Now showing items 9002-9021 of 20306

    • I Still Play: Exploring Play and Creativity in Early Adulthood Amongst Science, Technology, Engineering, Arts, and Mathematics Professionals

      Levine-Donnerstein, Deborah; Earl, Emily Charlotte; Levine-Donnerstein, Deborah; Burross, Heidi; Gaches, Sonya; Lopez, Francesca (The University of Arizona., 2015)
      Play is acknowledged as a fundamental need and right of the human experience. However, across the human lifespan is not always valued. Research on play has traditionally been on children, and while some attention is now being paid to older adults, there is little scholarship regarding play in adulthood. This exploratory study examined how early adulthood (25-40 years old) play, the influence playing has on creativity and career performance, and implications for future research on play. The study was completed utilizing traditional and non-traditional research methods with the intent to incorporate the participants' voice and perspectives into a human-centered research design. The end results of this study, demonstrated that early adults engage in a number of play experiences that shape their development and learning as well as influence their creativity and work performance. The use of human-centered research provided participants with the opportunity to individualize data collection, analyze results, and have a voice in the final product.
    • "I Thought this U.S. Place was Supposed to be About Freedom": Young Latinas Speak to Equity in Mathematics Education and Society

      Turner, Erin E; Gonzalez, Norma; Varley Gutierrez, Maura; Turner, Erin E; Gonzalez, Norma; Moll, Luis; Civil, Marta (The University of Arizona., 2009)
      This dissertation outlines findings from a critical ethnographic research study that attempted to document young Latinas engaging in critical mathematics education, with implications for shifting dominant ideas about the form and goals of education. As Latina youth are marginalized from classrooms and in society where their language, culture, practices, and community are seen as "problems," and particularly in mathematics classrooms where a dominant culture is said to further exclude girls, there is an exigency to understand how in fact Latina students could experience education as transformative. Critical race and feminist theories further argue for centralizing the experiences of women or girls of color as essential to understanding where change can happen in society because of the role that racism and sexism play in structuring educational experiences. Therefore, this study foregrounds the experiences of young Latinas as they engage in critical mathematics.A critical educational paradigm has been put forth whose purpose is to develop critical literacy in students where they investigate, make apparent and challenge oppressive societal structures. This critical ethnographic research study seeks to gain a more nuanced understanding of how young Latinas experience a social justice mathematics learning environment through the facilitation and research of an after-school, all girls mathematics club. More specifically, data in the form of field notes, videotaped sessions, classroom observations, student work and interviews offers a rich source for analysis of their practices in the learning environment, their perceptions of mathematics, themselves as learners of mathematics and as people who can make changes in their lives, communities and in the world. The construct of critical mathematical agency is employed in attempting to understand how the participants' actions expressed a sense of being able to use mathematics to critique and change their worlds. Analysis revealed they engaged in resistance, research and (re)authoring, as ways of expressing critical mathematical agency. In addition, their insight into critical mathematics education highlights the importance of incorporating critical funds of knowledge, fostering collectivity, and centering the experiences in authentic, community contexts. This understanding will inform arguments for seeking social justice through mathematics education and educational research, particularly for Latina youth.
    • "I Understand Everything You Say, I Just Don’t Speak It": The Role of Morphology in the Comprehension of Spanish by Receptive Heritage Bilinguals

