Theoretical Insight into the Conversion Mechanism of Glucose to Fructose Catalyzed by CrCl2 in Imidazolium Chlorine Ionic Liquids
Theoretical Insight into the Conversion Mechanism of Glucose to Fructose Catalyzed by CrCl2 in Imidazolium Chlorine Ionic Liquids
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咪唑氯离子液体中 CrCl2 催化葡萄糖转化果糖机理的理论探讨
DOI：
10.1021/acs.jpcb.6b11820
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发表时间：
2017-03-09
影响因子：
3.3
通讯作者：
Zhang, Dongju
中科院分区：
文献类型：
--
作者：
Jing, Yaru;Gao, Jun;Zhang, Dongju
为了更好地理解氯化铬在咪唑基离子液体（IL）中催化葡萄糖向果糖的有效转化，在描述CrCl2在1,3-二甲基咪唑氯（MMImCI）离子液体（IL）中催化反应的模型系统上进行了密度泛函理论计算。该反应涉及三个基本过程：开环、1,2-H 迁移和闭环。该反应计算为放能 3.8 kcal/mol，总势垒为 37.1 kcal/mol。在所有基本步骤中，CrCl2 和 MMImCI 都发挥着重要作用。 Cr中心作为路易斯酸，与葡萄糖的两个羟基氧原子配位以双齿铆接底物，咪唑鎓阳离子由于其固有的酸性性质而发挥质子穿梭和氢键供体的双重作用，而阴离子被确定为布朗斯台德/路易斯碱和氢键受体。我们目前的计算强调，在速率决定步骤中，1,2-H迁移与O 2 H羟基的去质子化协同发生，这本质上不同于早期文献中提出的逐步机制。目前的结果为咪唑氯离子液体中氯化铬催化的葡萄糖异构化为果糖的异构化机制提供了分子水平的理解。
To better understand the efficient transformation of glucose to fructose catalyzed by chromium chlorides in imidazoliumbased ionic liquids (ILs), density functional theory calculations have been carried out on a model system which describes the catalytic reaction by CrCl2 in 1,3-dimethylimidazolium chlorine (MMImCI) ionic liquid (IL). The reaction is shown to involve three fundamental processes: ring opening, 1,2-H migration, and ring closure. The reaction is calculated to exergonic by 3.8 kcal/mol with an overall barrier of 37.1 kcal/mol. Throughout all elementary steps, both CrCl2 and MMImCI are found to play substantial roles. The Cr center, as a Lewis acid, coordinates to two hydroxyl group oxygen atoms of glucose to bidentally rivet the substrate, and the imidazolium cation plays a dual role of proton shuttle and H-bond donor due to its intrinsic acidic property, while the anion is identified as a Bronsted/Lewis base and also' a H-bond acceptor. Our present calculations emphasize that in the rate-determining step the 1,2-H migration concertedly occurs with the deprotonation of 02 H hydroxyl group, which is in nature different from the stepwise mechanism proposed in the early literature. The present results provide a molecule-level understanding for the isomerization mechanism of glucose to fructose catalyzed by chromium chlorides in imidazolium chlorine ILs.