Fluorinated tetrapodal anion transporters

Substituent effects of fluorinated bambusurils on their anion transport

Anionophores are molecules that can transport ions across membranes. Several structural design criteria must be met for anionophores to be highly active. Fluorinated anionophores are usually more potent than their non-fluorinated analogues due to their higher lipophilicity and increased affinity for anions. Clear structure-activity relationships have been described for small and relatively simple anionophores. However, such studies are more challenging for large and macrocyclic anionophores, as their preparation is usually more complicated, limiting the number of compounds tested in anion transport studies. Here we present a series of twelve macrocyclic bambusuril anion transporters to investigate how variations in fluorinated substituents affect their transport properties. Measurements of Cl-/HCO3- antiport activities in liposomes revealed links between parameters such as lipophilicity or substituent polarity and transport activity. For some bambusurils, an unusually large effect of the presence of cholesterol in the membrane on transport activity was found. Further studies showed that for very potent anion receptors, such as the bambusurils described here, the binding selectivity towards anions becomes more important than the absolute binding affinity to anions when considering anion exchange across the membrane.

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.

Molecular clips with spatially proximal urea residues for efficient transmembrane co-transport of H+/Cl- ions

We report the design of bis(urea) functionalized amphiphilic molecular clips viz. 1a-1e to achieve efficient transmembrane co-transport of H+/Cl- ions. The most promising molecule 1a demonstrated a low nanomolar EC50 value (6.96 nM) to co-transport H+/Cl- ions via a carrier-mediated pathway and showed selective toxicity against cancerous HeLa cells as a result.