      Beaudrie, Sara; Nicol, Janet; Holmes, Bonnie Christina; Beaudrie, Sara; Nicol, Janet; Carvalho, Ana; Pascual y Cabo, Diego (The University of Arizona., 2017)
      This study contributes to what is known about the nature of unbalanced bilingualism that emerges in language contact situations by examining the morphological knowledge of Spanish receptive heritage bilinguals (RHBs). RHBs were exposed to Spanish in their homes and communities but received formal schooling in English. These bilinguals have been described as being "on the verge of culminating the language shift towards English monolingualism" (Beaudrie, 2009a, p. 86), although despite this they report the ability to understand but not speak their heritage language. While the interpretation and production of inflectional morphology are difficult for more proficient heritage bilinguals (Montrul, 2008, 2009), little is known about the extent to which knowledge of morphology is measurable in HRBs or how it contributes to their ability to comprehend spoken Spanish. To answer these questions, 33 adult Spanish RHBs completed four, aurally-presented on- and off-line experimental tasks designed to assess their underlying grammatical competence, their receptive comprehension skills, and their proficiency without requiring that participants speak, read or write in Spanish. These tasks and the skills they assessed are listed below. 1) A self-paced, aural grammaticality judgment task examined whether RHBs have access to the rules that govern the well-formedness of specific inflectional morphemes, including gender and subject/verb agreement, as well as tense, aspect, and mood morphemes. 2) A morpheme interpretation task assessed whether RHBs interpret the meaning supplied by bound morphemes and distinguish between semantic contrasts. 3) A contextualized listening comprehension task measured the listening comprehension abilities of RHBs. 4) An elicited imitation task measured the proficiency of RHBs. The results of this study show that RHBs do have underlying morphological competence and are able to distinguish between grammatical and ungrammatical morphemes despite their limited language skills in other domains. Additionally, these bilinguals interpret the meaning supplied by bound morphemes, although access to the rules governing both the structure and the semantics of these morphemes decreases in accordance with the order in which they were acquired in childhood. RHBs understand the majority of what they hear when listening to spoken Spanish, and on average their proficiency ranges from low to intermediate levels. An analysis of the linear relationship between the results of the four experimental tasks revealed that the extent to which listening comprehension abilities and proficiency correspond to morphological knowledge in Spanish RHBs is dependent on the degree of access that these bilinguals have to the semantic information provided by functional morphemes. The results of this study show that while the core syntax of Spanish RHBs is intact, semantic knowledge may not have been mapped to certain morphemes during the acquisition process. These results are analyzed in tandem with various hypotheses that have been recently put forth to account for the linguistic outcomes of contact bilingualism, and an argument is made for considering heritage grammars as completely acquired but distinct language varieties.
    • I Won't Live On, So I Create: Mortality Salience and Afterlife Belief Strength's Impact on Intention to Engage in Creation-Oriented Consumption

      Brucks, Merrie L; Greenberg, Jeff; Xu, Huimin; Brucks, Merrie L; Greenberg, Jeff; Erickson, Lance; Nielsen, Jesper (The University of Arizona., 2006)
      Creative behaviors are part of an average consumer's everyday life. For example, amateur people buy various art and craft supplies from stores like Michael's, purchase studio time to make pottery, and collect camera accessories to help demonstrate their originality in photography. Usually the final creative product can be preserved for a long period of time. These creative activities are avidly pursued primarily because they provide consumers with enjoyment and a sense of fulfillment. I am coining the term "creation-oriented consumption" to refer to this phenomenon, which is one specific type of creative consumption.Terror management theory is used to examine why people engage in creation-oriented consumption. I hypothesize that mortality salience boosts the intention to engage in creation-oriented consumption; and under mortality salience, weakened afterlife belief increases the intention for this type of consumption.Three experimental studies are conducted, each adopting a somewhat different perspective. Study 1 gauges intention to engage in creation-oriented consumption against inaction. It finds that mortality salience increases interest in creation-oriented consumption; and that under mortality salience, weakened afterlife belief increases interest in creation-oriented consumption. Study 2 examines durable creation-oriented consumption's appeal relative to other activities, namely, non-creative activities and creative consumption that does not leave durable traces. The proposed effect of mortality salience is observed only when individuals possess a low level of chronic afterlife belief. Unexpectedly, interest in creative consumption is reduced under mortality salience. Consistent with study 1, study 2 finds that under mortality salience, weakened afterlife belief raises interest in creation-oriented consumption. Study 3 replicates the finding of study 2 that mortality salience dampens general interest in creativity. Taken together, these studies suggest that although creation-oriented consumption ameliorates existential anxiety, it is not the most effective one in the short term.Apart from the major hypotheses, this dissertation also investigates some boundary conditions. Two of the three studies find that the question of whether creative consumption leaves a durable trace is of significance.
    • "I Wouldn't Change Anything": The Everyday Realities of Living with Autism from a Parent's Perspective

