Carbazole-Based Colorimetric Anion Sensors

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.

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

Synthetic ionophores able to transport bicarbonate and chloride anions across lipid bilayers are appealing for their wide range of potential biological applications. We have studied the bicarbonate and chloride transport by carbazoles with two amido/thioamido groups using a bicarbonate-sensitive europium(III) probe in liposomes and found a highly remarkable transporter concentration dependence. This can be explained by a combination of two distinct transport mechanisms: HCO₃^-/Cl^- exchange and a combination of unassisted CO₂ diffusion and HCl transport, of which the respective contributions were quantified. The compounds studied were found to be highly potent HCl transporters. Based on the mechanistic insights on anion transport, we have tested the antimicrobial activity of these compounds and found a good correlation with their ion transport properties and a high activity against Gram-positive bacteria.