Cucurbit[8]uril Mediated Donor-Acceptor Ternary Complexes: A Model System for Studying Charge-Transfer Interactions
Cucurbit[8]uril Mediated Donor-Acceptor Ternary Complexes: A Model System for Studying Charge-Transfer Interactions
复制标题
DOI：
10.1021/jp2110067
复制
发表时间：
2012-03-08
影响因子：
3.3
通讯作者：
Scherman, Oren A.
中科院分区：
文献类型：
--
作者：
Biedermann, Frank;Scherman, Oren A.
描述了一种超分子自组装方法，其允许在水溶液中方便地制备宽范围的电荷转移（CT）供体-受体复合物。当将一当量的大环主体瓜环[8]脲（CB[8]）加入到供体和受体的水溶液中时，在主体的空腔内形成具有供体和受体的明确限定的面对面π-π-堆叠几何形状的杂三元络合物。这种异元CB[8]介导的复合物提供了在低浓度下研究CT现象的机会，并且由于大的结合亲和力和对这些同元复合物形成的非常高的选择性，没有任何供体-供体和受体-受体相互作用引起的并发症。因此，这种超分子自组装策略是一种实用的供体-受体混合匹配方法，其合成优势超过了更繁琐的系链方案。虽然一些CB[8]三元体系的特征UV/维斯特征被描述为CT带，但我们首次提出了由宿主CB[8]介导的几个供体-受体对之间存在CT相互作用的系统证据。实验获得的CT λ（最大）计算HOMO-LUMO能量的相关性表明，CT过程中的主机的腔可以描述的Mulliken模型。此外，通过量热法（ITC）和ESI-MS测量仔细检查和评估了文献中关于CB[8]三元复合物形成的“CT驱动力”的声明。研究结果表明，无论是在水介质中，也不是在“气相”是CT的能量相关的吉布斯自由结合能。相比之下，结合溶剂化效应的静电考虑更适合合理化结合亲和力的观察到的趋势。此外，发现CB[8]腔内的CT λ（max）比任何极性有机溶剂或水中的红移（>= 75 nm）得多，表明CT激发态在主腔内的显著稳定，进一步证明了主腔的独特静电极性性质。
A supramolecular self-assembly approach is described which allows for the convenient preparation of a wide range of charge-transfer (CT) donor-acceptor complexes in aqueous solutions. When one equiv of the macrocyclic host cucurbit[8]uril (CB[8]) is added to an aqueous donor and acceptor solution, a heteroternary complex forms inside the host's cavity with a well-defined face-to-face pi-pi-stacking geometry of the donor and acceptor. This heteroternary, CB[8]-mediated complex offers the opportunity to study the CT phenomena at low concentrations and free from complications arising from any donor-donor and acceptor-acceptor interactions as a result of the large binding affinities and the very high selectivity over the formation of these homoternary complexes. Thus, this supramolocular self-assembly strategy is a practical donor-acceptor mix-and-match approach with synthetic advantages over much more cumbersome tethering schemes. While the characteristic UV/vis features of a few CB[8] ternary systems had been described as a CT band, we present for the first time systematic evidence for the existence of CT interactions between several donor-acceptor pairs that are mediated by the host CB[8]. Correlation of the experimentally obtained CT lambda(max) to computed HOMO-LUMO energies demonstrated that the CT process in the host's cavity can be described by the Mulliken model. Furthermore, the literature claim of a "CT driving force" for the formation of CB[8] ternary complexes was scrutinized and evaluated by calorimetric (ITC) and ESI-MS measurements. The findings indicated that neither in the aqueous medium nor in the "gas-phase" is CT of energetic relevance to the Gibbs free binding energy. In contrast, electrostatic considerations combined with solvation effects are much better suited to rationalize the observed trends in binding affinities. Additionally, the CT lambda(max) was found to be much more red-shifted (>= 75 nm) inside the CB[8] cavity than in any polar organic solvents or water, indicating a significant stabilization of the CT excited state within the host cavity, further demonstrating the unique electrostatic, polar properties of the host cavity.