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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.
221

Regenerable Organochalcogen Antioxidants : An Explorative Study

Yan, Jiajie January 2017 (has links)
Antioxidants are widely used to protect organic materials from damages caused by autoxidation, an oxidation process that occurs under normal aerobic conditions. In this thesis, novel multifunctional organoselenium and organotellurium antioxidants were designed, synthesized, and evaluated in search for compounds with better radical-trapping capacity, regenerability, and hydroperoxide-decomposing ability. Selenium was incorporated into ebselenols and hydroxy-2,3-dihydrobenzo[b]selenophenes and tellurium into diaryl disulfides and aryltellurophenols. All newly developed antioxidants were evaluated in a chlorobenzene/water two-phase lipid peroxidation system containing suitable co-antioxidants in the aqueous phase. Ebselenol carrying a hydroxyl group (OH) ortho to selenium showed a two-fold longer inhibition time than the reference α-tocopherol in the presence of aqueous-phase ascorbic acid. 2,3-Dihydrobenzo[b]selenophenes carrying a 5- or 7-OH outperformed α-tocopherol both when it comes to radical-trapping capacity and regenerability. Alkyltellurothiophenols, in situ formed from their corresponding disulfides by tris(2-carboxyethyl)phosphine, were also efficient regenerable radical-trapping antioxidants. The consumption of N-acetylcysteine in the water phase was followed and found to be limiting for the duration of the inhibition. The hydroperoxide-decomposing ability of all organoselenium antioxidants was evaluated. Ebselenols were often better glutathione peroxidase mimics than the parent. In an effort to find out more about antioxidant mechanisms, aryltellurophenols carrying electron donating and electron withdrawing groups in the phenolic or aryltelluro parts were synthesized and OH bond dissociation enthalpies, BDEO-Hs, were calculated. Compounds carrying electron donating groups in the phenolic or aryltelluro part of the molecule showed the best radical-trapping capacity. Deuterium labelling experiments suggested that hydrogen atom transfer could be the rate-limiting step in the antioxidant mechanism.
222

Development and Applications of Molybdenum-Catalyzed Chemoselective Amide Reduction

Slagbrand, Tove January 2017 (has links)
This thesis covers the development of catalytic methodologies for the mild and chemoselective hydrosilylation of amides. The first part describes the investigation of the Mo(CO)6-catalyzed reduction of carboxamides. It was found that the reduction could be controlled by tuning the reaction temperature and either amines or aldehydes could be obtained selectively. The system showed an unprecedented chemoselectivity and the amide reduction could take place in the presence of other reducible functional groups such as ketones, aldehydes, and imines. Moreover, the transformation could be performed on a preparative scale and was further employed in the synthesis of Donepezil, a pharmaceutical drug used in the treatment of Alzheimer´s disease. The third chapter concerns the development of the Mo(CO)6-mediated hydrosilylation protocol for the reduction of carboxamides containing acidic α-hydrogens. In this case, enamines were formed and a high level of chemoselectivity was observed. Enamines containing sensitive functional groups such as ketones, aldehydes and imines were generated. The enamines were not isolated but used in subsequent catalytic reductive functionalization of amides, which is described in the last part of the thesis (Chapters 4 – 7). The in situ formed enamines were reacted with a wide variety of electrophiles, generating heterocyclic compounds as triazolines, triazoles, 4,5-dihydroisoxazoles and pyrimidinediones. N-sulfonylformamidines as well as thioacrylamides could also be prepared with this approach. The protocols for the synthesis of triazolines, triazoles and N-sulfonylformamidines could additionally be performed on a preparative scale, showing the practicality of the methodology.
223

