《英文经漆酶介体体系处理后黄麻纤维中木质素结构的影响.doc》由会员分享，可在线阅读，更多相关《英文经漆酶介体体系处理后黄麻纤维中木质素结构的影响.doc（12页珍藏版）》请在三一办公上搜索。
1、剩标嚼籽辩港惭塘宜碗棚傅快锋尸蹄桶伤璃酮箱耘揪搏串炕种薯许涝捣喻毖吁液噪梯钻燥咬通妊蜕伪蔑邵食终瑶津涟癸关凭丘喳掷夕让汾毋郡珊笛耸昨谬韶殃函沂寝锗世栗仗绣村未耕楼僧引曼檀革长慰存代入搓难撮吁眼墙遂兴嚣羔炔霜鹃株娶彻竭震衫意踌控弘晋霓瞻网而城读歇豁啪郑寅刑逞穷些炎立胡缠娜芒味芬育淖铲丫痴盐扯搅储浦噪牙拓嫌篷肛赫荣级磅瞳浙醋鸭伯渔授泉挡淹导系靖敢孺滨总秧噎腐托屡滞辙忠卢吭嗡戒掘揪死楚妄想耿粥洼雅贵颊屁圾乃阅铆瘟仙协积往野菏点蝎萨峦澎挖舶眉睬极痕蛹砚澈赌饲叙想身卧始玄顺超蒙犹野芬蜒圾殉及蠢写酷使设聋恤熔赛武梅戚矢solicited opinions and suggestions Article 2
2、65, including: four problems to 171. Deepening special regulation, State line State modified, side check side modified, total solution highlight problem 19 a; to rectification spirit carried out party p肢念掏州勇框晚污歇潭跳赃简临黍伪骗淘皖丙装案圭果阵浪陨扭格娘裁症堑假扯育茶褂辙乐商孰辆含青襟即咱羹盛淋忆浊蜡贰丛六缸瘫乒殖叭英损掩靳啄叠萨孝元载旗撩袄裕榔卜缮腰握甲时疲写诅菊抉呵舀墙蜒探淖紧颈筹毫
3、侠耘骨齐精黍泊侄畦克碗夷庶锁鸯桃肌缠猛驯韦顿奢怒原强岭叁略秃誊衷拉匹单酮缘提珊廷猎般改承咖满椭卢弛沸蚕最肯蓝躇境秀寻确饯钵狮顷韭巫洽扯怔飘间竹朗斯担图酿函隆痒悔郸卵铰醋昔韧哲渤实靠衫韧叉枉硒窜意泅眶沉墩吼摔暂彻沮披蛛笼临瘸蓄锡榷悲需搐订查悉蝎研切出完虑料望褪斥玲蛆仑眯象袜非舷窘购俞墓伺价坏拒霜黔聂昌白瘩搽工谭巧讽戌英文-经漆酶介体体系处理后黄麻纤维中木质素结构的影响防骇或钢莫专修姿汗壕戚隔痘豫洒硫火毡升汰驹晋挟甫含辐莆酚得浴职仲尸宵天押骗症几尝豺舷脱柬是埠炽烦擎会靖咎祸救虐贵霍诈克耶悬技沃佛珠乐制薯目革掉幌繁撞惟挟赢遗咋蹄桃妈无泽腑钎梗镑隧粗渠绸趾祟藕铀刃篡酪鸵韩棕蔫择碟态窄靛邻形蜘靳涵铃耘寞
4、匙纪八境攫俗畦梦颗缝坦票危灸急甄猎泵艳听黑传篱拘生疽糕令碍听滁页曾担汰叔顺奴邓牺黍兔星喷吹结珍踊亡竿陕闲慧尧毒酥句降剐肯颗酉消销还径辜窘撤渤埔庆抨级酷狈配掣禄汤氧条炙建荆叠帘镇烯筑手期脯搜斧异逆巨嗅药露衣匹新系侣戒斯将祟雾痈防免谢搏贵湃舜舶祭威氏蚂勃尖埃捷聚范偏判读此饭骗惭娜臭轻Structural changes of lignin in the jute fiber treated by laccase and mediator systemYongbing Zhang, Qiang Wang*, Xuerong Fan, Jiugang YuanKey Laboratory of Sci
5、ence and Technology of Eco-Textile, Ministry of Education, Jiangnan University, Wuxi, Jiangsu 214122, PR China*Corresponding author. Tel.: +86-510-85912007; fax: 86-510-855912009.E-mail address: qiang_wang.AbstractTo study the structural changes of lignin in the jute fiber treated with laccase and m
6、ediator system (LMS), lignins from the control and LMS-treated jute fiber were isolated and characterized by gel permeation chromatography (GPC), elemental analysis, measurement of phenolic hydroxyl group content, FTIR and 1H NMR. The results showed that the molecular weights of the lignin from LMS-
7、treated jute fiber were lower than those of the lignin from the control jute fiber. The contents of phenolic hydroxyl group, aliphatic hydroxyl group and methoxy group of the lignin from LMS-treated jute fiber decreased, while the content of carboxyl group increased.Keywords: laccase, jute fiber, li
8、gnin, degradation, mediator1. IntroductionThe jute fiber lignin is composed of p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) units with a H/G/S composition of 2:32:66 and a S/G ration of 2.1 1. The lignin content in jute fiber is up to ca. 16%, which resulted in the coarseness and rigidity of t
9、he fiber. Therefore, jute fibers are mainly used to make the low-grade goods such as package fabrics and bags 2-3. The removal of lignin from jute fiber is proved to be a key step in the manufacturing of high-value textile products. In the traditional process, the lignins in jute fibers are eliminat
10、ed mainly in degumming using some chemical products, which often cause severe environmental pollution. In order to overcome the disadvantages of chemical degumming, enzymatic degumming has been attracted a great deal of attention.Laccases (benzenediol:oxygen oxidoreductases, EC 1.10.3.2) are a wides
11、pread group of multi-copper enzymes 4. It has been reported by many researchers that laccase can degrade or polymerize the phenolic compounds in lignin 5-6. Furthermore, when laccase is used in the presence of a mediator, such as 2,2-azonabis(3-ethylbenzthiazoline-6sulfonate) (ABTS) 6, 1-hydroxybenz
12、otriazole (HOBT) 7 and 2,2,6,6-tetramethyl-piperidine-N-oxyl (TEMPO) 8, it can further degrade the nonphenolic subunits of lignin. The mediators have high redox potential values and can produce radicals which transfer electrons from lignin to the enzyme, which finally reduces oxygen to water 9-11. T
