Mountain Scholar :: Browsing by Author "Prieto, Amy L., committee member"

Browsing by Author "Prieto, Amy L., committee member"

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Open Access
A multi-functional electrolyte for lithium-ion batteries
(Colorado State University. Libraries, 2016) Westhoff, Kevin A., author; Bandhauer, Todd M., advisor; Bradley, Thomas H., committee member; Prieto, Amy L., committee member
Thermal management of lithium-ion batteries (LIBs) is paramount for multi-cell packs, such as those found in electric vehicles, to ensure safe and sustainable operation. Thermal management systems (TMSs) maintain cell temperatures well below those associated with capacity fade and thermal runaway to ensure safe operation and prolong the useful life of the pack. Current TMSs employ single-phase liquid cooling to the exterior surfaces of every cell, decreasing the volumetric and gravimetric energy density of the pack. In the present study, a novel, internal TMS that utilizes a multi-functional electrolyte (MFE) is investigated, which contains a volatile co-solvent that boils upon heat absorption in small channels in the positive electrode of the cell. The inert fluid HFE-7000 is investigated as the volatile co-solvent in the MFE (1 M LiTFSI in 1:1 HFE-7000/ethyl methyl carbonate by volume) for the proposed TMS. In the first phase of the study, the baseline electrochemical performance of the MFE is determined by conductivity, electrochemical stability window, half and full cell cycling with lithium iron phosphate (LiFePO4), lithium titanate oxide (Li4Ti5O12), and copper antimonide (Cu2Sb), and impedance spectroscopy measurements. The results show that the MFE containing HFE-7000 has comparable stability and cycling performance to a conventional lithium-ion electrolyte (1 M LiPF6 in 3:7 ethylene carbonate/diethyl carbonate by weight). The MFE-containing cells had higher impedance than carbonate-only cells, indicating reduced passivation capability on the electrodes. Additional investigation is warranted to refine the binary MFE mixture by the addition of solid electrolyte interphase (SEI) stabilizing additives. To validate the thermal and electrochemical performance of the MFE, Cu2Sb and LiFePO4 are used in a full cell architecture with the MFE in a custom electrolyte boiling facility. The facility enables direct viewing of the vapor generation within the channel in the positive electrode and characterizes the galvanostatic electrochemical performance. Test results show that the LiFePO4/Cu2Sb cell is capable of operation even when a portion of the more volatile HFE-7000 is continuously evaporated under an extreme heat flux, proving the concept of a MFE. The conclusions presented in this work inform the future development of the proposed internal TMS.
Open Access
Applications of superatom theory in metal cluster chemistry
(Colorado State University. Libraries, 2016) Tofanelli, Marcus A., author; Ackerson, Christopher J., advisor; Prieto, Amy L., committee member; Shores, Mathew, committee member; Farmer, Delphine, committee member; Roberts, Jacob, committee member
One of the largest modern scientific debates is understanding the size dependent properties of a metal. While much effort has been performed on understanding metal particles from the top down to much less work has been accomplished from the bottom up. This has lead to a great deal of interest in metal clusters. Metal clusters containing 20 to 200 metal atoms are similar yet strikingly different to both to normal coordination chemistry and continuous bulk systems, therefore neither a classical understanding for bulk or molecular systems appears to be appropriate. Superatom theory has emerged as a useful concept for describing the properties of a metal cluster in this size range. In this model a new set of ‘superatomic’ orbitals arises from the valence electrons of all the metals in a cluster. From superatom theory the properties of a metal cluster, such as stability, ionization energy, reactivity, and magnetism, should depend on valence of the superatomic orbitals, similar to a normal atom. However superatom theory has largely been used to describe the high stabilities of metal clusters with completed electronic configurations. Thus many features of superatom theory have remained largely untested and the extent that the superatom model truly applies has remained in question for many years. Over the past decade increases in synthetic and analytical techniques have allowed for the isolation of a series of stable monodisperse gold thiolate monolayer protected clusters (MPCs) containing from 10 to 500 gold atoms. The wide range in sizes and high stability of gold thiolate clusters provides an instrumental system for understanding superatom theory and the transition from molecular-like cluster to bulk-like system. In the first part of this thesis the effects of the superatomic valence is investigated under superatomic assumptions. Au25(SR)18 (where SR= any thiolate) can be synthesized in 3 different oxidation states without any major distortions to the geometry of the cluster, thus it is possible to test 3 different superatomic configurations for a single cluster. These studies show that the superatom model correctly predicts changes observed in the stability, absorption spectrum, crystal structures, and magnetic susceptibility for each charge state of Au25(SR)18. In addition, the superatom model is shown to also apply to the isoelectronic PdAu24(SR)18 superatomic cluster. This work is discussed in Chapters 2, 3, and 4. The second part of this thesis focuses on the transition from superatomic metal clusters to metal nanoparticles. Au144(SR)60 is studied in order to understand this transition. Although the plasmon is not immediately apparent through linear absorption spectroscopy, a plasmonic feature is observed in transient absorption spectroscopy. This observation in combination with the absence of a HOMO-LUMO gap suggests that Au144(SR)60 can be treated with bulk assumptions. However Au144(SR)60 shows quantized behavior and powder x-ray diffraction reveals that symmetry of the metal core does not represent what is observed in the bulk. Au144(SR)60 appears to show both superatomic and bulk behavior making it an instrumental tool for understanding the transition from superatomic to bulk behavior. This work is discussed in Chapters 2, 5, and 6.
