Among all crystalline complexes of calix-type calix[n]arenes those with organic molecules which are biologically relevant are especially of interest due to their potential medical and pharmaceutical applications. The co-crystallization of drugs with water-soluble calixarenes offers the opportunity to modify chemical and physical properties of APIs (active pharmaceutical ingredients) and to control drug conformation. Such co-crystallization can improve solubility, bioavailability and stability of pharmaceutically active molecules and/or eliminate polymorphism. In this article the solid-state interactions between calixarene hosts and biologically relevant guest molecules are summarized for the currently available structures solved by single-crystal X-ray crystallography.

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[structure: see text]. A diastereomeric mixture of chiral 25-(1S)-camphorsulfonyloxy-26-isopropoxycalix[4]arene 2a (de 15%) and 25-isopropoxy-26-((1S)-10-camphorsulfonyl)calix[4]arene 2b has been obtained by asymmetrical lower rim (1S)-camphorsulfonylation of the monoisopropoxycalix[4]arene. Pure diastereomer 2a has been obtained by simple crystallization, and its absolute configuration has been determinated by X-ray analysis. Enantiomerically pure inherently chiral 5,11-dibromo-26-isopropoxycalix[4]arene 4 has been synthesized by the upper rim dibromination of the diastereomer 2a followed by hydrolytical removal of the auxiliary camphorsulfonyl group.

1 - ArticleThe solid state structures of the complexes between antiseptic chlorhexidine and three anionic calix[4] arene derivatives are described. Each of the three calixarenes shows typical self-organisation in the solid-state that will further impose a specific complexation of the active molecule in the co-crystal

The molecular recognition and self-assembly between host cucurbit[6]uril and guest adrenaline led to kinetic trapping and crystallization of the intermediate exclusion complex, which was characterized by X-ray diffraction. The crystalline kinetic complex undergoes slow spontaneous dissolution and subsequently recrystallizes as a thermodynamic inclusion complex.

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The solid state structures of four complexes between para-sulphonato-calix[4]arene and phenanthroline have been determined. Three are simple complexes between the two molecules however the fourth contains aluminium cations, from a solid state extraction involving aluminium foil used in the weighing step. The phenanthroline cations are involved both in inclusion and also in various assemblies formed by aromatic-aromatic stacking.

The crystal structure of the supramolecular exclusion complexes of cucurbit[6]uril with amino acid d-tryptophan and its decarboxylation product tryptamine have been determined. The supramolecular self-assembly of the cucurbit[6]uril with aromatic guests is guided by the combination of ion-dipole, hydrogen bonding, and stacking interactions between indole rings and glycouril groups of cucurbit[6]uril and leads to the formation of helical nanotubules in the case of tryptophan and stacked columns in the case of tryptamine. The formation of the solid-state complexes is dependent on the type of salt used for solubilization of cucurbit[6]uril which is explained in terms of the specific coordination mode of cucurbit[6]uril with magnesium ion.