Chemistry & Biochemistry Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2752
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Item Molecular Routes to Sorting Carbon Nanotubes(2017) Meany, Brendan; Wang, YuHuang; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Carbon nanotubes are molecular cylinders of graphene that are synthesized as heterogeneous mixtures consisting of an assortment of structures. Because the optical and electronic properties of nanotubes are strongly dependent on their atomic structure and bundling states, effectively dispersing and separating the nanotubes by the different structures is of great importance for their applications ranging from personal electronics and sensors to bioimaging and drug delivery systems. In this thesis, we describe new molecular approaches to address the challenge of dispersing and sorting carbon nanotubes. First, an open-ring molecular container, acyclic cucurbit[n]uril, clips onto small diameter nanotubes stabilizing them in water leaving the remaining larger diameter nanotubes to agglomerate. At a concentration 1000 times lower than typically required for surfactants, these C-shaped molecules complex with carbon nanotubes creating large exposed surface areas along the tube outerwall. Simple addition of surfactant, sodium dodecylbenzene sulfonate, patches the exposed areas creating a nanotube fluorescent turn-on effect. A second approach to dispersing carbon nanotubes uses ammonium laurate, a previously unused surfactant though similar in structure to the popular sodium dodecylsulfate. When compared to sodium dodecylsulfate, we observe selectivity towards small diameter nanotubes and cleaner substrate deposition which is important for future applications. Lastly, a gel chromatography method is designed utilizing diazonium chemistry to improve the selectivity allowing nearly identical structures to be sorted in high purity. The surface chemistry disrupts the typical interaction between surfactant dispersed nanotubes and gel resin leading to differences in flow rates based on nanotube structure and therefore significantly improve the capability to sort nanotubes. Finally, we show that optical excitation of individual single-walled carbon nanotubes in the semi-dilute concentration regime is capable of melting double-stranded DNA on the excited nanotubes. These molecular approaches open new opportunities to dispersing and sorting carbon nanotubes in cleaner and highly selective manners.Item Self-assembly of inorganic nanoparticle amphiphiles for biomedical applications(2015) Liu, Yijing; Nie, Zhihong; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ensembles of interacting nanoparticles (NPs) can exhibit novel collective properties ─ arising from the coupling between NPs ─ that can be radically different from individuals. Realizing the enormous potential of NPs in biomedical applications requires the organization of NPs into hierarchically ordered structures. My dissertation is focused on the design of NP amphiphiles (NPAMs) and the use of NPAMs as building blocks to construct polymer-inorganic hybrid materials. The NPAMs are made from NPs surface-grafted with amphiphilic block copolymers (BCPs). In this way, the NPAMs synergistically combine the properties of both inorganic NPs and grafted BCPs, such as optical and magnetic properties of NPs, and flexibility of BCPs. First, we demonstrated that NPAMs with relatively low polymer ligand densities (~0.03 chain/nm2) self-assembled into vesicular nanostructures composed of a single layer of NP chains in the membrane. The decrease in the interparticle distance between NPAMs in the chain vesicles led to strong plasmon coupling of NPs and hence enhanced efficiency in photoacoustic imaging. Second, we fabricated hybrid vesicles with well-defined shapes and surface patterns by co-assembling amphiphilic BCPs and NPAMs, which include Janus-like vesicles (JVs) with different shapes, patchy vesicles, and homogeneous vesicles. Third, we prepared magneto-plasmonic hybrid vesicles with various structures through concurrent self-assembly of NPAMs, free BCPs, and hydrophobic magnetic NPs. The hybrid vesicles were demonstrated for both light-triggered release of payload and magnetic resonance imaging. Particularly, the magnetic manipulation of vesicles to specific location can be used to enhance the photothermal effect of the vesicles in cancer imaging and therapy. Finally, we reported that the use of a microfluidic flow-focusing device for the self-assembly