Study on the multiple mechanisms underlying the reaction between hydroxyl radical and phenolic compounds by qualitative structure and activity relationship

A Multipurpose Metallophore and Its Copper Complexes with Diverse Catalytic Antioxidant Properties to Deal with Metal and Oxidative Stress Disorders: A Combined Experimental, Theoretical, and In Vitro Study

We report the discovery that the molecule 1-(pyridin-2-ylmethylamino)propan-2-ol (HL) can reduce oxidative stress in neuronal C6 glioma cells exposed to reactive oxygen species (O2-•, H2O2, and •OH) and metal (Cu+) stress conditions. Furthermore, its association with Cu2+ generates [Cu(HL)Cl2] (1) and [Cu(HL)2](ClO4)2 (2) complexes that also exhibit antioxidant properties. Potentiometric titration data show that HL can coordinate to Cu2+ in 1:1 and 1:2 Cu2+:ligand ratios, which was confirmed by monocrystal X-ray studies. The subsequent ultraviolet-visible, electrospray ionization mass spectrometry, and electron paramagnetic resonance experiments show that they can decompose a variety of reactive oxygen species (ROS). Kinetic studies revealed that 1 and 2 mimic the superoxide dismutase and catalase activities. Complex 1 promotes the fastest decomposition of H2O2 (kobs = 2.32 × 107 M-1 s-1), efficiently dismutases the superoxide anion (kcat = 3.08 × 107 M-1 s-1), and scavenges the hydroxyl radical (RSA50 = 25.7 × 10-6 M). Density functional theory calculations support the formation of dinuclear Cu-peroxide and mononuclear Cu-superoxide species in the reactions of [Cu(HL)Cl2] with H2O2 and O2•-, respectively. Furthermore, both 1 and 2 also reduce the oxidative stress of neuronal glioma C6 cells exposed to different ROS, including O2•- and •OH.

Oleogelation of extra virgin olive oil by different gelators affects lipid digestion and polyphenol bioaccessibility

The possibility to steer extra virgin olive oil (EVOO) digestion and polyphenol bioaccessibility through oleogelation was investigated. EVOO was converted into oleogels using lipophilic (monoglycerides, rice wax, sunflower wax, phytosterols) or hydrophilic (whey protein aerogel particles, WP) gelators. In-vitro digestion demonstrated that the oleogelator nature influenced both lipid digestion and polyphenol bioaccessibility. WP-based oleogels presented ∼100% free fatty acid release compared to ∼64% for unstructured EVOO and ∼40 to ∼55% for lipophilic-based oleogels. This behavior was attributed to the ability of WP to promote micelle formation through oleogel destructuring. Contrarily, the lower lipolysis of EVOO gelled with lipophilic gelators compared to unstructured EVOO suggested that the gelator obstructed lipase accessibility. Tyrosol and hydroxytyrosol bioaccessibility increased for WP oleogels (∼27%), while liposoluble-based oleogels reduced it by 7 to 13%. These findings highlight the deep effect of the gelator choice on the digestion fate of EVOO components in the human body.

Sunflower and Palm Kernel Meal Present Bioaccessible Compounds after Digestion with Antioxidant Activity

Sunflower (Helianthus annuus L.) and African palm kernel (Elaeis guineensis Jacq.) are among the most cultivated in the world regarding oil extraction. The oil industry generates a large amount of meal as a by-product, which can be a source of nutrients and bioactive compounds. However, the physiological effects of bioactive compounds in such matrices are only valid if they remain bioavailable and bioactive after simulated gastrointestinal digestion. This study evaluated the chemical composition and antioxidant and prebiotic potential of de-oiled sunflower (DS) and de-oiled palm kernel (DP) meal after in vitro digestion. The DS sample had the highest protein content and the best chemical score, in which lysine was the limiting amino acid. Digested samples showed increased antioxidant activity, measured by in vitro methods. The digested DS sample showed a better antioxidant effect compared to DP. Moreover, both samples managed to preserve DNA supercoiling in the presence of the oxidizing agent. The insoluble fractions after digestion stimulated the growth of prebiotic bacterium, similar to inulin. In conclusion, simulated gastrointestinal digestion promoted in both matrices an increase in protein bioaccessibility and antioxidant capacity, pointing to a metabolic modulation favorable to the organism.

