Browsing by Author "Shores, Matthew P., committee member"

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Open Access
Application of metallacycles for the synthesis of small molecules
(Colorado State University. Libraries, 2011) Williams, Catherine Marie, author; Rovis, Tomislav, advisor; Wood, John L., committee member; Finke, Richard G., committee member; Shores, Matthew P., committee member; McNeil, Michael R., committee member
A method for the nickel-catalyzed hydrocarboxylation of styrene derivatives has been developed that affords exclusively the branched carboxylic acids in moderate to excellent yields. The reaction scope is tolerant of a variety of electron-deficient ortho-, meta-, and para-styrene analogues containing ester, ketone, nitrile, and halide functionalities. The reaction is remarkably efficient, proceeding well with as little as 1 mol% Ni(acac)2 and 2 mol% Cs2CO3. A system for carbon dioxide sequestration and release in organic polymers has been investigated. Although evidence supporting successful carbon dioxide fixation has been found, the envisioned system is not a practical means of sequestration and release. A rapid approach for the synthesis of Abyssomicin C has been developed utilizing the desymmetrization of meso-dimethylglutaric anhydride. Closely modeled after Sorensen's synthesis, our route bypasses the more inefficient beginning steps to intercept the completed synthesis at the Diels-Alder precursor.
Open Access
Characterization and application of a novel composite nanomaterial comprised of porous protein crystals and synthetic DNA
(Colorado State University. Libraries, 2022) Stuart, Julius D., author; Snow, Christopher D., advisor; Kennan, Alan J., committee member; Shores, Matthew P., committee member; De Long, Susan K., committee member
Composite nanomaterials are systems comprised of multiple components boasting enhanced properties over those exhibited by the individual constituents when isolated. Such systems are highly tunable, allowing one to vary component types (e.g., polymer, metal, ceramic) for influencing performance in various contexts. Moreover, composite nanomaterials can be further modified using biofunctionalization for use in biological settings. Composite nanomaterials have been tested in applications including, but not limited to, textile, defense, food, energy and biomedical engineering. A sub-domain within composite nanomaterials involves porous protein crystals soaking, or, separately, encapsulating various guest molecules. Porous protein crystals are ordered, insoluble assemblies forming a network of nanopores capable of allowing inward diffusion of guest molecules. Moreover, recombinant protein variants can be engineered for probing guest molecule binding to host crystal nanopores further highlighting the tunability of this novel composite nanomaterial. The goal of this work is to evaluate a novel composite nanomaterial comprised of host porous protein crystals and guest double stranded DNA. We show that guest DNA loads into host crystals predominantly along the axial nanopores. Equilibrium adsorption isotherm results suggest guest DNA unbinds from host crystals relatively slowly. Computational modeling and Fluorescence Recovery After Photobleaching (FRAP) studies suggest intra-nanopore guest diffusion is attenuated relative to bulk diffusion. We also show that porous protein crystals loading with synthetic DNA barcodes can be used for tracking mosquitoes. Fluorescently labeled crystals can be ingested by mosquito larvae and adults, followed by detection using fluorescence confocal microscopy. Crystal-bound DNA can be liberated from host crystals by incubation with solution containing deoxynucleotide triphosphates (dNTPs). Previously ingested barcode-loaded crystals can be recovered using standard molecular biological techniques. Lastly, we show a DNA barcode sequence construction strategy that is modular, economical and scalable. Computational sequence design and scoring allowing identification of top candidates for experimental validation. Analysis of next-generation sequencing datasets informs barcode construction specificity while simultaneously reinforcing the multiplexing capabilities boasted by modular DNA barcodes.
