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131.
Historical or archaeological wooden objects are generally better conserved in wet environments than in other contexts. Nevertheless, anaerobic erosion bacteria can slowly degrade waterlogged wood, causing a loss of cellulose and hemicellulose and leading to the formation of water-filled cavities. During this process, lignin can also be altered. The result is a porous and fragile structure, poor in polysaccharides and mainly composed of residual lignin, which can easily collapse during drying and needs specific consolidation treatments. For this reason, the chemical characterization of archaeological lignin is of primary importance in the diagnosis and conservation of waterlogged wood artifacts. Current knowledge of the lignin degradation processes in historical and archaeological wood is extremely inadequate. In this study lignin extracted from archaeological waterlogged wood was examined using both Py-GC/MS, NMR spectroscopy and GPC analysis. The samples were collected from the Site of the Ancient Ships of San Rossore (Pisa, Italy), where since 1998 31 shipwrecks, dating from 2nd century BC to 5th century AD, have been discovered. The results, integrated by GPC analysis, highlight the depolymerization of lignin with cleavage of ether bonds, leading to an higher amount of free phenol units in the lignin from archaeological waterlogged wood, compared to sound lignin from reference wood of the same species. 相似文献
132.
Elucidation of interaction among cellulose, lignin and xylan during tar and gas evolution in steam gasification 总被引:1,自引:0,他引:1
Chihiro Fushimi Shingo Katayama Atsushi Tsutsumi 《Journal of Analytical and Applied Pyrolysis》2009,86(1):82-89
Time profiles of evolution rates of gas and tar in steam gasification of model biomass samples were examined using a continuous cross-flow moving bed type differential reactor to elucidate the interaction of the major biomass components (cellulose, xylan, lignin) during gas and tar evolution. Two types of model biomass samples (sample A: mixture of cellulose (65 wt%) and lignin (35 wt%); sample B: mixture of cellulose (50 wt%), xylan (23 wt%), and lignin (27 wt%)) were used for the experiment. In steam gasification of sample A, the evolutions of water-soluble tar and gaseous products (CO, H2, CH4 and C2H4) are significantly suppressed by the interaction between cellulose and lignin. The primary (initial) decomposition of lignin is hindered by the interaction with pyrolysate of cellulose. Then, the CO2 evolution appreciably enhanced and the evolution of water-soluble tar delays. These results may imply that the volatilization of water-soluble tar derived from cellulose is suppressed by lignin and then the decomposition of char derived from polymerized saccharides and lignin takes place, emitting mainly CO2. From the results using sample B, it was found that the addition of xylan greatly enhances the evolutions of gases (CO2, CO, CH4 and H2) and accelerates the evolution of water-soluble tar and CO2, implying that the enhancement of decomposition of water-soluble tar into gases and/or xylan decomposes into gases without significant interaction with cellulose or lignin. In addition, yields of the major tar components (levoglucosan, furfural and 5-methylfurfural) were measured using HPLC. It was observed that the interaction among cellulose, xylan and lignin suppresses the evolution of levoglucosan and significantly increases the evolution rate of 5-methylfurfural. There is an insignificant influence of interaction among cellulose, xylan and lignin for furfural evolution. 相似文献
133.
