Number Of Phenolic Groups Research Articles

A Global Study by 1H NMR Spectroscopy and SPME-GC/MS of the in Vitro Digestion of Virgin Flaxseed Oil Enriched or not with Mono-, Di- or Tri-Phenolic Derivatives. Antioxidant Efficiency of These Compounds.

The effect of enriching virgin flaxseed oil with dodecyl gallate, hydroxytyrosol acetate or gamma-tocopherol on its in vitro digestion is studied by means of proton nuclear magnetic resonance and solid phase microextraction followed by gas chromatography/mass spectrometry. The extent and pattern of the lipolysis reached in each sample is analyzed, as is the bioaccessibility of the main oil components. None of the phenolic compounds provokes inhibition of the lipase activity and all of them reduce the lipid oxidation degree caused by the in vitro digestion and the bioaccessibility of oxidation compounds. The antioxidant efficiency of the three tested phenols is in line with the number of phenolic groups in its molecule, and is dose-dependent. The concentration of some minor oil components such as terpenes, sesquiterpenes, cycloartenol and 24-methylenecycloartenol is not modified by in vitro digestion. Contrarily, gamma-tocopherol shows very low in vitro bioaccessibility, probably due to its antioxidant behavior, although this increases with enrichment of the phenolic compounds. Oxidation is produced during in vitro digestion even in the presence of a high concentration of gamma-tocopherol, which remains bioaccessible after digestion in the enriched samples of this compound.

Enzymatic-assisted polymerization of the lignin obtained from a macroalgae consortium, using an extracellular laccase-like enzyme (Tg-laccase) from Tetraselmis gracilis

In the past decade, Mexican coasts have received an enormous influx of macroalgae species, producing serious environmental and public health concerns. Here, we developed a green methodology to generate a new polymer from the lignin contained in the macroalgae. The methodology consists in lignin extraction-by-boiling and its subsequent polymerization with a laccase-like enzyme from the green algae Tetraselmis gracilis (Tg-laccase). Mass spectrometry revealed the presence of guaiacyl (G), p-hydroxyphenyl (H), and sinapyl alcohol as the main monolignols in the lignin from Sargassum sp. On the other hand, MALDI-TOF spectra shows an increase in the size of the lignin chain after enzymatic polymerization process with Tg-laccase. Besides, the characterization of the novel polymer -using 1H NMR, FTIR, SEC-FPLC, and UV/Vis- allowed establishing that during the polymerization process there is a decrease in the number of phenolic groups as well as loss of aromatic protons, which allowed proposing a polimerizacion mechanism. This methodology could be promising in the development of a new lignin-based polymer and would open a new direction for the environmental management of the macroalgae on the Mexican beaches.

Behavior of the potential antitumor VIVO complexes formed by flavonoid ligands. 3. Antioxidant properties and radical production capability

The radical production capability and the antioxidant properties of some VIVO complexes formed by flavonoid ligands were examined. In particular, the bis-chelated species of quercetin (que), [VO(que)2]2−, and morin (mor), [VO(mor)2], were evaluated for their capability to reduce the stable radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) and produce the hydroxyl radical •OH by Fenton-like reactions, where the reducing agent is VIVO2+. The results were compared with those displayed by other VIVO complexes, such as [VO(H2O)5]2+, [VO(acac)2] (acac=acetylacetonate) and [VO(cat)2]2− (cat=catecholate). The capability of the VIVO flavonoids complexes to reduce DPPH is much larger than that of the VIVO species formed by non-antioxidant ligands and it is due mainly to the flavonoid molecule. Through the 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin trapping assay of the hydroxyl radical it was possible to demonstrate that in acidic solution VIVO2+ has an effectiveness in producing •OH radicals comparable to that of Fe2+. When VIVO complexes of flavonoids were taken into account, the amount of hydroxyl radicals produced in Fenton-like reactions depends on the specific structure of the ligand and on their capability to reduce H2O2 to give •OH. Both the formation of reactive oxygen species (ROS) under physiological conditions by VIVO complexes of flavonoid ligands and their radical scavenging capability can be put in relationship with their antitumor effectiveness and it could be possible to modulate these actions by changing the features of the flavonoid coordinated to the VIVO2+ ion, such as the entity, nature and position of the substituents and the number of phenolic groups.

