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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Non-aqueous, capillary electrophoretic separations of enantiomers with a charged cyclodextrin highly-soluble in organic solvents

Sanchez Vindas, Silvia Elena 01 November 2005 (has links)
The synthesis of the sodium salt of heptakis (2, 3-di-O-acetyl-6-O-sulfo)-β-cyclodextrin was modified to increase the isomeric purity to 98.5%. This salt was used to obtain the organic-solvent-soluble, single-isomer, charged tetrabutylammonium salt of heptakis (2, 3-di-O-acetyl-6-O-sulfo)-β-cyclodextrin. Its isomeric purity was higher than 99%, as determined by CE, and its structure was confirmed by NMR and ESI-MS analysis. The hydrophobic single-isomer cyclodextrin was utilized to separate the enantiomers of weak base analytes in aprotic media by capillary electrophoresis. The effective mobilities and separation selectivities follow trends observed with negatively charged cyclodextrins in amphiprotic solvents. The properties of the dissolved cyclodextrin are altered by its counter ion, thereby affecting the separations of enantiomers. The aprotic media allow the modification of the separation selectivity, since the binding strength of the enantiomers to the cyclodextrin is intermediate between that reported in aqueous and methanolic buffers.
22

Non-aqueous, capillary electrophoretic separations of enantiomers with a charged cyclodextrin highly-soluble in organic solvents

Sanchez Vindas, Silvia Elena 01 November 2005 (has links)
The synthesis of the sodium salt of heptakis (2, 3-di-O-acetyl-6-O-sulfo)-β-cyclodextrin was modified to increase the isomeric purity to 98.5%. This salt was used to obtain the organic-solvent-soluble, single-isomer, charged tetrabutylammonium salt of heptakis (2, 3-di-O-acetyl-6-O-sulfo)-β-cyclodextrin. Its isomeric purity was higher than 99%, as determined by CE, and its structure was confirmed by NMR and ESI-MS analysis. The hydrophobic single-isomer cyclodextrin was utilized to separate the enantiomers of weak base analytes in aprotic media by capillary electrophoresis. The effective mobilities and separation selectivities follow trends observed with negatively charged cyclodextrins in amphiprotic solvents. The properties of the dissolved cyclodextrin are altered by its counter ion, thereby affecting the separations of enantiomers. The aprotic media allow the modification of the separation selectivity, since the binding strength of the enantiomers to the cyclodextrin is intermediate between that reported in aqueous and methanolic buffers.
23

Effects of Cyclodextrins on the Kinetics of Emulsion Polymerisation

El-Hadad, Omar January 2009 (has links)
Cyclodextrins (CD) are semi-natural oligosaccharides composed of a number of D-glucose units. They are produced from renewable resources, and have been found to be of catalytic effect for the emulsion polymerization of many monomers. Using monomers whose emulsion polymerization kinetics have been thoroughly studied, this research analyses the effect of CD on the entry and exit rate coefficients for the emulsion polymerization of styrene, and the entry and termination rate coefficients for the emulsion polymerization of MMA. Throughout the course of the work, CD was found to have a positive impact on the polymerization rate of styrene in a polystyrene latex stabilized with a cationic surfactant. Furthermore, the exit rate coefficient for this latex was found, via γ-relaxation experiments, to increase in proportion to the styrene solubility in water, exactly as predicted by theory. Of itself this would lead to a decrease in reaction rate. That there is still an overall increase in the reaction rate in the presence of CD is because of a quite strong effect on entry rate coefficients. Again, this is consistent with the prevailing theory for entry, that of Maxwell and Morrison, which says that increased aqueous phase solubility of monomer will lead to faster entry. Intriguingly, experiments done on a polystyrene latex stabilized with an anionic surfactant showed a different effect for CD: γ-relaxation experiments found very little effect of CD on exit rate, and chemically initiated experiments found the same for overall rate. This is consistent with CD having little effect on aqueous phase styrene solubility, which in fact is what direct measurements via UV-visible spectroscopy indicated. It is speculated that the anionic surfactant was successfully competing with styrene to occupy the CD cavities. On the other hand, measurements suggested that styrene successfully competes with cationic surfactant, which is consistent with kinetic results. Experiments of the above nature were then carried out with methyl methacrylate (MMA), a more water soluble monomer than styrene and one with emulsion polymerisation kinetics of a different nature (so-called pseudo-bulk). γ-relaxation experiments found no effect of CD on termination rate coefficients, exactly as one would expect given that termination is an intra-particle reaction whereas CD exists in the aqueous phase. However the same experiments also revealed an unexpected effect of CD on entry: the thermal entry rate coefficient was found to increase markedly in the presence of CD. It seems likely that this unusual effect stems from interaction of products of γ radiolysis with CD. Results for chemically-initiated polymerization of MMA were inconclusive. Under some conditions there was actually retardation in the presence of CD, which is actually consistent with measurements of MMA solubility in water, which suggested a slightly negative effect of CD. However it is hard to explain such a phenomenon. Further, under other conditions it was found that CD either had no effect on chemically-initiated rate or could even increase it slightly. The only safe conclusion at this stage is that CD has no major effect on MMA kinetics, which arguably is consistent with MMA being relatively water soluble: intuitively one would expect that CD is most useful (‘catalytic’) for the EP of monomers of low solubility.
24

Modified cyclodextrins and their complexes / Suzanna Dawn Kean.

