Chromatographic analyses of crude leaf extracts of Flaveria linearis L. revealed the presence of four acetylenic monothiophenes. Three of these metabolites were purified and structurally characterized by UV, NMR, IR, and GC-MS. Germination, growth, and survival/mortality studies with and without UVA, the activating wavelengths of these metabolites, were conducted with the crude leaf extracts and the purified compounds (taken individually and combined) against selected crop species (lettuce, radish, and carrot). Results suggest that acetylenic metabolites are phytotoxic against lettuce, carrot, and radish, but with variability in response among species. These variations in sensitivity and the allelopathic potential of F. linearis is discussed.

The removal of trace amounts of acetylene in ethylene streams is a high-volume industrial process that must possess high selectivity of alkyne hydrogenation over hydrogenation of alkenes. Current technology uses metallic nanoparticles, typically palladium or platinum, for acetylene removal. However, problems arise due to the deactivation of the catalysts at high temperatures as well as low selectivities at high conversions. Pore expanded MCM-41 is synthesized via a two-step strategy in which MCM-41 was prepared via cetyltrimethylammonium bromide (CTMABr) followed by the hydrothermal treatment with N,N-dimethyldecylamine (DMDA). This material was washed with ethanol to remove DMDA, or calcined to remove both surfactants. PE-MCM-41 based materials were impregnated with palladium, gold, and palladium-gold nanoparticles. The removal of DMDA had an effect on both the conversion and selectivity, in which they were found to drop significantly. However, by using the bimetallic PdAu catalysts, higher selectivity could be achieved due to increased electron density.

Electrodeposition is a novel method for fabrication of diamond-like carbon (DLC) films on metal substrates. In this work, DLC was electrochemically deposited on different substrates based on an anodic oxidation cyclization of acetylene in liquid ammonia. Successfully anodic deposition was carried out for DLC onto nickel substrate at temperatures below -40°C. Comparative studies were performed on a series of different carbon sources (acetylene, sodium acetylide, and a mixture of acetylene and sodium acetylide). The films were characterized using a variety of methods including Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), XPS valence band spectra, and/or scanning electron microscopy (SEM). Raman spectroscopy is used as a bench mark technique to verify the presence of deposited DLC films, to access the films homogeneities, and to provide the ratio of the different carbon phases, mainly disordered graphite (D) and graphite (G) phases in the films. A combination of the Raman with FTIR and valence band spectra analysis allowed the distinction between hydrogenated DLC and unhydrogenated DLC films. Three different kinds of DLC [(1) hydrogenated DLC (a-C:H); (2) tetrahedral hydrogenated DLC (ta-C:H); and (3) graphitic-like DLC] were deposited depending upon the deposition conditions and substrates. Temperature and current density are the most important parameters to govern the quality of the deposited films, where adding of acetylide into the electrolyte led to films with a higher degree of graphitic phases. The proposed mechanism for acetylene anodic oxidation does not involve direct electron transfer but electrochemical cyclization of acetylene radical cations and hydrogen abstraction at the termination steps. Sodium acetylide, however, dissociates to an acetylenic ion, C2H-, in liquid ammonia. The electrochemistry heterogeneity also leads to island and two-dimensional (2D) nucleation growth of DLC films. Different bond formations of metal to carbon and different chemisorptions of acetylene on metal play important roles in governing the film properties. Using mixed C2HNa and C2H2 as electrolyte, polycrystalline diamond and hexagonal diamond are formed on Mo and stainless steel, respectively. This is the first time to report that polycrystalline diamond can be grown electrochemically at temperature below -40ºC. The preliminary studies on substrate pretreatment with diamond powder and SiC 600 are studied. The effect of the substrate on the film quality for the electrodeposited DLC films described herein is similar to that for diamond deposition via chemical vapor deposition (CVD).

