Formation of a discrete helical assembly and packing pattern through charged hydrogen bonds and van der Waals interactions

Abstract

We report the selective formation of a self-assembled discrete helical assembly with handedness through charged hydrogen bonds in aqueous solution and solid state. A helical assembly is obtained by simply mixing tris(imidazoline) (1) and (rac)-trans-cyclohexane-1,2-dicarboxylic acid (2) in a 2 : 3 ratio in water and methanol. The formation of an ion aggregate is fully supported by NMR, MALDI-TOF mass spectroscopy, and X-ray analysis. Helicity of the 2 : 3 complex is determined by the chirality of 2. For example, (1R,2R)-trans-cyclohexane-1,2-dicarboxylic acid (2^RR) induces Mhelicity in [1₂·2₃] and vice versa. Each complex is enantiomerically pure as equal amounts of the P and M helical complexes are formed with racemic 2. P- and M-helical assemblies are stacked by turns because PMPM stacking is denser than PP or MM stacking.