Melamine, chiral cyanurate assembly

Achiral fm-Melamine with Chiral Cyanurate Assembly... 

Figure 37. Chiral bis-melamine derivatives and chiral cyanurates used in self-assembly studies.

Usually the H NMR spectra of the aggregates (135)3-(136)6 are simple, exhibiting for instance only two sharp singlets for the imide protons of the barbiturate (at 13-14 ppm in CDC13). This strong downfield shift is characteristic for the melamine-barbiturate hexamer, while the simple pattern in general is only in agreement with the formation of the chiral assembly with an overall D3 symmetry. However, the simultaneous formation of all three supramolecular diastereomers was detected by H NMR spectroscopy in the case of sterically hindered cyanurates... 

It should be mentioned, that larger assemblies consisting of nine calixarenes are available with the calixarene-monocyanurate 139,208a while the double-calixarene 140 forms a double-box with 136 consisting of 15 molecules (3 x 140 and 9 x 136).283 Polymeric aggregates are formed between bis-melamine and bis-cyanurate calix[4]arenes.284 In all these cases, chiral induction still remains to be explored. 

A number of other studies have utilized specific modes of association between the wedges to control the formation of disks. Zimmerman and others have shown that trimesic acid derivatives assemble to form honeycomb arrangements when a filler for the channel is cocrystallized [99]. Early work by Whitesides on the assembly of rosettes from cyanuric acid-melamine [100,101] and their covalent analogs [102] has produced remarkable multicomponent assemblies and one-dimensional superstructures. Building on this research, Reinhoudt and coworkers have investigated a number of new derivatives with remarkable fidelity in the assembly motif and unusual chiral assembly characteristics [103]. 

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