Characterization and antioxidative properties of condensed tannins from the mangrove plant Aegiceras corniculatum

Freeze‐dried leaf, stem bark, and root bark powders of Aegiceras corniculatum were extracted with three different types of polar solvents: methanol, ethyl acetate, and water. The methanol extracts had the highest concentrations in total phenolics and extractable condensed tannins, followed by water and ethyl acetate extracts. Analysis by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) suggested that condensed tannins from leaf, stem bark, and root bark contained prodelphinidins and procyanidins, with the predominance of prodelphinidins and high level of galloylation. Acid‐catalyzed degradation in the presence of benzyl mercaptan indicated that gallocatechin, epigallocatechin, epigallocatechin‐3‐O‐gallate, and epicatechin‐3‐O‐gallate occurred as the terminal units and (epi)gallocatechin, (epi)gallocatechin‐3‐O‐gallate, (epi)catechin, and (epi)catechin‐3‐O‐gallate occurred as the extension units. The mean degrees of polymerization (mDP) of condensed tannins from leaf, stem bark, and root bark were 13.5, 7.4, and 12.3, respectively. The condensed tannins from leaf and stem bark exhibited a higher DPPH radical scavenging activity and ferric reducing/antioxidant power compared to that of synthetic antioxidant butylated hydroxyanisole (BHA). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effects of sample drying and storage,and choice of extraction solvent and analysis method on the yield of birch leaf hydrolyzable tannins

In this study, I investigated the effects of different methods of sample drying and storage, and the choice of extraction solvent and analysis method on the concentrations of 14 individual hydrolyzable tannins (HTs), and insoluble ellagitannins in birch (Betula pubescens) leaves. Freeze- and vacuum-drying of birch leaves were found to provide more reliable results than air- or oven-drying. Storage of leaves at –20C for 3 months before freeze-drying did not cause major changes in tannin content, although levels of 1,2,3,4,6-penta-O-galloylglucose and isostrictinin were altered. Storage of dried leaf material at –20C is preferred because 1 year storage of freeze-dried leaves at 4C and at room temperature decreased the concentration of the pedunculagin derivative, one of the main ellagitannins of birch. Furthermore, storage at room temperature increased the levels of isostrictinin and 2,3-(S)-HHDP-glucose, indicating possible HT catabolism. Of the extraction solvents tested, aqueous acetone was superior to pure acetone, or aqueous or pure methanol. The addition of 0.1% ascorbic acid into 70% acetone significantly increased the yield of ellagitannins, presumably by preventing their oxidation. By comparing the conventional rhodanine assay and the HPLC–ESI-MS assay for quantification of leaf galloylglucoses, the former tends to underestimate total concentrations of galloylglucoses in birch leaf extract. On the basis of the outcomes of all the method and solvent comparisons, their suitability for qualitative and quantitative analysis of plant HTs is discussed, emphasizing that each plant species, with its presumably unique HT composition, is likely to have a unique combination of ideal conditions for tissue preservation and extraction.     

Methods and pitfalls of extracting condensed tannins and other phenolics from plants: Insights from investigations onEucalyptus leaves

Optimal conditions for extraction of tannins and other phenolics from tree foliage and their subsequent storage rarely have been investigated. We investigated methods of drying leaves, optimal solvents, and the effects of light and temperature on the extractability and stability of condensed tannins (proanthocyanidins) and total phenolics from leaves ofEucalyptus trees. Aqueous acetone was a better solvent than aqueous methanol for condensed tannins and total phenolics, but condensed tannins were less stable in aqueous acetone than aqueous methanol. Stability of condensed tannins also was decreased substantially by room temperature versus 4°C and by exposure to indirect sunlight, although the assay for total phenolics was unaffected. For quantitative estimation of condensed tannins, extraction with 50% acetone was better than methods of direct analysis of leaf tissue. The highest estimates of total condensed tannins were obtained by exhaustive extraction with 50% acetone followed by direct analysis of the residue. Lyophilization of fresh leaf increased yield of condensed tannin (although usually by less than 10%). Lyophilization and subsequent storage of extracts had little effect on assays for condensed tannins or total phenolics.     

Infrared spectroscopic investigation of tannins

Infrared spectroscopy is suggested as a diagnostic method for the characterisation and qualitative estimation of the two classes of tannins. Gallic acid, tannic acid and chebulinic acid have been taken as model compounds for the hydrolysable and catechin for the condensed tannins. The former class is marked by the presence of strong absorption maxima at 1710 – 35 cm^?1. The two classes have characteristic pattern of absorption, from which it is possible to characterise the particular type of tannin.     

