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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: Analysis of a method of training the mentally retarded
Creator: Yascolt, Marjorie Ann
Date: 1966
Collection: Electronic Theses & Dissertations

Title: A search for resonant Z' production in high-mass dielectron final states with the ATLAS detector in Run-2 of the Large Hadron Collider
Creator: Willis, Christopher G.
Date: 2018
Collection: Electronic Theses & Dissertations
Description: A search is performed for new resonant high-mass phenomena in the dielectron final state. The search uses 36.1 $\mathrm{fb}^{-1}$ of proton-proton collision data, collected at $\sqrt{s} = 13$ TeV by the ATLAS experiment at the Large Hadron Collider during its 2015 and 2016 data-taking runs. The dielectron invariant mass is used as the search variable. No significant deviations from the Standard Model prediction are observed. Upper limits at the 95\% credibility level are set on the cross...
Show moreA search is performed for new resonant high-mass phenomena in the dielectron final state. The search uses 36.1 $\mathrm{fb}^{-1}$ of proton-proton collision data, collected at $\sqrt{s} = 13$ TeV by the ATLAS experiment at the Large Hadron Collider during its 2015 and 2016 data-taking runs. The dielectron invariant mass is used as the search variable. No significant deviations from the Standard Model prediction are observed. Upper limits at the 95\% credibility level are set on the cross section times branching fraction to dielectron pairs for resonant $Z^{\prime}$ models considered in the search. Lower limits on the resonance pole mass are also presented. For the $Z^{\prime}_{\mathrm{SSM}}$, masses are excluded up to 4.5 TeV, while masses up to 4.1 TeV are excluded in the $E_{6}$-motivated $Z^{\prime}_{\chi}$ model. Limits are also derived in the Minimal $Z^{\prime}$ Model on the relative coupling strength $\gamma^{\prime}$. In addition, a series of studies are conducted in order to assess and reduce the dominant systematic uncertainty of this analysis, which arises from the imprecise knowledge of the Parton Distribution Functions in regions of very high parton $x$. While this uncertainty does not limit the discovery potential of the analysis presented here, it has the potential to do so in future searches. A novel approach is developed, and is shown to significantly reduce this systematic uncertainty in the high-mass search region of interest, thereby improving the discovery potential of future analyses.
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Title: An empirical investigation comparing the effectiveness of four scoring strategies for the Kuder Occupational Interest Survey form DD
Creator: Olejnik, Stephen Francis, 1950-
Date: 1974
Collection: Electronic Theses & Dissertations

Title: Farm mechanization of the small holdings in Surinam
Creator: Olf, Marius Eugene G.
Date: 1962
Collection: Electronic Theses & Dissertations

Title: "Flooding oil" : investigating poor health in vulnerable communities in the Niger Delta Region of Nigeria
Creator: Barry, Fatoumata Binta
Date: 2018
Collection: Electronic Theses & Dissertations
Description: The Niger Delta region in Nigeria has been exploited for decades due to extensive oil and gas deposits that have led to devastating livelihood and health consequences. In addition to oil and gas industry impacts, floods are intensifying in Niger Delta communities that have annual flooding during the rainy season (April to October). In 2012, Nigeria experienced a severe flooding event that damaged infrastructure and livelihoods with virtually no studies completed about the health consequences....
Show moreThe Niger Delta region in Nigeria has been exploited for decades due to extensive oil and gas deposits that have led to devastating livelihood and health consequences. In addition to oil and gas industry impacts, floods are intensifying in Niger Delta communities that have annual flooding during the rainy season (April to October). In 2012, Nigeria experienced a severe flooding event that damaged infrastructure and livelihoods with virtually no studies completed about the health consequences. This dissertation research study aims to fill this scholarly gap by disentangling the emerging health concerns in Niger Delta oil communities with particular attention to women and children as they are sensitive indicators of population health. It utilizes a mixed-methods approach with the inclusion of Eco-Syndemics and African womanism theoretical perspectives. It was found that the Niger Delta has multiple pre-existing vulnerabilities that put the population at more risk during flooding events. Also, through an evaluation of airborne concentrations of chemicals released by gas flares and a retrospective, cross-sectional comparison, women and children in Uzere (oil community) have greater exposure levels to toxic chemicals released and more health concerns than similar women and children in Aviara (non-oil community), even though both communities are located in flood-prone areas in the Niger Delta. Overall, this dissertation research advances our understanding of the complexity of health hazards in communities close to oil and gas activities in the midst of more severe flooding. It also enriches scholarly and policy debates by providing an initial assessment of the link between climate variability and health in vulnerable communities. -- Abstract.
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Title: Electromagnetic radiation from automotive ignition circuits
Creator: Schallhorn, Thomas Lee
Date: 1976
Collection: Electronic Theses & Dissertations

