Preparation and Characterization of Carbohydrate-Functionalized Nanomaterials for Use as Cellular Probes and Targeted Delivery Vehicles
DeShong, Philip R
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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.