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1.
Veratrylchitosan, a polysaccharide-supported lignin model compound, has been synthesised by covalently attaching 3-(3,4-dimethoxybenzyloxy)propionic acid to the polysaccharide chitosan through an amide linkage. When this polymer was used as a substrate in the oxidation promoted by lignin peroxidase (LiP), significant decomposition of the lignin model resulted in the formation of veratraldehyde. The oxidation mechanism involves an initial transfer of one electron from chitosan to the active species of LiP (LiP I) followed by C(alpha)-H deprotonation of an aromatic cation radical. A benzylic radical is then formed which is further oxidised to a benzyl cation. Reaction with water and hydrolysis of the hemiacetal then lead to veratraldehyde formation. An increase in the yields of the oxidation product is observed in the presence of the mediator 2-chloro-1,4-dimethoxybenzene, thus indicating that a more efficient degradation results from the transfer of an electron from the polymer to the radical cation of the mediator.  相似文献   

2.
In this study, glucose, a primary building-block of biomass was subjected to secondary pyrolysis in a reactor that was retrofitted subsequent to a primary micro-pyrolysis reactor. It was observed that incorporation of a secondary reactor resulted in producing significant amounts of gasoline range hydrocarbons. The hydrocarbon yields improved further as a result of increasing pyrolysis reactor pressure and temperatures. The temperature of the secondary reactor was varied between 400 and 800 °C and pressure between 0 and 150 psi. This study indicates that secondary cracking of primary pyrolysis products of biomass oxygenates undergo gas-phase homogenous molecular restructuring. The result of this process is production of substantial amounts of thermodynamically stable gasoline-range hydrocarbons even in the absence of a catalyst.  相似文献   

3.
It is generally accepted that peroxidases catalyze the final step in the biosynthesis of lignin. In this study, to examine how expression of prxA3a, a gene for an anionic peroxidase, might be related to lignification in plant tissues, we produced transgenic tobacco plants that harbored a gene for β-glucuronidase (GUS) fused to the prxA3a promoter. Histochemical staining for GUS activity indicated that the prxA3a promoter was active mainly in the lignifying cells of stem tissues. Further, to examine the effects of suppressing the expression of prxA3a, we transferred an antisense prxA3a gene construct into the original host, hybrid aspen (Populus sieboldii ×P. gradidentata), under the control of the original promoter of the prxA3a gene. Eleven transformed aspens were obtained and characterized, and the stable integration of the antisense construct was confirmed by PCR and Southern blotting analysis in all these lines. Assays of enzymatic activity showed that both total peroxidase activity and acidic peroxidase activity were lower in most transgenic lines than in the control plants. In addition, the reduction of peroxidase activity was associated with lower lignin content and modified lignin composition. Transgenic lines with the highest reduction of peroxidase activity displayed a higher syringyl/vanillin (S/V) ratio and a lower S+V yield, mainly because of a decreased amount of V units. Thus, our results indicate that prxA3a is involved in the lignification of xylem tissue and that the down-regulation of anionic peroxidase alters both lignin content and composition in hybrid aspen.  相似文献   

4.
The influence of lignin, lignin model compounds, and black liquor from the kraft pulping process on the hydrolysis of xylan by xylanase was investigated. Addition of vanillic acid, acetovanillone, and protocatechuic acid increased the rate of hydrolysis of xylan by as much as 18–50% at low concentrations, but reached maxima at about 0.05% concentration. Addition of vanillin caused a 15% improvement in xylan hydrolysis, while addition of guaiacol more than doubled the hydrolysis rate. Increasing concentrations of either lignin or black liquor also increased the hydrolysis rate of xylan. Circular dichroism spectroscopy indicated a change in the structure of xylanase in the presence of black liquor.  相似文献   

