The handling of metallic nanoparticles often requires their dispersion into several polar and nonpolar solvents. Solid-phase stages or polymer-based ligands are commonly required to complete the transfer. The construction of a thiol ligand based in oleic acid, and its ability to efficiently assist in gold and silver nanoparticle aqueous-organic phase transfer is reported. After the transfer, the particles are completely dispersed in an organic solvent, preserving their diameter and morphology, as confirmed by ultraviolet-visible spectroscopy and scanning transmission electron micrographs.

The aim of this project was to utilize chiral cation-directed catalysis in the asymmetric synthesis of novel hererocycles. This goal was initially realized by the synthesis of azaindolines in high yields and enantioselectivities (Chapter 2). Extension of this methodology to substrates bearing two stereogenic centres was successful, although control over both diastereoselectivity and enantioselectivity in this process was modest. Finally the synthesis of heterocycles utilizing cation-directed rearrangement processes was examined, with proof of concept obtained for a novel asymmetric cyclization to form xanthenes.

O objetivo deste estudo foi sintetizar nanopartículas de ouro (AuNPs) em meio aquoso, transferí-las para diferentes meios orgânicos, e avaliar sua estabilidade (não-agregação) nesses meios, com o intuito de otimizar a exploração de suas propriedades ópticas. Foi utilizado o ácido tetracloroáurico (HAuCl4) como precursor de ouro metálico em meio aquoso e fez-se a transferência para clorofórmio (CHCl3) e diclorometano (CH2Cl2). Como agente de transferência, utilizou-se o polietilenoglicol tiolado (PEGSH) junto com o dodecanotiol (DDT). O PEG-SH foi adicionado na fase aquosa para evitar a agregação das AuNPs, assim como em fase orgânica, o DDT foi adicionado como agente estabilizador, pois sua cadeia alifática promove interações hidrofóbicas entre as partículas. Avaliou-se dois diâmetros médios de nanopartículas. A eficiência de transferência e a distribuição de tamanho das AuNPs foram estudadas utilizando a espectroscopia UV-Vis, espalhamento dinâmica de luz e microscopia eletrônica de transmissão. As nanopartículas denominadas AuNPs1 apresentaram AbsRPLS média de 0,8314 em ʎmédio = 521 nm e as AuNPs2 AbsRPLS média de 1,2643 em ʎmédio = 526 nm. Quando as AuNPs foram transferidas para solventes orgânicos, os espectros de absorção obtidos por UV-Vis apresentaram deslocamento da banda RPLS para o vermelho, em CHCl3, ʎAuNPs1 = 531 nm e ʎAuNPs2 = 534 nm; em CH2Cl2, ambas as soluções apresentaram ʎ = 530 nm. Este deslocamento é um dos fatores que indicaram a não-agregação das AuNPs. Em DLS, foi confirmada a nãoagregação. Em CHCl3, as AuNPs1 apresentaram eficiência de transferência de 97,27% e as AuNPs 98,88%, enquanto, em diclorometano, apenas 80,21% das AuNPs foram transferidas. As AuNPs apresentaram ao longo do tempo maior estabilidade em CHCl3 do que em CH2Cl2. Após a transferência para o CHCl3, as AuNPs foram separadas deste solvente e redissolvidas em outros solventes orgânicos com diferentes índices de refração: álcool benzílico, etanol e dimetilsulfóxido (DMSO). As AuNPS permaneceram visivelmente estáveis somente em álcool benzílico, pois nos outros solventes foi observado que a solução coloidal apresentou perda da coloração e por UV-Vis foi verificada a diminuição da banda da RPLS em DMSO e a ausência em etanol. / The objective of this study was to synthesize gold nanoparticles (AuNPs) in aqueous media, transfer them to different organic media, and evaluate their stability (non-aggregation) in these media, in order to optimize the exploration of their optical properties. Tetrachlorouric acid was used as the gold precursor in aqueous medium and transferred to chloroform (CHCl3) and dichloromethane (CH2Cl2). As the transfer agent, thiolated polyethylene glycol (PEG-SH) was used along with dodecanethiol (DDT). PEG-SH was added in the aqueous phase to prevent AuNPs from aggregating, as well as in the organic phase, DDT was added as a stabilizing agent because its aliphatic chain promotes hydrophobic interactions between the particles. Two average nanoparticle diameters were evaluated. The transfer efficiency and size distribution of the AuNPs were studied using UV-Vis spectroscopy, dynamic light scattering and transmission electron microscopy. The nanoparticles named AuNPs1 presented mean AbsRPLS of 0,8314 in ʎmedium = 521 nm and the AuNPs2 AbsLSPR mean of 1,2643 in ʎmedium = 526 nm. When the AuNPs were transferred to organic solvents, the absorption spectra obtained by UV-Vis showed red band shift in CHCl3, ʎAuNPs1 = 531 nm and ʎAuNPs2 = 534 nm; in CH2Cl2, both solutions showed ʎ = 530 nm. This displacement is one of the factors that indicated the non-aggregation of AuNPs. In DLS, non-aggregation was confirmed. In CHCl3, AuNPs1 showed transfer efficiency of 97,27% and AuNPs 98.88%, while in dichloromethane only 80,21% of AuNPs were transferred. AuNPs showed greater stability over time in CHCl3 than in CH2Cl2. After transfer to CHCl3, the AuNPs were separated from this solvent and redissolved in other organic solvents with different refractive indexes: benzyl alcohol, ethanol and dimethylsulfoxide (DMSO). The AuNPS remained visibly stable only in benzyl alcohol, because in the other solvents it was observed that the colloidal solution showed a loss of coloration and, by UV-Vis, the reduction of the LSPR band in DMSO and absence in ethanol was verified.

