phenolic content and antiradical activity and between total phenolic content and reducing power were observed. Moreover, the total flavonoids content significantly correlated with antiradical activity and reducing power.     

Antioxidant activity of honey supplemented with bee products

The aim of this work was to evaluate the influence of supplementation of multiflower honey with bee products on the phenolic compound content and on antioxidant activity. Average total phenolic and flavonoids contents in the multiflower honeys were 36.06 ± 10.18 mg GAE/100 g and 4.48 ± 1.69 mg QE/100 g, respectively. The addition of royal jelly did not affect significantly the phenolic compound content and antioxidant activity. Supplementation of honey with other bee products, i.e. beebread, propolis, pollen, resulted in significant increase in the total phenolic and flavonoids contents, and in antiradical activity and reducing power, with the largest effect found for addition of beebread. Significant linear correlations between the total phenolic and flavonoids contents and antiradical activity and reducing power were found.     

Antiradical and cytotoxic activity of different Helichrysum plicatum flower extracts

Flowers of Helichrysum plicatum were extracted under different experimental conditions, and their antioxidant activity was determined by DPPH radical scavenging assay. Extracts obtained with higher concentration of ethyl acetate (90% or 100%) were found to contain the greatest amount of total phenolics (> 250 mg gallic acid equivalents/g of dried extract), and high correlation between total phenolic content and antiradical activity was observed (r = -0.79). Based on the total phenolic content and antiradical activity, some extracts were selected for investigation of cytotoxic activity toward PC3, HeLa and K562 human cancer cell lines in vitro. All tested extracts exhibited moderate activity against HeLa cells (41.9-42.1 microg/mL), whereas the extract obtained with 100% ethyl acetate was the most active against K562 and PC3 cell lines (25.9 and 39.2 microg/mL, respectively). Statistical analysis revealed significant correlation between total phenolic content and cytotoxic activity against PC3 and K562 cells. HPLC identification of phenolic compounds from the extracts indicated the presence of apigenin, naringenin and kaempferol as free aglycones, and glycosides of apigenin, naringenin, quercetin and kaempferol. Among aglycones, kaempferol displayed moderate cytostatic activity against all cell lines (24.8-64.7 microM).     

Are pterins able to modulate oxidative stress?

Pterins (also known as pteridines) are common animal colorants that constitute heterocyclic compounds and have the highest nitrogen content of any pigment analyzed from animals. It has been reported that pterins modulate oxidative stress as these molecules are able to scavenge free radicals. Previous reports suggest three possible mechanisms that are responsible for scavenging free radicals; these are electron transfer (ET) reaction, hydrogen atom transfer (HAT) and radical addition. In this paper, the facility to scavenge free radicals (antiradical power) of pterins is analyzed, using density functional theory calculations and considering two possible mechanisms: ET and HAT. For the electron transfer process, considering the electron donor facility of the free radical scavenger molecules, vertical ionization energy of pterins indicates that the antiradical power of those pterins is lower than the antiradical power of any carotenoids (except for tetrahydrobiopterin). In terms of the HAT mechanism, the bond dissociation energy involved in the removal of one hydrogen atom from pterins is higher than for carotenoids (except for sepiapterin and 7,8-dihydrobiopterin). It can be expected that the most reactive molecules are those that have the smallest dissociation energy since the dissociation of the hydrogen atom is the first step of the reaction. This could indicate that some pterins are depicted as poorer antiradicals than carotenoids in terms of the HAT mechanism. Further studies focusing on the third mechanism (radical addition) and the kinetics of the reactions are necessary in order to fully understand the antiradical power of these substances. For this reason, work continues in order to clarify these aspects.     

