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Title: Methodology towards accessing small molecule heterocycles for h20S and TB proteasome modulation
Creator: Bethel, Travis Kordero
Date: 2018
Collection: Electronic Theses & Dissertations
Description: "This dissertation focused on the development and advancement of methodology for accessing imidazoline scaffolds and other small heterocyclic molecules for biological evaluation. Past research within the Tepe group has correlated functionalized 2-imidazolines to proteasome modulation. Further diversification of the methodology for accessing these 2-imidazoline scaffolds, has allowed for the synthesis of a small library of analogs for SAR evaluation with the h20S proteasome. These finding were...
Show more"This dissertation focused on the development and advancement of methodology for accessing imidazoline scaffolds and other small heterocyclic molecules for biological evaluation. Past research within the Tepe group has correlated functionalized 2-imidazolines to proteasome modulation. Further diversification of the methodology for accessing these 2-imidazoline scaffolds, has allowed for the synthesis of a small library of analogs for SAR evaluation with the h20S proteasome. These finding were used to further experimentally model and synthesize more efficacious 2-imidazoline derivates for proteasome modulation. The proteasome is responsible for the degradation of polyubiquitinated proteins in the cell, producing amino acids that can then be used for alternative cellular functions. The introducition of small heterocyclic molecules like 2- imidazolines, bind to the proteasome and lower is efficacy for protein digestion through modulation of its activity."--Page ii.
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Title: Controlling the surface processes of X- and Z-type ligands to tailor the photophysics of II-VI semiconductor nanocrystals
Creator: Saniepay, Mersedeh
Date: 2018
Collection: Electronic Theses & Dissertations
Description: II−VI colloidal semiconductor nanocrystals (NCs), such as CdSe NCs, are often plagued by efficient nonradiative recombination processes that severely limit their use in energy-conversion schemes. While these processes are now well-known to occur at the surface, a full understanding of the exact nature of surface defects and of their role in deactivating the excited states of  NCs has yet to be established, which is partly due to challenges associated with the direct probing of the complex and...
Show moreII−VI colloidal semiconductor nanocrystals (NCs), such as CdSe NCs, are often plagued by efficient nonradiative recombination processes that severely limit their use in energy-conversion schemes. While these processes are now well-known to occur at the surface, a full understanding of the exact nature of surface defects and of their role in deactivating the excited states of  NCs has yet to be established, which is partly due to challenges associated with the direct probing of the complex and dynamic surface of colloidal NCs. In this dissertation, we report a detailed study of the surface of cadmium-rich zinc-blende CdSe NCs. The surfaces of these cadmium-richspecies are characterized by the presence of cadmium carboxylate complexes (CdX2) that act as Lewis acid (Z- type) ligands that passivate under-coordinated selenide surface species. The systematic displacement of CdX2 from the surface by N,N,N′,N′-tetramethylethylene-1,2-diamine (TMEDA) has been studied using a combination of 1H NMR and photoluminescence spectroscopies. We demonstrate the existence of two independent surface sites that differ strikingly in the binding affinity for CdX2 and that are under dynamic equilibrium with each other. A model involving coupled dual equilibria allows a full characterization of the thermodynamics of surface binding (free energy, as well as enthalpic and entropic terms), showing that entropic contributions are responsible for the difference between the two surface sites. Importantly, we demonstrate that cadmium vacancies only lead to important photoluminescence quenching when created on one of the two sites, allowing a complete picture of the surface composition to be drawn where each site is assigned to specific NC facet locale, with CdX2 binding affinity and nonradiative recombinationefficiencies that differ by up to two orders of magnitude.To understand the effect of steric hindrance and types of functional groups in different ligands on X-type ligand exchanges, using NMR, PL and UV-Vis absorption spectroscopy, we studied X-type exchanges on CdSe NCs capped with native carboxylates, with oleic acid, oleyl thiol, benzoic acid and benzenethiol ligands. We discussed the results and occurrence of undesired pathways including displacement of Z-type ligands, and suggested ligand exchange strategies that most likely lead to 100% X-type exchange.The structural complexity of surface of CdS NCs is also discussed in this dissertation. We demonstrate presence of two different sulfur surface defects on CdS NCs with ligand binding equilibrium constants that are two orders of magnitude apart and 20-60% smaller than those of selenium on similar size CdSe NCs. We also correlated the different surface defects to the PL quenching efficiency of CdS NCs.
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Title: Iridium catalyzed C-H activation borylations of fluorine bearing arenes and related studies
Creator: Jayasundara, Chathurika Ruwanthi Kumarihami
Date: 2018
Collection: Electronic Theses & Dissertations
Description: During the last two decades, iridium catalyzed aromatic borylation has emerged as one of the most convenient methodologies for functionalizing arenes and heteroarenes. The regioselectivity of Ir-catalyzed borylations are typically governed by sterics, therefore it complements the regioselectivity found in electrophilic aromatic substitution or directed ortho metalation. This unique regioselectivity and broad functional group tolerance (ester, amide, halogen, etc.) allows for synthesis of...
Show moreDuring the last two decades, iridium catalyzed aromatic borylation has emerged as one of the most convenient methodologies for functionalizing arenes and heteroarenes. The regioselectivity of Ir-catalyzed borylations are typically governed by sterics, therefore it complements the regioselectivity found in electrophilic aromatic substitution or directed ortho metalation. This unique regioselectivity and broad functional group tolerance (ester, amide, halogen, etc.) allows for synthesis of novel synthetic intermediates, many of which were previously either unknown or difficult to make. Since these reactions are mainly driven by sterics, it is possible to install boronic ester group (Bpin) next to small substituents like hydrogen, cyano, or fluorine. This feature is helpful but can also create challenges, specially in cases like borylation of fluoro arenes. These fluoro arenes tend give 1:1 mixture of steric (meta to fluorine) and electronic (ortho to fluorine) products. Therefore, to overcome this problem, we introduced a two-step Ir-catalyzed borylation/Pd-catalyzed dehalogenation sequence that allows one to synthesize fluoroarenes where the boronic ester is ortho to fluorine (electronic). Here, a halogen para to the fluorine is used as a sacrificial blocking group allowing the Ir-catalyzed borylation to favor the electronic product exclusively. Then the chemoselective Pd-catalyzed dehalogenation by KF activated polymethylhydrosiloxane (PMHS) is used to remove the halogen without compromising the Bpin group. Halosubstituted aryl boronates have the potential for orthogonal reactivity in cross-coupling reactions. We began exploring cross-coupling of triorganoindiums with these arylhalides bearing boronic esters in collaboration with Prof. P. Sestelo at University of da Coruña, Spain. We were able to synthesize borylated biaryls by merging Ir-catalyzed C–H borylations with Pd-catalyzed organoindium cross-couplings.As a part of the Dow–MSU-GOALI collaborations, we were able to synthesize a cobalt catalyst for C-H borylations of alkyl arenes and heteroarenes. This catalyst enables selective monoborylation of the benzylic position of alkyl arenes using pinacolborane (HBpin) as the boron source. In 2016, an internship opportunity led to the screening of ligands for C-H borylations at the Dow chemicals company in Midland, MI. From this internship opportunity, we discovered the first ligand controlled synthesis of 1,2-di and 1,2,3-tri borylated arenes. Also, I investigated a recyclable iridium heterogeneous catalyst for borylations during the internship. Finally, a bulky terphenyl incorporated bipyridine ligand is synthesized for selective iridium catalyzed para C–H borylations.
