Thesis (Ph. D.)--University of Wisconsin--Madison, 1972. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

The emergence of unique or enhanced physical, chemical and optical material properties at the nanoscale underlies the swift rise of nanomaterials science over recent decades. Within this interdisciplinary field, catalysis performed by nanomaterials (i.e. nanocatalysis) is one area where differences between nanoscale and bulk material properties offer particularly attractive opportunities for application. The consequent pursuit of viable nanomaterials with unprecedented catalytic activity has inevitably expanded across the periodic table, whereby a number of highly efficient precious metal, metal oxide and composite nanostructured catalysts have been developed for a wide range of synthetic organic and inorganic transformations. The lanthanide series has not been excluded from this search, but is still underrepresented in catalysis despite some rich chemistry and reactivity which sets these elements apart from many other metals. More recently however, the necessary paradigm shift away from commonly utilized but expensive, potentially toxic precious metal catalysts, and toward more sustainable alternatives, has seen an upsurge in the development of novel nanomaterials for heterogeneous catalysis: the general topic of this doctoral thesis. Heterogeneous nanocatalysis offers distinct advantages over homogeneous catalysis. Catalyst recyclability, ease of separation from reaction mixtures, and minimal product contamination all contribute to the higher overall effectiveness of heterogeneous catalysts relative to their homogeneous counterparts. The use of light as an abundant reagent, both in nanomaterial fabrication and for photocatalysis, is another attractive prospect. This dissertation addresses both points, describing the iterative development and application of photochemically-prepared samarium oxide based nanomaterials for heterogeneous catalysis and photocatalysis. Through a series of related peer-reviewed publications and associated commentary, the evolution of the application-driven design of a nanomaterial which is both efficient and effective for a diversity of heterogeneous catalytic and photocatalytic transformations is presented. Major findings include 1) both colloidal and supported samarium oxide nanoparticles can be prepared photochemically and comprise primarily Sm2O3 but may contain localized mixed valences or dynamic surface oxidation states; 2) colloidal samarium oxide nanoparticles possess high activity for Brønsted acid and oxidative catalysis, but recyclability and overall effectiveness is less than optimal due to a combination of polydispersity and size-dependent catalytic activity; 3) a similarly-prepared “second generation” samarium oxide/titanium dioxide nanocomposite presented several advantages over its predecessor, performing highly efficient and effective pure heterogeneous, dual photoredox-Lewis acid catalysis in two different types of synthetically relevant photocyclizations. Effects of different nanoparticle supports, rare insights into the catalytic mechanisms and behaviour of these nanomaterials‒obtained at the single molecule level by innovative application of Total Internal Reflection Fluorescence Microscopy (TIRFM) to catalysis research‒as well as advances in TIRFM data analysis protocols, are also discussed.

