Challenges in treating injuries, together with an increased need for repair of damaged tissues and organs, have made regenerative medicine a major research area today. Biomaterials such as silk fibroin (SF) have proven to be excellent tissue scaffolds possessing properties essential in tissue engineering such as biocompatibility, biodegradability and exceptional mechanical properties. SF nanofibres are especially attractive due to their large surface-to-volume ratio and high porosity which is beneficial in regenerative medicine. However, to design biomaterial scaffolds, chemical and physical properties of SF have to be sufficiently known. The thesis aims to contribute to knowledge by characterizing silk fibroin from the African wild silkworm species Gonometa rufobrunnae, Gonometa postica, Argema mimosae, Epiphora bahuniae and Anaphe panda. Moreover, the feasibility of producing nanofibrous biomaterial scaffolds from these fibroins is explored. The chemical composition of degummed fibres was investigated using Capillary electrophoresis whilst Infrared (IR) and Raman spectroscopic techniques were utilized to determine structural characteristics of the fibroin. In addition, thermal behaviour and mechanical properties of the fibroins were also investigated. Nanofibres were fabricated via electrospinning. The effects of solution concentration, voltage, polymer flow rate and tip to collector distance were studied to give optimum electrospinning conditions. IR spectroscopy was also utilized to observe the conformational structure of the degummed and electrospun fibres whilst scanning electron microscopy (SEM) provided information on the size and morphology of the fibres. The use of the nanofibres as biomaterials was evaluated using cytotoxicity tests. Results showed that glycine, alanine and serine constituted over 70% of the amino acid composition of all the fibroins. Gonometa fibroin had more glycine than alanine whilst the opposite was true for Argema mimosae, Epiphora bahuniae and Anaphe panda fibroin. The abundance of basic amino acids in Gonometa rufobrunnae, Gonometa postica, Argema mimosae and Epiphora bahuniae fibroin makes them prime candidates for cell and tissue culture. The amino acid composition of the fibroins influenced secondary structure as the β-sheet structure. Anaphe panda, Argema mimosae and Epiphora bahuniae silks was made up of mostly alanine-alanine (Ala-Ala)n polypeptides whilst Gonometa fibroin had an interesting mixture of both glycine-alanine (Gly-Ala)n and (Ala-Ala)n units. The unique structures impacted the mechanical and thermal properties of the fibroins. Production of Gonometa nanofibres was mainly dependent on fibroin solution concentration. A minimum of 27 % w/v was needed to produce defect free nanofibres. Diameters of the electrospun fibres produced ranged from 300 to 2500 nm. IR spectroscopy data highlighted that the β-sheet conformation of degummed fibroin was degraded during the formation of the nanofibres rendering them water soluble. It was however possible to regenerate the β-sheet structure in the nanofibres by exposing them to various solvents. Cytotoxicity tests using Sulforhodamine B (SRB) assay demonstrated that the nanofibres were not toxic to cells, a major prerequisite for use as a biomaterial. This thesis successfully provides useful data in an area that has been minimally explored. Results suggest that SF from African silkworm species offers diversity in properties and are therefore attractive for use as biomaterials, especially in cell and tissue engineering. As far as we could determine, we are the first to extend the use of fibroin from African silk species by producing Gonometa SF nanofibres that are of potential use as biomaterial scaffolds. / Chemistry / D. Phil. (Chemisty)

Thesis (MSc. (Chemistry)) -- University of Limpopo, 2013 / Drinkable water is water that is safe enough to be consumed by humans or used with low risk of immediate or long term harm. World-wide, insufficient access to portable water and use of sources contaminated with disease vectors, pathogens, and unacceptable levels of toxins is a huge problem. The use of such water for drinking and food preparation leads to the widespread of acute and chronic illnesses. This is a major cause of death and misery in many undeveloped countries. Reduction of waterborne diseases is a major public health goal in developing countries. Nanotechnology offers the possibility of an efficient removal of pollutants and microorganisms from water. Essentially, three classes of nanoscale