A major function assessed by Nature is the transport of a cargo between two different media, such as anions through cell membranes. Mimicking this function using complex systems is one of the biggest challenge of supramolecular chemistry. Metallo-organic cages are an important breakthrough in the encapsulation and transport of small molecules, providing a crucial platform for the development of systems chemistry. Binding a network member within a tetrahedral cage allows it to be hidden and then revealed upon receipt of a release signal, or transported as a cargo between spatially distant parts of a network. Larger capsules may also isolate subsystems from each other in the manner of vesicles. These dynamic architectures are synthesised by self-assembly, which involves the simultaneous formation of multiple coordinative and dynamic covalent linkages during the same overall synthetic process. Their shape and binding properties can be tuned by changing the subcomponents such as metals or ligands. Great progress has been reported in recent years in the development of three-dimensional cages that can interact with specific guest species, but there are limitations associated with the transport of these systems. Recent work by Nitschke et al. have successfully addressed practical separations problems by transporting a tetrahedral cage and its cargo from water into an ionic liquid layer. However, this system is not ideal as the process is triggered by an anion exchange not by a direct stimulus. This thesis reports the synthesis of an ionic liquid inspired tetrahedral system achieving reversible transport between water and an immiscible organic solvent driven by a change in temperature. Once the switchable capsules were obtained and characterised, their ability to move between different solvent phases upon heating was investigated. A capsule-mediated transport system as developed that is both directional and reversible. The flow of the capsule and its encapsulated cargo is directed using stimuli such as temperature modification. Ultimately an apparatus that allows the switchable capsules to move along a channel has been developed.

Palladium catalyzed Heck coupling with aryl and alkenyl halides has become a powerful means of carbon-carbon bond formation. This standard synthetic method has been developed to a high level of utility using various catalysts, conditions and substrates. Yet significant drawbacks remain, including poor reactivity, the need for high temperatures and base, limited substrate generality, and selectivity. Mixed products often suffer from olefin migration following insertion. N-Heterocyclic carbenes (NHC) have proven to be electron-rich donors which provide higher stability and reactivity than phosphines. In a previous paper reported by our research group the imidazolium-palladium carbene has proven to be highly efficient for the Suzuki-Miyaura cross couplings. The most active bis-2,6- diisopropylphenyl dihydroimidazolium chloride ligand 1 in that series together with palladium acetate were employed as the catalyst, to efficiently catalyze the Heck coupling of aryl diazonium ions with olefins with useful yields at room temperature. Added base is not needed either to form the carbene catalyst or for alkene product formation. Phase-Transfer Catalysis (PTC) is a very useful approach and has been widely used in synthetic organic chemistry. A novel class of fluoroanthracenylmethyl PTC catalysts were synthesized and explored for asymmetric glycolate and glycine alkylation. Phosphorous pentoxide was used for the challenging electron-deficient electrophilic aromatic substitution step. These new catalysts proved to have high selectivities for glycine alkylation under mild conditions.