Title: The mass fire potential of urban structure and form
Creator: Schar, Stephen Warren
Date: 1969
Collection: Electronic Theses & Dissertations

Title: The role of fetuin-A on adipose tissue lipid mobilization in dairy cows
Creator: Strieder-Barboza, Clarissa
Date: 2018
Collection: Electronic Theses & Dissertations
Description: Adipose tissue (AT) is a major modulator of metabolic functions by regulating energy storage and acting as an endocrine organ. In periparturient dairy cows, increased AT mobilization of free fatty acids (FFA) is one a major adaptive mechanism to cope with higher energy demand for rapid fetal growth and the onset of lactation. As lactation progresses, lipolysis rates decrease, and lipogenesis replenishes triacylglycerol (TAG) stores in adipocytes. However, dysregulated metabolic responses,...
Show moreAdipose tissue (AT) is a major modulator of metabolic functions by regulating energy storage and acting as an endocrine organ. In periparturient dairy cows, increased AT mobilization of free fatty acids (FFA) is one a major adaptive mechanism to cope with higher energy demand for rapid fetal growth and the onset of lactation. As lactation progresses, lipolysis rates decrease, and lipogenesis replenishes triacylglycerol (TAG) stores in adipocytes. However, dysregulated metabolic responses, characterized by altered AT sensitivity to hormonal and endocrine changes around parturition, lead to a massive release of FFA into circulation and an increased susceptibility of cows to disease. These maladaptive responses are underlined by an altered secretory pattern of adipokines and a marked unbalance in lipolysis and lipogenesis rates, favoring TAG breakdown in adipocytes. Thus, identifying adipokines that modulate AT function in periparturient dairy cows can facilitate the development of novel management, nutritional, or pharmaceutical interventions to reduce disease incidence. Fetuin-A (FetA; alpha-2-Heremans-Schmid glycoprotein, AHSG) is an adipokine that functions as a carrier of FFA in plasma and is associated with insulin-mediated inhibition of lipolysis and stimulation of lipogenesis in humans. FetA increases the incorporation of fatty acids (FA) into intracellular lipids and enhances cellular TAG in human cells. However, the mechanisms by which FetA induces TAG synthesis are not defined. FetA has also anti-inflammatory properties by inhibiting the production of pro-inflammatory cytokines and acting as a negative acute-phase protein (APP) in acute inflammation. These findings suggest that FetA may also be involved in lipid mobilization and inflammation in AT of dairy cows. In our first in vivo study with periparturient dairy cows, we observed that serum and AT FetA expression decreased at the onset of lactation when lipogenesis was downregulated and plasma FFA was increased. FetA expression dynamics in AT were analogous to the patterns of lipogenic markers suggesting its link with lipid mobilization in AT of dairy cows. We also demonstrated that FetA is negative-APP locally in AT of dairy cows. These results suggest that FetA could support physiological adaptations to NEB in AT of periparturient dairy cows. To explore the potential roles of FetA on AT lipid mobilization of dairy cows, we developed an in vitro model for culturing bovine adipocytes that closely mimics the in vivo AT environment. For the first time, we reported an abundant expression and secretion of FetA by primary bovine adipocytes, thus suggesting a potential autocrine effect of FetA in AT of dairy cows. We observed that FetA attenuates lipolytic responses and enhances both, FA uptake and TAG accumulation in bovine adipocytes. Our results reveal that the upregulation of the expression and activity of 1-acylglycerol-3-phosphate acyltransferase (AGAPT2), a rate limiting lipogenic enzyme for TAG synthesis, may be a potential mechanism by which FetA enhances lipogenic function of bovine adipocytes. Overall, our results indicate that FetA is a lipogenic adipokine with anti-inflammatory function in the AT of dairy cows. Our findings provide evidence that FetA could buffer increased plasma FFA during negative energy balance by stimulating AGAPT2 activity and the use of excess FFA for TAG synthesis in AT of dairy cows. The genetic selection of cows by variations of the FetA coding gene associated with its anti-lipolytic and pro-lipogenic functions (already known in humans), the identification of dietary supplements (i.e. FA) that enhance FetA function, as well as the parenteral use of FetA to stimulate AGAPT2 activity, could serve as potential strategies to be tested and implemented in dairy cows.
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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: Do changes in maize prices and input prices affect smallholder farmers' soil fertility management decisions? : panel survey evidence from Kenya
Creator: Olson, David William
Date: 2018
Collection: Electronic Theses & Dissertations
Description: Soil degradation, low cereal yields, and poor yield response to inorganic fertilizer are serious problems in many parts of sub-Saharan Africa (SSA), including Kenya. Soil fertility management (SFM) practices such as maize-legume intercropping and organic fertilizer use, particularly when used jointly with inorganic fertilizer, have the potential to increase yields and yield response to inorganic fertilizer and improve soil health. However, relatively little is known about the drivers of...
