Issue 3, 2020

Kinetically controlled Ag+-coordinated chiral supramolecular polymerization accompanying a helical inversion

Abstract

We report kinetically controlled chiral supramolecular polymerization based on ligand–metal complex with a 3 : 2 (L : Ag+) stoichiometry accompanying a helical inversion in water. A new family of bipyridine-based ligands (D-L1, L-L1, D-L2, and D-L3) possessing hydrazine and D- or L-alanine moieties at the alkyl chain groups has been designed and synthesized. Interestingly, upon addition of AgNO3 (0.5–1.3 equiv.) to the D-L1 solution, it generated the aggregate I composed of the D-L1AgNO3 complex (D-L1 : Ag+ = 1 : 1) as the kinetic product with a spherical structure. Then, aggregate I (nanoparticle) was transformed into the aggregate II (supramolecular polymer) based on the (D-L1)3Ag2(NO3)2 complex as the thermodynamic product with a fiber structure, which led to the helical inversion from the left-handed (M-type) to the right-handed (P-type) helicity accompanying CD amplification. In contrast, the spherical aggregate I (nanoparticle) composed of the D-L1AgNO3 complex with the left-handed (M-type) helicity formed in the presence of 2.0 equiv. of AgNO3 and was not additionally changed, which indicated that it was the thermodynamic product. The chiral supramolecular polymer based on (D-L1)3Ag2(NO3)2 was produced via a nucleation–elongation mechanism with a cooperative pathway. In thermodynamic study, the standard ΔG° and ΔHe values for the aggregates I and II were calculated using the van't Hoff plot. The enhanced ΔG° value of the aggregate II compared to that of the formation of aggregate I confirms that aggregate II was thermodynamically more stable. In the kinetic study, the influence of concentration of AgNO3 confirmed the initial formation of the aggregate I (nanoparticle), which then evolved to the aggregate II (supramolecular polymer). Thus, the concentration of the (D-L1)3Ag2(NO3)2 complex in the initial state plays a critical role in generating aggregate II (supramolecular polymer). In particular, NO3 acts as a critical linker and accelerator in the transformation from the aggregate I to the aggregate II. This is the first example of a system for a kinetically controlled chiral supramolecular polymer that is formed via multiple steps with coordination structural change.

Graphical abstract: Kinetically controlled Ag+-coordinated chiral supramolecular polymerization accompanying a helical inversion

Supplementary files

Article information

Article type
Edge Article
Submitted
02 Oct 2019
Accepted
11 Nov 2019
First published
14 Nov 2019
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2020,11, 721-730

Kinetically controlled Ag+-coordinated chiral supramolecular polymerization accompanying a helical inversion

H. Choi, S. Heo, S. Lee, K. Y. Kim, J. H. Lim, S. H. Jung, S. S. Lee, H. Miyake, J. Y. Lee and J. H. Jung, Chem. Sci., 2020, 11, 721 DOI: 10.1039/C9SC04958D

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