Mountain Scholar :: Browsing by Author "Finke, Richard, committee member"

Browsing by Author "Finke, Richard, committee member"

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Open Access
Advancements in organocatalyzed atom transfer radical polymerization by investigation of key mechanistic steps
(Colorado State University. Libraries, 2022) Corbin, Daniel Andreas, author; Miyake, Garret, advisor; Finke, Richard, committee member; Rappé, Anthony, committee member; Kipper, Matt, committee member
Organocatalyzed atom transfer radical polymerization (O-ATRP) is a controlled radical polymerization method employing organic photoredox catalysts to mediate the synthesis of well-defined polymers. The success of this method derives from its reversible-deactivation mechanism, where polymers are activated by reduction of a chain-end C-Br bond to generate a reactive radical for chain growth, followed by deactivation of the polymer by reinstallation of the dormant bromide chain-end group. As a result, the polymer chain can be grown by reaction of the polymer radical with alkene-based monomers, but undesirable termination and side reactions can be suppressed by minimization of the radical concentration through deactivation. In this work, key mechanistic steps of O-ATRP are investigated to understand the fundamental limitations of this method and improve upon them. When N,N-diaryl dihydrophenazines were investigated, side reactions were identified in which alkyl radicals add to the phenazine core, leading to new core-substituted PC derivatives with non-equivalent catalytic properties. Employing these core-substituted PCs in O-ATRP showed these side reactions can be eliminated to improve polymerization control. In addition, the deactivation step of O-ATRP and related intermediates were studied, which revealed new side reactions that can limit polymerization efficiency as well as influences on the rate of deactivation. Finally, methods to exert control over the deactivation process were developed as a means of improving polymerization outcomes in challenging systems. For example, the intermediate responsible for deactivation was isolated and added to a polymerization to increase the rate of deactivation and limit side reactions in O-ATRP. Alternatively, a similar outcome could be achieved through in-situ electrolysis to increase the concentration of the desired intermediate during the polymerization. Ultimately, this work has yielded insight into important mechanistic processes in O-ATRP that will continue to benefit the development of this method.
Open Access
Applications of inorganic nanoparticles in biological electron microscopy
(Colorado State University. Libraries, 2016) Ni, Thomas Wentung, author; Ackerson, Christopher, advisor; Prieto, Amy, committee member; Finke, Richard, committee member; Peersen, Olve, committee member
Electron microscopy is an immensely powerful for imaging at the cellular level. However, many of the macromolecules of interest are difficult to image due to low electron density. There has been an immense body of work in order to visualize these macromolecules. In the past, many of the methods of visualization revolved around staining samples with heavy metals, however these stains are non-specific. In order to develop more specific methods of tagging macromolecules, there are two different methods to consider: the first being a top-down approach, in which electron dense tags, in this case inorganic nanoparticles, are given specific ligands to take advantage of different chemistries to attach these nanoparticles to macromolecules of interest. The second method is through a bottom-up approach where biomolecules are given the specific ability to form inorganic nanoparticles. Inorganic nanoparticles have been investigated with various ligands in order to enhance binding capability to macromolecules. The chief method of functionalizing these inorganic nanoparticles comes from ligand exchange; much has been studied regarding ligand exchange, but there are still many unanswered questions. Herein, we endeavor to reveal both the mechanism of exchange and the functional unit of exchange. We also report progress towards understanding an enzyme that is capable of forming inorganic nanoparticles, which could be cloned onto proteins as well. This bottom up style has been studied in several other groups; however, none of the previously reported methods have seen much use. Herein, we report a potential NADPH-dependent enzyme that forms selenium nanoparticles.
Embargo
Cu-P-Se nanoparticles: understanding the reaction pathways for the colloidal synthesis of energy conversion and storage materials
(Colorado State University. Libraries, 2024) Neisius, Nathan A., author; Prieto, Amy L., advisor; Finke, Richard, committee member; Herrera-Alonso, Margarita, committee member; Paton, Robert, committee member
Nanotechnology has garnered considerable interest over the last 40 years, owing to the unique, desirable properties that can be targeted through established synthetic methods for tuning the size of materials at the nanoscale. As no one single material has properties suitable for a wide range of applications, property driven synthesis has been at the forefront of the nanoparticle (NP) field. Particularly, colloidal NP syntheses provide a large synthetic landscape to explore as a result of the vast synthetic tunability to target specific parameters such as, particle size, morphology, composition, and defects. Although significant efforts have been made toward deciphering the transformation processes of unary and binary NPs, traditionally the colloidal NP field has been driven by a top-down approach, driven by trial-and-error methods, limiting the design of desired, complex materials. Thus, to further progress nanoparticle technology, understanding the underlying transformation processes occurring throughout the formation of colloidal nanoparticles is essential to develop novel materials as well as control the structure/property relationships. The copious amounts of both organic and inorganic interactions, as well as the complexity of capturing the transformation from molecular to the solid-state regime, complicates the reaction landscape for more complex, ternary phases. The purpose of the work included and explained in this dissertation is to develop stoichiometric syntheses for both Cu-P-Se ternary phases, Cu3PSe4 and Cu7PSe6, and to then understand the reaction pathways for an improved retrosynthetic analysis and enable translation of the synthetic knowledge