Comparative kinetics of the induced radical autocondensation of polyflavonoid tannins. II. Flavonoid units effects

Comparative kinetics of the radical autocondensation induced by SiO₂ on a series of polyflavonoid tannins, namely, pine, pecan, mimosa, quebracho, gambier, sumach, and on the catechin monomer as a model compound were carried out by electron spin resonance. The induced radical autocondensation appeared to be independently catalyzed by the known base mechanism, as well as SiO₂ and Lewis acid attack directly at the heterocycle oxygen. The reaction occurs in two definite steps: the first, the radical anion formation, the second, the condensation proper with other flavonoid units of the reactive sites formed. The rate determining step depends on both the main flavonoid unit structure of each tannin and particularly, on the level of colloidal state of the tannin solution and the number-average degree of polymerization (DP_n), with the latter two parameters being the main determining ones for the second reaction step and the first two for the first reaction step. It is, however, the combination of the three parameters that determines the total observable effect for each of the flavonoid tannins. The SiO₂ attack at the heterocycle ether oxygen is of such an intensity that the A-rings, phenoxide radicals, which drive the reaction, surge very rapidly to such a higher proportion than the B-rings phenoxide radicals that the B-rings also start to surge later by shifting to the left of the ^*B ← A^* equilibrium. There are also indications that ionic mechanisms might be more important for the second step of the reaction. Different radical-anion species and the relative movements of the relevant equilibria involved can be clearly identified from the spectra peaks. The initial, maximum intensity of the peaks has been shown to be the parameter defining the first step of the reaction, while the radical decay rate has been shown to refer to the second step of the reaction. Hydrolyzable tannins have been shown not to undergo neither any silica-induced radical surge nor autocondensation as predictable from their structures. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 243–265, 1997     

X-ray photoelectron spectroscopy as a tool for in-situ study of the mechanisms of heterogeneous catalytic reactions

An ESCALAB High Pressure photoelectron spectrometer specially designed by Vacuum Generators Co. (UK) for in-situ measurements at high pressures has been modified for adsorption and catalytic experiments. New construction of a gas cell, which serves to create a high-pressure zone, allows us to measure photoemission spectra in-situ at pressures up to 0.2–0.5 mbar and to use a sample holder with independent heating of a sample. This makes it possible to measure temperature programmed desorption and reaction spectra and, as a consequence, to characterize the catalytic properties simultaneously with the acquisition of X-ray photoelectron spectroscopy (XPS) data. Capabilities of the modified spectrometer are demonstrated by the examples of studies of CO and methanol adsorption on Pd(111) single crystal and methanol oxidation over Cu_poly.The XPS study of high-pressure adsorption of CO on perfect and sputtered Pd(111) showed that raising the pressure has the same effect as decreasing the temperature. The CO coverage is increased due to adsorption of CO to weakly bound (on-top) state, which appears in addition to more strongly bound three-fold and bridged species. No indications of CO dissociation or carbonyl formation were found under the given experimental conditions (high pressure and sputtering-induced defects), provided that the CO gas was sufficiently clean.Two pathways of methanol decomposition to CH_{x, ads} (x3) and to CO_ads was unambiguously identified, with their contribution being dependent on P and T. The decomposition to carbon-originated species had a small contribution in UHV conditions at room temperature, but became more significant at higher pressures and temperatures.Analysis of the distribution of the reaction products and surface species during methanol oxidation over copper in the sub-millibar pressure range showed that an increase in catalytic activity observed on heating the sample from 420 to 670K is accompanied by transformation of the adlayer composition. At low temperatures, the surface is covered by methoxy- and, to a lesser extent, formate-groups. The active surface (T > 520 K) is metallic copper with two adsorbed oxygen species. The possible nature of these species is discussed.     

Use of antioxidants in extraction of tannins from walnut plants

The radial diffusion assay was applied to estimate the amount of total tannins in extracts from walnut plant materials. We found that the protein-precipitating activity of the tannin extracts were increased by 30–75 % when antioxidants (ascorbic acid or sodium metabisulfite, 5.5 mM) were added in extraction solvents (50% aqueous methanol). The extracts obtained with Na₂S₂O₅ were much less brown than control. Moreover, two-dimensional thin-layer chromatography revealed some additional polyphenolic compounds in the extracts made with Na₂S₂O₅. These results suggest that the amount of tannins and/or their protein-precipitating property may be strongly affected by oxidation events during extraction procedure. The addition of antioxidants in the extraction solvents is useful to limit this problem.     

