The mechanistic insights into the role of pH and solvent on antiradical and prooxidant properties of polyphenols - Nine compounds case study.

Polyphenols are the most widely intake exogenous antioxidants. Their properties prevent the accumulation of radicals in the body and the development of oxidative stress, a recognized trigger for some diseases and a manifestation of others. Nonetheless, apart from their beneficial effects, polyphenols might also exhibit prooxidant potential, often observed as the oxidation of transition state metals, resulting in amplified radical production. DFT studies at the B3LYP/6-311++G(d,p) level of theory were conducted on nine common polyphenolic compounds to assess both activities in physiologically relevant media. It has been found that there is a fine line between antioxidant and prooxidant character, and increasing pH values promote the occurrence of the latter. Anthocyanidins proved to be the most potent radical scavengers, particularly under slightly alkaline conditions, followed by flavonoids and phenolic acids last. Antiradical activity is better in a polar solvent than in apolar one, due to the possibility of dissociation.

The Antimicrobial Properties of Poplar and Aspen-Poplar Propolises and Their Active Components against Selected Microorganisms, including Helicobacter pylori.

There is a noticeable interest in alternative therapies where the outcome is the eradication of the Gram-negative bacterium, Helicobacter pylori (H. pylori), for the purpose of treating many stomach diseases (chronic gastritis and peptic ulcers) and preventing stomach cancer. It is especially urgent because the mentioned pathogen infects over 50% of the world's population. Recent studies have shown the potential of natural products, such as medicinal plant and bee products, on the inhibition of H. pylori growth. Propolis is such a bee product, with known antimicrobial activities. The main scope of the study is the determination of the antimicrobial activity of ethanolic extracts from 11 propolis samples (mostly from Poland, Ukraine, Kazakhstan, and Greece) against H. pylori, as well as selected bacterial and yeast species. The most effective against H. pylori was the propolis from Ukraine, with an MIC = 0.02 mg/mL while the rest of samples (except one) had an MIC = 0.03 mg/mL. Moreover, significant antimicrobial activity against Gram+ bacteria (with an MIC of 0.02-2.50 mg/mL) and three yeasts (with an MIC of 0.04-0.63 mg/mL) was also observed. A phytochemical analysis (polyphenolic profile) of the propolis samples, by ultra-high-performance liquid chromatography-diode array detector-mass spectrometry (UPLC-DAD-MS), was performed. An evaluation of the impact of the propolis components on antimicrobial activity, consisting of statistical analyses (principal component analysis (PCA) and hierarchical fuzzy clustering), was then performed. It was observed that the chemical composition characteristics of the poplar propolis correlated with higher antibacterial activity, while that of the poplar and aspen propolis correlated with weaker antibacterial activity. To summarize the activity in vitro, all tested propolis samples indicate that they can be regarded as useful and potent factors in antimicrobial therapies, especially against H. pylori.

A Statistically Supported Antioxidant Activity DFT Benchmark-The Effects of Hartree-Fock Exchange and Basis Set Selection on Accuracy and Resources Uptake.

Polyphenolic compounds are now widely studied using computational chemistry approaches, the most popular of which is Density Functional Theory. To ease this process, it is critical to identify the optimal level of theory in terms of both accuracy and resource usage-a challenge we tackle in this study. Eleven DFT functionals with varied Hartree-Fock exchange values, both global and range-separated hybrids, were combined with 14 differently augmented basis sets to calculate the reactivity indices of caffeic acid, a phenolic acid representative, and compare them to experimental data or a high-level of theory outcome. Aside from the main course, a validation of the widely used Janak's theorem in the establishment of vertical ionization potential and vertical electron affinity was evaluated. To investigate what influences the values of the properties under consideration, linear regression models were developed and thoroughly discussed. The results were utilized to compute the scores, which let us determine the best and worst combinations and make broad suggestions on the final option. The study demonstrates that M06-2X/6-311G(d,p) is the best fit for such research, and, curiously, it is not necessarily essential to include a diffuse function to produce satisfactory results.

Antiradical Activity of Beetroot (Beta vulgaris L.) Betalains.

Flavonoids, phenolic acids, and anthocyanidins are widely studied polyphenolics owing to their antiradical activity. Recently, beetroot dyes have drawn an attention as possible radical scavengers, but scant information can be found on this topic. In this study selected compounds were investigated using computational chemistry methods. Implicit water at physiological pH was chosen as the environment of interest. Betalains' dissociation process and electronic structure were examined, as well as the reactivity in six pathways against some common radicals, such as hydroxyl, hydroperoxide, superoxide, and nitric oxide. The study showed that all carboxyl groups are dissociated in the given conditions. The dissociation process impacts the electronic structure, which has consequences for the overall activity. Highly stabilized conjugated structures favor the electron-accepting type of scavenging reactions, primarily by a radical adduct formation mechanism. Betanidin and indicaxanthin were found to be the most promising of the compounds studied. Nevertheless, the study established the role of betalains as powerful antiradical dietary agents.