      Gilmore, Perry; Molina, Rudy Modesto, Jr.; Gilmore, Perry; Ruiz, Richard; Fletcher, Todd (The University of Arizona., 2014)
      Using qualitative methods, this study is about the attitudes and daily practices of parents who genuinely want the best for their children who have been diagnosed with autism. The study examined the everyday realities of living with autism from a parent's perspective. The purpose of this study was to describe the range of specific behaviors, practices, attitudes, and ways of being that families adopt when they engage in the world of autism. Three families were interviewed in these case studies. A content analysis of the interviews identified five thematic clusters that are described and examined in close detail. The five thematic clusters include (1) managing the diagnostic process, (2) child's behavior and educational needs, (3) impact on parent's well-being, (4) impact on the family as a whole, and (5) full integration into mainstream society. These themes were further categorized according to the "challenges" facing the families and the specific "strategies" families used to face these challenges. Parents shared their stories with the researcher with the hopes that their life experiences could be beneficial to other families facing the same challenges as they navigate complex educational, health, and social systems. The research presents a set of recommendations that were embedded in the participants' stories. These recommendations represent advice from the parents in the study to other parents with children diagnosed with autism. Their recommendations are based on what the participants have learned as they raised their own child with autism.
    • I'd Give My Right Kidney to Be Altruistic: The Social Biogeography of Altruism in the United States of America

      Figueredo, Aurelio Jose; Garcia, Rafael Antonio; Figueredo, Aurelio Jose; Jacobs, William Jake; Steklis, Horst Dieter; Davis, Melinda (The University of Arizona., 2017)
      The purpose of this dissertation is to model biosocial determinants of group-directed altruistic behavior – exploring the nomological net around it. To do this a study will be presented to determine existing associations among various biological and social predictors and test a life-history-derived causal cascade using a partially exploratory and partially confirmatory statistical technique called Sequential Canonical Analysis to ultimately predict living-donor, non-directed kidney donations (NDKD). Toward that end, some important methodological considerations first need to be discussed. The first consideration revolves around the level of analysis and how this frames the cascade model and its interpretation. Following a general discussion, an exercise in some of the general principles is provided – investigating the higher-order factor structure of the Big-5 personality constructs across two levels of analysis. The second consideration is the use of unit-weighted factor scores and their appropriateness. Following the theoretical discussion, a demonstration is provided – deriving an estimate of genetic relatedness from a set of heterogeneous data sets. Once the methodological considerations have been discussed, the primary cascade model is presented in two parts: 1) the measurement model – operationalizing the measures incorporated into 2) the structural model – testing the proposed causal cascade using Sequential Canonical Analysis. A discussion follows in which the results are summarized, limitations are articulated, and further research directions are explored.
    • I. A. Richards' new rhetoric: Metaphor and 'Ethos'.

      Enos, Theresa; Brown, Stuart Cameron.; Willard, Thomas; Roen, Duane (The University of Arizona., 1990)
      Initially acknowledged as leading to a revitalized rhetoric, I. A. Richards' contributions now are neglected. Three themes weave through this discussion of Richards' works and their value. First, he should be more thoroughly recognized as a pivotal force in twentieth-century rhetoric who brought rhetoric into modernity and thus set the stage for much of current rhetorical inquiry. Second, his speculations on the meaning of meanings provide the basis for a study of ethos that will pay close attention to the evaluations readers and writers, speakers and listeners, bring to rhetorical situations. Third, his inquiries into metaphor are germinal, initiating the growing perception that metaphor is the constituent of language use and meaning. Because he conjoins a new understanding of metaphor and of ethos, Richards provides the basis of a truly "new" rhetoric, one crucial to what he calls "the world we make for ourselves to live in." Current rhetorical theory, history of metaphor studies, and contemporary accounts of metaphor are discussed in relation to Richards' works.
    • I. Analysis of biological specimens by proton-induced x-ray emission spectroscopy (PIXE). II. Separation and purity of carbon₆₀ and carbon₇₀.

