Melville Laboratory for Polymer Synthesis, Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, UK.
Chem Asian J. 2010 Mar 1;5(3):530-7. doi: 10.1002/asia.200900510.
The host-guest chemistry between a series of 1-alkyl-3-methyl-imidazolium bromide ([C(n)mim]Br) guests and the macrocyclic host molecule cucurbit[6]uril (CB[6]) in an aqueous system is systematically studied in neutral aqueous media. Both 1D and 2D NMR experiments in conjunction with isothermal titration calorimetry (ITC) unveil the binding characteristics of the host-guest interaction. Solution binding constants (K(a)) up to 10(5) M(-1) are measured directly. Additionally, this [C(n)mim]Br-CB[6] interaction was found to significantly increase the solubility of CB[6] in neutral water, in some cases by at least four orders of magnitude. From these studies, a detailed host-guest binding model has been constructed and is fully discussed. In this model, the delocalized positive charge on the imidazolium ring becomes partially localized on either one of the nitrogen atoms upon complexation with CB[6]. Localization of the positive charge is directly related to the length of the "1-alkyl" chain on the imidazolium ring, which causes an induced local dipole subsequently allowing for an ion-dipole interaction with the carbonyl portal of CB[6].
在中性水介质中，系统研究了一系列 1-烷基-3-甲基-咪唑溴盐([C(n)mim]Br)客体与大环主体分子瓜环([CB[6]])之间的主客体化学。通过一维和二维 NMR 实验结合等温热滴定法 (ITC)，揭示了主客体相互作用的结合特征。直接测量了高达 10(5) M(-1)的溶液结合常数 (K(a))。此外，还发现这种[C(n)mim]Br-CB[6]相互作用显著提高了 CB[6]在中性水中的溶解度，在某些情况下至少提高了四个数量级。从这些研究中，构建并充分讨论了一个详细的主客体结合模型。在该模型中，咪唑环上的离域正电荷在与 CB[6]络合时部分定域在其中一个氮原子上。正电荷的定位与咪唑环上“1-烷基”链的长度直接相关，这导致诱导局部偶极子，随后允许与 CB[6]的羰基入口发生离子偶极相互作用。