Les complexes de van der Waals sont des entités constituées de différentes molécules liées par des interactions faibles (~kJ/mol). Ces agrégats présentent une réactivité particulière et jouent un rôle essentiel dans les phénomènes de solvatation et nucléation. Des moyens expérimentaux et théoriques pour étudier les complexes de van der Waals et en particulier ceux contenant de l’acétylène ont donc été développés dans ce travail. Nous avons utilisé et amélioré un montage expérimental appelé FANTASIO+ (Fourier trANsform, Tunable diode and quadrupole mAss spectrometers interfaced to a Supersonic expansIOn). Ce montage, composé d’un jet supersonique et d’un spectromètre à temps de déclin permet la production et la détection de ce genre de complexes. Le jet supersonique consiste en une détente adiabatique d’un gaz et assure par refroidissement à quelques Kelvins la production de complexes. La spectrométrie à temps de déclin mesure l’absorption d’un laser infra-rouge par ces molécules cibles assurant ainsi leur détection. <p>Une diode laser nous a permis d’exciter deux fois l’étirement CH de l’acétylène. Nous avons pu détecter et analyser le spectre de vibration-rotation des complexes suivants :C2H2-Ne, C2H2-Ar, C2H2-Kr, C2H2-CO2, C2H2-N2O, et C2H2-C2H2. La molécule C2H2-CO2 et des isotopologues de C2H2-C2H2 ont également été étudiés à plus basse énergie durant un séjour à Calgary au Canada. Nos études ont démontré que ces complexes restaient liés à une énergie pouvant aller jusqu’à 130 fois l’énergie d’interaction entre les deux monomères. L’obtention de données à haute résolution spectrale permet également d’obtenir des données de références pour la validation de modèles théoriques et la planétologie. En particulier, la première détection de C2H2-Kr permettra peut-être une future observation de cet agrégat dans des atmosphères planétaires comme par exemple Titan. <p>Pour avoir une approche globale de ces systèmes nous nous sommes tournés vers les outils de la chimie quantique pour caractériser l’interaction entre les entités du complexe. Des tests méthodologiques approfondis nous ont permis d’évaluer avec exactitude les surfaces d’énergie potentielle intermoléculaire des complexes contenant une molécule d’acétylène et un atome de krypton ou de xénon. <p><p>van der Waals complexes are molecular systems in which the units or molecules are held together by weak interactions (~kJ/mol). These complexes present a peculiar reactivity and play a critical role in solvation and nucleation. Theoretical and experimental means were developed in this work to study such systems and in particular, complexes containing acetylene. In the context of this work the FANTASIO+ (Fourier trANsform, Tunable diode and quadrupole mAss spectrometers interfaced to a Supersonic expansIOn) experimental set-up was used and improved. This set-up, composed of a supersonic expansion and a cavity ring-down spectrometer, provides a way to produce and detect these complexes. The supersonic expansion is an adiabatic expansion which produces the complexes by cooling of the gas to few Kelvin. The CRDS set-up detect those complexes by infra-red laser absorption.<p>Using laser diode to doubly excite the CH stretch of acetylene, one then succeeded to observe and analyze the ro-vibrational spectra of the following complexes: C2H2-Ne, C2H2-Ar, C2H2-Kr, C2H2-CO2, C2H2-N2O, et C2H2-C2H2. The C2H2-CO2 and isotopologues of C2H2-C2H2 were also studied at lower energy during a three months stay in Calgary, Canada. Our studies demonstrated that complexes stayed bound even at an energy 130 times higher than the energy holding the entities together. The high resolution data obtained during this work is also useful to validate theoretical models and planetology. The first detection of the C2H2-Kr complex, in particular, could allow its future detection in other atmospheres, i.e. on Titan.<p>To have a global approach to these systems, the quantum chemistry tools were used to characterize the interaction between the partners of the complexes. Numerous methodological tests allowed us to accurately evaluate the intermolecular potential energy surfaces of the complexes containing an acetylene molecule and a krypton or a xenon atom. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The aim of this thesis was to study structure-property relationships in porous materials using various adapted analytical techniques and in-house instruments. The thesis is divided into two sections, and the first section of work constitutes the majority of the thesis. The first section of work deals with the theoretical versus experimental classification of sorption selectivity in porous compounds. A transiently porous metallocycle that can adsorb acetylene and carbon dioxide served as a model host for this experiment. A volumetric sorption instrument had to be constructed to carry out sorption with acetylene. Even though the metallocycle should theoretically be selective for acetylene over carbon dioxide based on single-gas sorption