Helicity-driven chiral self-sorting supramolecular polymerization with Ag+: right- and left-helical aggregates.

Sung Ho Jung,Heekyoung Choi,Jong Hwa Jung,Shim Sung Lee,Jaeheung Cho,Mirae Ok,Ka Young Kim,Seonghan Kim

doi:10.1039/d1sc06413d

Abstract

The study of chiral self-sorting is extremely important for understanding biological systems and for developing applications for the biomedical field. In this study, we attempted unprecedented chiral self-sorting supramolecular polymerization accompanying helical inversion with Ag+ in one enantiomeric component. Bola-type terpyridine-based ligands (R-L1 and S-L1) comprising R- or S-alanine analogs were synthesized. First, R-L1 dissolved in DMSO/H2O (1 : 1, v/v) forms right-handed helical fibers (aggregate I) via supramolecular polymerization. However, after the addition of AgNO3 (0.2–1.1 equiv.) to the R-L1 ligand, in particular, it was found that aggregate II with left-handed helicity is generated from the [R-L1(AgNO3)2] complex through the [R-L1Ag]+ complex via the dissociation of aggregate I by a multistep with an off pathway, thus demonstrating interesting self-sorting properties driven by helicity and shape discrimination. In addition, the [R-L1(AgNO3)2] complex, which acted as a building block to generate aggregate III with a spherical structure, existed as a metastable product during the formation of aggregate II in the presence of 1.2–1.5 equiv. of AgNO3. Furthermore, the AFM and CD results of two samples prepared using aggregates I and III with different volume ratios were similar to those obtained upon the addition of AgNO3 to free R-L1. These findings suggest that homochiral self-sorting in a mixture system occurred by the generation of aggregate II composed of the [R-L1Ag]+ complex via the rearrangement of both, aggregates I and III. This is a unique example of helicity- and shape-driven chiral self-sorting supramolecular polymerization induced by Ag+ starting from one enantiomeric component. This research will improve understanding of homochirality in complex biological models and contribute to the development of new chiral materials and catalysts for asymmetric synthesis.

Highlights

These findings suggest that homochiral self-sorting in a mixture system occurred by the generation of aggregate II composed of the [R-L1Ag]+ complex via the rearrangement of both, aggregates I and III
We demonstrated unprecedented successive chiral self-sorting in supramolecular polymerization accompanied by helical inversion with Ag+ for a single enantiomeric component
The present chiral selfsorting was induced by self-discrimination in a mixture of differently shaped building blocks with different helicities

Summary

Introduction

Chiral metal-coordinated supramolecular assemblies have recently received much attention and are among the most promising structures in supramolecular chemistry,[1,2,3,4,5,6,7,8,9,10] because metal-coordinated systems play essential roles in the formation of superstructures such as coiled-coil helix bundle proteins,[11,12] DNA superhelices,[13] and protein-DNA hybrid superstructures.[14,15] better understanding of emergent chiral phenomena and the origin of chirality at the supramolecular level are essential for biomedical applications such as drug delivery,[16,17,18] gene delivery,[19] tissue engineering,[20,21] imaging,[22] and sensing.[23,24]Self-sorting is one of the high- delity self-recognitions or self-discriminations in living systems, in which a complex object is recognizable from non-self into well-organized supramolecular architectures.[25,26,27,28] Biomacromolecules have great selfsorting ability, for example proteins and enzymes can distinguish two enantiomers by supramolecular interactions and promote biological processes.[29,30] Chirality-driven self-sorting processes are mainly dependent on the handedness of the helical structures with the con guration of the enantiomer moiety. The [R-L1(AgNO3)2] complex, which acted as a building block to generate aggregate III with a spherical structure, existed as a metastable product during the formation of aggregate II in the presence of 1.2–1.5 equiv. The AFM image revealed a spherical structure (aggregate III) in the presence of AgNO3 (2.0 equiv.) (Fig. S18†), which originated from the selfassembled [R-L1(AgNO3)2] complex.

Results

Conclusion