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Title: Poly(ethylene glycol) tailored polymers : nanomicelles with tunable lower critical solution temperature behavior
Creator: Lien, Yu-Ling
Date: 2018
Collection: Electronic Theses & Dissertations
Description: Propargyl and 1,1-dimethyl propargyl substituted poly(ethyleneoxides) (propargyl substituted = poly(PGE), 1,1ʹ-dimethyl propargyl substituted = poly(MGE)) have been prepared by ring-opening polymerization of epoxides, which were synthesized from epichlorohydrin and propargyl or 1,1-dimethyl propargyl alcohol via Williamson ether synthesis. The resulting polymers were modified by Cu-catalyzed azide alkyne cycloaddition (CuAAC) of the polymer propargyl groups and organic azides. When these...
Show morePropargyl and 1,1-dimethyl propargyl substituted poly(ethyleneoxides) (propargyl substituted = poly(PGE), 1,1ʹ-dimethyl propargyl substituted = poly(MGE)) have been prepared by ring-opening polymerization of epoxides, which were synthesized from epichlorohydrin and propargyl or 1,1-dimethyl propargyl alcohol via Williamson ether synthesis. The resulting polymers were modified by Cu-catalyzed azide alkyne cycloaddition (CuAAC) of the polymer propargyl groups and organic azides. When these reactions were carried out with mixtures of azides, the ratios of azides incorporated in the polymer side chains were equal to the molar ratios of the organic azides reactants (± 2%). Mixtures of hydrophobic (decyl azide) and hydrophilic (mDEG azide) azides result in amphiphilic polymers that exhibited a lower critical solution temperature (LCST) behavior. The polymer LCSTs scaled from 48 to 97 ± 2 °C (poly(PGE) derived amphiphiles) and 4 to 46 ± 1 °C (poly(MGE) derived amphiphiles) in a roughly linear fashion with the mole fraction of hydrophilic side chains in the polymer. When charged azides, COOH azide and aminium azide, were used, the physical property as well as the LCST behavior oh the polymers were changed. The LCSTs of polymers incorporating charged azides were increased and the LCSTs were decreased by adding salts in the solutions. The hydrodynamic radii (RH) obtained from DLS measurements indicate that polymers form unimolecular micelles in water (Mn = 52,000 g/mol, PDI = 1.19, RH = 6 ± 2 nm), and TEM data showed monodisperse domains (20 ± 4 nm, for Mn = 52,000) when water was evaporated at room temperature from solutions cast on TEM grids. This length scale is consistent with domains that consist of single polymer chains. When the TEM grid was heated during evaporation, the domain size increased to 74 ± 45 nm. In solution, the unimolecular micelles can solubilize hydrophobic small molecules, such as trans-azobenzene (trans-PhN=NPh) in water. DLS data suggested that polymer encapsulating trans-PhN=NPh (trans-PhN=NPh@poly(PGE) or poly(MGE)) derived amphiphiles) showed signs of aggregation in one case (RH = 12 ± 8 nm) and no signs of aggregation in another case (RH = 5 ± 2 nm). When the resulting solutions were raised above the polymer LCST the polymer and small molecule precipitated. When the mixture was cooled below the LCST, the polymer and hydrophobic small molecule re-dissolved. The unimolecular micelles were used to encapsulate a hydrophilic macromolecule, Subtilisin Carlsberg (SC), in aqueous solution and organic media. Poly(PGE) or poly(MGE) derived amphiphiles with COOH pendant group slowed down SC aggregation in aqueous environment. Also, the activity of SC@poly(MGE) derived amphiphiles with COOH pendant group was assayed and the half-life of SC was increased to 10 h from 2 h at 50 °C. Initial studies of SC@poly(PGE) or poly(MGE) derived amphiphiles in organic media showed enzymatic activity in toluene after 16 h at 37 °C.
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Title: An exploration of mid- to high-valent transition metal complexes for application to catalysis
Creator: Aldrich, Kelly E.
Date: 2019
Collection: Electronic Theses & Dissertations
Description: "The valency or oxidation state of a transition metal in a complex plays a large role in determining the reactivity of the complex. With transition metal chemistry, historically accessible chemistry has often focused on metals in a low oxidation state. However, transformations involving transition metals in high oxidation states are of equal importance in providing complex products for use in consumer products. Expanding the applications and understanding of transition metal complexes in high...
Show more"The valency or oxidation state of a transition metal in a complex plays a large role in determining the reactivity of the complex. With transition metal chemistry, historically accessible chemistry has often focused on metals in a low oxidation state. However, transformations involving transition metals in high oxidation states are of equal importance in providing complex products for use in consumer products. Expanding the applications and understanding of transition metal complexes in high oxidation states is the focus of the research presented in this dissertation. Fundamental studies of how ligands interact with high valent metals is presented in chapters 2 and 3, where a chromium(VI) model complex has been used to study bonding interactions between this d0 transition metal and phosphine ligands. Practical application of high valent titanium(IV) catalysts to C--N bond forming reactions is presented in chapters 4--6. Finally, chapters 7 and 8 focus on the changes in the character of M--N double bonds, with M=Fe and Ru, as the metal is forced to higher oxidation states. Collectively, these studies demonstrate different approaches to the same general problems and questions of how chemists can better understand and utilize high valent transitions metals to do catalytically-target desired transformations."--Page ii.
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Title: I. Delivery of carbohydrate antigens by glycopolymers as potential anti-cancer vaccines : II. A study of the impacts of valency and density on immune response against a tumor associated carbohydrate antigen
Creator: Qin, Qian, 1981-
Date: 2019
Collection: Electronic Theses & Dissertations
Description: Tumor associated carbohydrate antigens (TACAs) are overexpressed on tumor cells, which renders them attractive targets for anti-cancer vaccines. To overcome the poor immunogenecity of TACAs, a polymer platform was designed for antigen presentation by taking advantage of the polymeric backbone to deliver TACA and helper T (Th) cell epitope on the same chain. The block copolymer was synthesized by cyanoxyl-mediated free radical polymerization followed by conjugation with a TACA Tn antigen and a...
