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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.
511

The stabilisation of epoxide hydrolase activity / Jana Maritz

Maritz, Jana January 2002 (has links)
Biocatalysis and enzyme technology represent significant research topics of contemporary biotechnology. The immobilisation of these catalysts on or in static supports serves the purpose of transforming the catalyst into a particle that can be handled through effortless mechanical operations, while the entrapment within a membrane or capsule leads to the restraint of the enzyme to a distinct space. This confinement leads to a catalyst with a superior stability, and cell durability under reaction conditions. Epoxide hydrolase is a widely available co-factor independent enzyme, which is known to have remarkable chemio-, regio- and stereoselectivity for a wide range of substrates. Recently it was found that certain yeasts, including Rhodosporidium toruloides, contain this enzyme and are able to enantioselectively catalyse certain hydrolysis reactions. The objective of this project was four-sided: a) to immobilise Rhodospridium toruloides in an optimised immobilisation matrix (calcium alginate beads), for the kinetic resolution of 1.2- epoxyoctane in order to obtain an optically pure epoxide and its corresponding vicinal diol, b) to determine the effect of immobilisation on activity as well as stability of the enzyme and gain better understanding of the parameters that influence enzyme activity in a support, c) to determine the effect of formulation parameters on some of the bead characteristics and, d) to gain some insight in the distribution of epoxide and diol in the water and bead phases and the formulation parameters that have an effect thereon. Rhodospridium toruloides was immobilised in calcium alginate beads consisting of different combinations of alginate and CaCl2 concentrations. Best results were obtained with a combination of 0,5 % (m/v) alginate and 0,2 M CaC12. The immobilised cells exhibited lower initial activity. but more than 40 times the residual activity of that of the free cells after a 12-hour storage period. Both the immobilised and free cells exhibited an increase in reaction rate (V) with an increase in substrate concentration. An increase in the alginate concentration lead to the formation of smaller beads, but a decrease in enzume activity, while an increase in the CaCl2 solution concentration had no effect on bead diameter or enzyme activity. Epoxide diffused preferentially into the beads (± 96 %), and the diol into the water phase, which leads to the natural separation of the epoxide and the diol. The CaCl2 concentration affected epoxide diffusion with no effect on diol diffusion, which opens up the possibility to regulate the diffusion of epoxide into the beads. Although only a very small fraction of the epoxide inside the beads could be extracted, the alginate proved to be chirally selective for the (R)-epoxide, improving the reaction efficiency by increasing the % ee, of the epoxide extracted from the beads between 26 % and 43 %. The possibility to develop a system where the product is formed, purified and concentrated in a one-step reaction by extracting the product from the bead phase was clearly demonstrated. / Thesis (M.Sc. (Pharm.) (Pharmaceutical Chemistry))--Potchefstroom University for Christian Higher Education, 2003.
512

I Wish I were a Tiger... Domestic Violence Research with Children Who Have Witnessed Domestic Violence

Jones, Margaret Pearman 11 June 2007 (has links)
This paper presents the results of a study conducted at a domestic violence safehouse for an undergraduate Honors Thesis. Twenty-three children ages 4-16 from African American and immigrant communities were interviewed while residing at a safehouse for victims of domestic violence regarding their beliefs and attitudes about perceptions of self, conflict resolution skills, and feelings of anger and coping strategies. The study found a strong relation between length of stay & positive coping strategies. Age & gender were also related to conflict resolution skills. Qualitative data provided interesting & potentially important insights into children’s internal experiences of being witnesses of domestic violence. The study did not support past research in terms of child witnesses exhibiting low self-esteem, poor conflict strategies, and high rates of aggression. This study concludes that more research needs to be conducted on protective factors and resiliency to the effects of domestic violence to explain this study’s results.
513