Open Access
Characterization and modification of carbon composite electrodes towards more affordable biosensing applications and integration into fluidic devices
(Colorado State University. Libraries, 2022) Clark, Kaylee M., author; Henry, Charles S., advisor; Van Orden, Alan, committee member; Prieto, Amy L., committee member; Volckens, John, committee member
Fast, accurate, and low-cost medical tests and platforms for biomolecule monitoring are essential to the diagnosis, management, and treatment of many diseases. Electrochemical detection allows for highly sensitive measurements with fast response times. Carbon composite electrodes are an attractive option for electrochemical detection due to their low cost, resistance to biological fouling, large electrochemical solvent windows, and ability to be patterned. However, they often suffer from poor electrocatalytic activity, inability to be molded, and need for complex modifications to effectively detect certain analytes. Combining electrochemistry with fluidics is attractive for a wide array of applications including multiplexing, automation, and high-throughput screening. However, fabrication of electrochemical fluidic devices with integrated carbon electrodes remains a challenge. Thermoplastic electrodes (TPEs) are a new class of composite electrodes discussed in this dissertation that exhibit superior electrochemical properties to typical carbon composite electrodes and can be easily molded into intricate structures. Overall, this dissertation aims to improve carbon composite materials for biosensing applications and integration of electrochemical sensors into fluidic devices. Chapter 2 introduces polycaprolactone (PCL) as a new binder material for TPEs and focuses on the electrochemical characterization of the new material. The PCL-based TPEs have excellent electrochemical activity towards a wide range of analytes as well as high electrical conductivity. Chapter 2 also introduces a simple technique for integrating PCL and carbon composite electrodes into microfluidics. The presented electrode-integrated microfluidic devices are quickly fabricated with a laser cutter using PCL as a bonding layer. As a proof-of-concept application, water-in-oil droplets are electrochemically analyzed. Chapter 3 focuses on use of PCL-based TPEs for enzymatic sensors. The simple fabrication of TPEs also allows catalysts and enzymes to be mixed directly into the material to enhance detection. In Chapter 3, the TPE material is bulk-modified with cobalt phthalocyanine, an electrocatalyst, and glucose oxidase, resulting in a robust glucose sensor that demonstrates long-term current response stability. These sensors can be molded into intricate shapes and sanded for surface renewal (without requiring additional steps to maintain the modification), allowing the sensors to be continuously reused even if damaged or fouled. Chapter 4 investigates the properties of TPEs using two different binders – polycaprolactone (PCL) and polystyrene (PS) – with sanded and heat-pressed surface treatment. XPS and SEM analysis suggested that sanded TPEs have a higher density of graphitic edge planes and improved electrochemistry as a result. Electrochemical detection of O2 and H2O2, which are typically difficult to detect on carbon composites without complex modification, was demonstrated on sanded PS-based TPEs. Additionally, Chapter 4 introduces a new 3D-printed TPE sensor module that is reversibly sealed with magnets. A proof-of-concept sensor for detecting H2O2 in flow with the sensor module is presented. Chapter 5 presents a low-cost flow device, made of inexpensive polyethylene terephthalate (PET) and adhesive films, developed to detect SARS-CoV-2 nucleocapsid (N) protein. Upon addition of a sample in the device, reagents and washes are sequentially delivered to an integrated screen-printed carbon electrode for detection thus automating a full sandwich immunoassay with a single end-user step. The modified electrodes are sensitive and selective for COVID-19 N protein and stable for over seven weeks. The flow device was also successfully applied to detect nine different SARS-CoV-2 variants, including Omicron. In summary, this dissertation presents work to improve carbon composite electrodes, their modification, and integration into fluidic devices for applications as biosensors and beyond. The TPEs presented show improved electrochemical and physical properties, that allow for simple modifications. This work also demonstrates simple electrode integration strategies in several types of fluidic devices for easier and more sensitive detection of biologically relevant analytes. Moreover, the platforms established in this dissertation can be easily adapted for a wide variety of analytes and applications. This work provides materials, methods, and platforms to create more affordable biosensors for medical and other biological sensing.
Open Access
Defect tolerance, anharmonicity, and organic-inorganic coupling in hybrid organic-inorganic semiconductors
(Colorado State University. Libraries, 2018) Maughan, Annalise E., author; Neilson, James R., advisor; Prieto, Amy L., committee member; Reynolds, Melissa M., committee member; Sites, James R., committee member
Implementing and improving sustainable energy technologies is predicated upon the discovery and design of new semiconducting materials. Perovskite halides represent a paradigm shift in solar photovoltaic technologies, as devices utilizing perovskites as the active semiconductor can achieve power conversion efficiencies rivaling those of commercial solar cells after less than a decade of dedicated research. In contrast to conventional semiconductors, perovskites are unique in that they exhibit excellent photovoltaic performance despite the presence of significant materials disorder. This disorder manifests as (1) a large concentration of crystallographic defects introduced by low-temperature processing, and (2) as dynamic disorder due to the deformable metal-halide framework and the presence of dynamic organic species within the crystalline voids. Vacancy ordered double perovskites of the general formula A2BX6 are a defect-ordered variant of the archetypal perovskite structure comprised of isolated [BX6] units bridged by cationic species at the A-site. The presence of ordered vacancies and relatively decoupled octahedral units presents an ideal system to investigate defects and lattice dynamics as they pertain to optical and electronic properties of perovskite halide semiconductors. This work aims to illuminate the fundamental structure-dynamics-property relationships in vacancy-ordered double perovskite and hybrid organic-inorganic semiconductors through a combination of advanced structural characterization, optical and electrical measurements, and insight from computation. We begin with a study of the Cs2Sn1-xTexI6 series of vacancy-ordered double perovskites to inform the chemical and bonding characteristics that impact defect chemistry in vacancy-ordered double perovskites. While the electronic properties of Cs2SnI6 are tolerant to the presence of crystallographic defects, introducing tellurium at the B-site yields an electronic structure that renders Cs2TeI6 defect-intolerant, indicating the importance of the B-site chemistry in dictating the optoelectronic properties in these materials. Next, we elucidate the interplay of the A-site cation with the octahedral framework and the subsequent influence upon lattice dynamics and optoelectronic properties of several tin-iodide based vacancy-ordered double perovskites. The coordination and bonding preferences of the A-site drive the structural and dynamic behavior of the surrounding octahedra and in turn dictate charge transport. A-site cations that are too small produce structures with cooperative octahedral tilting, while organic-inorganic coupling via hydrogen bonding yields soft, anharmonic lattice dynamics characterized by random octahedral rotations. Both regimes yield stronger electron-phonon coupling interactions that inhibit charge transport relative to undistorted analogs. The final study presented here details the discovery of two hybrid organic-inorganic semiconductors containing the organic tropylium cation within metal iodide frameworks. In C7H7PbI3, the tropylium electronic states couple to those of the lead iodide framework through organic-inorganic charge transfer. Electronic coupling between the organic and inorganic sublattices within a singular material provides an avenue to elicit unique optical and electronic properties unavailable to either components individually. The above work is then placed in context of other recent studies of vacancy-ordered double perovskite semiconductors, and a set of design principles are constructed. Future avenues of research are proposed. These structure-dynamics-property relationships represent an important step towards rational design of vacancy-ordered double perovskite semiconductors for potential optoelectronic applications.
Open Access
Efforts toward the total synthesis of quinine, synthesis of largazole analogs, and progress toward potential biosynthetic intermediates of taxol
(Colorado State University. Libraries, 2012) Bubb, Jennifer Marie, author; Williams, Robert M., advisor; Wood, John L., committee member; McNaughton, Brian R., committee member; Prieto, Amy L., committee member; Ishii, Douglas N., committee member
Herein we discuss our work involving three different projects, namely (1) efforts toward the total synthesis of quinine, (2) synthesis of largazole analogs, and (3) progress toward potential biosynthetic intermediates of taxol. Our efforts toward the synthesis of quinine have led us toward a route toward a pipecolic acid derivative that was further elaborated to a late-stage intermediate. Following an intramolecular cyclization and deoxygenation protocol, a formal synthesis of quinine could be realized. In the second project, we have successfully synthesized and tested analogs of the known HDAC inhibitor, largazole. These analogs have demonstrated good potency towards a series of HDAC isoforms. In the third project, efforts have been made to synthesis potential biosynthetic intermediates of taxol. Utilizing highly oxygenated intermediates isolated from the heartwood of the Japanese yew tree, we have explored the reactivities of these complex natural products in hope of devising a method to construct mono-acetylated derivatives.