Synthesis of Caffeoyl-Prolyl-Histidyl-Xaa Derivatives and Evaluation of Their Activities and Stability upon Long-Term Storage

Antioxidants play a critical role in the treatment of degenerative diseases and delaying the aging of dermal tissue. Caffeic acid (CA) is a representative example of the antioxidants found in plants. However, CA is unsuitable for long-term storage because of its poor stability under ambient conditions. Caffeoyl-Pro-His-NH₂ (CA-Pro-His-NH₂, CA-PH) exhibits the highest antioxidant activity, free radical scavenging and lipid peroxidation inhibition activity among the histidine-containing CA-conjugated dipeptides reported to date. The addition of short peptides to CA, such as Pro-His, is assumed to synergistically enhance its antioxidative activity. In this study, several caffeoyl-prolyl-histidyl-Xaa-NH₂ derivatives were synthesized and their antioxidative activities evaluated. CA-Pro-His-Asn-NH₂ showed enhanced antioxidative activity and higher structural stability than CA-PH, even after long-term storage. CA-Pro-His-Asn-NH₂ was stable for 3 months, its stability being evaluated by observing the changes in its NMR spectra. Moreover, the solid-phase synthetic strategy used to prepare these CA-Pro-His-Xaa-NH₂ derivatives was optimized for large-scale production. We envision that CA-Pro-His-Xaa-NH₂ derivatives can be used as potent dermal therapeutic agents and useful cosmetic ingredients.

An appraisal of natural products active against parasitic nematodes of animals

Here, the scientific and patent literature on the activities of purified natural compounds has been reviewed, with the aim of assessing their suitability as anthelmintic drug discovery starting points. Only compounds described as active against parasitic nematodes of animals or against the model nematode Caenorhabditis elegans have been analysed. Scientific articles published since 2010 and patents granted from 2000, both inclusive, have been included in this analysis. The results show a scarcity of novel chemical structures, a limited follow-up of compounds disclosed before 2010 and a bias towards the screening of plant products, almost to the exclusion of other sources, when microbial extracts have, historically, provided most starting points for anti-infective drugs. All plant products published in this period were previously known, alerting to the high re-discovery rates of a limited number of chemical classes from this source. The most promising compounds described in the literature reviewed here, namely the linear nemadectin-derivatives, are novel and of bacterial origin. Patented but otherwise unpublished spiroketal structures also appear as interesting scaffolds for future development. The patent literature confirmed that it is possible to patent derivatives of previously known products, making them valid starting points for translational research.

Colorimetric, electroanalytical and theoretical evaluation of the antioxidant activity of Syzygium aromaticum L., Origanum vulgare L., Mentha spicata L. and Eremanthus erythropappus M. essential oils, and their major constituents

Antioxidant mechanism of essential oils and their major constituents, and the synergism between them.

Increasing the Durability of Polymer Electrolyte Membranes Using Organic Additives

Herein, we utilize organic radical scavengers to mitigate the chemical degradation of polymer membranes without sacrificing their proton conductivity. Several hydrocarbon composite membranes based on sulfonated poly(arylene ether sulfone) (SPES50, degree of sulfonation = 50%) and containing organic radical scavengers were prepared and characterized in terms of water uptake, ion-exchange capacity, proton conductivity, and oxidative stability, being additionally exposed to hydrogen peroxide for accelerated oxidative stability testing. Precise analysis of the molecular weight and its distribution before and after the above test confirmed that the incorporation of radical scavengers enhanced the chemical durability of membranes while maintaining their proton conductivity. Finally, in an accelerated open circuit voltage durability test, composite membranes showed lifetimes exceeding 1400 h, whereas pristine SPES50 failed after 750 h. On the basis of the above, organic radical scavengers were concluded to be superior to those based on transition-metal compounds, not engaging in any interactions with the sulfonate groups of the membrane polymer and hence not compromising their proton conductivity.

