Chemistry & Biochemistry Theses and Dissertations
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Item ACYCLIC CUCURBIT[N]URIL MOLECULAR RECEPTORS: SEQUESTRANTS FOR DRUGS, MICROPOLLUTANTS, AND IODINE(2024) Perera, Wahalathanthreege Sathma Suvenika; Isaacs, Lyle; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Molecular containers are extensively utilized for their exceptional molecular recognition capabilities, making them suitable for use as sensors and sequestration agents. Cucurbit[n]urils, in particular, are recognized for their strong binding affinities, especially towards cationic guest molecules. These applications can be further enhanced by adjusting the size and shape of the host and incorporating functional groups.In Chapter 1, the concept of supramolecular chemistry is introduced, with a specific focus on cucurbit[n]urils. The chapter provides an overview of the development of cucurbit[n]urils and their potential applications. It also addresses the challenge of poor water solubility of cucurbit[n]urils, and discusses the enhancement of water solubility through the development of acyclic CB[n]s. Furthermore, the potential application of these containers as sequestration agents is explored. Chapter 2 describes the synthesis of a novel sulfated acyclic CB[n] receptor (Me4TetM0) and its recognition properties towards a panel of drugs of abuse. The obtained results were compared with two other sulfated acyclic CB[n]s (TetM0 and TriM0). Furthermore, in vivo studies were conducted with TetM0 to assess its efficacy as a sequestration agent for methamphetamine. Chapter 3 presents the synthesis of a series of water insoluble acyclic CB[n]-type receptors and studies their function as solid state sequestrants for organic micropollutants. The results are compared with CB[6] and CB[8]. The time course experiments performed with H4 show a rapid sequestration ability of the five micropollutants studied. Furthermore, under identical conditions, the micropollutant removal efficiency is higher than activated charcoal. Chapter 4 investigates the use of water-insoluble acyclic CB[n]-type receptors for the reversible capture of iodine from the vapor phase. H2 exhibits an iodine capture of 2.2 g g-1, equivalent to 12 iodine atoms per H2 molecule. Following iodine uptake, H2 undergoes partial oxidation, and the uptake of I3- and I5- was confirmed through Raman spectroscopy. Chapter 5 details the synthesis of glycoluril dimer bis(cyclic) ether-based hosts with diverse aromatic side walls. The chapter presents a comparative analysis of dye removal from a solid state and delves into the influence of distinct aromatic walls and various attached substituents.Item EXAMINING QUINONE CONTRIBUTION TO THE OPTICAL PROPERTIES OF CHROMOPHORIC DISSOLVED ORGANIC MATTER(2024) Ashmore, Rachel; Blough, Neil; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Chromophoric Dissolved Organic Matter (CDOM) in natural waters is largely responsiblefor absorption of light and photochemistry in the water, impacting environmental reactions and aquatic life. The composition of CDOM is greatly varied based on source, photochemical reactions, and natural cycles. The impact of quinone moieties on this structure and photochemical and redox reactions involving CDOM remains the subject of controversy. To investigate the impact of quinone structure on optical properties, model quinone compounds were thoroughly characterized by their optical properties and reactions with sodium dithionite and sodium sulfite. A series of methyl-substituted p-benzoquinones, a methoxy p-benzoquinone, and a range of napthoquinones and anthraquinones were investigated. These model compounds were characterized according to their quinone and hydroquinone molar absorptivities and fluorescence quantum yields. Sodium dithionite reduction of quinones and the impact of structure on the products of this reaction was investigated by reducing the quinones with both sodium dithionite and sodium sulfite and comparing the optical properties of the products to those of the quinone and hydroquinone. The spectra of dithionite reduced p-benzoquinones and napthoquinones suggested the presence of products other than the hydroquinone. Sulfite is produced in solution as a result of dithionite reduction of quinones. Model quinones were therefore also reduced with sodium sulfite to investigate the impact of this side reaction on the dithionite reduction products. High performance liquid chromatography (HPLC) was used to further investigate and quantify the products of dithionite reduction of quinones and the importance of sulfite interference. Although some of the model quinones react with sulfite to form a proposed sulfonated hydroquinone product, based on the observed extent of this reaction in dithionite reductions, the structures of quinones likely to be found in CDOM, and their relatively small contribution to CDOM optical properties, the sulfite reaction was determined to not significantly impact the study of quinone moieties in CDOM. Dithionite selectively reduces quinones, while borohydride reduces