Biological activity of acetylated phenolic compounds

In recent years an effort has been made to isolate and identify biologically active compounds that are included in the Mediterranean diet. The existence of naturally occurring acetylated phenolics, as well as studies with synthetic ones, provide evidence that acetyl groups could be correlated with their biological activity. Platelet activating factor (PAF) is implicated in atherosclerosis, whereas its inhibitors seem to play a protective role against cardiovascular disease. The aim of this study was to examine the biological activity of resveratrol and tyrosol and their acetylated derivatives as inhibitors of PAF-induced washed rabbit platelet aggregation. Acetylation of resveratrol and tyrosol was performed, and separation was achieved by HPLC. Acetylated derivatives were identified by negative mass spectrometry. The data showed that tyrosol and its monoacetylated derivatives act as PAF inhibitors, whereas diacetylated derivatives induce platelet aggregation. Resveratrol and its mono- and triacetylated derivatives exert similar inhibitory activity, whereas the diacetylated ones are more potent inhibitors. In conclusion, acetylated phenolics exert the same or even higher antithrombotic activity compared to the biological activity of the initial one.     

Digestion of lignin by termites

The termite Nasutitermes exitiosus (Hill) was fed natural and synthetic [¹⁴C]labelled lignins and related compounds, and the respired CO₂ collected. All the compounds were partially degraded to CO₂, from an average of 7% of the added ¹⁴C for ring-labelled phenate to 63% for methoxyl-labelled maize lignin and 64% for ring-labelled ferulic acid, during periods of 6–69 days. The breakdown commenced immediately and was linear until the food was consumed. Thereafter a slow release continued for some time. Termite bodies assayed at the end of the experiments contained only a small proportion of the added radioactivity. When live termites were separated from their faeces, it became apparent that most of the decomposition of lignin had taken place in the termites and not externally in the voided faeces. An estimate of respiration rates of N. exitiosus indicates a significant release of C as respired CO₂, and this species of termite would appear to return a considerable proportion of the C in litter lignin directly to the atmosphere.     

基于木质素部分脱除及其含量对生物质热解特性的影响

该研究采用固定床热解炉,研究不同木质素含量花生壳、核桃壳样品的裂解行为,利用元素分析、工业分析、气相色谱-质谱联用以及气相色谱法对原料和热解产物进行分析,探究木质素与综纤维素在原始交联结构下的交互作用及其对热解产物分布特性影响。研究结果发现,300℃热解条件下,随着木质素含量的增加,样品中固体产率增加,液体产率和气体产率下降。500、700℃热解条件下,固体产率相比300℃有大幅度的下降,且随样品中木质素含量的增加,固体产率无明显变化,液体产率稍微增加,气体产率下降。500℃时,H2产率很低,随样品中木质素含量的增加,CO2含量减少,CH4含量增加,CO含量有稍微的上升。而700℃时,综纤维素的脱氢、缩合、成环会生成大量的H2。同时,木质素能够促进综纤维素分解生成大量左旋葡聚糖,并抑制其分解;而综纤维素抑制木质素单体愈创木基的脱甲氧基反应,促进苯丙烷基的脱烷基反应,形成更多的酚类化合物。该研究对于生物质组分间交互和产物形成特性研究具有积极意义。     

Accuracy of Klason lignin and acid detergent lignin methods as assessed by bomb calorimetry.

An accurate method for estimation of lignin concentration is important for prediction of the digestible energy content of livestock feeds. The accuracy of lignin concentration estimates based on the Klason lignin and acid detergent lignin methods was compared. Ten diverse forage samples were analyzed for protein, carbohydrates, lipids, organic acids, ash, lignin (by both methods), and gross energy. The accuracy of the two lignin concentration estimates was examined by comparing the measured forage gross energy to a gross energy value calculated from the compositional analysis. Use of the acid detergent lignin estimate in this gross energy calculation accounted for 68-84% of the forage gross energy compared to 85-97% of the gross energy using Klason lignin. These results indicate that while Klason lignin estimates are substantially higher than acid detergent lignin estimates, Klason lignin is the more accurate lignin method and does not overestimate lignin because gross energy recoveries were less than 100%.     