Wave phenomena in phononic crystals

Sukhovich, Alexey 14 September 2007 (has links)
Novel wave phenomena in two- and three-dimensional (2D and 3D) phononic crystals were investigated experimentally using ultrasonic techniques. Resonant tunneling of ultrasonic waves was successfully observed for the first time by measuring the transmission of ultrasound pulses through a double barrier consisting of two 3D phononic crystals separated by a cavity. This effect is the classical analogue of resonant tunneling of a quantum mechanical particle through a double potential barrier, in which transmission reaches unity at resonant frequencies. For phononic crystals, the tunneling peak was found to be less than unity, an effect that was explained by absorption. The dynamics of resonant tunneling was explored by measuring the group velocities of the ultrasonic pulses. Very slow and very fast velocities were found at frequencies close to and at the resonance, respectively. These extreme values are less than the speed of sound in air and greater than the speed of sound in any of the crystal’s constituent materials. Negative refraction and focusing effects in 2D phononic crystals were also observed. Negative refraction of ultrasound was demonstrated unambiguously in a prism-shaped 2D crystal at frequencies in the 2nd pass band where the wave vector and group velocity are opposite. The Multiple Scattering Theory and Snell’s law allowed theoretical predictions of the refraction angles. Excellent agreement was found between theory and experiment. The negative refraction experiments revealed a mechanism that can be used to focus ultrasound using a flat phononic crystal, and experiments to demonstrate the focusing of ultrasound emitted by several point sources were successfully carried out. The importance of using phononic crystals with circular equifrequency contours, as well as matching the size of the contours inside and outside the crystal, was established. Both conditions were satisfied by a flat phononic crystal of steel rods, in which the liquid inside the crystal (methanol) was different from the outside medium (water). The possibility of achieving subwavelength resolution using this phononic crystal was investigated with a subwavelength line source (a miniature strip-shaped transducer, approximately lambda/5 wide, where lambda is sound wavelength in water). A resolution of 0.55lambda was found, which is just above the diffraction limit lambda/2.
514

The Mediator, the Negotiator, the Arbitrator or the Judge? Translation as Dispute Resolution

Hsieh, Hungpin Pierre 04 February 2014 (has links)
Metaphors have long shaped the way pure translation studies describe and justify the translation phenomenon by discovering and consolidating underlying principles. Ultimately, by means of metaphor, something that dwells on the interaction of two seemingly distinct things, translation theorists have obtained a better understanding of the category of translation. Human beings are gregarious, and disputes are inevitable in every society, ancient or modern, primitive or civilized. In fact, conflict is one iron law of life that mankind has had to improvise ways of resolving, from such formal ones as litigation to private ones such as self-help. We may not be able to eliminate dispute altogether, but we can, however, resolve it through creative and civilized means. Translation can be approached in a similar context, except it concerns a metaphorical dispute between cultures and/or languages—and probably on a more intangible and subtle platform. Disparate cultures, religions and languages in a clash can be brought closer to each other with skillful translation, and hence, translation is a variation of dispute resolution. That never went totally unnoticed. Over the years, countless translation metaphors have been constructed and exploited with very different results, which indicates how interdisciplinary a subject translation studies really is. Yet, apparently, translation is most often metaphorized as mediation and negotiation but rarely as arbitration or litigation, and one cannot but wonder whether this happened out of sheer coincidence or because of some misunderstanding. Thus, much as I appreciate what theorists have accomplished with translation metaphors, in regard to didactics and heuristics, my primitive observation is that translation theorists and practitioners have never made full use of metaphorization in that they might have had an incomplete idea of dispute resolution theory in general. After all, a metaphor is, ideally, meant to facilitate active learning and full integration of new knowledge, but there still remains a missing piece that is part and parcel of our metaphorization of translation. Specifically, translators have always embraced the amicable terms of negotiation and mediation, distancing themselves from non-mainstream ones such as arbitration and litigation. To that end, in my thesis, I will explore and examine translation through slightly renewed lenses, demonstrating how and why our metaphor schema and mapping should originate in dispute resolution, and why litigation, and perhaps even arbitration as dispute resolution mechanisms, would serve as good a metaphor—if not a better one—for translation. It is my resolute belief that the translator is more qualified as a judge, a respectable professional vested with immense judicial power, than as a mediator, who is but a third-party neutral facilitating dialogue between two disputants. Only in this way can metaphors do translation theory a great service by furnishing it with a renewed and objective description of translation.
515