Redox transformations and antiradical activity of triarylantimony(V) 3,6-di-tert-butyl-4,5-dimethoxycatecholates

Triarylantimony(V) catecholate complexes were synthesized by the oxidative addition of 3,6-di-tert-butyl-4,5-dimethoxy-o-benzoquinone to triarylstibines. The electrochemical properties and antiradical activity of the synthesized compounds were studied. According to cyclic viltammetry data, the complexes are oxidized via two consecutive quasi-reversible stages. Introduction of halogen atoms in para-position of phenyl groups at Sb(V) causes anodic shifts of the oxidation potentials and enhances stability of the mono- and dicationic forms of the compounds, which form in the course of electrochemical transformations. Triarylantimony(V) catecholate complexes exhibit appreciable antiradical activity in the auto-oxidation of oleic acid. In was found that the inhibitory activity of the complexes depends on their redox potential.     

Essential oil composition and antiradical activity of the oil of Iraq plants

This study examined the antiradical activity and chemical composition of essential oils of some plants grown in Mosul, Iraq. The essential oils of myrtle and parsley seed contained α-pinene (36.08% and 22.89%, respectively) as main constituents. Trans-Anethole was the major compound found in fennel and aniseed oils (66.98% and 93.51%, respectively). The dominant constituent of celery seed oil was limonene (76.63%). Diallyl disulphide was identified as the major component in garlic oil (36.51%). Antiradical activity was higher in garlic oil (76.63%) and lower in myrtle oil (39.23%). The results may suggest that some essential oils from Iraq possess compounds with antiradical activity, and these oils can be used as natural antioxidants in food applications.     

Evaluation of antiradical activity of Schiff bases

Russian Chemical Bulletin - Antioxidant activity of seven Schiff bases (SBs) was studied. The antiradical activity of SBs was determined by the chemiluminescence method from the interception of...     

Antioxidant activity of hydrazones with sterically hindered phenol fragments

Kinetic parameters of the antiradical activity of derivatives of hydrazones of 4-hydroxy-3,5-di-tert-butyl-benzaldehyde are determined photocolorimetrically in their reactions with a stable diphenylpicrylhydrazyl radical, and by chemiluminescence from the capture of peroxide radicals upon the initiated oxidation of ethylbenzene. It is found that during inhibited oxidation, the reactive centers (N-H and O-H) in hetaryl- and acylhydrazone molecules operate in parallel. Regularities of the compounds?? inhibiting effect are studied in heterogeneous systems upon the initiated oxidation of ethylbenzene in emulsion, and in a water-lipid model of the oxidation of phosphatidylcholine dispersion. It is established that hydrazone derivatives are antioxidants of combined action in heterophase processes of the oxidation of unsaturated substrates, displaying properties of hydroperoxide deactivators in addition to their antiradical activity.     

Effect of Succinic Acid on the Antiradical Properties of 5-Hydroxy-6-Methyluracil

Kinetics and Catalysis - The antiradical activity of the associates of 5-hydroxy-6-methyluracil with succinic acid, whose compositions differed in the succinic acid content, in a model system for...     

Influence of the γ-carboline and carbazole pharmacophore moieties on anticholinesterase and antiradical activity of multifunctional agents for the treatment of neurodegenerative diseases

Russian Chemical Bulletin - A comparative analysis of the esterase profile and antiradical activity of two groups of hybrid compounds, viz., tetrahydro-γ-carboline conjugates with carbazoles...     

Trialkylantimony(V) o-amidophenolates: Electrochemical transformations and antiradical activity

The electrochemical transformations and antiradical activity of trialkylantimony(V) o-amidophenolate derivatives, (AP)SbR₃ (AP = 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-amidophenolate); R = CH₃ (I), C₂H₅ (II), and C₆H₁₁ (III), are studied. The electrochemical oxidation of compounds I–III proceeds successively to form mono- and dicationic forms of the complexes. The presence of the donor hydrocarbon groups at the antimony(V) atom shifts the oxidation potentials to the cathodic range and decreases the stability of the monocationic complexes formed in electrochemical oxidation. The second anodic process is irreversible and accompanied by o-iminoquinone decoordination. The antiradical activity of compounds I–III is studied in the reaction with the diphenylpicrylhydrazyl radical and oleic acid autooxidation. The values obtained for indices EC₅₀ and IC₅₀ indicate the antiradical activity of the studied compounds. Complexes I–III were found to be the efficient inhibitors of oleic acid oxidation and act as efficient destructors of hydroperoxides.