Cucurbiturils, Synthesis and Applications

Abstract

The research on the chemistry of host–guest complexes based on noncovalent interactions involving a macrocyclic host and a guest has seen an upsurge in recent years due to their potential application in metal ion separation, molecular sensors, catalysis, nanomaterials and therapeutics, and other stimuli‐responsive systems. This article provides a brief account of a relatively new class of macrocyclic hosts, cucurbit[ n ]uril (CB n ), their molecular recognition properties with several important guest molecules, and their applications. Along with various synthetic approaches, an environmental friendly ( green ) method to isolate CB n homologues (CB[5–8]) by utilizing imidazolium salts has also been discussed. The noncovalent host–guest assemblies with cucurbiturils bring out a remarkable modulation of the physicochemical properties of the guest molecules such as solubility, stability, aggregation behavior, acidity constants, antibacterial activity, and cytotoxicity. Efforts have also been made to give specific examples of cucurbituril‐encapsulated guest assemblies and discuss their potential applications toward controlled uptake and release of drugs, construction of photofunctional devices, aqueous‐based dye lasers, molecular architectures, gas sensors, stimuli‐responsive hydrogel, chemoselective photoreactions, biological catalytic activity, and inhibition of amyloid fibrillation.

Locked and Loaded: Ruthenium(II)-Capped Cucurbit[n]uril-Based Rotaxanes with Antimetastatic Properties

“…grade were used as purchased without further purification. [RuCl 2 (cym)] 2 , [RuCl 2 (tol)] 2 , and [RuCl 2 (ben)] 2 were prepared according to reported procedures. − Cucurbit[6]­uril and cucurbit[7]­uril were prepared as described by Mohanty …”

“…90−92 Cucurbit [6]uril and cucurbit [7]uril were prepared as described by Mohanty. 93 Mass Spectrometry (MS). MS analyses were performed on an Agilent 6224 AccurateMass TOF LC-MS instrument coupled with a multimode ion source using electrospray ionization in positive mode.…”

Cucurbituril-Based Supramolecular Assemblies: Prospective on Drug Delivery, Sensing, Separation, and Catalytic Applications

“…The synthesis of cucurbit­[ n ]­urils (CBn) by Behrend dates back to 1905; however, active research in this area came up only after its complete characterization was achieved in the early 1980s. Cucurbiturils are made up of methylene-linked glycoluril monomers that construct symmetric hydrophobic cavities with n carbonyl groups at each portal. ,,, CBs are synthesized by the acid-catalyzed condensation of glycoluril with formaldehyde and separated by using acetone/water solvent mixtures. ,,, Like cyclodextrins (CDs) and calixarenes (CXs), homologues of cucurbit­[ n ]­uril (CBn), where n = 5–14, (Figure ), denote the number of glycoluril monomer units present and display varying cavity and portal dimensions. ,,, Though several other macrocyclic hosts have also been extensively used to study host–guest complexation, the uniqueness of each host in its portal group and the cavity dimensions, polarity, and aqueous solubility make them distinct in their applications. Cyclodextrin (CD) homologues of macrocycles (α-CD, β-CD, γ-CD) contain a hydrophobic central cavity and hydrophilic portals (secondary hydroxyl groups in the wider rim and primary hydroxyl groups in the narrow rim) and are shaped like a truncated cone.…”

“…Intriguingly, the larger CB10 host is capable of encapsulating its smallest homologue, CB5, and also conveniently forms a complex with metalated tetra-( N -methyl­pyridinium)­porphyrins . However, the largest CB n reported, CB14, exists in a folded figure-eight conformation and apparently does not contain the expected large CB cavity for the guest interaction. , On the other hand, metal ions interact with CBs via the two carbonyl rims, and because only a few of the oxygen atoms at the CBn portal interact during binding, several cations can be complexed with the same portal. , Anionic guests may also interact with CBs but via an altogether different mechanism of peripheral binding. , For example, the polyoxovanadate anion clusters bind strongly at the positively polarized equatorial periphery of CBs (CB6 and CB8) through C–H–O interactions . It has been shown recently that this class of macrocycles exhibits low in vitro as well as in vivo toxicity, enabling therapeutic and sensing applications that are relevant in the biological perspective .…”

“…Cucurbiturils are made up of methylene-linked glycoluril monomers that construct symmetric hydrophobic cavities with n carbonyl groups at each portal. 14,19,20,45 CBs are synthesized by the acid-catalyzed condensation of glycoluril with formaldehyde and separated by using acetone/water solvent mixtures. 14,19,20,35 Like cyclodextrins (CDs) and calixarenes (CXs), homologues of cucurbit[n]uril (CBn), where n = 5−14, (Figure 1), denote the number of glycoluril monomer units present and display varying cavity and portal dimensions.…”