No / The Raman spectrum of scytonin, a novel derivative of the parent scytonemin, is predicted from DFT calculations of the most stable, lowest energy, conformational structure. The diagnostic importance of this study relates to the spectral ability to discriminate between scytonemin and its derivatives alone or in admixture with geological matrices from identified characteristic Raman spectral signatures. The successful interpretation of biosignatures from a wide range of cyanobacterial extremophilic colonization in terrestrial and extraterrestrial scenarios is a fundamental requirement of the evaluation of robotic spectroscopic instrumentation in search for life missions. Scytonemin is produced exclusively by cyanobacterial colonies in environmentally stressed habitats and is widely recognized as a key target biomarker molecule in this enterprise. Here, the detailed theoretical analysis of the structure of scytonin enables a protocol to be established for the recognition of characteristic bands in its Raman spectrum and to accomplish the successful differentiation between scytonin and scytonemin as well as other scytonemin derivatives such as the dimethoxy and tetramethoxy compounds that have been isolated from cyanobacterial colonies but which have not yet been characterized spectroscopically. The results of this study will facilitate an extension of the database capability for miniaturized Raman spectrometers which will be carried on board search for life robotic missions to Mars, Europa, and Titan.

Foram determinadas as estruturas cristalinas de três 3-fenil-2- izoxazolin-5-ona-4-benzilideno substituídas com potencial atividade antiinflamatória, a partir dos dados difratométricos de raios-X, usando os Métodos Diretos. O refinamento foi obtido pelo método dos Mínimos Quadrados. O composto C16H11NO2 cristalizou no sistema cristalino monoclínico, grupo espacial P21/a, a = 11,786(5) Å, b = 5,745(1) Å, c = 17,862(5) Å, ß = 95,988(5)º, Z = 4, V = 1202,8(12) Å3 . O composto C17H13NO3 cristalizou no sistema cristalino ortorrômbico, grupo espacial Pna21, a = 11,652(5) Å, b = 6,000(5) Å, c = 19,542(5) Å, Z = 4, V = 1366,2(13) Å3. O composto C17H13NO4 cristalizou no sistema cristalino ortorrômbico, grupo espacial Pcab, a = 10,6983(9) Å, b = 12,6111(8) Å, c = 20,926(2) Å, Z = 8, V = 2823,3(4) Å3. Em todas as estruturas verificou-se semelhança estrutural para com a fenilbutazona. / The crystal structures of three substituted 3-phenyl-2- isoxazolin-5-one-4-benzilidene with potential biological activities have been determined from diffractometric X ray data using the Direct Method. The refinement has been obtained through the least squares method. The compound C16H11NO2 crystallized in the monoclinic crystal system, space group P21/a, a = 11,786(5) Å, b = 5,745(1) Å, c = 17,862(5) Å, ß = 5,988(5)º, Z = 4, V = 1202,8(12) Å3. The compound C17H13NO3 belongs to the orthorhombic crystal system, space group Pna21, a = 11,652(5) Å, b = 6,000(5) Å, c = 19,542(5) Å, Z = 4, V = 1366,2(13) Å3. The compound C17H13NO4 crystallized in the orthorhombic crystal system, space group Pcab, a = 10,6983(9) Å, b = 12,6111(8) Å, c = 20,926(2) Å, Z = 8, V = 2823,3(4) Å3. All these structures show structural similarities to the phenylbutazone.

