The design of synthetic transmembrane carriers for anions

Abstract

This thesis reports a number of novel receptors found to facilitate the transmembrane transport of anions in synthetic vesicle systems. A series of structurally simple thioureas were found to function as efficient Cl-/NO3- and Cl-/HCO3- antiporters while the corresponding ureas were inactive. Of these receptors, a simple indolylthiourea was found to be an extremely potent transporter which could function at concentrations as low as 1:25 000 (molar ratio with respect to lipid). Subsequently, a series of bipodal bis-alkyl-indolylureas were found to mediate Cl-/NO3 - antiport, with the observed anion transport found to be highly dependent on the length of the central alkyl chain bridging the two indolylurea moieties. The mechanism of transport and the structure-activity relationships were extensively investigated using a wide range of vesicle-based techniques. The solution phase anion binding properties of these receptors was found to be complex as a result of the flexibility of the receptors and the distance between the binding sites. The binding of dihydrogen phosphate and oxalate by receptors in this series was also demonstrated in the solid state. A series of bipodal bis-phenylthioureas were also found to mediate Cl-/NO3 - and Cl-/HCO3- antiport which was again found to be dependent on the alkyl chain length. The effect of substituent variation on transport activity was also examined, while the solution phase binding properties were found to be similarly complex to the bis-indolylurea receptors. The anion transport activity of a series of strapped calix[4]pyrroles provided by J. L. Sessler and C.-H. Lee was investigated. It was found that the straps were able to encourage transport mechanisms not exhibited by the parent macrocycle, while a series of control compounds were inactive

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ORCID for Philip A. Gale: orcid.org/0000-0001-9751-4910

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