Open Access
Elucidating structure-property-performance relationships of plasma modified tin(IV) oxide nanomaterials for enhanced gas sensing applications
(Colorado State University. Libraries, 2017) Stuckert, Erin P., author; Fisher, Ellen R., advisor; Barisas, B. George, committee member; Prieto, Amy L., committee member; Krummel, Amber T., committee member; Ma, Kaka, committee member
This dissertation examines structure-property-performance relationships of plasma modified tin(IV) oxide (SnO2) nanomaterials to successfully and efficiently create sensitive targeted gas sensors. Different project aspects include (1) materials characterization before and after plasma modification, (2) plasma diagnostics with and without a SnO2 nanomaterial, (3) sensor performance testing, and ultimately (4) elucidation of gas-surface relationships during this project. The research presented herein focuses on a holistic approach to addressing current limitations in gas sensors to produce desired capabilities for a given sensing application. Strategic application of an array of complementary imaging and diffraction techniques is critical to determine accurate structural information of nanomaterials, especially when also seeking to elucidate structure-property relationships and their effects on performance in specific applications such as gas sensors. In this work, SnO2 nanowires and nanobrushes grown via chemical vapor deposition (CVD) displayed the same tetragonal SnO2 structure as revealed via powder X-ray diffraction (PXRD) bulk crystallinity data. Additional characterization using a range of electron microscopy imaging and diffraction techniques, however, revealed important structure and morphology distinctions between the nanomaterials. Tailoring scanning transmission electron microscopy (STEM) modes and combining these data with transmission electron backscatter diffraction (t-EBSD) techniques afforded a more detailed view of the SnO2 nanostructures. Indeed, upon deeper analysis of individual wires and brushes, we discovered that despite a similar bulk structure, wires and brushes grew with different crystal faces and lattice spacings. Had we not utilized multiple STEM diffraction modes in conjunction with t-EBSD, differences in orientation related to bristle density would have been overlooked. Thus, it is only through methodical combination of several analysis techniques that precise structural information can be reliably obtained. To begin considering what additional features can affect gas sensing capabilities, we needed to understand the driving force behind SnO2 sensors. SnO2 operates widely as a gas sensor for a variety of molecules via a mechanism that relies on interactions with adsorbed oxygen. To enhance these interactions by increasing surface oxygen vacancies, commercial SnO2 nanoparticles and CVD-grown SnO2 nanowires were plasma modified by Ar/O2 and H2O(v) plasmas. Scanning electron microscopy (SEM) revealed changes in nanomaterial morphology between pre- and post-plasma treatment using H2O plasma treatments but not when using Ar/O2 plasmas. PXRD patterns of the bulk SnO2 showed the Sn4+ is reduced by H2O and not Ar/O2 plasma treatments. X-ray photoelectron spectroscopy (XPS) indicated Ar/O2 plasma treatment increases oxygen adsorption with increasing plasma power and treatment time, without changing Sn oxidation. With the lowest plasma powers and treatment times, however, H2O plasma treatment results in nearly complete bulk Sn reduction. Although both plasma systems increased oxygen adsorption over the untreated (UT) materials, there were clear differences in the tin and oxygen species as well as morphological variations upon plasma treatment. Given that H2O plasma modification of SnO2 nanomaterials resulted in reduction of Sn+4 to Sn0, this phenomenon was further explored. To develop a deeper understanding of the mechanism for this behavior, gas-phase species were detected via optical emission spectroscopy (OES) during H2O plasma processing (nominally an oxidizing environment), both with and without SnO2 substrates in the reactor. Gas-phase species were also detected in the reducing environment of H2 plasmas, which provided a comparative system without oxygen. Sn* and OH* appear in the gas phase in both plasma systems when SnO2 nanowire or nanoparticle substrates are present, indicative of SnO2 etching. Furthermore, H2 and H2O plasmas reduced the Sn in both nanomaterial morphologies. Differences in H* and OH* emission intensities as a function of plasma parameters show that plasma species interact differently with the two SnO2 morphologies. The H2O plasma gas-phase studies found that under most plasma parameters the ratio of reducing to oxidizing gas-phase species was ≥1. The final consideration in our holistic approach relied on sensor performance studies of SnO2 nanomaterials. Resistance was recorded as a function temperature for UT, Ar/O2 and H2O plasma treated nanoparticles and nanowires exposed to air, carbon monoxide (CO), or benzene (C6H6). Resistance data were then used to calculate sensor response (Rair/Rgas) and sensitivity (Rair/Rgas > 1 or Rgas/Rair > 1). Specifically, Ar/O2 and H2O plasma modification increase CO and C6H6 sensitivity under certain conditions, but H2O plasma was more successful at increasing sensitivity over a wider range of plasma parameters. In particular, certain H2O plasma conditions resulted in increased sensitivity over the UT nanomaterials at 25 and 50 °C. Overall, H2O plasma appears to be more effective at increasing sensitivity than Ar/O2 plasma. Furthermore, although certain treatments and temperatures for nanoparticles had greater CO or C6H6 sensitivity than nanowires, nanowire sensitivity was less temperature dependent than nanoparticle sensitivity. Prior materials characterization data were combined with resistance data to elucidate specific structure-property-performance relationships for the different UT and plasma treated materials.
Open Access
Highly relativistic laser interactions with ordered nanostructures
(Colorado State University. Libraries, 2019) Hollinger, Reed, author; Rocca, Jorge J., advisor; Prieto, Amy L., committee member; Menoni, Carmen, committee member; Marconi, Mario, committee member
Heating high density matter to extreme temperatures has been one of the primary motivations behind the construction of high power laser facilities around the world. The creation of simultaneously hot (multi-keV) and dense (on the order of a solid) plasma with small scale and mid-scale lasers is a difficult problem due to the barrier that the critical electron density imposes to optical lasers, typically limiting the heating to a very thin plasma into which the laser is inefficiently coupled. Experiments conducted at Colorado State University with joule level laser pulses have demonstrated that using high contrast, relativistic laser pulses it is possible to efficiently heat near solid density nanowire arrays volumetrically to multi-keV temperatures. This dissertation extends these results to the highly relativistic regime, demonstrating extremely high ionization states for volumes >5μm in depth. These relatively large volume plasmas have longer hydrodynamic cooling times while their radiative cooling time is greatly decreased due to the near solid electron densities. This results in very efficient conversion of optical laser light into x-rays since the plasma is able to radiate away more of its' energy as x-rays before cooling due to hydrodynamic expansion. With this technique, an x-ray conversion efficiency of nearly 20% was measured for photon energies greater than 1keV. After a significant upgrade to the laser, these interactions were explored at highly relativistic intensities up to 4x1021 Wcm−2, nearly 1000 times higher than initial experiments. Measurements of the energy deposition dynamics, including the time limit for energy coupling and the volume of the nanowire plasma were carried out in comparison to solid targets. The results show that at these intensities, it is possible to generate unprecedented degrees of ionization never before obtained with ultrashort pulse lasers, such as H-like Ni (27 times ionized) and Ne-like Au (69 times ionized).
