Department of Physical Chemistry, Institute of Chemical Technology, Technická 5, 166 28 Prague 6, Czech Republic.
J Phys Chem B. 2011 Sep 1;115(34):10285-97. doi: 10.1021/jp205039g. Epub 2011 Aug 9.
The interaction of natural α-, β-, and γ-cyclodextrins (CDs) with 14 hydrophobic ionic moieties of ionic liquids (ILs) was systematically examined in dilute aqueous solutions using isothermal titration microcalorimetry (ITC) and NMR spectroscopy. The studied cationic and anionic moieties involved some recently developed heavily fluorinated structures, as well as some others of common use. To isolate the effect of a given ion, the measurements were performed on salts containing the hydrophobic IL ion in question and a complexation-inactive counterion. Additional ITC experiments on ILs whose both cation and anion can interact appreciably with the CD cavity demonstrated that to resolve the effect of individual ions from such data is generally a tricky task and confirmed the superiority of the isolation strategy adopted for the purpose throughout this work. The binding constant, enthalpy and entropy determined at 298.15 K for the 1:1 (ion:CD) inclusion complex formation range in broad limits, being 0 < K < 2 × 10(5), 0 < -Δ(r)H°/(kJ·mol(-1)) < 44, and -28 < TΔ(r)S°/(kJ·mol(-1)) < 14, respectively. The stabilities of complexes of perfluorohexyl bearing ions with β-CD belong to the highest ever observed with natural CDs in water. The established binding affinity scales were discussed in both thermodynamic and molecular terms. The concepts of hydrophobic interaction and guest-host size matching supported by simple molecular modeling proved useful to rationalize the observed widely different binding affinities and suggest possible binding modes. Enthalpy and entropy contributions to the stability of the ion-CD complexes were found to compensate each other considerably obeying more or less the linear compensation relationship marked by existing literature data on binding other guests to natural CDs. As outliers to this pattern, the most stable complexes of -C(6)F(13) bearing ions with β-CD were found to receive an enhanced inherent entropy stabilization due to extraordinarily high extent of desolvation occurring in the course of binding.
在稀水溶液中，使用等温滴定量热法（ITC）和 NMR 光谱法系统地研究了天然 α-、β-和 γ-环糊精（CDs）与离子液体（ILs）的 14 个疏水性离子基团的相互作用。研究的阳离子和阴离子基团涉及一些最近开发的重氟化结构，以及一些常用的结构。为了分离给定离子的影响，在含有疏水 IL 离子和非配位离子的盐中进行了测量。在 IL 上进行的额外的 ITC 实验，其阳离子和阴离子都可以与 CD 空腔显著相互作用，证明了从这些数据中确定单个离子的影响通常是一项棘手的任务，并证实了为完成本工作而采用的隔离策略的优越性。在 298.15 K 下确定的 1:1（离子：CD）包合复合物形成范围的结合常数、焓和熵值在很宽的范围内变化，分别为 0 < K < 2 × 10(5)、0 < -Δ(r)H°/(kJ·mol(-1)) < 44 和 -28 < TΔ(r)S°/(kJ·mol(-1)) < 14。带有 β-CD 的全氟己基离子与天然 CD 形成的配合物的稳定性属于在水中与天然 CD 形成的配合物中观察到的最高稳定性。建立的结合亲和力标度从热力学和分子角度进行了讨论。通过简单的分子建模支持的疏水相互作用和客体-主体尺寸匹配的概念被证明有助于合理化观察到的广泛不同的结合亲和力，并提出可能的结合模式。发现离子-CD 配合物的稳定性的焓和熵贡献相互补偿相当大，或多或少地遵循现有文献中关于将其他客体结合到天然 CD 的线性补偿关系。作为这种模式的例外，与 β-CD 形成的带有 -C(6)F(13)的离子的最稳定配合物被发现由于结合过程中发生的极高程度的去溶剂化而受到增强的固有熵稳定化。
