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While the scientific literature is replete with examples of host:guest 1:1 complexes, their subsequent self-assembly into advanced architectures remains elusive. Cucurbiturils have now been observed to be triangulated as 3:3 complexes and nitroxide free radicals are non innocent in that process.
Cucurbiturils are synthetic macrocycles with several, specific outstanding properties. One of them is to commonly bind cationic hydrophobic compounds, with nano- to picomolar affinities in water. A plethora of examples has been reported about the inclusion of a variety of guest molecules in these synthetic hosts. Among the guest compounds, nitroxide free radicals have enabled to find the peculiar successive self-assembly of 1:1 cucurbit[8]uril complexes (CB[8]) into host:guest 3:3 assemblies, mediated by sodium or potassium cations.
In this work, the authors broadened the scope of CB[8] triangulation using a dinitroxide biradical and a diamagnetic guest showing that this triangulation is not limited to free radicals. Finally, the reticulation of the 3:3 triangular complexes was observed by several techniques using another biradical. This type of contol in host:guest assemblies could have relevance for magnetic or biohybrid materials or in supramolecular engineering where hierarchical self-assembly is required. »
Triangular Regulation of Cucurbit[8]uril 1:1 Complexes
S. Combes, K. T. Tran, M. M. Ayhan, H. Karoui, A. Rockenbauer, A. Tonetto, V. Monnier, L. Charles, R. Rosas, S. Viel, D. Siri, P. Tordo, S. Clair, R. Wang, D. Bardelang, O. Ouari, J. Am. Chem. Soc. 2019, 141, 5897-5907. DOI : 10.1021/jacs.9b00150