The crystallography of supramolecular complexes based on bambusuril, cucurbituril and similar macrocycles

Michal Babiak

CEITEC - Středoevropský technologický institut, Masarykova univerzita, Brno

Host-guest complexes are supramolecular entities in which molecules are held together by non‑covalent interactions; their formation, properties, and applications arouse considerable scientific interest. In case of inclusion compounds, the formation of the host-guest complex depends mainly on the interior of the host cavity and properties of the portals, whereas the exterior of the host influences properties such as solubility, interaction with the environment etc. Glycoluril-based macrocycles, such as bambus[n]urils and cucurbit[n]urils and their derivatives are popular hosts for such inclusion compounds and are often studied as potential signaling molecules, catalysts, pharmaceutical transporters and "preservatives", or models for biological processes occurring at the surface of the membranes.

For this type of complexes, X-ray crystallography (among various NMR experiments) is usually the preferred method of structural analysis. However, the crystals usually have large unit cells with considerable quantities of solvents, which makes them somewhat similar to protein crystals regarding the data collection and refinement. Defects in crystal structure, such as a disorder in the solvent “area” around the hosts do occur quite often. A chemist is usually interested in remaining “non-solvent” parts of the structure, which means that some simplifications can be introduced. Practical aspects of X-ray diffraction studies on selected inclusion compounds of glycoluril-based macrocycles will be discussed in greater detail.

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