Show moreTumor associated carbohydrate antigens (TACAs) are overexpressed on tumor cells, which renders them attractive targets for anti-cancer vaccines. To overcome the poor immunogenecity of TACAs, a polymer platform was designed for antigen presentation by taking advantage of the polymeric backbone to deliver TACA and helper T (Th) cell epitope on the same chain. The block copolymer was synthesized by cyanoxyl-mediated free radical polymerization followed by conjugation with a TACA Tn antigen and a mouse Th-cell peptide epitope derived from poliovirus (PV) to afford the vaccine construct. The glycopolymer vaccine elicited a robust immune response with significant titers of IgG antibodies and the antibodies generated recognized Tn antigens on tumor cell surface. For successful carbohydrate based anti-cancer vaccines, it is critical that B cells are activated to secret antibodies targeting TACAs. Despite the availability of many TACA based constructs, systematic understanding of the effects of structural features on anti-glycan antibody responses is lacking. In this study, a series of defined synthetic glycopolymers bearing a representative TACA, i.e., the Thomsen-nouveau (Tn) antigen, have been prepared to probe the induction of early B cell activation and antibody production via a T cell independent mechanism. Valency and density of the antigen in the polymers turned out to be critical. An average of greater than 6 Tn per chain was needed to induce antibody production. Glycopolymers with 40 antigens per chain and backbone molecular weight of 450 kDa gave the strongest stimulation to B cells in vitro, which correlated well with its in vivo activity. Deviations from the desired valency and density led to decreased antibody production or even antigen specific B cell non-responsiveness. These findings provide important insights on how to modulate anti-TACA immune responses facilitating the development of TACA based anti-cancer vaccines using glycopolymers.
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Title: Sweet nanomedicine in vivo : glyconanoparticle for imaging amyloid beta fibrils in Alzheimer's disease, and hyaluronan nanoparticles for imaging and therapy of inflammatory Atherosclerosis disease
Creator: Hossaini Nasr, Seyedmehdi
Date: 2018
Collection: Electronic Theses & Dissertations
Description: This dissertation is about design and synthesis of glyconanoparticles for certain in vivo applications including imaging amyloid beta fibrils in Alzheimer’s disease, imaging inflammatory atherosclerotic plaques and inhibition of atherosclerotic plaque inflammation. Amyloid beta (Aβ) accumulation and deposition in the brain tissue are one of the most important hallmarks of Alzheimer’s disease (AD). Therefore, Aβ is an attractive target for imaging AD, however, designing a nanoprobe with the...
Show moreThis dissertation is about design and synthesis of glyconanoparticles for certain in vivo applications including imaging amyloid beta fibrils in Alzheimer’s disease, imaging inflammatory atherosclerotic plaques and inhibition of atherosclerotic plaque inflammation. Amyloid beta (Aβ) accumulation and deposition in the brain tissue are one of the most important hallmarks of Alzheimer’s disease (AD). Therefore, Aβ is an attractive target for imaging AD, however, designing a nanoprobe with the ability to pass through the blood brain barrier (BBB) and reaching Aβ plaques is a significant challenge. The first part of this dissertation covers the synthesis of a glyconanoparticle enabling to pass the BBB and bind with Aβ fibrils. Briefly, synthesis, characterization and application of this glyconanoparticle for magnetic resonance imaging (MRI) of Aβ plaques in a mouse model of AD (B6C3) have been presented. Majority of patients that experience cardiac arrests have atherosclerosis, which is the inflammatory disease of arterial walls and the major cause of heart attacks and strokes. Imaging techniques that can enable detection of atherosclerotic plaques before clinical manifestation are urgently needed. CD44 is a cell surface protein overexpressed in the plaque tissues and its expression level is associated with the risk of plaque rupture. The second chapter explains atherosclerosis disease and nanomedicine for targeting inflammatory atherosclerotic plaques. The third chapter of this dissertation presents the development of hyaluronan (HA) coated iron oxide nanoparticles for active targeting of the plaques. These nanoprobes can not only bind with atherosclerotic plaques through their HA ligands but also function as T2 based MRI contrast agents for plaque diagnosis. Moreover, the effect of nanoprobe morphology on inflammation has been studied indicating that engineering nanoprobe shape could decrease inflammatory responses, which makes it a superior candidate for imaging inflammatory atherosclerotic plaques. Concisely, design and synthesis of HA conjugated nanoworm (HA-NW) have been explained. Then, inflammatory responses to HA conjugated nanoparticles in vitro and in vivo in apoE knockout mouse model have been presented. Finally, the ability of HA-NW for in vivo imaging of atherosclerotic plaques by MRI has been studied.The last part of this dissertation goes over design and synthesis of hyaluronan conjugated atorvastatin nanoparticle (HA-ATV NP). This therapeutic formulation has been designed to deliver ATV to the inflammatory atherosclerotic plaques to reduce plaque inflammation. Then, HA-ATV NP anti-inflammatory effects in vitro and its therapeutic effect in vivo in apoE knockout mouse model have been explained. It has been shown that intravenous administration of this formulation (high dose, 8.5 mg ATV/ kg), every other day for one week can significantly reduce the plaques inflammation.
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Title: Carbohydrate-silica nanoparticles for sirna delivery : synthesis, characterization, and gene delivery
Creator: Chesniak, Olivia Mariel
Date: 2019
Collection: Electronic Theses & Dissertations
Description: RNA interference (RNAi) has long been pursued for its therapeutic potential. Sequence-specific knockdown of gene expression requires that small interfering RNA (siRNA) gain access to cellular cytoplasm, presenting difficulties for both the transport of nucleic acids to cells and their voyage across cellular membranes. Numerous materials are under development as siRNA delivery vehicles to address this need. The carbohydrate dextran has been incorporated into amine-functionalized sil- ica...
Show moreRNA interference (RNAi) has long been pursued for its therapeutic potential. Sequence-specific knockdown of gene expression requires that small interfering RNA (siRNA) gain access to cellular cytoplasm, presenting difficulties for both the transport of nucleic acids to cells and their voyage across cellular membranes. Numerous materials are under development as siRNA delivery vehicles to address this need. The carbohydrate dextran has been incorporated into amine-functionalized sil- ica nanoparticles (Dex-SiO2-NPs), enhancing their biocompatibility and success as siRNA delivery vehicles. Inspired by the work of Stober and others, reagent concentrations in the synthesis of Dex- SiO2-NPs have been adjusted to tune nanoparticle diameter. The size, shape, and morphology of Dex-SiO2-NPs have been characterized using transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS). These methods have revealed that Dex-SiO2-NPs decrease in silicon density toward their centers, when compared with SiO2-NPs. Thermal and porosity analysis were used to profile Dex-SiO2-NPs both containing dextran and after its removal by calcination. Having measured an increase in mesopores and decrease in micropores with calcination, it has been concluded that dextran serves as a porogen in Dex-SiO2-NP synthesis. Not only does dextran imbue these materials with unique morphology, it also enhances their function as delivery vehicles. Dex-SiO2-NPs improve enhanced green fluorescent protein (EGFP) supression compared to silica nanoparticles synthesized in the absence of dextran in human lung and kidney cells in vitro.