isotherms, this was not the case during the sorption of a mixture of the two gases. Furthermore, high-pressure single-crystal diffraction was carried out utilising an in-house environmental gas cell, and structural elucidation indicated that both acetylene and carbon dioxide coexist in a single cavity of the host. Additional complementary techniques are discussed that were used to confirm that both gases are present in a single host cavity. The techniques included infrared spectroscopy as well as high-pressure florescence and Raman spectroscopy, which had to be conducted with a specially designed pressure vessel and with adapted instrumentation. Finally, density functional theory calculations were employed to explain how host-guest and guest-guest interactions lead to the change in adsorption selectivity. It is concluded that researchers need to show experimentally that a compound is selective for the adsorption of a specific gas, because theoretical models are not always accurate. The second part of this work focuses on a fundamental study of the structure-property relationships in a porous hydrogen-bonded organic framework. The section starts off by exploring the activation conditions and thermal stability of the framework. This is followed by an exploration of a possible phase transformation or thermal expansion in the framework, but neither of these occurred. Thereafter, an extended study of the framework’s sorption behaviour with various gases is discussed. Then, a structural study of its solvated phase is used to explain the framework’s stability. Finally, a novel analytical method is introduced, and two examples are used to demonstrate why the instrument is useful in the field of supramolecular chemistry. The chapter is concluded by stating the importance these fundamental studies, as well the development of new analytical techniques. / AFRIKAANSE OPSOMMING: Die doel van hierdie tesis was om die struktuur-afhanklike eienskappe van poreuse materiale te ondersoek. Die studie het gebruik gemaak van verskeie aangepasde analitiese metodes asook instrumente wat spesifiek vir die studie gebou was. Die werk word in twee dele verdeel, en die meerderheid van die tesis word in die eerste deel bevat. In die eerste deel van die tesis word die validiteit van teoretiese- teen eksperimentele adsorpsie selektiwiteit opgeweeg. ʼn Gasheer wat bestaan uit ringvormige koördinasie-verbindings en wat asetileen asook koolstof dioksied kan adsorbeer, dien as ʼn model gasheer vir die studie. ʼn Volumetriese sorpsie instrument was spesiaal vir die studie gebou sodat asetileen sorpsie gedoen kon word. Volgens asetileen en koolstof dioksied se enkel-gas adsorpsie isoterme moet asetileen teoreties met voorkeur geadsorbeer word gedurende ʼn adsorpsie eksperiment waarin beide gasse teenwoordig is, maar eksperimenteel was dit bepaal dat dit nie so is nie, dus is daar ʼn verandering in die gasheer se adsorpsie selektiwiteit. Hierna word strukturele data van die gasheer, onder ʼn hoë druk van die gas mengsel, versamel deur gebruik te maak van enkel-kristal diffraksie en ʼn spesiaal-gemaakde gas sel. Die strukturele data toon dat beide asetileen en koolstof dioksied teenwoordig is binne elke porie van die gasheer. Daar word dan van addisionele analitiese metodes gebruik te maak om die observasie te bevestig. Die analitiese metodes sluit in infrarooi spektroskopie asook hoë-druk fluoressensie en Raman spektroskopie wat geëis het dat ʼn spesiale druk-bestande monster houer gebou moes word en dat analitiese instrumente gemodifiseer moet word. Ten slotte was daar van “density functional theory” gebruik gemaak om te verduidelik dat die interaksie tussen die gasheer en gas sowel as die interaksie tussen twee gasse lei tot die verandering in adsorpsie selektiwiteit. Uit hierdie bevinding word die gevolgtrekking gemaak dat navorsers met meer eksperimentele data vorendag sal moet kom voordat ʼn gevolgtrekking gemaak kan word dat ʼn raamwerk selektief een gas adsorbeer. Die tweede afdeling van die werk fokus op ʼn fundamentele studie van die struktuur-afhanklike eienskappe van ʼn poreuse waterstof-verbinde organies raamwerk. Die afdeling begin deur ʼn ondersoek van die aktivering kondisies sowel as die temperatuur-afhanklike stabiliteit van die raamwerk. Dit word gevolg deur te soek na moontlike fase veranderings of temperatuur-afhanklike uitsetting van die raamwerk, maar nie een van die twee eienskappe word waargeneem nie. Daarna word die deeglike ondersoek van die raamwerk se adsorpsie vermoë met verskeie gasse bespreek. Dit word gevolg deur ʼn strukturele studie van die solvaat van die raamwerk, wat dan gebruik word om die stabiliteit van die raamwerk te verduidelik. Ten slotte word ʼn analitiese metode bekend gestel, en twee voorbeelde word gebruik om te wys hoe nuttig die metode is om ʼn kombinasie van resultate te bekom. Die hoofstuk word saamgevat deur te verduidelik hoekom dit belangrik is om hierdie tipe fundamentele studies te doen asook waarom nuwe analitiese metodes ontwerp moet word.