Solution-state nuclear magnetic resonance study of the similarities between milled wood lignin and cellulolytic enzyme lignin

The structures of milled wood lignin (MWL) and cellulolytic enzyme lignin (CEL) have been analyzed using traditional chemical methods and solution-state NMR techniques. Comparisons of the results obtained reveal that subtle differences exist between the two lignin preparations. Thioacidolysis produced higher monomer yields from CEL than MWL, suggesting MWL has a more condensed structure. Quantitative (13)C NMR determined the degree of condensation in MWL to be 0.43 unit per aromatic moiety as compared to 0.36 in CEL. The MWL also contained a lower amount of beta-O-4' substructures per aromatic ring than CEL, 0.41 versus 0.47, respectively. Carbohydrate analysis revealed that the MWL may contain a higher proportion of middle lamella material as compared to the CEL. Because the middle lamella is considered to have a more condensed lignin structure, on the basis of the bulk polymerization theory, these results could explain the differences in beta-O-4' and degree of condensation.     

木质素对木质纤维素降解性能的影响

木质素影响木质纤维素降解性能,明确木质素影响木质纤维素降解的程度和机理,对于植物基因改造、纤维素酶基因改造/筛选、预处理工艺优化均具有重大意义。但是由于木质素和木质纤维素结构的复杂性,木质素对木质纤维素影响的程度和机理尚无定论。该文综述了关于目前研究主要集中在木质素的含量和结构对木质纤维素降解性能的影响上,初始木质素含量和残留木质素含量对同物种和不同物种木质纤维素降解性能的影响;木质素单体比例(syringyl units/guaiacyl units)、键连方式、官能团对木质纤维素降解性能的影响;纯化木质素对木质纤维素降解性能的影响。该文为木质素对纤维素降解性能的影响的相关研究工作提供指导。     

Use of lignin extracted from different plant sources as standards in the spectrophotometric acetyl bromide lignin method

A nongravimetric acetyl bromide lignin (ABL) method was evaluated to quantify lignin concentration in a variety of plant materials. The traditional approach to lignin quantification required extraction of lignin with acidic dioxane and its isolation from each plant sample to construct a standard curve via spectrophotometric analysis. Lignin concentration was then measured in pre-extracted plant cell walls. However, this presented a methodological complexity because extraction and isolation procedures are lengthy and tedious, particularly if there are many samples involved. This work was targeted to simplify lignin quantification. Our hypothesis was that any lignin, regardless of its botanical origin, could be used to construct a standard curve for the purpose of determining lignin concentration in a variety of plants. To test our hypothesis, lignins were isolated from a range of diverse plants and, along with three commercial lignins, standard curves were built and compared among them. Slopes and intercepts derived from these standard curves were close enough to allow utilization of a mean extinction coefficient in the regression equation to estimate lignin concentration in any plant, independent of its botanical origin. Lignin quantification by use of a common regression equation obviates the steps of lignin extraction, isolation, and standard curve construction, which substantially expedites the ABL method. Acetyl bromide lignin method is a fast, convenient analytical procedure that may routinely be used to quantify lignin.     

Optimization of lipase-catalyzed synthesis of acetylated tyrosol by response surface methodology

The ability of a noncommercial immobilized lipase from Staphylococcus xylosus (SXLi) to catalyze the transesterification of tyrosol and ethyl acetate was investigated. Response surface methodology was used to evaluate the effects of the temperature (40-60 degrees C), the enzyme amount (50-500 UI), and the ethyl acetate/hexane volume ratio (0.2-1) on the tyrosol acetylation conversion yield. Two independent replicates were carried out under the optimal conditions predicted by the model (reaction temperature 54 degrees C, enzyme amount 500 UI, and volume ratio ethyl acetate/hexane 0.2). The maximum conversion yield reached 95.36 +/- 3.6%, which agreed with the expected value (96.8 +/- 3.7%). The ester obtained was characterized by spectroscopic methods. Chemical acetylation of tyrosol was performed, and the products were separated using HPLC. Among the eluted products from HPLC, mono- and diacetylated derivatives were identified by positive mass spectrometry. Tyrosol and its monoacetylated derivative exert similar antiradicalar activity on 2,2-diphenyl-1-picrylhydrazyle.     

