A biomimetic chiral-driven ionic gate constructed by pillar[6]arene-based host–guest systems

Inspired by glucose-sensitive ion channels, herein we describe a biomimetic glucose-enantiomer-driven ion gate via the introduction of the chiral pillar[6]arene-based host–guest systems into the artificial nanochannels. The chiral nanochannels show a high chiral-driven ionic gate for glucose enantiomers and can be switched “off” by d-glucose and be switched “on” by l-glucose. Remarkably, the chiral nanochannel also exhibited a good reversibility toward glucose enantiomers. Further research indicates that the switching behaviors differed due to the differences in binding strength between chiral pillar[6]arene and glucose enantiomers, which can lead to the different surface charge within nanochannel. Given these promising results, the studies of chiral-driven ion gates may not only give interesting insight for the research of biological and pathological processes caused by glucose-sensitive ion channels, but also help to understand the origin of the high stereoselectivity in life systems.


Synthetic and characterization of L-AP6 and AZO.
Reagents were commercially available and used as received. Solvents were either employed as purchased or dried according to procedures described in the literature. 1 H and 13 C NMR spectra were recorded on a Mercury-Plus spectrometer (400 MHz).
Elemental analyses were performed on a Perkin-Elmer 240 C analyzer.

The interaction between AZO and L-AP6
To determine the stoichiometry and association constant (Ka) between L-AP6 and AZO. 1

Fabrication of single conical nanochannel
The single conical nanochannel was prepared in a PET polymer film using the well-known ion track etching technique. Before etching process, each side of the PET membranes were exposed in UV light (365 nm) for 1 h. In order to obtain the conical

SEM Characterization
The diameter of the base was estimated from the multitrack membrane by field-emission scanning electron microscopy (FESEM) which was etched under the same conditions as the single-channel sample. In this work, before modification the base diameter was about 580 nm and tip diameter was estimated by the above relation, tip was about 18 nm.

The modification process of chiral nanochannel
As a result of chemical etching, carboxyl groups are generated on the nanochannel surface. These can be activated with EDC/NHS, forming an amine-reactive ester intermediate. Then these reactive esters were further condensed with AZO through the formation of covalent bonds. In this paper NHS ester was formed by soaking PET film in an aqueous solution of 30 mg EDC and 6 mg NHS for 1 hour. After that washing this film with distilled water and treated it with 1 mM AZO solution overnight.
Then, the L-AP6 were attached to the AZO-channel by self-assembling. Finally, the modified-film was washed three times with distilled water.

Contact angles measurement
Contact angles were measured using an OCA20 (DataPhysics, Germany) contact

The K values (binding constants) in the nanochannels
In previous literature, it was discovered that the Langmuir model provided a perfect fit to the experimental data for nanochannels. S4 In our work, furthermore, the variation of the rectification ratio (R-/+) with increasing concentration of saccharides, was similar to the trend of the Langmuir absorption isotherm. Consequently, we speculated that it would be possible to describe the binding of saccharides enantiomers on the internal surface of the L-AP6-channel using the Langmuir model.

The electroosmotic flow (EOF) experiments
We conducted a series of electroosmotic flow (EOF) experiments, which is an electrokinetic phenomenon that occurs when an ionic current is passed through nanochannel that contains excess surface charge. EOF was driven through the where iA− and iHA can be determined by the average values of the high pH (> 6) and low pH (< 4), respectively. Hence, a plot of peak current i versus pH can elucidate the pKa of a surface.
The current at -2 V can be determined and plotted against pH as shown in Supplementary Fig. S18. This plot looks similar to the equivalence part of a titration curve, and using eq 3, the pKa can be elucidated. Hence, the surface pKa at the neutral condition before adding the D-/L-Glu is approximately 6.08. After binding with glucose enantiomers, the surface pKa at the neutral condition is approximately 6.71 for binding D-Glu and is approximately 6.14 for binding L-Glu.