Made available in DSpace on 2014-10-09T12:32:05Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:56Z (GMT). No. of bitstreams: 1 02298.pdf: 1286663 bytes, checksum: ed62610cdfd3bfac1a6ef998fc9615de (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:51:58Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:07:37Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:37:17Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:08Z (GMT). No. of bitstreams: 1 02043.pdf: 5558929 bytes, checksum: ab3263582fdb04b85c3f8792873017c1 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:32:05Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:56Z (GMT). No. of bitstreams: 1 02298.pdf: 1286663 bytes, checksum: ed62610cdfd3bfac1a6ef998fc9615de (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:51:58Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:07:37Z (GMT). No. of bitstreams: 0 / A utilização das terras raras (TR) em larga escala teve início com a patente de Welsbach em 1903, que é ainda aplicada na fabricação de pedras de isqueiros. Hoje as TR estão presentes nas mais diferentes áreas, como na produção de superligas, vidros especiais, pigmentos, cerâmicas, imãs permanentes, lasers, eletroeletrônicos, catalisadores, ressonância magnética nuclear, etc., movimentando, na última década, um mercado de US$ 2 bilhões por ano. Devido às suas propriedades muito semelhantes, os elementos das TR são difíceis de serem separados, requerendo, normalmente, processos complexos, o que os torna de elevado preço de comercialização. Elementos como o európio (Eu) e o samário (Sm), cujos teores nos materiais que contém TR são baixos (cerca de 0,05% e 2%, respectivamente, na monazita), são caros e os campos de aplicação destes materiais justificam a busca por outros processos de separação, que sejam no mínimo mais simples e/ou mais eficientes. O estado trivalente é característico para todas as TR, mas alguns elementos podem apresentar outros estados de oxidação, como o Ce, Eu, Sm e Yb. No caso do Eu e do Sm, foco de estudo neste trabalho, o estado divalente é facilmente obtido por redução eletroquímica nos potenciais –0,65V e –1,55V (vs. SCE), respectivamente. Este fato torna possível a separação destes elementos das demais terras raras e entre eles mesmos. Portanto, fazendo uso desta característica, propôs-se um processo de separação individual do Eu e do Sm em meio (NH4)2SO4 por eletro-redução/precipitação, onde o Sm é separado primeiramente como sulfato e o Eu, que permanece em solução, é precipitado após a diminuição da temperatura e do potencial aplicado. O processo desenvolvido a partir de uma solução sintética de Eu e Sm foi aplicado a uma mistura de óxidos de TR semi-pesadas produzida no IPEN-CNEN/SP, obtendo-se a separação do Sm. Este produto foi analisado por espectrofotometria, indicando elevado grau de pureza. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:37:17Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:08Z (GMT). No. of bitstreams: 1 02043.pdf: 5558929 bytes, checksum: ab3263582fdb04b85c3f8792873017c1 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Chemistry has been defined by some as an art, by others as a science and people have gone as far as dismissing it as pure alchemy. Overall, however, one cannot help but come to the conclusion that chemistry is a unique blend of all three. The work contained within this manuscript is an attempt to delve deep into the mysteries of but one type of transformation - a ¡¥simple¡¦ cyclisation step in which one couples two different moieties to form a cyclobutane ring with the aid of SmI2. There are two opposing forces of nature which control the outcome of this reaction, namely elimination and cyclisation and it is the contest between these two driving forces that ultimately decides the fate of these transformations. This work was born from previous attempts in RAU¡¦s laboratories to synthesise chiral cyclobutane derivatives from carbohydrates as well as the apparent discrepancies in two independent scientists¡¦ publications on the effect of SmI2 on reactions utilising 1,4-diketones. Hoffmann from Germany had managed to form 1,2-cyclobutanediols from a pinacol reaction promoted by SmI2 while Ghosh in India had experienced fragmentation products under similar conditions. The information contained herein provides a bird¡¦s eye view of cyclisation vs. fragmentation in 1,4-disubstituted compounds as well as an insight into how one might avoid or exploit the particular reaction pathways. The effects of various moieties in a ¡§ƒ×¡¨ disposition to the ketone have been investigated to obtain a broader understanding of the scope of the cyclobutane ring formation. These findings also provide the information necessary for effecting cyclobutane ring closures within the realm of carbohydrate chemistry. One will learn that the ¡¥geminal¡¦ effect is not the only efficacious method for the coupling of a ketyl radical and an activated alkene to form a four-membered ring. The thesis concludes with a strategic route towards the synthesis of a potential antiviral compound containing the cyclobutane substructure, originating from the simple sugar D-ribose. / Prof. D.B.G. Williams

The increasing emergence of multi-drug-resistant microorganisms has led the World Health Organisation to plead for action to be taken against antimicrobial resistance. The fungal secondary metabolite (+)-pleuromutilin displays antibacterial activity with a novel mode of action: pleuromutilin derivatives bind to functionally important nucleotides within the peptidyl transfer centre of the prokaryotic ribosome and inhibit bacterial protein synthesis. The first non-racemic total synthesis of the antibiotic natural product pleuromutilin has been developed. A chiral pool strategy has been employed to gain access to the cyclisation substrate, which underwent a SmI2-mediated cyclisation cascade to give the 5,6,8 tricyclic core in a single step. The reaction proceeded with excellent diastereocontrol at the four contiguous stereocentres generated during the cascade. Elaboration of the cyclisation product to (+)-pleuromutilin was achieved by electron transfer reduction of the hindered ester at C5, stereoselective introduction of the hydroxyl at C11 and installation of the quaternary stereocentre at C12. Finally the first efficient conversion of (+)-mutilin to the target was developed. This strategy is now being used for the synthesis of simplified novel analogues of pleuromutilin: access to a range of simplified cores has been demonstrated in 5 steps.