Thermal behavior of beta-1 subunits in lignin: pyrolysis of 1,2-diarylpropane-1,3-diol-type lignin model compounds

1,2-Diarylpropane-1,3-diol-type lignin model compounds, 1,2-bis(4-hydroxy-3-methoxyphenyl)propane-1,3-diol (1) and 1-(3,4-diethoxyphenyl)-2-(4-methoxyphenyl)propane-1,3-diol (2), were pyrolyzed at 500 degrees C for 4 s to clarify the thermal behavior of beta-1 subunits in lignin. Products were monitored by gas chromatography/mass spectrometry. The cleavage of the Calpha-Cbeta bond to produce benzaldehydes such as 4-hydroxy-3-methoxybenzaldehyde (9) and phenylethanals as the counterparts such as 4-hydroxy-3-methoxyphenylethanal (10) occurred in pyrolyses of both 1 and 2. In pyrolysis of 1, an oxetane pathway leading to the formation of Z/E-stilbenes without the gamma-CH2OH group such as Z/E-4,4'-dihydroxy-3,3'-dimethoxystilbene (3) was predominant. In pyrolysis of 2, the oxetane pathway was minor, while pathways producing a dimer with a =CgammaH2 group by loss of water and a dimer with an alpha-carbonyl group were predominant. Pyrolysis of Japanese cedar wood provided 3 and 10 in approximately 0.8% and 0.6% yields, respectively, based on the Klason lignin content, while pyrolysis of a guaiacyl bulk dehydrogenation polymer gave them in a very small amount.     

Inhibition by soil humic acids of native and acetylated proteolytic enzymes

The activities of acetyltrypsin and acetylcarboxypeptidase were unaffected by neutralized solutions of soil humic acids in concentrations which markedly inhibited the non-acetylated enzymes. Further, acetyltrypsin, unlike trypsin, did not coprecipitate with humic acids. The results support the conclusion that humic acids bind the proteases by a cationexchange mechanism whereby protease amino groups are linked to humic acid carboxyl groups.     

工业木质素的热裂解试验研究

本文研究了木薯水解剩余木质素在N2氛围下的TG和DTG曲线,以及在不同升温速率下热裂解产物的组成随温度的变化情况。试验结果表明,在290~430℃之间热裂解速率最快;在400~800℃之间时,焦炭产量随着温度的升高而降低,焦油产量首先会随着温度升高而增加,在达到一个最大值后,随着温度的进一步升高,部分挥发分的二次热解会使焦油产量降低,气体产量随着温度的升高而增加,H2、CO、CH4和CO2等组分也随着温度的升高而有相应的变化;快速热解在600℃以下有利于焦油和焦炭的生成,在600℃以上有利于气体的生成。通过GC—M S分析发现焦油中的组分主要是苯酚类化合物。     

Decomposition of lignin in soil microcompartments: A methodical study with three different C-14-labelled lignin substrates

Summary C mineralization of three different C-14-labelled lignin substrates (Klason-lignin, dioxane-lignin, lignocellulose) was investigated in four microcompartments, consisting of white-rotted beechwood (Fagus sylvatica L)., brown-rotted beechwood, earthworm [Octolasion lacteum (Örley)] faecal particles mixed with white-rotted beechwood, and earthworm feacal particles mixed with brown-rotted beechwood, incubated at 10°C for 193 days. Conversion of the labelled substrates to ¹⁴CO₂ was low in both white-rotted and brown-rotted wood without faecal particles. Overall C mineralization followed the order Klason-lignin > dioxane-lignin > lignocellulose, indicating that there were different amounts of labelled contaminants in the lignin substrates. Lignin degradation was more pronounced in earthworm faeces mixed with wood materials, and overall C mineralization ranged between 4.4% and 6.3% of the inital C content. C mineralization of the lignin substrates increased considerably in faecal particles after about 90 days, presumably due to nutrient immobilization and microbial succession. The usefulness of the three lignin substrates in monitoring the time-course and extent of lignin degradation in soil microcompartments is discussed.     

