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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

Surface Chemistry of C3H3 Groups on Ag(111) : Bond Dissociation, Formation and Rearrangement

Kung, Hsuan 25 July 2007 (has links)
In organometallic chemistry, metal complexes bearing unsaturated hydrocarbon ligands are of extensive interest, especially the C3H3-M system which includes propargyl (HC¡ÝCCH2-M), allenyl (H2C=C=CH-M), and acetylide (H3CC¡ÝC-M) forms. To study the chemistry of these species on metal surfaces, we used proprargyl bromide (HC¡ÝCCH2-Br) as precursor to produce C3H3(ad) on Ag(111) under ultrahigh vacuum (UHV) conditions. The thermal reactions pathway was investigated by Temperature-Programmed Desorption (TPD), and Reflection-Absorption Infrared Spectroscopy (RAIRS). In addition, density functional theory (DFT) calculations were conducted to obtain the optimized geometry for the adsorbates, and the computed IR spectra facilitated the vibrational mode assignments. TPD spectra showed that hydrogenation products C3H4 evolved at 310 K and 475 K. However, the desorption peak at 310 K was broad, indicating that more than one species were encompassed. Besides the hydrogenation product, a coupling product C6H6 (2,4-hexadiyne) was also unveiled as part of the desorption feature at 475 K. The identity of the possible C3H4 hydrogenation products (propyne and/or allene) was not discriminable by the mass spectrometry. The problem was circumvented by using £\,£\-dimethyl-substituted propargyl chloride because this dimethyl-substituted species also resulted in hydrogenatioin products around 310 K and 475 K, respectively; and the corresponding allenic and acetylenic end-products are distinguishable by the mass spectrometry. The results indicated that the broad feature at 310 K, in fact, contained both allene (lower temperature) and propyne (higher temperature), whereas the hydrogenation product at 475 K was propyne. The RAIR spectrum at 200 K showed that all C3H3(ad) on Ag(111) readily took on the allenyl form after the C-Br bond scission. It is thus obvious that allene at 310 K was generated by adding one hydrogen to the £\-carbon of the surface allenyl. RAIR spectroscopy revealed a drastic change after annealing the surface to 250 K, where the spectrum was almost identical to that obtained from using propynyl iodide (H3C-C¡ÝC-I) as a direct source for methylacetylide (H3C-C¡ÝC-Ag). Consequently, the products of propyne and 2,4-hexadiyne could be reasoned out.
22

The molecular mechanism of snake venom phospholipase A2 enzymes on damaging phospholipid membrane

Kao, Pei-Hsiu 28 July 2007 (has links)
Phospholipase A2 (PLA2) extensively exists in various snake venom. Till now, a controversy remained to elucidate whether the PLA2 activity exclusively associates with the manifestation of the pharmacological activities. In the present study, we used liposome to imitate cell membrane for excluding the effects of receptor and membrane proteins, and estimating the molecular mechanism of snake venom phospholipase A2 on damaging liposome. Although a greater membrane damaging activity of Naja naja atra phospholipase A2 (NNA-PLA2) and notexin was noted in the presence of Ca2+, inhibitions of PLA2 activity by Sr2+ and Ba+2 were unable to abolish the membrane damaging effect. In addition, modification of Lys-82 and Lys-115 of notexin retained the full PLA2 activity, but the membrane damaging activity notably decreased. Fluorescence quenching studies, CD measurement, and tryptophan fluorescence lifetime assay indicated that liposome induced the £\-helix conformation change and the tryptophan residues microenviroment change with the addition of Ca2+, Sr2+ or EDTA. Rhodamine quenching assay revealed that NNA-PLA2 and notexin formed oligomers when they bound with liposome. Besides, the modified PLA2 (BPB-PLA2) only formed monomer when it bound with liposome and lost the membrane damaging activity. Taken together, these results indicate that the membrane damaging effects of NNA-PLA2 and notexin are not critically caused by their enzymatic activitys and are probably associated with oligomerization.
23

Bacteriocidal Effects of Ozonated Seawater Added with Bromide or Chloride on Marine Fish Pathogens