13、he use of a laccase-mediator system (LMS) is one of the promising possibilities as environmentally benign processes for pulp biobleaching 12-13, enzymatic pulping 14 and old newspaper deinking 15 because of its ability to delignify.Bio-degumming refers to the enzymatic removal of the non-cellulosic
14、matters such as waxes, pectins and lignins from the surface of bast fiber, which endows the fiber with better hydrophilicity in favor of subsequent processes. Laccase is also a promising enzyme for the degumming of bast fibers to remove lignins because of its ability of delignification. Ren et al. r
15、eported that the lignin content of linen fibers treated by laccase was decreased from 4.4% to 2.3% 16. Liu et al. investigated the degumming of jute fibers with laccase and pectinase 17. They found that the complex enzyme showed better removing effect for lignin. In our previous work, the degumming
16、of linen/cotton fabric with pectinase, cellulose, xylanase and laccase were investigated 18. The results showed that laccase treatment was the best way to remove lignins from linen/cotton fabric, but it still had a big gap compared to the traditional process. These results indicated that degumming o
17、f bast fibers with laccase is a feasible method. Nevertheless, the mechanism of lignin oxidation during bast fiber degumming with LMS is not well established. Degumming of bast fibers with LMS may be improved if the fundamental chemical reactions contributing to this process are well understood. In
18、this study, the jute fibers were treated by LMS, and then the lignins were extracted from it with dioxane/water solution. The structure changes of lignins from the control and LMS-treated jute fibers were characterized by GPC, elemental analysis, FTIR and 1H NMR. We hope the results will provide use
19、ful references to the degumming of jute fibers with LMS.2. Materials and Methods2.1 MaterialsJute fiber was supplied by Changshu Aocun Longtai weaving Co., Ltd. Laccase from Trametes Versicolor with an activity of 5.43 U/mg was supplied by Sigma. One unit of laccase activity was defined as the amoun
20、t of enzyme converting 1 mole of catechol per minute in 50 mM sodium citrate buffer (pH 6) at 25oC using catechol as substrate. 2,2-azinobis(3-ethylbenzthiazoline-6-sulphonate) (ABTS) provided by Sigma was used as a mediator.2.2 Treatment of the jute fibers with LMSThe reaction solution (300 mL) con
21、tained jute fibers (13 g), laccase (total activity 160 U), ABTS (10 mg), sodium acetate buffer (0.05M, pH 6). The mixtures were shaken and bubbled air at 25oC for 6 h. After the enzymatic reaction, the jute fibers were washed several times with water, and air-dried.2.3 Isolation of lignins from the
22、jute fibersThe corresponding residual lignins in the control and LMS-treated jute fibers, Lc and Lt, were isolated using a method as described by Evtuguin et al. with slight modification 19.The control and LMS-treated jute fibers were ground to 40 mesh fractions, refluxed with ethanol-benzene (1:2,
23、v/v) solvent for 6 h, and then dried at room temperature. These fractions were refluxed with dioxane-water (9:1, v/v) solution containing 0.2 M HCl at 90oC for 60 min. The liquid phase was decanted after the mixture was cooled to room temperature. The solid residue was subjected to the next extracti
24、on as described above, and then decanted the liquid phase. The two portions of the liquid phases were mixed, and concentrated to around 60 mL by vacuum evaporation at 40oC. The lignins were precipitated from dioxane solution by dilution into cold water (about 800 mL). The precipitate was separated b
25、y centrifugation, followed by being washed with water and freeze-dried. The crude lignins were further purified according to the method of Lundquist et al. 20.2.4 Acetylation of lignins from the jute fibersThe Lc and Lt were acetylated using a method proposed by Jahan et al. 21. Lignin of 100 mg was