木质素对灵芝菌丝体生长的影响

为了解添加外源木质素对灵芝菌丝体生长的影响,该研究通过在灵芝培养基中添加纤维素、半纤维素和木质素,考察了外源添加木质纤维素主要组分对灵芝菌体生长的影响,发现木质素添加明显促进灵芝菌丝体生长;进一步考察添加不同浓度木质素灵芝菌丝体生长情况以及灵芝产多糖、三萜变化规律。结果表明少量添加木质素对灵芝菌丝体生长有明显促进作用,木质素加量为1.0%时,灵芝菌丝体生长情况最好,生物量比对照提高了56%,同时灵芝胞外多糖、胞内多糖及灵芝胞外三萜、胞内三萜的合成均有明显提高,其中胞内多糖提高43%;4种灵芝菌株发酵产多糖、三萜结果对比分析表明1.0%木质素添加均能提高不同菌株发酵多糖、三萜含量,木质素作为营养基质在不同灵芝菌株培养过程中添加均能促进菌丝体活性物质合成。研究结果可为灵芝菌生长代谢研究及人工栽培提供科学依据和参考。     

Comparison of the acetyl bromide spectrophotometric method with other analytical lignin methods for determining lignin concentration in forage samples

Present analytical methods to quantify lignin in herbaceous plants are not totally satisfactory. A spectrophotometric method, acetyl bromide soluble lignin (ABSL), has been employed to determine lignin concentration in a range of plant materials. In this work, lignin extracted with acidic dioxane was used to develop standard curves and to calculate the derived linear regression equation (slope equals absorptivity value or extinction coefficient) for determining the lignin concentration of respective cell wall samples. This procedure yielded lignin values that were different from those obtained with Klason lignin, acid detergent acid insoluble lignin, or permanganate lignin procedures. Correlations with in vitro dry matter or cell wall digestibility of samples were highest with data from the spectrophotometric technique. The ABSL method employing as standard lignin extracted with acidic dioxane has the potential to be employed as an analytical method to determine lignin concentration in a range of forage materials. It may be useful in developing a quick and easy method to predict in vitro digestibility on the basis of the total lignin content of a sample.     

Preparation of lignopolyols from wheat straw soda lignin

Wheat straw soda lignin was modified and characterized by several qualitative and quantitative methods such as (31)P NMR spectroscopy to evaluate its potential as a substitute for polyols in view of polyurethane applications. Chemical modification of the lignin was achieved with propylene oxide to form lignopolyol derivatives. This was performed by a two-step reaction of lignin with maleic anhydride followed by propylene oxide and by direct oxyalkylation under acidic and alkaline conditions. The physical and chemical properties of lignopolyols from each method and the subsequent chain-extended hydroxyl groups were evaluated. Direct oxyalkylation of lignin under alkaline conditions was found to be more efficient than acidic conditions and more effective than the two-step process for preparing lignopolyol with higher aliphatic hydroxyl contents.     

Abundance and reactivity of dibenzodioxocins in softwood lignin

To define the abundance and comprehend the reactivity of dibenzodioxocins in lignin, model compound studies, specific degradation experiments on milled wood lignin, and molecular modeling calculations have been performed. Quantitative (31)P NMR measurements of the increase of biphenolic hydroxyl groups formed after a series of alkaline degradations in the presence of hydrosulfide anions (kraft conditions) showed the presence of 3.7 dibenzodioxocin rings/100 C9 units in milled wood lignin. The DFRC degradation protocol (Derivatization Followed by Reductive Cleavage) was chosen as an independent means to estimate their abundance. Initial experiments with a dibenzodioxocin model compound, trans-6,7-dihydro-7-(4-hydroxy-3-methoxyphenyl)-4,9-dimethoxy-2,11-dipropyldibenzo[e,g][1,4]dioxocin-6-ylmethanol, showed that it is not cleaved under DFRC conditions, but rather it isomerizes into a cyclic oxepine structure. Steric effects precluded this isomerization from occurring when DFRC was applied to milled wood lignin. Instead, monoacetylated biphenolic moieties were released and quantified by (31)P NMR, at 4.3 dibenzodioxocin rings/100 C9 units. The dibenzodioxocin content in residual lignins isolated from kraft pulps delignified to various degrees showed that during pulp delignification, the initial rate of dibenzodioxocin removal was considerably greater than the cleavage rate of arylglycerol-beta-aryl ether bonds. The activation energy for the degradation of dibenzodioxocins under kraft conditions in milled wood lignin was 96 +/- 9 kJ/mol, similar to that of arylglycerol-beta-aryl ether bond cleavage.     