ketones, aldehydes, and quinones. Therefore, in CDOM samples, dithionite can be used to isolate the effects of quinone moieties on the optical properties. Dithionite reduction was used to analyse CDOM standards and natural water extracts from the North Pacific Ocean and the Chesapeake Bay to investigate quinone contribution to their optical properties. These results are compared to borohydride reduction results from Cartisano and McDonnell to compare the contribution of quinones to that of ketones and aldehydes. (1, 2) Dithionite reduction showed small impacts on absorbance and fluorescence, whereas significant changes in both were observed for borohydride reduction. Therefore, the optical changes observed under borohydride reduction are attributed to primarily ketones and aldehydes rather than quinones. Model quinones showed significant changes in fluorescence intensity due to dithionite reduction, which are largely not observed for CDOM standards and natural water extracts, further supporting the conclusion that their role in CDOM optical properties is small.Item Controlled Nucleation and Growth of Carbon Nanotubes(2024) Alibrahim, Ayman; Wang, YuHuang; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Single-walled carbon nanotubes (SWCNTs) exhibit exceptional electrical, mechanical, and optical properties, making them potential game changers for diverse applications. However, the synthesis of SWCNTs faces significant challenges, including low yield, inadequate control over catalyst particle size, and prevalent impurities. This dissertation focuses on elucidating SWCNTs' nucleation and growth mechanisms to address these challenging issues. First, I applied in-situ absorption spectroscopy to monitor the SWCNT production by chemical vapor deposition. Second, I investigated the factors affecting metal catalyst nucleation and introduced a confinement strategy that enabled a record-breaking growth rate of 4500 meters per hour for SWCNTs. Furthermore, I developed a novel “seed doping” technique to control the nucleation of metal catalysts, significantly reducing catalyst particle size and producing purer, smaller-diameter SWCNTs continuously. Finally, I explored the role of ethanol in enabling the controlled growth of double-walled carbon nanotubes by building on SWCNTs as templates.Item SCALING NANOFABRICATION: CARBON NANOTUBE-BASED SMART MATERIALS AND DEVICES(2024) Lin, Qinglin; Wang, YuHuang Y.H.W; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation introduces groundbreaking approaches to scaling up the nanofabrication of carbon nanotube (CNT)-based materials and devices, with diverse applications ranging from biosensors to smart textiles. The research begins in Chapter 2 with developing a CNT hydrogel that enables the direct alignment of CNTs across a trench. This approach paves the way for a new sensor design that detects SARS-CoV2 RNA with high sensitivity. In Chapter 3, I optimized this hydrogel system and applied it to effectively align CNTs simply by spin-coating. The alignment is comprehensively characterized by multiple methods, and I further demonstrated that this method could be applied to aligning other 1D nanostructures for innovative semiconductor device design. In Chapter 4, I further applied the CNT hydrogel to achieve an ultrafast assembly of CNTs on polymer fibers, with production rates reaching 100 meters per second. This rapid assembly process facilitates the development of cutting-edge FET-on-a-fiber devices, crucial for advanced biosensing of neurotransmitters. Finally, Chapter 5 explores the design of a humidity-responsive fiber for personal thermal regulation. This composite fiber, driven by torsional actuation, features dynamic inter-fiber distance control, making the material suitable for next-generation smart textiles.Item BLANKET AND PATTERNED REPROGRAMMING OF AZOPOLYMER NANORIDGES AND APPLICATIONS TO CELLULAR BIOPHYSICS(2024) Abostate, Mona Hamdy Abdelrahman; Fourkas, John J; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The objective of this project is to tailor nanotopographies previously fabricated on large areas through photomodification. The original master patterns consist of nanoridges created using conventional lithography. Using an azopolymer as a photoresponsive material, replicas of the original master were prepared using soft lithography. The entire surface of the azopolymer nanoridges underwent photomodification using a 532 nm laser with varying polarizations and durations, in a process referred to as blanket reprogramming. This process resulted in controllable widening, buckling, or removal of the nanoridges due to photoisomerization and subsequent mass migration of the azopolymer. To replicate the reprogrammed surfaces, a molding procedure was employed using an acrylatic resin. The blanket reprogramming process was monitored in situ during exposure through diffraction of another reading laser beam. Cellular behaviors can be modulated in various biological contexts through interactions with their surroundings. The relationship between nanotopography and cell behavior is crucial, and