materials were investigated as functional materials for water purification in this study. Silver nanoparticles, carbon nanotubes and beta ()-cyclodextrin polymers were synthesised and characterised specifically for purification of water samples. β-cyclodextrin is soluble in both water and other aqueous media. In order to render cyclodextrins insoluble, they were converted into highly cross-linked polymers, by polymerisation with a bifunctional linker, hexamethylene diisocyanate. Cyclodextrins were functionalised and synthesised with either the allyl or the benzoyl group. Characterisation with fourier transform infrared (FTIR) spectrophotometer confirmed the functionalisation process. Thereafter the scanning electron microscopy (SEM) analysis confirmed the polymers’ morphology to be spongy, and capable of absorbing contaminants. Multi-walled carbon nanotubes (MWCNTs) were treated with a mixture of sulphuric and nitric acid in order to introduce the carboxyl and hydroxyl groups. These were characterised by SEM, transmission electron microscopy (TEM), X-ray diffraction (XRD) and FTIR spectroscopy to confirm the functionalisation process. Silver nanoparticles were synthesised from sodium citrate and silver nitrate, using sodium dodecyl sulphate as a surfactant. Their characterisation was done by SEM, energy dispersive X ray (EDX) spectroscopy, TEM, UV/Vis spectroscopy and XRD to confirm a face centred cubic structure with an estimated crystallite size ranging from 50 to 100 nm.β-cyclodextrin polymers, functionalised multi-walled carbon nanotubes and silver nanoparticle-doped MWCNTs/cyclodextrin composites were characterised by SEM, TEM, XRD, Brunauer-Emmet-Teller (BET) and EDX. Analysis of the phenolic compound, 4-hydroxynitrobenzene in water, using these nanocomposites, demonstrated good capabilities of removing organic contaminants from water samples as indicated by their high absorption efficiencies of the contaminants. The synthesised metal-organic composites were tested for their effectiveness in removing organic contaminants as well as for eliminating Escherichia coli bacteria from water. The synthesised composites presented up to 97% absorption efficiency of organic contaminants and up to 100% inactivation of the bacteria. There was complete destruction of bacteria from the water analysed at various times and varying concentrations. After a long exposure of the nanocomposites to E. coli, pits were noticeable on the external morphology of the bacteria, thus suggesting that the nanocomposites are bactericidal. The bacterial activity increased with temperature,when studied between 10 oC and 30 oC.

En aquesta tesi s'ha desenvolupat i utilitzat una potent estrategia computacional per a l'estudi, tant estructural, dinàmic i energètic, de nous [2]rotaxanes que van ser sintetizats i caracteritzats experimentalment pel grup de recerca col·laborador del Prof. Donald Fitzmaurice de la University College Dublin, a Irlanda. Com a etapa preliminar, es van estudiar uns pseudorotaxans formats per les mateixes estacions que presentaven els nous [2]rotaxans. Es va modelitzar el comportament dels pseudorotaxans en diferents dissolvents (CH3CN i CH3OH) i amb la presència de dos tipus de contraions (PF6- i Br-). Es va voler aprofundir en el coneixement de les interaccions entre el macrocicle i les estacions. En aquesta direcció, es van determinar les energies de complexació dels complexes estació-macrocicle i també la variació energètica davant la posició del macrocicle respecte l'eix del pseudorotaxà. Els results obtinguts computacionalment van ser comparats amb els resultats obtinguts en estudis experimentals en dissolució (RMN, espectroscòpia d'absorció òptica, voltametria cíclica). Posteriorment, es va examinar el moviment traslacional del macrocicle degut a la reducció de les estacions del [2]rotaxà realitzant simulations de Perturbació d'Energia Lliure. Existeix una important contribució metodològica present en el desenvolupament de les parametritzacions per a modelitzar amb AMBER els ions PF6- i Br- i les estacions utilitzades en aquesta tesi. També s'han detectat deficiències en el mòdul RESP durant la comprovació del seu funcionament.Els [2]rotaxans estudiats són interessants ja que presenten força aplicacions pràctiques en el futur. Un dels grups bloquejador del [2]rotaxà es pot quedar unit a la superfície d'un elèctrode o alguna nanopartícula semiconductora. Així doncs, com a resultat de la col·laboració de tots dos grups es pot concloure que s'ha generat informació útil que pot ajudar