Tetramethylammonium hydroxide (TMAH) thermochemolysis of 2-arylcoumaran lignin model compounds 总被引:1,自引:0,他引:1
Ken-ichi Kuroda Akiko Nakagawa-izumi Tatsuya Ashitani Koki Fujita 《Journal of Analytical and Applied Pyrolysis》2009,86(1):185-191
Phenolic 2-arylcoumarans 1–6 were used to examine the behaviors of β-5 subunits in lignin during tetramethylammonium hydroxide (TMAH) thermochemolysis. Products were monitored by gas chromatography/mass spectrometry. The process predominantly provided dimeric products with the opened hydrofuran ring. Substituent changes at the γ-position of ring A and at the 5-position of ring B had a large effect on the product compositions. 2-Arylcoumarans 1 and 6 with the γ-CH2OH substituent predominantly gave 2,3,3′,4′-tetramethoxystilbenes involving the elimination of the γ-CH2OH substituent, while 2–5 with the γ-CH3 substituent gave a mixture of 2,3,3′,4′-tetramethoxy-α-methylstilbenes and α-methoxy-α-(3′,4′-dimethoxyphenyl)-β-(2,3-dimethoxyphenyl)propanes. Substituent –CHCHCH3 on ring B remained unaffected. Substituents –CHCHCH2OH and –COOH on ring B produced the corresponding methyl ether and ester, respectively, by methylation. The –CHCHCHO substituent on ring B was converted to the –CHO substituent. 相似文献
134.
Structure and Action Mechanism of Ligninolytic Enzymes 总被引:2,自引:0,他引:2
Wong DW 《Applied biochemistry and biotechnology》2009,157(2):174-209
Lignin is the most abundant renewable source of aromatic polymer in nature, and its decomposition is indispensable for carbon
recycling. It is chemically recalcitrant to breakdown by most organisms because of the complex, heterogeneous structure. The
white-rot fungi produce an array of extracellular oxidative enzymes that synergistically and efficiently degrade lignin. The
major groups of ligninolytic enzymes include lignin peroxidases, manganese peroxidases, versatile peroxidases, and laccases.
The peroxidases are heme-containing enzymes with catalytic cycles that involve the activation by H2O2 and substrate reduction of compound I and compound II intermediates. Lignin peroxidases have the unique ability to catalyze
oxidative cleavage of C–C bonds and ether (C–O–C) bonds in non-phenolic aromatic substrates of high redox potential. Manganese
peroxidases oxidize Mn(II) to Mn(III), which facilitates the degradation of phenolic compounds or, in turn, oxidizes a second
mediator for the breakdown of non-phenolic compounds. Versatile peroxidases are hybrids of lignin peroxidase and manganese
peroxidase with a bifunctional characteristic. Laccases are multi-copper-containing proteins that catalyze the oxidation of
phenolic substrates with concomitant reduction of molecular oxygen to water. This review covers the chemical nature of lignin
substrates and focuses on the biochemical properties, molecular structures, reaction mechanisms, and related structures/functions
of these enzymes.
Reference to a company and/or products is only for purposes of information and does not imply approval of recommendation of
the product to the exclusion of others that may also be suitable. All programs and services of the US Department of Agriculture
are offered on a nondiscriminatory basis without regard to race, color, national origin, religion, sex, age, marital status,
or handicap. 相似文献
135.
整合共聚焦显微荧光和拉曼光谱成像技术系统研究了黄藤藤茎组织中不同类型细胞以及同一细胞不同形态区域的木质素区域化学特点。共聚焦荧光成像表明黄藤藤茎组织中木质素主要汇聚于初生木质部导管、次生木质部导管、维管束间的薄壁组织细胞以及纤维细胞角隅区。基于荧光光谱差异的光谱成像线性拆分结果显示纤维细胞次生壁由宽、窄层交替的同心层状结构组成,且窄层具有更高的木质化程度。比较黄藤、毛竹、芒草、毛白杨和虎皮松拉曼光谱发现黄藤材细胞壁拉曼光谱与阔叶木毛白杨类似,证实了黄藤材的化学组成更加趋近于阔叶木毛白杨。对拉曼光谱中木质素特征峰成像进一步揭示出纤维细胞中木质素不均一的分布规律: 其中细胞角隅胞间层和复合胞间层的拉曼信号强度最高,表明较高的木质化程度,其次是次生壁中的窄层,而次生壁宽层中拉曼特征峰强度最低,这一分布规律与竹材纤维细胞中木质素分布规律类似。宽、窄层中木质素不仅存在浓度上的差异,而且木质素基本结构单元的比例亦不同。采取光谱去卷积的方法排除了碳水化合物的影响,发现窄层中愈创木基(G型)木质素与紫丁香基木质素(S型)比例为0.19,而在宽层中这一比值为0.14,这一结果亦解释了宽、窄层荧光光谱间的差异。该研究结果对探索黄藤细胞壁生物合成及力学响应机制研究具有重要理论指导意义。 相似文献
136.
