Lignin is an abundant polymer found in wood and grasses, but due to its heterogeneity and complex macromolecular structure it has been less utilized than cellulose. While the building blocks are known, the way they are linked is less understood. Here, Molecular Dynamics simulations were used to systematically characterize seven linkages found in native lignin. Their influence on lignin and water structure, and their interactions were analyzed. The study is limited to guaiacyl (G-G) dimers connected by the following common softwood linkages; 5-5′, 4-O-5′, α-O-4′, β-1′, β-5′, β-O-4′ and β-β′. The simulations show that the linkage has a significant effect on conformational preference and lignin-water interaction. Especially, the behavior of the β-O-4′ shows unique properties, both in terms of conformational freedom and interaction with water. Within the β-O-4′ dimer, π–π stacking between the aromatic rings is possible. The molecule has two distinct common conformations, one compressed and one extended. These preferences also lead to a different effect of β-O-4′ dimer on the surrounding water, where water is found close to the linkage itself but expelled from the aromatic rings to a larger extent than the other linkages. These findings are important for lignin solubility as well as its depolymerization mechanisms.

中文翻译：

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通过分子动力学模拟研究木质素二聚体的结构、灵活性和水合特性

木质素是木材和草中发现的一种丰富的聚合物，但由于其异质性和复杂的大分子结构，其利用率低于纤维素。虽然构建块是已知的，但它们的链接方式却鲜为人知。在这里，分子动力学模拟被用来系统地表征天然木质素中发现的七个连接。分析了它们对木质素和水结构的影响及其相互作用。该研究仅限于通过以下常见软木键连接的愈创木基 (GG) 二聚体；5-5', 4-O-5',α-O-4′，β-1′,β-5′,β-O-4′ 和β-β′。模拟表明，这种联系对构象偏好和木质素-水相互作用有显着影响。尤其是，以下人士的行为β-O-4' 在构象自由度和与水的相互作用方面都显示出独特的性质。内β-O-4′二聚体，π–π芳香环之间的堆积是可能的。该分子具有两种不同的常见构象，一种是压缩的，一种是延伸的。这些偏好也导致了不同的效果β-O-4'二聚体位于周围的水上，其中水靠近键本身，但从芳香环中排出的程度比其他键更大。这些发现对于木质素溶解度及其解聚机制很重要。