Nyanser av tillväxt : Investmentbolags syn på organisk och extern tillväxt

Karlberg, Tony, Echardt, Pontus January 2017 (has links)
Tidigare forskning har tydligt etablerat hur mycket företag växer. Det här examensarbetet har tagit sig an uppgiften att beskriva och förklara hur företag växer. Vi har särskilt försökt hitta nyanser av tillväxt genom ett investmentbolags perspektiv. Till det har vi haft ett teoretiskt perspektiv med två huvudsakliga strategier för tillväxt. Litteraturen pekar ut organisk tillväxtstrategi och extern tillväxtstrategi. Organisk tillväxt är stabilt och mindre riskfyllt, medan extern tillväxt gör att företag kan växa snabbt men det innebär mer och en annan typ av risk. Genom en extern tillväxtstrategi kan företag snabbt få en nödvändig konkurrensfördel genom till exempel unik kunskap på en lokal marknad. Syftet med detta examensarbete är att bidra till en djupare kunskap för hur investmentbolag ser på organisk eller extern tillväxt hos företag. Totalt gjordes tio intervjuer med svenska investmentbolag. För att besvara forskningsfrågan har vi varit analytiskt deduktiva. Teorin i examensarbetet användes som verktyg för att förklara med olika aspekter hur investmentbolag ser på organisk och extern tillväxt hos företag. Resultatet visar att den organiska tillväxtformen är mindre riskfylld samt att eventuella risker lättare kan hanteras genom en högre grad av kontroll internt. Skillnader uppstår när varje aktör har olika strategier för hur deras verksamhet ska bedrivas. Examensarbetet bidrar till att med det teoretiska förhållningssättet utöka kunskapen om organisk och extern tillväxtstrategi. Det är även ett bidrag till forskningen om hur företag växer. Vidare stimuleras debatten om tillväxtteorier.
224

Magnetic Materials for Cool Applications : Relations between Structure and Magnetism in Rare Earth Free Alloys

Cedervall, Johan January 2017 (has links)
New and more efficient magnetic materials for energy applications are a big necessity for sustainable future. Whether the application is energy conversion or refrigeration, materials based on sustainable elements should be used, which discards all rare earth elements. For energy conversion, permanent magnets with high magnetisation and working temperature are needed whereas for refrigeration, the entropy difference between the non-magnetised and magnetised states should be large. For this reason, magnetic materials have been synthesised with high temperature methods and structurally and magnetically characterised with the aim of making a material with potential for large scale applications. To really determine the cause of the physical properties the connections between structure (crystalline and magnetic) and, mainly, the magnetic properties have been studied thoroughly. The materials that have been studied have all been iron based and exhibit properties with potential for the applications in mind. The first system, for permanent magnet applications, was Fe5SiB2. It was found to be unsuitable for a permanent magnet, however, an interesting magnetic behaviour was studied at low temperatures. The magnetic behaviour arose from a change in the magnetic structure which was solved by using neutron diffraction. Substitutions with phosphorus (Fe5Si1-xPxB2) and cobalt (Fe1-xCox)5PB2 were then performed to improve the permanent magnet potential. While the permanent magnetic potential was not improved with cobalt substitutions the magnetic transition temperature could be greatly controlled, a real benefit for magnetic refrigeration. For this purpose AlFe2B2 was also studied, and there it was found, conclusively, that the material undergoes a second order transition, making it unsuitable for magnetic cooling. However, the magnetic structure was solved with two different methods and was found to be ferromagnetic with all magnetic moments aligned along the crystallographic a-direction. Lastly, the origin of magnetic cooling was studied in Fe2P, and can be linked to the interactions between the magnetic and atomic vibrations.
225