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.

Evaluation of phenolic composition and antioxidant activity changes in olive flowers during development using HPLC/DAD and LC-MS/MS

Olive fruit and leaves have been extensively studied for their chemical compositions and biological activities. However, less attention has been given to its flowers. The present research was achieved on Tunisian olive flowers. It aimed at studying the effects of flower development on phenolic compounds and antioxidant activity. The extracts were analyzed using high performance liquid chromatography coupled to diode array detection (HPLC/DAD) and coupled to mass spectrometry (LC-MS/MS). The HPLC/DAD analysis indicated that oleuropein aglycon (from 1.158 to 3.746 g/kg), followed by hydroxytyrosol (from 0.168 to 1.581 g/kg) and oleoside (from 0.143 to 1.325 g/kg) were the predominant phenolics in olive flowers extracts during development stages. Twenty compounds have been identified, revealing the complex profile of olive flowers, composed, in order of abundance, by secoiridoids, phenolic alcohols, lignans, flavonoids and phenolic acids. Total phenolic contents increased from 2.455 to 8.541 g/kg Gallic acid equivalent per kg of fresh flowers during all steps of the flower development. A correlation between antioxidant activity and total phenolic contents was determined.

Antioxidant Properties of Kynurenines: Density Functional Theory Calculations

Kynurenines, the main products of tryptophan catabolism, possess both prooxidant and anioxidant effects. Having multiple neuroactive properties, kynurenines are implicated in the development of neurological and cognitive disorders, such as Alzheimer's, Parkinson's, and Huntington's diseases. Autoxidation of 3-hydroxykynurenine (3HOK) and its derivatives, 3-hydroxyanthranilic acid (3HAA) and xanthommatin (XAN), leads to the hyperproduction of reactive oxygen species (ROS) which damage cell structures. At the same time, 3HOK and 3HAA have been shown to be powerful ROS scavengers. Their ability to quench free radicals is believed to result from the presence of the aromatic hydroxyl group which is able to easily abstract an electron and H-atom. In this study, the redox properties for kynurenines and several natural and synthetic antioxidants have been calculated at different levels of density functional theory in the gas phase and water solution. Hydroxyl bond dissociation enthalpy (BDE) and ionization potential (IP) for 3HOK and 3HAA appear to be lower than for xanthurenic acid (XAA), several phenolic antioxidants, and ascorbic acid. BDE and IP for the compounds with aromatic hydroxyl group are lower than for their precursors without hydroxyl group. The reaction rate for H donation to *O-atom of phenoxyl radical (Ph-O*) and methyl peroxy radical (Met-OO*) decreases in the following rankings: 3HOK ~ 3HAA > XAA_OXO > XAA_ENOL. The enthalpy absolute value for Met-OO* addition to the aromatic ring of the antioxidant radical increases in the following rankings: 3HAA* < 3HOK* < XAA_OXO* < XAA_ENOL*. Thus, the high free radical scavenging activity of 3HAA and 3HOK can be explained by the easiness of H-atom abstraction and transfer to O-atom of the free radical, rather than by Met-OO* addition to the kynurenine radical.

Kynurenines, the tryptophan metabolites with multiple biological activities, regulate the production of reactive oxygen species (ROS) during several neurodegenerative diseases. Many experiments show that kynurenines can be both prooxidants and antioxidants depending on their concentration, mode of action, and cell redox potential. However, there is lack of computational studies of kynurenines properties which could help us better understand the biophysical mechanism of their antioxidant activity. We performed the computations of kynurenines' hydrogen and electron donating power, both in the gas phase and in water solution. We found that aromatic hydroxyl group facilitates hydrogen and electron abstraction by kynurenines, in agreement with experimental data and computations earlier performed for phenolic antioxidants. We revealed the correlations of kynurenines' antioxidant power with their electronic structure, charge, and surroundings. We also found that 3-hydroxykynurenine and 3-hydroxyanthranilic acid can fastly quench free radicals by hydrogen atom donation. Hence both of them are potent antioxidants. The therapeutic strategy may be to inhibit their oxidative dimerization leading to ROS production.

