第三章-木质素chapter-3-lignin

1、第三章 木质素chapter 3 lignin,十九世纪30年代开始，1893年，Klason发表了木质素是由松柏醇coniferyl alcohol构成的想法，后确立了木质素定量fix quantity方法。 In 1897, Peter Klason studied the composition of lignosulfonates and put forward the idea that lignin was chemically related to coniferyl alcohol. In 1907, he proposed that lignin is a macromole

2、cular substance and, ten years later, that coniferyl alcohol, units are joined together by ether linkages. 1952年，Freudenberg的结构单元的脱氢聚合学说 木质素的化学研究始于1930年,至今不足70年的历史。,了解,3.1.1 木质素（ lignin）资源 一、木质素资源lignin resource 地球上资源丰富的天然聚合物nature polymer，在植物中的存在量仅次于纤维素second to cellulose。全球陆生植物每年可合成500万亿木质素。 按热焓en

3、thalpy容量计算，生物学上产生能量40%储存在木质素中store in lignin，来源丰富、价格低廉的可再生植物资源regenerated plant resource。 工业木质素industrial lignin：主要来源于造纸制浆蒸煮废水come from pulp industry waste（固含物中木质素含量为65%80%）。每生产1t草浆至少要生产1.31.5的黑液固体物。,3.1 植物细胞壁的木质素化作用 lignification of plant cell wall,二、木质素资源分类classification 工业木质素：木质素磺酸盐lignosulfonate

4、 、碱木质素alkali lignin 、木质素硫酸盐kraft lignin。 1.木质素磺酸盐（ lignosulfonate） 亚硫酸盐sulfite或亚硫酸氢盐hydrogen sulfite法造纸中存在于纸浆废液中的木质素磺化sulfonate产物。 Na2SO3,。 Mg2+, NH4+,3.1 植物细胞壁的木质素化作用 lignification of plant cell wall,2.碱木质素(alkali lignin) 烧碱法caustic soda，NaOH制浆。特点： （1） 经历强碱和高温作用后，发生大量的降解decomposition和缩合condensation

5、反应，使组成结构和成分复杂； （2）分子量分布molecular weight distribution较宽，平均分子量average molecular weight低（草类碱木质素一般在3000-10000之间，其重均相对分子质量为20003000，木质素磺酸盐lignosulfonate一般为2000050000）,3.1 植物细胞壁的木质素化作用 lignification of plant cell wall,（3）碱木质素alkali lignin因分子上缺乏be short of the hydrophilic and hydrophobic groups 亲油亲水性均较理想的官

6、能团，在有机相和水相中的溶解度solubility均不高，溶于碱性介质； （4） 组成不稳定unstable，使产品性能波动大。； （5）利用率很低。,3.1 植物细胞壁的木质素化作用 lignification of plant cell wall,3.木质素硫酸盐kraft lignin 方法：NaOH + Na2S 木材原料制浆,3.1 植物细胞壁的木质素化作用 lignification of plant cell wall,3.1.2 木质素生物合成过程Biosynthesis of Lignin 1.主要可分为两部分two steps： 木质素结构单元生物合成biosynthesi

7、s of lignin Precursors 莽草酸途径via shikimic acid route 木质素高分子生物合成脱氢聚合enzymic dehydrogenation and combination of the monomeric radicals 2.形成区域顺序 细胞角隅的初生壁primary wall of cell corner复合胞间层middle lamella初生壁次生壁 3.研究方法： 原子示踪atom(14C) labeling和紫外显微镜UV microscope,3.1 植物细胞壁的木质素化作用 lignification of plant cell wal

8、l,3.1.3 木质素结构单元phenylpropane units的生物合成 CO2 松柏醇、芥子醇和 对羟基香豆醇 (p-coumaryl, coniferyl, and sinapyl alcohols ) 莽草酸途径shikimic acid route,3.1 植物细胞壁的木质素化作用 lignification of plant cell wall,从葡萄糖到木质素丙烷结构单元的新陈代谢,1.光合作用产物葡糖糖D-Glucose generated in photosynthesis ，经莽草酸途径shikimic acid route合成苯丙氨酸phenylalanine、酪氨酸

