磺甲基化木质素的辣根过氧化物酶催化聚合研究

Horseradish Peroxidase Catalyzed Polymerization of Sulfomethylated Alkali Lignin

以碱木质素为原料,采用磺甲基化反应,得到磺甲基化木质素(SAL),并进一步采用辣根过氧化物酶(HRP)催化以提高其分子量,制备了高分子量高磺化度磺甲基化木质素(HPSAL).采用凝胶渗透色谱、红外光谱、核磁共振氢谱、紫外光谱和顶空气相色谱等研究了改性前后SAL的结构特征.结果表明,经HRP催化后,与SAL相比,HPSAL的重均分子量和磺化度显著增加,分别提高20倍和30%以上,羧基含量升高,而甲氧基和酚羟基含量降低.HRP使SAL形成酚氧自由基,活化其酚羟基的邻、对和侧链Cβ位,增加磺化反应活性,而磺化度的提高又有利于增加HRP催化SAL的聚合反应活性,其聚合方式主要为β-O-4'、β-β'、β-1'和β-5'联结.分子模拟结果表明,甲氧基含量的降低和磺酸基含量的增加能显著提高以β-O-4'连接键为主的聚合反应活性.

Alkali lignin was used as raw material to prepare sulfomethylated alkali lignin （SAL）. SAL was then further incubated by horseradish peroxidase （HRP） to obtain the products （HPSAL） with high degree of sulfonation and high molecular weight. The gel permeation chromatography （GPC）, infrared spectroscopy （IR） , nuclear magnetic resonance （NMR） , ultra violet-visible spectrum （UV-Vis） and headspace gas chromatography （HS-GC） were used to investigate the structural characteristics of HPSAL. Compared with SAL,the molecular weight （M） and the sulfonation degree of HPSAL increased by above 20-fold and 30% after HRP incubation,respectively. It was also indicated that the earboxyl content increased while the phenolic and methoxyl groups decreased after HRP incubation. HRP incubation could oxidize phenolic group to form phenoxyl radicals. The free electron of the phenoxyl radicals could transfer to the ortho-,para- positions of phenolic groups and Ca of SAL side chains,inducing the increase of sulfonation reactivity. On the other hand, the increase of sulfonic group content was beneficial to the polymerization of SAL by HRP incubation. The polymerization was achieved by radicals coupling,includingβ-0-4＇ ,β-β＇ ,β-1＇ andβ-5＇ linkages. The results of molecular simulation indicated that the chances ofβ-0-4＇ linkage increased significantly due to the decrease of methoxyl content and increase of sulfonic group content.