Use of Synthetic Transporters to Facilitate Anion Transport across Vesicle and Cell Membranes

This dissertation describes three classes of synthetic anion transporters which facilitate chloride transport across vesicle and cell membranes. Fluorescent and potentiometric transport assays uncovered the important structural features that produce high transport rates, and the effect of the transporters on cell functions was also evaluated. The first class of transporters is the cholates, which use a mobile carrier mechanism to transport chloride across membranes via an anion exchange process. As a general trend, the better anion binder is the better transporter and that the combination of a lipophilic backbone with a preorganized binding pocket produces excellent chloride transporters with high anion binding affinity and high transport at low cholate concentration. The second class of transporters is the prodigiosin mimics, consisting of synthetic pyrrole and pyridine transporters. Both sets of transporters use a mobile carrier mechanism to promote two transport processes, anion exchange and HCl co-transport, attributed to the pH sensitive imidazole substituent. Subtle structural changes greatly impact the transporter conformation and lipophilicity, which directly alters transport rates. The third class of transporters employs a synthetic phospholipid that is functionalized with an anion binding affinity group. Mechanistic studies indicate that transport occurs via a novel anion relay mechanism, combining the anion selectivity of a mobile carrier with the membrane spanning ability of channels. The kinetically active aggregate complex is composed of two or four monomer units, depending on bilayer thickness, and transport stops upon reaching a threshold bilayer thickness. Finally, investigations of transporter function in cells reveals that the transporters act on mitochondria and late endosomes/lysosomes, depending on their chloride and HCl transport ability, respectively. This research has improved the mechanistic understanding of three different transporter designs and identified their effects on cellular function, suggesting that they have potential applications in cell biology research.