Department of Chemistry and Biochemistry , University of Notre Dame , 236 Nieuwland Science Hall, Notre Dame , Indiana 46556 , United States.
J Org Chem. 2019 Mar 1;84(5):2808-2816. doi: 10.1021/acs.joc.8b03197. Epub 2019 Feb 15.
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) and the structure of the associated complex. K 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 macrocycle's NH residues and aromatic sidewalls. The highest measured K of 7.9 × 10 M 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.
合成受体可以识别离子对，在许多技术应用中具有潜在的用途，但迄今为止，对季铵（Q）离子对的选择性识别研究甚少。本研究在氯仿溶液中测量了四环酰胺大环对 11 种不同 Q·Cl 盐的亲和力。在每种情况下，NMR 光谱都用于确定结合常数（K）和缔合复合物的结构。发现 K 强烈依赖于 Q 的分子形状，并且当 Q 能够穿透大环腔并与大环的 NH 残基和芳香侧链发生吸引力的非共价相互作用时，K 会增强。当 Q 为 p-CN 取代的苄基三甲基铵时，测得的最高 K 值为 7.9×10 M。该高亲和力 Q·Cl 离子对被用作模板，以提高产生四环酰胺受体或结构相关衍生物的大环化反应的合成产率。此外，通过封端由反应性苄基阳离子穿入的四环酰胺大环形成的非共价配合物，制备了一个永久性互锁轮烷。该合成方法提供了一种新的轮烷化离子对家族，这些离子对可能作为阴离子传感器、分子穿梭体或运输分子发挥作用。