a realitzar un millor disseny de [2]rotaxans i supermolècules relacionades que tinguin la capacitat de funcionar com a interrupturs bi-estables i puguin ésser utilitzats en la contrucció de futurs sistemes electrònics, en particular, com a dispositius bi-estables d'emmagatzematge d'informació. / En esta tesis se ha desarrollado y utilizado una potente estrategia computacional para el estudio, tanto estructural, dinámico como energético, de nuevos [2]rotaxanos que fueron sintetizados y caracterizados experimentalmente por el grupo de investigación colaborador del profesor Donald Fitzmaurice de la University College Dublin, en Irlanda. Como etapa preliminar, se estudiaron unos pseudorotaxanos formados por las mismas estaciones que presentaban los nuevos [2]rotaxanos. Se modelizó el comportamiento de pseudorotaxanos en diferentes disolventes (CH3CN y CH3OH) y con la presencia de dos tipos de contraiones (PF6- y Br-). Se quería profundizar en el conocimiento de las interacciones entre el macrociclo y las estaciones. En esta dirección, se determinaron las energías de complejación de los complejos estación-macrociclo y también la variación energética según la posición del macrociclo respecto el eje del pseudorotaxano. Los resultados obtenidos computacionalmente fueron comparados con los resultados obtenidos en estudios experimentales en disolución (RMN, espectroscopía de absorción óptica, voltametría cíclica). Posteriormente, se examinó el movimiento traslacional del macrociclo debido a la reducción de las estaciones del [2]rotaxano realizando simulaciones de Perturbación de Energía Libre. Existe una importante contribución metodológica presente en el desarrollo de las parametrizaciones para modelizar en AMBER los iones PF6- y Br- y las estaciones utilizadas en esta tesis. También se han detectado deficiencias en el módulo RESP durante la comprobación de su funcionamento.Los [2]rotaxanos estudiados son interesantes ya que presentan numerosas aplicaciones prácticas en el futuro. Uno de los bloqueadores del [2]rotaxano se puede unir a la superficie de un electrodo o a alguna nanopartícula semiconductora. Por tanto, como resultado de la colaboración de ambos grupos se puede concluir que se ha generado información útil que puede ayudar a realizar un mejor diseño de [2]rotaxanos y supermoléculas relacionadas que tengan la capacidad de funcionar como interruptores bi-estables y puedan ser utilizados en la construcción de futuros sistemas electrónicos, en particular, como dispositivos bi-estables de almacenamiento de información. / Powerful computational strategy is outlined and tested for studying the structure, dynamics and the energetics of novel modified [2]rotaxanes which were synthesized and experimentally characterized by a collaborative group of Prof. Donald Fitzmaurice from the University College Dublin, Ireland. As a first necessary step, [2]pseudorotaxanes had been examined that contain in the axles the same bipyridinyl stations of the [2]rotaxanes. The behavior of the pseudorotaxanes in two different solvents, acetonitrile and methanol is modeled at the presence of two types of counterions, PF6- and Br-. In this way an insight is gained into the interactions between the crown ether ring and the stations. Complexation energies for the viologen-crown complexes were determined, as well as the energy profiles for the movement of the crown macroring along the axle of the pseudorotaxane. The computed data for the [2]rotaxanes are compared with results from solution studies (NMR, optical absorption spectroscopy, cyclic voltametry). In addition, the shuttling of the ring in the [2]rotaxane induced by stepwise reduction of the viologen stations is examined by FEP simulations. An important methodological contribution presents the development of parameterizations for the modeling with AMBER of the hexafluorophosphate and the bromine anions and the viologens. Some deficiencies of RESP have been also noticed when testing its performance. The [2]rotaxanes studied present an interesting case with probable future practical applications. Namely, one of the bulky stoppers of the [2]rotaxane can be used to attach the rotaxane to the surface of an electrode or semiconductor nanoparticle. Thus the joint efforts of the two groups could be expected to produce useful information that can help in the rational design of [2]rotaxanes and related supermolecules capable of functioning as bi-stable switches for use in the next generation electronics, in particular as bistable devices for information storage.

