Hamburg, Universiẗat, Diss., 2000.

Frankfurt (Main), Universiẗat, Diss., 2001.

No description available.

Ion chromatography (IC) as developed by Small et. al. in 1975 has become an efficient and reliable analytical technique for simultaneous analysis of multiple ions in solution. The principle requirement prior to use the IC for an analysis is sample preparation; these include sample decomposition, solvent extraction, and trapping in case the target element is in the gas phase, etc. Solvent extractions for fluoride, chloride, sodium, ammonium, and potassium ions which are soluble in soils are described. Sample decompositions include silicate rocks using hydrofluoric acid for the determination of phosphorus; organic pesticides using lithium fusion technique for the determination of halide and cyanide ions are also described. After these sample preparation techniques, the aqueous solutions obtained were analyzed on the ion chromatograph for the analyses of the anions and cations mentioned above. Recovery and reproducibility of each technique is in general quite good and the comparison between the results obtained from the IC method and other instrumentation are given.

No description available.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. May 2016. / The thermodynamic and equilibrium data for Na+/RH+ exchange reactions were generated using the batch method. The experimental data is unique in that the reactions were carried out at elevated temperatures (50oC–90oC), using low level counter ion solutions (0.001100–1.258 mg/l, Na+). The equilibrium data was modeled against the non-linear Langmuir and Freundlich isotherm models. The model parameters were determined by an iterative approach, using the ‗SOLVER‘ function of Microsoft Excel. The coefficient of determination, R2 was used to evaluate the goodness of fit. The R2 values for both models were satisfactory (R2 > 0.9) to a certain extent. From the experimental data, the equilibrium parameters; Selectivity coefficient, , and Corrected selectivity coefficient KI were computed. Irrespective of the initial solution concentration, the equilibrium parameters were found to decrease with increasing reaction temperature, indicating a poor uptake of Na+ from solution by candidate ion exchange resins. Thermodynamic parameters; enthalpy of reaction, ΔH (J/mol.K), and entropy, ΔS (J/mol.K) were calculated from the slope and intercept of the Van‘t Hoff plot respectively. The reaction‘s Gibbs free energy change, ΔG was calculated from the values of ΔH, and ΔS, and reaction temperature. Generally, ΔG was positive and increased with increasing reaction temperature, which proved that an elevated reaction temperature favours the reverse reaction. The reactions were found to be exothermic process with negative entropy. The effect of pH on the exchange reactions was also studied. There was a decrease in the equilibrium Na+ concentration in solution after pH conditioning, with a considerable difference when compared with that obtained from reactions without pH conditioning. The equilibrium quotient was used to define the selectivity coefficient for reactions carried out at varying pH. The equilibrium quotient increased across the initial solution concentration and was highest for reactions carried out at 1.258 mg/L. The equilibrium quotient decreased across the pH range, per initial solution concentration, indicating the pH effect. / GR 2016

No description available.

abstract / Chemistry / Doctoral / Doctor of Philosophy

In recent decades, small molecules have been widely applied to the generation of functional ion transporters. Major discoveries disclosed in this thesis include a self-assembled chloride-dependent potassium channel candidate, a physiological chloride and bicarbonate dual-transporter, and a series of efficient synthetic ion transporters. In nature, K+ channels play an important role in Ca2+ signaling, volume regulation, secretion, proliferation, and migration. The extracellular K+ concentration (4 mM) is about 40 times lower than the intracellular K+ concentration (160 mM). The opening of K+ channels consequently generates an efflux of positive charge, which hyperpolarizes or repolarizes the cellular membrane. In this research, by using fluorescence assays, NMR and patch clamp experiments, compound ZHY-CM23 was found to self-assemble into a chloride-dependent K+ selective channel mediating K+ transport across lipid bilayers and cell membranes. In addition, the synthetic K+ channel formed by ZHY-CM23 was found to be capable of generating and modulating the membrane potential of liposomes and to significantly hyperpolarize the resting membrane potential of HEK 293 cells. This finding provides new insight into developing drugs for the treatment of severe human diseases caused by K+ channel malfunction, such as arrhythmia, neurological disorders and autoimmune diseases. Cystic fibrosis is a chronic recessive disease resulting from the loss of function mutations in the gene encoding of the cystic fibrosis transmembrane conductance regulator (CFTR), a member of the ABC family of membrane transporters. Recent findings reveal that restoring bicarbonate transport might be useful for the treatments of the underlying defect in cystic fibrosis. On the basis of fluorescence assays, NMR and short circuit current experiments, the small molecule ZHY-CM11 has been discovered to not only act as a bicarbonate transporter in lipid membranes, but also to induce chloride-dependent bicarbonate secretion in cultured calu-3 epithelia. It is a promising lead compound to be developed for the treatment of cystic fibrosis and other diseases related to chloride and bicarbonate transport defects. Through structural modifications on the bioactive ion channels and the transporters ZHY-CM23 and ZHY-CM11, some valuable information on the structure-activity relationship has been obtained, and a series of potentially biologically applicable synthetic ion transporters have been discovered. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

No description available.