Control of Photoisomerization of an Azoazacryptand by Anion Binding and Cucurbit[8]uril Encapsulation in an Aqueous Solution.

Control of isomerization of a receptor bearing multiple light-switchable subunits in a confined space is critical for the design of synthetic molecular machines. Toward this goal, a new azacryptand containing three azobenzene subunits has been developed, and its photoisomerization in an aqueous solution has been studied depending on anion coordination and recognition by a larger host-cucurbit[8]uril (CB[8]). The cryptand in its hexaprotonated form shows considerable affinity for fluoride and perchlorate, which in turn affects the isomer distribution of the receptor under UV-light irradiation, stabilizing the isomers of the cryptand with Z-configurations. CB[8] was found to be able to encapsulate the isomers of the cryptand by forming a Matryoshka-type complex. The irradiation of a 10:1 CB[8]-cryptand mixture has led to a selective conversion of the cryptand to the E,E,Z isomer inside CB[8]. It has been demonstrated that the addition of fluoride to the resulted complex induces the release of the cryptand as a major E,E,E isomer, while other studied anions were ineffective in this reaction. To our knowledge, this work presents a first example of a host-controlled photoisomerization of an anion receptor bearing multiple switching azobenzenes that model the function of naturally occurring chaperones.

Anthracene-Based Amido-Amine Cage Receptor for Anion Recognition under Neutral Aqueous Conditions.

Invited for this month's cover picture is the group of Evgeny A. Kataev at the Technical University Chemnitz. The cover picture shows the authors' association of fluorescence anion sensing with pearl hunting - the activity of recovering pearls from wild molluscs. In the presented work, the group of Kataev has developed a new water-soluble amido-amine azacryptand bearing a fluorescence anthracene dicarboxamide fragment. With the help of the fluorescent receptors (a hand) one can catch the phosphate anion (a glowing pearl) and visualize this binding event. The recognition of phosphate and oxalate has led to a fluorescent enhancement in a selective manner. Read the full text of their Communication at https://doi.org/10.1002/open.201900309.

Anthracene-Based Amido-Amine Cage Receptor for Anion Recognition under Neutral Aqueous Conditions.

A new amido-amine cage receptor, which combines 1,8-anthracene diacarboxamide subunit and a polyammonium azamacrocycle, is reported. Bearing both the hydrogen bond donor and the acceptor binding sites, the receptor is able to bind phosphate selectively under neutral (pH 7.2) aqueous conditions. The recognition events for phosphate and dicarboxylates are accomplished by a fluorescence enhancement in the anthracene emission. As revealed by experimental and theoretical studies, phosphate and oxalate show different recognition modes. Phosphate demonstrates hydrogen bond acceptor properties, while the coordination of oxalate favours the protonation of the receptor.

Anthracene-Based Receptors with a Turn-on Fluorescence Response for Nitrate.

Herein we describe the design, synthesis, and anion binding properties of bicyclic receptors with two or three anthracenes, which show a turn-on fluorescence response in the presence of nitrate and chaotropic anions in a buffered aqueous solution. The receptor with two anthracenes binds nitrate with 103 M-1 affinity and stabilizes it in the inner cavity though electrostatic, hydrogen bonding, and anion-π interactions.

Selective recognition of oxalate in water: effect of pH on binding strength and sensing mechanisms.

Bicyclic receptors bearing anthracene as a strap were designed for selective oxalate binding in a buffered aqueous solution. The receptors were found to possess two mechanisms of fluorescence response depending on the pH of a buffered solution. Receptor 2 binds oxalate at pH 6.2 showing a 10-fold fluorescence enhancement and a two orders of magnitude selectivity over other anions.

Design of anion-selective PET probes based on azacryptands: the effect of pH on binding and fluorescence properties.

Design of PET probes for anions working in an aqueous buffered solution is described. The design has been used to develop selective fluorescent probes for sulfate and pyrophosphate. The relationship between the selectivity of receptors towards anions, their conformation, fluorescence response and the pH of the solution has been studied in detail.