This thesis describes the development of an ion channel system exhibiting dissipative assembly characteristics. In this system an active transporter based on an oligoester fragment terminated in a thioester of 6-aminohexanoic acid (HO2C-Hex-Adip-OctS-Hex-NH2) undergoes thioester cleavage to form a thiol terminated oligoester (HO2C-Hex-ADip-Oct-SH). This fragment was expected to be inactive for ion transport but previous work showed high activity in planar bilayer experiments. In this work, the high activity was shown to be due to the oxidized form of the thiol, the disulfide HO2C-ADip-Oct-SS-Oct-ADip-Hex-CO2H. Air oxidation was found to be quite rapid for the thiol based on ESI-MS (negative ion) and HPLC analysis. Under anaerobic conditions, the thiol fragment was an inactive species for ion transport. In situ air oxidation initiated transport activity associated with the disulfide. The transporter HO2C-Hex-Adip-Oct-Hex-NH2 was active in planar bilayer experiments and was compared to the disulfide via activity grids. The activity of these two compounds was shown to be distinct from each other by conductance and channel duration differences. The activity of HO2C-Hex-Adip-Oct-Hex-NH2 was shown to die off in a period of 30 minutes at pH 8.2. Techniques were developed to stimulate and monitor activity and bilayer quality so that an inactive condition could be confirmed. The addition of Pr-S-Hex-NH3+-Cl as a fuel was shown to extend the activity of HO2C-Hex-Adip-Oct-Hex-NH2 by eight-fold in 1M CsCl electrolyte. Previous work had established the capability of thioester exchange reactions by a reaction between Pr-S-Hex-NH3+-Cl and benzyl thiol in a homogenous solution. The extended activity indicated that the same process may occur in a heterogeneous bilayer system. An inactive system created by the die-off in activity of HO2C-Hex-Adip-Oct-S-Hex-NH2 was treated with Pr-S-Hex-NH3+-Cl to regenerate activity. This cycle could be repeated once the activity died off again. All these findings are consistent with the dissipative assembly of a membrane transport system. / Graduate / 0490

No description available.

Beams of polarized protons play an important part in the study of the spin dependence of the nuclear force by measuring the analyzing power in nuclear reactions. The source at iThemba LABS produces a beam of polarized protons that is pre-accelerated by an injector cyclotron (SPC2) to a energy of 8 MeV before acceleration by the main separated-sector cyclotron to 200 MeV for physics research. The polarized ion source is one of the two external ion sources of SPC2. Inside the ion source hydrogen molecules are dissociated into atoms in the dissociator and cooled to a temperature of approximately 30 K in the nozzle. The atoms are polarized by a pair of sextupole magnets and the nucleus is polarized by RF transitions between hyperfine levels in hydrogen atoms. The atoms are then ionized by electrons in the ionizer. The source has various sensitive devices, which influence beam intensity and polarization. Nitrogen gas is used to prevent recombination of atoms after dissociation. The amount of nitrogen and the temperature at which it is used plays a very important role in optimizing the beam current. The number of electrons released in the ionizer is influenced by the size and shape of the filament. Optimization of the source will ensure that beams of better quality (a better current and stability) are produced.

Kinetic data is presented for a variety of ion-neutral reactions which are relevant to the atmosphere of Titan and to the chemistry occurring in interstellar clouds. The data were recorded with a Selected Ion Flow Tube (SIFT) operating at room temperature (294 ± 4 K) and at a pressure of 0.46 Torr. Results of the recent Cassini-Huygens mission to Saturn and Titan have identified several species in the atmosphere of Titan not predicted by pre-Cassini models of the atmosphere. In order to determine the fate of three of these species (methylenimine, propionitrile and cyanodiacetylene) in Titan's ionosphere, their reactivity with the principal ions in Titan's upper ionosphere has been examined. As expected, collision rate proton transfer reactions dominate the chemistry with association channels also observed with many of the hydrocarbon ions. The results of the Cassini mission also identified several individual reactions as being of potential importance to models of Titan's atmosphere and this chemistry has also been examined. The above studies are also relevant to the interstellar medium where each of the neutral reactants have also been detected. The results of some proton transfer equilibrium studies are also presented. The gas phase basicities of propyne and acetylene have been determined to be 681 kJ mol⁻¹ and 617.4 kJ mol⁻¹ respectively. Their relative proton affinities can be estimated from these values. A combined experimental/theoretical study of the proton affinity of cyanodiacetylene (HC₅N) has enabled this value to be estimated at 770 ± 20 kJ mol⁻¹. Details of an attempt to complete the first laboratory measurement of the crucial reaction between H₃⁺ and atomic carbon are presented. The generation of atomic carbon in sufficient quantities for reaction in the SIFT was not possible with the microwave discharge source used. Other generation methods have also been explored with the laser photolysis of carbon suboxide expected to provide a possible solution to the problems encountered. The results of an investigation into the applicability of lithium ions (Li⁺) to SIFT-MS are presented. The lithium ions associated with each of the twenty-one neutral analytes examined to form pseudo-molecular ions. The association reactions were rapid (k ~ 10⁻⁹ cm³ s⁻¹) for large hydrocarbons but were much slower for smaller analytes (k < 10⁻¹¹ cm³ s⁻¹). In order to clarify some unusual experimental observations, the effect of water molecules on the observed chemistry has been examined in detail. The measured chemistry has important consequences for the applicability of Li⁺ to SIFT-MS where the presence and detection of an identifiable ion of the analyte is essential. Details of new SIFT operating software which can be run on a modern computer are given. Mass spectra and kinetic data recorded with the new software are also presented.

Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 4 uppsatser.

Thesis (M.S.)--University of Michigan, 1968.

Thesis (M.S.)--University of Michigan, 1968.

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 103-117).

Thesis (Ph. D.)--Lehigh University, 1999. / Includes vita. Bibliography: leaves 243-258.

Universiẗat, Diss., 1999--Bremen.