      Lowe, Timothy Paul.; Fernando, Quintus; Pemberton, Jeanne E.; Enemark, John H.; Vemulapalli, G. K.; Rund, John V. (The University of Arizona., 1993)
      Proton induced x-ray emission spectroscopy (PIXE) is a rapid and sensitive analytical technique for the non-destructive simultaneous determination of elemental concentrations above atomic number 11 (sodium) and is the only analytical technique that can determine 20-30 elements nondestructively in a single small sample (≈5 mg) with detection limits of 1- 5 ppm (dry weight). Part I of this dissertation outlines work done on the optimization of instrumental parameters and sample preparation for the analysis of biological tissue. Cultured rabbit renal slices were used as the biological system to demonstrate the use of PIXE analysis. The renal slices were exposed to HgCl₂, CdCl₂, K₂Cr₂0₇, or NaAsO₂ alone or in a mixture. The analysis of biological samples by PIXE provides information on inter-elemental interactions in tissue and body fluids. A computer program for spectrum processing and quantitation, which decomposes overlapped peaks, corrects for thick target matrix effects and calculates results without resorting to the use of standards, is explored. In part II of this dissertation, a convenient method of removing solvent from a benzene extract of graphitic soot containing fullerenes using sublimation, is outlined. Separation of macroscopic quantities of the fullerenes C₆₀ and C₇₀ has been accomplished using a combination of selective precipitation of C₆₀ and chromatography. C₆₀ is selectively crystallized by freezing and thawing a benzene solution of mixed fullerenes, then using the C₇₀ enriched supernatant as starting material in the chromatographic separation of C₆₀ and C₇₀. In the separation scheme, a bed of modified silica sorbent is charged with the fullerene mixture and the fullerenes are eluted using a hexanes/THF mobile phase. The methods of uv-Visible and infrared spectroscopy, as well as high performance liquid chromatography (HPLC) are evaluated for their ability to determine the purity of a C₆₀ or C₇₀ sample.
    • I. Causes of Multiple Diffusing Populations of Fluorescently Labeled Probes in Lipid Membranes II. Evaluation of Phospholipid Membranes Incorporating the Polymerizable Lipid Bis-Denpc (16, 16) and Suitability as Ultra-Stable Platforms for Ion Channel Based Sensors

      Saavedra, S. Scott; Smith, Christopher M.; Aspinwall, Craig A.; Pemberton, Jeanne E.; Denton, Bonner; Brown, Michael F. (The University of Arizona., 2019)
      This dissertation is composed of two major projects, though some capabilities and findings from the first project were applied to the second. Project I focuses on advancements made in the understanding of the chemical interactions of a number of commonly used fluorescently labeled phospholipid probes. These probes are used for a variety of studies, including labeling of cellular or artificial membranes, examining transport and communication between different membranes, and determining membrane fluidity. Understanding the chemical behavior and interactions of these probes in membranes can be key for the proper interpretation of experimental data. Utilizing fluorescent recovery after photobleaching (FRAP), in combination with other spectroscopic techniques, multiple diffusing populations of commonly used probes in various artificial lipid membrane formats were identified, as were the causes for these populations. This allows for a fuller description of the fluidity of lipid membranes. These findings are the focus of Chapters 3 and 4 while the hardware developed that enabled critical measurements is the focus of Chapter 2. Project II focuses on addressing key limitations in developing ion channel (IC) based biosensors utilizing artificial lipid membranes. Among these limitations are the weak mechanical, chemical, and electrical stabilities of artificial lipid bilayers due to the weak noncovalent interactions involved in the membrane. To address these limitations, the polymerizable lipid bis-dienoyl phosphatidylcholine (bis-DenPC(16, 16)) was characterized for its ability to form ultra-stable membranes suitable for IC based sensors using the model IC gramicidin A (gA). Special attention was given to determining the membrane fluidity given the requirement of gA that two subunits must laterally diffuse to converge and dimerize to form a conductive pore. These studies are the focus of Chapters 5 and 6.
    • I. Cyclopropyl anions II. Charge-transfer monomers and polymers

      Brand, Richard Allen, 1947- (The University of Arizona., 1975)
    • I. Development of Rapid Conductance-Based Protocols for Measuring Ion Channel Activity; II. Expression, Characterization, and Purification of the ATP-Sensitive, Inwardly-Rectifying K+ Channel, Kir6.2, and Ion Channel-Coupled Receptors