Nanocatalysis, catalysis using particles on the nanoscale, is an emerging field that has tremendous potential. Nanoparticles have different properties than bulk material and can be used in different roles. Macro sized precious metals, for example, are inert, but nanoparticles of them are becoming more widely used as catalysts. Understanding the manner in which these particles work is vital to improving their efficacy. This thesis focuses on two aspects of nanocatalysis. Chapter 1 begins with a brief introduction into nanotechnology and some of the areas in which nanoparticles are different than bulk particles. It then proceeds into an overview of catalysis and nanocatalysis more specifically. Focus is brought to the definitions of the different types of catalysis and how those definitions differ when applied to nanoparticles. Chapter 2 is in finding an inert support structure to more easily assist in recycling the nanoparticles. Polystyrene microspheres were studied and found to prevent platinum nanoparticles from aggregating in solution and possibly aid in recycling of the nanoparticles. These nanoparticles were used in catalysis, aiding in the reduction of 4-nitrophenol in the presence of sodium borohydride. While the rate decreased by a factor of ~ 7 when using the polystyrene, the activation energy of the reaction was unaltered, thus confirming the inactivity of the polystyrene in the reaction. In Chapter 3, nanocatalysis was studied by examining bimetallic hollow nanoparticles with specific attention to the effect of altering the ratios of the two metals. Ten different bimetallic nanocages were tested in an electron transfer reaction between hexacyanoferrate and thiosulfate. Five PtAg nanocages and five PdAg with varying metal ratios were prepared and studied. It was found that while silver cubes immediately precipitate out of solution when combined with thiosulfate, a small amount of either platinum or palladium allows the particles to remain in solution and function as a substantially more effective catalyst. However, as additional Pt was added the activation energy increased. To obtain a better understanding of the catalysis using bimetallic cages, the evolution of these cages was studied as the 2nd metal was added. Initially the particle edge length increased and then slowly decreased back to the size of the template cubes. The increase in edge length suggests of addition of material to the nanoparticles. This indicated the 2nd metal is on the outside of the cage, which was confirmed using UV-Vis spectroscopy and EDS mapping. By understanding how these bimetallic particles evolve, we may be able to manipulate these synthetic methods to more precisely design nanoparticles for catalysis.

The present research involves two projects: a surface science study of the room-temperature adsorption and thermal evolution of allylamine and ethanolamine on Si(100)2×1, studied by using temperature-dependent X-ray photoelectron spectroscopy (XPS) and thermal desorption spectrometry (TDS), as well as Density Functional Theory (DFT) calculations; and a materials science study on the shape control of copper nanoparticles (Cu NPs) deposited on H-terminated Si(100) substrate with an extended size regime of 5-400 nm, by using a simple, one-step electrochemical method. The Cu NPs of three primary shapes were characterized with scanning-electron microscopy (SEM), glancing-incidence X-ray diffraction (GIXRD) and XPS. In the first surface science study, the presence of broad N 1s XPS features at 398.9-399.1 eV, corresponding to N–Si bonds, indicates N–H dissociative adsorption for both allylamine and ethanolamine on Si(100)2×1. For allylamine, the presence of C 1s features at 284.6 eV and 286.2 eV, corresponding to C=C and C−N, respectively, and the absence of the Si−C feature expected at 283.5 eV show that the reactions involving the ethenyl group such as the [2+2] C=C cycloaddition or those producing the [N, C, C] tridentate adstructures do not occur at room temperature. For ethanolamine, the O 1s feature at 533.1 eV indicates the formation of Si−O bond and O−H dissociation, which confirms an [O, N] bidentate adstructure and excludes the N−H and O−H dissociation unidentate structures. These XPS data are consistent with the N−H unidentate, and N−H and O−H double dissociation [O, N] bidentate adstructures for allylamine and ethanolamine, respectively, as predicted by the DFT calculations. TDS and temperature-dependent XPS data further show the desorption of propene and ethylene at 580 K and of acetylene at 700 K for allylamine and the desorption of ethylene at 615 K for ethanolamine, while the lack of N- or O-containing desorbates suggests that the dissociated N and O species are likely bonded to multiple surface Si atoms or diffused into the bulk at elevated temperatures (as confirmed by the corresponding temperature-dependent XPS spectra). Unlike the multidentate allyl alcohol and allylamine adstructures that have been found to be not favored kinetically, the present [O, N] bidentate ethanolamine adstructure appears to be kinetically favored on Si(100)2×1. In the second materials science study, Cu NPs of three primary shapes have been deposited on H-terminated Si(100) by a simple, one-step electrochemical method. By precisely manipulating the electrolyte concentration [CuSO4.5H2O] below their respective critical values, cubic, cuboctahedral, and octahedral Cu NPs of ranges of average sizes and number densities can be easily obtained by varying the deposition time. Combined GIXRD and depth-profiling XPS studies show that these Cu NPs have a crystalline core-shell structure, with a face-centered cubic metallic Cu core and a simple cubic Cu2O shell with a CuO outerlayer. The shape control of Cu NPs can be understood in terms of a progressive growth model under different kinetic conditions as dictated by different [CuSO4.5H2O] concentration regimes. The two studies in the present work lay the foundation for future investigation of surface biofunctionalization of these fascinating Cu NPs with different shapes and therefore different surface chemistries as controlled by the relative amounts of the (100) and (111) facets, and their boundaries.

