Lignocellulosic biomass is mainly constituted by cellulose, hemicellulose, and lignin and represents an important resource for the sustainable production of biofuels and green chemistry materials. Xylans, a common hemicellulose, interact with cellulose and often exhibit various side chain substitutions including acetate, (4-O-methyl) glucuronic acid, and arabinose. Recent studies have shown that the distribution of xylan substitutions is not random, but follows patterns that are dependent on the plant taxonomic family and cell wall type. Here, we use molecular dynamics simulations to investigate the role of substitutions on xylan interactions with the hydrophilic cellulose face, using the recently discovered xylan decoration pattern of the conifer gymnosperms as a model. The results show that α-1,2-linked substitutions stabilize the binding of single xylan chains independently of the nature of the substitution and that Ca2+ ions can mediate cross-links between glucuronic acid substitutions of two neighboring xylan chains, thus stabilizing binding. At high temperature, xylans move from the hydrophilic to the hydrophobic cellulose surface and are also stabilized by Ca2+ cross-links. Our results help to explain the role of substitutions on xylan-cellulose interactions, and improve our understanding of the plant cell wall architecture and the fundamentals of biomass pretreatments.

译文

木质纤维素生物质主要由纤维素,半纤维素和木质素组成,是可持续生产生物燃料和绿色化学材料的重要资源。木聚糖 (一种常见的半纤维素) 与纤维素相互作用,并经常表现出各种侧链取代,包括乙酸盐,(4-o-甲基) 葡萄糖醛酸和阿拉伯糖。最近的研究表明,木聚糖取代的分布不是随机的,而是遵循取决于植物分类家族和细胞壁类型的模式。在这里,我们使用分子动力学模拟,以最近发现的针叶树裸子植物的木聚糖装饰图案为模型,研究取代物对木聚糖与亲水性纤维素表面相互作用的作用。结果表明,α-1,2-连接的取代稳定了单个木聚糖链的结合,而与取代的性质无关,并且Ca2离子可以介导两个相邻木聚糖链的葡萄糖醛酸取代之间的交联,从而稳定了结合。在高温下,木聚糖从亲水性表面移动到疏水性纤维素表面,并且还通过Ca2交联稳定。我们的结果有助于解释取代在木聚糖-纤维素相互作用中的作用,并增进我们对植物细胞壁结构和生物质预处理基础的理解。

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