Open Access
Fluoroalkyl and fluoroaryl fullerenes, polycyclic aromatic hydrocarbons, and copper(I) complexes: synthesis, structure, electrochemical, photophysical, and device properties
(Colorado State University. Libraries, 2020) Reeves, Brian J., author; Strauss, Steven H., advisor; Shores, Matthew P., committee member; Rappé, Anthony K., committee member; McNally, Andrew, committee member; Ridley, John, committee member
In many fields of research, ranging from materials chemistry to medicinal chemistry, understanding the structural, electrochemical, and photophysical properties of materials is essential to establishing trends and predicting usefulness and future performance. This work has focused on the impact of strongly electron withdrawing perfluoroaryl and perfluoroalkyl substituents on the properties of fullerenes, polycyclic aromatic hydrocarbons (PAHs), hetero-PAHs, and copper(I) complexes with the goal of establishing and understanding the fundamental reasons for any observed trends. In Chapter 1, the first successful example of vacuum-deposited organic photovoltaic cells (OPVs) based on a fullerene derivative and a small-molecule donor is reported. A series of thermally robust fluorous fullerene acceptors with experimental gas-phase electron affinities ranging from 2.8 to 3.3 eV are paired with new dicyanovinyl thiophene-based molecular donors to enable direct comparison of their performance in planar and bulk heterojunction architectures in cells fabricated by vacuum deposition. Unprecedented insights into the role of the acceptor intrinsic molecular and electronic structures are obtained, which are not obscured by solvent and additive effects as in the typical solution-processed fullerene-based OPVs. Additionally, the fullerene derivative, C60CF2, was utilized in vacuum-deposited organic field effect transistors (OFETs), and it was shown to have superior device lifetime compared to C60 based OFETs. In Chapter 2, a new synthesis of 9,10-bis(perfluorobenzyl)anthracene, a promising blue organic light emitting diode (OLED) material is reported. The yield was improved from 7% to 17%, while the separations conditions were improved to only require one stage of HPLC. In Chapters 3 and 4, the trifluoromethylation of two hetero-PAHs, phenanthroline and phenanthridine, is discussed. The structure, solid-state packing, and electronic properties of the products are examined. Previously unknown structure-property relationships were established between the electronic properties and the position of CF3 groups. Additionally, the synthesis and excited-state dynamics for a series of homoleptic copper(I) phenanthroline complexes with 2, 3, and 4 trifluoromethyl groups are reported. Surprisingly, the observed time-resolved dynamics and emission trend is that addition of trifluoromethyl groups past two decreases the excited state lifetime and increases excited-state distortion.
Open Access
From colloidal solution to single particles: investigating energy flow from semiconductor nanocrystals to molecules
(Colorado State University. Libraries, 2021) Nilsson, Zach N., author; Sambur, Justin B., advisor; Barisas, B. George, committee member; Shores, Matthew P., committee member; Wilson, Jesse W., committee member
The interaction of nanomaterials and molecules is at the heart of many modern processes (catalysis, chemical synthesis, lighting, etc.). The presence of crystallographic defects in the nanomaterials can strongly influence this interaction or open up pathways for unintended interactions. The location of the defect sites plays a large role in determining how a defect sites will interact with the environment around it. Determining the location of defect sites in nanomaterials is a challenge. Transmission electron microscopy (TEM) is the obvious choice to observe atomic scale defects however, in situ TEM measurements are difficult and expensive. Forster resonance energy transfer (FRET) spectroscopy has the power to reveal nanoscale distances from optical data. FRET has been applied to nanomaterial defects in the past but never to reveal the location of defect sites. The following work describes the application of FRET spectroscopy to an ensemble of zinc oxide nanoparticles. It was found that for large nanoparticles (6 nm diameter) FRET could distinguish between surface and interior defect sites. However, the ensemble level approach has limitations. To overcome these, the system was observed on the single particle level using optical microscopy. Single particle studies revealed that energy transfer events appear to be very rare in this system. No conclusive evidence of energy transfer was observed on the single particle level.
Open Access
Fundamental insights into the alloy miscibility and surface chemistry of metal nanoclusters
(Colorado State University. Libraries, 2022) Anderson, Ian David, author; Ackerson, Christopher J., advisor; Shores, Matthew P., committee member; Van Orden, Alan, committee member; Prenni, Jessica E., committee member
The fascinating and varied properties of metals have captured people's imaginations long before the advent of modern chemistry. Basic metallurgy, dating as far back as the fourth millennium BC, remains one of the most consequential processes in human history. Today we enjoy an effective mastery over metals in their continuous bulk state, complete with alloy phase diagrams which describe properties as a function of temperature and percent composition. The coordination chemistry of single-metal complexes is similarly well-studied, initiated by the pioneering work of Alfred Werner in 1893. Size-dependent properties found at these two extremes (continuous bulk versus discrete molecular) have facilitated a myriad of applications in nearly every aspect of society through the development of unique materials. Between bulk metals and coordination complexes exists a new and rapidly growing area of chemistry concerned with clusters containing several to hundreds of metal atoms. Although there are commonalities shared with both molecular and bulk systems, these clusters also exhibit notable behavioral differences which can often not be explained through simple classical interpretations. The challenge of working with these species has been considerably eased within the past fifteen years from advancements in synthesis and characterization, in particular for monolayer-protected clusters (MPCs) of gold. These MPCs can be synthesized to precise monodispersity and are therefore defined by a molecular formula instead of the more general