Anion receptors can be used to transport ions across lipid bilayers, which has potential for therapeutic applications. Synthetic bicarbonate transporters are of particular interest, as defects in transmembrane transport of bicarbonate are associated with various diseases. However, no convenient method exists to directly observe bicarbonate transport and study the mechanisms involved. Here, an assay is presented that allows the kinetics of bicarbonate transport into liposomes to be monitored directly and with great sensitivity. The assay utilises an encapsulated europium(III) complex, which exhibits a large increase in emission intensity upon binding bicarbonate. Mechanisms involving CO 2 diffusion and the dissipation of a pH gradient are shown to be able to lead to an increase in bicarbonate concentration within liposomes, without transport of the anion occurring at all. By distinguishing these alternative mechanisms from actual bicarbonate transport, this assay will inform the future development of bicarbonate transporters.

The TFPB "superweak anion" effectively induces the threading of a scarcely preorganized calix[6]arene (1) with weakly interacting tertiary ammonium axles (2(+)-3(+)). The pseudorotaxanes (4(+)-5(+)) thus formed show an unexpected chirality due to an unprecedented formation of a threading-induced stereogenic ammonium center.

“Macrocyclization of Cycles with a Macrocycle.” The intramolecular cooperation of metal centres in a novel dinuclear complex has been postulated as responsible for the observed high rate of formation of macrocyclic polyesters.

Bambusurils are macrocyclic molecules that are known for their high binding affinity and selectivity toward anions. Here, we present the preparation of two bambusurils bearing fluorinated substituents and one carboxylic function. These monofunctionalized bambusurils were conjugated with crown ether and cholesterol units. The resulting conjugates were successfully tested in liquid–liquid extraction of inorganic salts and chloride/bicarbonate transport across lipid bilayers.

An upper-rim functionalized calix[4]arene-based thiourea installed onto the ( R, R)-1,2-cyclohexanediamine scaffold was synthesized with a view to investigate its catalytic ability in enantioselective Michael additions. The reactions were found to conveniently proceed under solvent-free conditions, observing good to high enantioselectivities. From this preliminary study, the calix[4]arene unit is likely to play a role in affecting the conversion and to a lesser extent to the stereochemical outcome of the reactions through van der Waals contacts and C-H···π interactions with the substrates.

The recognition abilities of chiral calixarene hosts toward alkali cation guests have been exploited for the first time in asymmetric phase‐transfer catalysis. The binding affinities of a series of chiral α‐methylbenzylamine‐derived calix[4]arene‐amides toward Na+ guest have been determined by 1H NMR spectroscopic titration experiments. The good apparent association constant values are consistent with the macrocycles' catalytic efficiency in the asymmetric alkylation reaction of N‐(diphenylmethylene)glycine esters under phase‐transfer conditions.

Invited for the cover of this issue are Dr. Stephen Butler, Dr. Hennie Valkenier and co‐workers at Université Libre de Bruxelles, Loughborough University, Masaryk University, and the University of Bristol. The image depicts the transport of bicarbonate anions versus the spontaneous diffusion of CO 2 across the lipid bilayer of a liposome. Read the full text of the article at 10.1002/chem.202100491 .

<p>The transmembrane transport of bicarbonate is a key step in many important biological processes, while problems with bicarbonate transport are at the origin of various diseases. Over the past 10 years, many anionophores that have been developed for the transport of chloride, have also been tested as bicarbonate transporters. However, methodology to directly monitor the kinetics of transport of bicarbonate is lacking, hence indirect methods have been used, which mainly rely on the monitoring of chloride concentrations.</p>Here we present an assay that allows the kinetics of bicarbonate transport into liposomes to be monitored directly, using emission spectroscopy. The assay utilises an encapsulated europium(III) complex, which exhibits a large increase in emission upon binding of bicarbonate. The advantages of this assay over existing methodology are that concentrations of bicarbonate are monitored directly and with a high sensitivity. This allows studies at very low concentrations of anionophores, and for the mechanisms of bicarbonate transport to be unravelled. We have distinguished classical antiport with bicarbonate from mechanisms involving CO₂ diffusion and the dissipation of a pH gradient. Furthermore, the use of a standard fluorescence spectrometer and liposomes with a diameter ~200 nm makes this assay readily and reliably applicable in many laboratories, where it can facilitate the development of bicarbonate transporters for applications in physiological studies or therapies.