Open Access
I. Cognitive and instructional factors relating to students' development of personal models of chemical systems in the general chemistry laboratory. II. Solvation in supercritical carbon dioxide/ethanol mixtures studied by molecular dynamics simulation
(Colorado State University. Libraries, 2014) Anthony, Seth, author; Rickey, Dawn, advisor; Ladanyi, Branka M., advisor; Szamel, Grzegorz, committee member; Prieto, Amy L., committee member; DeLosh, Edward L., committee member
Part I. Students' participation in inquiry-based chemistry laboratory curricula, and, in particular, engagement with key thinking processes in conjunction with these experiences, is linked with success at the difficult task of "transfer" - applying their knowledge in new contexts to solve unfamiliar types of problems. We investigate factors related to classroom experiences, student metacognition, and instructor feedback that may affect students' engagement in key aspects of the Model-Observe-Reflect-Explain (MORE) laboratory curriculum - production of written molecular-level models of chemical systems, describing changes to those models, and supporting those changes with reference to experimental evidence - and related behaviors. Participation in introductory activities that emphasize reviewing and critiquing of sample models and peers' models are associated with improvement in several of these key aspects. When students' self-assessments of the quality of aspects of their models are solicited, students are generally overconfident in the quality of their models, but these self-ratings are also sensitive to the strictness of grades assigned by their instructor. Furthermore, students who produce higher-quality models are also more accurate in their self-assessments, suggesting the importance of self-evaluation as part of the model-writing process. While the written feedback delivered by instructors did not have significant impacts on student model quality or self-assessments, students' resubmissions of models were significantly improved when students received "reflective" feedback prompting them to self-evaluate the quality of their models. Analysis of several case studies indicates that the content and extent of molecular-level ideas expressed in students' models are linked with the depth of discussion and content of discussion that occurred during the laboratory period, with ideas developed or personally committed to by students during the laboratory period being likely to appear in students' post-laboratory refined models. These discussions during the laboratory period are primarily prompted by factors external to the students or their laboratory groups such as questions posed by the instructor or laboratory materials. Part II. Solvation of polar molecules within non-polar supercritical carbon dioxide is often facilitated by the introduction of polar cosolvents as entrainers, which are believed to preferentially surround solute molecules. Molecular dynamics simulations of supercritical carbon dioxide/ethanol mixtures reveal that ethanol molecules form hydrogen-bonded aggregates of varying sizes and structures, with cyclic tetramers and pentamers being unusually prevalent. The dynamics of ethanol molecules within these mixtures at a range of thermodynamic conditions can largely be explained by differences in size and structure in these aggregates. Simulations that include solute molecules reveal enhancement of the polar cosolvent around hydrogen-bonding sites on the solute molecules, corroborating and helping to explain previously reported experimental trends in solute mobility.
Embargo
Investigations of low-temperature reaction pathways in solid-state reactions
(Colorado State University. Libraries, 2024) Tran, Gia Thinh, author; Neilson, James R., advisor; Prieto, Amy L., committee member; Sambur, Justin B., committee member; Chen, Hua, committee member
Advances in our technology are limited by our knowledge of functional materials, and access to new, possibly better, functional materials is limited by our synthesis methods. This dissertation discusses different synthesis methods for a variety of solid state materials. At the core of this thesis are metathesis reactions i.e. double displacement reactions. Metathesis reactions allow for control over product selectivity and reaction kinetics with choice of the spectating ions. We demonstrate these characteristics with different spectating ions in metathesis and cometathesis (e.g., combining 2 halides) reactions. LaMnO3 was chosen to probe the product selectivity of anion cometathesis towards specific off-stoichiometries of LaMnO3. The metathesis reaction for BiFeO3 illustrates that prediction of thermodynamic selectivity is important, but reaction kinetics remain important as well. Kinetic studies of metathesis reactions that form YMnO3 demonstrate the importance of crystalline intermediates to modulate the reaction rates. The complexity of solid-state kinetics their kinetic regimes within a reaction can be identified through synchrotron X-ray diffraction. We attempted to synthesize LiMoO2 as precursors for the proposed phase LaMoO3. We demonstrate our considerations on the synthesis challenges and offer gained insights into alternative Mo-based systems (nitrides). Aside from metathesis reactions, we employ learned concepts to flux reactions to influence the chemical potential of N2. Synthesis of Li-Fe-O-N and Li-Mn-O-N phases was attempted under the hypothesis that alkali halide salt mixtures solubilize nitrogen and pin nitrogen's chemical potential to prevent N2 formation. Cs2SbCl6 was chosen as a single crystal target to gain clearer insights into the electronic structure. Single crystals were synthesized via hydrothermal synthesis, but preliminary conductivity measurements suggest that Cs2SbCl6 has a photoconductance below our limit detection.
Open Access
Investigations of the identity of the true catalyst in three systems, including the development of catalyst poisoning methodology
(Colorado State University. Libraries, 2012) Bayram, Ercan, author; Finke, Richard G., advisor; Chen, Eugene Y.-X., committee member; Prieto, Amy L., committee member; Bernstein, Elliot R., committee member; Dandy, David S., committee member
Following brief reviews of the pertinent "who is the catalyst?" and "M4 (M= transition-metal) cluster catalysis" literature, the research presented herein is focused on the investigations of the true catalyst for three different catalytic systems. The studies include: (i) the investigation of the true catalyst for neat benzene hydrogenation beginning with commercially available [Ir(cod)Cl]2 (cod= 1,5-cyclooctadiene) at 22 °C and 40 psig initial H2 pressure; (ii) the investigation of the true catalyst for benzene hydrogenation beginning with commercially available [RhCp*Cl2]2 (Cp*= pentamethylcyclopentadienyl) at 100 °C and 50 atm (740 psig) initial H2 pressure; and (iii) the investigation of the true catalyst for cyclohexene hydrogenation beginning with the well-characterized, site isolated [Ir(C2H4)2]/zeolite-Y complex at 22 °C and 40 psig initial H2 pressure, studies done collaboratively with Professor Bruce C. Gates and his group at the University of California-Davis. All three investigations aimed at identifying the true catalyst were studied via an arsenal of complimentary techniques including kinetics, in operando and post-catalysis X-ray absorption fine structure (XAFS) spectroscopy, kinetic quantitative poisoning experiments, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and high-angle annular dark-field scanning electron microscopy (HAADF-STEM). The data obtained for each system presented herein provide compelling evidence that the proposed species in each chapter are the true catalyst of the given system, specifically (and respectively) for (i), (ii), and (iii) above Ir(0)n nanoparticles and aggregates, Rh4 sub-nanometer clusters, and atomically dispersed, mononuclear Ir1/zeolite Y catalysts. The results emphasize the need to use complimentary, multiple methods in order to correctly identify the true catalyst in such catalytic systems. The final study elucidates kinetic quantitative catalyst poisoning via two model catalysts: Rh(0)n nanoparticles and Rh4 clusters, providing detailed analyses of linear as well as non-linear kinetic quantitative poisoning plots. The resulting quantitative kinetic catalyst poisoning studies of Rh(0)n nanoparticles and Rh4 clusters led to estimates of the equivalents of poison bound, quantitative catalyst poisoning association constants, and the numbers of active sites for each catalyst.
