In 1981, the macrocyclic methylene-bridged glycoluril hexamer (CB[6]) was dubbed "cucurbituril" by Mock and co-workers because of its resemblance to the most prominent member of the cucurbitaceae family of plants--the pumpkin. In the intervening years, the fundamental binding properties of CB[6]-high affinity, highly selective, and constrictive binding interactions--have been delineated by the pioneering work of the research groups of Mock, Kim, and Buschmann, and has led to their applications in waste-water remediation, as artificial enzymes, and as molecular switches. More recently, the cucurbit[n]uril family has grown to include homologues (CB[5]-CB[10]), derivatives, congeners, and analogues whose sizes span and exceed the range available with the alpha-, beta-, and gamma-cyclodextrins. Their shapes, solubility, and chemical functionality may now be tailored by synthetic chemistry to play a central role in molecular recognition, self-assembly, and nanotechnology. This Review focuses on the synthesis, recognition properties, and applications of these unique macrocycles.

The cucurbit[n]uril family

The supramolecular chemistry of cucurbituril, a synthetic receptor, is fascinating because of the remarkable guest binding behavior of the host. Studies in the field, however, have met with limitations, since the only species known was the hexameric macrocyclic compound, cucurbit[6]uril. Recently we synthesized its homologues, cucurbit[n]uril (n = 5, 7, 8), and derivatives. These new members of the cucurbituril family have expanded the scope further, and interest in them has grown enormously. This Account is a compilation of recent literature covering the syntheses of the homologues and derivatives, and their supramolecular chemistry.

Cucurbituril homologues and derivatives: new opportunities in supramolecular chemistry.

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Cucurbituril-Based Molecular Recognition.

Artificial Molecular Rotors

In the wide area of supramolecular chemistry, cucurbit[n]urils (CBn) present themselves as a young family of molecular containers, able to form stable complexes with various guests, including drug molecules, amino acids and peptides, saccharides, dyes, hydrocarbons, perfluorinated hydrocarbons, and even high molecular weight guests such as proteins (e.g., human insulin). Since the discovery of the first CBn, CB6, the field has seen tremendous growth with respect to the synthesis of new homologues and derivatives, the discovery of record binding affinities of guest molecules in their hydrophobic cavity, and associated applications ranging from sensing to drug delivery. In this review, we discuss in detail the fundamental properties of CBn homologues and their cyclic derivatives with a focus on their synthesis and their applications in catalysis.

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Cucurbiturils: from synthesis to high-affinity binding and catalysis

The acid-catalyzed synthesis of cucurbit[n]urils from formaldehyde and glycoluril is poorly understood. In this paper, we examine a wide range of reaction conditions that include the effects of acid type, acid concentration, reactant concentrations, and temperature to both probe the mechanism and optimize the yields of isolated cucurbit[n]urils, where n = 5−10. A mechanism for the formation of these cucurbit[n]urils is presented. Individual cucurbit[n]urils were unambiguously identified in reaction mixtures using ESMS and 13C NMR.

Barry Snushall

Papers

Controlling factors in the synthesis of cucurbituril and its homologues.