木质纤维细胞壁大分子取向研究进展

Research progress in macromolecular orientation of lignocellulosic cell wall

木质纤维细胞壁主要是由纤维素、半纤维素以及具网络结构的木质素交联形成的高度有序的三维立体结构,是植物最基本的力学承载单元。本文首先概述了国内外有关木质纤维细胞壁中纤维素、半纤维素和木质素3种结构大分子的模量、强度等微力学特性,其次就纤维素-半纤维素、纤维素-木质素以及半纤维素-木质素大分子间的交联结构、分子间的有序组装规律进行了总结。在此基础上,对比分析了光学显微成像、电子显微成像、原子力显微成像、显微红外光谱、线偏振显微拉曼光谱、和频振动光谱以及同步辐射X射线衍/射技术在细胞壁大分子取向研究过程中的异同点。重点讨论通过分子光谱化学成像技术揭示的木质纤维原料不同类型细胞以及同一类型细胞不同亚层中3种结构大分子取向排列规律。最后,展望了木质纤维原料大分子取向研究可能的发展趋势:系统表征木质纤维细胞壁纤维素超分子结构、三大组分间连接键类型、纤维素构象对半纤维素糖苷键及木质素芳香环有序组装的影响机制;在纳米尺度揭示木质纤维发育过程中,各类细胞壁中纤维素纤丝聚集体结构、取向和微力学变化规律;在细胞壁水平非破坏性地对木质纤维大分子取向进行三维立体成像和定量研究;基于分子结构表征、分子模拟和三维成像研究结果实现针叶、阔叶及禾本科植物纤维细胞壁骨架模型的构建。

Lignocellulosic cell wall is composed of cellulose, hemicelluloses and lignin, which are entangled together to form a 3D network system. The physical and chemical interactions and ordered assembly of these macromolecular has been proved to contribute to the optimal mechanical properties of plant fiber. In the present work, the micromechanical features of cellulose, hemicelluloses and lignin were summarized, while the macromolecular interactions between cellulose-hemicelluloses, cellulose-lignin, hemicelluloses-lignin as well as the cellulose molecular conformation modulated orientation correlation among these macromolecular were reviewed. Furthermore, the characteristics among light microscopy, SEM, TEM, AFM, FT-IR microscopy, polarized laser confocal Raman microscopy, sum frequency generation spectroscopy and X-ray diffraction/scattering techniques were compared. Especially, the application of molecular spectroscopy imaging approaches in revealing the macromolecular orientation of lignocellulosic fiber was discussed.Finally, the further research in macromolecular orientation was listed as following: systematically elucidating the effects of supramolecular structure of cellulose in lignocellulosic cell wall, the types of three intermolecular bonds, and the conformation of cellulose on the ordered assembly of the hemicellulose glycosidic bonds and lignin aromatic rings;revealing the structure, orientation and micromechanical changes of cellulose filament aggregates in various cell walls during the development of lignocellulosic fibers at the nanoscale;three-dimensional imaging and quantitative study of macromolecular orientation of wood fibers at the cell wall level;constructing fiber cell wall skeleton models of conifer, broadleaved and gramineous plants based on the results of molecular structure characterization, molecular simulation and 3D imaging.