Combining in vitro and in silico approaches to evaluate the multifunctional profile of rosmarinic acid from Blechnum brasiliense on targets related to neurodegeneration

Natural products are important sources of chemical diversity leading to unique scaffolds that can be exploited in the discovery of new drug candidates or chemical probes. In this context, chemical and biological investigation of ferns and lycophytes occurring in Brazil is an approach adopted by our research group aiming at discovering bioactive molecules acting on neurodegeneration targets. In the present study, rosmarinic acid (RA) isolated from Blechnum brasiliense showed an in vitro multifunctional profile characterized by antioxidant effects, and monoamine oxidases (MAO-A and MAO-B) and catechol-O-methyl transferase (COMT) inhibition. RA showed antioxidant effects against hydroxyl (HO(•)) and nitric oxide (NO) radicals (IC50 of 29.4 and 140 μM, respectively), and inhibition of lipid peroxidation (IC50 of 19.6 μM). In addition, RA inhibited MAO-A, MAO-B and COMT enzymes with IC50 values of 50.1, 184.6 and 26.7 μM, respectively. The MAO-A modulation showed a non-time-dependent profile, suggesting a reversible mechanism of inhibition. Structural insights on RA interactions with MAO-A and COMT were investigated by molecular docking. Finally, RA (up to 5 mM) demonstrated no cytotoxicity on polymorphonuclear rat cells. Taken together, our results suggest that RA may be exploited as a template for the development of new antioxidant molecules possessing additional MAO and COMT inhibition effects to be further investigated on in vitro and in vivo models of neurodegenerative diseases.

Optimization Extraction Process of Polysaccharides from Suillus granulatus and Their Antioxidant and Immunological Activities In vitro

BACKGROUND

Suillus granulatus is an edible and medicinal fungus in China. S. granulatus polysaccharide (SGP) was considered as the main bioactivity compounds in S. granulatus. Therefore, the extraction of SGP and their antioxidant activities were studied in this work.

MATERIALS AND METHODS

Fruiting bodies of S. granulatus were purchased from a local market (Fushun, China). Response surface methodology was adopted to optimize the extraction conditions of SGP. The antioxidant and immunological activities in vitro were also assayed.

RESULTS

The extraction of SGP was optimized by a Box-Behnken design. The optimal conditions for the extraction of polysaccharides were as follows: Pre-extraction time, 2 h; extraction temperature, 94°C; ratio of water to raw material, 25; and extraction frequency, 2. Under these conditions, the experimental yield of polysaccharides was 5.38% ±0.15%, which agreed with the predicted yield. The antioxidant assay in vitro showed that SGPs had relatively high scavenging ability for hydroxyl radicals and higher scavenging ability for 1,1-diphenyl-2-picrylhydrazyl radical. However, the scavenging ability of SGPs for superoxide anion radical and reducing power was relatively low. The polysaccharides also significantly increased splenocyte proliferation in vitro.

CONCLUSION

SGP possessed good antioxidant and immunological activities in vitro and explored as a novel natural antioxidant or functional food.

SUMMARY

The predictive model of Suillus granulatus polysaccharide (SGP) extraction is adequate for the extraction processSGP possessed a good antioxidant activity in vitroLymphocyte proliferation in vitro was significantly increased by SGPPictorial abstract (in MS Powerpoint Format) is submitted as a separated file in the online submission system. Abbreviation used: SGP: Suillus granulatus polysaccharides, RSM: Response surface methodology, BBD: Box-Behnken design, Vc: Ascorbic acid, DPPH: 1,1-diphenyl-2-picrylhydrazyl, MTT: 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, ConA: Concanavalin A, LPS: lipopolysaccharide, RPMI-1640: Roswell Park Memorial Institute-1640.

