Theses and Dissertations at Montana State University (MSU)
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Item Unusual isomerization behavior of organic solutes at the aqueous-silica interface(Montana State University - Bozeman, College of Letters & Science, 2019) Purnell, Grace Elizabeth; Chairperson, Graduate Committee: Robert Walker; Robert A. Walker was a co-author of the article, 'Hindered isomerization at the silica/aqueous interface: surface polarity or restricted solvation?' in the journal 'Langmuir' which is contained within this dissertation.; Robert A. Walker was a co-author of the article, 'Surface solvation and hindered isomerization at the water/silica interface explored with second harmonic generation' in the journal 'The journal of chemical physics' which is contained within this dissertation.; Marshall T. McNally, Patrik R. Callis and Robert A. Walker were co-authors of the article, 'Buried liquid interfaces as a form of chemistry in confinement: the case of 4-dimethylaminobenzonitrile at the silica-aqueous interface' submitted to the journal 'The journal of the American Chemical Society' which is contained within this dissertation.; Marshall T. McNally, and Robert A. Walker were co-authors of the article, 'Isomerization at aqueous-silica interfaces and the role of solute structure' submitted to the journal 'Chemical physics letters' which is contained within this dissertation.Experiments described in this thesis address the question of how strong association between water molecules and the silica surface alter the solvation and isomerization behavior of adsorbed organic molecules from bulk solution limits. The work was motivated by the hypothesis that the ice-like structure induced by strong hydrogen bonding with the surface silanol groups would restrict solute isomerization. This hypothesis was tested using 2 surface-specific spectroscopic techniques: second harmonic generation (SHG) and time-correlated single photon counting in a total internal reflection geometry (TIR-TCSPC). This work examined two different 7-aminocoumarin dyes (Coumarin 151 and Coumarin 152) and dimethylaminobenzonitrile (DMABN). Coumarin 152 and DMABN both isomerize to form a twisted intramolecular charge transfer (TICT) state upon photoexcitation, whereas Coumarin 151 forms a simple (planar) intramolecular charge transfer state. SHG studies characterized the local solvation environment surrounding adsorbed molecules by providing electronic excitation energies that were compared to bulk excitation energies in different representative solvents. TIR-TCSPC measured the time-resolved emission of adsorbed molecules and quantified a solute's tendency to form TICT (or ICT) isomers at the aqueous-silica interface. Together, SHG and TIR-TCSPC provide a cohesive description of the local polarity across an aqueous-silica interface and how restricted solvent dynamics change a solute's photophysical chemistry. TIR-TCSPC studies reported that both C152 and DMABN are unable to isomerize to TICT states at the aqueous-silica interface, acting as if they were solvated in a nonpolar solvent or in a confined geometry. SHG studies confirm that the aqueous-silica interface is, in fact, more polar than the bulk aqueous limit, strongly implying that the observed effects are dynamic in origin rather than polarity driven. In contrast, studies of C151 show that this solute is largely insensitive to anisotropic, restrictive surface effects. Together results from these three molecules lead us to conclude that adsorption to the strongly associating aqueous-silica interface restricts large amplitude isomerization in organic molecules. Adsorption to less strongly associating interfaces does not cause this restriction. In the event that photo-induced isomerization does not require large amplitude motion, interfacial solvation has little effect on adsorbed solute behavior.Item The synthesis of N-acetyllactosamine functionalized dendrimers, and the functionalization of silica surfaces using tunable dendrons and beta-cyclodextrins(Montana State University - Bozeman, College of Letters & Science, 2017) Ennist, Jessica Helen; Chairperson, Graduate Committee: Mary J. Cloninger; Mary J. Cloninger was a co-author of the article, 'The synthesis of N-acetyllactosamine functionalized dendrimers and their role in galectin-3 mediated cancer cellular aggregation studies' which is contained within this thesis.; Eric A. Gobrogge, Kristian H. Schlick, Robert A. Walker and Mary J. Cloninger were co-authors of the article, 'Cyclodextrin-functionalized chromatographic materials tailored for reversible adsorbtion' in the journal 'ACS applied materials and interfaces' which is contained within this thesis.Galectin-3 is beta-galactoside binding protein which is found in many healthy cells. In cancer, the galectin-3/tumor-associated Thomsen-Friedenreich antigen (TF antigen) interaction has been implicated in heterotypic and homotypic cellular adhesion and apoptotic signaling pathways. However, a stronger mechanistic understanding of the role of galectin-3 in these processes is needed. N-acetyllactosamine (LacNAc) is a non-native ligand for galectin-3 which binds with comparable affinity to the TF antigen and therefore an important ligand to study galectin-3 mediated processes. To study galectin-3 mediated homotypic cellular aggregation, four generations of polyamidoamine (PAMAM) dendrimers were functionalized with N-acetyllactosamine using a four-step chemoenzymatic route. The enzymatic step controlled the regiochemistry of the galactose addition to N-acetylglucosamine functionalized dendrimers using a recombinant beta-1,4-Galactosyltransferase-/UDP-4'-Gal Epimerase Fusion Protein (lgtB-galE). Homotypic cellular aggregation, which is promoted by the presence of galectin-3 as it binds to glycosides at the cell surface, was studied using HT-1080 fibrosarcoma, A549 lung, and DU-145 prostate cancer cell lines. In the presence of small LacNAc functionalized PAMAM dendrimers, galectin-3 induced cancer cellular aggregation was inhibited. However, the larger glycodendrimers induced homotypic cellular aggregation. Additionally, novel poly(aryl ether) dendronized silica surfaces designed for reversible adsorbtion of targeted analytes were synthesized, and characterization using X-ray Photoelectron Spectroscopy (XPS) was performed. Using a Cu(I) mediated cycloaddition 'click' reaction, beta-cyclodextrin was appended to dendronized