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

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-, d-, and d-) possessing hydrazine and d- or l-alanine moieties at the alkyl chain groups has been designed and synthesized. Interestingly, upon addition of AgNO (0.5-1.3 equiv.) to the d- solution, it generated the aggregate I composed of the d-AgNO complex (d- : 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-)Ag(NO) 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-AgNO complex with the left-handed (M-type) helicity formed in the presence of 2.0 equiv. of AgNO and was not additionally changed, which indicated that it was the thermodynamic product. The chiral supramolecular polymer based on (d-)Ag(NO) was produced a nucleation-elongation mechanism with a cooperative pathway. In thermodynamic study, the standard Δ° and Δ values for the aggregates I and II were calculated using the van't Hoff plot. The enhanced Δ° 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 AgNO confirmed the initial formation of the aggregate I (nanoparticle), which then evolved to the aggregate II (supramolecular polymer). Thus, the concentration of the (d-)Ag(NO) complex in the initial state plays a critical role in generating aggregate II (supramolecular polymer). In particular, NO 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 multiple steps with coordination structural change.