Light-responsive nanochannels based on the supramolecular host-guest system

Abstract

The light-responsive nanochannel of rhodopsin gained wider research interest from its crucial roles in light-induced biological functions, such as visual signal transduction and energy conversion, though its poor stability and susceptibility to inactivation in vitro have limited its exploration. However, the fabrication of artificial nanochannels with the properties of physical stability, controllable structure, and easy functional modification becomes a biomimetic system to study the stimulus-responsive gating properties. Typically, light-responsive molecules of azobenzene (Azo), retinal, and spiropyran were introduced into nanochannels as photo-switches, which can change the inner surface wettability of nanochannels under the influence of light; this ultimately results in the photoresponsive nature of biomimetic nanochannels. Furthermore, the fine-tuning of their stimulus-responsive properties can be achieved through the introduction of host-guest systems generally combined with a non-covalent bond, and the assembling process is reversible. These host-guest systems have been introduced into the nanochannels to form different functions. Based on the host-guest system of light-responsive reversible interaction, it can not only change the internal surface properties of the nanochannel and control the recognition and transmission behaviors but also realize the controlled release of a specific host or guest molecules in the nanochannel. At present, macrocyclic host molecules have been introduced into nanochannels including pillararenes, cyclodextrin (CD), and metal-organic frameworks (MOFs). They are introduced into the nanochannel through chemical modification or host-guest assemble methods. Based on the changes in the light-responsive structure of azobenzene, spiropyran, retinal, and others with macrocycle host molecules, the surface charge and hydrophilic and hydrophobic properties of the nanochannel were changed to regulate the ionic and molecular transport. In this study, the development of photoresponsive host and guest-assembled nanochannel systems from design to application is reviewed, and the research prospects and problems of this photo-responsive nanochannel membrane are presented.

Keywords: functional nanochannels; host–guest system; light response; mass transport; supramolecule.

SCHEME 1

Different host–guest system-assembled nanochannels.

FIGURE 1

(A) Schematic diagram of optical inclusion and de-inclusion of azobenzene (Azo) derivatives and β-CD; (B) changes in ionic current in Azo modified nanochannels before and after β-CD assembly under UV and visible light; (C) hydrophobic nanochannels modified by Azo opened under −2.6 V; (D) schematic diagram of the assembly of β-CD-Azo host-guest compounds in nanochannels regulated by photo and electricity (G. H. Xie, P. Li, Z. J. Zhao, Z. P. Zhu, et al., 2018) Copyright @ 2018 (ACS).

FIGURE 2

Schematic diagram of reversible assembly of azobenzene derivatives in NH₂-β-CD-modified nanochannels (Liu et al., 2018) Copyright @ 2018 (Springer Nature).

FIGURE 3

(A) Schematic diagram for the reversible assembly of poly-L-lysine-derived azobenzenes assembled in α-CD-modified nanochannels through the host–guest interaction with light- and pH-responsive properties; (B) schematic diagram for the reversible assembly of poly-n-isopropyl acrylamide-derived azobenzenes assembled in α-CD-modified nanochannels through the host–guest interaction with light- and temperature-responsive properties (Liu Y. Z. et al., 2017) Copyright @ 2017 (Wiley).

FIGURE 4

(A) Cyclodextrin transporter of artificial nanochannel systems; (B) schematic diagram of inclusion and de-inclusion of cyclodextrin–azobenzene in UV/visible light response; (C) selective transport behavior of azo groups on the inner surface of nanochannel under the different irradiation of visible light (blue) and ultraviolet light (purple). A single high intensity of visible or ultraviolet light will reduce the transmission rate of β-CD. Only the matching intensity of visible and ultraviolet light can promote the transmission of β-CD (Xie et al., 2018b) Copyright @ 2018 (Wiley).

FIGURE 5

β-CD-carboxyl azobenzene modified assembly into nanochannels in UV/visible light response regulating glutathione transport (Wang et al., 2021) Copyright @ 2021 (Elsevier).

FIGURE 6

(A) Molecular structure diagram of carboxylate-derived pillar[6]arene and quaternary ammonium azobenzene, Copyright @ 2017 (Springer Nature); (B) under visible light irradiation, carboxylate-derived pillar[6]arene-assembled nanochannels showed selective transport behaviors for cations, Copyright @ 2017 (Springer Nature). After irradiated by UV light, quaternary ammonium azobenzene-modified nanochannels showed selective transport behaviors for anions (Sun et al., 2017); (C) molecular structures of chiral alanine pillar[6]arene and quaternary ammonium azobenzene, Copyright @ 2018 (Springer Nature); (D) D-glucose responds to current changes in ionic-gated nanochannels (Sun et al., 2018) Copyright @ 2018 (Springer Nature).

FIGURE 7

(A) Synthesis process of the ethyl urea-derivative pillar[6]arene and the cis-trans structure change of the retinal molecule; (B) changes in the ionic current in the nanochannel before and after irradiation by visible light. This process was recycled seven times by the test of I-T current (Quan et al., 2021) Copyright @ 2021 (Wiley).

FIGURE 8

(A) Chemical structures of cationic (P+) and anionic (P−) pillar[5]arene, and azobenzene-derived cationic pillar[5]arene (AZo-P+); (B) schematic diagram of photo-responsive p-DNB adsorption in sub-nanometer molecular channels; (C) absorption, storage, and release of the guest molecule of p-DNB are regulated by UV and visible light and the addition of excessive 1,4-dicyanbutane in the solution (Ogoshi et al., 2018) Copyright @ 2018 (ACS).

FIGURE 9

(A) Photoisomerization of SP and MC forms in ZIF-8, Copyright @ 2020 (Wiley); (B) photoisomerization of SP in the ZIF-8 cavity leads to the on-off state for proton transport (Liang et al., 2020) Copyright @ 2020 (Wiley); (C) adsorption and desorption of ions regulated by the UV/visible light response of spiropyran in the MIL-53 MOF (Ou et al., 2020) Copyright @ 2020 (Springer Nature).

FIGURE 10

(A) Structural changes of Azo in the cavity of UiO-67 under different light conditions, and the schematic diagram of its influence on the transport of gas molecules. The gating mechanism is described by the filling space model. On the left is the aperture window of cis conformation, and on the right is the trans-conformation of UiO-67 and AZB; (B) controlled thermal desorption of Azo from the supporting UiO-67 layer. This desorption of Azo (from the membrane fully loaded with Azo) is indirectly traced to an increase in the permeability of CO₂. During in situ desorption process of Azo, the surface of the Azo@UiO-67 film is irradiated by LED at 365 nm continuously, thus transforming Azo from trans- to cis-isomer. When Azo is desorbed to a certain extent, CO₂ conduction increases rapidly after heating is stopped; (C) reversible gas permeation of the H₂/CO₂ mixture during in situ reversible switching of UiO-67 under constant and reduced Azo loads. The mixed gas separation factor α (H₂/CO₂) changes sinusoidal (Knebel et al., 2017) Copyright @ 2017 (ACS).