average size and dispersity used to define larger (typically > 3 nm) colloidal nanoparticles. Minor adjustments to the nuclearity, metal atom identity, or surface chemistry of gold MPCs have been shown to induce extensive changes in their observed properties and overall stability. Complete regiochemical control over both the metal core composition and surface ligand environment is therefore of immediate interest. This goal is especially important for potential applications in catalysis, electronics, biolabeling, energy conversion/storage, and theranostics. The work described herein covers two overarching themes: i) examining the alloying ability of gold MPCs with various late transition metals, and ii) an investigation of MPC surface chemistry through the introduction of multidentate ligands. Synthesis and analysis of the classically-immiscible rhodium-gold system using Au25(SR)18 as a template offers a fresh perspective of alloy gold MPCs containing metals with an open d-shell, alongside an updated framework for understanding MPC stability. Acetylide-for-thiolate, thiolate-for-acetylide, and intercluster exchange between acetylide- and thiolate-protected gold MPCs reveal lability which cannot be adequately rationalized through traditional MPC ligand exchange arguments. The first example of a thiolated gold MPC co-protected by several oxygen-containing diglyme ligands is described, which exhibits enhanced thermal stability as a result of the robust gold-diglyme, thiolate-diglyme, and diglyme-diglyme interactions. A straightforward synthetic pathway to fully dithiolate-protected gold MPCs is also described, as well as a post-synthetic ligand exchange study showcasing their resistance against incoming monodentate thiol exchange. Lastly we provide a series of vignettes detailing our efforts towards the synthesis of various MPCs using metals such as osmium, iridium, and bismuth. Overall these studies afford fundamental advancements in the understanding of soluble, air-stable metal nanoclusters and open up new opportunities for their applications.
Open Access
Heterotrimeric coiled-coils as viral fusion protein mimics
(Colorado State University. Libraries, 2010) Johnson, Dana E., author; Kennan, Alan J., advisor; Finke, Richard G., committee member; Peersen, Olve B., committee member; Rovis, Tomislav, committee member; Shores, Matthew P., committee member
The a-helical coiled-coil, formed by the association and supercoiling of two or more a-helices, is a ubiquitous protein structure that mediates a wide range of biological activity. It is characterized by a heptad repeat of amino acids that serve to form both the hydrophobic core and electrostatic interfaces of the coiled-coil. Previous work in our lab showed the viability of designing a self-assembling heterotrimeric coiled-coil by sole manipulation of the hydrophobic core. This technique utilized a steric matching approach whereby one large side chain packed against two small ones. An added benefit to this type of control is that it allowed the freedom to explore additional interactions specific to the electrostatic interface. Many enveloped viruses, including HIV-1, incorporate trimeric coiled-coils in their fusion proteins, and, consequently, are involved in the pathway to infection. Through interactions at the electrostatic interfaces of the coiled-coils, these fusion proteins form a six-helix bundle called a trimer-of-hairpins. The formation of this structure is a precursor to membrane fusion of the viral and host cells, and, as a result, it has become a therapeutic target. The steric matching technique developed in our lab allows us to graft key contacts from the native 111 sequences onto a stable, heterotrimeric system and construct a mimic of the trimer-of-hairpins, as was done with HIV-I previously in our lab. The work that follows shows that a viable mimic of the Human Respiratory Syncytial Virus is also possible. A stable, self-assembling mimic was designed, synthesized and validated through various spectroscopic methods. Additionally, a mutant study was conducted to further refine our knowledge of the importance of the residues thought to be key to the formation of the trimer-of-hairpins. Other work was performed extending the process to the Human T-cell Leukemia Virus, bringing the possibility of a complete and stable mimic ever closer.
Open Access
Investigations into magnetic relaxation for vanadium complexes
(Colorado State University. Libraries, 2022) Jackson, Cassidy Elizabeth, author; Zadrozny, Joseph M., advisor; Shores, Matthew P., committee member; Chen, Eugene, committee member; Ross, Katherine, committee member
Magnetic molecules represent an emerging class of complexes that can be used to understand quantum phenomena impactful for quantum computing, non-invasive magnetic resonance imaging, and information storage. These organometallic complexes have the electronic spin is centered on the metal ion. Magnetic molecules based on electronic spins are extremely sensitive to changes in their local environment, such as nuclear spins. Electronic spins on a metal ion were employed to understand how nuclear spins in the local environment modulate electron spin dynamics. In this work, vanadium(IV) was chosen to study with varying catechol ligands. Electron paramagnetic resonance (EPR) was used to study two properties of these metal complexes, spin-lattice relaxation (T1) and phase memory relaxation (Tm or T2). Investigation of these parameters and fitting of these parameters provided information of how the local environment played a role in shortening these lifetimes. The complexes developed in this work indicates that the local environment is an extremely important piece of relaxation due to drastic changes in relaxation times. Chapter 1 introduces provides motivation for the work conducted in this dissertation and gives a thesis structure overview. Chapter 2 gives a broad summary of the field of molecular magnetism and provides metaphors for the synthetic chemist to learn about electron spin relaxation. Chapters 3 gives the first report of nuclear spin patterning on a ligand shell impacting spin relaxation times Chapter 4 details high-field, high-frequency orientation dependence on spin relaxation times for the V(IV) ion. Chapter 5 explores proton nuclear spin dynamics as they relate to nuclear spin patterns on a ligand and ligand complexed to a diamagnetic metal ion. Chapter 6 explores counterion dynamics and how they impact spin relaxation times. Chapter 7 gives a summary and future directions.
