Spherical assemblies of cyclo[6]aramide with polar side chains

Abstract

Cyclic aromatic oligoamides are a new class of recently discovered shape-persistent macrocycles. These molecules are prepared in high yields based on a one-step macrocyclization strategy that relies on hydrogen bond enforced folding of the corresponding uncyclized oligomeric precursors. Macrocycle 1 is a member of a series of six residue macrocycles dubbed cyclo[6]aramides and bears polar side chains derived from tri(ethylene glycol) monomethyl ether. We investigated its self-assembly using multiple techniques including UV-Vis spectrum, dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Results from these experiments demonstrated that 1 aggregates in apolar solvents such as 1,2dichloroethane. As temperature increases, the supramolecular aggregates gradually disintegrate into molecularly dissolved species. For example, at 70 °, compound 1 exists mainly in its molecularly dissolved form. In mixed solvents consisting of good (dichloromethane) and poor (aromatic hydrocarbons) components, compound 1 aggregates into spherical assemblies. These self-assembling spheres were shown by studies on thermal stability and by TEM imaging to be solid balls instead of hollow vesicles. The formation of the microspheres was found to be dependent on the properties of the poor solvents as their formation was promoted in aromatic hydrocarbons and obliteratedin aliphatic and polar solvents. In aliphatic and polar solvents, macrocycle 1 was found to assemble into films. © Editorial office of Acta Physico-Chimica Sinica.