The thesis begins with a brief introduction and relevant literature references. The novelty of synthesis, methodology and results of the work reported in the thesis and highlighted subsequently. The thesis consist of three parts, Part A of the thesis consist of five chapters describing new methods of synthesis of orthovanadates, mainly dealing with the structure and photocatalytic properties of synthesized materials. Part B of the thesis consist of two chapters dealing with an unique crystallization methodology for subliming and low melting organic compounds and the crystal structure determination via single crystal X-ray diffraction. Part C consists of one chapter presenting the ab-initio approach of structure determination via powder X-ray diffraction methods. Chapter 1 of the thesis presents the synthesis of three zircon type lanthanide orthovanadates, LnVO4 (Ln = Ce, Pr and Nd) via a new solution based approach at room temperature and photodegradation of a variety of water pollutants have been investigated. Chapter 2 describes the importance of microwave synthesis to produce nano particles of the zircon type lanthanide orthovanadates LnVO4. The importance of the surface area in photocatalysis is evaluated. Chapter 3 consist of the synthesis of a series of new compounds, Ln0.95φ0.05Mo0.15V0.85O4 (Ln = Ce, Pr and Nd) via solid state method. The photocatalytic activities of these compounds are investigated both under UV exposure and sunlight. Chapter 4 presents the synthesis of MxCe1-xVO4+ (M = Li, Ca and Fe) with x = 0.1, 0.25 and 0.05 respectively. Different kinds of dyes and organics are degraded under UV radiation and the specificity towards the same are evaluated. Chapter 5 describes a comparative photocatalytic conversion of cyclohexane and benzene to cyclohexanol, cyclohexanone and phenol respectively by LnVO4, LnMo0.15V0.85O4 and MxCe1-xVO4+ (Ln = Ce, Pr and Nd, M= Li, Ca and Fe with x = 0.1, 0.25 and 0.05 respectively). Kinetics of above photoconversions are established by proposing a mechanism and determining the rate constants. Chapter 6 describes the development of a novel apparatus for the crystallization of anhydrous adenine, whose structure has not been solved over the last few decades. The crystal structure is solved via single crystal X-ray diffraction. Chapter 7 presents a modified design for crystallization of low melting organic compounds and co-crystals. A new polymorph of anhydrous thymine has been grown with this apparatus and its structure has been analyzed and compared with the known form of thymine. Chapter 8 presents the ab-initio approach of structure determination via powder X-ray diffraction methods. The methodology of using the direct space approach for the determination of the crystal structure of N-(2-fluorophenyl) benzamide (a drug intermediate), which could not yield good quality single crystals, is outlined.

Electron paramagnetic resonance (EPR) spectroscopy is a powerful tool for obtaining structural information about chemical centres with unpaired electrons. In complex biological systems, EPR spectroscopy can be used to probe these paramagnetic centres and the long-range interactions between them. This thesis investigates two important types of enzymes, and in particular the role of the iron-sulfur electron-transfer centres they contain, with a variety of EPR techniques. Complex I (NADH:Ubiquinone Oxidoreductase) plays a key role in the electron transfer chain essential to the formation of ATP, and its malfunction has been related to numerous human diseases. It is a giant enzyme that contains the longest relay of iron-sulfur clusters known. EPR experiments conducted on complex I from bovine mitochondria yield crucial insight into the mechanism of efficient long-range electron transfer and bring us a step closer to understanding the functioning of this important complex. Hydrogenases are produced by micro-organisms and catalyse the reversible oxidation of H2. Most hydrogenases, including Hyd-2 from Escherichia coli, are very air-sensitive, but some, including E. coli Hyd-1 and Salmonella Hyd-5, are able to function in the presence of atmospheric levels of O2. Understanding the origins of this 'O2-tolerance' is of paramount importance if hydrogenases are to be exploited in future energy technologies. In this thesis, native E. coli Hyd-1 and Hyd-2, Salmonella Hyd-5, as well as O2-tolerant and O2-sensitive variants of E. coli Hyd-1 are characterised using EPR. The EPR investigations elucidate properties of the active site and the electron-transfer relay and, in conjunction with other techniques, reveal structural and mechanistic details of how a highly unusual iron-sulfur cluster in the electron-transfer chain enables some hydrogenases to sustain catalytic activity in the presence of O2.