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Title: Functional control of soluble rhodopsin mimics using high resolution structure-based design and evaluation
Creator: Ghanbarpour, Alireza
Date: 2019
Collection: Electronic Theses & Dissertations
Description: Visualizing the microenvironments of protein/small molecule interactions is the missing link in evaluating the structure-function relationship in many "redesigned" protein systems requiring small molecule binding. The primary goal of this thesis is to manage protein/small molecule interactions to achieve new functions through rational protein engineering in a protein scaffold, which is "evolutionarily naive." The snapshots of each engineering step are collected using high resolution protein...
Show moreVisualizing the microenvironments of protein/small molecule interactions is the missing link in evaluating the structure-function relationship in many "redesigned" protein systems requiring small molecule binding. The primary goal of this thesis is to manage protein/small molecule interactions to achieve new functions through rational protein engineering in a protein scaffold, which is "evolutionarily naive." The snapshots of each engineering step are collected using high resolution protein crystallography, opening doors to the design strategies of future measures. Finally, the mechanism of the system is elucidated by connecting structural information and biochemical assays. The protein scaffolds used in our study are hCRBPII and CRABPII, belonging to the iLBP protein family. By reengineering their binding pockets, we generated a rhodopsin mimic ligating with small molecules with aldehyde functionalities through protonated Schiff base formation. In Chapter I, we employ the aforementioned strategy to create a new model system based on reengineered CRABPII, mimicking the critical steps of microbial rhodopsin isomerization in a single crystal. Using atomic resolution crystal structures, different mechanisms of retinal/protein interactions with light are demonstrated. Specially, a new photoswitchable protein is identified that does not require chromophore isomerization or a conformational change. In Chapter II, the effect of ligand binding on the conformational states of the domain-swapped dimer of hCRBPII is investigated. A new protein conformational switch is created through a designed disulfide bond that can be activated and adopt new conformations in response to retinal/fatty acid binding and/or reduction potential of the environment. A novel allosterically regulated zinc-binding site is engineered, whose binding affinity can be tuned by the conformational states of our protein. Additionally, using merocyanine, a synthetic fluorophore, a new "swap back" domain-swapped dimer is identified in hCRBPII at atomic resolution, leading to the largest conformational change in the protein. This demonstrates the power of our system to adopt new conformations with different small molecules. Through systematic mutational studies and high resolution crystal structures, the role of the hinge loop region in imposing new conformations/functions in the iLBP family is explored. In Chapter III, the discovery of the domain-swapped trimer as an unprecedented fold for the iLBP family is mentioned. Through a designed disulfide bond and metal- binding site, we are able to favor trimer formation. The mechanism of each step is examined using crystal structures and binding and stability assays. Finally, in Chapter IV, the mechanism of a new class of fluorescent protein tags using the hCRBPII rhodopsin mimic bound with synthetic fluorophores is inspected. By exploiting high resolution crystallography, the microenvironments of protein/ligand interactions is visualized in different fluorescent protein tags applications.
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Title: DETECTION OF COHERENT ENERGY TRANSFER PATHWAYS IN PHOTOSYNTHESIS WITH TWO-DIMENSIONAL ELECTRONIC SPECTROSCOPY
Creator: Roscioli, Jerome Daniel
Date: 2018
Collection: Electronic Theses & Dissertations
Description: Light harvesting proteins in photosynthetic organisms contain highly ordered arrays of chromophores responsible for the collection of energy from solar photons. The organization of the chromophores may lead to collective excitations (excitons) that are delocalized over many molecules in the array. The delocalized excitations allow for coherent, or wavelike, energy transfer between the chromophores, rather than a particle-like, incoherent, energy transfer process. It has been proposed that...
Show moreLight harvesting proteins in photosynthetic organisms contain highly ordered arrays of chromophores responsible for the collection of energy from solar photons. The organization of the chromophores may lead to collective excitations (excitons) that are delocalized over many molecules in the array. The delocalized excitations allow for coherent, or wavelike, energy transfer between the chromophores, rather than a particle-like, incoherent, energy transfer process. It has been proposed that these collective excitations may direct the flow of energy along the most efficient pathway to enhance the fitness of photosynthetic organisms. Photosynthetic organisms may also favor closely packed chromophore arrays because the structure is compact whilst optimizing large optical cross sections for absorption. Control of the coupling between chromophores may lead to a photoregulatory mechanism, which could control the energy transfer rate as a function of ambient light intensity fluctuations. Broad-band two- dimensional electronic spectroscopy (2DES) can be used to elucidate donor–acceptor pathways and mechanisms for both coherent and incoherent excitation energy transfer (EET) in photosynthetic light-harvesting proteins. In this dissertation, 2DES is applied to determine how quantum coherent energy transfer occurs between carotenoids and chlorophylls (Chls) in the peridinin-chlorophyll protein (PCP), a mid-visible peripheral light-harvesting protein in marine dinoflagellates that delivers excitation energy to photosystem II. PCP is unique in that it uses a carotenoid, peridinin, as the main light harvesting chromophore and that it can be reconstituted with different chlorophylls to change the energy landscape without causing structural changes. Through 2DES experiments on native PCP with Chl a, we show that although the collective excitations of chromophores are very short lived, they lead to an enhanced quantum yield compared to that for conventional, incoherent energy transfer mechanisms. Replacing the native Chl a acceptor chromophores with Chl b slows energy transfer from peridinin to Chl despite narrowing the donor–acceptor energy gap. The formyl substituent on the Chl b macrocycle hastens decoherence by sensing the surrounding electrostatic noise, leading to lower EET efficiencies. This work is significant because it improves our understanding of the role of coherent energy transfer in photosynthetic light harvesting. This information may prove useful when designing materials featuring strongly interacting electronic chromophores for the collection of solar energy for the generation of fuels or for use in photocatalysis.
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Title: I. amhb : (anti)aromaticity-modulated hydrogen bonding. ii. evaluation of implicit solvation models for predicting hydrogen bond free energies
Creator: Kakeshpour, Tayeb
Date: 2019
Collection: Electronic Theses & Dissertations
Description: My doctoral research under Professor James E. Jackson focused on hydrogen bonding (H-bonding) using physical organic chemistry tools. In the first chapter, I present how I used quantum chemical simulations, synthetic organic chemistry, NMR spectroscopy, and X-ray crystallography to provide robust theoretical and experimental evidence for an interplay between (anti)aromaticity and H-bond strength of heterocycles, a concept that we dubbed (Anti)aromaticity-Modulated Hydrogen Bonding (AMHB). In...
