Enantiomers of a chiral counterion can induce totally different effects on the intermolecular interactions during the self-assembly of chiral macroions into supramolecular structures. For example, one enantiomer of an amino acid has stronger binding to chiral macroion than the other, so it is able to suppress the self-assembly process and/or change the properties of the assemblies such as their size. This is called “chiral discrimination”. Cationic cuboctahedron chiral metal-organic cages (MOCs), based on alanine (Pd12Ala24), valine (Pd12Val24), and leucine (Pd12Leu24) are successfully synthesized. From Pd12Ala24 to Pd12Leu24, MOCs are getting bulkier due to the presence of bulkier amino acids in their structure. These chiral MOCs can self-assemble into single-layered hollow spherical blackberry-type structures through counterion-mediated attraction due to the presence of additional nitrates, as the original counterions, in the self-assembly environment. Among hydrophobic amino acids which were used as chiral counterions, such as alanine, valine, and leucine, the ones with a bulkier side group, compared to the amino acids used in the structure of MOCs, are not able to induce chiral discrimination. For instance, only alanine can induce chiral discrimination during the self-assembly of Pd12Ala24; while, alanine, valine, and leucine can induce chiral discrimination during the self-assembly process of Pd12Leu24. Moreover, using anionic amino acid-based surfactants in the self-assembly environment reveals that increasing hydrophobic interaction among chiral counterion and chiral macroion vanishes chiral discrimination.

Chiral discrimination induced by non-covalent interactions between amino acids and chiral macroions

ACS Spring 2022

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