The effect of specific surface area on the activity of nano-scale ceria catalysts for methanol decomposition with and without steam at SOFC operating temperatures

Nano-particulate high surface area CeO₂ was found to have a useful methanol decomposition activity producing H₂, CO, CO₂, and a small amount of CH₄ without the presence of steam being required under solid oxide fuel cell temperatures, 700-1000 °C. The catalyst provides high resistance toward carbon deposition even when no steam is present in the feed. It was observed that the conversion of methanol was close to 100% at 850 °C, and no carbon deposition was detected from the temperature programmed oxidation measurement.The reactivity toward methanol decomposition for CeO₂ is due to the redox property of this material. During the decomposition process, the gas-solid reactions between the gaseous components, which are homogeneously generated from the methanol decomposition (i.e., CH₄, CO₂, CO, H₂O, and H₂), and the lattice oxygen on ceria surface take place. The reactions of adsorbed surface hydrocarbons with the lattice oxygen ( can produce synthesis gas (CO and H₂) and also prevent the formation of carbon species from hydrocarbons decomposition reaction (C_nH_m⇔nC+m/2H₂). V_O^·· denotes an oxygen vacancy with an effective charge 2⁺. Moreover, the formation of carbon via Boudouard reaction (2CO⇔CO₂+C) is also reduced by the gas-solid reaction of carbon monoxide with the lattice oxygen .At steady state, the rate of methanol decomposition over high surface area CeO₂ was considerably higher than that over low surface area CeO₂ due to the significantly higher oxygen storage capacity of high surface area CeO₂, which also results in the high resistance toward carbon deposition for this material. In particular, it was observed that the methanol decomposition rate is proportional to the methanol partial pressure but independent of the steam partial pressure at 700-800 °C. The addition of hydrogen to the inlet stream was found to have a significant inhibitory effect on the rate of methanol decomposition.     

Influence of Myriophyllum spicatum-derived tannins on gut microbiota of its herbivore Acentria ephemerella

The submerged living larvae of Acentria ephemerella were fed in the laboratory with either M. spicatum or Potamogeton perfoliatus, two of their host plants. Larvae exhibited a reduced growth when fed M. spicatum, a freshwater angiosperm that contains high concentrations of tannins, secondary metabolites known for their herbivore-deterrent and antimicrobial properties. In this study, we investigated the influence of food-derived tannins on gut microbiota. Bacterial densities in the guts did not differ between the food regimes, ranging from 2.8 to 13.3 × 10⁶cells per gut. Gut bacteria were characterized with cultivation techniques and subsequent identification of the strains by molecular methods. We isolated 17 bacterial strains belonging to all subdivisions, i.e., we identified -, - and -proteobacteria, Cytophyaga/Flavobacteria (CF) and several Gram-positive bacteria. All except one Gram-positive strain were found in the guts of larvae fed with P. perfoliatus. Gram-positive bacteria and bacteria of the CF cluster were more sensitive to polyphenol-containing extracts of M. spicatum in an agar diffusion assay than strains of the - or -proteobacteria subdivision. Our results suggest an influence of food-derived tannins on gut microbiota in A. ephemerella.     

Removal of vegetal tannins from wastewater by electroprecipitation combinedwith electrogenerated Fenton oxidation

Synthetic solutions containing up to 2000 ppm of gallotannic acid and real wastewater from vegetal tanning processes with values of chemical oxygen demand (COD) exceeding 100 000 ppm were decontaminated by electrolysis using a sacrificial iron anode coupled to either a titanium-platinised or an O₂-diffusion cathode. Experiments were performed in the presence of oxidants and oxidation promoters such as air, oxygen and hydrogen peroxide, the latter being directly added to the solution or electrogenerated by the O₂-diffusion cathode. COD and UV-visible absorbance evolution showed that tannins are removed from electrolysed solutions down to relatively low values, permitting more than 94% elimination. Partial oxidation of the mother compound generates short-chain by-products (mostly carboxylic acids) responsible for the remaining low COD values. Contaminants (tannins and non-tannins) contained in industrial wastewater were removed by combining electroprecipitation with a Fenton-assisted process; a final oxidation step, carried out on a boron-doped diamond electrode, was performed in order to decrease the COD to very low final values.     

A new type of selectivity by using bimetallic catalysts

The results demonstrate a very interesting change in selectivity for the bimolecular reaction between benzophenone and methanol in the presence of hydrogen to produce ether; 1-methoxy-1,1-diphenylmethane by using silica supported bimetallic Ni-Cu (7525) and Ni-Fe (7525) catalysts as compared to Ni/SiO₂. However, no suppression of C-O bond hydrogenolysis was observed for bimetallic as well as for TiO₂ supported catalysts.Deceased.     

