Lee Areum, Yang Ju Ho, Oh Ju Hyun, Hay Benjamin P, Lee Kyounghoon, Lynch Vincent M, Sessler Jonathan L, Kim Sung Kuk
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 USA.
Chem Sci. 2022 Dec 26;14(5):1218-1226. doi: 10.1039/d2sc06376j. eCollection 2023 Feb 1.
A cyclo[2]carbazole[2]pyrrole (2) consisting of two carbazoles and two pyrroles has been synthesized by directly linking the carbazole 1- and 8-carbon atoms to the pyrrole α-carbon atoms. Macrocycle 2 is an extensively conjugated 16-membered macrocyclic ring that is fixed in a pseudo-1,3-alternate conformation. This provides a preorganized anion binding site consisting of two pyrrole subunits. H NMR spectroscopic analysis revealed that only the two diagonally opposed pyrrole NH protons, as opposed to the carbazole protons, take part in anion binding. Nevertheless, cyclo[2]carbazole[2]pyrrole 2 binds representative anions with higher affinity in CDCl than calix[4]pyrrole (1), a well-studied non-conjugated tetrapyrrole macrocycle that binds anions four pyrrolic NH hydrogen bond interactions. On the basis of computational studies, the higher chloride anion affinity of receptor 2 relative to 1 is rationalized in terms of a larger binding energy and a lower host strain energy associated with anion complexation. In the presence of excess fluoride or bicarbonate anions, compound 2 loses two pyrrolic NH protons to produce a stable dianionic macrocycle [2-2H] displaying a quenched fluorescence.
一种由两个咔唑和两个吡咯组成的环[2]咔唑[2]吡咯（2）已通过将咔唑的1-和8-碳原子直接连接到吡咯的α-碳原子上合成。大环化合物2是一个广泛共轭的16元大环，其固定在假1,3-交替构象中。这提供了一个由两个吡咯亚基组成的预组织化阴离子结合位点。核磁共振氢谱分析表明，与咔唑质子不同，只有两个对角相对的吡咯NH质子参与阴离子结合。然而，环[2]咔唑[2]吡咯2在CDCl中比杯[4]吡咯（1）（一种经过充分研究的通过四个吡咯NH氢键相互作用结合阴离子的非共轭四吡咯大环）以更高的亲和力结合代表性阴离子。基于计算研究，受体2相对于1对氯离子具有更高亲和力的原因在于与阴离子络合相关的更大结合能和更低的主体应变能。在存在过量氟离子或碳酸氢根阴离子的情况下，化合物2失去两个吡咯NH质子，生成一个稳定的二价阴离子大环[2 - 2H]，其荧光猝灭。
