Interplay between physical interactions controls chiral discrimination during the self-assembly of chiral metal-organic cages

Cationic Pd₁₂L₂₄ metal-organic cages (MOCs), based on hydrophobic amino acids including D- and L-alanine, D- and L-valine, and D- and L-leucine, can self-assemble into supramolecular structures through counterion-mediated attractions by the addition of extra nitrates. Previously, we showed that presence of N-(tert-Butoxycarbonyl) (Boc)-protected D- and L-alanine as chiral counterions can induce totally different self-assembly behavior. For example, L-alanine can suppress the self-assembly of D-MOCs based on alanine; while, L-alanine does not change the self-assembly behavior i.e., chiral discrimination exists. Here, it is revealed that chiral discrimination can be induced only when chiral counterion is less bulky or as bulky as the amino acid used in the MOCs’ structure. For example, only Boc-alanine can induce chiral discrimination to alanine-based MOCs; while, Boc-alanine, -valine, and -leucine induce chiral discrimination to leucine-based MOCs. Besides, utilizing alanine-based anionic surfactants indicated that increasing hydrophobicity of chiral counterion vanishes chiral discrimination. This study unveils the interplay of physical intermolecular interactions and their effect on the self-assembly of homochiral supramolecular structures.