Anion encapsulation and complexation by cucurbit[n]urils and their derivatives

Large anion binding in water

Large water-soluble anions with chaotropic character display surprisingly strong supramolecular interactions in water, for example, with macrocyclic receptors, polymers, biomembranes, and other hydrophobic cavities and interfaces. The high affinity is traced back to a hitherto underestimated driving force, the chaotropic effect, which is orthogonal to the common hydrophobic effect. This review focuses on the binding of large anions with water-soluble macrocyclic hosts, including cyclodextrins, cucurbiturils, bambusurils, biotinurils, and other organic receptors. The high affinity of large anions to molecular receptors has been implemented in several lines of new applications, which are highlighted herein.

Trimetallic coordination cage formation for nitrate encapsulation: transformation of kinetic products into thermodynamic products

A procedure for the formation of a nitrate-encapsulating tripalladium(II) cage via self-assembly of Pd(NO₃)₂ with 1,3-bis(dimethyl(pyridin-4-yl)silyl)propane (L) was developed. The self-assembly reaction initially produces spiro-type macrocycles, PdL₂, and finally results in transformation into a nitrate-encapsulated cage, [(NO₃)@Pd₃L₆], in the mother liquor. The reaction of PdX₂ (X^- = BF₄^-, ClO₄^-, PF₆^-, and CF₃SO₃^- instead of NO₃^-) with L gives rise to a spiro species, PdL₂, as the final product, and anion exchange of the spiro products, [PdL₂](X)₂, with NO₃^- produces the tripalladium cage [(NO₃)@Pd₃L₆].

Cucurbit[n]uril-Based Supramolecular Frameworks Assembled through Outer-Surface Interactions

Porous materials, especially metal-organic frameworks, covalent organic frameworks, and supramolecular organic frameworks, are widely used in heterogeneous catalysis, adsorption, and ion exchange. Cucurbit[n]urils (Q[n]s) suitable building units for porous materials because they possess cavities with neutral electrostatic potential, portal carbonyls with negative electrostatic potential, and outer surfaces with positive electrostatic potential, which may result in the formation of Q[n]-based supramolecular frameworks (QSFs) assembled through the interaction of guests within Q[n]s, the coordination of Q[n]s with metal ions, and outer-surface interaction of Q[n]s (OSIQ). This review summarizes the various QSFs assembled via OSIQs. The QSFs can be classified as being assembled by 1) self-induced OSIQ, 2) anion-induced OSIQ, and 3) aromatic-induced OSIQ. The design and construction of QSFs with novel structures and specific functional properties may establish a new research direction in Q[n] chemistry.

Cucurbituril-Oriented Nanoplatforms in Biomedical Applications

Cucucrbituril (CB) belongs to a family of macrocycles that are easily accessible. Their structural specificity provides excellent molecular recognition capabilities, with the ability to be readily chemically modified. Because of these properties, researchers have found CB to be a useful molecular carrier for delivering drug molecules and therapeutic biomolecules. Their significance lies in the fact that CB not only increases the solubility and stability of an encapsulated guest but also provides the possibility to achieve targeted delivery of the guest molecule. Therefore, the emergence of CB undoubtedly provides opportunities for the development of targeted drug delivery in an era where intelligent drugs have attracted considerable attention. It has also been found that CB can enhance fluorescent dyes, allowing the preparation of biosensors with enhanced sensitivity for use in clinical settings. In the present review, the acquisition, properties, and structural modifications of CB are first comprehensively described, and then the value of this macrocycle in applications within the medical field is discussed. In addition, we have also summarized patent applications of CB in this field over recent years, aiming to illustrate the current status of developments of this molecule. Finally, we discuss the challenges faced by CB in the medical field and future trends in its development.

Evaluation of the supramolecular interaction of Congo red with cucurbiturils using mass spectrometry and spectroscopic methods

Cucurbit[n]urils decolourise aqueous solutions of Congo red by forming outer-surface adducts, which are also detected in gas-phase ESI-MS studies.

Batista AP, Demets GJF. Formation of the non-classical interhalide anion [I2Cl]− in methyl-bambus[6]uril cavity

Methyl-bambus[6]uril may form a variety of inclusion compounds, especially with anionic species. Uncommon interhalide species may be produced in its cavity.

Phase-transfer extraction for the fast quantification of perchlorate anions in water

Supramolecular approaches for the quantitative anion analysis in water remain scarce due to the lack of receptors that effectively bind anions in this medium. Herein, we present a novel, fast and easy, supramolecular approach for a selective and quantitative analysis of perchlorate anions in water, coupling the UV-Vis spectroscopic method and phase-transfer extraction of anions by a water-insoluble anion receptor.

Anion-adaptive crystalline cationic material for 99TcO4- trapping

Efficient anion recognition is of great significance for radioactive 99TcO4- decontamination, but it remains a challenge for traditional sorbents. Herein, we put forward a tactic using soft crystalline cationic material with anion-adaptive dynamics for 99TcO4- sequestration. A cucurbit[8]uril-based supramolecular metal-organic material is produced through a multi-component assembly strategy and used as a sorbent for effective trapping of TcO4-. Excellent separation of TcO4-/ReO4- is demonstrated by fast removal kinetics, good sorption capacity and high distribution coefficient. Remarkably, the most superior selectivity among metal-organic materials reported so far, together with good hydrolytic stability, indicates potential for efficient TcO4- removal. The structure incorporating ReO4- reveals that the supramolecular framework undergoes adaptive reconstruction facilitating the effective accommodation of TcO4-/ReO4-. The results highlight opportunities for development of soft anion-adaptive sorbents for highly selective anion decontamination.

The lanthanide contraction effect and organic additives impact the coordination structures of lanthanide ions with symmetrical octamethyl-substituted cucurbit[6]uril ligands

Two facts, the lanthanide contraction effect and the “bridge” role of organic additives, impact the coordination structures of lanthanide ions with OMeQ[6] ligands.