Highly potent but structurally simple transmembrane anion transporters are reported that function at receptor to lipid ratios as low as 1 : 1 000 000. The compounds, based on the simple ortho-phenylenediamine-based bisurea scaffold, have been studied for their ability to facilitate chloride/nitrate and chloride/bicarbonate antiport, and HCl symport processes using a combination of ion selective electrode and fluorescence techniques. In addition, the transmembrane transport of dicarboxylate anions (maleate and fumarate) by the compounds was examined. Molecular dynamics simulations showed that these compounds permeate the membrane more easily than other promising receptors corroborating the experimental efflux data. Moreover, cell based assays revealed that the majority of the compounds showed cytotoxicity in cancer cells, which may be linked to their ability to function as ion transporters.

The transport of anions across biological membranes by small molecules is a growing research field due to the potential therapeutic benefits of these compounds. However, little is known about the exact mechanism by which these drug-like molecules work and which molecular features make a good transporter. An extended series of 1-hexyl-3-phenylthioureas were synthesized, fully characterized (NMR, mass spectrometry, IR and single crystal diffraction) and their anion binding and anion transport properties were assessed using ¹H NMR titration techniques and a variety of vesicle-based experiments. Quantitative structure–activity relationship (QSAR) analysis revealed that the anion binding abilities of the mono-thioureas are dominated by the (hydrogen bond) acidity of the thiourea NH function. Furthermore, mathematical models show that the experimental transmembrane anion transport ability is mainly dependent on the lipophilicity of the transporter (partitioning into the membrane), but smaller contributions of molecular size (diffusion) and hydrogen bond acidity (anion binding) were also present. Finally, we provide the first step towards predictable anion transport by employing the QSAR equations to estimate the transmembrane transport ability of four new compounds.

We report DNA binding studies of the dinuclear ruthenium ligand [{Ru(phen)₂}₂tpphz]⁴⁺ in enantiomerically pure forms. As expected from previous studies of related complexes, both isomers bind with similar affinity to B-DNA and have enhanced luminescence. However, when tested against the G-quadruplex from human telomeres (which we show to form an antiparallel basket structure with a diagonal loop across one end), the ΛΛ isomer binds approximately 40 times more tightly than the ΔΔ, with a stronger luminescence. NMR studies show that the complex binds at both ends of the quadruplex. Modeling studies, based on experimentally derived restraints obtained for the closely related [{Ru(bipy)₂}₂tpphz]⁴⁺, show that the ΛΛ isomer fits neatly under the diagonal loop, whereas the ΔΔ isomer is unable to bind here and binds at the lateral loop end. Molecular dynamics simulations show that the ΔΔ isomer is prevented from binding under the diagonal loop by the rigidity of the loop. We thus present a novel enantioselective binding substrate for antiparallel basket G-quadruplexes, with features that make it a useful tool for quadruplex studies.