surfaces via triazole formation and also to a non-dendronized surface for comparison purposes. First generation G(1) dendrons have more than 6 times greater capacity to adsorb targeted analytes than slides functionalized with monomeric beta-cyclodextrin and are 2 times greater than slides functionalized with larger generation dendrons. This study reported beta-cyclodextrin functionalized surfaces can undergo a triggered release of the adsorbent, but otherwise retained the targeted analyte through multiple aqueous washes. Therefore, a new generation of G(1) dendronized surfaces capable of reversible adsorption were developed by heterogeneously appending sulfonic acid/pyridine end-groups. Auger Electron Spectroscopy (AES) was used to quantify the ratio of groups installed. Furthermore, G(1) dendronized surfaces were functionalized homogenously with sulfonic acid and pyridine for comparison and with chiral amino acids for chiral recognition studies.Item Linear and nonlinear optical studies of molecular adsorption to silica/liquid interfaces(Montana State University - Bozeman, College of Letters & Science, 2015) Woods, Brittany Lauren Gray; Chairperson, Graduate Committee: Robert Walker; Rob Walker was a co-author of the article, 'pH effects on molecular adsorption and solvation of p-nitrophenol at silica/aqueous interfaces' in the journal 'Journal of physical chemistry A' which is contained within this thesis.; Jenna K. George, Alex M. Sherman, Patrik R. Callis and Robert A. Walker were co-authors of the article, 'Adsorption and aggregation at silica/methanol interface: the role of solute structure' submitted to the journal 'Journal of physical chemistry C' which is contained within this thesis.; Jenna K. George and Robert Walker were co-authors of the article, 'Spectroscopic solvation mechanisms at silica/acetonitrile interfaces' submitted to the journal 'Physical chemistry and chemical physics' which is contained within this thesis.Adsorption mechanisms at buried interfaces are difficult to predict a priori, with many interactions to consider including those between the substrate and solvent, the substrate and adsorbate, and the solvent and adsorbate. Studies described in this thesis examine the roles these variables have on controlling interfacial behavior, including molecular adsorption and aggregation at solid/liquid interfaces. Specifically, second harmonic generation (SHG) was employed to characterize adsorption environments and adsorption energies at different silica/liquid interfaces, due to the technique's surface specificity. Additionally, time resolved fluorescence was used to quantify emission lifetimes within these same interfacial regions. By systematically changing the substrate, solvent identity, and adsorbate functionality, the impact of each contribution was identified and quantified. Initial studies examined the role played by interfacial pH in controlling adsorption. Above pH 5, silica surfaces become negatively charged and promote two distinct adsorption mechanisms. Adsorption due to these mechanisms requires very long equilibration times (>3hrs). Subsequent experiments studied the role played by solvent identity on interfacial solvation. At a methanol/silica interface a non-polar interfacial environment was produced, independent of solute choice. Non-polar solvents conversely create polar interfacial solvation environments. At these different solid/liquid interfaces, similarly structured coumarin dyes, C151 and C152, were examined. Slight changes in structure lead to differing behaviors at the surface, C151 terminates at monolayer coverage while C152 shows clear signs of multilayer formation. This observation is explained by the difference in hydrogen bonding opportunities for each adsorbate: C151 can accept and donate H-bonds while C152 can only accept H-bonds, resulting in more degrees of freedom for C152 at an interface and thus the possibility of aggregation.Item Diatom biofuels : optimizing nutrient requirements for growth and lipid accumulation in YNP isolate RGd-1(Montana State University - Bozeman, College of Letters & Science, 2012) Moll, Karen Margaret; Chairperson, Graduate Committee: Brent M. PeytonThe world's crude oil supply is decreasing at an alarming rate and no longer represents a long-term solution to meet energy needs. Development of renewable energy sources is required to meet transport fuel demands. Algal biofuels represent a potentially viable option. Diatom strain, RGd-1, isolated from Yellowstone National Park, produces high concentrations of lipids that can be used for biodiesel production. To increase cell numbers, RGd-1 was grown in six silica concentrations: without added silica, four silica concentrations within the soluble range (0.5-2mM), and one just above the soluble range (2.5 mM). Increasing the silica concentration resulted in an increase in total cell numbers and dry cell weight (DCW) with R ²=0.965. Silica depletion was verified by inductively coupled plasma mass spectrometry (ICP-MS). When grown in higher silica concentrations the medium reached a higher pH, which remained elevated. Nile Red fluorescence can be used as measurement of triacylglycerol (TAG). Once silica was depleted, Nile Red fluorescence increased. Unlike green algae and other diatoms, nitrate was never depleted when using the standard Bolds Basal Medium concentration (2.94 mM). RGd-1 never depleted nitrate from the growth medium and utilized only 1/3 of the original nitrate concentration (1 mM) by the time cells reached stationary phase. Therefore, the nitrate concentration was decreased to 1mM to induce a dual nitrate and silica stress. To increase the lipid content further, sodium bicarbonate was added to cells grown with each nitrate concentration (2.94 and 1 mM NO ₃-). Coupling nitrate limitation with sodium bicarbonate addition resulted in higher Nile Red fluorescence. RGd-1 fatty acids were primarily observed as C16:0, C16:1, C18:1-3 and C20:5, averaging at approximately 35, 30, 16 and 10%, respectively of the total lipid content. With exception of cells grown without added silica, the percent lipid content was approximately the same (30-40% (w/w) TAG (Triacylglycerol) and 70-80% (w/w) fatty acid methyl ester (FAME) grown under all conditions within the soluble range. However, when factoring in the dry cell weight from each system, it was observed that the TAG and FAME yields increased with silica concentration when normalized to DCW.