Revealing the Dynamic Process of Ion Pair Recognition by Calix[4]pyrrole: A Case Study of Cesium Chloride

Ion pair receptors based on meso-octamethylcalix[4]pyrrole (CP) have been extensively investigated over recent years. However, the nature of their ion pair recognition has barely been reported, even for CP itself. Herein, cesium chloride was used as a guest ion pair to investigate the dynamic process of ion pair recognition by CP, and the "capture-bind" mechanism for this process is proposed for the first time. The results reveal that Cs⁺ can be first captured by Cl^- at long distances, and then it is bound to the cavity through almost equal contributions of Cl^- and CP. Although the effective charge of Cl^- is obviously reduced by charge-transfer, the electrostatic interactions between Cl^- and Cs⁺ are still strong even at long distances in the presence of CP.

Strapped calix[4]pyrroles: from syntheses to applications

Supramolecular chemistry is a central topic in modern chemistry. It touches on many traditional disciplines, such as organic chemistry, inorganic chemistry, physical chemistry, materials chemistry, environmental chemistry, and biological chemistry. Supramolecular hosts, inter alia macrocyclic hosts, play critical roles in supramolecular chemistry. Calix[4]pyrroles, non-aromatic tetrapyrrolic macrocycles defined by sp³ hybridized meso bridges, have proved to be versatile receptors for neutral species, anions, and cations, as well as ion pairs. Compared to the parent system, octamethylcalix[4]pyrrole and its derivatives bearing simple appended functionalities, strapped calix[4]pyrroles typically display enhanced binding affinities and selectivities. In this review, we summarize advances in the design and synthesis of strapped calix[4]pyrroles, as well as their broad utility in molecular recognition, supramolecular extraction, separation technology, ion transport, and as agents capable of inhibiting cancer cell proliferation. Future challenges within this sub-field are also discussed.

New dimensions in calix[4]pyrrole: the land of opportunity in supramolecular chemistry

The quest for receptors endowed with the selective complexation and detection of negatively charged species continues to receive substantial consideration within the scientific community worldwide. This study is encouraged by the utilization of anions in nature in a plethora of biological systems such as chloride channels and proteins and as polyanions for genetic information. The molecular recognition of anionic species is greatly interesting in terms of their favourable interactions. In this comprehensive review, in addition to giving accounts of some selected syntheses, we illustrated diverse applications ranging from molecular containers to ion transporters and drug carriers of a supramolecular receptor named calix[4]pyrrole. We believe that the present review may act as a catalyst in enhancing the novel applications of calix[4]pyrrole and its congeners in the other dimensions of science and technology.

The quest for receptors endowed with the selective complexation and detection of negatively charged species continues to receive substantial consideration within the scientific community worldwide.