published_or_final_version / Physics / Master / Master of Philosophy

No description available.

The thesis is a summary and discussion of six papers. The purpose of the investigation was to study the influence of (i) environmental factors and (ii) the physiological condition of the thallus on nitrogen fixation in the lichen Stereocaulon paschale (L.) Fr. The nitrogen input to the site, a sparsely stocked pine forest in northern Sweden, was also studied. Nitrogen fixation (nitrogenase activity) was measured as acetylene reduction both in the field and in the laboratory. Usually intact lichen thalli were used, but also excised cephalodia were studied. All nitrogenase activity was located in the external cephalodia containing the blue-green alga Stigonema sp. There was always a reduction in nitrogenase activity when the cephalodia were quantitatively excised from the thallus. Moisture was found to be the most important environmental factor in the field during the snow free part of the year. At the site, with 14 % of the ground covered by S. paschale3 the yearly nitrogen fixation was estimated to c. 0.1 g nitrogen per m^. The lichen thalli could withstand several months in a very dry condition and at a low temperature without significant decrease in nitrogenase activity. A higher capacity for nitrogenase activity was found in lichen thalli collected from bare ground than in thalli collected under the snow. The light conditions before as well as during the nitrogenase activity measurements affected the nitrogenase activity. Thalli incubated with acetylene in the dark had only c. two thirds of their activities in the light. Lichen thalli pretreated in the light showed increased nitrogenase activities, probably due to raised content of carbohydrates available for nitrogenase activity. The necessary energy for nitrogenase activity is supplied by either oxidative phosphorylation or photophosphorylation. / digitalisering@umu

In this dissertation, the ion mobility technique is used to determine the structures of small acetylene cluster ions, (C2H2)1-3+, mass-selected from the largest ever reported ionized acetylene clusters. The technique is also used to characterize the reaction of acetylene clusters with water in an effort to elucidate thermochemistry and kinetics of some interesting ion-molecule reactions suspected to occur in interstellar clouds and other interplanetary bodies.A combination of ion mobility measurements, collision induced dissociation (CID), and theoretical calculations are used to provide the most conclusive evidence for the frequently hypothesized trimerization of ionized acetylene to form the benzene ion. The results also provide evidence for the isomerization of the acetylene dimer ion, (C2H2)2+, to form the cyclobutadiene and vinylacetylene ions.Investigation of the reactions of acetylene radical ions (C2H2∙+) with water reveals competing kinetics for two primary, C2H4O∙+ and C2H3O+, and a secondary, H+(H2O)n, product with an overall reaction rate coefficient of 2.0 × 10-11 cm3s-1. By comparing experimentally observed reactions to theoretically (G3MP2) predicted thermochemistry, the C2H4O∙+ ion is suggested to be the ethenolium ion (vinyl alcohol ion, CH2CHOH∙+) and the C2H3O+ ion is suggested as either the 1-hydroxy-ethenylium (CH2COH+) or cyclic 2H-oxirenium (c-CH2CHO+) ion. Investigation of the temperature dependence of the equilibrium constant for the association reaction (C2H2)3 + + (H2O)n-1 ↔ (C2H2)3∙+(H2O)n using the van't Hoff plot revealed binding energies and reaction entropies identical to those recently published for the benzene+/water system thus providing even more evidence for the formation of benzene ions from ionized acetylene clusters.We also provide a density functional (UB3LYP/Wachters+ f) investigation of Fe+, Co+, and Ni+(C2H2)n clusters (where n = 1-3) to supplement mass spectrometric analysis of the acetylene-solvated cations. For the Co+(C2H2)n clusters, the mass spectrum revealed an intriguing behavior of oscillating magic numbers which we suspect to be the consequence of a Co+-mediated polymerization reaction to form covalent Co+CnHn complexes. The UB3LYP/Wachters+f predicted barrier and exothermicity for the initial step of the proposed trimerization reaction are 25.4 and 101.4 kcal/mol respectively. Our results suggest the efficiency of this reaction is facilitated by cooperative interactions and favorable orientations of acetylenes in the cluster.

