Chemistry & Biochemistry Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2752
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Item Design and Assembly of Block Copolymer-Modified Nanoparticles into Supracolloidal, Molecular Mimics(2023) Webb, Kyle; Fourkas, John T; Nie, Zhihong; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Large strides have been achieved in nanoparticle self-assembly, using various strategies to achieve ordered, supracolloidal structures, ranging from dimers to chains and vesicles to 3-D lattices. However, these methods, while expanding the scope and accessibility of design, face inherent limitations in targeting complex structures with high yields, particularly when using isotropic building blocks (e.g. gold nanoparticles and polystyrene nanoparticles). Additionally, research studying the reversibility of nanoparticle assemblies is mostly limited to small-ligand-modified particles rather than polymer-modified nanoparticles. Polymers are particularly advantageous as they provide a higher degree of functionality to the nanoparticle surface and allow for increased control in directing particle interactions. This control is necessary to continue furthering the advancement of gold nanoparticles in plasmonics, sensors, and catalysts. Here, we introduce two strategies to assemble gold nanoparticles into supracolloidal nanostructures. Gold nanoparticles are modified with complementary, functionalized-block-copolymers that drive the assembly of the nanoparticles. The first strategy uses a diblock copolymer composed of a hydrophilic outer block and an acid or base-functionalized inner block. Upon mixing, particles are assembled due to the acid–base neutralization between the complementary block copolymers. The resultant supracolloids consist of nanoparticles precisely arranged in space, which mimic the geometries of small molecules. The particle interactions are fine tuned by varying the size and feeding ratio of the nanoparticles, along with the length and composition of the block copolymers. Careful tuning of these parameters yields nanostructures with different valences that were produced in high yield. Additionally, the implementation of a long outer, hydrophilic polymer block provided the assembled nanostructures stability when transferred from THF to water. Colloidal stability in an aqueous medium could allow for expanded use of these nanostructures in cellular uptake studies and biomedical applications. The second strategy uses a diblock copolymer composed of a hydrophilic outer block and an inner block containing either complementary host or guest moieties. Particularly, we take advantage of the well-established interactions between β-cyclodextrin and adamantane as the host and guest molecules. Upon the slow addition of water, particles assemble due to the host–guest interactions between the complementary block copolymers, as the hydrophobic adamantane moieties are driven within the β-cyclodextrin macrocycles. Fine tuning of the nanoparticle sizes and feeding ratios and the block copolymer lengths and compositions results in high yields of targeted supracolloids that also mimic the geometries of molecules. Interestingly, the size difference between the host and guest-modified particles led to different types of nanostructures. In addition, due to the reversibility of the host–guest interactions, we demonstrate the ability of our system to reorder in response to competitive host moieties. Upon addition of free β-cyclodextrin, the host–guest interactions are disrupted, resulting in disassembly of the nanostructures, which we could reassemble upon removal of the free cyclodextrin. Finally, due to the strength of the nanoparticle interactions, we also tested the selectivity of the nanoparticle interactions by assembling the host building block with different guest building blocks. We showed that when assembled with competing guest building blocks, the β-cyclodextrin building blocks preferentially interact the adamantane building blocks due to the stronger particle interactions. This reversibility and selectivity make our system a potential candidate for use in biosensors.Item DESIGN AND SYNTHESIS OF POLYOLEFIN MATERIALS FOR NANOSTRUCTURED SELF-ASSEMBLY: BUILDING BLOCKS, COPOLYMERS, AND POLYMER CONJUGATES(2022) Wentz, Charlotte Maria; Sita, Lawrence R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Polyolefin based materials are essential to today’s society in both simplistic commodity plastics to complex nanostructured materials and optoelectronic devices. In order to better understand these materials and make new impactful innovations, there is a barrier of fabrication, scalability, versatility, and programmability. The answer to the world’s plastic waste problem lies not in removing our use of polymers but relies in better understanding their properties, utilizing them as building blocks in advanced materials, and creating a long-lasting advanced material. Towards the goal of overcoming limitations in fabrication and scalability the work herein presents on utilizing a toolbox of living polymerization techniques such as living chain transfer polymerization (LCCTP) where new functionalities, stereochemical microstructures, optical properties, and physical properties of the polyolefin can be designed and systematically controlled. The polyolefins made through these techniques are scalable and versatile with end-group functionalization creating a seemingly endless choice of polymer building blocks and polymer materials. In line with creating new technologies that are programable the polyolefin building blocks made herein are utilized in multiple conjugates to create and understand methods and mechanisms of solid-state nanostructured self-assembly and access rare nonclassical phases that are highly desirable for their properties and uses in a plethora of applications. The conjugates investigated involve either a sugar-based head group covalently bond to a polymer tail to access rare and misunderstood Frank Kasper phase order-order transitions, or a perylene chromophore core covalently bond on both sides of the core in a linear fashion to polymer domains to create highly florescent or optically active materials that are useful in organic technologies such as solar cells, light emitting diodes, or nanotechnology. These perylene based conjugates can self-assemble into unique columnar phases and single gyroid phase. These results with conjugates provide methods for reliable and programmable access to rich phase behavior through the design of the polyolefin domains.Item INVESTIGATION OF SOLID-STATE SELF-ASSEMBLY OF ONE- AND MULTI- COMPONENT SUGAR POLYOLEFIN CONJUGATES AND MECHANISMS FOR FRANK-KASPER MESOPHASE TRANSITIONS(2020) Lachmayr, Katchen K.; Sita., Lawrence R.