Antioxidant Activity of Selected Phenolic Acids-Ferric Reducing Antioxidant Power Assay and QSAR Analysis of the Structural Features.

Phenolic acids are naturally occurring compounds that are known for their antioxidant and antiradical activity. We present experimental and theoretical studies on the antioxidant potential of the set of 22 phenolic acids with different models of hydroxylation and methoxylation of aromatic rings. Ferric reducing antioxidant power assay was used to evaluate this property. 2,3-dihydroxybenzoic acid was found to be the strongest antioxidant, while mono hydroxylated and methoxylated structures had the lowest activities. A comprehensive structure-activity investigation with density functional theory methods elucidated the influence of compounds topology, resonance stabilization, and intramolecular hydrogen bonding on the exhibited activity. The key factor was found to be a presence of two or more hydroxyl groups being located in ortho or para position to each other. Finally, the quantitative structure-activity relationship approach was used to build a multiple linear regression model describing the dependence of antioxidant activity on structure of compounds, using features exclusively related to their topology. Coefficients of determination for training set and for the test set equaled 0.9918 and 0.9993 respectively, and Q2 value for leave-one-out was 0.9716. In addition, the presented model was used to predict activities of phenolic acids that haven't been tested here experimentally.

Flavones' and Flavonols' Antiradical Structure-Activity Relationship-A Quantum Chemical Study.

Flavonoids are known for their antiradical capacity, and this ability is strongly structure-dependent. In this research, the activity of flavones and flavonols in a water solvent was studied with the density functional theory methods. These included examination of flavonoids' molecular and radical structures with natural bonding orbitals analysis, spin density analysis and frontier molecular orbitals theory. Calculations of determinants were performed: specific, for the three possible mechanisms of action-hydrogen atom transfer (HAT), electron transfer-proton transfer (ETPT) and sequential proton loss electron transfer (SPLET); and the unspecific-reorganization enthalpy (RE) and hydrogen abstraction enthalpy (HAE). Intramolecular hydrogen bonding, catechol moiety activity and the probability of electron density swap between rings were all established. Hydrogen bonding seems to be much more important than the conjugation effect, because some structures tends to form more intramolecular hydrogen bonds instead of being completely planar. The very first hydrogen abstraction mechanism in a water solvent is SPLET, and the most privileged abstraction site, indicated by HAE, can be associated with the C3 hydroxyl group of flavonols and C4' hydroxyl group of flavones. For the catechol moiety, an intramolecular reorganization to an o-benzoquinone-like structure occurs, and the ETPT is favored as the second abstraction mechanism.

Microbiological, antioxidant and lipoxygenase-1 inhibitory activities of fruit extracts of chosen Rosaceae family species.

BACKGROUND: Extracts from the Rosaceae family fruits are rich in natural, biologically active polyphenols, but their antibacterial properties are still poorly understood. Therefore, we focused our research on their activity against uropathogenic Escherichia coli strains. This research also concerned the proof of their ability to reduce oxidative stress and modulate the activity of lipoxygenase-1 (LOX-1). It is well-known that plants represent a source of bioactive compounds whose antioxidant activity may be useful in protecting against oxidative damage in cells, which have been linked to the pathogenesis of many oxidative diseases. OBJECTIVES: The study determined the biological activity of methanol (ME) and water (WE) extracts rich in polyphenols from the hawthorn (Crataegus monogyna Jacq.), dog rose (Rosa canina L.), quince (Cydonia oblonga Mill.), and Japanese quince (Chaenomeles speciosa (Sweet) Nakai). MATERIAL AND METHODS: The antioxidant capacity was evaluated using 1,1diphenyl-2-picrylhydrazyl (DPPH▪) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS+▪) radical scavenging methods. The inhibition of liposome membrane oxidation was studied using the thiobarbituric acid reactive substances assay. Lipoxygenase-1 inhibitory activity was measured using the spectrophotometric method. Bacterial growth was determined by evaluating the number of colony forming units per milliliter (CFU/mL). Hydrophobicity was established with salt aggregation hydrophobicity test (SAT). Swimming and swarming motilities were evaluated using soft-agar plates. Production of curli fimbriae was estimated on CFA agar. The P fimbriae were detected using the hemagglutination of erythrocytes. Adhesion of bacteria to human uroepithelial cells was assessed. The amount of biofilm was determined spectrophotometrically. RESULTS: We showed that most of these extracts are effective antioxidants and free radical scavengers, possess reasonable potential anti-inflammatory activity, reduce the adhesion of E. coli to uroepithelial cells, and reduce the ability of these bacteria to form biofilm. CONCLUSIONS: The extracts examined, showing very promising biological properties, seem to be able to join the list of substances that can be used as dietary supplements aimed at preventing, for example, urinary tract infections, or as support of drug treatment in many diseases.