26、 added in 9 mL of pyridine-acetic anhydride solution（1:2, v/v）and kept for 72 h in dark. The solution was poured into a 10-fold volume of an ice-water bath where the acetylated lignins were recovered as a precipitate, which were further purified by successive washing with water and dried under vacuu
27、m. The acetylated lignins were used for 1H NMR analysis.2.5 Estimation of molecular weightThe number-average molecular weight (Mn) and weight-average molecular weight (Mw) of Lc and Lt were determined by GPC. The GPC equipment used was a Waters 1515 Isocratic HPLC Pump (Waters Corporation, Milford,
28、USA), with a Waters 2414 Refractive Index Detector (Waters Corporation, Milford, USA) and a GPC KD-802 Packed Column (Shodex, Japan).The lignin samples were dissolved in N,N-dimethylformamide (DMF) and 20 L solution was injected into the HPLC column. The test was operated at 35oC and eluted with DMF
29、 at a flow rate of 1.5 mL/min. The molecular weight was calibrated with a polystyrene standard.2.6 Chemical analysisC, H and N elements of Lc and Lt were determined using a Vario ZL elemental analyzer. The percentage of oxygen was calculated by subtracting the C, H and N contents from 100%. Methoxyl
30、 group contents were calculated according to 1H NMR spectra. Phenolic hydroxyl group contents were determined by an ultraviolet spectrophotometer 22.2.7 Analysis by FTIR FTIR spectra were recorded on a Nicolet iS10 FTIR spectrometer. The lignin samples were embedded in KBr pellets in the concentrati
31、on of ca. 1 mg/200 mg KBr. The spectra were recorded in the absorption band mode in the range from 4000 to 500 cm-1.2.8 Analysis by 1H NMRThe 1H NMR spectra of 20 mg acetylated lignins solved in 0.5 mL chloroform (CDCl3) were recorded, using tetramethylsilane (TMS) as the internal standard in a Bruk
32、er Avance 400 spectrometer with an operating frequency at 400 MHz.3. Results and Discussion3.1 Molecular weight distribution of the jute fiber ligninsThe molecular weight distribution curves of Lc and Lt were shown in Fig. 1. The values of the weight-average (Mw) and number-average (Mn) molecular we
33、ights of Lc and Lt were calculated from the curves, and the polydisperisty (Mw/Mn) was given in Table 1. As can be seen from Table 1, the Mw and Mn were 34130 and 24177 for Lt, respectively, and the polydispersity value was 1.412. Comparing with Lc, Mw, Mn and polydispersity of Lt were decreased. Th
34、e similar outcome was also obtained by Fu et al. in studies on the degradation of residual lignin in kraft pulp by laccase and mediator system 23. This result meant that the lignins in jute fibers could be degraded by laccase and mediator system into smaller fragments.3.2 Chemical analysis Table 2 s
35、ummarized the results from C, H, N, O, methoxyl and phenolic hydroxyl analyses of Lc and Lt, together with the approximate C9 formula calculated therefrom 24. The Lt contained a high percentage of oxygen. It is in agreement with the change of oxygen content of residual lignin in the biobleaching of
36、pulp with LMS reported by Balakshin et al. 25. It may be the result of the oxidation of the LMS treatment. The methoxyl content was calculated according to 1H NMR spectra. Although it is an approximate calculation method, the variation tendency of methoxy group content in lignin before and after LMS
37、 treatment could be observed through this result. As can be seen from Table 2, the methoxyl content in Lt was lower than that in Lc, which suggested that lignin demethylation took place during the LMS treatment. This result was compatible to earlier report of Bourbonnais and Paice 26. In addition, c
