Global ETD Search

1	Studies towards the synthesis of marine polysulfide natural products Robinson, Paul A. January 2010 (has links) Biologically active compounds isolated from marine sources have had increasing interest in recent years with significant research going into the discovery and isolation of novel marine polysulfide natural products. Varacin, probably the most widely studied marine polysulfide to date was the subject of much debated structure elucidation attempts, and more recently several successful synthetic approaches have been published. The work published aims to increase our understanding of marine polysulfide compounds existence in nature and determine the origins of their biological activity. (+)-Aplidium trisulfide which was isolated from Aplidium Sp. D in 1989 by Munro et al has been shown to exhibit in vitro antimicrobial, antileukemic and cytotoxic properties. These intriguing biological effects have led our work towards developing a novel synthetic route toward aplidium trisulfide by both chiral and racemic routes. Aplidium trisulfide is of special significance as it is very rare to isolate enantiomeric compounds from marine sources. Two other closely related marine alkaloids fasmerianamine A and B are also of synthetic interest to us due to their close resemblance to the structure of aplidium trisulfide. The fasmerianamines were isolated by Copp et al from the marine ascidian Hypsistozoa fasmeriana in 2001. 547.7
2	Studies towards the total synthesis of the Perophora viridis Trithiocane Fuchs, Christian January 2010 (has links) The influence of solvent and steric hindrance on the conversion of thiolsulfinates to trisulfides with hexamethyldisilathiane was investigated and a new polar mechanism, based on acceleration of the reaction by polar solvents and by fluoride ions, was proposed. The mono and dialkylation of 2,2-disubstituted 1,3-dithiane-1-oxides was investigated. Whereas those derived from menthone form only one diastereomer which cannot be alkylated further, those derived from acetone form two diastereomers. Only one of them can be alkylated further. Dehydration of the diastereomeric tertiary alcohols derived from directed aldol-reaction of γ-butyrolactones and methyl ketones yields diastereomeric conjugated enes in high yield and d.e. Michael-addition of benzyl thiols to these gives good yields and d.e. of the Michael-adducts. Deprotection of PMB-protected thiols with concomitant formation of disulfides was achieved by bromine in methanol or CH2Cl2. A seven-membered cyclic disulfide which contains the carbon backbone of the Perophora viridis trisulfide, albeit with two stereocentres in the incorrect configuration, was prepared. 547.6
3	Synthesis, Structures and Reactions of Aluminum(I) and Aluminum(III) Compounds / Darstellungen, Strukturen und Reaktionen von Aluminium(I)- und Aluminium(III)-Verbindungen Peng, Ying 03 November 2004 (has links) No description available. 540 Chemie Mathematics and Computer Science Aluminium Salicylaldiminato Diketiminato Adamantyl Phosphor Trisulfid Aluminum Salicylaldiminato Diketiminato Adamantyl Phosphorus Trisulfide 35.60 STL 150: Aluminium {Anorganische Chemie}
4	Towards Direct Writing Of 3-d Photonic Circuits Using Ultrafast Lasers Zoubir, Arnaud 01 January 2004 (has links) The advent of ultrafast lasers has enabled micromachining schemes that cannot be achieved by other current techniques. Laser direct writing has emerged as one of the possible routes for fabrication of optical waveguides in transparent materials. In this thesis, the advantages and limitations of this technique are explored. Two extended-cavity ultrafast lasers were built and characterized as the laser sources for this study, with improved performance over existing systems. Waveguides are fabricated in oxide glass, chalcogenide glass, and polymers, these being the three major classes of materials for the telecommunication industry. Standard waveguide metrology is performed on the fabricated waveguides, including refractive index profiling and mode analysis. Furthermore, a finite-difference beam propagation method for wave propagation in 3D-waveguides is proposed. The photo-structural modifications underlying the changes in the material optical properties after exposure are investigated. The highly nonlinear processes of the light/matter interaction during the writing process are described using a free electron model. UV/visible absorption spectroscopy, photoluminescence spectroscopy and Raman spectroscopy are used to assess the changes occurring at the atomic level. Finally, the impact of laser direct writing on nonlinear waveguide applications is discussed. femtosecond ultrafast laser waveguide fused silica arsenic trisulfide chalcogenide PMMA index profile color center Raman spectroscopy photoluminescence spectroscopy Electromagnetics and Photonics Optics
5	Transition metal solar absorbers Altschul, Emmeline Beth 02 July 2012 (has links) A new approach to the discovery of high absorbing semiconductors for solar cells was taken by working under a set of design principles and taking a systemic methodology. Three transition metal chalcogenides at varying states of development were evaluated within this framework. Iron pyrite (FeS��) is well known to demonstrate excellent absorption, but the coexistence with metallic iron sulfides was found to disrupt its semiconducting properties. Manganese diselenide (MnSe��), a material heavily researched for its magnetic properties, is proposed as a high absorbing alternative to iron pyrite that lacks destructive impurity phases. For the first time, a MnSe�� thin film was synthesized and the optical properties were characterized. Finally, CuTaS��, a known but never characterized material, is also proposed as a high absorbing semiconductor based on the design principles and experimental results. / Graduation date: 2013 Solar absorber absorption copper tantalum trisulfide chalcogenide metal pyrite manganese diselenide band structure solar energy inverse design design principle density of states thin film photovoltaic Solar cells -- Materials Transition metal compounds Chalcogenides Semiconductor films Metallic films Solar cells -- Design and construction

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