9、tyrosine； 2.苯丙氨酸解氨酶(PAL,phenylalanine ammonia-lyase)作用于L-苯丙氨酸,生成肉桂酸cinnamic acid， PAL广泛存在于树木形成层cambium和禾本科gramineae中； 3.酪氨酸解氨酶(TAL,tyrosine ammonia-lyase)作用于L-酪氨酸，生成对香豆酸， TAL存在于禾本科和竹科中，木材中无发现； 4. PAL 和TAL均参加禾本科和竹科木质素的生物合成，而木材只经过PAL合成木质素；,3.1 植物细胞壁的木质素化作用 lignification of plant cell wall,5.羟基hydroxyl

10、ate化与甲基化methylate 针叶材的酶enzyme只催化catalyze咖啡酸生成阿魏酸，而对5-羟基阿魏酸向芥子酸的反应不催化。 阔叶木、禾本科和竹类的酶对阿魏酸、芥子酸两者生成均催化。 6.OMT:O-甲基methyl转移酶与木质素合成类型密切相关 针叶木木质素不具有形成紫丁香基木质素syringyl lignin的能力； 7.还原三个阶段酶反应CoA, NADP还原, NADP氢化 CoA,只对对香豆酸和阿魏酸高活性，与芥子酸不反应；对5-羟基阿魏酸有活性。,3.1 植物细胞壁的木质素化作用 lignification of plant cell wall,3.1.3木质素结构单

11、元的脱氢聚合 Freudenberg（1940-1970）1952年提出：脱氢聚合。 实验：松柏醇coniferyl alcohol (磷酸液5%) 伞菌酶（漆酶） 白色沉淀（60%）, 产物与针叶材木质素相似。 同样芥子醇和松柏醇共同反应，产物与阔叶木木质素相似。 伞菌酶（漆酶）：脱氢酶 木质素结构单元Lignin precursors 酶脱氢enzymic dehydrogenation 苯氧游离基phenoxy radical 二聚dimer、三聚trimer 木质酚氧化偶合oxidative coupling 木质素,3.1 植物细胞壁的木质素化作用 lignification of

12、plant cell wall,For an understanding of the formation and structure of lignin, investigations conducted by H. Erdtman in 1930 were of great importance. He studied the oxidative dimerization of various phenols in the biogenesis of natural produces and reached the conclusion that lignin must be formed

13、 from ，-unsaturated C6C3 precursors of the coniferyl alcohol type via enzymic dehydrogenation. The polymerization of precursors to lignin in nature does indeed occur in this manner, as has been demonstrated by comprehensive studies by Freudenberg and co-workers during the period 1940 to 1970.,松柏醇被过氧

14、化酶和H2O2hydrogen peroxide的脱氢dehydrogenation作用 p80,Formation of resonance-stabilized phenoxy radicals by the enzymic dehydrogenation of coniferyl alcohol.,The enzymic dehydrogenation reaction is initiated by an electron transfer which results in the formation of resonance-stabilized phenoxy radicals.

15、The combination of these radicals produces a variety of dimers and oligomers, termed lignols. It can be readily shown that further oxidative coupling of di- and oligolignols (bulk polymerization) would lead to a product containing a large number of unsaturated side chains.,Combination of the monomer

16、ic radicals to the phenolic end groups exclusively through-O-4 and-5 coupling modes would lead to a linear polymer. However, branching of the polymer may take place through the formation of benzyl aryl ether structures. In addition, 5-5 coupling to biphenyl structures and 5-O-4 coupling to diaryl et

17、her units produce additional branched elements. The formation of biphenyl and diaryl ether structures primarily occurs in the coupling of two end group radicals rather than in the combination of monomer radicals to the end group radicals.,The dominating structures in the lignin molecule together wit

18、h a variety of minor structural elements have been elucidated gradually as the methods for the identification of anon products and for the synthesis of model compounds have been improved.,A variety of dimers and oligomers have been identified among the acidolysis products of MWL, revealing the high

19、frequency of such elements as the guaiacylglycerol-aryl ether and the phenylcoumaran structures. A particularly useful structural method consists of the oxidation of methylated lignin by permanganate and hydrogen peroxide to aromatic acids followed by identification of the reaction products by gas-l

20、iquid chromatography. More than two thirds of the phenylpropane units in lignin are linked by ether bonds, the rest by carbon-to-carbon bonds.,木质素重要结构单元间的连接linkage,木质素重要结构单元间的连接linkage,木质素模型物中单元间各种连接的方式linkage types和频率frequency（100个单元）,3.1 植物细胞壁的木质素化作用,3.1.4 植物中木质素的分布distribution 分布规律： 分布不均匀uneven；