Kean, Suzanna Dawn January 1999 (has links)
Addendum page pasted onto front end paper. / Copies of author's previously published articles inserted. / Includes bibliographical references. / x, 204 leaves : ill. (many col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Investigates the factors that govern the stability of cyclodextrin inclusion complexes with a range of systematically modified cyclodextrins. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemistry, 2000
25

Modified cyclodextrins and their complexes /

Kean, Suzanna Dawn. January 1999 (has links) (PDF)
Thesis (Ph.D.) -- University of Adelaide, Dept. of Chemistry, 2000. / Addendum page pasted onto front end paper. Copies of author's previously published articles inserted. Includes bibliographical references.
26

Cyclodextrins : molecular wheels for supramolecular chemistry /

Lock, Julia. January 2004 (has links) (PDF)
Thesis (Ph.D.)--University of Adelaide, School of Chemistry and Physics, Discipline of Chemistry, 2005? / "July 2004" Includes copies of publications by the author as appendix. Includes bibliographical references.
27

Thin-layer chromatography on cyclodextrins

Sittichai, Nantana. January 1974 (has links)
Thesis (M.S.)--University of Wisconsin--Madison, 1974. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 60-63).
28

Modified cyclodextrins and their complexes

Kean, Suzanna Dawn. January 1999 (has links) (PDF)
Addendum page pasted onto front end paper. Copies of author's previously published articles inserted. Includes bibliographical references. Investigates the factors that govern the stability of cyclodextrin inclusion complexes with a range of systematically modified cyclodextrins.
29

Synthesis, characterization and capillary electrophoretic studies of thiolated [alpha]-cyclodextrin-capped gold nanoparticles

Paau, Man Chin 01 January 2009 (has links)
No description available.
30

Thermal and photostability studies of triprolidine hydrochloride and its mixtures with cyclodextrin and glucose

Ndlebe, Vuyelwa Jacqueline January 2004 (has links)
Triprolidine hydrochloride (C₁₉H₂₂N₂.HCl.H₂O) (TPH) is a well-known antihistamine drug. It melts between 118°C and 122°C and the amount of water present is 4.5 mass percent. TPH is reported as being photosensitive and must be stored in sealed, light-tight containers. The thermal stabilities of TPH and of 1:1 molar and 1:1 mass ratio physical mixtures of TPH with beta-cyclodextrin (BCD) and with glucose have been examined using DSC, TG and TG-FTIR, complemented by X-ray powder diffraction (XRD) and infrared spectroscopic (IR) studies. Thermal studies of the solid TPH/BCD mixtures indicated that interaction between the components occurs and it is possible that the TPH molecule may be least partially accommodated in the cavity of the BCD host molecule. XRD results support this indication of inclusion. The results for mixtures of TPH/glucose also suggest that there is interaction between the two components. The results of molecular modelling suggest that TPH is most likely to be accommodated in the BCD cavity as a neutral triprolidine molecule with the toluene portion of the molecule entering first. There is also an indication that the Z-isomer should be accommodated slightly more readily than the E-isomer. Photostability studies were done by irradiating thin layers of solid samples of TPH and its mixtures for various times at 40°C using an Atlas Sun test CPS lamp operating at 550 W h m⁻². An analytical method using HPLC was developed and validated to determine the amounts of any photodegradants. DSC, TG, FTIR, XRD and IR were also used examine the irradiated samples. XRD results showed that changes in the TPH crystal structure occurred during irradiation and that these changes increased with the time of irradiation. Irradiation for 20 hours with UV or exposure to sunlight showed the presence of degradants. The results obtained illustrate the general stability of TPH, especially in the solid state. Although the potential for isomerization to the pharmaceutically inactive Z-isomer exists, this transformation would require extreme light conditions. The study has also shown TPH to be compatible with both glucose and BCD, which are potential excipients both in solid and liquid dosage forms. The presents of these excipients in dosage forms will thus not adversely affect the stability and the therapeutic efficacy of TPH. . An analytical method using HPLC was developed and validated to determine the amounts of any photodegradants. DSC, TG, FTIR, XRD and IR were also used examine the irradiated samples. XRD results showed that changes in the TPH crystal structure occurred during irradiation and that these changes increased with the time of irradiation. Irradiation for 20 hours with UV or exposure to sunlight showed the presence of degradants.

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