Metabolic disposition and biological significance of simple phenols of dietary origin: hydroxytyrosol and tyrosol

Hydroxytyrosol and tyrosol are dietary phenolic compounds present in virgin olive oil and wine. Both compounds are also endogenously synthesized in our body as byproducts of dopamine and tyramine metabolisms, respectively. Over the last decades, research into hydroxytyrosol and tyrosol has experienced an increasing interest due to the role that these compounds may play in the prevention of certain pathologies (e.g. cardiovascular, metabolic, neurodegenerative diseases and cancer). The translation of promising in vitro and in vivo biological effects from preclinical studies to the context of human disease prevention initially depends on whether the dose ingested becomes available at the site of action. In this regard, information regarding the bioavailability and metabolic disposition of hydroxytyrosol and tyrosol is of most importance to evaluate the impact they may have on human health. In this review, we discuss and summarize the state of the art of the scientific evidence regarding the processes of absorption, distribution, metabolism and excretion of both hydroxytyrosol and tyrosol. We also examine the impact of these compounds and their metabolites on biological activity in terms of beneficial health effects. Finally, we evaluate the different analytical approaches that have been developed to measure the plasma and urinary levels of hydroxytyrosol, tyrosol and their metabolites.

Computational studies of free radical-scavenging properties of phenolic compounds

For more than half a century free radical-induced alterations at cellular and organ levels have been investigated as a probable underlying mechanism of a number of adverse health conditions. Consequently, significant research efforts have been spent for discovering more effective and potent antioxidants / free radical scavengers for treatment of these adverse conditions. Being by far the most used antioxidants among natural and synthetic compounds, mono- and polyphenols have been the focus of both experimental and computational research on mechanisms of free radical scavenging. Quantum chemical studies have provided a significant amount of data on mechanisms of reactions between phenolic compounds and free radicals outlining a number of properties with a key role for the radical scavenging activity and capacity of phenolics. The obtained quantum chemical parameters together with other molecular descriptors have been used in quantitative structure-activity relationship (QSAR) analyses for the design of new more effective phenolic antioxidants and for identification of the most useful natural antioxidant phenolics. This review aims at presenting the state of the art in quantum chemical and QSAR studies of phenolic antioxidants and at analysing the trends observed in the field in the last decade.

Antiradical and reductant activities of anthocyanidins and anthocyanins, structure-activity relationship and synthesis

Eight anthocyanidins, seven anthocyanins and two synthesized 4'-hydroxy flavyliums were examined as hydrogen donors to DPPH, ABTS and hydroxyl radicals, and as electron donors in the FRAP assay. Most compounds gave better activities than trolox and catechol. A structure-activity relationship (SAR) study showed that, in the absence of the 3-OH group, radicals of the 4, 5 or 7-OH groups can only be stabilized by resonance through pyrylium oxygen, while 3-OH group improved hydrogen atom donation because of the stabilization by anthocyanidin semiquinone-like resonance. Electron donation was also enhanced by the 3-OH group. Both anthocyanidins and their respective anthocyanins showed similar trends and close activities. Different types of sugar unit bonded to the 3-OH group or counter ion had minor effect on activities. The catechol structure improved both hydrogen and electron donation. Compounds lacking the catechol structure had a decreasing order of H-atom and electron donation (Mv>Pn>Pg>Ap>4'-OH-flavylium) consistent with the decreasing number of their hydroxyl and/or methoxy groups.

Computational and Investigative Study of Flavonoids Active against Trypanosoma cruzi and Leishmania spp

Flavonoid compounds active against Trypanosoma cruzi and Leishmania species were submitted to several methodologies in silico: docking with the enzymes cruzain and trypanothione reductase (from T. cruzi), and N-myristoyltransferase, dihydroorotate dehydrogenase, and trypanothiona reductase (from Leishmania spp). Molecular maps of the complexes and the ligands were calculated. In order to compare and evaluate the antioxidant activity of the flavonoids with their antiprotozoal activity, quantum parameters were calculated. Considering the energies, interactions, and hydrophobic surfaces calculated, the flavonoids chrysin dimethyl ether against T. cruzi, and ladanein against Leishmania sp. presented the best results. The antioxidant activity did not show any correlation with anti-parasitic activity; only chrysin and its dimethyl ether showed favorable anti-parasitic results. This study hopes to contribute to existing research on these natural products against these tropical parasites.

