Synthesis and Self-Assembly of an Oligoaramide Containing Multiple Hydrogen Bonds

Abstract

An oligoaramide duplex containing multiple hydrogen bonds was found to undergo self-assembly in the absence of its corresponding complementary strand. The self-assembly behavior of the molecular oligoaramide was examined using multiple techniques including ultraviolet-visible (UV-Vis) spectrum, dynamic light scattering (DLS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The result from the UV-Vis experiment indicated a hypsochromic shift within the ultraviolet region in 1,2-dichloroethane with increasing temperature, suggesting partial disintegration of supramolecular aggregates. The oligoaramide was found to self-assemble in solvents of different polarity presenting different types of morphologies. For example, reticulation-like morphology was observed when using toluene as a solvent; an irregular honeycomb appeared in the mixed, relatively less polar dichloromethane and cyclohexane. In addition, stable solid balls formed instead of vesicles upon self-assembling in a mixed polar solvent of chloroform and methanol. The diameters of these spherical aggregates increased with concentration. Furthermore, the transformation of assemblies from tubular fibers in hot acetonitrile to solid spherical aggregates was observed upon cooling.