Tailoring molecularly imprinted polymer beads for alternariol recognition and analysis by a screening with mycotoxin surrogates

Molecularly imprinted porous polymer microspheres have been prepared for selective binding of alternariol (AOH), a phenolic mycotoxin produced by Alternaria fungi. In order to lead the synthesis of recognition materials, four original AOH surrogates have been designed, prepared and characterized. They bear different number of phenol groups in various positions and different degree of O-methylation on the dibenzo[b,d]pyran-6-one skeleton. A comprehensive library of mixtures of basic, acidic or neutral monomers, with divinylbenzene or ethyleneglycol dimethacrylate as cross-linkers, were polymerized at a small scale in the presence of the four molecular mimics of the toxin molecule. This polymer screening has allowed selection of the optimal composition of the microbeads (N-(2-aminoethyl)methacrylamide, EAMA, and ethylene glycol dimethacrylate). The latter are able to bind AOH in water–acetonitrile (80:20, v/v) with an affinity constant of 109±10mM−1 and a total number of binding sites of 35±2μmolg−1, being alternariol monomethylether the only competitor species. Moreover, 1H NMR titrations have unveiled a 1:2 surrogate-to-EAMA stoichiometry, the exact interaction sites and a binding constant of 1.5×104M−2. A molecularly imprinted solid phase extraction (MISPE) method has been optimized for selective isolation of the mycotoxin from aqueous samples upon a discriminating wash with 3mL of acetonitrile/water (20:80, v/v) followed by determination by HPLC with fluorescence detection. The method has been applied, in combination to ultrasound-assisted extraction, to the analysis of AOH in tomato samples fortified with the mycotoxin at five concentration levels (33–110μgkg−1), with recoveries in the range of 81–103% (RSD n=6). To the best of our knowledge, this is the first imprinted material capable of molecularly recognizing this widespread food contaminant.

Dimethyl carbonate synthesis from methyl nitrite and CO over activated carbon supported Wacker-type catalysts: The surface chemistry of activated carbon

A series of supported Wacker-type catalysts under treatment of nitric acid were prepared and utilized in the synthesis of dimethyl carbonate from CO and methyl nitrite. Nitrogen adsorption, Boehm titration, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and H2-temperature-programmed reduction (H2-TPR) were employed to explore the relationship between the physicochemical properties and reactivity of catalysts. Correlated with the results of Boehm titration, it was found that catalytic activities increased monotonically with the number of phenolic group on activated carbon surface. XPS spectra showed that the catalysts, which had much more amount of phenolic group, were possessed of large amount of Cu2+ species. H2-TPR results indicated that the phenolic group contributed to the easier reducibility of Cu2+ species, further facilitating the oxidation cycle between Pd and Cu species and consequently the catalytic performance.

Effects of Molecular Structure on Kinetics and Dynamics of the Trolox Equivalent Antioxidant Capacity Assay with ABTS+•

Reaction kinetics in the Trolox equivalent antioxidant capacity (TEAC) assay between ABTS(+•) [2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) cation radical] and compounds with different structure, molecular weight, number of OH groups, and redox potential were investigated by recording loss of ABTS(+•) absorbance (734 nm) continuously over time. Curves showed six distinguishable kinetic patterns, including both immediate and extended reaction components. Radical quenching rates in the immediate component most relevant to reactions in foods and tissues depended on phenol structure and steric accessibility to the hindered radical, while reaction stoichiometry correlated with the number of phenol groups (>0.81) but not redox potential. Current assay procedures measure antioxidant capacity under conditions not relevant to actual applications and do not determine radical quenching rates. Results raise serious questions regarding the ability of reactions with the hindered ABTS(+•) to rank actual radical quenching by compounds with different structures and invalidate reporting antioxidant activity as Trolox equivalents.

