咪唑醋酸离子液体催化CO_2交联壳聚糖的微观机理研究

Theoretical Study of the Molecular Mechanism of CO_2 Cross-Linked Chitosan Catalyzed by an Imidazolium-Based Ionic Liquid

通过密度泛函理论计算研究了CO_2交联壳聚糖的分子机理,分析了水分子和1-丁基-3-甲基咪唑醋酸离子液体对反应性的影响,发现交联反应历经亲电加成、脱水和亲核加成三个基元步骤,其中水分子在亲电加成过程中作为质子梭传递质子,咪唑醋酸离子液体的阴、阳离子分别作为布朗斯特碱、酸协助脱水和亲核加成过程。在水分子和1-丁基-3-甲基咪唑醋酸离子液体的协同催化下,交联反应的势垒降低至29.1 kcal/mol。计算结果合理解释了温和的实验条件下CO_2容易交联壳聚糖的实验结果。

Density functional theory（ DFT） calculations have been conducted to study the formation mechanism of CO2 cross-linked chitosan. By analyzing the effect of water and 1-butyl-3-methyl imidazolium acetate ionic liquid on the reactivity,we found that the reaction occurs via three elementary steps： electrophilic addition,dehydration and nucleophilic addition.The water molecular acts as H-shuttle to transfer H-proton during the electrophilic addition step,and the anion and cation of the ionic liquid act as a Br9 nsted base and a Br9 nsted acid respectively,assisting the dehydration and nucleophilic addition steps.With the help of water and the ionic liquid,the calculated energy barrier of the cross-linked reaction is reduced to 29. 1 kcal/mol. Theoretical results verified the experimental finding that CO2 cross-linked chitosan can be formed at mild reaction conditions.