High Antimicrobial Efficacy, Antioxidant Activity, and a Novel Approach to Phytochemical Analysis of Bioactive Polyphenols in Extracts from Leaves of Pyrus communis and Pyrus pyrifolia Collected During One Vegetative Season.

Dried leaf samples of Pyrus communis L. var. 'Conference' and Pyrus pyrifolia Burm. f. (Nakai) var. 'Shinseiki' were subjected to the successful extraction procedures using various solvents, followed by filtering and/or drying liquid plant preparations under reduced pressure. As a result of this, for each Pyrus leaf sample examined, four dried residues were obtained, including methanolic (EA), ethyl acetate (EC), water (EB), and the residue obtained from aqueous solution (ED). Antiradical activity of these preparations was measured using the ABTS+• assay, and antimicrobial activity was examined using various strains of bacteria and yeasts. The highest antiradical activity was observed for EC from leaves of P. communis var. 'Conference' collected in May, but the highest average antibacterial activity was noted for EC residues from P. pyrifolia var. 'Shinseiki' collected in May. Antibacterial activity positively correlated with concentration of hydroquinone in extracts. No antifungal activity was observed for any extract. In addition, qualitative and quantitative analyses of active polyphenolic components in extracts from Pyrus were performed. Hydroquinone and hydroxycinnamic acid derivatives were analyzed using a new optimized method comprising reversed-phase high-performance liquid chromatography (RP-LC) coupled with simultaneous photodiode-array and fluorescence detection.

Profile of Polyphenolic and Essential Oil Composition of Polish Propolis, Black Poplar and Aspens Buds.

In this work, we studied similarities and differences between 70% ethanol in water extract (70EE) and essential oils (EOs) obtained from propolis, black poplars (Populus nigra L.) and aspens (P. tremula L.) to ascertain which of these is a better indicator of the plant species used by bees to collect propolis precursors. Composition of 70EE was analyzed by UPLC-PDA-MS, while GC-MS was used to research the EOs. Principal component analyses (PCA) and calculations of Spearman's coefficient rank were used for statistical analysis. Statistical analysis exhibited correlation between chemical compositions of propolis and Populus buds' 70EE. In the case of EOs, results were less clear. Compositions of black poplars, aspens EOs and propolises have shown more variability than 70EE. Different factors such as higher instability of EOs compared to 70EE, different degradation pattern of benzyl esters to benzoic acid, differences in plant metabolism and bees' preferences may be responsible for these phenomena. Our research has therefore shown that 70EE of propolis reflected the composition of P. nigra or complex aspen⁻black poplar origin.

ANTIRADICAL AND ANTIMICROBIAL ACTIVITY OF PHENOLIC FRACTIONS OBTAINED FROM HONEYS.

Honey is a natural product consisting of multiple components which determine its dietary and medicinal properties. In this work there were studied methanol fractions obtained from seven honeys from Lower Silesia (Poland) collected in different seasons of three successive years. Melissopalynologic studies revealed that two of them were polyfloral, and five were classified as monofloral (two buckwheat and three rapes). The amount of phenolic compounds in honeys varied from 0.09 to 0.38 mg per g of honey. Honeys harvested in 2010 were the richest in phenolic compounds and especially rich was buckwheat honey, comparing to 2011- 2012. Determination of antioxidant potential with the DPPH radical revealed that the strongest antiradical activity was exhibited by extracts obtained from polyfloral (1.22 TAU(515/mg)) and buckwheat (1.06 TAU(515lmg)) honeys, while the highest number of antiradical units was observed for rape honey (3.64 TAU(515/g)). Polyphenolic fractions exhibited various bactericidal activities against Klebsiella pneumoniae and Staphylococcus aureus and weak or no activity was observed against Pseudomonas aeruginosa.

Analysis of Polyphenolic Compounds in Extracts from Leaves of Some Malus domestica Cultivars: Antiradical and Antimicrobial Analysis of These Extracts.

