Kinetically controlled Ag+-coordinated chiral supramolecular polymerization accompanying a helical inversion. Issue 3 (19th November 2019)

• Record Type: Journal Article
• Authors: Choi, Heekyoung; Heo, Sojeong; Lee, Seonae; Kim, Ka Young; Lim, Jong Hyeon; Jung, Sung Ho; Lee, Shim Sung; Miyake, Hiroyuki; Lee, Jin Yong; Jung, Jong Hwa
• Is Part Of: Chemical science. Volume 11:Issue 3(2020)
• Page Start: 721
• Page End: 730
• Publication Date: 2019-11-19
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c9sc04958d
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : The nanoparticles were transformed into the supramolecular polymer as the thermodynamic product, involving a helical inversion from left-handed to right-handed helicity. 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 -L 1, l -L 1, d -L 2, and d -L 3 ) 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 -L 1 solution, it generated the aggregate I composed of the d -L 1 AgNO3 complex (d -L 1 : 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 -L 1 )3 Ag2 (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 -L 1 AgNO3 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 -L 1 )3 Ag2 (NO3 )2 was produced via a nucleation–elongation mechanism with a cooperative pathway. In thermodynamic study, the standard Δ G ° and Δ H e values for the aggregates I and II were calculated using the van't Hoff plot. The enhanced Δ G ° 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 -L 1 )3 Ag2 (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.