[supramolecular assembly] triangular assembly based on Cucurbit [8] urea

In the macro world, even in the early childhood, we can rely on instinct to put some materials into various shapes But in the micro world, how to control molecules to form specific geometry is a difficult and fascinating thing Many scientists control molecules by various chemical and physical means, so that they are arranged and combined according to the pre-designed route to form various graphs Among them, the triangle, as the basic figure, has attracted the attention of numerous scholars However, it is found that most of the synthesized triangular molecules or aggregates are formed by covalent bond or metal coordination bond (JACS: self-assembly of tripyridine to form fractal geometry) As an important element in the field of molecular architecture, supramolecular triangles based on host guest copolymers, especially those with the ratio of host guest 1:1, are very rare Figure 1 The triangle structure formed by cucurbit [8] urea and isodox (a), AK (b) and btht (c) (photo source: J am Chem SOC.) recently, Olivier ouari and David bardelang of the University of Aix Marseille in France, together with Professor Wang ruibing of the University of Macau, reported the triangle aggregation based on Cucurbit [8] urea The authors found that cucurbit [8] urea and a cationic diazoxide radical (isodoxa) can form triangular aggregates in the presence of sodium ions (Fig 1a) Moreover, by changing the cationic diazo radicals, the author further obtained a larger triangular structure (Fig 1c) In addition, diamagnetic triangular aggregates were obtained by cucurbit [8] urea (Fig 1b) This achievement was published in the Journal of the American Chemical Society (DOI: 10.1021 / JACS 9b00150) under the title of "triangular regulation of curibit [8] uril1:1 complexes" Fig 2 EPR map of isodoxa and cucurbit [8] urea before and after combination (photo source: J am Chem SOC.) the author first studied the combination of Cucurbit [8] urea and isodoxa by EPR At room temperature, isodoxa molecules in aqueous solution appeared 9 groups of peaks in the center of EPR spectrum (Fig 2a), but after adding cucurbit [8] urea, the number and position of peaks changed (Fig 2b) This shows that the addition of Cucurbit [8] urea greatly affects the spin interaction in isodoxa molecule (Fig 2E, j 1), and the addition of a certain amount of sodium ion into the solution will further change the EPR profile of the system (Fig 2C), and the new profile shows a wider peak pattern The author speculates that this is due to the formation of triangular copolymers between the inclusion complex of Cucurbit [8] urea and isodoxa, which leads to the occurrence of spin interaction between isodoxa molecules (Fig 2E, j 2), but it is difficult to distinguish the two types of spin interaction on the map Therefore, the author demonstrated the existence of triangular structure by inhibiting the intramolecular spin interaction by ascorbic acid (Fig 2D) Fig 3 Molecular simulation results of Cucurbit [8] urea and isodoxa in different binding modes (photo source: J am Chem SOC.) because cucurbit [8] urea is only about 9.1 μ m high, it is not enough to completely cover the whole isodoxa molecule Therefore, cucurbit [8] urea can only selectively cover one end (i-end or d-end) of isodoxa, which leads to the formation of four possible triangle structures, I-I-I, i-i-d, i-d-d and d-d-d However, the author found that I-I-I structure has the lowest energy and the most stable through DFT calculation, so its relative content in the solution should be the highest After that, the author confirmed the existence of diamagnetic cucurbit [8] urea triangle and larger cucurbit [8] urea triangle by means of DOSY-NMR, SEM, AFM and EPR The author also made some conjectures on the causes of their formation: first, the rigid cucurbit [8] urea itself tends to form a triangular structure to make Ch Secondly, the guest molecules with appropriate binding strength and geometry also contribute to the formation of triangular structure Finally, the addition of cations will increase the possibility of forming triangular structure S é Bastien Combes, khoatruong tran, Mehmet menaf Ayhan, Hakim karoui, antalrockenbauer, Alain tonetto, Val é RIE Monnier, laurencecharles, Roselyne Rosas, St é phane viel, Didier Siri, Paul tordo, Sylvain Clair, ruibingwang, David bardelang, and Olivier ouari.