Show moreSoil degradation, low cereal yields, and poor yield response to inorganic fertilizer are serious problems in many parts of sub-Saharan Africa (SSA), including Kenya. Soil fertility management (SFM) practices such as maize-legume intercropping and organic fertilizer use, particularly when used jointly with inorganic fertilizer, have the potential to increase yields and yield response to inorganic fertilizer and improve soil health. However, relatively little is known about the drivers of adoption of such SFM practices, including their joint use. Moreover, it is often suggested that African farmers will respond to an increase in the maize price they expect to receive at the next harvest by increasing investment in their soils or that they might alter their use of SFM practices in response to changes in input prices. Yet previous studies largely ignore the role of such prices. Using nationwide household panel survey data from Kenya, we first predict the maize price a household can expect to receive at the upcoming harvest based on observables at the time they make SFM decisions; we then estimate the effects of changes in this predicted maize price and input prices on household adoption decisions for individual SFM practices and combinations thereof. Likely due to multiple market failures, we find that Kenyan smallholders’ SFM adoption decisions are largely insensitive to changes in prices; however, there is some evidence that they are more likely to use organic fertilizer and use less inorganic fertilizer per acre when inorganic fertilizer prices rise.
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Title: A multidimensional treatment integrity assessment of parent coaching in a telehealth parent training program for autism spectrum disorder
Creator: Tran, Shannon Quyen
Date: 2018
Collection: Electronic Theses & Dissertations
Description: An important principle of evidenced-based practice (EBP) is using interventions with strong empirical support for their effectiveness, commonly known as evidence-based interventions (EBIs). Evidence of an intervention’s effectiveness is strongest when supported by treatment integrity data. Treatment integrity refers to the degree to which an intervention is implemented as intended by the original design. The assessment’s purpose is to provide researchers and practitioners with data about the...
Show moreAn important principle of evidenced-based practice (EBP) is using interventions with strong empirical support for their effectiveness, commonly known as evidence-based interventions (EBIs). Evidence of an intervention’s effectiveness is strongest when supported by treatment integrity data. Treatment integrity refers to the degree to which an intervention is implemented as intended by the original design. The assessment’s purpose is to provide researchers and practitioners with data about the implementation process to enable valid conclusions to be drawn about an intervention’s effectiveness.The present study focused on the treatment integrity assessment of Project ImPACT (Improving Parents as Communication Teachers; Ingersoll & Dvortcsak, 2010), a parent training program that aims to improve parents’ competence in teaching social communication skills to children diagnosed with autism spectrum disorder (ASD). The parent coaching portion of the training program was the focus of this study. Treatment integrity assessment occurred at two stages: The coaching delivery and the treatment delivery.This study used videos of coaching sessions from two randomized controlled trial (RCT) studies that examined the effectiveness of delivering Project ImPACT via telehealth with and without parent coaching. Dane and Schneider’s (1998) treatment integrity conceptual framework was used to guide the assessment. For the coaching delivery, the assessment focused on the therapists’ adherence to the coaching procedure, provision of feedback, and quality of coaching delivery, and the parents’ responsiveness during the coaching session. For the treatment delivery, the assessment focused on the parents’ adherence to the intervention strategies and quality of the treatment delivery. Descriptive statistics provided a general overview of the therapists’ coaching performance and the parents’ teaching performance. Multilevel regression analysis determined which components of the coaching delivery best predicted how parents used the intervention techniques and structured the play session for their child during the coaching sessions.Overall, the therapists consistently completed the essential steps of the coaching process. They frequently provided comprehensive feedback, attention, and reassurance. They did not provide as many opportunities for the parents to engage in collaborative problem-solving or to reflect on their implementation progress. In turn, the parents fully participated in the coaching session and demonstrated sufficient capacity to implement the intervention techniques and structure a meaningful play session for their child.Results from a multilevel regression analysis indicated that none of the treatment integrity components of the coaching delivery significantly predicted the parents’ treatment adherence. The quality of coaching delivery did, however, significantly predict the parents’ structure of the play segment, albeit in a negative direction. The study’s results, along with its limitations, provided a platform for continuing the conversation about treatment integrity assessment in intervention studies. In particular, the study concluded with new questions about the conceptualization and operationalization of different parent coaching aspects for parent-implemented interventions. Seeking to understand the concept and improve the measurement of these parent coaching aspects can lead to a more accurate identification of the active ingredients of parent coaching in ASD parent-implemented interventions.
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Title: Effect of centrifugation on root initiation in Vaccinium corymbosun, L. and Salix alba, L
Creator: Siripong, Dusit
Date: 1966
Collection: Electronic Theses & Dissertations

