Thumbnail Image
Publication or External Link
Okunola, Oluyomi Adeola
Davis, Jeffery T
Functional, "small" molecule anion transporters have been identified and developed from natural products and synthetic organic compounds. The major discoveries include the design of a transmembrane Cl<super>-</super> transporter whose activity is pH-tunable, a NO<sub>3</sub><super>-</super> transporter that displays unique selectivity for NO<sub>3</sub><super>-</super> over Cl<super>-</super> anions, and a series of small molecules that efficiently transport HCO<sub>3</sub><super>-</super> across liposomal membranes via a HCO<sub>3</sub><super>-</super>/Cl<super>-</super> exchange mechanism. An assay for detecting transmembrane HCO<sub>3</sub><super>-</super> transport using paramagnetic Mn<super>2+</super> and <super>13</super>C NMR is also described. Modulated Cl<super>-</super> transport was achieved by lipophilic calix[4]arene amides <bold>2.2-2.4</bold>, all in the cone conformation. Modulation was achieved through functional group modification to one of the four side-chains. The cone conformation was confirmed by both <super>1</super>H NMR and X-ray crystallography. Significantly, Cl<super>-</super> transport was gated by pH in the presence of triamido calixarene TAC-OH <bold>2.3</bold>, which possesses a phenolic hydroxyl group. Using fluorescence assays, the rate of Cl<super>-</super> transport by TAC-OH <bold>2.3</bold> across liposomal membranes decreased with increasing pH, while transport rate by cone-H <bold>2.2a</bold>, lacking an OH group, was not affected by pH. Nitrate was selectively transported over Cl<super>-</super> in the presence of nitro tripod <bold>3.1</bold>, a small molecule receptor for both anions. The selective transport of NO<sub>3</sub><super>-</super> by <bold>3.1</bold> is a significant discovery as most known synthetic Cl<super>-</super> transporters also transport NO<sub>3</sub><super>-</super> ions and vice versa. Nitrate transport across liposomal membranes was confirmed by enzyme-coupled and fluorescence assays. Tripod <bold>3.1</bold> induced an increase in the intravesicular pH of liposomes that were not experiencing a pH gradient, while no pH changes occurred in the presence of calixarene <bold>2.1</bold> a known Cl<super>-</super> and NO<sub>3</sub><super>-</super> transporter. This result suggests that <bold>3.1</bold> is an H<super>+</super>/NO<sub>3</sub><super>-</super> symporter. Transmembrane HCO<sub>3</sub><super>-</super> transport was achieved using the natural product, prodigiosin, <bold>4.1</bold>, and synthetic isophthalamides <bold>4.2-4.4</bold>. The Cl<super>-</super>/HCO<sub>3</sub><super>-</super> exchange mechanism by which compounds <bold>4.1-4.4</bold> transport HCO<sub>3</sub><super>-</super> was elucidated by ISE and NMR assays. The <super>13</super>C NMR assay provided direct evidence for HCO<sub>3</sub><super>-</super> transport in the presence of paramagnetic Mn<super>2+</super> ions, and was adaptable to various assay conditions.