Elucidation of the Corrosion Inhibition of Mild Steel in 1.0 M HCl by Catechin Monomers from Commercial Green Tea Extracts

The inhibitive action of commercial green tea extracts on mild steel (MS) in a 1.0 M hydrochloric acid solution was investigated by weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). A high-performance liquid chromatographic (HPLC) analysis showed conclusively that of the eight catechin monomers and caffeine found in the original extracts, only four components were responsible for the inhibition of MS. The decreasing adsorption capacity of monomers on MS is related to the stereochemistry of molecules and the number of phenolic groups, and it is as follows: epigallocatechin gallate > epicatechin gallate > epigallocatechin > epicatechin. Adsorption of green tea extract constituent was found to follow Langmuir adsorption isotherm and the calculated Gibb’s free energy values indicated the physisorption of inhibitor over MS surface. Physisorption was supported well by the potential zero charge (PZC) and molecular surface energy-level calculations.

Molecular modelling and QSAR analysis of the estrogenic activity of terpenoids isolated from Ferula plants

The relationship between chemical structure and estrogenic activity in a series of terpenoid esters with aromatic and aliphatic acid substituents isolated from Ferula plants, was studied. The fragments of the terpenoid structure that are potentially responsible for estrogenic activity were revealed. A quantitative structure-estrogenic activity study has been carried out using the QSAR approach with use of data derived from quantum-chemical calculations as well as data generated from three-dimensional structures of terpenoids. A number of molecular descriptors was obtained from the density functional theory (DFT) at the B3LYP/6-31G(d, p) level of calculation. Comparative analysis of the quantum-chemical computational data was also performed to confirm hypothesis concerning importance of the distance between the oxygen of alcohol hydroxyl group and the functional group in the para-position of the benzene ring (the hydroxyl or methoxy group). Use of the Genetic Algorithm in the QSAR analysis allowed the structural and physicochemical parameters of the terpenoids responsible for estrogenic activity to be determined. A significant QSAR model was obtained with an r 2 value of 0.892. The resulting model showed a reliable dependence of estrogenic activity of the terpenoids on such parameters as molecular shape, number of phenolic groups, surface polarity and the energy of the highest occupied molecular orbital.

Antioxidant profile of dihydroxy- and trihydroxyphenolic acids-A structure–activity relationship study

Eight structurally similar dihydroxy and trihydroxyphenolic acids (protocatechuic acid, 3,4-dihydroxyphenylacetic acid, hydrocaffeic acid, caffeic acid, gallic acid, 3,4,5-trihydroxyphenylacetic acid, 3-(3,4,5-trihydroxyphenyl)propanoic acid and 3-(3,4,5-trihydroxyphenyl)propenoic acid) were examined for their total antioxidant capacity (TAC). Furthermore, their ability to scavenge peroxyl radicals, generated by AAPH in liposomes, was determined. The antioxidant/pro-oxidant activity of the compounds was screened using the 2′-deoxyguanosine assay. All compounds behave as radical scavengers, with 3,4,5-trihydroxyphenylacetic acid being the most potent. Nevertheless, in the lipid peroxidation assay an inverse ranking order was observed, 3,4-dihydroxyphenylacetic acid being the most effective compound. All the dihydroxylated compounds showed a pro-oxidant behaviour leading to an increase of 50% in 8-OH-dG induction. From the structure–antioxidant activity relationship studies performed it may be concluded that the number of phenolic groups and the type of the alkyl spacer between the carboxylic acid and the aromatic ring strongly influence the antioxidant activity.