O objetivo deste trabalho foi iniciar o estudo de uma nova metodologia sintética para a obtenção do sistema 11-oxabiciclo[6.2.1]undecano, o esqueleto estrutural básico de uma classe de produtos naturais conhecidos como furanoeliangolidos. A abordagem sintética proposta envolveria a formação de um composto bicíclico através da reação de Diels-Alder com derivados de furano, seguida pela formação de um hexanel e, finalmente, ruptura de uma ligação central para formação do sistema macrocíclico. Além disso, a reação de Diels-Alder entre derivados de furano e acetileno dará origem a compostos que apresentam como esqueleto estrutural o sistema 7-oxabiciclo[2.2.1]heptano, que podem ser utilizados como material de partida para a síntese de diversos produtos naturais. Iniciamos este estudo com a reação de Diels-Alder entre o 3,4-dimetoxi-2-metil furano e o bromopropiolato de metila, onde foi obtido o produto 85, que após algumas modificações deu origem ao composto 92. Entretanto, após inúmeras tentativas não conseguimos transformar o composto 92 no triciclo desejado. Para evitar essas transformações que se mostraram problemáticas, resolvemos estudar a reação de Diels-Alder entre derivados de furano e benzoquinonas 2,5-dissubstituídas, que dará origem aos adutos devidamente funcionalizados para serem transformados no derivado do sistema 11-oxabiciclo [6.2.1]undecano. No entanto, após o estudo dessas reações de cicloadição, observamos que elas têm o equilíbrio fortemente deslocado no sentido dos materiais de partida. Por esse motivo, a continuidade desta metodologia sintética mostrou ser inviável. Iniciamos então, um estudo da reação de Diels-Alder entre os diverso derivados de furanos e acetilenos. Após o estudo dessas reações de Diels-Alder foi possível verificar que a maioria dos adutos derivados dos furanos é instável no meio reacional. Os melhores resultados obtidos nessas reações de Diels-Alder foram usando o acetilenodicarboxilato de dimetila como dienófilo. Os adutos obtidos são intermediários importantes e bem funcionalizados, que podem ser utilizados na continuidade do estudo de desenvolvimento de nova metodologia sintética para a obtenção do sistema 11-oxabiciclo[6.2.1]undecano / The aim of this work was to start the study of a new methodology to synthesize the 11-oxabicycle[6.2.1]undecane system, the main carbon skeleton of the furanoheliangolides. The proposed synthetic approach involves the preparation of a bicyclic compound through a Diels-Alder reaction with furan derivatives, followed by formation of a six membered ring and, finally, cleavage of the central bond to obtain of the macrocyclic system. The Diels-Alder reaction between furan and acetylene derivatives gives a compound with the 7-oxabicyclico[2.2.1]heptane system, that is a potential starting material for the synthesis of several natural products. We started this study with the Diels-Alder reaction between the 3,4-dimethoxy-2-methylfuran and methyl bromopropiolate, and obtained the product 85 that after some modifications furnished the compound 92. However, after various attempts we were unable to convert the compound 92 into the desired tricycle. We have then decided to study the Diels-Alder reaction between furan and 2,5-disubstituted benzoquinone derivatives, that could furnish the adducts properly functionalized to be transformed in the 11-oxabicyclico[6.2.1]undecane system. However, we observed that the equilibrium is strongly shifted towards the starting materials in these cycloaddition reactions. This methodology has thus showed to be impracticable. As a third alternative, we affected the study the Diels-Alder reaction between the furans derivatives and the acetylenes. The adducts obtained present 7-oxabicyclico[2.2.1]heptane system that could be used to synthesizes of structural skeleton of furanoheliangolide.