5.
F2-isoprostanes (F2-iPs) comprise four classes of isomers produced non-enzymatically by free radical attack on arachidonic acid, a component of the cell membrane. This paper describes a new method for the quantification of F2-isoprostanes in urine samples from thoroughly diagnosed Alzheimer's disease (AD) patients. The sample pretreatment consisted of liquid extraction of 900 microl urine with diethyl ether, its subsequent evaporation, and finally, reconstitution in 50 microl water. Of this, 20 microl was injected into a HPLC system with a 15 mm x 1 mm porous graphitic carbon column coupled to a triple quadrupole mass spectrometer running in negative electrospray ionization mode. The F2-isoprostanes were separated in 15 min using a linear solvent gradient comprising water, methanol, acetonitrile and ammonium hydroxide at a pH of 9.5. The average recovery obtained was approximately 75%. The limit of detection (3S/N) was calculated for iPF2alpha-III to be 0.7 pg injected on column, corresponding to 0.1 nM. The average level of iPF2alpha was 241 +/- 163 pg/mg creatinine in the urine samples from AD patients (average +/- standard deviation). The corresponding control values were 216 +/- 101 pg/mg creatinine, i.e. no statistically significant difference was noticed. No correlation pattern specific to Alzheimer's disease was revealed by principal component analysis of the isoprostane peaks obtained either. The results from this study support earlier findings that levels of peripheral isoprostanes are not increased in patients with Alzheimer's disease.  相似文献   

6.
Kraft lignins (KL), bleached kraft lignins (BKL), and lignin sulfonates (LS) were prepared from synthetic 14C-lignins labeled in the aromatic nuclei or in the propyl side chains. These and control lignins (CL) were incubated with the lignin-decomposing white-rot fungus, Phanerochaete chrysosporium Burds., in a defined culture medium containing cellulose as growth substrate. Decomposition was monitored by measuring the 14CO2 evolved. Average percentages of the [ring-14C]- and [side chain-14C]-lignins, respectively, recovered as 14CO2 at the cessation of 14CO2 evolution were: KL, 41 and 31; BKL, 42 and 26; LS, 28 and 21; and CL, 26 and 24. Gel permeation chromatography of radiolabeled materials extracted from spent cultures showed that substantial degradation to nonvolatile products had occurred. The polymeric components in the extracts were further degraded in fresh cultures. These results indicate that industrial lignins are significantly bioalterable, and that under favorable conditions industrial lignins are substantially biodegradable.  相似文献   

7.
This study aimed to characterise the parameters governing the non-specific adsorption of a xylanase from Thermobacillus xylanilyticus (Tx-Xyn11) onto lignin isolated from maize stems. Such adsorption may be due to hydrophobic interactions between Tx-Xyn11 and lignin. Our strategy was to mutate hydrophobic residues present on the surface of Tx- Xyn11 into non-hydrophobic residues. Three mutants (P1, P2, and P3) with altered hydrophobic regions were produced and characterised. The thermostability of the P1 mutant was largely decreased compared with the thermostable Tx-Xyn11. The rate of adsorbed enzyme onto lignin was reduced to a similar extent for the P1 and P2 mutants, whereas the adsorption of the P3 mutant was less affected compared with that of Tx-Xyn11. When considered separately, the hydrophobic residues did not affect xylanase adsorption onto lignin. The addition of Tween 20 also led to the decreased adsorption of Tx-Xyn11 onto lignin. These results suggest that hydrophobic interactions are a key parameter in the interaction of Tx-Xyn11 with isolated lignin.  相似文献   

8.
Several processes have been suggested to convert various types of lignocellulosic biomass into lignin products and saccharides. This paper evaluates the suitability of an organosolv process, a process using soda, a hydrothermal process and a process developed in this work, called the “Aquasolve process” for inclusion into a lignocellulosic biorefinery concept. Part II of this paper investigates the influence of the different pretreatment processes on the properties of rye straw lignin and evaluates their ability to produce high recoveries of high quality lignin.Specifications for high quality lignin products are defined and the isolated lignin fractions are analysed by Klason lignin, carbohydrate and ash content, elemental analysis, thermo-gravimetric analysis, 31P NMR, and size exclusion chromatography. The organosolv process shows the largest lignin recovery, followed by the soda and Aquasolve processes. Lignin products from the soda process, the Aquasolve process and with reservation the organosolv process show interesting properties for polymer applications.  相似文献   

9.
This work presents here a new fundamental strategy for bio-converting Kraft lignin (KL) into useful products. Cupriavidus basilensis B-8 (here after B-8) was able to use KL as the sole carbon source. Fully 41.5% of lignin, 37.7% of total carbon (TC) and 43.0% of color were removed after 7 days of incubation. At the same time, lignin was depolymerized into small fragments, which was confirmed by scanning electron microscopy (SEM) and gel permeation chromatography (GPC). Bacterial biomass accumulated to 735.6 mg/L at the initial KL concentration of 5 g L−1, and the corresponding volumetric productivity of polyhydroxyalkanoate (PHA) was 128 mg/L. PHA productivity was significantly improved through fed batch fermentation and reached to 319.4 mg/L. GC–MS analysis showed that PHA polymer was composed of three basic monomers: 98.3 mol% of (S)-3-hydroxy-butanoic acid (S3HB), 1.3 mol% of ®-3-hydroxybutyric acid (R3HB) and 0.4 mol% of 3-hydroxy-butanoic acid (3HB).  相似文献   