      Aspinwall, Craig A.; Saavedra, Steve S.; Agasid, Mark Tadashi; Aspinwall, Craig A.; Saavedra, Steve S.; Hruby, Victor J.; Heien, Michael L. (The University of Arizona., 2017)
      Ligand-gated and ligand-modulated ion channel (IC) sensors have received increased attention for their ability to transduce ligand-binding events into a readily measurable electrical signal. Ligand-binding to an IC modulates the ion flux properties of the channel in label-free manner, often with single-molecule sensitivity and selectivity. As a result, ICs are attractive sensing elements in biosensoring platforms, especially for ligands lacking optical (e.g. fluorescent) or electrochemical properties. Despite the growing number of available ligand-gated and ligand-modulated ICs and artificial lipid bilayer platforms for IC reconstitution, significant work remains in defining the analytical performance capabilities of IC sensors. Particularly, few studies have described platforms for making measurements with rapid temporal resolution and high sensitivity. In this work, we describe an artificial lipid bilayer platform which enables rapid measurement of ion channel activity, a key parameter for developing IC sensors suitable for studying biological events, e.g. single cell exocytosis (Chapter 2 and 3). Additionally, we developed expression, purification, and reconstitution protocols for Kir6.2, a model ligand-gated ion channel, for use in sensor development (Chapter 4). The final goal is to reconstitute ion channel-coupled receptors (ICCRs), G protein-coupled receptor-Kir6.2 fusion proteins, into artificial lipid bilayers to detect small molecules and hormones targeting GPCRs. Towards this goal, we characterized the expression and function of two ICCRs, M2-Kir and D2-Kir, in HEK293 cells (Chapter 5).

      REINEKE, KARL EDWARD, II. (The University of Arizona., 1983)
      In Part 1, the Diels-Alder adducts of trimethyl cyclopentadienylstannane (I.3) with maleic anhydride and fumaronitrile are prepared in 61% yield. The molecular structure of the adduct with maleic anhydride (1.6) is unequivocally established as 7-syn-trimethy1stannyl-endo- bicyclo[2.2.1]hept-5-enyl-2,3-dicarboxy1ic anhydride by single crystal X-ray structure analysis. In Part II, the high yield preparation of some new S-a1ky1-Saryl- N-p-toluenesu1fonylsu1foximines, by ruthenium tetroxide oxidation of the corresponding su1filimine, is described. Dehydrochlorination of S-chloroethy1-N-p-toluenesu1fonyl-S-p-toly1su1foximine and its S-phenyl analog with triethylamine gives the previously unknown N-p-to1uenesu1fony1- S-p-to1y1-S-viny1sulfoximine (II.17) and its S-phenyl analog. The Diels-Alder reaction of II.17 with a variety of 1,3-dienes and the known N-phtha1imido-S-p-tolyl-vinylsu1foximine (11.14) and the previously unreported S-p-nitropheny1-N-phtha1imido-viny1su1foximine (11.39) with cyclopentadiene are described. All of the reactions give mixtures of the possible adducts. The configuration of the major diastereomer (II.19d) of the adducts of II.14 with cyclopentadiene is known from a single crystal X-ray structure analysis. The structures of the other adducts are determined by ¹H NMR spectroscopic analysis. Chemical correlation of II.19d with the adducts of II.17 with cyclopentadiene confirm the assignment made by ¹H NMR. A competition Die1s-Alder reaction between II.17 and p-toly1-viny1sulfone shows that the vinylsulfoximine is more reactive. Sodium amalgam reduction of the cyclohexadienyl adducts of II.17 gives bicyclo[2.2.2Joctene and hydrazine in allyl alcohol reduction of adduct II.19d gives the corresponding sulfoxide II.20d.