Source and transformations of lignin in Carex-dominated peat

We identified the effects of vegetation changes, and aerobic and anaerobic decay on the lignin composition in the Penido Vello peat record (Galicia, Spain). The ombrotrophic part of this peat record was dominated by graminoids and has significant contributions of ericoids at some depths. The organic matter (OM) of different peat fractions (bulk, NaOH-extractable fraction, and non-extractable residues) of 15 samples from the upper meter was analysed with pyrolysis-gas chromatography/mass spectrometry (pyrolysis-GC/MS). In addition, the dominant plant species were analysed, including Carex durieui, Agrostis curtisii, Molinia caerulea, Deschampsia flexuosa, Festuca rubra, Eriophorum angustifolium, Erica mackaiana and Calluna vulgaris, and their lignin composition compared to that of the peat OM. The high abundance of guaiacol and 4-formylguaiacol in fresh plant tissue compared to peat OM suggests that in addition to p-coumaric and ferulic acid (which are abundant in graminoids), other non-lignin phenolic monomers are contributed by graminoid species. For the non-lignin phenolics, graminoids differed from ericoids in the high abundance of ferulic acid (4-vinylguaiacol), while p-coumaric acid (4-vinylphenol) showed high and similar abundances in ericoids and graminoids. This result suggests that ratios between p-hydroxyphenyl (or p-coumaric acid) and other lignin moieties in (pyrolysates of) peat cannot be used as source indicator. Comparison of plant and peat fractions using factor analysis allowed a distinction between the effects of source (plant identity) and decay on the lignin composition of the Penido Vello peat, and different stages of decomposition were identified. Preferential decay of guaiacyl over syringyl moieties was found for the first stage of decay. This preferential decay is probably related to the large abundance of guaiacyl moieties in easily degradable non-lignin phenolics. Preferential decay of syringyl moieties occurred during subsequent aerobic decay.     

Extraction and isolation of lignin for utilization as a standard to determine lignin concentration using the acetyl bromide spectrophotometric method.

Lignin extracted with acidic dioxane was investigated as a possible standard for quantitatively determining lignin content in plant samples using the spectrophotometric method employing acetyl bromide. Acidic dioxane lignins were analyzed for carbohydrate, total protein, nitrobenzene oxidation products, and UV spectral characteristics. Total carbohydrate content of isolated lignins ranged from 2.21 to 5.70%, while protein ranged from 0.95 to 6.06% depending upon the plant source of the original cell wall sample. Nitrobenzene analysis indicated differences in the amount of guaiacyl and syringyl units making up the lignins, but this did not alter the UV spectrum of lignin solubilized in acetyl bromide. Regression equations developed for the acetyl bromide method using the isolated lignins for all the plant samples were similar to each other. Lignin values obtained by the acetyl bromide method were similar to the lignin values obtained as acid insoluble residues following a Klason lignin procedure.     

Changes in the elemental composition of lignin during humification

Lignin was extracted with aqueous dioxane in the genetic series of humification: dead nonhumified plants → plant residues at the initial stage of humification (during the first 1–3 annual cycles) → weakly decomposed peat → highly decomposed peat. In the course of the humification and peat formation, the lignin was subjected to profound redox transformation; therefore, the elemental composition of the dioxane lignin in the humified peat-forming plants differed from that in the original plants by the higher contents of hydrogen and nitrogen and the lower contents of oxygen and carbon. As a result of the redox reactions, the lignin was partly oxidized and converted to humic substances during the humification of the dead plants. Therefore, it could not be extracted with aqueous dioxane. The reduced part of the lignin remained in the humified materials. The proportion of aromatic fragments in the molecules of the remaining lignin was smaller and that of aliphatic fragments larger than in the lignin of the original plants.