Department of Chemistry and Research Institute of Natural Science, Gyeongsang National University, Jinju-si, Gyeongsangnam-do 52828, Korea.
Supramolecular Design Institute, Oak Ridge, Tennessee 37830, United States.
J Am Chem Soc. 2022 Sep 21;144(37):16996-17009. doi: 10.1021/jacs.2c06284. Epub 2022 Sep 8.
A molecular capsule () consisting of two calix[4]pyrroles connected via ethylene diamide linkers has been prepared as an anion receptor. H NMR spectroscopic studies carried out in CDCl revealed that receptor recognizes a variety of anions with different binding modes and stoichiometries. For instance, receptor binds fluoride and acetate with 1:2 receptor/anion stoichiometry and other test anions with 1:1 stoichiometry in solution when their respective tetrabutylammonium (TBA) salts were used. In contrast, with tetraethylammnium (TEA) salts, receptor forms 1:2 complexes with chloride and bromide in addition to fluoride, overcoming expected Columbic repulsions between the anions co-bound in close proximity. Receptor is also able to bind oxoanions, such as oxalate (CO), dihydrogen phosphate (HPO), sulfate (SO), and hydrogen pyrophosphate (HPO), in the form of 1:1 complexes as the result of presumed cooperation between the two calix[4]pyrrole subunits. The selectivity of receptor for fluoride versus dihydrogen phosphate varies depending on their relative concentrations. For instance, in the presence of less than 1.0 equiv of an equimolar mixture of fluoride and dihydrogen phosphate, receptor shows high selectivity for dihydrogen phosphate. In contrast, in the presence of ≥2.0 anion equiv, receptor binds fluoride preferentially, forming a 1:2 complex. Moreover, when treated with F, the preformed 1:1 HPO complex of receptor is converted to the corresponding 1:2 receptor/fluoride complex with the release of the prebound dihydrogen phosphate anion. As inferred from gas-phase computations, this seemingly counterintuitive behavior is rationalized in terms of the precomplexed dihydrogen phosphate serving to reduce the reorganization energy required to bind two fluoride anions. The presence of a water molecule in addition to the bound fluoride anions may also favor the formation of the 1:2 F complex. The present study provides a new approach for fine-tuning the binding selectivity of polytopic anion receptors.
一种由两个通过乙二胺连接的杯[4]吡咯组成的分子胶囊（）已被制备为阴离子受体。在 CDCl 中进行的 NMR 光谱研究表明，受体 以不同的结合模式和化学计量比识别各种阴离子。例如，当使用相应的四丁基铵（TBA）盐时，受体 以 1:2 的受体/阴离子化学计量比与氟化物和乙酸盐结合，而与其他测试阴离子以 1:1 的化学计量比结合。相比之下，用四乙基铵（TEA）盐，受体 除了氟化物外，还与氯离子和溴离子形成 1:2 配合物，克服了在紧密结合的阴离子之间预期的库仑斥力。受体 还能够以 1:1 配合物的形式结合氧阴离子，如草酸盐（CO）、二氢磷酸盐（HPO）、硫酸盐（SO）和焦磷酸盐（HPO），这是两个杯[4]吡咯亚基之间的假定协同作用的结果。受体 对氟化物与二氢磷酸盐的选择性取决于它们的相对浓度。例如，在低于 1.0 当量的氟化物和二氢磷酸盐等摩尔混合物的存在下，受体 对二氢磷酸盐表现出高选择性。相比之下，在存在≥2.0 阴离子当量的情况下，受体 优先结合氟化物，形成 1:2 配合物。此外，当用 F 处理时，受体 的预形成的 1:1 HPO 配合物转化为相应的 1:2 受体/氟化物配合物，同时释放预结合的二氢磷酸盐阴离子。从气相计算推断，这种看似违反直觉的行为可以用预先配合的二氢磷酸盐阴离子来降低结合两个氟化物阴离子所需的重组能来合理化。除了结合的氟化物阴离子之外，水分子的存在也可能有利于 1:2 F 配合物的形成。本研究为精细调整多齿阴离子受体的结合选择性提供了一种新方法。
