Helix Induction and Inversion of Polymeric Foldamer Regulated by the Single Enantiomers

Abstract

Generally, a single enantiomer can induce a foldamer into a preferred‐handed helix, while another condition is required for the helical inversion. Herein, it is found that the helix induction and subsequent inversion of poly(m‐phenylene diethynylene)‐based foldamer bearing aza‐18‐crown‐6 pendants (Poly‐1) can be realized by increasing the concentration of sterically hindered l‐amino acid perchlorate salts. When the amount of chiral enantiomers is small, one enantiomer tends to complex with two non‐adjacent aza‐18‐crown‐6 rings via three N+H···O hydrogen bonds in a sandwich mode. Notably, the transition dipole moment is perpendicular to the aza‐18‐crown‐6 ring, so that the induced helical chirality in Poly‐1 backbone is opposite to the chirality of enantiomers. When the amount of chiral enantiomers is large enough, each aza‐18‐crown‐6 is occupied by one enantiomer, which causes the transition dipole moment in a parallel direction to aza‐18‐crown‐6 ring. In this case, the increased steric hindrance can facilitate the inversion of screw sense of Poly‐1 backbone, which is directed by chiral center of enantiomers. As a result, a helix inversion has been achieved successfully. This work not only provides a novel strategy for regulating the two‐stage folded helical conformations by the single enantiomers, but opens a window to develop chiral recognition materials.

Thermotropic chirality enhancement of nanoparticles constructed from foldamer/bis(amino acid) complexes

“…Accordingly, in order to ensure that Poly-1 folds into a helical conformation, we choose a chloroform/acetonitrile co-solvent system with a small ratio of chloroform. 31 Given that Poly-1 exhibits good solubility in chloroform/acetonitrile (1/9, v/v), such a solvent ratio is selected for the subsequent investigations. First, the helical folding behavior of Poly-1 is studied by fluorescence spectroscopy.…”

“…According to our previous report, the size of Poly-1 is estimated to be 4.0 nm. 31 In general, the size of the dried polymer in vacuo is usually about 40% of the diameter of the swollen one. 42,43 So, the estimated dried size is about 1.6 nm for Poly-1, which is in agreement with that obtained from TEM observation.…”

“…30 With this in mind, we have synthesized a poly(m-phenylene diethynylene) derivative (Poly-1, Scheme 1) bearing aza-18crown-6 pendants, whose number-average molecular weight (M n ) and polydispersity (M w /M n ) are estimated to be 1.16 × 10 4 and 2.68, respectively. 31 On the other hand, L-homocystine, as a typical kind of bis(amino acid), is a cheap and commercially available chiral source. After the protonation of its two amino groups, it can act as a chiral inducer and cross-linker at the same time.…”

Visualization of Conformational Transitions of Artificial Polymeric Foldamers by AIEgen

“…Over the decades, many artificial foldamers have been designed because they can mimic the folding behavior that occurs in biomacromolecules . In particular, unlike biomacromolecules, artificial foldamers can undergo the reversible conformational transitions in response to external stimuli including temperature, pH, light, solvents, , and additives − (Figure a). Therefore, artificial foldamers can serve as the ideal systems to simulate the structure–activity relationship of biomacromolecules …”