Abstract
Cucurbituril-type hosts are highly symmetric, but there are means to break their symmetry. This review will present examples from three directions of induction of chirality in or by cucurbituril-type hosts: first, through the incorporation of stereogenic elements into host molecules; second, through complexation with achiral guests, which leads to axial supramolecular chirality and helical structures; third, through the formation of complexes with chiral guests in multi-molecule complexes and induction of supramolecular chirality. In addition, a list of chiral guests used in binding studies with cucurbiturils is collected. We would envision that encouraged by the outlined examples of outstanding applications of chiral cucurbituril-supramolecular systems, the boundaries of chiral applications of cucurbiturils would be widened.
Highlights
Cucurbituril (CB)-type hosts are oligomeric compounds, where cyclic urea monomers are connected through methylene bridges
Core CBs are double-bridged macrocycles, which are made from glycoluril and formaldehyde [1,2,3,4]
The research group of Tao and Liu [57] reported the formation of a pair of homochiral 1-D-helical coordination polymers of CB[5] with Dy3+ upon crystallization in the presence of achiral hydroquinone (Figure 15)
Summary
Cucurbituril (CB)-type hosts are oligomeric compounds, where cyclic urea monomers are connected through methylene bridges. Core CBs are double-bridged macrocycles, which are made from glycoluril and formaldehyde [1,2,3,4]. All CBs have hydrophobic cavities, but electronic binding properties are different for single- and double-bridged. CBs. Double-bridged CBs bind cations at the portals and single-bridged CBs anions in their cavity. All single-bridged CBs can be viewed as derivatives of hemicucurbiturils (HCs). CB chemistry has been reviewed from various aspects [5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28], though so far, only one focused on the chirality of CBs [29]. A list of chiral guests that have been used in studies with CB-type hosts is collected
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