Open Access
Kinetic and mechanistic studies of supported-nanoparticle heterogeneous catalyst formation in contact with solution
(Colorado State University. Libraries, 2011) Mondloch, Joseph E., author; Finke, Richard G., advisor; Bailey, Travis S., committee member; Ferreira, Eric M., committee member; Prieto, Amy L., committee member; Shores, Matthew P., committee member
This dissertation begins with a comprehensive and critical review of the literature addressing the kinetics and mechanism(s) of supported-nanoparticle heterogeneous catalyst formation. The review chapter that follows makes apparent that routine kinetic monitoring methods, as well as well-defined supported-nanoparticle formation systems, are needed in order to gain fundamental insights into the mechanisms of supported-nanoparticle heterogeneous catalyst formation--a somewhat surprising finding given the long history as well as commercial importance of heterogeneous catalysis. Hence, the research presented within this dissertation is focused on (i) developing a kinetic monitoring method (i.e., in what follows, the cyclohexene reporter reaction method) capable of measuring supported-nanoparticle formation in contact with solution, and (ii) developing a well-defined supported-nanoparticle formation system, also in contact with solution, that is amenable to rigorous mechanistic studies. Development of the cyclohexene reporter reaction has allowed for the rapid and quantitative monitoring of the kinetics of Pt(0)n/Al2O3 and Pt(0)n/TiO2 supported-nanoparticle heterogeneous catalyst formation in contact with solution from H2PtCl6/Al2O3 and H2PtCl6/TiO2 respectively. Importantly, those kinetic studies revealed conditions where the most desirable, chemical-reaction-based, supported-nanoparticle formation conditions are present rather than diffusional-limited kinetic regimes. The largest drawback when utilizing the H2PtCl6 as a supported-precatalyst is its speciation--that is, other solvated Pt-based species form when in contact with solution. Such non-uniform speciation leads to a large variation in the supported-nanoparticle formation kinetics, observations that were obtained through the use of the cyclohexene reporter reaction kinetic monitoring method. Due to the large variability in the formation kinetics associated with the H2PtCl6 precatalyst speciation, synthesized next as a part of this dissertation work was the well-defined, fully characterized, speciation-controlled supported-organometallic precatalyst, Ir(1,5-COD)Cl/γ;-Al2O3. When in contact with acetone, cyclohexene and H2 this supported-precatalyst was found to evolve into a highly active and long-lived Ir(0)~900/γ;-Al2O3 supported-nanoparticle catalyst. The kinetics of Ir(0)~900/γ-Al2O3 formation were successfully followed by the cyclohexene reporter reaction method and found to be well-fit by a two-step mechanism consisting of nucleation (A → B, rate constant k1) followed by autocatalytic surface growth (A + B → 2B, rate constant k2) previously elucidated by Finke and Watzky. More specifically, nucleation was found to occur in solution from Ir(1,5-COD)Cl(solvent), while nanoparticle growth occurs on the γ-Al2O3 support, but in a reaction that involves the Ir(1,5-COD)Cl(solvent) species in solution. Most importantly, the fits to the two-step mechanism suggest that the nine synthetic and mechanistic insights, of nanoparticle formation in solution, should now be applicable to the formation of supported-nanoparticle heterogeneous catalysts in contact with solution. That is, it seems reasonable to expect that these studies will allow a more direct avenue for transferring both the mechanistic and synthetic insights that have resulted from the modern revolution in nanoparticle science to the synthesis of size, shape and compositionally controlled supported-nanoparticle catalysts under the nontraditional, mild and flexible conditions where supported organometallics and other precursors are in contact with solution.
Open Access
New approaches to fluoromodifications of electron acceptor molecules for organic photovoltaics
(Colorado State University. Libraries, 2021) Brook, Colin P., author; Strauss, Steven H., advisor; Prieto, Amy L., committee member; Kennan, Alan J., committee member; Gelfand, Martin P., committee member
The overall goal of this work is to advance fundamental science and applications of organic electron acceptors based on fluorinated fullerenes and polycyclic aromatic hydrocarbons. The synthetic part of the dissertation focused on the development of new synthetic approaches towards the fluoromodification of large conjugated organic molecules and on the improvements of existing methods for the preparation of high-performing fullerene-based n-type semiconductors. Chapter 1 describes development and application of a new configuration of the gradient-temperature gas-solid reactor for the efficient and high-yielding trifluoromethylation of fullerenes. Significant improvements were achieved in the yields and selectivity of bis-trifluoromethylated C60 and C70 fullerenes: 2-fold and 10-fold yield increase compared to prior state of the art, respectively. An approach to maintain a constant reactive gas pressure in the reactor has been introduced by creating a liquid-gas reservoir of CF3I by submerging the reservoir in one of several low-temperature slush baths available that resulted in improvements in both yields and selectivity for trifluoromethylfullerenes, while also solving a problem of previously unproductive use of the gaseous reagent. Chapter 2 presents the author's work in partnership with the National Renewable Energy Lab (NREL) aimed at investigation of the prominent stabilizing effect of perfluoroalkylated fullerenes on the rate of photobleaching of common high-performance donor-polymers used in OPV devices, compared to the pure polymer films and blends with prototypical non-fluorinated fullerene, PC60BM. It is demonstrated that rationalizing complex photobleaching behaviour ultimately required consideration of the electron affinity of the fullerene as well as the relative miscibility of the polymer–fullerene blend. The ability of the bis-trifluoromethylfullerene and Fauxhawk fullerene to stabilize certain donor materials against photodegradation, to blend well with fluorinated (and even certain non-fluorinated) polymers, and to quench excited states efficiently was thoroughly studied and correlated with structure-property relationships amongst several polymer donor and fullerene acceptor combinations. Chapter 3 describes a new approach to the direct fluoromodification of polycyclic aromatic hydrocarbons based on replacing commonly used perfluoroalkyl groups (CnF2n+1, or RF) with perfluorobenzyl groups (C6F5CF2, or BnF). For the first time, solution-phase direct perfluorobenzylation of an electron-rich perylene (PERY) and electron-poor perylene diimide (PDI), has been achieved. Five new bay- and peri-substituted compounds of perylene, PERY-(BnF)n, where n = 1, 2 and 3; and three new bay-substituted compounds of perylene diimide, PDI-(BnF)n, where n = 1, 2; were synthesized and fully characterized, revealing that electron withdrawing BnF group is comparable to RF in increasing acceptor strength of new compounds. Chapter 4 deals with a new type of annulative pi-extension (APEX) reaction discovered in this work that occurs via reductive dehydrofluorination/aromatization reactions involving perfluorobenzylated PDI compounds, that afforded fluorinated benzoperylene and coronene-based derivatives with prodigious electron acceptor properties. Another type of annulation leading to the transition-metal free formation of new compounds with all-carbon seven-membered rings across the bay regions of PDIs, consequently forming as rare examples of a newly-recognized fundamental type of conformational isomers, named akamptisomers, is also reported here for the first time. Studies of the likely reaction pathways in both types of reactions and effects of varying reaction parameters on the preferred product formation are presented. Single crystal crystallographic studies of many of the new compounds prepared in this work provide rich and unique data for in-depth analysis of the solid-state packing motifs and influences of the type and position of fluorinated functional groups on the intermolecular interactions, and ultimately, charge transport in these new organic n-type semiconductor materials.
