Belesov Artyom V, Mazur Dmitrii M, Faleva Anna V, Varsegov Ilya S, Pikovskoi Ilya I, Ulyanovskii Nikolay V, Kosyakov Dmitry S
Core Facility Center 'Arktika', Northern (Arctic) Federal University, Arkhangelsk 163002, Russia.
Department of Materials Science, MSU-BIT University, Shenzhen 517182, China.
Int J Mol Sci. 2024 Nov 25;25(23):12623. doi: 10.3390/ijms252312623.
N,N'-Dialkylimidazolium-based ionic liquids are capable of completely dissolving lignocellulosic biomass at elevated temperatures and are considered as promising green solvents for future biorefining technologies. However, the obtained ionic liquid lignin preparations may contain up to several percent nitrogen. This indicates strong interactions between the biopolymer and the IL cation, the nature of which has not yet been clarified. The present study investigates mechanisms and pathways of the formation of nitrogen-containing lignin compounds. To achieve this goal, eight monomeric lignin-related phenols bearing different functional groups (ketone, aldehyde, hydroxyl, carbon-carbon double bonds) were treated with 1-butyl-3-methylimidazolium acetate (BmimOAc) under typical conditions of IL-assisted lignocellulose fractionation (80-150 °C). A number of the resulting products were tentatively identified, for all the studied model compounds, by two-dimensional NMR spectroscopy and high-performance liquid chromatography-high-resolution mass spectrometry. They all possess covalently bonded Bmim residues and occur through the nucleophilic addition of an N-heterocyclic carbene (deprotonated Bmim cation) to electron-deficient groups. The reactivity of lignin functional groups in their interaction with Bmim is greatly affected by the temperature and dissolved oxygen. IL's thermal degradation products act as additional reactive species toward lignin, further complicating the range of products formed. The obtained results made it possible to answer the question posed in this article's title and to assert that N,N'-dialkylimidazolium-based ILs act as active reagents with respect to lignin during the dissolution of lignocellulose.
基于N，N'-二烷基咪唑鎓的离子液体能够在高温下完全溶解木质纤维素生物质，被认为是未来生物精炼技术中很有前景的绿色溶剂。然而，所得到的离子液体木质素制剂可能含有高达百分之几的氮。这表明生物聚合物与离子液体阳离子之间存在强烈的相互作用，但其本质尚未阐明。本研究调查了含氮木质素化合物的形成机制和途径。为实现这一目标，在离子液体辅助木质纤维素分级分离的典型条件（80-150℃）下，用1-丁基-3-甲基咪唑鎓乙酸盐（BmimOAc）处理了八种带有不同官能团（酮、醛、羟基、碳-碳双键）的单体木质素相关酚类。通过二维核磁共振光谱和高效液相色谱-高分辨率质谱对所有研究的模型化合物得到的一些产物进行了初步鉴定。它们都含有共价键合的Bmim残基，并且是通过N-杂环卡宾（去质子化的Bmim阳离子）对缺电子基团的亲核加成而产生的。木质素官能团与Bmim相互作用的反应活性受温度和溶解氧的影响很大。离子液体的热降解产物对木质素起到额外的活性物种作用，进一步使形成的产物范围复杂化。所获得的结果使得能够回答本文标题中提出的问题，并断言基于N，N'-二烷基咪唑鎓的离子液体在木质纤维素溶解过程中对木质素起到活性试剂的作用。