Show moreMy doctoral research under Professor James E. Jackson focused on hydrogen bonding (H-bonding) using physical organic chemistry tools. In the first chapter, I present how I used quantum chemical simulations, synthetic organic chemistry, NMR spectroscopy, and X-ray crystallography to provide robust theoretical and experimental evidence for an interplay between (anti)aromaticity and H-bond strength of heterocycles, a concept that we dubbed (Anti)aromaticity-Modulated Hydrogen Bonding (AMHB). In the second chapter, I used accurately measured hydrogen bond energies for a range of substrates and solvents to evaluate the performance of implicit solvation models in combination with density functional methods for predicting solution phase hydrogen bond energies. This benchmark study provides useful guidelines for a priori modeling of hydrogen bonding-based designs.Coordinates of the optimized geometries and crystal structures are provided as supplementary materials.
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Title: Electrochemistry of nanostructured carbon materials in aqueous electrolytes and room temperature ionic liquids
Creator: Jarosova, Romana
Date: 2019
Collection: Electronic Theses & Dissertations
Description: Carbon is one of the most plentiful elements on the planet. From a materials perspective, carbon is unique because of the microstructurally distinct allotropes it forms. These include single and polycrystalline diamond, diamond-like carbon, glassy carbon, and graphite. All of these carbon materials are commonly used in electroanalysis, energy storage and conversion, separation, and chemical analysis, due to numbers of reasons, including low cost, high mechanical strength, wide usable...
Show moreCarbon is one of the most plentiful elements on the planet. From a materials perspective, carbon is unique because of the microstructurally distinct allotropes it forms. These include single and polycrystalline diamond, diamond-like carbon, glassy carbon, and graphite. All of these carbon materials are commonly used in electroanalysis, energy storage and conversion, separation, and chemical analysis, due to numbers of reasons, including low cost, high mechanical strength, wide usable potential range, rich surface chemistry, chemical inertness, and compatibility with a variety of solvents and electrolytes. For the optimal usage of carbon electrodes in electrochemistry, it is critical to fully understand and control the variables that impact background voltammetric current, capacitance, and heterogeneous electron-transfer kinetics at these materials. Over the years of carbon electrode usage in electrochemistry, much knowledge has been gained about the structure-function relationship at sp2- and sp3- bonded carbon electrodes. Nevertheless, as most of this knowledge pertains to aqueous electrolyte solution, there is still a significant gap about the properties of the electric double layer and the transport processes near the electrode interface in room temperature ionic liquids. The room temperature ionic liquids are solvent-free medium, composed purely of ions, with a melting point near or below room temperature. In electrochemistry, they are appreciated for several of their excellent properties, such as wide working potential window, moderate electrical conductivity, high thermal and chemical stability, negligible vapor pressure etc. As the RTILs does not contain any solvent, their interfacial structure at an electrified interface is significantly distinguished from the conventional Gouy-Chapman-Stern model describing the double layer in aqueous solutions. Additionally, also the redox analyte environment in RTILs is expected to different compared to those in aqueous solutions. The work in this dissertation thesis is focused on the electrochemical performance of microstructurally different carbon electrodes in aqueous electrolytes and room temperature ionic liquids. The physical, chemical and electronic properties of glassy carbon, boron-doped diamond, and tetrahedral amorphous carbon electrodes are discussed. Furthermore, the microstructure of carbon electrodes is correlated to the heterogeneous electron transfer rate constants of soluble inorganic and organic redox couples in aqueous electrolytes and room temperature ionic liquids. The attention was primarily focused on tetrahedral amorphous carbon electrode that can be doped with nitrogen, resulting in significant physical, chemical an electrochemical properties. Moreover, the electrode surface chemistry was alternated by an oxygen plasma modification and its effect on the electrochemical performance (background voltammetric current, capacitance and electron transfer kinetics), as well as potential surface damage was studied. Lastly, as it is believed that the nitrogen incorporated tetrahedral amorphous material possesses an equally superb properties compared to the boron doped diamond, both electrode materials were used for determination of endocrine disruption compounds, specifically estriol, estradiol and estrone, using high-pressure liquid chromatography with electrochemical detection. The detection figures of merit for both boron doped diamond and nitrogen-incorporated tetrahedral amorphous carbon thin-film electrodes were determined.
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Title: Selective synthesis of aromatic and saturated organoboron compounds
Creator: Shannon, Timothy Michael
Date: 2019
Collection: Electronic Theses & Dissertations
Description: C-H borylation (CHB) is a method to functionalize C-H bonds. The development of CHB has taken many years but is getting to the point of well-established chemistry. The directed CHB is possible for a variety of differing substrates and differing loctions of direction. A new method for ortho directed CHB of esters amides and ketones was developed through the use of pyridine based monodentate ligands.Using 4-cyano-2-methoxypyridine as a ligand iridium catalyzed CHB of esters ketones and amides...
Show moreC-H borylation (CHB) is a method to functionalize C-H bonds. The development of CHB has taken many years but is getting to the point of well-established chemistry. The directed CHB is possible for a variety of differing substrates and differing loctions of direction. A new method for ortho directed CHB of esters amides and ketones was developed through the use of pyridine based monodentate ligands.Using 4-cyano-2-methoxypyridine as a ligand iridium catalyzed CHB of esters ketones and amides were performed. The mechanism of CHB in this process likely operates through a different rate-determining step than the other C-H borylation methods used as it was found that the kinetic isotope effect data did not clearly support C-H activation as rate-determining.The development of sp3 C-H borylation is not as advanced as sp2 CHB; a 2-step process to generate the same products could be equally desirable. Utilizing a borylation-hydrogenation process the selectivity that have already been developed for sp2 C-H borylation can be used to generate the sp3 carbon boron bond at the desired location. This process has been developed and limitations of it have been investigated.
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Title: Semi-synthesis of aromatic diacids and biosynthesis of kanosamine in Escherichia coli
Creator: Miller, Kelly (Kelly Knight)
Date: 2018
Collection: Electronic Theses & Dissertations
Description: Microbial synthesis of chemicals from biobased feedstocks is an alternative to manufacture of materials derived from petroleum or unconventional gases, such as shale gas and coalbed methane. Aromatic diacids, terephthalic acid, isophthalic acid , and phthalic acid, are valuable compounds for the polymers and plasticizers industry. These diacids are currently manufactured via Amoco Mid-Century oxidation of petroleum-derived para-, meta- and ortho-xylenes, respectively; a process not without...
