Understanding the chemical structure of lignin in willow bark is an indispensable step to design how to separate its fiber bundles. The whole cell wall and enzyme lignin preparations sequentially isolated from ball-milled bark, inner bark, and wood were comparatively investigated by nuclear magnetic resonance (NMR) spectroscopy and three classical degradative methods, i.e., alkaline nitrobenzene oxidation, derivatization followed by reductive cleavage, and analytical thioacidolysis. All results demonstrated that the guaiacyl (G) units were predominant in the willow bark lignin over syringyl (S) and minor p-hydroxyphenyl (H) units. Moreover, the monomer yields and S/G ratio rose progressively from bark to inner bark and wood, indicating that lignin may be more condensed in bark than in other tissues. Additionally, major interunit linkage substructures (β-aryl ethers, phenylcoumarans, and resinols) together with cinnamyl alcohol end groups were relatively quantitated by two-dimensional NMR spectroscopy. Bark and inner bark were rich in pectins and proteins, which were present in large quantities and also in the enzyme lignin preparations.

中文翻译：

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柳树皮和木材中木质素的结构表征

了解柳树皮中木质素的化学结构是设计如何分离其纤维束的必不可少的步骤。从球磨的树皮，内部树皮和木材中依次分离出的全细胞壁和酶木质素制剂，通过核磁共振波谱和三种经典的降解方法进行了比较研究，即碱性硝基苯氧化，衍生化然后还原裂解，和分析硫代酸解。所有结果表明，柳树皮木质素中的愈创木基（G）单元比丁香基（S）和次要p占主导地位。-羟基苯基（H）单元。此外，从树皮到内部树皮和木材，单体的收率和S / G比逐渐提高，这表明木质素在树皮中的凝结程度可能高于其他组织。另外，主要的单元间连接亚结构（β-芳基醚，苯基香豆素和树脂醇）与肉桂醇端基一起通过二维NMR光谱进行了相对定量。树皮和内树皮富含果胶和蛋白质，果胶和蛋白质大量存在，也存在于木质素酶制剂中。