Development of Mild Methods for Selective Covalent Functionalization of Graphene

Lundstedt, Anna January 2017 (has links)
This thesis discusses methods for the comparatively mild covalent functionalization of graphene. Several graphene models were investigated: polycyclic aromatic hydrocarbons (PAHs), chemical vapor deposition (CVD)-graphene on SiO2/Si substrate, graphite foil, graphite flakes, kish graphite and highly oriented pyrolytic graphite. The PAHs were viewed as graphene edge analogs with the following molecules representing different edge motifs: pyrene, perylene, benzo[a]pyrene, benzo[e]pyrene, triphenylene, acenapthylene, and anthracene. Ozone was used in combination with different solvents to functionalize PAHs, graphite, and CVD-graphene on SiO2/Si. Ozonation in water or methanol resulted in trapping of the carbonyl oxide intermediate that was formed in the reaction, producing a variety of functional groups. Ozonation in hydrogen peroxide solution with sonication promoted radical formation, possibly resulting in edge-oxidation of graphite. The regioselectivity for addition reactions (ozonolysis) and electrophilic aromatic substitution reactions with graphene edges is discussed. To achieve functionalization of the basal plane of graphite or graphene, white light irradiation was used in combination with several transfer hydrogenation reagents. Formic acid treatment under irradiation resulted in the expected hydrogenation, whereas iso-propanol treatment resulted in iso-propanol attachment to the graphene. The developed methods provide opportunities for graphene functionalization without the need for metal based reagents or harsh conditions.
226

Asymmetric Synthesis and Mechanistic Studies on Copper(I)-Catalyzed Substitution of Allylic Substrates

Norinder, Jakob January 2006 (has links)
This thesis deals with the copper-catalyzed substitution of allylic substrates. In the first part of this thesis, the synthesis of a series of metallocenethiolates is described. The thiolates were examined as ligands in the enantioselective copper(I)-catalyzed γ-substitution of allylic acetates. The second part describes a study on copper-catalyzed α-substitution of enantiomerically pure secondary allylic esters. It was observed that the degree of chirality transfer is strongly dependent on the reaction temperature. The loss of chiral information is consistent with an equilibration of the allylCu(III) intermediates prior to product formation, which is essential in order to realize a copper-catalyzed dynamic kinetic asymmetric transformation process. The third part describes a study on copper-catalyzed stereoselective α-substitution of enantiopure acyclic allylic esters. This method, when combined, with ruthenium and enzyme catalyzed dynamic kinetic resolution of allylic alcohols, provides a straightforward route to pharmaceutically important α-methyl carboxylic acids. The fourth part is a mechanistic study on the reaction of perfluoroallyl iodide with organocuprates. Experimental studies as well as theoretical calculations were used to explain the contrasting reactivity of perfluoroallyl iodide vs. allyl iodide in cuprate allylation reactions. In the fifth part, the development of a practical and useful method for the preparation of pentasubstituted acylferrocenes is presented.
227

Hydrogen Bonded Phenols as Models for Redox-Active Tyrosines in Enzymes

Utas, Josefin January 2006 (has links)
This thesis deals with the impact of hydrogen bonding on the properties of phenols. The possibility for tyrosine to form hydrogen bonds to other amino acids has been found to be important for its function as an electron transfer mediator in a number of important redox enzymes. This study has focused on modeling the function of tyrosine in Photosystem II, a crucial enzyme in the photosynthetic pathway of green plants. Hydrogen bonds between phenol and amines in both inter- and intramolecular systems have been studied with quantum chemical calculations and also in some solid-state structures involving phenol and imidazole. Different phenols linked to amines have been synthesized and their possibilities of forming intra- and intermolecular hydrogen bonds have been studied as well as the thermodynamics and kinetics of the generation of phenoxyl radicals via oxidation reactions. Since carboxylates may in principle act as hydrogen bond acceptors in a manner similar to imidazole, proton coupled electron transfer has also been studied for a few phenols intramolecularly hydrogen bonded to carboxylates with the aim to elucidate the mechanism for oxidation. Electron transfer in a new linked phenol—ruthenium(II)trisbipyridine complex was studied as well. The knowledge is important for the ultimate goal of the project, which is to transform solar energy into a fuel by an artificial mimic of the natural photosynthetic apparatus
228

Development and preliminary evaluation of novel materials for selective detection of oseltamivir in waste water / Utveckling och utvärdering av nya material för selektiv detektion av oseltamivir i vatten