137.
M. Zain H. Kazmi Abhoy Karmakar Vladimir K. Michaelis Florence J. Williams 《Tetrahedron》2019,75(11):1465-1470
A mild method for the separation of cellulose/hemicellulose from extractives free sawdust is described. Sequential treatments with an equimolar mixture of BCl3 and BBr3 remove polysaccharide components from a white pine sawdust sample. Spectroscopic analyses, including solution and solid-state NMR spectroscopy, confirm a reduction in the amount of aliphatic sugars in solid samples and show that extracted components consist only of polymeric sugars and are free of aromatics. Staining with fluorescent and colorimetric dyes confirm that the sawdust sample after boron trihalide treatment is primarily lignin, with no detectable polysaccharides. 相似文献
138.
In recent decades, sustainable superhydrophobic surfaces from natural materials and sustainable processes have attracted increased interest due to their lower environmental footprint and potential applications in self-cleaning surfaces and biomedical devices. Although there is significant progress on selecting suitable nano and micro particles to prepare superhydrophobic surfaces, a comprehensive review on the direct use of sustainable colloidal particles (SCPs) is lacking. In this review, we highlight the recent advances on sustainable superhydrophobic surfaces using SCPs. The composition and properties, extraction methods, and chemical modifications are described, including cellulose nanocrystals, chitin/chitosan nanoparticles, and lignin nanoparticles. In addition to the physico–chemical properties and tunable dimensionality, the fabrication methodologies of superhydrophobic surfaces using modified colloids are described. Finally, the potential applications of these sustainable superhydrophobic surfaces ranging from oil/water separation, biomedical, water harvesting, biofabrication, microfluidic reactor, and food packaging are discussed together with a future perspective on the advances made. 相似文献
139.
A lignin‐based adsorbent for metallic ions, nanoparticles and various agricultural organophosphate pesticides in hexane is immobilized on silica gel without further fractional purification. For most organophosphate analytes examined in this study under the same conditions, the percentage of adsorption achieved was well above 90% in 15 min, was found to be highly related to the dipole‐dipole attractions that occurred among the oxygen‐containing functional groups attached to analyte and lignin molecules and was greatly enhanced in hexane. The adsorption is believed to be reversible and surface oriented; furthermore, the interaction leading to the adsorption is not as significantly subject to the steric hindrance effect caused by the bulky group or elements surrounding the phosphorus element. Other types of interactions enhanced in hexane, such as the π‐π interaction, and hydrogen bonding in some cases, were also observed and contributed less to the percentage of adsorption. However, the adsorption of ions and nanoparticles under aqueous conditions is thought to be mainly a result of the complexation of the oxygen‐bearing hydrophobic cleft of the lignin molecule. In all cases, the nature of the analyte, the amount of adsorbent and the acidic or basic origin of the additive in matrix also affect the percentage of adsorption. 相似文献
140.
木质素及其在高分子材料方面的利用课程教学方法与实践 总被引:1,自引:0,他引:1
木质素是一种重要的天然高分子,其开发利用已成为材料科学的热点之一。木质素及其在高分子材料方面的利用课程内容涉及木质素的结构与性质、木质素化学品、木质素热固性材料、木质素热塑性材料、木质素新材料、木质素材料的性能评价等。针对该门课程知识点多且内容分散、知识面宽、知识点新的特点,提出了教学方法:(1)采用案例教学法,密切联系生产实践;(2)采用翻转课堂教学法,提高学生自学能力;(3)加强双语教学,培养国际化专业人才;(4)采用灵活有效的考核方式,着实提高学生综合能力。 相似文献