School of Chemistry - Theses
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ItemWater soluble fullerene and SPIO based nanoparticles by solvent exchange and polymer self-assembly methods( 2017)The synthesis of nanomaterials with tailored components and structures has drawn significant attention for industrial and research applications. Buckminsterfullerene (C60), metallofullerene and related materials have potential uses in varied fields such as MRI contrast agents, solar cells, bio-medicines and drug delivery systems. In particular, gadofullerene (Gd@C82) has drawn research attention as a new type of MRI contrast agent taking advantage of the Gd atom inside the fullerene cage. However, one of the main challenges of C60 or metallofullerene Gd@C82 for application in the biological sciences is their negligible solubility in aqueous solution due to their hydrophobic surfaces. In this research, different strategies have been investigated to explore water-soluble fullerene or related inorganic nanoparticles for potential MRI applications. A number of different strategies were investigated to design water-soluble fullerenes. In the second chapter, the solvent exchange technique was explored, which is a method for transferring C60 from an organic solvent into water under stirring or sonication. The use of tetrahydrofuran (THF) as a solvent to produce water dispersable fullerenes has been widely reported and extensively utilised. In this research, we have developed a related method of solvent exchange based on the use of N,N-dimethylformamide (DMF). The DMF approach results in the formation of fullerene nanoparticle agglomerates that are highly stable in phosphate buffered saline solution and also in water, while the THF agglomerates are only stable in water as previously reported. Moreover, we found that both of these approaches result in the significant degradation of the fullerene cage as shown by various techniques such as matrix assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H NMR). This discovery was not previously reported in the literature. Our results have shown that the solvent exchange technique using THF results in partial oxidation and degradation of C60. In contrast, the DMF evaporative method results in greater oxidation and degradation of C60 but significantly enhanced colloidal stability in buffer solution. Another approach to modify fullerenes is through the use of polymers. RAFT polymerization is one of the widely used controlled living polymerization processes as it allows the synthesis of tailored polymer structures with controlled molecular weight and narrow molecular weight distribution. In our research, the parameters of RAFT polymerization of poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) were explored by the high throughput instrument, the Chemspeed platform, to explore the optimal polymerization conditions. The Chemspeed is a parallel synthesis platform with high-through output and automated robot synthesis instrument, which have been used to systematically investigate the parameters of different polymerizations and to discover new materials with accelerated efficiency. The polymers synthesised were pH responsive, meaning they changed structure with variation in pH. In particular, PDEAEMA polymers are attractive for its pH responsiveness with pKa ~ 7 which is between the pH values of healthy and cancerous tissues. The kinetics of RAFT polymerization of both PDEAEMA and PEGMA were investigated and homopolymers with different chain length were synthesized. These pre-synthesized PEGMA-b-PDEAEMA amphiphilic block copolymers have a great potential as a smart platform for both MRI contrast agent and drug delivery. In the forth chapter, the polymer/fullerene complex nanoparticles (PEGMA-b-PDEAEMA/C60 and PEGMA-b-PDEAEMA/Gd@C82) were successfully synthesized via a self-assembly method and then were characterized by dynamic light scattering (DLS), ultraviolet-visible (UV-vis) spectrophotometry, cryo transmission electron microscopy (cryo-TEM) and matrix assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. The disassembly of the complex PEGMA-b-PDEAEMA/C60 nanoparticles could be triggered by lowering the pH in the solution which makes the nanoparticle as a smart platform with pH responsiveness. In addition, the PEGMA-b-PDEAEMA/Gd@C82 nanoparticles were also explored utilizing the self-assembly strategy developed for PEGMA-b-PDEAEMA/C60 nanoparticles. The particles demonstrated stable incorporation of Gd@C82. The MRI contrast behavior of these materials showed variation with the different length of block copolymers used. Our results indicate these materials are interesting as potential MRI contrast agents. In chapter five, this self-assembly synthetic strategy was applied to synthesize PEGMA-b-PDEAEMA/iron oxide nanoparticles as superparamagnetic iron oxide (SPIO) nanoparticles which have been widely used as MRI T2 contrast agents to improve the MRI imaging quality. The pH responsive PEGMA-b-PDEAEMA/Fe3O4 nanoparticles fabricated by the self-assembly method were characterized in detail by dynamic light scattering (DLS) and cryo transmission electron microscopy (cryo-TEM). Moreover, the pH responsive behavior of the complex PEGMA-b-PDEAEMA/Fe3O4 nanoparticles was also investigated via DLS and cryo-TEM. The complex PEGMA-b-PDEAEMA/Fe3O4 nanoparticles as a new MRI T2 contrast agent was also explored. The results indicated that the MRI response was tunable based on the polymer building block and also on the concentration of polymer used in the formulation. The simple and modular synthesis of water soluble C60, Gd@C82 and superparamagnetic iron oxide nanoparticles using pH responsive polymers provides a potential smart system for advanced MRI imaging, bio-medicines and drug delivery in the future.