Show moreMicrobial synthesis of chemicals from biobased feedstocks is an alternative to manufacture of materials derived from petroleum or unconventional gases, such as shale gas and coalbed methane. Aromatic diacids, terephthalic acid, isophthalic acid , and phthalic acid, are valuable compounds for the polymers and plasticizers industry. These diacids are currently manufactured via Amoco Mid-Century oxidation of petroleum-derived para-, meta- and ortho-xylenes, respectively; a process not without environmental and economic challenges. In this work, a semi-synthesis of terephthalic, isophthalic, and phthalic acids is outlined using 2-hydroxymuconic acid as a common synthetic precursor. Recombinant Escherichia coli was utilized combining protocatechuic acid anabolic and catabolic pathways to achieve 1.2 g/L 2-hydroxymuconic acid from D-glucose in fed-batch fermentation. Lewis-acid catalysis was explored in a cycloaddition of 2-hydroxymuconic acid with ethylene to produce terephthalic acid. Cyclization of 2-hydroxymuconic acid afforded 6-carboxy-2-pyrone which was reacted with propiolic acid to afford mixtures of isophthalic and phthalic acids. Propiolic acid from biogas methane and ethylene from bioethanol could maximize the amount of renewable carbon in this semi-synthetic strategy, producing all three petroleum-derived aromatic diacids without the need for Amoco Mid-Century oxidation process. In an additional research trajectory, the production of kanosamine (3-amino-3-deoxy-D-glucose) is evaluated in fed-batch fermentation of recombinant E. coli. Two biosynthesis pathways are reported in the literature: one native to Bacillus subtilis and the other reported in Amycolatopsis mediterranei and Bacillus pumilus. Genes encoding kanosamine biosynthetic enzymes from B. subtilis, A. mediterranei, and B. pumilus are expressed in Escherichia coli to determine whether heterologous expression results in kanosamine accumulation and if the system can be manipulated to maximize kanosamine production. Recombinant E. coli expressing genes from B. subtilis 168 produces 12.7 ± 0.6 g/L kanosamine in a 6% mol/mol yield from D-glucose. Kanosamine yields were increased to 18 ± 1% mol/mol by blocking the Embden-Meyerhoff-Parnas pathway through a mutation in pgi-encoded phosphoglucose isomerase. Enzymes native to A. mediterranei proved to be challenging to efficiently express in E. coli, prompting examination of B. pumilus kanosamine biosynthesis. Expression of B. pumilus SH-B11 genes in E. coli results in 6.3 g/L kanosamine titers in 4.4% mol/mol yield from D-glucose in fed-batch fermentation. In vitro feeding experiments suggest a departure from what is in the literature regarding kanosamine production in Bacillus pumilus.
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Title: Indirect neutron-capture cross sections for the weak r-process
Creator: Lewis, Rebecca L.
Date: 2019
Collection: Electronic Theses & Dissertations
Description: Understanding the production of the heaviest elements requires a wealth of information on the nuclear properties of short-lived nuclei. The rapid neutron capture process (r-process) is responsible for the majority of the production of the heaviest elements. The r-process utilizes neutron-capture reactions on heavy, neutron-rich nuclei. The nuclei involved in the r-process are very neutron-rich, short-lived, and very difficult to produce, so little information is known about them. The lack of...
Show moreUnderstanding the production of the heaviest elements requires a wealth of information on the nuclear properties of short-lived nuclei. The rapid neutron capture process (r-process) is responsible for the majority of the production of the heaviest elements. The r-process utilizes neutron-capture reactions on heavy, neutron-rich nuclei. The nuclei involved in the r-process are very neutron-rich, short-lived, and very difficult to produce, so little information is known about them. The lack of directly measured neutron-capture cross sections has led to the development of indirect techniques that can be used to reduce the uncertainty in the neutron-capture cross sections, which can vary by orders of magnitude between different calculations. The b-Oslo method is one indirect technique which aims to reduce the uncertainty in the two statistical properties of the nucleus that contribute the largest sources of uncertainty in the r-process calculations: the nuclear level density (NLD) and g-ray strength function (gSF). Both are required to calculate a neutron-capture cross section in the Hauser-Feshbach statistical framework, along with the neutron optical model. The b-Oslo method utilizes decay to populate high-energy excited states in the same nucleus that would have been formed in the neutron-capture reaction of interest. The g rays from the de-excitation are observed in the Summing NaI (SuN) detector to determine the total excitation energy of the nucleus as well as the g-ray cascade to the ground state. With this information, the NLD and gSF can be extracted, after normalization to other data or theoretical calculations. With experimentally constrained NLD and gSF, the overall uncertainty of a neutron-capture cross section has been showed to be significantly reduced.The neutron-capture cross sections of four neutron-rich nuclei (73Zn, 70,71,72Ni) were experimentally constrained using the b-Oslo method. The 73Zn(n,g)74Zn data was also used to compare the constrained neutron-capture cross sections obtained from three different Hauser-Feshbach codes to determine additional sources of systematic uncertainty. The three Ni reactions were also compared to the 68,69Ni cross sections that were previously constrained using the b-Oslo method.
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Title: Characterization of students' reasoning about atomic emission spectra : a design-based research study to improve students' understanding of light-matter interactions
Creator: Minter, Christopher Joel
Date: 2019
Collection: Electronic Theses & Dissertations
Description: The research presented in this dissertation looks at how students in general chemistry reason about atomic emission spectroscopy. Situated within the context of a transformed general chemistry curriculum called Chemistry, Life, the Universe, and Everything (CLUE), the goal of this study was to (1) characterize the various ways in which students explain atomic emission spectra, and to (2) refine the treatment of spectroscopy concepts within CLUE to improve students' understanding of light...
Show moreThe research presented in this dissertation looks at how students in general chemistry reason about atomic emission spectroscopy. Situated within the context of a transformed general chemistry curriculum called Chemistry, Life, the Universe, and Everything (CLUE), the goal of this study was to (1) characterize the various ways in which students explain atomic emission spectra, and to (2) refine the treatment of spectroscopy concepts within CLUE to improve students' understanding of light-matter interactions. Using a design-based research methodology, a series of evidence-based curriculum changes were implemented within CLUE from Fall 2013 to Fall 2016. The specific changes that were made during each phase of this study were directly informed by observations of student understanding from the prior year. To assess the effect that these changes to curriculum and assessment had on students' reasoning, a robust coding scheme was developed to characterize the extent to which students link and integrate their knowledge of spectroscopy concepts. In F13, students were interviewed to gain insight into how they understand atomic spectroscopy. Findings showed that students had difficulty explaining the mechanistic process for how spectral lines are created. To address this issue, the curriculum materials (i.e. homework, recitation activities, summative assessment tasks, and instruction) were refined in F14 to provide a more explicit emphasis on the mechanistic process by which an atomic emission spectrum is created. These changes led to an improvement in the percentage of students who reasoned about electronic transitions; however, there was no improvement in the number of students who reasoned about energy quantization. Based on this observation, the formative and summative assessments were refined in F15 to emphasize the quantized nature of energy. However, these changes did not lead to any observable differences in students' reasoning. To see if a more explicit question prompt would better elicit a more detailed explanation of atomic emission spectra, only the summative assessment task was changed in F16. Findings showed that the summative assessment task used in F16 elicited more sophisticated reasoning. Based on an analysis of four separate cohorts of general chemistry students who were enrolled in CLUE during different phases of curriculum refinement, it appears that general chemistry students' explanations of atomic emission spectra ranged from simple descriptions of properties of light to highly complex responses in which students applied their understanding of the mechanistic process for how an atomic emission spectrum is created to explain how different colored spectral lines are produced or why each element has its own unique emission spectrum. The effect that the curriculum and assessment changes had on students' reasoning is presented within this study.