Elucidation of hydroxyl groups-antioxidant relationship in mono- and dihydroxyflavones based on O-H bond dissociation enthalpies

Radical scavenging potential is the key to anti-oxidation of hydroxyflavones which generally found in fruits and vegetables. The objective of this work was to investigate the influence of hydroxyl group on the O-H bond dissociation enthalpies (BDE) from a series of mono- and dihydroxyflavones. Calculation at the B3LYP/6-31G(d,p) level reveals the important roles of an additional one hydroxyl group to boost the BDE of hydroxyflavones that were a stabilization of the generated radicals through attractive H-bond interactions, an ortho- and para-dihydroxyl effect, and a presence of the 3-OH in dihydroxyflavones. On the other hand, the meta-dihydroxyl effect and range-hydroxyl effect especially associated with the either 5-OH or 8-OH promoted greater BDE. Results did not only confirm that dihydroxyflavones had lower BDE than monohydroxyflavones but also suggest the selective potent hydroxyflavone molecules that are the 6'-hydroxyflavone (for monohydroxyflavone) and the 5',6'-, 7,8- and 3',4'-dihydroxyflavone which the corresponding radical preferable generated at C6'-O•, C8-O• and C4'-O•, respectively. Electron distribution was limited only over the two connected rings of hydroxyflavones while the expansion distribution into C-ring could be enhanced if the radical was formed especially for the 2',3'- and 5',6'dihydroxyflavone radicals. The delocalized bonds were strengthened after radical was generated. However the 5-O• in 5,6-dihydroxyflavone and the 3-O• in 3,6'-dihydroxyflavone increased the bond order at C4-O11 which might interrupt the conjugated delocalized bonds at the keto group.

Extraction optimization of polysaccharide from Zanthoxylum bungeanum using RSM and its antioxidant activity

Polysaccharide prepared from pericarp of Zanthoxylum bungeanum was proved to possess excellent antioxidant activities in vitro by using reducing ferric iron power, DPPH radical scavenging activity, chelating ferrous iron capacity, and hydroxyl radical scavenging activity assays in the present study. In those four antioxidant assay models, Z. bungeanum polysaccharide (ZBP) displayed prominent antioxidant activities with low EC50 values of 0.011, 0.021, 0.056 and 0.008 mg/mL, respectively. Moreover, the extraction process of ZBP was further optimized by response surface methodology combined with Box-Behnken design. The highest polysaccharide yield 13.96%, which agreed closely with the predicted yield 13.20%, was obtained under the optimal extraction conditions as follows: extraction temperature 89 °C, extraction time 3h, ratio of water volume (mL) to raw material weight (g) 29 (v/w), and extraction number two times. The present research not only provide theoretical basis for exploitation of natural polysaccharide antioxidants, but also establish the foundation of large-scale production and further system utilization of ZBP.

Enzymolysis-ultrasonic assisted extraction, chemical characteristics and bioactivities of polysaccharides from corn silk

An enzymolysis-ultrasonic assisted extraction (EUAE) procedure of corn silk polysaccharides (CSPS) was established and the physicochemical properties, antioxidant and anticancer activities of CSPS were studied. Orthogonal test and response surface methodology were applied to optimize the extraction parameters. The optimum enzymolysis and ultrasonic conditions were cellulase content of 7.5% for 150 min at 55 °C and liquid-solid ratio of 31.8 for 34.2 min at 66.3 °C, respectively. Under these conditions, the yield of CSPS increased from 4.56% to 7.10%. CSPS obtained by hot water and EUAE were composed of rhamnose, arabinose, xylose, mannose, galactose and glucose with molecular ratios of 4.17:17.33:5.59:18.65:19.11:35.14 and 8.83:15.77:7.92:12.39:11.15:43.94, respectively. Their molecular weight distributions were 10.52 × 10(4) and 6.88 × 10(4)Da, respectively. CSPS obtained by EUAE showed morphological and conformation changes and higher antioxidant and anticancer activities compared with CSPS extracted by hot water.