When War Ends: Building Peace in Divided Communities

Francis, David J. January 2012 (has links)
This volume critically examines what happens when war formally ends, the difficult and complex challenges and opportunities for winning the peace and reconciling divided communities. By reviewing a case study of the West African state of Sierra Leone, potential lessons for other parts of the world can be gained. Sierra Leone has emerged as a 'successful' model of liberal peacebuilding that is now popularly advertised and promoted by the international community as a powerful example of a country that they finally got right. Concerns about how successful a model Sierra Leone actually is, are outlined in this project. As such this volume: provides a critical understanding of the nature, dynamics and complexity of post-war peacebuilding and development from an internal perspective; critically assesses the role and contribution of the international community to state reconstruction and post-war peacebuilding and evaluates what happens when war ends; and explores the potential relevance and impact of comparative international efforts of post-war state building and reconstruction in other parts of Africa and the world. The collection focuses not only on understanding the root causes of conflict but also identifying and appreciating the possibilities and opportunities for peace. The lessons found in this book resonate well beyond the borders of Sierra Leone and Africa in general.
516

High resolution imaging of bio-molecular binding studies studies using a Widefield surface Plasmon Microscope.

Denyer, Morgan C.T., Jamil, M.M. Abdul, Twigg, Peter C., Youseffi, Mansour, Britland, Stephen T., Liu, S., See, Chung Wah, Zhang, J., Sommekh, M.G. 14 September 2009 (has links)
Surface plasmon microscopes are mostly built around the prism based Kretschmann configuration. In these systems, an image of a sample can be obtained in terms of an intensity map, where the intensity of the image is dependent on the coupling of the light into the surface plasmons. Unfortunately the lateral resolution of these systems relies on the ability of plasmons to propagate along the metallised layer and is usually limited to a few microns unless special measures are taken. The widefield surface plasmon microscope (WSPR), used here enables surface plasmon imaging at significantly higher lateral resolutions than prism based systems. In this study we demonstrate the functionality of the WSPR by imaging a sequence of binding events between micro-patterned extracellular matrix proteins and their specific antibodies. Using the WSPR system a change in contrast was observed with each binding event. Images produced via the WSPR system were analyzed and compared qualitatively and quantitatively. Consequently, we confirm that the WSPR microscope described here can be used to study sequential monomolecular layer binding events on a micron scale. These results have significant implications in the development of new micron scale bioassays.
517

Transnational civil society and the dynamics of alliance-building: managing inter-group conflict among socio-economic organizations

Smith, Janel 22 December 2007 (has links)
This thesis investigates the potential and emerging roles of the Social Economy at the level of global governance by examining how transnational civil society (TCS) has organized in an attempt to influence global policy-making. One of this study’s principal aims is to glean insights into the dynamics of civil society coalitions, gaining a better understanding of how they combine the collective knowledge, resources and strengths of members and drawing out some of the “best practices” and challenges inherent in past civil society alliances. This study seeks to explore the complex nature of the relationships that exist among civil society actors and the unique challenges such groups face in forming partnerships by examining these relationships through the lens of Inter-Group Conflict Theory. A Case Study of one TCS partnership, the Make Poverty History (MPH) campaign, is conducted and an Inter-Group Dispute Resolution Analysis of MPH is carried out.
518

