Institut für Chemie, Martin-Luther-Universität Halle-Wittenberg, von-Danckelmann-Platz 4, D-06120 Halle, Germany.
Molecules. 2020 Aug 2;25(15):3539. doi: 10.3390/molecules25153539.
We present 1,2,3-triazolium- and imidazolium-based ionic liquids (ILs) with aromatic anions as a new class of cellulose solvents. The two anions in our study, benzoate and salicylate, possess a lower basicity when compared to acetate and therefore should lead to a lower amount of -heterocyclic carbenes (NHCs) in the ILs. We characterize their physicochemical properties and find that all of them are liquids at room temperature. By applying force field molecular dynamics (MD) simulations, we investigate the structure and dynamics of the liquids and find strong and long-lived hydrogen bonds, as well as significant π-π stacking between the aromatic anion and cation. Our ILs dissolve up to 8.5 wt.-% cellulose. Via NMR spectroscopy of the solution, we rule out chain degradation or derivatization, even after several weeks at elevated temperature. Based on our MD simulations, we estimate the enthalpy of solvation and derive a simple model for semi-quantitative prediction of cellulose solubility in ILs. With the help of Sankey diagrams, we illustrate the hydrogen bond network topology of the solutions, which is characterized by competing hydrogen bond donors and acceptors. The hydrogen bonds between cellulose and the anions possess average lifetimes in the nanosecond range, which is longer than found in common pure ILs.
我们提出了基于 1,2,3-三唑鎓和咪唑鎓的离子液体(ILs),它们具有芳香阴离子,是纤维素溶剂的一类新型化合物。在我们的研究中,两种阴离子(苯甲酸盐和水杨酸盐)的碱性比醋酸盐低,因此应该导致 ILs 中更少的 -杂环卡宾(NHCs)。我们对它们的物理化学性质进行了表征,发现所有这些 ILs 在室温下均为液体。通过应用力场分子动力学(MD)模拟,我们研究了液体的结构和动力学,发现存在强而持久的氢键,以及阴离子和阳离子之间的显著 π-π 堆积。我们的 ILs 可以溶解高达 8.5wt.-%的纤维素。通过溶液的 NMR 光谱,我们排除了链降解或衍生化,即使在高温下几周后也是如此。基于我们的 MD 模拟,我们估计了溶剂化焓,并为纤维素在 ILs 中的溶解度的半定量预测推导了一个简单的模型。借助 Sankey 图,我们说明了溶液的氢键网络拓扑结构,其特点是存在竞争的氢键供体和受体。纤维素与阴离子之间的氢键具有平均寿命在纳秒范围内,比常见的纯 ILs 中的寿命要长。
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