Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 186-198).

Thesis (Ph.D.)--McMaster University, 2004. / Adviser: Bernardo Trigatti. Includes bibliographical references (leaves 153-178). Also available online.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 130-155). Also available on the Internet.

Thesis (PhD) - Environment and Biotechnology Centre, Faculty of Life and Social Sciences, Swinburne University of Technology, 2008. / Submitted for the degree of Doctor of Philosophy, Environment and Biotechnology Centre, Faculty of Life and Social Sciences, Swinburne University of Technology, 2008. Typescript. Includes bibliographical references (p. 215-247)

The synthesis and characterization of simple mimics of pore forming antibiotics such as amphotericin B were explored. A sub-unit approach to the synthesis was employed which allowed for construction of a set of candidate structures. The targets are assembled by joining two "wall" units via a "linkage" unit with subsequent addition of polar head groups to either end of the structure. The wall units are macrocyclic diene tetraesters derived from maleic anhydride prepared by either acid catalyzed ester formation from diols or carboxylate substitution of dihalides (compounds 14, 15, 22, 23, 24, 30, 31, 34). Either set of reaction conditions limit the range of functionality possible in the starting diol or dihalide. Macrocycles 22, 23, and 24 were linked with m-xylylene dithiol via a 2:1 Michael addition reaction to give bis-macrocyclic alkene precursors. Alternatively, macrocycles 22 and 23 reacted with 3-thio-1-propanol and the mono-alcohol products were converted to iodides which were linked with 2R,3R-(+)-tartaric acid. Three types of polar head groups--neutral (1-thio-β-D-glucose and 3-thio-1-propanol), cationic (2-aminoethanethiol), and anionic (2-thioacetic acid)--were added to the bis-macrocyclic alkene precursors via Michael addition reactions. A total of fourteen candidate structures were prepared for transport evaluation. The activity of the fourteen mimics synthesized were determined by the pH-stat technique in which the transport of alkali metal cations across large unilamellar lipid bilayer vesicles were monitored by the collapse of a proton gradient. All the active compounds showed a zero order decay in proton gradient. Of the fourteen mimics surveyed, three had activities comparable to amphotericin B (compounds 51, 52, and 59). The other eleven compounds were not sufficiently active for further characterization. The "add back" experiments, the kinetic orders, and the alkali metal ion selectivity studies are consistent with the proposal that the mimics behave as pore formers. / Graduate

No description available.

