Chemistry & Biochemistry Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2752
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Item UNVEILING THE SELF-ASSEMBLY OF POLYMER-GRAFTED NANOPARTICLES IN SELECTIVE SOLVENTS(2023) Lamar, Chelsey; Nie, Zhihong; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The self-assembly of inorganic nanoparticles (NPs) has garnered considerable attention due to the potential for fabricating functional structures with unique collective properties. In recent years, polymers have emerged as valuable candidates in assisting the organization of NPs into complex architectures with multiple capabilities. Researchers have shown that polymer-grafted nanoparticles (PGNPs) facilitate the use of advanced nanostructures with tailored properties in biomedical applications. Although, continued exploration of the rational design and tailoring of PGNP assemblies is needed to expand our understanding before we can fully realize the potential of these structures in desired applications. My dissertation aims to investigate the fundamental aspects and elucidate the underlying mechanisms in the self-assembly of PGNPs for modern biomedical applications. A facile and versatile solution-based strategy was utilized to explore the individual self-assembly of PGNPs with anisotropic NPs and the co-assembly of binary PGNPs with distinct sizes. We focused on designing, characterizing, and exploring the optical properties of hierarchical assembly structures produced from inorganic NPs tethered with amphiphilic block copolymers (BCPs). Individual PNGPs with anisotropic NPs and binary mixtures of small and large PGNPs produce vesicle structures with well-defined packing arrangements. My work shows how key parameters, including polymer chain length, nanoparticle size, and concentration, influence the self-assembly behavior and the formation of vesicles in each system. Through a combination of experimental observations and theoretical considerations, I highlight the significance of polymer shell shape in dictating the self-assembly behavior of individual anisotropic PGNPs. Moreover, I demonstrate that elevated temperatures impacted the stability and optical responses of the vesicle structures. In co-assembly studies, my work describes the macroscopic segregation of PGNPs with different sizes in the vesicular membrane, which is attributed to the conformation entropy gain of the grafted copolymer ligands. This research will provide valuable insights into the self-assembly behavior and fundamental design of PGNP structures relevant to biomedical applications.Item Preparation and Characterization of Carbohydrate-Functionalized Nanomaterials for Use as Cellular Probes and Targeted Delivery Vehicles(2008) Park, Juhee; DeShong, Philip R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Carbohydrates are the most abundant biomolecules found in living organisms. In addition to their roles such as fuel storage and structural components, carbohydrates encode molecular recognition information. Carbohydrates presented on the cell surface interact with cell surface receptors. These carbohydrate-receptor interactions are involved in a variety of biological processes including intercellular adhesion, microbial attachment, and signal transduction. Research in the DeShong laboratory has been focused on the development of cellular probes and targeted delivery vehicles utilizing carbohydrate-cell surface receptor interactions. The work reported herein details (1) the synthesis of glycoconjugates to functionalize the surface of gold, silica, nanoparticles, and surfactant vesicles, and (2) the preparation and characterization of carbohydrate-functionalized gold nanospheres and surfactant vesicles. A variety of N-linked glycoconjugates tethered to thiols, siloxanes, and hydrocarbons were synthesized via modified Staudinger methodology with a high stereoselectivity. The stereochemistry at the anomeric center (alpha vs. beta) was readily controlled by choosing the appropriate reaction conditions. Typically, the alpha-stereochemistry arose from the reaction of ester derivatives with isoxazolines generated in-situ via epimerization of beta-phosphorimines at high temperature. The ability to control tether length has been demonstrated. Carbohydrate-functionalized gold nanospheres were prepared by two methods: (1) in-situ reduction of gold salt in the presence of thiolated glycoconjugates to provide ca. 2 nm particles and (2) a stepwise method where thiolated glycoconjugates were self-assembled on the surface of pre-formed, citrate-capped gold nanospheres to provide nanospheres with larger diameters (15 - 73 nm). Carbohydrate-functionalized surfactant vesicles were prepared by mixing a cationic surfactant cetyltrimethylammonium tosylate (CTAT) and an anionic surfactant sodium dodecylbenzenesulfonate (SDBS) in the presence of lipidated glycoconjugates. The resulting surfactant vesicles were stable, in mean diameter of ca. 140 nm, and showed significant amounts of glycoconjugate incorporation. The bioactivity of carbohydrates on the surface of gold nanospheres and surfactant vesicles was investigated through agglutination assays using carbohydrate-binding lectins concanavalin A and peanut agglutinin. These agglutination results indicated that both gold nanospheres and surfactant vesicles display multiple presentations of carbohydrates on their surfaces that can be used for binding of receptors. The suitability of the resulting glycosylated nanomaterials for use as cellular probes and targeted delivery vehicles is being investigated.