Electrochemical behaviour of AISI 321 stainless steel in methanol-H2SO4 mixtures

The electrochemical corrosion behaviour (passivity, pitting and repassivation) of austenitic stainless steel AISI 321 containing titanium has been investigated in methanol containing different concentrations of sulphuric acid (0.001–1 M). The cathodic reaction is observed to be hydrogen evolution. Anodic polarization of the stainless steel reveals a characteristic cathodic loop in methanol with higher concentrations of H₂SO₄ (0.1 M and 1 M). A clear and stable passivity is also observed in each solution mixture which breaks down at higher potentials due to pitting. The passivation current, passivity range, pitting intensity and pitting potential are found to vary with variation of acid concentration in the methanol. The kinetics of pitting and the morphology of the pits have been studied. A variation in concentration of acid and scan rate has been found to influence the protection potential of the stainless steel.     

Determination of ethylene oxide oligomer distributions in alcohol ethoxylates by HPLC using a rotating disc-flame ionization detector

A high performance liquid chromatographic (HPLC) method has been developed for the quantitative determination of ethylene oxide (EO) oligomer distributions (% wt) in acetylated alcohol ethoxylates, R(OCH₂CH₂)_nOH, from n=0, 1 to n=30 using a rotating disc-flame ionization detector. Both single carbon number and mixed carbon number alcohol-based (NEODOL® ethoxylates) samples have been analyzed by gradient elution with 2 different solvent systems on a Waters μ-Porasil column. With both solvent systems, 95% hexane is the initial solvent but with one system, 100% acetone is the final solvent and with the other, 10% methanol/90% acetone is used. The latter solvent elutes the higher ethoxylates from n=21 to n=30 quantitatively from the μ-Porasil column which the 100% acetone solvent fails to do. The 100% acetone solvent separates n=2 and n=3 from n=0,1 which the methanol-containing solvent does not do. Response factors for n=3 and n=8 have been experimentally determined and the response factors for the other EO units have been calculated from these 2 results. The corrected EO oligomer distributions for both NEODOL® 25-9 and NEODOL® 23-6.5 determined by HPLC are in good agreement with those determined earlier by circular thin layer chromatography (up to n=16 can be determined by this method). The average EO numbers determined by the HPLC method and by a wet chemical (phthalic anhydride) method are in excellent agreement for the above 2 samples and a sample of NEODOL® 23-7.5. The results are discussed in terms of Snyder’s theory for gradient elution in HPLC using the gradient steepness parameter.     

Preparation and characterization of bismaleimide-diamine prepolymers and their thermal-curing behavior

Various bismaleimide-diamine Michael addition type prepolymers were prepared through melt condensation and using acetone, dimethylformamide, and m-cresol as solvents in a molar ratio of 1 : 1. Structures of the prepolymers, such as terminal moieties and molecular weight of main chain, depended strongly on the preparation conditions used. More terminal double bonds were observed in the molecule of the prepolymer (sample 3) prepared in dimethylformamide solution without a catalyst. In contrast, the prepolymer produced in m-cresol solution had a polyaspartimide structure with a higher molecular weight. The differential scanning calorimetry and Fourier transform infrared spectra results demonstrated that the molecular structure of the prepolymer had a noticeable effect on their thermal-curing behavior. Thermal properties (T_g and T_d) of cured polymers were evaluated. The polyimide (sample 3b) from sample 3 exhibited the highest T_g and but still retained very good processing properties for film casting. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2471–2477, 1998     

Removal of tannins and polyhydroxy phenols by electro‐chemical techniques

The removal of tannins and their basic molecules such as catechol, pyrogallol, phloroglucinol and resorcinol was studied by electro‐flotation and electro‐oxidation techniques. Iron rods and triple oxide (TaO₂/RuO₂/IrO₂) coated titanium rods were used as electrodes for electro‐flotation and electro‐oxidation respectively. Interaction of tannins and polyhydroxy phenols with iron oxy‐hydroxide formed by anodic dissolution of iron was studied by UV‐Visible, FT‐IR and zeta‐potential measurements. GC–MS was used to identify the intermediate compounds formed during electro‐oxidation. Catechol, pyrogallol, phloroglucinol and resorcinol were found to be mineralized in the presence of triple oxide (TaO₂/RuO₂/IrO₂) coated titanium electrodes. Catechol and pyrogallol were found to form insoluble organo‐metal complexes while resorcinol and phloroglucinol were found to adsorb on iron oxy‐hydroxide. The sludge thus formed was simultaneously separated from the aqueous phase by hydrogen bubbles. It was observed that the power consumption is relatively high for electro‐oxidation compared with electro‐flotation. The effects of pH and reaction time on their removal were also studied and the results are discussed. Copyright © 2005 Society of Chemical Industry     