      ANDRUSKI, STEPHEN WALTER. (The University of Arizona., 1987)
      An X-ray crystal analysis of l,8-Bis(methylthio)naphthalene (1.1) revealed that the molecule has a geometry in which the naphthalene ring is twisted to place the 1,8- substituents symmetrically above and below the naphthalene plane. The methyl groups are rotated out of the naphthalene plane. X-ray crystal analysis of Naphtho [1, 8-b, c] -1, 5- dithiocin (1.2) showed that naphthalene ring is twisted as in 1.1, however the disposition of the sulfurs above and below the plane is unsymmetrical. The aliphatic portion of the molecule is in a chair-like conformation. Comparison of these two structures indicates that the bond asymmetry across the naphthalene ring is due largely to bond stretching to relieve steric overcrowding. MNDO calculations on 1.1 and 1.2 give HOMO's which are predominantly naphthalene in character. Our MNDO eigenvalues for 1.1 and naphtho[l,8-d,e]-l,3-dithiin (2.1) correlate well with their PES ionization potentials. We predict an ionization potential of -7.60-7.76eV for 1.2. Reduction of the ethylene hemithioketal of norcamphor is shown to proceed with heterolysis of the carbon-oxygen bond and hydride attack on the resulting thionium ion occurring from the sterically less hindered exo face of the norbornane moiety. The stereochemistry of the resulting substituted norbornanes (3.4 and 3.5) is proved to be endo. In the reduction of N-phthalimido sulfoximines to sulfoxides with hydrazine in ethanol, a species is formed which gives reduction of certain unsaturated compounds. The reducing species is shown not to be diimide. Formation of 1,1-diazene is a possible explanation for the experimental results. The cycloaddition of (±)-S-2'-thienyl-S-vinyl-Nphthalimidosulfoximine ((±)-5.1g) with cyclopentadiene proceeds in good yield, however asymmetric induction in the resulting adducts is negligible. This strongly indicates that steric factors are controlling the asymmetric induction in this cycloaddition. (±)-Thiochromone-l-oxide (±)-5.8) and (±)-N-phthalimido-l-imino-4-thiochromone-l-oxide (±)- 5.6) are shown to undergo Diels-Alder reactions with cyclopentadiene in good yields giving only endo products with good diastereoselectivity. The diastereoselectivity of the reaction of (±)-5.8 with cyclopentadiene is shown to increase when the reaction is run at -78° with AlCl₃ as a catalyst. These results can be interpreted on the basis of approach of the diene on the less hindered face of the more reactive conformer.
    • I. Hadamard Transform Capillary Electrophoresis for the Analysis of Biologically Active Species II. Characterization and Application of Two-Photon Activatable Proton and Radical Generators

      Aspinwall, Craig A.; Perry, Joseph W.; Braun, Kevin L; Aspinwall, Craig A.; Perry, Joseph W.; Sanov, Andrei; McGrath, Dominic V.; Monti, Oliver L. A.; Saavedra, S. Scott (The University of Arizona., 2005)
      PART I. A modified Hadamard transform has been developed and applied to the analysis of biologically active species using capillary electrophoresis. Hadamard transformations, a matrix based multiplexing technique, when coupled with a capillary electrophoresis instrument capable of rapid sample injection, provides a means to semi-continuously inject samples. The multiple injections separate, interpenetrate, and are detected as the summation of the multiple injections. Deconvolution of the multiplexed signal by multiplication with the inverse of the injection matrix yields a single injection electropherogram that exhibits improved S/N. In modified Hadamard transform capillary electrophoresis (mHTCE), an injection sequence of half the length as conventional HTCE (cHTCE) is utilized. Modifying the manner in which the raw data is manipulated before deconvolution facilitates the reduced injection sequence. When coupled with software, mHTCE can reduce the collection time for a Hadamard sequence by up to 48%. The substantial time reduction afforded by mHTCE is utilized to demonstrate the first time-resolved application of Hadamard transformations for the analysis of neurotransmitters. Additionally, mHTCE has been demonstrated as a means to improve the sensitivity for analysis of amino acids and proteins including gamma-aminobutyric acid, dopamine, and enhanced green fluorescent protein (EGFP) with picomolar detection limits.Part II. Two-photon excitation provides a means to activate chemical and physical processes with high spatial resolution and improved depth penetration compared to one-photon excitation. When combined with three-dimensional lithographic microfabrication (3DLM), these advantages provide a means to fabricate complex structures through radical and cationic two-photon induced polymerization (TPIP). A strategy for realizing high-fidelity microstructures is reported that considers the inherent structural limitations of acrylate monomers. Utilizing this strategy, a series of high-fidelity microstructures is reported for application in microfluidic devices, microelectromechanical systems (MEMS), and microoptical devices such as photonic bandgap (PBG) crystals. Improved periodicity is reported here for f.c.c. PBG crystals compared to earlier examples through addition of micromechanical supports that provide increased strength to the high-aspect ratio crystals. To extend TPIP to cationic polymerization, a series of two-photon activatable photoacid generators has been developed. The new PAGs exhibit one to two orders of magnitude lower polymerization threshold intensities than conventional ultraviolet-sensitive initiators.
    • I. Morphological and Nanomechanical Studies of Lipid Bilayers Composed of Polymerizable and Non-Polymerizable Lipids II. Fluidity Studies of Platelet Plasma Membranes