Wällstedt, Elin January 2019 (has links)
This project aims to investigate whether it is possible to detect consentrations down to 0,3 µg/L of oseltamirir in waste water by Quartz Crystal Microbalance. The risks linked to this contaminant could be not only environmental, scientists have found that infuence recistence can propagate due to contaminats of this kind. Cases similar to the bird- and swine-flu could occure if the drug spreads through animals and mutate.   Four systems of different character was synthesised. As a result it was found that MAA functional monomer systems probably was interfering with charges within it’s own nanowires. Reference systems could not detect 0,01 mg/mL and HEMA polymer surfaces was the only reliable system, pH of 5,1. Lowest limit of detection (LOD) was found in Molecular Imprinted Polymer nanowires (MIP Nw) at 0,01 mg/mL and could be scaled down to 0,1 mg/L with increased loop size (injection at 10x that of 0,01 mg/mL at about 500 µL and a halved flow rate.)   An alternative could be nano structuring such as ”polystyrene balls” that possibly could be able to achieve surfaces with even more binding sites needed to detect the lowest limit at 0,3 µg/L.
229

Synthesis of SARS-CoV-2 Main Protease Inhibitors

Elfström, Mia January 2021 (has links)
Coronaviruses have been responsible for several global disease outbreaks over the last 20 years, including the “Severe Acute Respiratory Syndrome” in 2002/2003, the “Middle East Respiratory Syndrome” in 2012, and the “Coronavirus Disease of 2019 (COVID19)”. These viruses are highly contagious and can cause multiple medical disorders upon contraction, such as common cold or lower respiratory infections. SARS-CoV-2, the newly emerged coronavirus variant of 2019, has been confirmed as the cause of the ongoing COVID19 pandemic, which infected over 167 million people worldwide and, by the end of May 2021, has a death toll of over 3 million people. Even though several SARS-CoV-2 vaccines have made it to the market, no proven options have yet been discovered for treating COVID19 infections. The aim of this project is, therefore, to improve the potency of two active SARS-CoV-2 main protease (Mpro) inhibitors (ML188 and X77) by performing a structure-activity-relationship study where two specific sites of the inhibitors are altered. The inhibition activity of these compounds is then tested on isolated SARS-CoV-2 Mpro. The four-component Ugi reaction was utilized to synthesize the ML188 and X77 analogs, which were purified by column chromatography before testing. During this project, six pure analogs were successfully synthesized and will be sent shortly for testing. Inhibitors with good activity against SARS-CoV-2 Mpro will be further tested for their antiviral activity in cell-based infection assays. The results obtained from this study will later be used to perform a second structure-activity-relationship study to further improve the potency of the two inhibitors by developing a 2nd generation library.
230

Tabasam Kwa Maisha : A Creative School in Tanzania / Tabasam Kwa Maisha : En Kreativ Skola i Tanzania

Augustyniak, Sandra January 2013 (has links)
This is not yet another ordinary primary school in Tanzania. This is an idea about a new way of learning where architecture and its materiality create inspiring spaces. Set in between 3 small villages in an area heavily affected by AIDS and Malaria the aim is to make good quality education viable for everyone.The idea is to learn by doing. The compound will have several workshops for practical education and music and dance will play a central role. With a smaller scale and more intimate green in-between spaces it resembles more of a small village than an ordinary Tanzanian school. Smart solutions with green roofs solve the over heating problem by the strong sun, as well as filter rain water that is collected for use. A semi-open bamboo facade on the inner walls of the compound create natural ventilation as well as let daylight in. / Det här är ingen vanlig ny skola i Tanzania. Det är en ide om ett nytt sätt av lärande där arkitekturen och dess materialitet skapar inspirerande miljöer. Med en position mellan tre små byar som är starkt utsatta för AIDS och Malaria är tanken att skolan ska göra god kvalitativ undervisning tillgänglig för alla. Här lär man sig genom praktisk undervisning. Skolområdet kommer att ha flera verkstäder för praktisk undervisning och dans och musik kommer att spela en central roll. Med en mindre skala och mer intima gröna rum mellan byggnaderna påminner skolan mer om en liten by än en vanlig Tanzaniansk skola. Smarta lösningar med gröna tak löser problem med överhettning av stark sol och filtrering av regnvatten som samlas upp i behållare för att användas. En uppluckrad bambufasad på områdets innerväggar skapar naturlig ventilation och insläpp av dagsljus.

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