Chemistry & Biochemistry Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2752
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Item Bringing New Chemistry to Guanosine Hydrogels(2020) Xiao, Songjun; Davis, Jeffery T; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Molecular self-assembly is a powerful method to construct functional materials such as supramolecular hydrogels. Hydrogels contain mostly water but show solid-like rheology. Nucleosides and nucleotides contain rich recognition information, which opens up opportunities for gelator design. Hydrogels derived from these natural products have seen a resurgence in the past decade due to the high biodegradability and biocompatibility. Guanosine (G 1) and its analogs are powerful supramolecular hydrogelators. The structural basis for most guanosine hydrogels is G4•M+ quartet with K+ being the best metal to stabilize such a structure. These hydrogen-bonded macrocycles further stack to form 1D G-quadruplex that traps water to give hydrogels. Guanosine hydrogels have been used for applications such as bioactive molecule trap and release, environmental remediation, sensing and cell culture. While the H-bonded G-quadruplex is critical for gelation, G 1 can be synthetically modified to introduce new functions. The work presented here is focused on G-quartet hydrogels made from synthetic guanosine analogs. Guanosine analogs containing sulfur on 8- and 5ʹ-position are purified and their hydrogelation properties in water were examined. The resulting hydrogels can potentially be applied to environmental remediation. Substitution of 5ʹ-OH in G 1 into a hydrazine group in HG 2 significantly improves the hydrogelation properties. The resulting HG 2 KCl hydrogel can be used to non-covalently bind anionic dyes and covalently trap toxic electrophiles such as acrolein. A binary mixture of G 1 and HAG 15 forms a stable hydrogel with KCl. The hydroxamic acid group in HAG 15 serves as a pH-switchable group that can be applied as a carboxylic acid substitute in hydrogelator design. Furthermore, the hydrogel serves as a supramolecular siderophore and binds Fe3+ to generate patterns on the gel surface. The surface can be erased with a reducing agent and rewritten with Fe3+.Item PHOTO-GUIDED SHAPE TRANSFORMATION OF COMPOSITE HYDROGEL SHEETS(2018) Guo, Hongyu; Nie, Zhihong; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Shape-changing hydrogel material has numerous potential applications in biomimetics, soft robotics, biomedicine, etc. Light as a clean energy source can be remotely delivered to material with high spatial and temporal resolution, which brings new controllability to shape-transformation of hydrogel material. However, the current strategy of using light to control deformation of hydrogel is limited. This dissertation aims to develop new approaches to program shape-transformation of hydrogel material by using light. First, I developed a simple and efficient approach to re-program shape-transformation of composite hydrogel sheet with homogeneously distributed silver nanoparticle. By modulating light irradiation pattern, the same hydrogel sheet transformed to multiple distinct geometries, which were verified by finite element method. Secondly, I developed a simple and reliable approach to pattern various types of photo-thermal converting nanoparticles in hydrogel sheet. The approach enables nanoparticle patterning in both lateral and thickness-direction of hydrogel, which cannot be readily achieved by other approaches such as microcontact printing and photo-lithography. Thirdly, I explored shape transformation of composite hydrogel sheet with spatially patterned plasmonic gold nanoparticles fabricated by using the approach mentioned above. The same patterned composite hydrogel sheet can be designed to exhibit distinct shape transformation modes, highly depending on light irradiation direction, which has not been reported before. Fourthly, I studied shape transformation of composite hydrogel sheet spatially patterned with erasable and rewritable iron oxide nanoparticles. The same hydrogel sheet was re-programmed to exhibit various distinct shape transformations by changing nanoparticle pattern. This provides a new method to reprogram shape transitions of hydrogel material by using external light source. In addition, a hydrogel tube was also readily patterned with iron oxide nanoparticles and its deformation was studied as well. Lastly, I developed a simple and general approach to fabricate multifunctional composite hydrogel tube. The hydrogel tube was formed via self-rolling of 2D hydrogel sheet after releasing stress introduced during photo-polymerization. The introduced magnetic nanorod brought multi-functionality to the hydrogel tube. The self-rolled tube was used to load, transport and release cargo manipulated by capillary force, magnet and light, respectively. This dissertation provides a new, simple and efficient toolset to program and re-program shape transformation of composite hydrogel material by using external light. It is believed that the toolset and concept developed in