has a wide range of biological consequences and medical applications. For example, nanotopography is employed to design antibacterial surfaces, preventing the adhesion of bacteria and biofilm formation, thereby reducing the risk of infections associated with medical devices. Nanostructured surfaces can inhibit the migration of cancer cells, offering insights into potential therapeutic strategies. Nanotopography is also used in nerve-regeneration scaffolds to guide neurite outgrowth, aiding in the repair of damaged neural tissue. We investigated the response of MCF10A breast epithelial cells to buckled acrylic nanoridges replicated from a master of azopolymer ridges photomodified by laser. The nanoridges became buckled after exposure to 532 nm light polarized parallel to the ridges. The impact of buckling on the dynamics and location of actin polymerization was investigated, as well as the distribution of lengths of contiguous polymerized regions. Azopolymers, known for their biocompatibility, have been employed by various research groups to create nanotopographies on which cells are plated and imaged. We conducted experiments using a spinning-disk confocal fluorescence microscope, testing exposure wavelengths ranging from 405 nm to 640 nm. Our objective was to assess the feasibility of live-cell imaging on azopolymer nanotopographies without inducing surface alterations. Our findings revealed the capability of live-cell imaging at high frame rates across a wide range of wavelengths. This result stands in contrast to prior studies, in which the selection of fluorescent dyes compatible with these materials was limited to those excited in the red spectrum and emitting in the near-infrared. I demonstrate that different patterns can be created through patterned reprogramming of the azopolymer nanoridges. A periodic arrangement of light strips was projected perpendicular to the ridges, thereby projecting an amplitude grating onto the azopolymer nanoridges. The spacing of this pattern can be adjusted by altering the mask or adjusting the magnification of the optical system. Furthermore, varying the direction of light polarization expands the potential for creating a wider variety of designs. Different types of reprogramming motifs can be implemented by projecting patterns at angles that are not perpendicular to the substrate, by tilting the incoming laser beam away from the horizontal. Various intriguing patterns, such as repeating curves, were observed, dependent on both the angle of the incident light and the direction of light polarization relative to the direction of the ridges.Item Characterization of a novel Escherichia coli exopolysaccharide and its biosynthesis by NfrB(2024) Fernando, Sashika Hansini Lakmali; Poulin, Myles B; Biochemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Biofilms are made from an association of bacterial cells and extracellular products dominated by a plethora of exopolysaccharides. Accumulating evidence have demonstrated that the bacterial second messenger cyclic-di-guanosine monophosphate (c-di-GMP) promotes the synthesis of these exopolysaccharides through direct allosteric activation of glycosyltransferase enzymes. The Escherichia coli inner membrane protein NfrB, which together with the outer membrane protein NfrA acts as a receptor system for phage N4, contains a N-terminal glycosyltransferase domain and C-terminal c-di-GMP binding domain. Recent research revealed that NfrB is a novel, c-di- GMP controlled glycosyltransferase that is proposed to synthesize a N-acetylmannosamine containing polysaccharide product, though the exact structure and function of this remains unknown. Nfr polysaccharide production impedes bacterial motility, which suggests a possible role of the Nfr proteins in bacterial biofilm formation. Here, we carry out in-vivo synthesis of novelNfr polysaccharide followed by its structural characterization. Preliminary data from MALDI- TOF mass spectrometry and Solid State 13C NMR spectroscopy indicated that the Nfr polysaccharide is mainly a homo polymer of poly-?-(1®4)-N-acetylmannosamine, bound to an aglycone. In addition, we report efforts to develop of a Nfr polysaccharide binding and detection tool, through the mutation of YbcH, a putative Nfr polysaccharide hydrolase enzyme. These studies advance the understanding of Nfr polysaccharide biosynthesis and could offer potential new targets for the development of antibiofilm and antibacterial therapies.Item Using Electric Fields to Modulate Polymeric Materials: Electro-adhesion, Electro-gelation and Electro-carving(2023) XU, WENHAO; Raghavan, Srinivasa R.