Chiral self-sorting process\xa0in the self-assembly of homochiral coordination cages from axially chiral ligands

Shuichi Hiraoka,Tomoki Tateishi,Tatsuo Kojima

doi:10.1038/s42004-018-0020-4

Shuichi Hiraoka, Tomoki Tateishi + Show 1 more

Open Access

https://doi.org/10.1038/s42004-018-0020-4

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Abstract

Chiral self-sorting is a phenomenon wherein racemic components are spontaneously sorted into homo- or heterochiral molecular assemblies through chiral discrimination between the components. Chiral self-sorting may be related to biological molecular systems where chiral biomolecules are concerned, but the detail of this sorting process has been unclear. Here we show the chiral self-sorting process in the formation of a homochiral Pd2L4 coordination cage from a racemic mixture of a binaphthol-based ditopic ligand by quantitative analysis of self-assembly process (QASAP). The self-assembly of the cage mainly takes place through two pathways that branch off from the intermolecular reaction of mononuclear complexes. Even though the homochiral cages are thermodynamically the most stable, heterochiral intermediates were preferentially produced at first under kinetic control, which were eventually converted into the homochiral cages. Our results reveal complicated pathways in chiral self-sorting.

Highlights

Chiral self-sorting is a phenomenon wherein racemic components are spontaneously sorted into homo- or heterochiral molecular assemblies through chiral discrimination between the components
We have developed a method for the investigation of molecular self-assembly processes based on the concept that the information about the intermediates transiently produced during molecular self-assembly, most of which cannot be detected by spectroscopy, can indirectly be obtained as the average composition of all the intermediates by the quantification of all the substrates and the products (QASAP: quantitative analysis of selfassembly process)[54,55,56,57,58,59,60,61,62,63]
We report the chiral self-sorting process of an enantiomeric pair of homochiral cages consisting of two Pd(II) ions and four one-handed BINOL-based ditopic ligands[64] along the self-assembly pathways of the cage revealed by quantitative analysis of self-assembly process (QASAP)

Summary

Introduction

Chiral self-sorting is a phenomenon wherein racemic components are spontaneously sorted into homo- or heterochiral molecular assemblies through chiral discrimination between the components. We show the chiral self-sorting process in the formation of a homochiral Pd2L4 coordination cage from a racemic mixture of a binaphthol-based ditopic ligand by quantitative analysis of self-assembly process (QASAP). Chiral self-sorting is not directly related to the selection of one of the enantiomers in the origin of life, it may be relevant to biological molecular systems where chiral biomolecules are concerned. We report the chiral self-sorting process of an enantiomeric pair of homochiral cages consisting of two Pd(II) ions and four one-handed BINOL-based ditopic ligands[64] along the self-assembly pathways of the cage revealed by QASAP. The correction of chirality in the heterochiral cages and the dinuclear intermediates takes place with the aid of free ditopic ligands to lead to the homochiral cages, indicating complicated pathways in the chiral self-sorting

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