of JVs that can act as vesicular motors. The vesicles can be used to encapsulate active compounds, and the release of this payload can be effected using near-infrared light. This systematic study will help us gain deeper understanding of the self-assembly of NPAMs into controllable nanostructures and control the collective properties of NP ensembles for various applications. This research will also provide new insights into the fundamental questions that must be overcome before the hybrid materials can be utilized in effective cancer imaging and treatment.Item Building Block Approach to the Synthesis of a Cucurbit[7]uril Derivative Bearing Sulfonate Functional Groups(2014) Brownlow, Lorene Elizabeth; Isaacs, Lyle; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Low aqueous solubility prevents 40-70% of new pharmaceutical agents from reaching their full potential. The use of molecular containers as solubilizing agents is one solution currently under development. Chapter 1 introduces molecular containers under investigation as drug delivery excipients. Synthetic approaches, properties and important derivatives of cyclodextrins and cucurbiturils are briefly reviewed. Chapter 2 describes the tested hypothesis that the addition of sulfonate functional groups to CB[7] will enhance the aqueous solubility of the CB[7] derivative as compared to CB[7] itself. The building-block approach to obtain a difunctionalized CB[7] derivative by the condensation of glycoluril hexamer (21) and ((¬CH2)4SO3Na)2 glycoluril bis(cyclic ether) (30) is described. The new CB[7] derivative had surprisingly low aqueous solubility (20.2 mM), but very similar molecular recognition properties to those of CB[7]. The CB[7] derivative was investigated for its use as an excipient for drug solubilization and found to have no enhancement compared to CB[7].Item Synthesis of Magnetic Nanotubes as Magnetic Resonance Contrast Agents and Drug Carriers and the Study of Their Cytotoxicity(2008-11-20) Bai, Xia; Lee, Sang Bok; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The increasing interest in the medical application of nanotechnology has heightened the need for synthesizing nanoparticles with well-defined dimensions and multifunctionalities. Studies on template synthesis demonstrate relatively reliable reproducibility of the nanostructures. Moreover, differential modification can be achieved with template synthesis method. Based on template synthesis method, magnetic nanotubes (MNT), silica nanotubes (SNT) loaded with superparamagnetic iron oxide nanoparticles (SPION), were successfully prepared. The magnetic properties of MNTs including saturation magnetization (Msat) and magnetic resonance (MR) relaxivities were investigated. Results revealed that Msat of MNTs is as high as 95 emu/gFe, which is on the highest side of reported value for magnetite nanoparticles. The MR study showed that MNTs enhanced proton MR relaxation considerably, especially transverse relaxation T2 (*). The transverse relaxivities (r2(*)) of MNTs are higher than that of Feridex, a FDA approved MR contrast agent, indicating that MNTs could potentially act as efficacious T2(*)-weighted MR contrast agents. MNTs were also studied as drug carriers to control the loading and release of Doxorubicin (Dox: a cancer drug model). The inner surfaces of MNTs were modified with C18- and pyridine-silane with various ratios. The results showed that Dox molecules held in the MNTs were stable at pH 7.2, and released at pH 4.5. With proper modification, MNTs can be used to control drug release profiles. The magnetic nanoparticles in MNTs helped in loading drug molecules due to barrier effect. Cytotoxicity and cellular uptake of SNTs with two different sizes and surface charges were investigated for two cell models, primary (non-malignant) and cancer cells. The nanotubes showed limited toxicity which was concentration-, surface charge-, and length- dependent. The internalization was confirmed with both confocal microscopy and TEM studies. Confocal microscopic images demonstrated that endocytosis was one of the main mechanisms for internalization of nanotubes. A novel method was developed in this thesis to improve multifunctionality of SNT as a drug delivery system by modifying the nanotubes segmentedly between the entrance and the remainder. Ideally, we can make a universal delivery vehicle with SNTs as the constitute structure which can be filled with therapeutic and imaging payloads and have biological surface modifiers for targeting.