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.

We disclose the results of our investigations on the influence that the insertion method of aryl‐extended calix[4]pyrrole into liposomal membranes exerts on their properties as anion carriers. We use the standard HPTS assay to assess the transport properties of the carriers. We show that the post‐insertion of the carrier, as DMSO solution, assigns better transport activities to the “two‐wall” α,α‐aryl‐extended calix[4]pyrrole 1 compared to the “four‐wall” α,α,α,α‐counterpart 2 . Notably, opposite results were obtained when the carriers were pre‐inserted into the liposomal membranes. We assign this difference to an improved incorporation of carrier 2 into the membrane when delivered by the pre‐insertion method. On the other hand, carrier 1 shows comparable levels of transport independently of the method used for its incorporation. Thus, an accurate comparison of the chloride transport activities featured by these two carriers demands their pre‐incorporation in the liposomal membranes. In contrast, using the lucigenin assay with the pre‐insertion method both carriers displayed similar transport efficiencies.

A calix[6]arene with three preorganised halogen bond donating groups gives >100-fold selectivity for Cl− uniport over HCl symport, in contrast to analogous compounds with strong hydrogen bond donating groups.

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Synthetic anion transporters can be developed using anion receptors that are able to bind the anion and stabilize it in the lipophilic interior of a bilayer membrane, and they usually...

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.

Small peptides and peptomimetic compounds are valuable tools to probe and study biological systems. Small synthetic peptide analogues adopt a given secondary structure driven by structural modules that organize the compound architecture. Among them, β‐ and α‐turn mimetics are widely used. This work reports SQ4 and SQ5 squaramido‐based turn modules that combine tertiary and secondary squaramide bonds in their structure to control their conformational properties. The efficacy of this combination has been evaluated to promote folding in peptide‐like compounds to obtain parallel and antiparallel‐hairpin model compounds in hydrogen‐bonding competitive media. Crystallographic structures of model compounds and conformational studies based on NMR spectroscopic analysis of the squaramido‐peptides confirm that secondary‐tertiary squaramides are more prone to adopt the E,Z‐conformation than di‐secondary squaramides, and consequently are more suitable to gain conformational control over foldable peptidomimetic compounds.

The development of synthetic anion transporters is motivated by their potential application as treatment for diseases that originate from deficient anion transport by natural proteins. Transport of bicarbonate is important for crucial biological functions such as respiration and digestion. Despite this biological relevance, bicarbonate transport has not been as widely studied as chloride transport. Herein we present an overview of the synthetic receptors that have been studied as bicarbonate transporters, together with the different assays used to perform transport studies in large unilamellar vesicles. We highlight the most active transporters and comment on the nature of the functional groups present in active and inactive compounds. We also address recent mechanistic studies that have revealed different processes that can lead to net transport of bicarbonate, as well as studies reported in cells and tissues, and comment on the key challenges for the further development of bicarbonate transporters.