This dissertation explores the potential applications of nanotechnology in the oilfield including poly(vinyl alcohol) stabilized carbon black nanoparticles for oil exploration and temperature-responsive carbon black nanoparticles for enhanced oil recovery. Also, it describes the rational design of graphene nanoribbons via intercalating reactive metals into multi-walled carbon nanotubes followed by addition of vinyl monomers or haloalkanes. Efficient production and modification of these aforementioned nanomaterials will make them more attractive for applications in the oilfield and electronics materials. A method is reported for detecting the hydrocarbon in the porous media with stabilized nanoparticles that are capable of efficiently transporting hydrophobic molecules through oil-containing rocks and selectively releasing them when a hydrocarbon is encountered. Nano-sized carbon black was oxidized and then functionalized with poly(vinyl alcohol) via a coupling reaction between the polymer's hydroxyl groups and the carboxylic groups on oxidized carbon black. Breakthrough curves show that poly(vinyl alcohol)-coated oxidized carbon black was stable in synthetic sea brine at room temperature and could carry the 14C-labeled radioactive tracer 2,2ˊ,5,5ˊ-tetrachlorobiphenyl through rocks and then released the tracer upon exposure to hydrocarbon. Due to the temperature-sensitivity of hydrogen bonds, higher molecular weight poly(vinyl alcohol) was used to improve the stability of carbon black nanoparticles in synthetic sea brine at higher temperatures. After sulfation, high molecular weight poly(vinyl alcohol) could stabilized carbon black nanoparticles in American Petroleum Institute standard brine at high temperatures. Those nanoparticles could efficiently transport mass-tagged probe molecules through a variety of oil-field rock types and selectively released the probe molecules into the hydrocarbon-containing rocks. Those proof-of-concept chemical nanoreporters can potentially be used under conditions commonly observed in the reservoir, and aid in the recovery of oil that remains in place. Amphiphilic carbon nanoparticles have been prepared that are capable of reversibly transferring across the water/oil interface in a temperature-controlled manner. Nano-sized carbon black was oxidized and then functionalized with amphiphilic diblock polyethylene-b-poly(ethylene glycol) copolymers that were water-soluble at low-to-moderate temperatures but oil-soluble at higher temperatures. The correlation between the phase transfer temperature and the melting temperature of the hydrophobic block of the copolymers and the weight percent of hydrophilic block were investigated. The amphiphilic nanoparticles were used to stabilize oil droplets for demonstrating potential applications in reducing the water/oil interfacial tension, a key parameter in optimizing crude oil extraction from downhole reservoirs. Graphene nanoribbons free of oxidized surfaces can be prepared in large batches and 100% yield by splitting multi-walled carbon nanotubes with potassium vapor. If desired, exfoliation is attainable in a subsequent step using chlorosulfonic acid. The low-defect density of these GNRs is indicated by their electrical conductivity, comparable to that of graphene derived from mechanically exfoliated graphite. Additionally, cost-effective and potentially industrially scalable, in situ functionalization procedures for preparation of soluble graphene nanoribbons from commercially carbon nanotubes are presented. To make alkane-functionalized graphene nanoribbons, multi-walled carbon nanotubes were intercalated by sodium/potassium alloy under liquid-phase conditions, followed by addition of haloalkanes, while polymer-functionalized graphene nanoribbons were prepared via polymerizing vinyl monomers using potassium-intercalated graphene nanoribbons. The correlation between the splitting of MWCNTs, the intrinsic properties of the intercalants and the degree of graphitization of the starting MWCNTs has also been demonstrated. Those functionalized graphene nanoribbons could have applications in conductive composites, transparent electrodes, transparent heat circuits, and supercapcitors.

No description available.

No description available.

Thesis (Ph. D.)--Brigham Young University. Dept. of Chemistry and Biochemistry, 2007. / Includes bibliographical references.

This thesis describes two new phase-transfer catalysed processes, in which asymmetry is mediated via ion-pairing with a chiral cation. In the first chapter, an enantioselective method for N functionalization of pyrroles is described and a phase-transfer catalysed approach to axial chirality via a cation-directed SNAr reaction is discussed in Chapters 3, 4 and 5.