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
Lewis acid-mediated controlled anionic polymerization at high temperature
(Colorado State University. Libraries, 2011) Bornhoft, Laura O'Neill, author; Chen, Eugene Y.-X., advisor; Shores, Matthew P., committee member; Kipper, Matthew J., committee member
Lewis acid-mediated controlled anionic polymerization under industrially desired conditions (ambient or higher temperature) is described in this thesis. The central theme focuses on the utilization of Lewis acids, primarily trialkylaluminum tris(pentafluorophenyl)alane and isoelectronic silylium cation, in three different anionic polymerization systems to mediate, or act as catalyst, for the controlled anionic polymerization of (meth)acrylic monomers or the anionic coordination ring opening polymerization of bio-derived cyclic monomers ɛ-caprolactone and meso-lactide. The first system uses potassium hydride as an anionic initiator, activated with aluminum Lewis acids of varied acidity, sterics and equivalents, for the controlled polymerization of methyl methacrylate (MMA) and block copolymerization of MMA with other alkyl methacrylates such as n-butyl methacrylate and 2-ethylhexyl methacrylate. The second system involves the synthesis of nonpolar-polar block copolymer of poly(styrene-b-methacrylate) in aliphatic solvents at high temperature. Aluminum Lewis acids or non-polymerizable monomers such as N,N-dimethyl methacrylamide are added between blocks to control the propagation crossover from the styrenic block to the methacrylate block. The third system utilizes silylium ions to catalyze anionic polymerization, focusing on the anionic coordination polymerization of cyclic esters and the development of new dinuclear catalysts exhibiting potential to new polymerization pathways that could promote faster polymerization under dilute conditions and enhanced polymerization stereochemical control.
Open Access
N-Heterocyclic carbene catalysis: application to the total synthesis of cephalimysin A, and development of multicatalytic cascade reactions
(Colorado State University. Libraries, 2011) Lathrop, Stephen Paul, author; Rovis, Tomislav, advisor; Wood, John L., committee member; Crans, Debbie Catharina, committee member; Shores, Matthew P., committee member; Kanatous, Shane B., 1968-, committee member
Application of the N-Heterocyclic carbene catalyzed Stetter reaction to the total synthesis of 9-epi-cephalimysin A has been realized. The approach centers on the use of an asymmetric catalytic Stetter reaction to access the spirocyclic core of cephalimysin A. Specifically it was found that a photoisomerization/Stetter protocol allows rapid access to an intermediate readily amenable for further functionalization. This intermediate was further elaborated to three stereoisomers of the naturally occurring cephalimysin A. During the investigation of cephalimysin A an interesting side product was observed that led to the development of several multicatalytic cascade reactions utilizing N-heterocyclic carbenes. Specifically the pairing of secondary-amine catalysts with N-heterocyclic carbenes allowed for the synthesis of densely functionalized cyclopentanones in a single step. Moreover, a synergistic relationship was observed between the two catalysts. This partnership allowed for the products to be achieved in higher selectivity than would have been possible if conducting the reactions in a stepwise fashion.
Open Access
Part I: Electroreductive polymerization of nanoscale solid polymer electrolytes for three-dimensional lithium-ion batteries. Part II: Physical characterization and hydrogen sorption kinetics of solution-synthesized magnesium nanoparticles
(Colorado State University. Libraries, 2010) Arthur, Timothy Sean, author; Prieto, Amy L. (Amy Lucia), advisor; Bailey, Travis Slade, committee member; Elliott, Cecil Michael, committee member; Shores, Matthew P., committee member; Williams, John D., committee member
To view the abstract, please see the full text of the document.
