Hierarchical Self-Organization and Disorganization of Helical Supramolecular Columns Mediated by H-Bonding and Shape Complementarity

Abstract

H-bonding, shape complementarity, and quasi-equivalence are widely accepted as some of the most influential molecular recognition events mediating biological and synthetic self-organizations. H-bonds are weaker than ionic but stronger than van der Waals forces. However, the directionality of H-bonds makes them the most powerful among all nonbonding interactions. Here, we selected two taper-shaped self-assembling dendrons, one flexible and one rigid, and equipped them with −CO₂CH₃, −CH₂OH, and −COOH at their apex. They demonstrated the hierarchical way in which shape-complementarity in the presence of −CO₂CH₃ mediated highly ordered helical self-organization for the case of the rigid building block and less ordered helical arrays for the flexible one. Weak H-bonding by −CH₂OH unwound the helix from the rigid dendron, yielding a porous column. Due to its quasi-equivalence, the flexible dendron tolerated better the H-bonding by −CH₂OH self-organizing a different helical column. The rigid and the flexible dendrons yielded only disorganized nonhelical columns in the presence of −COOH at the apex. This balance between rigidity, flexibility, and tolerance or lack of it to diverse H-bonding architectures indicates that mechanistic elucidation of the self-organization process helps endow it with the same building block, both helical organizations approaching biological precision, and disorganized nonhelical arrangements.