Dissecting transmembrane bicarbonate transport by 1,8-di(thio)amidocarbazoles

Therapeutic synthetic anion transporters

This short review highlights recent examples of small-molecule anion transporters reported in the literature that have potentially useful biological activity. This includes anionophores with antibiotic or antifungal activity, anticancer activity, or the potential to treat channelopathies such as cystic fibrosis. Additionally selective and targeted anion transporters are also discussed.

Synthetic transporters for oxoanions

This brief review highlights recent advances in the transport of oxoanions using synthetic carriers, focusing on both progress and ongoing challenges in the field. The difficulty of transporting these oxoanions increases with their hydration enthalpies, with less hydrated nitrate and perchlorate being relatively easy to transport. Recent progress has focused on the transport of moderately hydrated anions such as bicarbonate and carboxylates, where studies are influenced by the free diffusion of neutral species obtained by (de)protonation equilibria. Despite significant innovations in the design of synthetic carriers, the transport of the highly hydrated oxoanions sulfate and phosphate remains a major challenge. Progress on sulfate transport has stalled, while the first example of phosphate transport was reported only last year.

A new generation of 1,8-diaminocarbazole building blocks for the construction of fluorescent anion receptors

We describe the synthesis of a new generation of 1,8-diaminocarbazole building blocks for the construction of anion receptors and fluorescent sensors. These new building blocks feature mildly electron-withdrawing ester substituents at positions 3 and 6 of the carbazole core, which improve anion affinities and significantly enhance solubilities, without compromising fluorescent response. To demonstrate the advantages of the new building blocks, three of them were converted into model diamide receptors R1-R3. The resulting ester-substituted receptors showed greatly improved solubilities and fluorescent response in comparison to their 3,6-dichloro-substituted predecessors, while retaining very high affinity and selectivity for oxyanions, particularly dihydrogen phosphate, even in partially aqueous solutions. In view of these promising results and the known synthetic versatility of primary amines, we envisage that the new building blocks will be useful for the construction of various classes of fluorescent anion receptors with improved solubility, affinity, and fluorescent response.

A photocaged, pH-sensitive anion transporter with AND logic dual-stimuli activation

A pH-switchable anion transporter 1 was photocaged with two photolabile groups to enhance spatiotemporal control over its chloride transport activity. Simultaneous application of light irradiation and acidic pH restores the activity of 1, while either stimulus alone results in no or very low activity. The double activation strategy described herein has potential to yield more selectively cytotoxic anionophores for future medical applications.

Pyridyl-Linked Hetero Hydrazones: Transmembrane H+/Cl- Symporters with Efficient Antibacterial Activity

The development of potent antibacterial agents has become increasingly difficult as bacteria continue to evolve and develop resistance to antibiotics. It is therefore imperative to find effective antimicrobial agents that can address the evolving challenges posed by infectious diseases and antimicrobial resistance. Using artificial transmembrane ion transporters is an emerging and promising avenue to address this issue. We report pyridyl-linked hetero hydrazones as highly efficient transmembrane HCl symporters. These compounds offer an appropriate HCl binding site through cooperative protonation, followed by recognition of chloride ions. HCl transport by these compounds inhibits the growth of different Gram-negative bacterial strains with high efficacy by affecting the cell envelope homeostasis. This specific class of compounds holds substantial promise in the ongoing pursuit of developing highly efficient antibacterial agents.

Transmembrane transport of fluoride studied by time-resolved emission spectroscopy

Here we present a new method to monitor fluoride transmembrane transport into liposomes using a europium(III) complex. We take advantage of the long emission lifetime of this probe to measure the transport activity of a fluorescent transporter. The high sensitivity, selectivity, and versatility of the assay allowed us to study different types of fluoride transporters and unravel their mechanisms of action.

Transmembrane Transport of Bicarbonate by Anion Receptors

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.