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Title: Allied studies on total sythesis of cyclic tripeptide TMC-95 via an iridium catalyzed borylation/deborylation strategy and teaching organic chemistry in "words"
Creator: Shen, Fangyi
Date: 2019
Collection: Electronic Theses & Dissertations
Description: Arylboronate esters are versatile synthetic building blocks. Iridium catalyzed C-H activation/borylation reactions are a green way of making such building blocks as these reactions often obviate the need for prior functionalization (e.g. halogenation), the use of pyrophoric reagents, cryogenic conditions, etc. Installation of multiple boron substituents about the starting arene and then Ir catalyzed selective deborylation of the individual borons can allow for the formation of an even greater...
Show moreArylboronate esters are versatile synthetic building blocks. Iridium catalyzed C-H activation/borylation reactions are a green way of making such building blocks as these reactions often obviate the need for prior functionalization (e.g. halogenation), the use of pyrophoric reagents, cryogenic conditions, etc. Installation of multiple boron substituents about the starting arene and then Ir catalyzed selective deborylation of the individual borons can allow for the formation of an even greater diversity of borylated building blocks.The regioselectivity of Ir-catalyzed borylation is usually driven by sterics, however heterocycles are known to borylated at positions that exhibit heightened C-H acidity through the influence of the heteroatom. The regioselective borylation attained with a tryptophan derivative has been utilized in the development of a novel convergent route to the TMC-95 core. While pursuing a model synthesis of this natural product, the ability of bismuth salts to catalyze deborylations was discovered. These bismuth salts mediated methods can be highly selective in the in the deborylation of di and triborylated indoles. Furthermore, bismuths compounds are safe and less expensive as compared to the Ir-catalysts that facilitated deborylation. Numerous screening experiments on both substrates and other metal salts afforded a better understanding of how these novel deborylations can be applied in various synthetic settings and provided insight into possible mechanisms.Also, while I was a teaching assistant and a fixed-term instructor during my graduate studies at Michigan State University, I gradually realized that teaching is my passion and I am prepared to start my independent career and be an independent thinking teacher for the organic chemistry area.Owing to the nature of the subject, organic chemistry can be very visually distracting, and the image can be overpowering during student's learning. Like it or not students will try memorization first, our hypothesis is that once they know the "organic transformation formula" in words, via memorization or any other method, then introducing them to the structures of these functional groups will come with added context, and once they make that jump from word to structure they will be in a better position to understand reaction mechanisms. More importantly, understanding those reaction mechanisms will enable the student to progress to more complex topics.By introducing functional group transformations without the "clutter" of structures, we predict that once structures are introduced students will prioritize what's important because they will have trained their minds to ask what is the functional group, not "where did I see that structure in my notes".In short, we aim to train students to focus their attention on the reactive functional group of an organic molecule by emphasizing the use of WORDS to describe functional group transformation and teach the organic chemistry as the second language.
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Title: Telescoping C-H borylations with photoredox and imidazolylsulfonate chemistry : a way to avoid haloaromatics and potentially genotoxic impurities in Suzuki reactions
Creator: Perera, Damith
Date: 2018
Collection: Electronic Theses & Dissertations
Description: ABSTRACTTELESCOPING C–H BORYLATIONS WITH PHOTOREDOX AND IMIDAZOLYLSULFONATE CHEMISTRY: A WAY TO AVOID HALOAROMATICS AND POTENTIALLY GENOTOXIC IMPURITIES IN SUZUKI REACTIONSByDamith PereraCross-coupling reactions are a mainstay of drug candidate synthesis. Owing to this prominence, the American Chemical Society’s Green Chemistry Institute's Pharmaceutical Roundtable deemed cross-couplings that avoid halogenated aromatics (C–H activation) as their top aspirational reaction. To meet this...
Show moreABSTRACTTELESCOPING C–H BORYLATIONS WITH PHOTOREDOX AND IMIDAZOLYLSULFONATE CHEMISTRY: A WAY TO AVOID HALOAROMATICS AND POTENTIALLY GENOTOXIC IMPURITIES IN SUZUKI REACTIONSByDamith PereraCross-coupling reactions are a mainstay of drug candidate synthesis. Owing to this prominence, the American Chemical Society’s Green Chemistry Institute's Pharmaceutical Roundtable deemed cross-couplings that avoid halogenated aromatics (C–H activation) as their top aspirational reaction. To meet this aspiration, we have worked to develop iridium-catalyzed C–H borylations as a practical approach for directly converting arenes and heterocycles into nucleophilic cross-coupling partners. This chemistry not only obviates the need for halogens in the preparation of aryl and heteroarylboronic esters, but with hydrogen gas as the only stoichiometric byproduct of these chemoselective reactions, we and others have shown that Ir catalyzed borylations can be combined with other chemical events enabling a multitude of one-pot processes. Among these telescoped reaction sequences, we established C–H borylation/oxidations as a novel route to phenols, including phenols that often bear otherwise difficult to access contra-electronic substitution patterns. Herein we discuss the development and further advancement of the scope and green features of this chemistry by performing in situ oxidation of the boron under photoredox conditions. Furthermore, as phenols can be readily converted to sulfonates, we have expanded the reach of iridium-catalyzed borylations and use C–H activation to eliminate the need for halogenated cross-coupling electrophiles. Thus we have developed a one-pot C–H borylation/ photoredox oxidation/ sulfonation sequence. In recognition of the potential safety-genotoxicity issues related to triflates, mesylates and tosylates this sequence was built so as to enable the generation of imidazolylsulfonates (ArOSO2Im) as the final cross-coupling electrophile. We also telescoped sequence that does not conclude with the imidazolylsulfonate formation. Rather the final aim was the establishment of a one-pot sequence that joins the efficiency of C–H borylation with the environmentally friendly aspects of photoredox chemistry and the safety features of imidazolylsulfonates. Namely we have established a one-pot C–H borylation/photoredox oxidation/imidazolylsulfonation/Suzuki coupling sequence.In the second part of this dissertation, the use of high-throughput experimentation for the discovery of cheap, readily available catalytic systems, namely bismuth(III) acetate and silver oxide for selective deborylation of polyborylated substrates will be discussed. Bismuth (III) acetate is a safe, inexpensive, and selective facilitator of sequential protodeboronations, which when used in conjunction with Ir-catalyzed borylations allows access to a diversity of borylated indoles. The versatility of combining Ir-catalyzed borylations with Bi(III)-catalyzed protodeboronation is demonstrated by selectively converting 6-fluoroindole into products with Bpin groups at the 4-, 5-, 7-, 2,7-, 4,7-, 3,5-, and 2,4,7- positions and the late-stage functionalization of sumatriptan. Further elaboration of the reactivity of Bi(OAc)3 for heteroarene substrates and Ag2O for arene substrates including deborylation/deuteration studies are discussed. Ir-catalyzed C–H borylations of aromatic compounds often allowed achieving the kinetically favored product. Herein a procedure to achieve reversibility in the catalytic borylation was studied with excess borylating agents and higher catalyst loads to obtain a novel thermodynamic borylated product, which cannot be obtained under usual Ir-catalyzed borylation methods.
