Stimulus-Controlled Anion Binding and Transport by Synthetic Receptors

Abstract

Anionic species are omnipresent and involved in many important biological processes. A large number of artificial anion receptors has therefore been developed. Some of these are capable of mediating transmembrane transport. However, where transport proteins can respond to stimuli in their surroundings, creation of synthetic receptors with stimuli-responsive functions poses a major challenge. Herein, we give a full overview of the stimulus-controlled anion receptors that have been developed thus far, including their application in membrane transport. In addition to their potential operation as membrane carriers, the use of anion recognition motifs in forming responsive membrane-spanning channels is discussed. With this review article, we intend to increase interest in transmembrane transport among scientists working on host–guest complexes and dynamic functional systems in order to stimulate further developments.

Photo‐ and Redox‐Regulated Transmembrane Ion Transporters

“…Light is attractive due to the prospect of spatiotemporal activation using biocompatible wavelengths, and a wide range of switchable receptors for anions have been reported, some of which have been applied to regulating transport. [8] On the other hand, the development of redox responsive systems is motivated by targeting cellular redox environments such as reactive oxygen species and glutathione (both of which are increased during rapid proliferation of cancer cells, for example). In this mini review we highlight the various approaches through which photo-and redox-responsive behavior may be engineered into ion transport systems…”

Molecular Machines For The Control Of Transmembrane Transport

“…In nature, ion transport is mediated primarily by transmembrane protein channels or sophisticated biomolecular machine ion pumps and, to a lesser extent, by mobile carrier (also referred to as ionophores). A wide range of synthetic ion channels and mobile carriers have emerged, , including those with stimuli-responsive behavior. − Channels provide a pore through which ions may flow down their concentration gradient (Figure .i) while mobile carriers shuttle ions across the membrane, via consecutive binding, translocation, and release steps (Figure .ii). A range of different intermolecular interactions have been employed for the binding of ions to promote transport; we direct the reader to recent reviews on metal-organic-based transporters, , hydrogen bonding systems , and transporters utilizing sigma-hole interactions. , For reviews concerning the methods developed for the study of ion transport, we direct the reader to the following. − …”

Dual-Stimulus-Driven Dynamically Controllable [3]Rotaxane with Tunable Organic Room-Temperature Phosphorescence

“…Photochromic molecular switches such as diarylethene, azobenzene, spiropyran, and stiff stilbene (SSB) have been extensively applied in the construction of smart materials with functions of memory storage, anticounterfeiting, photorecording, topological transformation, controlled release, photoswitchable imaging, and so on. − SSB derivatives undergo reversible interconversion of Z and E configurations upon encountering diverse light irradiation, where their geometric structures dramatically change. Based on this, functionalized SSB derivatives have been frequently applied in photoswitchable catalysis, artificial receptors, molecular motors, and G-quadruplex DNA regulators. − In previous research, integration of some SSB groups into macrocyclic hosts enabled fabrication of supramolecular systems for molecular machines and controllable molecular recognition. , Recently, Qu, Feringa, and co-workers developed stiff-stilbene-based motorized macrocyclic hosts regulated by photodriven molecular rotary motors, enabling switchable chiral guest recognition . Wezenberg’s group reported a photoswitchable strapped calix[4]­pyrrole receptor with function of highly effective chloride binding and release .…”