21、采集部位愈高，木质素含量愈低； 胞间层middle lamella的木质素浓度concentration最高； 细胞内部浓度减小，次生壁内层又增高； 如花旗松的胞间层木质素浓度为60%-90%，细胞腔cell lumen附近约10%-20%。,不同形态学区域中的木质素浓度 Cl-Ka X-射线计数指示试样厚度的变化； CC-细胞角隅； CML-胞间层； S-次生壁,3.1.5 木素的不均一性,1. 不同种属植物的木素结构差别 Softwood: 主要为愈疮木基guaiacyl（G）型 Hardwood:主要为愈疮木基guaiacyl（G）-紫丁香基syringyl （S）型 guaiacyls

22、yringyl lignin 对-羟苯基木质素 p-hydroxyphenyl lignin 2. 不同植物部位和生长情况的木素结构差别 成熟木质部紫丁香基比例较高 心材木素有较高的分子量并且是重缩合的 3. 不同植物细胞形态学（细胞壁的不同位置）的木素结构差别,3.2 木质素的命名nomenclature和分类classification,1.木质素的命名 Lignins are polymers of phenylpropane units. （1）含义与范围 木质素、原本木质素、木质素衍生物、木质素产物的区别和含义。 （2）侧链的标志 （3）略写: P(丙烷基); G; S; (联接),

23、木质素结构单元苯丙烷中碳原子标志PhenylpropaneThe basic structural unit of lignin,木质素略式的应用,3.2.2 木质素的命名nomenclature和分类classification,1.木质素的分类 （1）愈疮木基木质素（G-木质素） 针叶木、蕨类植物等。 （2）愈疮木基-紫丁香基木质素(GS-木质素) 被子植物中 温带阔叶木； 热带阔叶木： 草木植物：,一、木质素分离前的准备（研究用试样） 1.取样：木材木粉（40-60目） 2.提取试样Lignin can be isolated from extractive-free wood 目的：防

24、止少量组分缩合。 3.提取液组成：能提取有机物，又不与木质素反应，乙醚、乙醇、苯-乙醇、二氧六环。 二、木质素分离 两类：an insoluble residue （不溶解木质素）after hydrolytic removal of the polysaccharides. Alternatively, lignin can be hydrolyzed and extracted from the wood or converted to a soluble derivative（溶解木质素）.,3.3 木质素的分离和测定,Soluble lignin derivatives (lignos

25、ulfonates) are formed by treating wood at elevated temperatures with solutions containing sulfur dioxide and hydrogen sulfite ions. Lignin is also dissolved as alkali lignin when wood is treated at elevated temperatures (170) with sodium hydroxide, or better, with a mixture of sodium hydroxide and s

26、odium sulfide (sulfate or kraft lignin). Lignin is further converted to an alkali-soluble derivative at 100.,三、分离木质素 的一般方法,3.3 木质素的分离和测定,3.3 木质素的分离和测定,结构研究用样品 一、Bjorkman磨木木质素(MWL，milled Wood Lignin)的分离 （一）标准方法 1.制样 20目以上木粉，苯醇抽提，P2O5干燥。 2.磨碎 二甲苯做分散剂，除去水分，球磨。 3.提取 分离二甲苯的木粉，二氧六环：水（9：1）溶液抽提。,3.3 木质素的分离和

27、测定,了解,4.提纯 分离碳水化合物（LCC复合体）低于1%。 (1)含木质素的二氧六环溶液50-60真空蒸干残渣用10%醋酸溶解（g/20ml）加水(g/250ml)沉淀分离不溶物水分蒸发残渣用1,2-二氯乙烷和乙醇（2：1）溶解分离不溶物清液加入乙醚，木质素沉淀离心分离反复用乙醚和石油醚洗P2O5真空干燥，用放射线除去静电。,了解,3.3 木质素的分离和测定,3.3 木质素的分离和测定,Bjorkman磨木木质素(MWL，milled Wood Lignin)的分离 Besides cellulolytic enzyme lignin, the so-called Bjrkman lign

28、in, alternatively referred to as milled wood lignin (MWL) is the best preparation known so far, and it has been widely used for structural studies. When wood meal is ground in a ball mill either dry or in the presence of nonswelling solvents, e.g., toluene , the cell structure of the wood is destroyed and a portion of lignin (usually not more than 50%) can be obtained from the suspension by extraction with a dioxane-water mixture. MWL preparations always contain some carbohydrate material