Open Access
Photo-induced electron transfer in cu(i) bis-phenanthroline based assemblies. Part I: Chromophore-acceptor diads. Part II: Donor-chromophore-acceptor triads
(Colorado State University. Libraries, 2013) Lazorski, Megan, author; Elliott, C. Michael, advisor; Shores, Matthew P., committee member; Chen, Eugene, committee member; Bailey, Travis S., committee member; Sites, James R., committee member
The photophysical behavior of [Cu(I)P2] (P=2,9-disubstituted-1,10-phenanthroline ligands) in donor-chromophore-acceptor (D-C-A) triads and chromophore-acceptor (C-A) diads is a complex and fascinating area of under developed, yet fundamental, electron transfer chemistry. In metal polypyridyl D-C-A and C-A triads/diads, metal polypyridyl chromophores (C) in which the polypyridyl ligands are covalently linked to acceptor (A) and/or donor (D) moieties, photo-excitation of the chromophore initiates a series of electron transfer events that result in the formation of a charge separated (CS)/charge transfer (CT) state, respectively. The majority of high-performing metal polypyridyl D-C-A/C-A complexes, on which [Cu(I)P2] D-C-A/C-A research is based, incorporate ruthenium (as [Ru(II)L3] where L=polypyridyl ligand) or other rare, expensive, and sometimes toxic metals such as osmium, rhenium and platinum. Although [Ru(II)L3] D-C-A/C-A's have historically set the benchmark for metal polypyridyl D-C-A/C-A performance, it is clear that these complexes are not a practical choice if D-C-A's or C-A's were incorporated into a device for large scale production. However, bisphenanthroline complexes of copper, a much more earth abundant, cheaper and less toxic metal, exhibit very similar photophysical properties to [Ru(II)L3] and have thus gained recognition as promising new materials for D-C-A/C-A triad/diad construction. In order to understand the electron transfer (ET) events occurring in [Cu(I)P2] D-C-A/C-A triads/diads, a complex must be synthesized that is capable of forming a CS with high quantum efficiency (Φcs/ct) and a long CS/CT lifetime (τcs/ct). Therefore, the intent of the research reported herein is to synthesize novel, yet functional heteroleptic [Cu(I)P2] D-C-A/C-A triads/diads and study their fundamental, photo-initiated electron transfer chemistry, specifically the formation of a CS/CT state. Many challenges, which are not present for [Ru(II)L3], make the design and synthesis of [Cu(I)P2] D-C-A/C-A assemblies an art in itself. Therefore, a significant amount of effort was spent on fabricating ligand architectures that (1) are appended with acceptor and/or donor moieties capable of being reduced/oxidized resulting in the formation of a CS/CT, (2) are able to be easily modified so the amount of energy stored in the CS/CT can be tuned, (3) favor the self-assembly of [Cu(I)P2] complexes, (4) are able to facilitate processes that maximize the Φcs/ct. Once the ligands were obtained, the complexation equilibria behavior of these [Cu(I)P2] triads and diads were studied. Despite efforts to design ligand architectures that favor heteroleptic formation, the thermodynamic driving force for heteroleptic D-C-A triad formation is less favor-able than expected. Thus, mixing stoichiometric quantities of D, C and A results in a statistical mixture of C-A, C-D and D-C-A products. Furthermore, since the ligands are labile and will re-arrange to the most thermodynamically stable configuration of products when these complexes are dissolved, isolation of the D-C-A product is impossible. However, recent advances in ligand design have shown promise for resolving this on-going issue. Despite having a mixture of products with the D-C-A, the electron transfer processes of the [Cu(I)P2] D-C-A triads and C-A diads were investigated. Using Transient Absorption (TA) laser spectroscopy, the CT state in the constructed C-A diads and the CS state in the D-C-A triads were detected and the lifetimes were determined. However, it was found that those lifetimes could be modulated to a small degree by solvent in the C-A diads (c.a. 6x longer in polar solvents), and drastically via the application of a magnetic field in D-C-A triads (c.a. 60x longer). The ability to modulate the lifetimes enabled the deconvolution of the effects due to the C-A diad vs D-C-A triad in the statistical product mixtures. Although the response in a magnetic field was a somewhat expected result, as similar effects occur in the [Ru(II)L3 D-C-A/C-A's, the magnitude of change in the lifetime and the quantum efficiency offers new insight into the electron transfer events that occur in the CS/CT formation process for [Cu(I)P2] D-C-A/C-A complexes.