The cellular mechanisms responsible for rectal acidification in the desert locust, Schistocerca gregaria, were investigated in isolated recta mounted as flat sheets in modified Ussing chambers. In the absence of exogenous CO₂, HCO₃⁻, and phosphate, the isolated rectum (under both open- and short-circuit current conditions) was capable of rates of net acid secretion (J[subscript]H+) similar to those observed in vivo, demonstrating the viability of the preparation and suggesting that rectal acidification was due to proton secretion rather than selective movements of HCO₃⁻ or phosphate. The possibility that trace levels of metabolic CO₂ might be generating sufficient HCO₃⁻ to account for the observed rates of rectal acidification (via HCO₃⁻ reabsorption) was assessed by adding exogenous CO₂/HCO₃⁻ to the contraluminal bath. The small increases in J[subscript]H+ observed after addition of 2% or 5% CO₂ were shown to be due to simple hydration of CO₂ which had diffused into the lumen (from the contraluminal bath), rather than changes in rates of HCO₃⁻ reabsorption. Since measurable quantities of luminal HCO₃⁻ did not directly affect the apical acid/base transport mechanism per se, it was concluded that metabolic CO₂ could not generate sufficient HCO₃⁻ in the lumen to account for the rates of rectal acidification observed under nominally CO₂/HCO₃⁻-free conditions and that J[subscript]H+ must be due to a proton secretory rather than bicarbonate reabsorptive mechanism. Microelectrode measurements of intracellular pH (pHi) and apical and basolateral membrane potentials (Va and Vb respectively) indicated that luminal pH was not in equilibrium with either contraluminal pH or pHi and that the mechanism responsible for active luminal acid secretion resided on the apical membrane. Preliminary measurements of bath total ammonia (ie. NH₃ + NH₄+) levels in the previous experiments suggested that the rectum was actively secreting ammonia at significant rates across the apical membrane into the lumen. If the ammonia crossed the apical membrane as NH₃ rather than NH₄+, rates of luminal ammonia secretion (J[subscript]Amm) would have to be added to J[subscript]H+ to obtain corrected values of luminal proton secretion. In the absence of exogenously added ammonia and CO₂, ammonia was preferentially secreted into the lumen under both open- and short-circuit current conditions. J[subscript]Amm was dependent on the presence of luminal amino acids and was relatively unaffected by K[superscript]+ removal or changes in luminal pH from 7.00 to 5.00. Bilateral Na+ substitution or luminal addition of ImM amiloride reduced J[subscript]Amm by 63% and 65% respectively. The data consistently demonstrate that the rectum secretes significant quantities of endogenously produced ammonia preferentially into the lumen as NH₄+ rather than NH₃ via an apical Na[superscript]+/NH₄[superscript]+ exchange mechanism. Clearly, rates of net acid secretion estimated by titratable acidity do not have to include a correction for luminal ammonia secretion. Although J[subscript]H+ was completely unaffected by changes in contraluminal pH, it could be progressively reduced (and eventually abolished) by imposition of either transepithelial pH gradients (lumen acid) or transepithelial electrical gradients (lumen positive). Under short-circuit current conditions, the bulk of J[subscript]H+ was not dependent on Na[superscript]+, K[superscript]+, CI⁻, Mg₂+, or Ca+ and was due to a primary electrogenic proton translocating mechanism located on the apical membrane. A small component (10-16%) of J[subscript]H+ measured under these conditions could be attributed to an apical amiloride-inhibitable Na[superscript]+/H[superscript]+ exchange mechanism. Inhibition of JH+ by anoxia or reduction of luminal pH unmasked a significant proton diffusional pathway on the apical membrane in parallel with the active proton pump. The fact that J[subscript]H+ was significantly inhibited (42%-66%) by contraluminal addition of ImM cAMP and relatively unaffected by changes in contraluminal pCO₂ or pH suggests that net acid secretion in the locust rectum in vivo is modulated by circulating hormonal factors rather than haemolymph pH or pCO₂ per se. / Science, Faculty of / Zoology, Department of / Graduate

The effects of pentachlorophenol (PCP), a widely used pesticide, on the electrical characteristics of lipid bilayer membranes has been studied. When a small amount of PCP (even at a concentration of a few micromoles per liter) is present in the electrolytic solution surrounding the membrane, the electrical conductivity of the membrane significantly increases. The present work was concerned with detailed measurements of the changes in the conductivity caused by PCP under chemically controlled conditions. The experimental results were analyzed to determine the permanent species in the membrane, and an attempt was made to correlate the data with existing models of transport.

The effect of the following pesticides on DC electrical conductivity of lecithin-cholesterol membranes has been studied: endothall, paraquat, diquat, 2,4-D, 2,4-DB, 2,4,5-T, 2,4-DCP. It has been found that the ions of endothall, paraquat and diquat are essentially membrane impermeable and that they do not bind to the membrane surface. In contrast, 2,4-D, 2,4-DB, 2,4,5-T and 2,4-DCP induce electrical conductivity in lecithincholesterol membranes and in addition they also cause an increase in the nonactin-K+ membrane conductivity. The compounds 2,4-D, 2,4-DB, 2,4,5-T and 2,4-DCP basically behave as class II uncouplers. The kinetic scheme of charge transfer across the membrane, based on the assumption that the membrane is permeable both to the negatively charged dimers and to the neutral molecules of pesticides, satisfactorily explains the basic features of the experimental results: the concentration dependence of pesticide-induced membrane conductance, effect of proton concentration on membrane conductance, and the effect of pesticide concentration on the voltage dependence of membrane conductance. It fails to predict the effect of proton concentration on the voltage dependence of membrane conductance. The enhancement of nonactin-K+ membrane conductance by the pesticide is presumably due to the adsorption of the ionized form of the pesticide at the membrane surface. It was found that the Gouy-Chapman diffuse double layer theory was not applicable for the calculation of surface membrane potential due to the adsorbed ions.