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Title: Characterization of molecular interactions and organization in solution and interfacial systems
Creator: Hay, Christine Ella
Date: 2014
Collection: Electronic Theses & Dissertations
Description: Liquid solutions and liquid-liquid interfaces are the media for numerous chemical reactions, where the local environments are conducive to interactions and exchanges. As a means of broadening our understanding of the molecular organization in liquid solutions and in proximity to phase boundaries, we report on the rotational diffusion dynamics of probe molecules in increasingly complex systems. Neat liquids represent the simplest systems interrogated. In our first study, we measure the induced...
Show moreLiquid solutions and liquid-liquid interfaces are the media for numerous chemical reactions, where the local environments are conducive to interactions and exchanges. As a means of broadening our understanding of the molecular organization in liquid solutions and in proximity to phase boundaries, we report on the rotational diffusion dynamics of probe molecules in increasingly complex systems. Neat liquids represent the simplest systems interrogated. In our first study, we measure the induced orientational anisotropy function, R(t), using time-correlated single photon counting of two chromophores, resorufin and 6-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)hexanoic acid (NBDHA) in water and in N-octyl-2-pyrrolidone (NOP). Our data show distinctly different anisotropy decays in aqueous solution compared to NOP solutions, and taken in the context of the Chuang and Eisenthal model, this indicates a change in effective rotor shape swept out by the solute's rotation. The similarity in the behavior of the two different chromophores in these solvent systems points to solvent-solvent interactions and local organization as the dominant factors in mediating motional dynamics. By adding varying concentrations of electrolyte to aqueous and NOP systems, the rotational diffusion dynamics of the anionic chromophore, resorufin, are altered as a result of interaction with electrolyte cations. In aqueous solutions containing lithium perchlorate (LiClO4), resorufin exhibits a single exponential anisotropy decay as was the case in pure water, however, reorientation times are dependent on electrolyte concentration. In contrast to the observed behavior of resorufin in pure NOP, where bi-exponential decay occurs, we observe a single exponential anisotropy decay for resorufin in NOP with the addition of non-aqueous electrolyte. For resorufin in NOP, the reorientation time constant increases with increasing electrolyte concentration, consistent with formation of a complex between the resorufin anion and the electrolyte cation. Elucidating the local organization near phase boundaries compared to bulk solutions represents a more complex problem to interrogate. We use a TCSPC confocal imaging instrument to obtain depth-resolved fluorescence lifetime and anisotropy decay data for lissamine rhodamine B sulfonyl chloride (LRSC) in NOP saturated with water and in ethylene glycol (EG) supported on a glass surface. The fluorescence anisotropy data of LRSC in NOP and EG as a function of distance from NOP|glass and EG|glass interfaces reveal a gradient spanning tens of micrometers from the NOP|glass interface into the NOP phase, and no corresponding gradient in EG. From these data, we assert there is a compositional heterogeneity in the form of water nano-droplets in the NOP phase, where water molecules solvate LRSC. NOP is miscible with small amounts of water allowing for the presence of water inclusions in solution, while phase separation occurs for sufficiently high water concentrations. By forming a liquid-liquid interface composed of water and NOP supported on glass, we observe both compositional and dielectric gradients. We report on spatially resolved fluorescence lifetime and anisotropy decay time constant data of LRSC in the NOP phase near the liquid-liquid (NOP|water) interface and the liquid-solid (NOP|glass) interface. These data reveal a micron-scale position-dependent molecular environment characterized by an anisotropy decay gradient as a function of distance from the NOP|glass interface. In addition, the presence of a fluorescence lifetime gradient normal to the NOP|water interface indicates the existence of a gradient in the concentration of water nano-droplets.
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Title: Modification of thin-film hematite prepared by atomic layer deposition for improved solar water oxidation
Creator: Young, Kelley Marie H.
Date: 2015
Collection: Electronic Theses & Dissertations
Description: The stimulus for my research stems from the immediate need to reduce our planet’s dependence of carbon-based fuel in order to minimize the potential detrimental effects of climate change. It is known that the sun irradiates the surface of our planet with enough energy in one hour to meet our ever growing energy needs; with the potential to completely supplement our dependence on carbon based fuels. Since a majority of energy uses necessitate the need for liquid fuels, developing materials...
Show moreThe stimulus for my research stems from the immediate need to reduce our planet’s dependence of carbon-based fuel in order to minimize the potential detrimental effects of climate change. It is known that the sun irradiates the surface of our planet with enough energy in one hour to meet our ever growing energy needs; with the potential to completely supplement our dependence on carbon based fuels. Since a majority of energy uses necessitate the need for liquid fuels, developing materials that have the ability to store energy in chemical bonds are of great interest. This work has focused on the fabrication, modification, characterization, and analysis of semiconductor metal oxides for photoanode materials, primarily hematite (α-Fe2O3). Hematite has ideal photoanode characteristics such as good light absorption, stable in contact with neutral and basic aqueous electrolytes, and has a low enough valence band energy to drive water oxidation via photogenerated holes. In addition, hematite is abundant, making it a cost effective material for potential scalability.Although hematite has many desirable characteristics as a photoanode material, its performance has been less than desirable. Water oxidation efficiency is controlled by three processes of the photoanode: light harvesting by the material, the transport of photogenerated holes to the solution interface, and hole collection via water oxidation at the electrode surface. Specifically, this work aimed to reduce the detrimental recombination of photogenerated holes on the surface of hematite before they are able to facilitate water oxidation by treating the surface with a known water oxidation catalyst, Ni(OH)2 using ALD. In my work, I have shown that mitigating this recombination has had a drastic effect of the performance of hematite as a photoanode, moving it closer to being a viable photoanode material. Once the recipe for Ni(OH)2 was established and reproducible, this was deposited onto well characterized thin films of Fe2O3 and was fabricated as a photoanode for photoelectrochemical studies. I was able to develop an electrochemical conditioning method for the electrodes that yielded stable, reproducible results. Using photoelectrochemical measurements such as cyclic voltammetry, transient spectroscopy, and impedance spectroscopy I was able to determine that the addition of Ni(OH)2 to the surface of Fe2O3 did in fact inhibit detrimental recombination of photogenerated holes. Ni(OH)2 acted as a charge storage medium (akin to that of a battery) that collected photogenerated holes from Fe2O3, which in turn oxidized Ni2+ to Ni3+, which then oxidized water at its surface. This result showed the greatest onset for water oxidation with a catalyst at the surface of hematite (with a shift in photovoltage on approximately 300 mV), which is vastly important for improving the efficiency for Fe2O3 as a photoanode material.
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