Open Access
Progress towards the total synthesis of the welwitindolinone alkaloids and the discovery of a novel tandem O-H insertion Conia-ene cyclization
(Colorado State University. Libraries, 2011) Freeman, David Blandy, author; Wood, John L., advisor; Kennan, Alan J., committee member; Ferreira, Eric M., committee member; Shores, Matthew P., committee member; McNeil, Michael R., committee member
The broth of blue-green algae Hapalosiphon wewitschii and Westiella intricate was shown to possess interesting biological activity, including insecticidal and P-glycoprotein inhibiting capabilities. Upon further investigation, the welwitindolinone alkaloids were isolated from the lipophilic extracts and shown to be responsible for the observed biological activity. Herein are described efforts towards the total synthesis of the welwitindolinone alkaloids and novel chemistry developed in the process. In efforts towards N-methylwelwitindolinone C isothiocyanate, we employed a sequential O-H insertion Claisen rearrangement to provide compounds capable of undergoing a [3+2] dipolar cycloaddition to access the bicyclo[4.3.1] core. Attempts to install the requisite quaternary center of N-methylwelwitindolinone C isothiocyanate during the [3+2] dipolar cycloaddition event were unsuccessful. Ultimately, a chloronium-ion semi-Pinacol rearrangement was utilized to install the key quaternary center. Due to complications encountered during the synthesis of N-methylwelwitindolinone C isothiocyanate we shifted our focus to N-methylwelwitindolinone D isonitrile. Investigation into the construction of the bridged ether embedded within N-methylwelwitindolinone D isonitrile led to the discovery of a novel tandem O-H insertion Conia-ene cyclization.
Open Access
Single potential electrodeposition of nanostructured battery materials for lithium-ion batteries
(Colorado State University. Libraries, 2010) Mosby, James Matthew, author; Prieto, Amy L. (Amy Lucia), advisor; Elliott, Cecil Michael, committee member; Ladanyi, Branka M., committee member; Manivannan, Venkatesan, committee member; Shores, Matthew P., committee member
To view the abstract, please see the full text of the document.
Open Access
Synthesis of fluoromodified carbon rich electron acceptors and exploration of their structural, electronic, and device properties
(Colorado State University. Libraries, 2020) DeWeerd, Nicholas J., author; Strauss, Steven H., advisor; Shores, Matthew P., committee member; Ackerson, Chris J., committee member; McCullagh, Martin J., committee member; Gelfand, Martin P., committee member
The electronic and structural characterization of fluoro-modified carbon-rich compounds is critical to the successful implementation of these materials by physicists, biochemists, materials scientists, medicinal chemists, and most significantly for this work, organic electronics chemists. By adding powerful electron-withdrawing groups, the electron acceptor and solid-state structural properties of carbon rich substrates such as polyaromatic hydrocarbons (PAHs) and fullerenes can be improved, making these derivatives attractive semiconductor materials for organic electronics applications. This work will discuss research which has focused on expanding the library of electron acceptor compounds, elucidating the electronic and structural properties of those compounds, and exploring their physicochemical properties, focusing on properties that are important for the performance of organic electronic devices. This was accomplished by exploring reaction conditions which had not been previously reported at pressures and temperatures exceeding the operational limits of conventional reactors, developing purification methods that allow for chromatographic separation of constitutional isomers, and structural characterization of those purified materials by mass spectrometry, NMR, and most importantly X-ray crystallography. As a complement to this research, the stability of organic electronic active layers was studied to better understand how organic semiconductor active layer's degradation affects device performance over time and to better inform which active layer material properties should be pursued. Based on those findings and literature precedent, one family of compounds, C60 and C70 fauxhawk fullerenes, found to have favorable characteristics were then utilized in OFET devices as n-type semiconductors resulting in record-setting charge carrier mobilities.
