Shape-Selective Recognition of Quaternary Ammonium Chloride Ion Pairs
Shape-Selective Recognition of Quaternary Ammonium Chloride Ion Pairs
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DOI：
10.1021/acs.joc.8b03197
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发表时间：
2019-03-01
影响因子：
3.6
通讯作者：
Smith, Bradley D.
中科院分区：
文献类型：
--
作者：
Li, Dong-Hao;Smith, Bradley D.
识别离子对的合成受体在许多技术应用中具有潜在的用途，但迄今为止，在选择性识别季铵盐（Q(+)）离子对方面的工作很少。本研究测定了四内酰胺大环对氯仿溶液中11种不同的Q(+)Cl（-）盐的亲和力。在每种情况下，采用核磁共振波谱法确定缔合常数（K-a）和缔合物的结构。发现K-a强烈依赖于Q（+）的分子形状，当Q（+）能够穿透大环腔并与大环NH残基和芳香侧壁进行有吸引力的非共价相互作用时，K-a增强。当Q（+）为p- cn取代的苯基三甲基铵时，测得的K-a最高为7.9 x 103 M-1。该高亲和力的Q(+)Cl（-）离子对被用作模板，以提高生成四内酰胺受体或结构相关衍生物的大环化反应的合成收率。此外，一个永久互锁轮烷是由四内酰胺大环组成的非共价配合物的末端由一个活性的苯基阳离子组成的封顶。该合成方法提供了一种新的旋烷化离子对家族，可以作为阴离子传感器、分子穿梭器或运输分子。
Synthetic receptors that recognize ion pairs are potentially useful for many technical applications, but to date there has been little work on selective recognition of quaternary ammonium (Q(+)) ion pairs. This study measured the affinity of a tetralactam macrocycle for 11 different Q(+)Cl(-) salts in chloroform solution. In each case, NMR spectroscopy was used to determine the association constant (K-a) and the structure of the associated complex. K-a was found to depend strongly on the molecular shape of Q(+) and was enhanced when Q(+) could penetrate the macrocycle cavity and engage in attractive noncovalent interactions with the macrocycles NH residues and aromatic sidewalls. The highest measured K-a of 7.9 x 103 M-1 was obtained when Q(+) was a p-CN-substituted benzylic trimethylammonium. This high-affinity Q(+)Cl(-) ion pair was used as a template to enhance the synthetic yield of macrocyclization reactions that produce the tetralactam receptor or structurally related derivatives. In addition, a permanently interlocked rotaxane was prepared by capping the end of a noncovalent complex composed of the tetralactam macrocycle threaded by a reactive benzylic cation. The synthetic method provides access to a new family of rotaxanated ion pairs that can likely act as anion sensors, molecular shuttles, or transport molecules.