Lin, Chen-hung 12 July 2005 (has links)
Ozone is a powerful oxidant which can be use for bacterial inactivation, deodorizing, and bleaching. In aquatic farms, it can improve larvae hatching and keep water quality under control. The primary object of this research is to investigate the influence of ozone solubility by the concentrations chloride¡]Cl-¡^and bromide¡]Br-¡^in seawater. The indigo colorimetric method was used to detect the variation of total residual oxidants¡]TROs¡^after ozonation. The bacteriocidal effects of ozone with added Cl- or Br- were tested on three common marine fish pathogens. The results showed that the ozone solubility in reverse osmosis¡]RO¡^treated water was about 2.3 mg/L, and rapidly decreased to 0.5 mg/L when ozonation stopped. The process of ozonation in seawater from start to equilibrium, the TROs concentration could reach 8.5 mg/L and then decreased slowly to a stable concentration of about 6 mg/L. When Cl- was added in RO water, the TROs concentration varied from 2 to 3.5 mg/L, and rapidly disappeared after stop ozonation. It was concluded that Cl- could not effectively increase ozone solubility in seawater. In contrast, adding Br- in RO water not only efficiently increased the solubility of ozone but also maintained the TROs concentrations after stop ozonation, and the TROs concentrations were proportional to the Br- concentrations. The same trends were also observed in seawater added with Br-. In the bacteriocidal effect of ozone, compare with pure seawater, adding of Br- in seawater could effectively reduce the TROs concentrations needed to completely inhibit each pathogen. Such practice may be extended to aquatic farms to eliminate or reduce the bacterial pathogens in seawater.
24

The Role of the Ocean in the Atmospheric Budgets of Methyl Bromide, Methyl Chloride and Methane

Hu, Lei 2012 August 1900 (has links)
The ocean is both a source and a sink for atmospheric methyl bromide (CH3Br) and methyl chloride (CH3Cl). It plays a significant role in their global biogeochemical cycling. In response to the Montreal Protocol, the atmospheric CH3Br is declining and the saturation state of CH3Br in the surface ocean is becoming more positive. Results from two large-scale transect studies in the eastern Pacific and the eastern Atlantic suggest that the ocean became near equilibrium with atmospheric CH3Br in 2010. Results from a "top-down" two-box model indicate that, if the remaining anthropogenic emissions are eliminated, atmospheric CH3Br is likely to drop to the pre-industrial level and the ocean would become a net source to atmospheric CH3Br. This study also represents an effort to improve current understanding of the oceanic and atmospheric budgets of CH3Cl. The global net sea-to-air flux of CH3Cl was estimated at 335 (210 ? 480) Gg yr-1 with improved parameterizations on the solubility, seasonal saturation anomaly ? (sea surface temperature, wind speed) relationships and the use of an updated parameterization on gas transfer velocity. For the first time, we estimated the gross oceanic emission and gross oceanic uptake rates of CH3Cl in the surface ocean, which was 700 (490 to 920) Gg yr^-1 and -370 (-440 to -280) Gg yr^-1, respectively. The ocean accounts for 10 - 19 % in the global CH3Cl emission and 6 - 9 % in its global sinks. Methane (CH4) is a potent greenhouse gas, which has a warming potential 72 times that of carbon dioxide over a 20 year time horizon. Gas hydrates are the largest CH4 reservoir in the planet. How much CH4 is transported from marine gas hydrates to the atmosphere is under debate. In this study, we investigated CH4 fluxes over three deepwater hydrocarbon seeps in the northern Gulf of Mexico using continuous air-sea flux measurements. Extrapolating the highest daily flux from this study to other deepwater seeps in the northern Gulf of Mexico suggests that CH4 fluxes to the atmosphere from the deepwater hydrocarbon seeps in this region are an insignificant source to atmospheric CH4 budget.
25

An investigation of the stereochemistry of the free radical addition of hydrogen bromide to olefins

Abell, Paul Irving, January 1951 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1951. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves [80]-82).
26

Gas phase photochemical reactions and reactions of photochemically produced hot hydrogen atoms initiated by 1850 Å radiation

Martin, Richard McKelvy. January 1964 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1964. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 207-212).
27

I. The oxygen effect in the reaction of cyclopropane with bromine and with hydrogen bromide. II. The oxygen effect in the reaction of bromine with neopentane, tert-butylbenzene and trimethylacetic acid ...

Fineman, Morton Zalmon, January 1945 (has links)
Thesis (Ph. D.)--University of Chicago, 1941. / Reproduced from type-written copy.
28

I. The peroxide effect in the addition of hydrogen bromide to methyl-acetylene. II. Exchange reactions of deuterium ...

McNab, John George, January 1939 (has links)
Thesis (Ph. D.)--University of Chicago, 1936. / Lithoprinted. "Private edition, distributed by the University of Chicago libraries, Chicago, Illinois." Description based on print version record. Bibliographical foot-notes.
29

The infrared dispersion of hydrogen bromide and carbon tetrafluoride

Schurin, Bertram D., January 1955 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1955. / Typescript. Abstracted in Dissertation abstracts, v. 16 (1956) no. 5, p. 978. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 37-38).
30

Der Einfluß elektronischer Anregungen des Wirtskristalles auf die Fluoreszenzdynamik von Tm 3+ - und Tm 3+ -Ho 3+ -dotiertem Cs CdBr 3

Altwein, Mark Unknown Date (has links)
Techn. Univ., Diss., 2000--Darmstadt

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