Reducing power: the measure of antioxidant activities of reductant compounds?

Electrochemical assay has been employed recently to study the activity of antioxidants; however, there is controversy as to whether reducing power fully characterizes the antioxidant activity. This study provides some essential further evidence on this point based on the reported data and mechanisms underlying the antioxidant functions as well as the anodic oxidation of phenolic antioxidants, indicating that further consideration and investigation should be made before reducing power is used as the absolute measure of antioxidant activity.

Structural features, kinetics and SAR study of radical scavenging and antioxidant activities of phenolic and anilinic compounds

BACKGROUND

Phenolic compounds are widely distributed in plant kingdom and constitute one of the most important classes of natural and synthetic antioxidants. In the present study fifty one natural and synthetic structurally variant phenolic, enolic and anilinic compounds were examined as antioxidants and radical scavengers against DPPH, hydroxyl and peroxyl radicals. The structural diversity of the used phenolic compounds includes monophenols with substituents frequently present in natural phenols e.g. alkyl, alkoxy, ester and carboxyl groups, besides many other electron donating and withdrawing groups, in addition to polyphenols with 1-3 hydroxyl groups and aminophenols. Some common groups e.g. alkyl, carboxyl, amino and second OH groups were incorporated in ortho, meta and para positions.

RESULTS

SAR study indicates that the most important structural feature of phenolic compounds required to possess good antiradical and antioxidant activities is the presence of a second hydroxyl or an amino group in o- or p-position because of their strong electron donating effect in these positions and the formation of a stable quinone-like products upon two hydrogen-atom transfer process; otherwise, the presence of a number of alkoxy (in o or p-position) and /or alkyl groups (in o, m or p-position) should be present to stabilize the resulted phenoxyl radical and reach good activity. Anilines showed also similar structural feature requirements as phenols to achieve good activities, except o-diamines which gave low activity because of the high energy of the resulted 1,2-dimine product upon the 2H-transfer process. Enols with ene-1,2-diol structure undergo the same process and give good activity. Good correlations were obtained between DPPH inhibition and inhibition of both OH and peroxyl radicals. In addition, good correlations were obtained between DPPH inhibition and antioxidant activities in sunflower oil and liver homogenate systems.

CONCLUSIONS

In conclusion, the structures of good anti radical and antioxidant phenols and anilines are defined. The obtained good correlations imply that measuring anti DPPH activity can be used as a simple predictive test for the anti hydroxyl and peroxyl radical, and antioxidant activities. Kinetic measurements showed that strong antioxidants with high activity have also high reaction rates indicating that factors stabilizing the phenoxyl radicals lower also the activation energy of the hydrogen transfer process.

Attenuation of renal ischemia/reperfusion injury by a polysaccharide from the roots of Dipsacus asperoides

Renal ischemia-reperfusion (I/R) injury is a leading cause of acute renal failure and one of the major problems after I/R is the production of large amounts of reactive oxygen species (ROS). The present study was performed to evaluate the interference of a polysaccharide (WRDAP-1) from the roots of Dipsacus asperoides in I/R-induced renal injury in rats to determine whether it was mediated by the protective mechanism against oxidative stress to kidney. In vitro experiment, WRDAP-1 exhibited a potent scavenging ability on superoxide radical and hydroxyl radical. Renal protective effect of WRDAP-1 was evaluated in serum levels of blood urea nitrogen (BUN), creatinine, lactate dehydrogenase (LDH), superoxide dismutase (SOD) and serum malonaldehyde (MDA), as well as some renal tissue antioxidant enzymes activities like SOD glutathion peroxidase (GSH-Px) and catalase (CAT). Pretreatment with WRDAP-1 produced reduction in serum levels of BUN, creatinine and LDH caused by I/R injury and significantly improved serum enzymatic activity of SOD and serum MDA level. Additionally, antioxidant enzymes activities of SOD, GSH-Px and CAT in renal tissue were also elevated by WRDAP-1. Collectively, administration with WRDAP-1 significantly improved renal function of I/R rats especially in the rats treated with higher dose of the polysaccharide. Therefore the findings of this study imply that the protective effect of WRDAP-1 against renal I/R injury in rat kidneys could be due to its antioxidant and free radical scavenging activities. WRDAP-1 seems to be a highly promising agent for protecting tissues from oxidative damage and preventing kidney damage due to renal I/R.