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation concerns the effects of electric fields on aqueous polyelectrolytes (solutions and gels), including those of polysaccharides and proteins. Electrical effects on such polymeric systems have not been studied in detail thus far. In this work, we apply electric fields as stimuli to trigger responses in these materials. We have discovered three novel responses: electro-adhesion of a gel to a solid electrode; electro-gelation of a polymer solution, which allows gels to be made in 3D, and localized electro-disruption of gels, which allows gels to be carved or sculpted. In our first study, we show that it is possible to adhere a soft ionic conductor (like a polymeric hydrogel) to a hard, electronically conductive electrode using a low DC voltage without any adhesive. When 5 to 10 V DC is applied between a pair of electrodes (e.g., graphite, copper, etc.) spanning a cylindrical hydrogel (e.g., acrylamide, gelatin, etc.), in 3 to 15 min, the gel strongly adheres to either or both electrodes. The ultimate adhesion strength can exceed 150 kPa and is only limited by the strength of the soft material. This hard-soft electro-adhesion applies to not only lab-synthesized hydrogels but also animal or plant tissues, such as beef, pork, apples, bananas, etc. We show that this adhesion results from electrochemical reactions that form chemical bonds between the polymers in the gel backbone and the electrode surface. Hard-soft electro-adhesion can be used to assemble hybrid materials with hard and soft compartments, which could be useful in robotics, energy storage, underwater adhesion etc. Next, we demonstrate how an electric field can be used to gel a polymer solution with spatial control thereby, we can ‘print’ gels in 3D. When a solution of alginate (an anionic biopolymer) is subjected to a DC electric field (~ 10 V) using a platinum (Pt) needle as the anode, a gel is formed right around the anode within seconds. By using a mobile anode, gel “voxels” can be formed sequentially and these merge into 3D structures. Similar electro-gelation can also be done with the cationic biopolymer chitosan, but at the cathode instead of the anode. The mechanism for gelation with both alginate and chitosan involves the polymer chains losing their charge next to the electrode. A loss of charge leads to insolubility, and insoluble domains act as crosslinks and connect the chains into networks. We have built a prototype for a 3D-printer that can translate a 3D design into a robust biopolymer gel formed by electro-gelation. Lastly, we show that an electric field applied by an electrode can be used like a knife to carve or sculpt hydrogels into 3D shapes. When we apply a DC electric field across certain gels, the gel shrinks near the anode, while water is expelled out of the gel near the cathode. Ultimately the gel shrinks by more than 50% of its original size. Such shrinkage is observed with a range of anionic gels, including both physical gels of biopolymers like agar and alginate as well as covalent gels such as sodium acrylate. If the ionic strength of the gel is high, the shrinkage does not occur. The origin of this effect lies in a combination of electroosmosis as well as pH changes near the electrodes. Finally, we show that with a focused electric field, the shrinkage can be limited to a specific location in a gel, thereby allowing us to electro-carve gels in 3D.Item Nature-Inspired Polymeric Materials: Unveiling Unique Responsive Properties(2023) Rath, Medha; Woehl, Taylor J.; Raghavan, Srinivasa R.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In nature, biological systems are able to respond autonomously to environmental cues. Drawing inspiration from nature, scientists have been creating materials that change their appearance, shape, or properties (e.g., optical or mechanical) in response to various stimuli. This work is our contribution to the field - we have designed a range of nature-inspired polymeric materials that reconfigure their properties in response to either physical cues (e.g., temperature) or chemicals in the external medium. In our initial study, our point of inspiration is the natural pearl, which displays a bright sheen (called ‘pearlescence’) due to light reflection from plate-like particles. We show, for the first time, that pearlescence can be reversibly induced in soft capsules that contain no plate-like particles. Our millimeter-sized capsules have an outer shell (~ 500 µm thick) of N-isopropylacrylamide (NIPA) gel, which shrinks above its lower critical solution temperature (LCST) of ~ 32°C. When a transparent capsule is heated above this LCST, it turns pearlescent, and the transparent state is recovered upon cooling. Specular reflectance measurements confirm that the pearlescence of the capsules is comparable to that of natural pearls. We attribute the pearlescence to light reflection from nanoscale domains in the shrunken NIPA shell above the LCST. Next, we draw inspiration from the skin of chameleons - the brilliant colors of the skin are due to ordered arrays (photonic crystals) of particles within the skin cells. To mimic this structure, we first create ‘photonic capsules’ with silica nanoparticles (NPs) in their liquid cores. When the capsules are placed in a polymer solution, the shell is impermeable to the polymer chains but is permeable to water. The resulting osmotic gradient induces the silica NPs to form close-packed arrays, i.e., photonic crystals, which deposit on the inner wall of the capsule. The capsules thereby show brilliant colors (iridescence), with the exact color depending on the NP size. We then further use these capsules as building blocks and fuse them together to form a free-standing sheet. The sheet is thus analogous to a tissue, with the capsules analogous to the constituent cells. We are thereby able to create a sheet of colored capsules, resembling the chameleon skin. Lastly, we take a step towards creating an ‘artificial muscle’. The muscles in our body are nature’s ideal machines as they can expand and contract at will. To mimic this ability, materials that change their size autonomously are of interest. With this goal in mind, we start with an anionic hydrogel with microscale pores - the gel expands by 300% when placed in water. When a carbodiimide is added to the water, it converts the carboxylates on the gel strands to anhydrides, and the loss of charge makes the gel shrink by 50%. The anhydrides are metastable, however, and hydrolyze over time - thereby, the charge on the chains is restored and the gel expands back to its initial size. A cycle of gel expansion and contraction is completed in ~ 40 min, which is ~ 10x faster than any previous soft autonomous material. The rapid response moves our gels closer to the timescales required for use in practical actuators or soft robots.Item Crystallographic Studies of Intercalated Transition Metal Chalcogenides(2023) Balisetty, Lahari; Rodriguez, Efrain; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Crystallography, in simplest terms, is the study of crystals, their atomic arrangement,symmetry, and morphology. This knowledge is applied across disciplines ranging from determining the structure of geological minerals to biologically important compounds such as deoxyribonucleic acid(DNA) to high-temperature superconductors and quasi-crystals. The work presented in this dissertation involves structure and property studies of iron chalcogenide heterostructures prepared via intercalation. The tetragonal iron chalcogenides, FeCh (Ch = S, Se) studied in this work possess a layer structure made by linking edge-shared tetrahedra with chalcogen atoms at the corners and an iron atom at the center of each tetrahedron. The weak van der Waals forces holding these layers together make introducing intercalants into the interlayer space feasible. Iron chalcogenide heterostructures were prepared by bottom-up solvothermal growth technique and primarily focused on two kinds of intercalants: layered double hydroxides (LDHs) and metal-amine complexes. Both the intercalants are positively charged and can interact with the chalcogenide layer through electrostatic interactions. Along with electrostatics, the intercalants are strong hydrogen bond donors (O-H, N-H, respectively), and can participate in H-bond formation with chalcogenide anions of the host layers. In this work, we provide structural descriptions for two kinds of intercalated iron heterostructures. First is a twisted layer structure of ethylenediamine intercalated FeS. Layered van der Waals materials are susceptible to disorder and can form various stacking polymorphs through translations and twisted structures due to rotations between layers. We study the influence of intercalation of ethylenediamine molecules on such layer-to-layer twist stacking behavior in iron sulfide. The second type is LDH-iron chalcogenide heterolayered materials. They belong to the family of naturally occurring mineral, tochilinite. A new structure model for the heterolayered material is built using prior knowledge of individual components. The structural insights into this material were applied to synthesize new compositions of tochilinite. A synergistic relationship between the host layers and intercalants can lead to superior properties than constituent components or new emergent properties that are not present in the individual bulk compounds, making these compounds interesting.Item Progress in Nitrogen Vacancy Nuclear Magnetic Resonance Detection(2023) Huckestein, Emma Kaye; Walsworth, Ronald L; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful analytic tool of use in the physics, chemistry, and biology disciplines, yet the resource costs to buy, maintain, and use the spectrometer limit the tool's accessibility and the limited sensitivity and spectral resolution limit its application space. In recent years, Nitrogen Vacancy (NV) centers have emerged as an alternative NMR sensor due to their atomic-scale resolution and minimal resource costs. However, NV-NMR similarly suffers from limited sensitivity and spectral resolution due to the technical challenges associated with increasing the applied magnetic field. In this work, the sensitivity of an existing NV-NMR setup is characterized to determine the experimental modifications necessary for measurements at higher magnetic fields (>0.5 T). As a consequence of this characterization, a coplanar waveguide integrated with a microfluidic channel is designed. Finally, metabolomics, particularly spheroids, are reviewed for a potential high-impact NV-NMR application given historically relevant sample concentration sensitivities.