The present research involves two projects: a surface science study of the room-temperature adsorption and thermal evolution of allylamine and ethanolamine on Si(100)2×1, studied by using temperature-dependent X-ray photoelectron spectroscopy (XPS) and thermal desorption spectrometry (TDS), as well as Density Functional Theory (DFT) calculations; and a materials science study on the shape control of copper nanoparticles (Cu NPs) deposited on H-terminated Si(100) substrate with an extended size regime of 5-400 nm, by using a simple, one-step electrochemical method. The Cu NPs of three primary shapes were characterized with scanning-electron microscopy (SEM), glancing-incidence X-ray diffraction (GIXRD) and XPS. In the first surface science study, the presence of broad N 1s XPS features at 398.9-399.1 eV, corresponding to N–Si bonds, indicates N–H dissociative adsorption for both allylamine and ethanolamine on Si(100)2×1. For allylamine, the presence of C 1s features at 284.6 eV and 286.2 eV, corresponding to C=C and C−N, respectively, and the absence of the Si−C feature expected at 283.5 eV show that the reactions involving the ethenyl group such as the [2+2] C=C cycloaddition or those producing the [N, C, C] tridentate adstructures do not occur at room temperature. For ethanolamine, the O 1s feature at 533.1 eV indicates the formation of Si−O bond and O−H dissociation, which confirms an [O, N] bidentate adstructure and excludes the N−H and O−H dissociation unidentate structures. These XPS data are consistent with the N−H unidentate, and N−H and O−H double dissociation [O, N] bidentate adstructures for allylamine and ethanolamine, respectively, as predicted by the DFT calculations. TDS and temperature-dependent XPS data further show the desorption of propene and ethylene at 580 K and of acetylene at 700 K for allylamine and the desorption of ethylene at 615 K for ethanolamine, while the lack of N- or O-containing desorbates suggests that the dissociated N and O species are likely bonded to multiple surface Si atoms or diffused into the bulk at elevated temperatures (as confirmed by the corresponding temperature-dependent XPS spectra). Unlike the multidentate allyl alcohol and allylamine adstructures that have been found to be not favored kinetically, the present [O, N] bidentate ethanolamine adstructure appears to be kinetically favored on Si(100)2×1. In the second materials science study, Cu NPs of three primary shapes have been deposited on H-terminated Si(100) by a simple, one-step electrochemical method. By precisely manipulating the electrolyte concentration [CuSO4.5H2O] below their respective critical values, cubic, cuboctahedral, and octahedral Cu NPs of ranges of average sizes and number densities can be easily obtained by varying the deposition time. Combined GIXRD and depth-profiling XPS studies show that these Cu NPs have a crystalline core-shell structure, with a face-centered cubic metallic Cu core and a simple cubic Cu2O shell with a CuO outerlayer. The shape control of Cu NPs can be understood in terms of a progressive growth model under different kinetic conditions as dictated by different [CuSO4.5H2O] concentration regimes. The two studies in the present work lay the foundation for future investigation of surface biofunctionalization of these fascinating Cu NPs with different shapes and therefore different surface chemistries as controlled by the relative amounts of the (100) and (111) facets, and their boundaries.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2007. / Title from PDF title page (viewed Jan. 28, 2010). Additional advisors: Derrick R. Dean, Wiliam K. Nonidez, Andrei Stanishevsky, Charles L. Watkins. Includes bibliographical references.

Thesis (M.S.)--Rochester Institute of Technology, 2008. / Typescript. Includes bibliographical references (leaves 49-50).

Thesis (Ph. D.)--University of Oregon, 2008. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 164-192). Also available online in Scholars' Bank; and in ProQuest, free to University of Oregon users.

Thesis (Ph. D.)--Mississippi State University. Department of Chemistry. / Title from title screen. Includes bibliographical references.