Part of work presented in this thesis has been published: Regulation of gene expressions by GC-rich DNA cis-elements / J.P. Hapgood, J. Riedemann and S.D. Scherer in Cell biology international, vol. 25, 2001. / Thesis (MSc)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: The sea urchin G-string binding factor 1 (suGF1) has previously been shown to bind with high affinity and selectivity to stretches of contiguous deoxyguanosine residues, a DNA motif found in the upstream regions of many unrelated genes from several organisms. It has been proposed that suGF1 plays a role in transcriptional regulation. Homopurine.homopyrimidine stretches have been shown to form unusual DNA structures, in vitro. To investigate the potential of the suGF1 binding site to form unusual structures under certain conditions, synthetic oligodeoxyribonucleotides containing the suGF1 poly(dG).(dC) binding site were subjected to circular dichroism (CD) analyses. The CD results indicate that the suGF1 binding site forms a mixture of unusual DNA structures, as deduced by comparison with the spectra obtained for B-DNA, triplex and quadruplex conformations. These results are consistent with the hypothesis that suGF1 specifically recognises G-strings that exhibit unusual structures. Exhaustive database searches showed that suGF1 has no significant homology with any previously identified proteins or cDNAs from any species. Given the relevance of mammalian models to medical science, and since no sea urchin cell lines are currently available, the identification of a mammalian functional homologue would facilitate determination of the in vivo function of such a potentially important, putative, novel DNAbinding protein in mammalian cell lines. In this study sequence analysis tools were used to identify hORFX, a putative human functional homologue of suGF1. Similarities in the domain organisation of the two proteins, prompted an investigation into the DNA-binding properties of hORFX, as well as a more detailed structure prediction analysis, with a view to determining whether hORFX is a functional homologue of suGF1. hORFX was successfully expressed in vitro, but lacked the ability to specifically bind G-strings. Theoretical predictions suggest that suGF1 has a DNA-binding domain belonging to a different family to that predicted for hORFX, consistent with differences in their respective DNA-binding specificities. suGF1 and hORFX were predicted to have helix-turn-helix and helix-loop-helix DNA-binding domains, respectively. Taken together the results do not support the hypothesis that hORFX is a suGF1 homologue. To date, no direct evidence for the in vivo function of suGF1 has been obtained. With a view to performing transactivation assays in the future, the expression of suGF1 in yeast was investigated in this project. An suGF1 expression construct was engineered and transformed into a protease-deficient yeast strain. Nuclear extracts were prepared and subjected to SOS-PAGE and electrophoretic mobility shift assays (EMSAs). suGF1 was shown to be successfully expressed in yeast cells and exhibited similar G-string-binding properties to that of native and in vitro transcribed and translated (IVT) suGF1. The suGF1 eDNA was also subjected to in si/ico expression, which together with the SDSPAGE results of yeast nuclear extracts and IVT suGF1, indicated that the protein might be expressed as multiple truncated products, due to the utilisation of multiple AUG translation start sites. These in vitro results are crucial for the ultimate outcome and correct interpretation of future transactivation experiments and lay the foundation for further investigation into the possible role of suGF1 in transcriptional regulation. / AFRIKAANSE OPSOMMING: In die verlede is bewys dat die seepampoentjie G-string-bindende faktor (suGF1) hoë affiniteit en spesifisiteit vir aaneenlopende volgordes van deoksiguanosien residue besit. Hierdie DNA motief kom algemeen voor in die stroom-op gebiede van verskeie gene in verskillende organismes. Daar is 'n veronderstelling dat suGF1 betrokke is by die regulering van geenuitdrukking. Vroeër is bewys dat homopurien.homopirimidien-ryke areas die vermoë besit om in vitro ongewone DNA-strukture te vorm. Die potentiaal van die suGF1-bindingsetel om ongewone DNA-strukture te vorm is gevolglik deur sirkulêre dikroïsme (SD) analise ondersoek. Vergelyking van die spektra vir B-DNA-, tripleks- en kwadrupleks-strukture met dié van die suGF1-bindingsetel, toon duidelik dat laasgenoemde 'n mengsel van ongewone DNA konformasies, onder die spesifieke eksperimentele omstandigehede, aanneem. Deeglike inspeksie van die beskikbare geen- en proteïendatabasisse vir alle spesies het aangetoon dat suGF1 geen merkbare kDNA- of proteïenhomoloë besit nie. As gevolg van die belang van soogdiermodelsisteme in die mediese wetenskappe, asook die onbeskikbaarheid van seepampoentjie-sellyne, is 'n soektog na 'n funktionele suGF1 homoloog in soogdiere geloods. Die ontdekking van só 'n homoloog sal dit moontlik maak om die rol van hierdie potensiaal belangrike en unieke DNA-bindingsproteïen te ondersoek. Tydens hierdie soektog is spesiale analise-programme gebruik en 'n potensiële menshomoloog van suGF1, hORFX, is geïdentifiseer. Die mees prominente ooreenkoms tussen die twee proteïene is die soortgelyke rangskikking van funksionele motiewe. Gevolglik is die DNA-bindings eienskappe van die hORFX-proteïen ondersoek, insluitende 'n detaileerde struktuur-funksie-voorspelling ten einde vas te stel of dit wél 'n homoloog van suGF1 is. hORFX is suksesvol uitgedruk in vitro, maar besit nie die vermoë om dieselfde G-string waaraan suGF1 spesifiek bind te herken nie. Teoretiese analise het voorspel dat suGF1 en hORFX aan verskillende DNA-bindings proteïen-families behoort, aangesien suGF1 'n heliks-draai-heliks en hORFX 'n heliks-lus-heliks motief bevat. Hierdie inligting, tesame met die eksperimentele resultate, dui aan dat hORFX nie 'n homoloog van suGF1 is nie. Tot op hede is daar niks bekend aangaande suGF1 se funksie in vivo nie. Met die oog op transaktiveringseksperimente in die toekoms, is die ekspressie van suGF1 in gisselle tydens hierdie navorsingsprojek ondersoek. 'n suGF1 ekspressievektor is berei en gebruik om 'n protease-negatiewe gissellyn te transformeer. Kernekstrakte is ondersoek deur SDS-PAGE en elektroforetiese mobiliteitsessais. Daar is gevind dat suGF1 suksesvol uitgedruk is in die gisselle. Die rekombinante suGF1 besit G-volgorde bindingsaktiwiteite soortgelyk aan dié van suGF1 in kernekstrakte van seepampoentjies, asook in vitro getranskribeerde-en getransleerde suGF1. Die kDNA vir suGF1 is ook in silico uitgedruk. Tesame met die SDS-PAGE-resultate het laasgenoemde aangetoon dat die suGF1-kDNA veelvuldige AUG-kodons bevat vir die inisiasie van proteïentranslasie. Dit lei moontlik tot die translasie van 'n reeks proteïenprodukte wat verkort is aan die N-terminale kant, afgesien van die volledige suGF1-proteïen. Die in vitro resultate in geheel is essensieel vir die toekomstige uitvoering en interpretasie van transaktiveringseksperimente. Hierdie projek lê gevolglik die fondasie vir 'n verdere ondersoek na die rol van suGF1 in die regulering van geenuitdrukking.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2008. / In this study linear low density polyethylene (LLDPE), a copolymer consisting of ethylene and 1-butene, was fractionated by the use of temperature rising elution fractionation (TREF). These fractions were then analyzed by crystallisation analysis fractionation, 13C NMR, high temperature size exclusion chromatography and DSC. The molecular distribution of the polymer was investigated. It was found that the polymer had a very broad distribution in its chemical composition. From these results it was also clear that the catalysts used for the polymerisation consist out of different active sites, producing chains with different molecular architecture. Subsequently the polymer was fractionated again by TREF and certain fractions were removed and the remaining material recombined. The removed fractions and recombined material were analyzed by 13C NMR, high temperature size exclusion chromatography, DSC and DMA. The results were compared with the bulk material and from this we could conclude the influence of the fractions removed on the material properties. This gave us more information on the influence of the chemical structure of the polymer on its mechanical properties. It was clear that by removing certain fractions with a certain chemical composition, the properties of the polymer are significantly influenced.

No description available.

No description available.

No description available.

No description available.