The liver-protecting activity of melanin-like pigment derived from black tea

The liver-protecting activity of melanin-like pigment (MLP) derived from tea was studied using hydrazine intoxication. The non-reduced MLP demonstrated the lack of activity. Reduction of MLP caused an increase in the number of phenol groups. Administration of reduced MLP (rMLP) to rats (i.p., 20 mg/kg, 30 min before hydrazine) to rats prevented development of heavy liver intoxication. Pretreatment of animals with rMLP prevented the rise of serum alanine transferase activity and the decrease of glutathione level in the liver challenged by hydrazine. It also lowered the hepatic malondialdehyde concentration. Reduced MLP significantly restored the ability for rats to metabolize antipyrine. The introduction of MLP alone did not affect pharmacokinetics of antipyrine nor introduce toxicity to rats. Biochemical and pharmacokinetical data proved that the rMLP protects the liver against hydrazine-induced injury.

Soil organic matter–metal interactions in Chilean volcanic soils under different agronomic management

The organic matter existing in volcanic soils must be investigated not only in quantity, but also in quality in order to understand its role in soils and thus ensure adequate levels of stable organic polymers contributing to soil humification. The meaningful contribution proposed by this investigation is based on the study of the interaction of soil organic matter (SOM) in its fractions humic acid and fulvic acid with metallic elements that are macro- and micronutrients and also contaminants. The study was carried out in Chilean soils of the type Andisols and Ultisols. To this end, humic acids and fulvic acids were fractionated to determine phenolic, carboxylic and total acidity. In addition cation holding capacity was determined. From the knowledge of this organic matter–metal interaction, the behavior and actual contribution of organic matter to soil may be inferred in relation to storage and availability of metallic elements, both nutrients and contaminants. The results of this study demonstrate the existence of electron-donor sites in the organic fractions of soil, which may be highly specific for heavy metals. They also confirm the possibility that metal-ion, especially micronutrient, bioavailability is affected by retention mechanisms involving the nature of SOM. Thus, the content of carboxylic groups in fulvic acid is higher than in humic acid. The number of phenolic groups is about the same in both. In addition, comparison of the maximum binding ability among the cations leads to the conclusion that the most frequent tendency is to retain cadmium (Cd)>zinc (Zn)>calcium (Ca) at the used concentrations. In wild forest, soils exhibit organic polymers with a higher content of phenolic groups and total acidity compared with the soils subjected to agronomic management and to some other use. Fulvic polymers exhibit a higher maximum cation binding ability in wild forest.

Study on Thermal and Mechanical Properties of Biodegradable Blends of Poly(ε-caprolactone) and Lignin

The phase structure and physical property were investigated for blends of poly(ε-caprolactone) (PCL) and lignin, both of which were biodegradable polymers. The blend was prepared by mechanical mixing and solution casting. The thermal analysis (DSC and DMTA) indicated there was no detectable evidence that PCL/lignin blends prepared by mechanical mixing was miscible obviously. But it was found the obvious shift of glass transition temperature Tg of the blends prepared by solution casting. This was the strong evidence to support the fact that these two polymers were at least partially miscible. According to the results of FT-IR, no obvious changes in the shape and peak position of carbonyl absorption caused by formation of hydrogen bond between PCL carbonyl and lignin phenol hydroxyl groups were observed due to the fact that the number of phenol groups in lignin molecule is too small to induce detectable changes of carbonyl absorption. With increasing the lignin content in the blends, the position of O-H stretching band obviously shifted from 3397 to 3412 cm−1. This shift to lower frequency was characteristic for intermolecular hydrogen bonding. Studying the mechanical property of the blends, we found that the maximum strength, elongation at maximum strength and elongation at break decreased but Young’s modulus increased with the increasing content of lignin. Within the lignin content of 25%, the material had good mechanical property. It was also found that the samples prepared by solution casting had better mechanical properties because of the higher dispersity. The result suggested that to blend PCL with lignin could contribute to increase Young’s modulus and reduce the production cost of PCL materials.