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The self-assembly of molecules provides the basis of life and has become ubiquitous for the development of nanostructured materials. Nanostructured materials have long reaching impacts for the furtherment of science, as the next revolution in technology requires the ability to fabricate nanostructured materials with sub-10-nm feature sizes. To this end, the work herein, presents on methods and mechanisms of solid-state nanostructured mesophase formation, through the isolation of complex phases and understanding of thermotropic order-order transition pathways. This extends to both solid-state classical and nonclassical phases, including the highly desirable, bicontinuous double gyroid, and uncommon Frank-Kasper (FK) phases resulting from self-assembly of the sugar polyolefin conjugates. The sugar polyolefin conjugates are produced through practical and scalable bulk quantities that demonstrate the dynamic self-assembly on the nanometer-scale, which results from rapid thermally induced order-order phase transitions. Production of different derivatives of the sugar polyolefin conjugates and blended systems, can significantly lower the barriers to access uncommon and complex mesophases through the elucidation of transition mechanisms for FK mesophases. To better understand the basic principles and mechanisms of formation that result in the complex packing motifs of FK phases, single- and multi-component systems were devised. These mechanisms avoid the need for large structural reconfigurations of spheres, and dynamic mass transfer, as previous solid-state thermotropic mechanisms have required. Additionally, a general strategy for design, modulation, and utilization of functionally competent soft matter solid-state FK phases is provided from developments with a two-component system utilizing a small molecule additive. These results demonstrate the sugar polyolefin conjugates as an exceptional class of self-assembling amphiphilic materials, which provide methods for reliably producing Frank-Kasper phases from single- and multi-component systems, in addition to remarkable classical phase behavior.Item End-Group Functionalized Poly(α-olefinates) as Modular Building Blocks(2016) Thomas, Tessy S.; Sita, Lawrence R.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The development of living coordination chain transfer polymerization (LCCTP) has provided a viable path to practical and scalable bulk quantities of structurally well-defined polyolefins that are further characterized by having tunable molecular weight, narrow polydispersity and end-group moieties through the functionalization of the Zn(polymeryl)2 intermediate. These low molecular weight, atactic poly(α-olefinates) are attractive non-polar building blocks for new types of self-assembling polyolefin materials with tunable occupied volumes and lengths. In the present work, the investigation of self-assembled morphology manipulation through tunable occupied volume required a model α-olefin. Living coordinative group-transfer polymerization techniques were employed to determine the viability of low molecular weight, atactic poly(α-olefinates) (X-PAOs) as building blocks with bulky pendent groups. Application of these X-PAOs for the synthesis and self-assembly of high χ, low N amphiphilic diblock copolymers demonstrated the ability to manipulate the morphology of the thin film nanostructures through variation in occupied volume of the X-PAO domain. The resulting materials proved the combination of X-PAOs and polyester blocks provided a high enough χ in order to demonstrate self-assembly with an N as low as 50 monomer units while maintaining sub-20 nm domain spacings. It was of significant interest to develop a higher χ, lower N system to achieve sub-10 nm domain spacings. As a result a novel system using sugar-hybrid-PAO conjugates was developed. This system also demonstrated that variation in occupied volume of the X-PAO domain could influence thin-film morphology. The sugar-hybrid-PAO conjugates also demonstrated the ability to self-assemble in solution and encapsulate hydrophobic molecules. The sugar-hybrid-PAO conjugates proved to be a highly versatile system that has simplified the polysaccharide/synthetic block copolymer designs that have been previously used in the literature to obtain sub-10 nm domain spacings. The ability to generate hydrophobic building blocks using LCCTP has opened up the possibility of further investigations of new, advanced self-assembling materials and applications thanks to these readily-available X-PAOs modular building blocks.Item Lipophilic G-Quadruplexes: Structural Studies, Post-Assembly Modification, and Covalent Capture(2006-08-29) Kaucher, Mark Steven; Davis, Jeffery T; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)New nanostructures and functional materials are built through the self-assembly of guanosine. Both the size and regiochemistry of these noncovalent structures are controlled. Lipophilic G-quadruplexes are further stabilized through covalent capture techniques. These new nanostructures demonstrate the ability to bind cations and transport monovalent cation through phospholipid membranes. Diffusion NMR is demonstrated as a valuable technique in characterizing the size of lipophilic G-quadruplexes. Control over the size of self-assembled G-quadruplexes is demonstrated through modifying the guanosine nucleosides and the cation concentration. The solution structure of [G 8]16 4K+ 4pic- is determined to be a hexadecamer using diffusion NMR. Additionally, G 24 is also shown to form a hexadecamer G-quadruplex, which has an octameric intermediate structure. Two different octamers, a singly and doubly charged octamer, formed by G 29 are elucidated by diffusion NMR. The information gained from the diffusion NMR technique allowed for a better understanding of the self-assembly processes, especially regarding the roles of cation, anion and solvent. The use of a kinetically controlled exchange reaction to effect regioselective modification of a hydrogen-bonded assembly is discussed. The pseudo-regioselective exchange of isotopically labeled G 35-d into [G 8-h]16 4K+ 4pic- is demonstrated. Both the bound anion and cation can control the exchange of ligand into the different layers of a synthetic G-quadruplex. This regioselective exchange process allows for functionalized G-quadruplex structures to be built. Covalent capture of lipophilic G-quadruplex 60 with reactive groups on the periphery generates a unimolecular G-quadruplex 61. This unimolecular G-quadruplex 61 shows exceptional stability in nonpolar and polar solvents, even without the presence of cations. Furthermore, this unimolecular G-quadruplex transports monovalent cation across phospholipid membranes. The design of transmembrane transporters is of particular interest for their potential as new ion sensors, catalysts and anti-microbial agents.