A 13C and 15N Solid State NMR Study of the Reactions of Acetone Oxime Adsorbed on FeZSM-5

The reactions of acetone oxime, a proposed reaction intermediate for the SCR (Selective Catalytic Reduction) of NO with propane on FeZSM-5, have been studied with ¹³C and ¹⁵N solid state MAS NMR (magic angle spinning nuclear magnetic resonance). FeZSM-5 with three different loading levels was prepared by the sublimation method. The thermal reactions of acetone [2-¹³C] oxime adsorbed on FeZSM-5 samples with different iron loadings were monitored by ¹³C MAS NMR by heating to the desired temperature and then cooling to room temperature for data acquisition. For the sample with the lowest iron loading (Fe/Al = 0.11), acetic acid and N-methyl-2-propanamine were formed by the decomposition of acetone oxime. For the samples with the higher iron loadings (Fe/Al = 0.69 and 0.91), acetone, N,N-methyl-2,2-propanediamine, and N-methyl-2-propanimine were formed by the decomposition of acetone oxime. ¹⁵N MAS NMR was used to investigate reactions of ¹⁵NO and acetone oxime on the FeZSM-5 samples. The formation of gas phase N₂ and N₂O was observed.     

Study on the structure of mangrove polyflavonoid tannins with MALDI-TOF mass spectrometry

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry is a suitable method for examining polyflavonoid tannin oligomers as it is capable to determine aspects of their oligomeric structure and characteristics, which are otherwise too difficult to determine by other techniques. It has been possible to determine by MALDI-TOF for Rhizophora apiculata mangrove polyflvonoid tannins that: (i) procyanidins oligomers formed by catechin/epicatechin, epigallocatechin, and epicatechin gallate monomers are present in great proportions; (ii) oligomers, up to nonamers, in which the repeating unit at 528–529 Da is a catechin gallate dimer that has lost both the gallic acid residues and an hydroxy group which are the predominant species; (iii) oligomers of the two types covalently linked to each other also occur. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Novel Catalytic Properties of Rh Sulfide for the Synthesis of Methanol from CO + H2 in the Presence of H2S

Rh sulfide yielded 800 gkg-cat^–1h^–1 of methanol at 593 K and 5.1 MPa from CO + H₂ (syngas) even in the presence of H₂S 100 ppm in concentration. The obtained space-time yield of methanol was comparable with that obtained with a commercial Cu/Zn/Al catalyst at a conventional reaction condition (523 K and 5.1 MPa) from a feed containing both syngas and CO₂.     

Acetone/Water as a new photoinitiating system for photografting: A theoretical study

Acetone can function as a high efficient photoinitiator for photografting copolymerization when it is mixed with water. The initiation mechanism of acetone/water as a new photoinitiating system for photografting copolymerization has been theoretically investigated at the B3LYP/6-31G** level. Acetone exists in the form of hydrates in its aqueous solution. Acetone dihydrate CH₃COCH₃·2H₂O is readily excited to a triplet state (T₁) under UV irradiation (254 nm) and then generates a radical C₃H₈O₂ involving two single electrons. The photolysis of C₃H₈O₂ is difficult to occur. However, the hydrogen abstraction from a polymer substrate by the ketonic oxygen of the radical is easier to take place, due to its lower energy requirement. The latter path produces a macromolecular radical that can initiate a photografting reaction easily. The photochemical reactions of acetone dihydrate produce less free radicals, leading to less termination reactions of the growing grafted chains. This study elucidates the photoinitiation mechanism of acetone/water photoinitiating system reasonably.     

Catalytic oxidation of methanol to methyl formate over silver – a new purpose of a traditional catalysis system

Catalytic reaction was performed in the unregarded temperature region over silver catalysts with long catalytic lifetime for the conversion of methanol to methyl formate. O-saturated or O-saturated silver catalysts were studied individually to identify the roles of O, O in the oxidative esterification of methanol over an unsupported polycrystalline silver catalyst. A synergic process is proposed based on the coexistence of -oxygen species and -oxygen species on the surface of polycrystalline silver at about 573 K.