Uranyl ion complexation by medium and large homooxacalixarenes: from mono- to poly-uranate complexes

Crystal structures of dioxouranium(VI) complexes of three homooxacalix[n]arenes (n = 4, 6 or 8) have shown the possibility to complex metal moieties of variable nuclearity, depending upon the number of phenolic groups and ether links they contain. p-tert-Butyltetrahomodioxacalix[6]arene embraces a single uranyl unit through tetraphenoxide coordination as commonly observed in calixarene complexes, whereas p-methyloctahomotetraoxacalix[4]arene binds a doubly bridged binuclear species coordinated to both phenoxide and ether oxygen donors, while the large p-tert-butyloctahomotetraoxacalix[8]arene binds a unique tetrauranate cluster containing both double and single oxygen bridges between uranium atoms and involving only phenoxide-oxygen coordination to the macrocycle. An additional crystal structure determination on the triethylammonium complex of the singly deprotonated homooxacalix[6]arene enables some comments to be made on the effects of coordination on the macrocycle conformation. The relation between the nuclearity of the uranyl complexes with ligands in the calixarene/homooxacalixarene family and the size of the ligands is discussed.

Bioflavonoid effects on in vitro cultures of Plasmodium falciparum: Inhibition of permeation pathways induced in the host cell membrane by the intraerythrocytic parasite

A series of polyhydroxyphenol glycosides including bioflavonoid-glycosides structurally-related to phlorizin (phloretin-2-β-glucoside) have been tested for their capacity to inhibit permeation pathways induced in red cell membranes by intraerythrocytic Plasmodium falciparum parasites. The permeation through these pathways has been assessed on trophozoites by sorbitol-mediated hemolysis based on a novel technique of high sensitivity and time resolution which has been adapted for handling relatively large number of samples in mutitration plates. Changes in the number of phenolic groups and to a lesser extent changes in the relative position of these groups had a substantial effect on the inhibitory efficacy of the phlorizin derivatives. Diglycoside derivatives were completely ineffective while various monoglycoside derivatives had comparable effects. Structure-activity relationship (SAR) studies of 3-monosubstituted phlorizin derivatives indicate that the inhibitory potency varied considerably with the chemical nature of the group substituted in the 3 position. Inhibition correlated best ( r = 0.90) with Hammett's constant, underscoring the role of the electron withdrawing capacity of the chemical groups substituted on the hydroxydihydrochalcone moiety. On the other hand, substitution with lipophilic groups had either minimal effects or reduced the inhibitory power of the derivatives. Inhibition of transport correlated with the inhibition of intraerythrocytic parasite growth and provides a basis for new therapeutic approaches of malaria. Based on the SAR studies, a 3-isothiocyano analog of phlorizin was synthesized and shown to block irreversibly the above permeation pathways (20 μM, 10 min reaction at ambient temperature) as well as the intraerythrocytic growth of the parasite. The present study provides proof for the involvement of amino groups in red cell membrane components as controlling elements of the permeation pathways induced by the intraerythrocytic parasite. The putative groups could serve as targets for affinity labeling of the membrane components associated with the permeation function.

The uncoupling activity of substituted anthracene derivatives on isolated mitochondria from Phaseolus aureus

Unsubstituted anthraquinones and anthrones have a low uncoupling activity on isolated mitochondria. The presence of phenolic groups is a prerequisite for a marked effect. The number of phenolic groups is of minor importance but their substitution pattern is important. The methylene group of the anthrones increases the activity.

Study of oxidation of polypropylene, stabilized with tri- and tetranuclear phenols

An increase in the number of phenol groups in the antioxidant molecule from two to either three or four is not accompanied by an increase in the antioxidation efficiency, when measured by the time of delaying the oxidation.

Inhibition of indoleacetic acid-oxidase by soil humic acids fractionated on sephadex

Humic acid fractions of different molecular weights inhibit IAA-oxidase activity to varying extents. The higher the molecular weight, the lower the IAA-oxidase inhibition; the parent material, however, having the greatest effect. A direct relationship was found between the degree of enzyme inhibition and the number of phenolic groups, C/H ratio and the carbon and nitrogen contents of the humic acid fractions, whereas the relationship was negative for oxygen and hydrogen percentages. The ash content of the humic acid preparations was not related to their effects on the enzyme. These results seem to suggest that phenolic groups, not carboxyl groups, are responsible for the influence of humic acids on enzyme activity.