Open Access
The development of portable electrochemical sensors for environmental and clinical analysis
(Colorado State University. Libraries, 2020) Kava, Alyssa A., author; Henry, Charles S., advisor; Shores, Matthew P., committee member; Sambur, Justin B., committee member; Dandy, David S., committee member
The ability to perform chemical and biochemical analysis at the point-of-need (PON) has become increasingly sought. PON sensing is critical in both environmental and clinical monitoring applications to reduce cost and time of analysis and achieve early detection of potentially harmful pollution and health indicators. Electroanalysis is very well suited to PON sensing applications with miniaturized instrumentation available, fast analysis times, high sensitivity, low detection limits and the ability to be interfaced with both conventional and paper-based microfluidics (μPADs). The primary focus of this thesis is to improve electrochemical sensors for PON applications by: 1) reducing the number of liquid handling steps required by the end user, 2) further development of better performing disposable electrode materials and 3) the proper integration of electrodes with disposable microfluidic paper-based devices. The first half of this thesis, Chapter 2 through Chapter 4, focuses on the development of a new functionality in μPADs coupled with high quality boron doped diamond paste electrodes (BDDPESs). The electrochemical PAD (ePAD) is referred to as the Janus-ePAD after the two- faced Greek god. The Janus-ePAD developed in Chapter 2 takes advantage of the ability to store reagents within porous paper matrices. In the Janus-ePAD, reagents were stored in two separate channels connected by a sample inlet to adjust the sample pH and perform multiplexed electrochemical detection at two analytes' optimal pH conditions. Therefore, the device is able to carry out several liquid handling and operator steps in situ, further simplifying electrochemical PON sensing. In Chapter 3, fundamental electrochemical characteristics of the BDDPEs are then studied in order to improve their electroanalytical utility, providing a guide to the use of this new composite electrode material. Then, in Chapter 4, a second generation Janus-ePAD is developed to overcome several problems typically encountered in ePADs, namely, slow flow rates and analysis times and lowered electrochemical detection sensitivities due to the paper-electrode interface. Both of these problems are addressed by developing a multi-layer Janus-ePAD that consists of a wax-patterned paper layer taped to a transparency film layer, generating microfluidic channel in the gap between the two layers. Passive fluid transport is still achieved within the channel gap via capillary action but at much faster flow rates decreasing analysis time by over 20 times compared to a one-layer Janus- ePAD. The paper-electrode interface is removed by placing screen-printed carbon electrodes (SPCEs) on the transparency film layer, providing increased reproducibility and bulk solution sensitivity. The second main focus of this thesis is the development of better performing electrode materials that retain the simplicity and disposability required for on-site electroanalysis. In Chapter 5, this goal is accomplished by the development of a novel SPCE composition using glassy carbon (GC) microparticles as the active electrode component and a conductive commercial ink as the binder component of this composite electrode material. The GC-SPE is then applied to the detection of the toxic heavy metals Cd and Pb using anodic stripping voltammetry (ASV). The use of GC microparticles as opposed to the widely used graphite powders in the bulk SPCE formulation allows for the GC-SPE to sensitively and quantitatively detect Cd and Pb at environmentally relevant levels without the need for any post-fabrication modification which is typically required for graphite based SPCEs. Following the development of the GC-SPE in Chapter 5, in Chapter 6, a systematic study was carried out to understand the relationship between SPCE composition, or carbon particle type, and electrochemical performance with the goal of improving the electrochemical performance of these single-use, mass producible, inexpensive and disposable electrode materials in their native, or unmodified state. Significantly, it was found that SPCE composition can be optimized and tuned to provide electrochemical sensing performance on par with other types of carbon composites historically believed to outperform SPCEs. The work contained within this thesis achieves the goal of developing better performing PON electrochemical sensing motifs while retaining maximum simplicity of fabrication and operation of ePADs and SPCEs. Through automation of liquid handling steps using a paper-based device, further simplification of sensitive multiplexed electrochemical detection was achieved. The fundamental understanding of the electrochemical performance of SPCEs allowed for further applications without extensive post-fabrication modifications which have historically hindered their translation from academic to real-world settings. The work presented herein can be used to guide further development of electrochemical PON sensors for a variety of environmental and clinical applications.
Open Access
Understanding the amide-assisted synthesis and olivine structure-directed twinning of Fe₂GeS₄ nanoparticles
(Colorado State University. Libraries, 2020) Miller, Rebecca Caroline, author; Prieto, Amy L., advisor; Shores, Matthew P., committee member; Sites, James R., committee member; Ackerson, Christopher J., committee member