In this study, methanol, ethyl acetate, water extracts, and precipitate were obtained from leaves of Malus domestica cultivars: Golden delicious, Jonagold, Elstar, Ligol, and Mutsu. Antiradical activity of these extracts was measured using the ABTS+∙ radical, and antimicrobial activity was measured with the disk-diffusion method. Phenolic compounds were measured with the colorimetric method and identified with high performance liquid chromatography (HPLC). The highest antiradical activity was observed for the Jonagold variety, and in particular strong activity was noted for ethyl acetate extracts. Antimicrobial activity was observed against strains of Staphylococcus aureus, Enterococcus faecalis, and the fungus Candida glabrata. Particularly susceptible to the extracts activity appeared to be Staphylococcus aureus, but the growth of Candida glabrata was inhibited in the presence of ethyl acetate extracts. With the HPLC method we identified a high amount of phloridzin (above 500 mg per g of ethyl acetate extracts), lower amounts of hyperoside, isoquercitrin, and quercitrin, and traces of p-hydroxybenzoic and chlorogenic acids. The contribution of phloridzin to antiradical activity of methanol and ethyl acetate extracts was very high (above 90%). In water extract the contribution of phloridzin was between 38.9 and 55.2%, chlorogenic acid 22.7 and 36.1%, and hyperoside 12.2 and 13.3%.

Biological activity of the methanol and water extracts of the fruits of anthocyanin-rich plants grown in south-west Poland.

In this study we focused on the chemical composition, antioxidant, anti-inflammatory and antibacterial properties of methanol and water extracts of fruits of six species grown in south-west Poland: blackberry, blackcurrant, chokeberry, cherry, gooseberry and raspberry. No general correlation could be drawn between extract chemical properties (i.e. antioxidant and free radical scavenging) and observed biological effects. However, blackcurrant and blackberry extracts (both methanol and water) appeared to be good antioxidants and free radical scavengers, as well as effective inhibitors of E. coli adhesion to the uroepithelial cells. On the other hand, the poorest antioxidants and free radical scavengers, cherry and gooseberry extracts, also poorly affected bacterial growth, swimming ability and adhesion to epithelial cells. Surprisingly, gooseberry extracts, which showed generally weak effects, appearedto be the most effective inhibitor of bacterial biofilm formation. Additionally, most of the studied extracts showed reasonably strong anti-inflammatory properties.

Antioxidant activity of selected phenols estimated by ABTS and FRAP methods.

INTRODUCTION: Phenols are the most abundant compounds in nature. They are strong antioxidants. Too high level of free radicals leads to cell and tissue damage, which may cause asthma, Alzheimer disease, cancers, etc. Taking phenolics with the diet as supplements or natural medicines is important for homeostasis of the organism. MATERIALS AND METHODS: The ten most popular water soluble phenols were chosen for the experiment to investigate their antioxidant properties using ABTS radical scavenging capacity assay and ferric reducing antioxidant potential (FRAP) assay. RESULTS AND DISCUSSION: Antioxidant properties of selected phenols in the ABTS test expressed as IC50 ranged from 4.332 µM to 852.713 µM (for gallic acid and 4- hydroxyphenylacetic acid respectively). Antioxidant properties in the FRAP test are expressed as µmol Fe2+/ml. All examined phenols reduced ferric ions at concentration 1.00 x 10-3 mg/ml. Both methods are very useful for determination of antioxidant capacity of water soluble phenols.

Antiradical and anti-H2O2 properties of polyphenolic compounds from an aqueous peppermint extract.

Polyphenolic compounds such as eriocitrin, luteolin-7-O-rutinoside, diosmin, hesperidin, narirutin, isorhoifolin, rosmarinic and caffeic acids were identified in an aqueous extract (Ex) obtained from peppermint leaves (Menthae x piperitae folium). The content of polyphenols in Ex was as follows: eriocitrin 38%, luteolin-7-O-rutinoside 3.5%, hesperidin 2.9%, diosmin 0.8%, isorhoifolin 0.6%, narirutin 0.3%, rosmarinic acid 3.7% and caffeic acid 0.05%. The strongest antiradical activity (determined as DPPH* scavenging features) was observed for luteolin-7-O-rutinoside, eriocitrin and rosmarinic acid. Caffeic acid and hesperidin revealed a lower antiradical activity while isorhoifolin, narirutin and diosmin showed the lowest activity. The strongest anti-H2O2 activity was observed for eriocitrin, a little lower for rosmarinic acid. The rate of hydrogen peroxide scavenging activity displayed by luteolin-7-O-rutinoside and caffeic acid was lower than that of rosmarinic acids. Hesperidin appeared to be a very weak scavenger of hydrogen peroxide. Almost no anti-H2O2 activity was demonstrated for diosmin, narirutin and isorhoifolin. Among examined flavonoids, the strongest antiradical and anti-H2O2 activity was shown for compounds with two hydroxy groups bound to the Bring in ortho position in relation to each other. Replacement of one hydroxy group in the Bring with a methoxy group or removing one hydroxy group leads to decrease of antiradical and anti-H2O2 activity of flavonoids. Our results suggest that eriocitrin is a powerful peppermint antioxidant and a free radical scavenger.