this dissertation can be applied to other light-responsive hydrogel material.Item Tailoring Guanosine Hydrogels for Various Applications(2018) Plank, Taylor Nicole; Davis, Jeffery T; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Supramolecular hydrogels are of current interest for their ease of use, potential biocompatibility, and reactivity to stimuli. These gel materials have found use in a number of fields ranging from drug delivery and tissue engineering to sensing and environmental remediation. For over a century, guanosine (G 1) and its derivatives have been known to form hydrogels based on self-assembled G4-quartet structures. Recent research has focused on extending the lifetime stability of these hydrogels and modifying their properties to better suit the gels for applications in multiple fields. One such method involves the mixing of G 1 (or G-derivatives) with 0.5 eq of KB(OH)4, which results in the formation of guanosine-borate (GB) diesters. The GB-diesters self-assemble into G4-quartets stabilized by K+, the G4-quartets then stack to form wires that entangle to make a fibrous hydrogel network. This thesis details modifications of this GB-hydrogel system and explores applications of the resulting hydrogels. Modification of the 5ʹ-OH group of G 1 to form 5ʹ-deoxy-5ʹ-iodoguanosine (5ʹ-IG 2) results in a hydrogel that self-destructs via intramolecular cyclization to 5ʹ-deoxy-N3,5ʹ-cycloguanosine (5ʹ-cG 3). Guanine analog drugs can be incorporated into this hydrogel network and then released upon self-destruction of the gel. Substitution of boric acid with benzene-1,4-diboronic acid (BDBA 4) to form hydrogels with G 1 and K+ results in hydrogels that can be crosslinked with Mg2+. These G-BDBA-Mg hydrogels have a lower critical gelator concentration (cgc) than their non-crosslinked counterparts and can be used for cell growth applications. Utilizing binary mixtures of 8-aminoguanosine (8AmG 5) with G 1 allows for the formation of hydrogels with various salts. Hydrogels made of different salts preferentially absorb either cationic or anionic dyes from water, making them candidates for use in environmental remediation. Other 8-substituted G-analogs, including, 8-bromoguanosine (8BrG 6), 8-iodoguanosine (8IG 7), and 8-morpholinoguanosine (8morphG 8) can be used in binary mixtures with G 1 to form gels at room temperature upon mixing with KB(OH)4. Room temperature hydrogels have potential applications in enzyme immobilization, drug encapsulation, and environmental cleanup.Item Guanosine-borate hydrogels- Form and function(2015) Peters, Gretchen Marie; Davis, Jeffery T; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Due to their biocompatibility and stimuli-responsive nature, supramolecular hydrogels derived from natural products are attractive for a number of biomedical applications, including diagnostics, targeted drug delivery and tissue engineering. Nucleosides, the building blocks of nucleic acids, are desirable candidates for forming supramolecular gels as they readily engage in reversible, noncovalent interactions. Guanosine (G 1), in particular, is unique in that it has multiple faces for noncovalent interactions and can self-associate into stable higher-order assemblies, such as G4-quartets and G-quadruplexes. This self-assembly of G 1 and its derivatives into G4-quartets has long been known to induce hydrogelation. However, the requirement of excess salt and the propensity of G 1 to crystallize persist as limitations for G4-hydrogels. Thus, recent interest has focused on developing G4-hydrogels with improved lifetime stabilities and lower salt concentrations. The work described here focuses on a long-lived G4-hydrogel made from G 1 and 0.5 equiv. of KB(OH)4. Gelation occurs through the formation of guanosine-borate (GB) diesters and subsequent assembly into cation-templated G4•K+-quartets. The physical properties and stability of the GB hydrogel can be readily manipulated by varying the gelation components. For example, merely altering the identity of the cation drastically alters the gel’s physical properties. Namely, while GB hydrogels formed with K+ are self-supporting and robust, mixing G 1 with LiB(OH)4 results in a weak gel that readily dissociates upon physical agitation. Small molecules, such as cationic dyes and nucleosides, could be selectively incorporated into the GB hydrogel through reversible noncovalent and covalent interactions. One such dye and known G4-quartet binding ligand, thioflavin T (ThT) fluoresces in the presence of the GB hydrogel. The ThT fluorescence increases as a function of gelator concentration with a sharp increase correlating to the gel point. Thus, this ThT fluorescence assay is a new method for probing the formation of G4-hydrogels. Additionally, ThT acts as a molecular chaperone for Li+ GB hydrogelation. Substoichiometric amounts of ThT results in faster hydrogelation, increased gel strength and improved recovery of a hydrogel destroyed by external stress. Insights gained from this research have implications towards development of biomaterials, biomolecule sensing, and drug delivery.