The reality of detrimental anthropogenic effects on the environment requires the development of a number of sustainable practices and technologies. The Prieto Group strives to advance the synthesis and understanding of materials for use in energy conversion and storage. Advances in computational solid-state chemistry have resulted in the identification of a number of earth-abundant, relatively non-toxic compounds as promising photovoltaic absorber materials. However, the synthesis of solids remains a step behind, requiring empirical exploration of precursors and conditions. As reaction intermediates and mechanisms are discovered, general synthetic strategies can be translated from one material system to the next. Inorganic nanoparticle (NP) syntheses rely on the interdisciplinary expertise of solid-state, organometallic, and organic chemistry and show interesting complexity. The work herein has advanced the understanding of amide-assisted NPs syntheses and examined the microstructure of twinned Fe2GeS4 NPs. Chapter 1 presents a history of solution-based, amide-assisted NP reactions. As scientists understand the in situ speciation of precursors, more efficient reactions can be designed. This understanding allows the use of more benign and safe (both in terms of human and environmental) precursors and provides higher synthetic control over the end products. The presence of amide bases has generally provided access to higher NP nucleation rates and accessed smaller, more monodisperse particles. The increased monomer reactivity has also allowed the formation of ternary NPs free from binary or unary impurities by balancing the reactivity of cations of different valency. The most common amide base is LiN(SiMe3)2, and I relate this field to the use of its conjugate acid, hexamethyldisilazane or HMDS, in NP syntheses. Its addition has aided the production of NPs, but its chemical role remains unclear. This chapter was written utilizing a portion of an invited review paper written by myself, Jennifer M. Lee, Lily J. Moloney, and Amy L. Prieto in the Journal of Solid State Chemistry (2019, 273, 243-286.). Section 2.2 of the review outlined the evolution of understanding of amide-assisted NP syntheses and was adapted and expanded upon herein. In Chapter 2, I report the redesign of a Fe2GeS4 NP synthesis. In 2013, the Prieto group was the first to report a NP synthesis for the compound, which had been predicted to be a promising photovoltaic absorber material in 2011. The original reaction relied on HMDS as an additive and employed the highly-reactive S precursor, hexamethyldisilathiane. Herein, I speculate on these precursors' roles and exchange their use for LiN(SiMe3)2 and S powder, eliminating the formation of an Fe1–xS intermediate and reducing the growth time from 24 h to 10 min. I thoroughly map the reaction landscape of this system and provide structural, compositional, and optical characterization of the particles. This work was published in the Journal of the American Chemical Society (J. Am. Chem. Soc. 2020, 142 (15), 7023–7035.). The Fe2GeS4 NPs show an interesting star-shaped morphology, so I examine the microstructure via electron microscopy and identify the presence of crystal twinning in Chapter 3. The particles exist as three sets of stacked nanoplates intersecting at 60˚ angles, which forms a triplet of twins or trillings. In the products, 98% of the particles are twinned. Because crystal twinning, and especially trilling formation, in macroscopic crystals is rare, a synthetic route to a massive collection of twinned particles stands as a valuable resource for understanding the fundamentals of crystal twinning in olivine compounds. I relate the twinning to the underlying hexagonal pseudosymmetry of the orthorhombic, olivine crystal structure. Because of the ratio of the unit cell dimensions (a_Pnma/b_(Pnma )≈√3), the compound is susceptible to forming twins with growth of the [010] direction off the {310} faces. This can occur for other olivine compounds of similar unit cell dimension ratios, so I rank all of the olivine compounds listed in the Inorganic Crystal Structure Database according to this metric in Appendix A. This chapter is a manuscript prepared for submission. Finally, Chapter 4 outlines our recommendations for future work to advance the understanding of amide-assisted NP syntheses and translate this synthetic system to other compounds. I suggest the systematic development of SnS NP reactions utilizing each of the precursors: Sn silylamide, alkali silylamides, and HMDS. I outline a set of complementary techniques to characterize the reaction intermediates and mechanisms. This type of investigation has been done by the Kovalenko group for the formation of unary Sn0 NPs, but the interaction of the chalcogen species remains unknown. Further, no systematic mechanistic study exists for the use of HMDS in NP synthesis. This work would advance the understanding and use of amide-assisted syntheses for all metal chalcogenide compounds. In addition, I present preliminary data in our extrapolation of the Fe2GeS4 NP synthesis to the following solid solutions: Fe2GeS4–xSe (including the end member Fe2GeSe4) and Fe2–xMnxGeS4. One composition of each solid solution was formed and characterized by powder X-ray diffraction, and I present electron microscopy to show twinning in the Fe2GeS4–xSex (x = 0.96, 24 mol% Se) NPs. Lastly, I consider the possibility for twinning in an important olivine compound for battery science, LiFePO4, which is a common cathode material. The crystal structure shows a high degree of hexagonal pseudosymmetry, indicating that the energetics of forming twin domains may be favorable. I discuss the possible ramifications this may have on battery cycling performance. Thus, the scope of this work focuses on one compound, Fe2GeS4, but investigation into its synthesis and microstructure has opened a number of avenues for promising research. This compound itself presents a promising material for both photovoltaic and thermoelectric energy conversion, and the syntheses herein provide a launching point for property measurement and application evaluation. Further, the general examination of twinning in olivine compounds identifies questions for evaluating the function of other compounds useful for a number of applications. Lastly, analogous calculations to the geometrical evaluation done for orthorhombic olivine compounds could be carried out for other crystal structure types with unit cells that exist close to higher orders of symmetry. The advances presented herein on understanding the reactivity and roles of NP precursors are fundamental for progressing the field of NP synthesis. The reproducible formation and structural characterization of these twinned NPs provide a promising system for future explorations in crystal twinning and its effect on material properties.