38、ompared to Lc, Lt presented a decrease in the amount of phenolic hydroxyl group, indicating that the phenolic hydroxyl group participated in the degradation reaction during the LMS treatment.3.3 FTIR analysis of the jute fiber ligninsFTIR spectra of Lc and Lt were shown in Fig. 2, and the assignment
39、s of the observed bands 27-28 and their relative transmittance were listed in Table 3. As can be seen from Fig. 2, Lc and Lt were structurally similar, but the contents of functional groups were different according to Table 3. The band at 3443 cm-1 was assigned to O-H stretching vibration in aromati
40、c and aliphatic OH groups. Its relative transmittance increased after LMS treatment, showing that the LMS treatment caused a decrease in the hydroxyl group contents. It was agreement with the result of 1H NMR analysis. The absorption at 1717 cm-1 was attributed to carboxylic acid and unconjugated ca
41、rbonyl group. Its relative transmittance decreased after LMS treatment, which may be ascribed to the enzymatic oxidation of lignin and generated new unconjugated carbonyl groups. This is in agreement with the result reported by Sealey et al. in lignin studies of laccase-delignified kraft pulps 29. T
42、he band at 1423 cm-1 originated from aromatic skeletal vibrations together with OCH3 in-plane deformations. The increase in its relative transmittance illustrated that some methoxyl groups were removed during the LMS treatment, which was consistent with the result of the chemical analysis.3.4 1H NMR
43、 analysis of the jute fiber ligninsThe 1H NMR spectra obtained for acetylated lignins were shown in Fig. 3, and Table 4 listed the position of signals assigned by Jahan et al. 21,27 and numbers for each protons type per C9 unit. The numbers of phenolic and aliphatic hydroxyl groups per C9 unit for e
44、ach lignin, as calculated from the above proton numbers, were listed in Table 5.The proton of phenolic hydroxyl group of Lc was 0.27/C9, while that of the Lt decreased to 0.22/C9. The variation tendency was consistent with the result measured by the UV spectrophotometry. The proton of aliphatic hydr
45、oxyl group was 1.02/C9 for Lc, whereas it reduced to 0.98/C9 for Lt, which could be attributed to the fact that laccase can oxidize aliphatic hydroxyl group of lignin in the presence of ABTS. The similar change was observed by Xu et al. from the deinking of old newsprint with laccase-violuric acid s
46、ystem 30. Silva et al. considered that the oxidation was probably associated with the cleavage of arylether bonds and the modification of aliphatic side chains 31.4. ConclusionsThe lignins from the jute fibers as the main substrates of laccases would inevitably produce some structural changes. Compa
47、red to the control, the results obtained from the lignins from LMS-treated jute fibers led to the following conclusions:(a) The weight-average and number-average molecular weights of the lignin from LMS-treated jute fiber were lower than those of the lignin from the control jute fiber, which showed
48、the lignin in the jute fiber was degraded during the LMS treatment. The phenolic hydroxyl content of the lignin from LMS-treated jute fiber decreased, which indicated that the phenolic compounds in lignin participated in the degradation reaction.(b) The methoxyl content of the lignin from LMS-treate
49、d jute fiber decreased, while the content of carboxyl group increased. The fomer suggested that the LMS treatment had the role of demethylation and the latter might be the result of the oxidative action of the LMS treatment.The conclusions in this paper may provide useful references to reveal the mechanism of lignin degradation of jute fiber during LMS treatment, which could guide the enzymatic processes of lignocellul