      Saavedra, S. Scott; Fonseka, Nelusha Malithi; Aspinwall, Craig A.; Pemberton, Jeanne E.; Montfort, William (The University of Arizona., 2019)
      Two main projects are discussed in this dissertation. The first project: Morphological and nanomechanical studies of planar supported lipid bilayers (PSLB) composed of polymerizable and non-polymerizable lipids as potential platforms for biosensors, is discussed in Chapters 2 through 4. Chapters 2 and 3 focus on PSLBs composed of the polymerizable lipid, bis-SorbPC and Chapter 4 focuses on bis-DenPC16,16. These studies are important because PSLBs are widely studied as platforms for receptor-based biosensors. PSLBs composed of fluid lipids lack the stability necessary for many technological applications due to the relatively weak non-covalent interactions between lipid molecules. Lipid polymerization enhances bilayer stability, but greatly reduces lipid diffusion and membrane fluidity. In an effort to enhance bilayer stability while maintaining fluidity, PSLBs composed of mixtures of polymerizable lipids and fluid lipids were prepared and characterized. Fluidity studies of these bilayers showed that considerable fluidity is retained even when the polymer fraction is substantial, which suggests that these bilayers are phase segregated, composed of polymerized and fluid domains. However, domains had not been observed previously. Chapter 2 of this dissertation describes the work done with atomic force microscopy (AFM) to study the phase segregation of mixed PSLBs composed of the polymerizable lipid bis-SorbPC and the fluid lipid DPhPC. This work provided direct evidence for polymerization-induced phase segregation of these mixed PSLBs, forming membranes composed of fluid and poly(lipid) domains. In these mixed bilayers, DPhPC formed a semi-continuous phase of greater height surrounding island-like domains of poly(bis-SorbPC) of lesser height. Numerous studies demonstrate that retention of bioactivity upon reconstitution of transmembrane proteins typically requires both membrane fluidity and elasticity. Thus, AFM force mapping was employed to study the nanomechanical properties of lipid bilayers, which is described in Chapter 3. This is the first study done to quantify the nanoscale mechanical properties of bis-SorbPC before and after polymerization, and mixed bilayer composed of bis-SorbPC and DPhPC. The results showed that the resistance to rupture and elastic modulus of bis-SorbPC increased upon polymerization. In addition, the results showed that the breakthrough force and the elastic modulus of DPhPC in mixed bilayers were different to pure bilayers due to the size (interface/edge effects) and the purity of the domains in mixed PSLBs. Findings similar to Chapters 2 and 3 are discussed in Chapter 4, with a different polymerizable lipid; bis-DenPC16,16. Comparing the results of bis-SorbPC (Chapter 3) and bis-DenPC (Chapter 4) showed that the position of the polymerizable moiety significantly changed the nanomechanical properties of PSLBs. In addition, no direct evidence of phase segregation was observed in mixed PSLBs composed of bis-DenPC and DPhPC during sub-micron scale morphological and nanomechanical studies. The second project: Fluidity studies of platelet plasma membranes, is the focus of Chapter 5. Therein, the feasibility of employing fluorescence recovery after photobleaching (FRAP) to determine the diffusion coefficient of platelet plasma membranes in response to lipophilic molecules is investigated. Mechanical circulatory devices, used in patients with heart failure to restore blood flow, cause thrombosis due to the abnormal flow of blood and supra-physiologic shear on blood platelets when blood passes through these devices, known as shear-mediated platelet activation (SMPA). It has been hypothesized that the membrane fluidity plays a role in treating SMPA and that the fluidity can be modulated with lipophilic molecules. Accordingly, the possibility of employing FRAP to study the lateral diffusion coefficient of platelet plasma membranes was investigated and a protocol was developed. The results showed that FRAP of platelet membranes is a suitable technique to determine the lateral fluidity of platelets before and after treating with exogenous lipophilic molecules. Therefore, the protocol established here will be helpful to study the fluidity of shear-activated platelets allowing to test the hypothesis. Further, this protocol will be beneficial to investigate the fluidity of platelet plasma membranes in the development of treatment methodologies targeting the material properties of platelets to reduce SMPA.

      Ottaviani, Robert Augustine, 1940- (The University of Arizona., 1970)

      Londrigan, Michael Edward Carlson (The University of Arizona., 1972)