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12.
Protoplasts from a lignolytic fungus Fomes annosus were prepared through enzymatic hydrolysis of mycelium utilizing Novozym, a wall lytic enzyme preparation. Isolated protoplasts and living mycelium were compared in their ability to degrade 14C-labelled lignin related phenols and dehydropolymers of labelled coniferyl alcohol (synthetic lignin). The amounts of 14CO2 released from O14CH3-groups, 14C-2-side chains and 14C-rings by protoplasts was in the same range as those for intact mycelium. The methoxyl groups of synthetic lignin were more rapidly metabolized by protoplasts than by mycelium. When calculated in dpm of released 14CO2 per mg protein the decomposition of 14C-labelled synthetic lignin and lignin-related monomers in a hyphae-free system of protoplasts was considerable higher than that obtained by the intact mycelium. The presence of intact hyphae is thus not necessary for lignin degradation to occur.Non-common-abbreviations used DHP Dehydropolymer of coniferyl alcohol - LS lignosulfonates prepared from DHP  相似文献   

13.
Abstract: The mechanism of oxidation of veratryl alcohol and β-0–4 dimeric lignin models is reviewed. Veratryl alcohol radicals are intermediates in both oxidation pathways. The possible role of the veratryl alcohol radical cation as a mediator is discussed. The lignin peroxidase (LIP) redox cycle is analyzed in terms of the Marcus theory of electron transfer. Reduction of both LiP-Compound I (LiP-I) and LiP-Compound II (LiP-II) by veratryl alcohol occurs in the endergonic region of the driving force. The reduction of LiP-II has a higher reorganization energy due to the change in spin state and the accompanying conformational change in the protein. It is suggested that a reversible nucleophilic addition of a carbohydrate residue located at the entrance of the active site channel plays a key role in the LiP redox cycle. Moreover. (polymeric) hydroxysubstituted benzyl radicals may reduce LiP-II via long-range electron transfer.  相似文献   

14.
Endophytic fungi occur on various types of leaf litter, but few studies have been done on their roles as saprophytes in decomposition. This study examined the succession of fungi in live, newly shed, and decomposing leaves at 2 months of decomposition of Camellia japonica and chemical changes in decomposing leaves colonized by endophytes. Coccomyces nipponicum, Lophodermium sp., Geniculosporium sp. 1, and Colletotrichum gloeosporioides were isolated from living leaves. Coccomyces nipponicum and Lophodermium sp. were also isolated frequently from newly shed and decomposing leaves. These two fungi caused a decrease of lignin content and bleaching in decomposing leaves under field and laboratory conditions. Total hyphal length in decomposing leaves was higher in bleached portions than in surrounding nonbleached portions, which probably reflected the early onset of hyphal growth of endophytes inside leaf tissue at leaf senescence or death. Incubation of newly shed leaves that were sterilized to exclude previously established endophytes resulted in no occurrence of bleached portions in decomposing leaves on the forest floor. This result indicated that these endophytes were incapable of colonizing leaves directly after litterfall and that the persistence of endophytes from live leaves was crucial for their colonization in decomposing leaves.  相似文献   

15.
【背景】微生物降解木质素因其具有降解效率高和环保等特点而备受关注。【目的】筛选高效木质素降解真菌,并对其降解条件进行优化。【方法】通过愈创木酚-马铃薯葡萄糖琼脂(potato dextroseagar,PDA)和苯胺蓝平板法筛选高效木质素降解菌株,利用单因素筛选及响应面试验对培养条件进行优化。【结果】筛选到一株高效木质素降解菌BYL-7,经形态和多序列分析初步确定为Trametes versicolor。单因素试验证明初始pH、温度和接种量为降解木质素显著影响因子,响应面试验确定降解木质素最优条件为:初始pH 6.7,温度25°C,接种量8%。在此条件下,碱性木质素降解率为36.5%,比未优化前提高54.0%;水稻秸秆木质素、半纤维素和纤维素降解率分别为32.8%、21.5%、13.2%,其中木质素降解率比未优化前提高36.1%;漆酶活性在第6天达到峰值120.0 U/L,比未优化前提高25.0%;木质素过氧化物酶活性在第6天达到峰值1343.8U/L,比未优化前提高36.0%;锰过氧化物酶活性在第5天达到峰值463.8U/L,比未优化前提高31.7%。【结论】研究结果为木质素的降解提...  相似文献   