Open Access
Organocatalytic, Michael-Stetter reaction and rhodium(I)-catalyzed hydroheteroarylation of acrylates with benzoxazoles: reaction development and investigations into origins of enantioselectivity
(Colorado State University. Libraries, 2015) Filloux, Claire M., author; Rovis, Tomislav, advisor; McNaughton, Brian R., committee member; Prieto, Amy L., committee member; Crans, Debbie C., committee member; Hentges, Shane T., committee member
The chapters that follow describe two independent investigations. Both relay the development of experimental methods for the catalytic, asymmetric addition of carbon-hydrogen bonds to alkenes. In the first chapter, nucleophilic amine and N-heterocyclic carbene cocatalysts cooperate in the organocatalytic, cascade synthesis of benzofuranone products in good yields and high enantioselectivities. Importantly, the cascade protocol is found to outperform a two-pot procedure in which reaction intermediates are isolated and purified before the second step. Mechanistic studies reveal that additives and geometry of an olefin intermediate crucially influence reaction enantioselectivity. In the second method, a bulky Rh(I)-bisphosphine complex catalyzes the asymmetric, intermolecular addition of benzoxazoles to methacrylate derivatives in fair to excellent yields and good to excellent enantioselectivities. Detailed deuterium labeling and epimerization studies provide considerable insight into the reaction mechanism: C-H activation is reversible; migratory insertion is likely enantiodetermining; and the bulky- bisphosphine ligand likely boosts reactivity and selectivity by discouraging deleterious ligation of benzoxazole starting materials to on- or off-cycle rhodium complexes and by impeding coordination-induced product epimerization.
Open Access
Part I - Access to UV photocured nanostructures via selective morphological trapping of block copolymer melts. Part II - Morphological phase behavior of poly(RTIL) containing block copolymer melts
(Colorado State University. Libraries, 2012) Scalfani, Vincent F., author; Bailey, Travis S., advisor; Finke, Richard G., committee member; Henry, Charles S., committee member; Kipper, Matt J., committee member; Prieto, Amy L., committee member
A thermally stable photocuring system was developed for high fidelity translation of block copolymer based melt-state morphologies into their equivalent solid analogs. Cationic photoacids were combined with partially epoxidized polyisoprene-b-poly(ethylene oxide) (PI-PEO) block copolymers, forming composite blends that allow for extended thermal processing prior to cure, in addition to precise trapping of selected morphologies, a consequence of the temperature independent UV curing mechanism. The parent PI-PEO block copolymer exhibited multiple melt-state morphologies including crystalline lamellae (Lc), hexagonally packed cylinders (C), bicontinuous gyroid (G), and an isotropic disordered state (Dis). Modification of the PI-PEO backbone with epoxy groups and addition of a UV cationic photoacid acted only to shift transition temperatures quantitatively, leaving the overall morphological behavior completely unmodified. UV irradiation exposure of the composite blends directly in the melt-phase at selected temperatures resulted in permanent trapping of both the cylinder and gyroid morphologies from a single block copolymer sample. The studied photocuring chemistry was extended to produce spherical nanostructured hydrogel networks. Fabricated hydrogel networks are built from a pre-structured lattice of body-centered cubic spheres (SBCC), produced via melt-state self-assembly of blended AB diblock and ABA triblock copolymers. Added ABA triblock serves to produce active tethered junction points between the AB diblock spherical micelles. The integrated thermally stable photocuring chemistry allows for in situ trapping of these spherical domains directly in the melt phase, independent from the required thermal processing necessary to achieve the tethered BCC lattice. Specifically, the hydrogel networks were fabricated from partially epoxidized blends of polybutadiene-b-poly(ethylene oxide) diblock (PB-PEO) and PB-PEO-PB triblock copolymers. UV cured samples of composite copolymer disks containing an added amount of UV activated cationic photoinitiator samples retained the SBCC structure with high fidelity, which serves to pre-structure the hydrogel network prior to swelling. Photocured disks preserved their original shape when swollen in water or organic media, were highly elastic and had excellent mechanical properties. Control experiments with uncured samples immediately dissolved or dispersed when swollen. Simple photopatterning of the cross-linked hydrogel system is also explored. The developed pre-structured hydrogel network was then adapted to incorporate light sensitive anthracene groups into the spherical forming AB diblock copolymer for in situ generation of tethering ABA triblock. Pressed disks of anthracene terminated poly(styrene)-b-poly(ethylene oxide) diblock (PS-PEO-An) were photocoupled with UV 365 nm filtered light directly in the melt-phase, post the necessary thermal self-assembly process. Photocoupled disks swelled in water, were highly elastic, had tunable mechanical properties (based on UV irradiation time), and showed complete preservation of initial shape. Swollen photocoupled disks were found to exhibit similar properties to pre-blended PS-PEO/PS-PEO-PS hydrogels with slight differences likely resulting from an asymmetric distribution of triblock in the photocoupled gels. The PS-PEO-An based hydrogels are proposed to be possible future candidates for the development of new asymmetric hydrogels because of their simple fabrication and excellent mechanical properties. In part II of this dissertation, a new poly(room temperature ionic liquid) (RTIL) BCP platform was developed based on the sequential, living ring-opening metathesis polymerization (ROMP) of a hydrophobic non-charged dodecyl ester norbornene monomer followed by a cationic imidazolium norbornene ionic liquid (RTIL) monomer. The synthesized BCPs were found to exhibit surfactant behavior in solution and form highly periodic nanoscale melt morphologies. Extensive control experiments with homopolymer blends do not show any surfactant behavior in solution nor microphase separation in the neat melt phase. After an initial study optimizing the synthesis and verifying the block architecture, a series of 16 poly(RTIL)-based BCP samples were synthesized with varying compositions of 0.42-0.96 vol% poly(norbornene dodecyl ester). A phase diagram was developed through a combination of small-angle X-ray scattering and dynamic rheology. Morphologies identified and assigned within the phase space studied include lamellae (Lam), hexagonally packed cylinders (Hex), a coexistence of Hex and Lam domains in place of the gyroid region, spheres on a body-centered cubic lattice (SBCC), and a "liquid like" packing of spheres (LLP). Annealing samples containing a coexistence of Lam and Hex domains suggest extremely slow ordering kinetics disposing one of the morphologies. The studied poly(RTIL)-based BCPs containing highly charges species are very strongly segregated (large Chi parameter), resulting in limited if any access to the disordered and gyroid regime. Finally, in Appendix I a supramolecular polymer system comprised of benzene-1,3,5-tricarboxamide (BTA) and 2-ureido-4[1H]-pyrimidinone (UPy) functional hydrogenated polybutadiene was developed that forms two unique and independent nanorods motif assemblies. When the two supramolecular motifs are end-capped to different homopolymers, the motifs self-assemble independent of each other into separate nanorod stacked structures. However, when a telechelic polymer is introduced into the system containing both supramolecular motifs (one on each end), a network is formed between the nanorod assemblies. Without the telechelic polymer, the supramolecular material is a viscous liquid with little mechanical integrity. In contrast, addition of the telechelic polymer acts as a cross-linker and results in a networked material that is highly elastic with excellent mechanical properties.
