Noncovalent synthesis of shape-persistent cyclic hexamers from ditopic hydrazide-based supramolecular synthons and asymmetric induction of supramolecular chirality.

With properly encoded recognition sites and a well-defined algorithm for intermolecular and intramolecular interactions, the 120 degrees spacer linked ditopic hydrazide-based supramolecular synthons were found to self-assemble into shape-persistent cyclic hexamers in apolar solvents. The two hydrazide motifs displayed separate sets of signals in the NMR spectra because of the interlocked conformation. While in hydrogen bonding competitive solvent such as DMSO-d(6) the spectra were in agreement with the structures with C(2) axes. Moreover, the terminative groups were found to affect the stability of the assemblies substantially. Consequently, the monomer with ureido-hydrazide terminative groups could form the most stable cyclic hexamer in solution for the attractive spectator secondary electrostatic interactions. Owing to the dynamically and kinetically stable nature of these kinds of assemblies, the assembly from the monomer with chiral auxiliary terminative groups also displayed supramolecular chirality in solution, which was confirmed by concentration-dependent CD spectra.