16.
The syringyl to guaiacyl (S:G) ratio of hardwood lignin has long been identified as a significant parameter in delignification processes and more recent results have shown that it is also important in determining the amount of ethanol that can be obtained from fermentation of hydrolyzed wood. Acidolysis of Klason or acid insoluble lignin in dioxane/water/HCl was being investigated when syringyl and guaiacyl nuclei with a diketone-containing sidechain were observed as the major products. The area ratio of the two gas chromatogram peaks appeared to be indicative of the S:G ratio. After optimization of the method the relative standard deviation was found to be in the range of 0.3–3.76% for Klason lignin from a wide range of Eucalyptus grandis grown in South Africa. The method was then compared to nitrobenzene oxidation (NBO) using 13 poplars in a double-blind study. The respective S:G ratios were used to calculate percentages of S units and when these values were plotted against each other a linear correlation was obtained with a slope of approximately 1.0 (R2 = 0.86). The largest discrepancy for any poplar was 6.9% (62% vs. 58% S units). Both methods convincingly demonstrated a significant decrease in lignin content with an increase in the S:G ratio. Discussion is presented on a series of reaction that could lead to the formation of the two diketones.  相似文献   

17.
《Process Biochemistry》2014,49(12):2191-2198
Laccase and peroxidases mainly cause polymerization of lignin in vitro due to the random coupling of the phenoxy radicals or quinoid intermediates. White rot fungi may avoid polymerization in vivo by reduction of these intermediates. Pyranose oxidase is suggested to play such a role based on its quinone-reducing activity, but direct evidence has been lacking. In this study, a pyranose oxidase was purified from the white rot fungus Irpex lacteus and partially characterized. The enzyme is composed of four subunits of 71 kDa as determined by SDS-PAGE. It exhibits maximum activity at pH 6.5 and 55 °C and is rather stable. d-glucose is the preferred substrate, but d-galactose, l-sorbose and d-xylose are also readily oxidized. In addition to O2, the enzyme can also transfer electrons to various quinones and the ABTS [2,2′-azinobis(3-ethylbenzthiazoline-6-sulfonic acid)] cation radical. Laccase-generated quinoids are also reduced by the enzyme. Four different technical lignins were treated with laccase with and without pyranose oxidase. Subsequent gel permeation chromatography analysis demonstrated that the pyranose oxidase efficiently inhibited the polymerization of lignin caused by laccase and even brought about degradation.  相似文献   

18.
粉刺侧孢霉产木质素过氧化物酶酶活性与pH值的关系   总被引:3,自引:1,他引:3  
研究了粉刺侧孢霉 (Phanerochaetechrysosporium)在以微晶纤维素为C源时 ,木素过氧化酶与 pH值的关系 .试验采用 37~ 39°C下液体振荡培养 ,藜芦醇为产酶诱导剂 ,测试不同起始 pH值所得木素过氧化物酶活性 .结果表明 ,起始 pH值 6.0所得酶活最高达 0 .1 2 6U·ml- 1 ,说明以微晶纤维素代替葡萄糖为C源 ,其最佳 pH值相对较高 .菌丝球直径与酶活呈正相关 .  相似文献   

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20.
Non-isothermal thermogravimetric analysis (TGA) data of biomasses and pulps originating from non-wood and alternatives materials (i.e., Tagasaste or rice straw) have been fitted with refined models, which include autocatalytic kinetics. Data sets were obtained for different experimental conditions, such as variations of heating rate and atmosphere, i.e., inert (pyrolysis) versus oxidative atmosphere (combustion). Besides the access to classical kinetic parameters (pre-exponential factor, activation energy, and reaction order), the improved data analysis enabled the determination of the chemical composition of the samples (cellulose, hemicellulose, extractives, lignin). The latter compared very well with those obtained by conventional methods (chemical analysis, HPLC). Given the reduced environmental impact and rapidness of the method, potential applications for research related to new biomasses and industrial processes can be foreseen.  相似文献   

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