Open Access
Quantum dot clusters as single-molecules: deciphering collective fluorescence and energy transfer signatures
(Colorado State University. Libraries, 2016) Ryan, Duncan P., author; Gelfand, Martin P., advisor; Van Orden, Alan, advisor; Roberts, Jacob L., committee member; Prieto, Amy L., committee member
Applications of quantum dot nanocrystals span from the individual single-molecule use to large, densely-packed bulk solids. Already, the fluorescence behavior of individual particles is complex and nuanced, particularly involving the blinking phenomenon. When particles are combined into higher-order structures where interaction may occur, a complete description becomes intractable. However, clusters---between two and ten particles---can be effective model systems to explore the local behaviors that occur in larger networks. A benefit of small clusters is the viability of using single-molecule spectroscopic techniques, which are often more informative than bulk measurements. In this work we combine fluorescence microscopy with structure-probing electron microscopy to elucidate the fluorescence dynamics clusters of semiconductor nanocrystals. The spectral characteristics of clusters are explored in the context of an energy transfer model showing low-intensity emission is blue-shifted, corresponding to the weaker emission from donor particles with a larger band gap. Because energy transfer depends intimately on the specific topographical structure of the cluster, the inter-particle spacing, and relative alignment, characterization of specific cluster behavior is better informed by correlated measurements. Next, we present the mapping results from super-resolution microscopy where the spatial distributions of fluorescence in the sub-10 nanometer realm is clearly correlated with scanning electron microscopy imaging of the same clusters. Stochastic blinking events enable such observations. The enhanced blinking associated with energy transfer has practical implications for donor and acceptor roles in clusters. Finally, the dynamic evolution of the emission dipole orientation for single nanocrystals and nanocrystal clusters is measured. The orientation signature suggests coupling strengths and constitutes a first-step towards determining corrections to Förster resonant energy transfer theory involving nanocrystals.
Open Access
Steady-state and time-resolved spectroscopy to probe the effects of confinement on Cy3 and the dynamics of AOT/iso-octane reverse micelles
(Colorado State University. Libraries, 2010) McPhee, Jeffrey, author; Van Orden, Alan K., advisor; Levinger, Nancy E., committee member; Barisas, B. George, committee member; Prieto, Amy L., committee member; Luger, Karolin, committee member
This dissertation describes the use of steady-state and time-resolved spectroscopy to probe the effects of localized confinement on the water soluble dye Cyanine-3 (Cy3) and the dynamics of intermicellar interactions using fluorescence correlation spectroscopy (FCS). The first set of experiments presents a wide range of steady-state and time-resolved spectroscopy data which indicate that the Cy3 molecules form H-aggregates at concentrations so dilute (nM) that this behavior is not observed in bulk aqueous solution. This unique behavior allowed for a series of FCS and dynamic light scattering measurements to be performed on the same system. These results indicate the formation of a transient reverse micelle dimer, whose lifetime has been identified to be on the order of 15 μs. Furthermore, preliminary experiments are presented on the same reverse micelle system containing the Rhodamine 6G and the results are consistent with those obtained for Cy3 in the reverse micelles. Lastly, fluorescence resonance energy transfer within the reverse micelles was investigated using Cy3 and Cy5. The preliminary results suggest that FRET may be occurring within this extremely confined environment. The work as a whole provides insight into the nature of confinement as well as the dynamics occurring within the world of reverse micelles.
Open Access
Synthesis and characterization of low-dimensional paramagnetic acetylide complexes
(Colorado State University. Libraries, 2011) Hoffert, Wesley A., author; Shores, Matthew P., advisor; Anderson, Oren P., committee member; Prieto, Amy L., committee member; Bailey, Travis, committee member; Patton, Carl, committee member
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Open Access
Synthesis and evaluation of fluorous polycyclic aromatic hydrocarbon derivatives for organic electronics
(Colorado State University. Libraries, 2019) Rippy, Kerry C., author; Strauss, Steven H., advisor; Prieto, Amy L., committee member; Sites, James R., committee member; Szamel, Grzegorz, committee member
Advances in the performance of electron acceptor materials for organic electronics critically depend on the efficiency of synthetic routes for new materials and fundamental understanding of the correlation between molecular structure and electronic and solid-state properties. The research presented here endeavors to address both of these needs, by developing original methods for synthesis of new organic electron acceptor materials, and by characterizing relevant properties of the resulting materials. In total, synthesis and analysis of more than 60 new molecules is presented in this work. These molecules are derivatives of polycyclic aromatic hydrocarbons (PAHs) and hetero-PAHs functionalized with fluorous moieties, synthesized via development of substrate-specific efficient, single-step direct-substitution methods. Investigation of solid-state and electronic properties focused upon effects of structural motifs including (i) the type, number, and position of electron withdrawing fluorous substituents (ii) the size and shape of aromatic π systems, and (iii) presence of hetero atoms within the aromatic core. The first chapter of this work details the development and optimization of a gas-phase radical reaction between the perfluoroalkyl diiodide 1,4-C4F8I2 and the PAH triphenylene (TRPH). The perfluoroalkyl diiodide, with two C–I bonds, one at either end, has the unique ability to bind to vicinal C atoms, forming a 6-membered ring. A family of TRPH derivatives functionalized with such rings was synthesized, and the reaction was optimized. Additionally, reductive partial defluorination of the perfluoroalkyl ring was achieved, leading to aromatization of the fluorous substituent (RD/A). The extension of the π-system, as well as the effect of fluorine atoms bound directly to the aromatic system, was examined with respect to solid-state packing and electronic levels. In Chapter 2, results of screening of 13 new PAH and n-hetero PAH substrates with respect to their reactivity towards 1,4-C4F8I2 are described. Pure compounds derived from these reactions are presented, adding several new families to the library of fluorous PAH derivatives. Unique reactivities and interesting potential applications are discussed for several of these families. Solid-state packing and electronic properties are analyzed for selected derivatives. A particularly promising family of fluorous acceptors is presented and analyzed in greater depth in Chapter 3. It is based on the substrate phenazine (PHNZ). This family of molecules is notable because several derivatives exhibit enhanced acceptor strength and linearly-fused molecular structures resembling the acene class of PAHs, a high performing class of materials widely used in organic electronics. Results suggest that the molecules investigated in this chapter would be suitable for applications as air-stable n-type semiconductors in electronic devices. Finally, in Chapter 4, the characterization of a family of trifluromethylated acridine (ACRD) derivates is described. This investigation yields new insights into the reactivity of ACRD. Furthermore, detailed structural, spectroscopic and electronic property analysis combined with computational data revealed that not only the number of substituents, but also the position of substituents affects electronic energy levels. This finding not only expands basic understanding of how molecular structure affects electronic properties of PAHs, but also provides a valuable new tool for molecular design of acceptors with desirable properties.