Laser spectroscopy of caesium dimers

Butcher, Louise Sara January 1997 (has links)
We have obtained spectra of 10 vibrational bands of the Cs<sub>2</sub> (2)<sup>3</sup>∏<sub>u</sub> ← ϰ<sup>3</sup>∑<sup>+</sup><sub>9</sub> system. The molecules were formed in a supersonic free jet expansion, and were excited by light from a single mode CW dye laser. The total laser induced fluorescence was measured at 90° to the incident light and molecular beam, using a photomultiplier. Using a slit system to image a selected part of the interaction region, we have reduced the Doppler width to about 350MHz. We have been able to resolve the discrepancy between the different vibrational band positions given in two previous papers. Our vibrational bands show broad rotational contours, but we have not been able to resolve individual rotational lines. We have also obtained rotationally resolved spectra of the bandhead region of 22 vibrational bands of the Β<sup>1</sup>∏<sub>9</sub> ← X<sup>1</sup>∑<sup>+</sup><sub>u</sub> system. We found that the frequencies of the bandheads agreed with the bandhead positions deduced from the Dunham coefficients of a previous work. We have developed a theoretical model of the rotational structure and intensity distribution, taking into account optical pumping and the small solid angle subtended by the detector. By fitting this model to the experimental spectrum of the v' = 3,u∿ = 0 band using least squares optimization, we were able to extract rotational constants and line positions. We found that these line positions were in good agreement with those from the previous work. We have discussed how such spectroscopic data may be used in a determination of the s-wave scattering length of caesium, and we have reviewed the validity of the scattering length and other pararneterisations of low energy Cs-Cs interactions.
519

Organocatalytic Acylation for the Kinetic Resolution of Secondary Aryl Alcohols : Synthetic Applications and Mechanistic Studies

Mesas Sánchez, Laura January 2014 (has links)
The research described in this thesis focuses on the catalytic acylative kinetic resolution (KR) of aromatic secondary alcohols, using a planar-chiral 4-(dimethylamino)pyridine (DMAP) organocatalyst. In the first part of this thesis, the substrate scope of the above mentioned process was expanded to aromatic secondary alcohols that contain an extra functional group in the alkyl moiety, such as 1,2-azido alcohols, 2-hydroxy-2-aryl-ethylphosphonates and 2-hydroxy-2-aryl esters. Thus, the preparation of highly functionalized compounds in their enantiomerically pure form with excellent enantiomeric excess (up to 99% ee) was achieved. Furthermore, the synthetic applicability of this methodology was illustrated through the synthesis of two high value compounds, (R)-Pronethalol and (S)-3-hydroxy-N-methyl-3-phenylpropanamide, which is an immediate precursor of bioactive molecules such as (S)-Fluoxetine. The second part of this thesis deals with the mechanistic study of the acylative KR catalyzed by the planar-chiral DMAP derivative. Reaction Progress Kinetic Analysis methodology was used in the investigation of the reaction mechanism, probing that no notable product inhibition or decomposition of the catalyst occurs in the studied system. The reaction rate showed fractional order dependence on the concentration of both reactants. Furthermore, NMR spectroscopy was utilized to study the equilibrium between the different catalyst states, which explains the measured kinetics of the reaction.
520

