Polypyridine‐Based Helical Amide Foldamer Channels: Rapid Transport of Water and Protons with High Ion Rejection

Abstract

Synthetic strategies that enable rapid construction of covalent organic nanotubes with an angstrom‐scale tubular pore remain scarcely reported. Reported here is a remarkably simple and mild one‐pot polymerization protocol, employing POCl3 as the polymerization agent. This protocol efficiently generates polypyridine amide foldamer‐based covalent organic nanotubes with a 2.8 nm length at a yield of 50 %. Trapping single‐file water chains in the 2.8 Å tubular cavity, rich in hydrogen‐bond donors and acceptors, these tubular polypyridine ensembles rapidly and selectively transport water at a rate of 1.6×109 H2O⋅S−1⋅channel−1 and protons at a speed as fast as gramicidin A, with a high rejection of ions.

Bioinspired and biomimetic membranes for water purification and chemical separation: A review

“…By tuning the backbones, their polypyridine-based aquafoldamer was able to transport water at a rate of 1.6 Â 10 9 water molecules per second (Fig. 4e, e2) (Shen et al, 2020a). Their latest aquafoldamer channel expanded the pore volume by 20% and achieved a permeability of~3 Â 10 9 water molecules per second (Fig.…”

“…4d) by Hou group (Hu et al, 2012;Chen et al, 2013;Shen et al, 2015Shen et al, , 2018Li et al, 2019a), aquafoldamer channels by Zeng group (Fig. 4e) (Zhao et al, 2012a(Zhao et al, , 2014aHuo and Zeng, 2016;Shen et al, 2020aShen et al, , 2020b and macrocyclic channels by Gong group (Fig. 4f) (Zhou et al, 2012) are the representative examples.…”

“…4e) (Zhao et al, 2014a;Shen et al, 2020aShen et al, , 2020b. These channels are formed by either self-assembly of these oligomers with specially designed sticky ends (Zhao et al, 2014a;Shen et al, 2020a) (i.e., interaction between ester and benzyloxycarbonyl groups), or through polymerization (Shen et al, 2020b). The inner diameter of the channels is~2.8 Å, which is the similar size compared to the narrowest cavity of AQPs.…”

“…3~4 Å at the narrowest site of the aperture is required for salt rejection. Imidazole channels (Leduc et al, 2011;Licsandru et al, 2016), aquafoldamer channels (Shen et al, 2020a;2020b) and PAH[4] channels (Song et al, 2020) can achieve high salt rejection because of the appropriate size exclusion while the other candidates with larger pore sizes have been found to be less efficient in excluding salts. Secondly, the internal hydrophobic requirement within channels is necessary for fast water translocation.…”

“…This means, in the case of incomplete rejection of solutes, the apparent osmotic gradient decreases which offsets the volume change. The reflection coefficient (s) is calculated to evaluate the rejection properties of a channel (Meinild et al, 1998;Kumar et al, 2007;Shen et al, 2015Shen et al, , 2020aShen et al, , 2020bLicsandru et al, 2016;Li et al, 2019a;.…”