Inhibitory effects of resveratrol analogs on mushroom tyrosinase activity

Skin pigmentation disorders typically involve an overproduction or uneven distribution of melanin, which results in skin spots. Resveratrol can inhibit tyrosinase, the active enzyme in the synthesis of melanin, but it does not inhibit the synthesis of melanin to an extent that enables its use alone as a skin whitening agent in pharmaceutical formulations, so its use as a coadjuvant in treatment of hyperpigmentation is suggested. Six resveratrol analogs were tested for tyrosinase inhibitory activity in vitro. Among the analogs tested, compound D was the most powerful tyrosinase inhibitor (IC(50) = 28.66 µg/mL), two times more active than resveratrol (IC(50) = 57.05 µg/mL), followed by the analogs A, E, B, F and C, respectively. This demonstrated that the hydroxylation at C4' on the phenolic ring was the molecular modification with most importance for the observed activity.

Photooxidation of benzene-structured compounds: influence of substituent type on degradation kinetic and sum water parameters

The combined influence of substituent type and UV/H(2)O(2) process parameters on the degradation of four aromatic water pollutants was investigated using modified 3(3) full factorial design and response surface methodology. Degradation kinetics was described by the quadratic polynomial model. According to the applied ANOVA, besides pH and [H(2)O(2)], model terms related with the pollutant structure are found to be significant. Different optimal operating conditions and values of observed degradation rate constants were determined for each of the pollutants indicating that the type of substituent influences the overall process effectiveness over structurally defined degradation pathway. Biodegradability (BOD(5)/COD) and toxicity (TU) were evaluated prior to the treatment and at the reference time intervals t(1/2)(P), t(3/4)(P), t(1/4)(OC) and t(1/2)(OC) corresponding to the real time required to reduce the concentration of parent pollutant and organic content for 1/2, 3/4, 1/4 and 1/2 of initial amount. The observed differences are correlated to the structural differences of studied aromatics.

Free radical scavenging and reducing power of Lawsonia inermis L. seeds

OBJECTIVE

To determine the antioxidant activity, total phenolic and flavonoid content of Petroleum ether extract (PE), Dichloromethane extract (DCM), Ethanol extract (ET) and aqueous extract (AQ) of henna seeds.

METHODS

Total antioxidant assay (phosphomolybenum method), DPPH radical scavenging assay, reducing power assay and lipid peroxidation inhibition assay were used to ascertain the potential of seeds as an antioxidant.

RESULTS

In all the assays carried out ET showed a greater potential to scavenge DPPH radical, reduce MO (VI) to MO (V) complex and Fe (III) to Fe (II) and to inhibit lipid peroxidation. The IC(50) of ET was far greater than that of the standard, ascorbic acid (AS) in the lipid peroxidation assay. The activity of AQ was lesser when compared with that of ET but greater than PE and DCM. The amount of phenolics and flavonoids were present in higher amounts in ET followed by AQ. Trace amounts of phenolics were detected in PE and DCM, but the amount of flavonoids were below the detection level. The study showed that the antioxidant activity and the concentrations of phenolics and flavonoids are proportionate to each other.

CONCLUSIONS

Ethanolic extract of henna seeds are efficient antioxidants, which can be utilized for further isolation of active compounds and pharmaceutical applications.