Non-covalent interactions and their role in biological and catalytic chemistry

Kennedy, Matthew R. 12 January 2015 (has links)
The focus of this thesis is the question of how non-covalent interactions affect chemical systems' electronic and structural properties. Non-covalent interactions can exhibit a range of binding strengths, from strong electrostatically-bound salt bridges or multiple hydrogen bonds to weak dispersion-bound complexes such as rare gas dimers or the benzene dimer. To determine the interaction energies (IE) of non-covalent interactions one generally takes the supermolecular approach as described by the equation \begin{equation} E_{IE} = E_{AB} - E_{A} - E_{B}, \end{equation} where subscripts A and B refer to two monomers and AB indicates the dimer. This interaction energy is the difference in energy between two monomers interacting at a single configuration compared to the completely non-interacting monomers at infinite separation. In this framework, positive interaction energies are repulsive or unfavorable while negative interaction energies signify a favorable interaction. We use prototype systems to understand systems with complex interactions such as π-π stacking in curved aromatic systems, three-body dispersion contributions to lattice energies and transition metal catalysts affect on transition state barrier heights. The current "gold standard" of computational chemistry is coupled-cluster theory with iterative single and double excitation and perturbative triple excitations [CCSD(T)].\cite{Lee:1995:47} Using CCSD(T) with large basis sets usually yields results that are in good agreement with experimental data.\cite{Shibasaki:2006:4397} CCSD(T) being very computational expensive forces us to use methods of a lower overall quality, but also much more tractable for some interesting problems. We must use the available CCSD(T) or experimental data available to benchmark lower quality methods in order to ensure that the low quality methods are providing and accurate description of the problem of interest. To investigate the effect of curvature on the nature of π-π interactions, we studied concave-convex dimers of corannulene and coronene in nested configurations. By imposing artificial curvature/planarity we were able to learn about the fundamental physics of π-π stacking in curved systems. To investigate these effects, it was necessary to benchmark low level methods for the interaction of large aromatic hydrocarbons. With the coronene and corannulene dimers being 60 and 72 atoms, respectively, they are outside the limits of tractability for a large number of computations at the level of CCSD(T). Therefore we must determine the most efficient and accurate method of describing the physics of these systems with a few benchmark computations. Using a few benchmark computations published by Janowski et al. (Ref. \cite{Janowski:2011:155}) we were able to benchmark four functionals (B3LYP, B97, M05-2X and M06-2X) as well as four dispersion corrections (-D2, -D3, -D3(BJ), and -XDM) and we found that B3LYP-D3(BJ) performed best. Using B3LYP-D3(BJ) we found that both corannulene and coronene exhibit stronger interaction energies as more curvature is introduced, except at unnaturally close intermolecular distances or high degrees of curvature. Using symmetry adapted perturbation theory (SAPT)\cite{Jeziorski:1994:1887, Szalewicz:2012:254}, we were able to determine that this stronger interaction comes from stabilizing dispersion, induction and charge penetration interactions with smaller destabilizing interactions from exchange interactions. For accurate computations on lattice energies one needs to go beyond two-body effects to three-body effects if the cluster expansion is being used. Three-body dispersion is normally a smaller fraction of the lattice energy of a crystal when compared to three-body induction. We investigated the three-body contribution using the counterpoise corrected formula of Hankins \textit{et al.}.\cite{Hankins:1970:4544} \begin{equation} \Delta ^{3} E^{ABC}_{ABC} = E^{ABC}_{ABC} - \sum_{i} E^{ABC}_{i} - \sum_{ij} \Delta ^{2} E^{ABC}_{ij}, \end{equation} where the superscript ABC represents the trimer basis and the E(subscript i) denotes the energy of each monomer, where {\em i} counts over the individual molecule of the trimer. The last term is defined as \begin{equation} \Delta ^{2} E^{ABC}_{ij} = E^{ABC}_{ij} - E^{ABC}_{i} - E^{ABC}_{j}, \end{equation} where the energies of all dimers and monomers are determined in the trimer basis. Using these formulae we investigated the three-body contribution to the lattice energy of crystalline benzene with CCSD(T). By using CCSD(T) computations we resolved a debate in the literature about the magnitude of the non-additive three-body dispersion contribution to the lattice energy of the benzene crystal. Based on CCSD(T) computations, we report a three-body dispersion contribution of 0.89 kcal mol⁻¹, or 7.2\% of the total lattice energy. This estimate is smaller than many previous computational estimates\cite{Tkatchenko:2012:236402,Grimme:2010:154104,Wen:2011:3733,vonlilienfeld:2010:234109} of the three-body dispersion contribution, which fell between 0.92 and 1.67 kcal mol⁻¹. The benchmark data we provide confirm that three-body dispersion effects cannot be neglected in accurate computations of the lattice energy of benzene. Although this study focused on benzene, three-body dispersion effects may also contribute substantially to the lattice energy of other aromatic hydrocarbon materials. Finally, density functional theory (DFT) was applied to the rate-limiting step of the hydrolytic kinetic resolution (HKR) of terminal epoxides to resolve questions surrounding the mechanism. We find that the catalytic mechanism is cooperative because the barrier height reduction for the bimetallic reaction is greater than the sum of the barrier height reductions for the two monometallic reactions. We were also able to compute barrier heights for multiple counter-ions which react at different rates. Based on experimental reaction profiles, we saw a good correlation between our barrier heights for chloride, acetate, and tosylate with the peak reaction rates reported. We also saw that hydroxide, which is inactive experimentally is inactve because when hydroxide is the only counter-ion present in the system it has a barrier height that is 11-14 kJ mol⁻¹ higher than the other three counter-ions which are extremely active.

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