Title: A study of empathic ability and of the validity of some indices of job satisfaction
Creator: Schell, William Adolph
Date: 1954
Collection: Electronic Theses & Dissertations

Title: Characteristics observed of infant's swimming ability : a four month study conducted in order to establish teaching methods for this level
Creator: Scheunemann, Virginia Lee
Date: 1961
Collection: Electronic Theses & Dissertations

Title: Labor's image of its place in the community power structure : an exploratory study
Creator: Sauer, Warren Louis
Date: 1958
Collection: Electronic Theses & Dissertations

Title: Fundamental studies and engineering modeling of hydrogen bonding
Creator: Bala Ahmed, Aseel Mohamed Ahmed
Date: 2018
Collection: Electronic Theses & Dissertations
Description: This project aims to enhance the engineering modeling of hydrogen bonding, or association, by blending ab initio quantum calculations, fundamental molecular level findings from experimental techniques, and thermodynamic models. Because of the ubiquity of hydrogen bonding, applications for an improved association model are extensive, ranging from drug design to plastics manufacturing. Therefore, a substantial amount of work has been aimed at improving traditional thermodynamic tools, which...
Show moreThis project aims to enhance the engineering modeling of hydrogen bonding, or association, by blending ab initio quantum calculations, fundamental molecular level findings from experimental techniques, and thermodynamic models. Because of the ubiquity of hydrogen bonding, applications for an improved association model are extensive, ranging from drug design to plastics manufacturing. Therefore, a substantial amount of work has been aimed at improving traditional thermodynamic tools, which often fail to capture the behavior of associating systems accurately. To guide models, spectroscopic techniques have been leveraged to gain insight into the interactions between molecules in the liquid phase, but interpretation is difficult. Moreover, with the advancement of computational chemistry technology, molecular dynamics (MD) and quantum mechanical (QM) calculations have also been utilized to understand the characteristics of hydrogen bonded clusters. However, few studies have combined all 3 techniques (the thermodynamic model, spectroscopy and ab initio calculations) in a rigorous way. To this end, an activity coefficient model for association is developed using Wertheim’s perturbation theory and its capabilities and limitations are explored with parameters from literature. Furthermore, a sequential MD and QM protocol is designed which facilitates the interpretation of the hydroxyl vibration in infrared spectroscopy and a method is developed to quantify the entire band. Finally, the methods are used to calculate the value of the association constant for an alcohol + alkane system.
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Title: Vicarious interaction with politicians by identifying with surrogates on social media : a social identification mechanism based on multiple salient social categories
Creator: Dai, Yue (College teacher)
Date: 2018
Collection: Electronic Theses & Dissertations
Description: New media platforms display politicians’ interactions with people from a variety of social categories. Previous research shows that observers could vicariously experience parasocial intimacy toward a public figure by identifying with a surrogate—an individual who directly interacts with the public figure and who is considered an ingroup member by the observer based on a salient social category (Dai & Walther, 2018). Developments in the social identity literature call for further examination...
Show moreNew media platforms display politicians’ interactions with people from a variety of social categories. Previous research shows that observers could vicariously experience parasocial intimacy toward a public figure by identifying with a surrogate—an individual who directly interacts with the public figure and who is considered an ingroup member by the observer based on a salient social category (Dai & Walther, 2018). Developments in the social identity literature call for further examination of this surrogacy effect in contexts where multiple social categories are activated as bases upon which observers identify with surrogates. Through two experiments involving a total sample of 1,068 participants, this research demonstrates that when a surrogate’s identity is presented as different combinations of political affiliation (democratic or republican) and social status (ordinary voter or politician), the more categories observers share in common with the surrogate, the more they identify with the surrogate, and thereby experiences greater parasocial intimacy toward a politician who is seen replying to the surrogate on Twitter. These findings extend previous findings on a social identification-based mechanism of the surrogacy effect and inform online impression management practices of politician.
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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: Aerial photography
Creator: Schaeffer, Robert Owen
Date: 1938
Collection: Electronic Theses & Dissertations

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