Open Access
Synthetic strategies toward the total synthesis of tetrapetalone A
(Colorado State University. Libraries, 2012) Howell, Jennifer Marie, author; Wood, John L., advisor; Kennan, Alan J., committee member; Ferreira, Eric M., committee member; Prieto, Amy L., committee member; Brennan, Patrick J., committee member
In 2003 Hirota and coworkers reported the isolation of tetrapetalone A (1) from the culture filtrate of Streptomyces sp. USF 4727, a Streptomyces strain isolated from a soil sample taken from Yada, Shizuoka City, Japan. The molecular structure of 1 was initially reported and then revised in a series of two papers which both appeared in 2003. In addition to the interesting molecular architecture, 1 demonstrated inhibition of soybean lipoxygenase (SBL) (IC50 of 190 μM) comparable to well-known human lipoxygenase and cyclooxygenase inhibitors. While no total synthesis has been reported to date, the groups of Porco, Hong and Sarpong have disclosed synthetic approaches toward the tetrapetalone core. Efforts in the Wood group to synthesize 1 are based on highly convergent synthetic strategies, the first of which was directed at constructing an advanced indanone coupling partner via a Stetter reaction. To this end, a route employing a diastereoselective Claisen rearrangement afforded a highly substituted Stetter reaction precursor but we were unable to realize the latter chemistry. We developed a synthetic route employing a Dieckmann condensation to furnish a highly functionalized tetramic acid. Coupling the tetramic acid with ortho substituted aryl halides under aryl amidation conditions proved futile. In an effort to promote an intramolecular aryl amidation we pursued an alternative coupling strategy, which relied on an extremely challenging ring closing metathesis. The desired ring closing metathesis product was not realized. Relay ring closing metathesis investigations provide confidence that the desired olefins will engage in metathesis chemistry. Current synthetic efforts are focused on a diastereoselective intramolecular Tsuji-Trost allylation to furnish a highly functionalized indanone, which has proven to be a competent coupling partner with allylamine under Pd(0)-catalyzed aryl amination conditions. Elaboration of this advanced indanone intermediate is expected to eventually provide a total synthesis of 1.
Open Access
The application of carbon composite electrodes for the analysis of environmental and biological pathogens
(Colorado State University. Libraries, 2023) McMahon, Catherine J., author; Henry, Charles S., advisor; Prieto, Amy L., committee member; Farmer, Delphine, committee member; Geiss, Brian, committee member
Fast, reliable, and accurate detection of heavy metals is crucial in preventing adverse health effects. Heavy metal contamination comes from various human anthropological endeavors, and can leach into water, food, and consumer products such as cosmetics. Electrochemical detection of heavy metals has become a popular alternative to traditional analysis, using highly sensitive spectroscopic techniques. Carbon composite electrodes have been used for electrochemical sensors due to their chemical inertness, large potential window, and resistance to fouling. However, they can often suffer from poor electrocatalytic behavior, resulting in the need for extensive surface modifications. Moreover, traditional carbon composite electrodes have been limited in their pattern-ability and difficultly in fabrication. Thermoplastic electrodes were developed in 2017 to address these needs and are further discussed and characterized in this dissertation for applications towards heavy metal analysis. Overall, this dissertation seeks to use carbon composite electrodes to improve detection efforts for both environmental pollutants (i.e heavy metals) and biological analytes. Chapter 2 introduces the use of stencil-printed carbon electrodes (SPCEs) for the analysis of heavy metals in cosmetic samples from Nepal, Ghana, and Uganda. The approach utilizes a previously developed method and adapts it, expanding its utility. The goal of the work is to develop a method that is capable of screening for heavy metal pollutants outside of traditional laboratory settings. An alternative sample extraction approach is detailed as well as the development of a laboratory standard for heavy metal analysis in cosmetics. In addition to the electrochemical analysis, extensive analysis using inductively coupled plasma optical emission spectroscopy is conducted on the cosmetics samples, to better understand the Pb contamination and matrix complexity of the samples. Chapter 3 focuses on the use of TPEs for the detection of heavy metals. Six formulations of TPEs, with different graphites and polymer binders, are characterized to better understand how the unique surface properties impact the analysis of heavy metals. The detection of Pb is used as a proof-of-concept model. The results illustrate that both the polymer and graphite can have intensive impact on the application of TPEs. Of the various formulations tested, polystyrene and polymethyl methacrylate show promise in detecting heavy metals within relevant ranges. Chapter 4 pivots from heavy metal analysis and investigates the use of SPCEs for the detection of SARS-CoV-2 nucleocapsid protein. With the onset of the COVID-19 pandemic in 2020, my research focus pivoted to address the need to develop reliable, accurate, and fast point-of-care diagnostics for SARS-CoV-2 to help manage the spread of the virus. SPCEs are modified based on an ELISA (enzyme-linked immunosorbent assay) for the electrochemical detection of the N-protein. The assay developed sets the framework for a potential POC diagnostic, while meeting the industry need for fewer false negatives and lower limits of detection. In summary, this dissertation seeks to implement and expand the utility of different kinds of carbon composite electrodes for the detection of heavy metals and biological analytes. The work described in this dissertation sets the framework for improving upon carbon-based electrochemical sensors for environmental and biological sensors. This work provides materials, methods, and fundamental characterization of carbon composite electrodes, and how different surface treatments and modifications can expand their utility in electrochemically sensing applications.