Light-Controlled Ion Transport through Biomimetic DNA-Based Channels

Conjugated microporous polymer membranes for light-gated ion transport

Inspired by the light-gated ion channels in cell membranes that play important roles in many biological activities, herein, we developed an artificial light-gated ion channel membrane out of conjugated microporous polymers. Through bottom-up design of the monomer molecular structure and by the electropolymerization method, the membrane pore size and thickness were precisely controlled on the molecular level. The obtained membrane exhibited uniform pore size and highly sensitive light-switchable response. The photoisomerization of the polymer chain resulted in a reversible "on and off" light control over the pore size and subsequently led to light-gated ion transport across the membrane for a series of ions including hydrogen, potassium, sodium, lithium, calcium, magnesium, and aluminum ions.

An Ultraviolet/Visible Light Regulated Protein Transport Gate Constructed by Pillar[6]arene-based Host-Guest System

Protein transport is an interesting and intrinsic life feature that is highly relevant to physiology and disease in living beings. Herein, inspired by nature, based on the supramolecular host-guest interaction, we have introduced the classical azobenzene light switches and L-phenylalanine derived pillar[6]arene (L-Phe-P6) into the artificial nanochannel to construct light-responsive nanochannels that could regulate protein transport effectively under the control of ultraviolet (UV) and visible (Vis) light. The light-controlled distribution of L-Phe-P6 in the channel led to the difference in surface charges in the nanochannel, which eventually brought the difference in protein transport. This research may not only provide a convenient theoretical model for biological research, but also a flexible light-responsive protein transport model, which will play a crucial role in light-controlled release of protein drugs and so on.

Light-Controlled Ionic/Molecular Transport through Solid-State Nanopores and Nanochannels

Biological nanochannels perfectly operate in organisms and exquisitely control mass transmembrane transport for complex life process. Inspired by biological nanochannels, plenty of intelligent artificial solid-state nanopores and nanochannels are constructed based on various materials and methods with the development of nanotechnology. Specially, the light-controlled nanopores/nanochannels have attracted much attention due to the unique advantages in terms of that ion and molecular transport can be regulated remotely, spatially and temporally. According to the structure and function of biological ion channels, light-controlled solid-state nanopores/nanochannels can be divided into light-regulated ion channels with ion gating and ion rectification functions, and light-driven ion pumps with active ion transport property. In this review, we present a systematic overview of light-controlled ion channels and ion pumps according to the photo-responsive components in the system. Then, the related applications of solid-state nanopores/nanochannels for molecular sensing, water purification and energy conversion are discussed. Finally, a brief conclusion and short outlook are offered for future development of the nanopore/nanochannel field.

A Visible-Light-Regulated Chloride Transport Channel Inspired by Rhodopsin

Inspired by the light-regulating capabilities of naturally occurring rhodopsin, we have constructed a visible-light-regulated Cl^- -transport membrane channel based on a supramolecular host-guest interaction. A natural retinal chromophore, capable of a visible-light response, is used as the guest and grafted into the artificial channel. Upon introduction of an ethyl-urea-derived pillar[6]arene (Urea-P6) host, threading or de-threading of the retinal and selective bonding of Cl^- can be utilized to regulate ion transport. Based on the visible-light responsiveness of the host-guest interaction, Cl^- transport can be regulated by visible light between ON and OFF states. Visible-light-regulated Cl^- transport as a chemical model permits to understand comparable biological ion-selective transport behaviors. Furthermore, this result also supplies a smart visible-light-responsive Cl^- transporter, which may have applications in natural photoelectric conversion and photo-controlled delivery systems.

Bacteriorhodopsin-Inspired Light-Driven Artificial Molecule Motors for Transmembrane Mass Transportation

In nature, biological machines and motors can selectively transport cargoes across the lipid membranes to efficiently perform various physiological functions via ion channels or ion pumps. It is interesting and challengeable to develop artificial motors and machines of nanodimensions to controllably regulate mass transport in compartmentalized systems. In this work, we show a system of artificial molecular motors that uses light energy to perform transmembrane molecule transport through synthetical nanochannels. After functionalizing the polymer nanochannels with azobenzene derivatives, these nanomachines exhibit autonomous selective transport behavior over a long distance upon simultaneous irradiation with UV (365 nm) and visible (430 nm) light. With new strategies or suitable materials for directed molecular movement, such device can be regarded as a precursor of artificial light-driven molecular pumps.

QM/MM Studies on Photoisomerization Dynamics of Azobenzene Chromophore Tethered to a DNA Duplex: Local Unpaired Nucleobase Plays a Crucial Role

The photoresponsive azobenzene-tethered DNAs have received growing experimental attention because of their potential applications in biotechnology and nanotechnology; however, little is known about the initial photoisomerization of azobenzene in these systems. Herein we have employed quantum mechanics/molecular mechanics (QM/MM) methods to explore the photoisomerization dynamics of an azobenzene-tethered DNA duplex. We find that in the S₁ state the trans-cis photoisomerization path is much steeper in DNA than in vacuo, which makes the photoisomerization much faster in the DNA environment. This acceleration is primarily caused by complex steric interactions between azobenzene and the nearby unpaired thymine nucleobase, which also change the photoisomerization mechanism of azobenzene in the DNA duplex.