to other systems. Cu-P-Se ternary chalcogenide NPs are of particular interest, owing to the synthetic complexity of navigating a rich phase space with thermodynamically stable binary phases close in energy to the desired ternary phases, as well as applicable structural properties for thermoelectrics, photovoltaics, and battery applications. Therefore, to contribute to the progression of the nanoparticle field the general objectives of this study are, (1) analyzing the transformation of commonly employed precursors and solvents (2) capture the influence of precursor reactivity on ternary phase formation, and (3) perform careful characterization of speciation and final nanoparticles, all of which to establish a full scope of Cu-P-Se nanoparticle formation and the impact of individual synthetic parameters on chalcogenide-based precursors. In Chapter 1, the relevant literature for the following chapters is reported and reviewed to provide the essential background information. This chapter is divided into 6 subsections; (1) Need for renewable energy and how nanoparticles provide solutions, (2) State of nanoparticle synthesis field, current limitations, and progress towards developing a better understanding of nanoparticle reaction pathways, (3) Motivation for exploring the Cu-P-Se phase space, (4) Se reactivity in NP syntheses, (5) Cu3P – the required precursor for Cu-P-Se formation, (6) Dissertation overview, publications, and presentations. The first colloidal NP synthesis report on Cu3PSe4 was developed by a previous group member, Dr. Jennifer Lee, which demonstrated that the phase purity of Cu3PSe4 requires the use of Cu3P NPs and selenium powder (Se) in ODE as precursors. Alternate reaction precursors, and therefore pathways, were disproven throughout this study, leading to the working hypothesis that the interactions of Se and ODE were a necessary step to form active species that then react with Cu3P NPs. Although frequently employed in NP research, and heavily characterized, the implications of the Se/ODE solution on Cu3PSe4 phase formation are still misunderstood. Therefore, the studies presented in Chapter 2 are aimed at probing the Cu3PSe4 reaction landscape and the findings are separated into (1) ex situ reactions that are characterized with molecular and solid-state characterization techniques to determine the implications of the solution dynamics on Cu-P-Se NP phase formation, and (2) how different Se/ODE speciation can be isolated and subsequently favor the alternate, metastable Cu-P-Se phase, Cu7PSe6. A persistent limitation to the previous study is that ODE contaminates the final products, making the findings and analysis of Se/ODE rather difficult to interpret, thus requiring a simplified, cleaner reaction to produce phase pure Cu3PSe4. For that reason, Chapter 3 shifts the direction of the Cu3PSe4 synthesis towards a more stoichiometric, atom-economical reaction by eliminating ODE as the solvent. Rather, a long-chain, aliphatic solvent, octadecane (ODA) is employed that proves to be an operationally inert solvent under the standard synthetic conditions and produces cleaner, phase pure Cu3PSe4 NPs as determined by powder X-ray diffraction (PXRD) and transmission electron microscopy (TEM). If ODA was reacting with Se0 powder, the most favorable pathway, commonly cited in literature, is the formation of H2Se and oxidized ODA (alkene). Hence, molecular characterization techniques, nuclear magnetic resonance (NMR, 1H and 13C) and fast-Fourier infrared spectroscopy (FT-IR), were utilized to demonstrate the absence of oxidized ODA species, which is consistent with Se0 preferentially reacting with Cu3P, promoting a more direct reaction pathway. Eliminating the presence of alternate, competing reaction pathways in the ODE synthesis and establishing a near-stoichiometric reaction, allows us to capture the underlying transformation process of Cu3P to Cu3PSe4. From these systematic improvements, we hypothesize that Se0 powder is dispersed in ODA, which promotes a formal eight-electron transfer between Cu3P and 4 Se0. Extracting the synthetic information from the previous chapters to target the metastable Cu-P-Se phase, Cu7PSe6, provides the framework for Chapter 4. Previous methods to isolate Cu7PSe6 are based on traditional, solid-state techniques, where the elemental precursors are ground and subsequently heated to high temperatures (>1000K). Although a colloidal or solution-based synthesis has yet to produce phase-pure Cu7PSe6 particles, attempts explained in Chapter 2 provide a basis on the phase space complexity, where the products consisted of Cu7PSe6 but with thermodynamic byproducts, Cu-Se phases and Cu3PSe4 present. Therefore, an alternate Se precursor, diphenyl diselenide (Ph2Se2), is employed to form the metastable phase, which effectively avoids Cu3PSe4 formation. Importantly, an alternate route to form Cu3PSe4 is with analogous dialkyl diselenide precursor, dibenzyl diselenide, where a key finding is the presence of amorphous phosphorus (P) on Cu1-xSe binaries at low temperatures, which then efficiently reincorporates once the desired 300 ˚C reaction temperature is reached. Thus, in Chapter 4 we investigate why Cu7PSe6 is favored with Ph2Se2 as a precursor, which is predicated on the formation of byproduct species that effectively "trap" P. A proof of concept is explored to further demonstrate the dynamics of P in solution, where the Cu-P-Se phase space can be controllably toggled across by injecting P(5+) species. A drawback for the Cu-P-Se syntheses is the lack of compositional understanding of the pre-synthesized Cu3P NPs, thus further complicating the reaction stoichiometries. Chapter 5 first investigates the previously published synthesis by Liu et al., by thoroughly characterizing the final Cu3P nanoparticles under identical reaction conditions and exploring alternate reaction stoichiometries to reduce the presence of residue precursors. From such, it is determined that the particles substantially deviate from the stoichiometric Cu3P composition, with a Cu:P ratio around 1.5:1.0. Particular focus is also placed on monitoring the degradation of a green phosphorous source, triphenyl phosphite, P(OPh)3. Although triphenyl phosphite (TPOP) has been previously used for transition metal phosphide systems, a lack of systematic investigations leads to questions on the reduction of TPOP en route to forming Cu3P, a formal P(3+) to P(3-) event. Additionally, limited characterization of the final organic byproducts in the original synthesis, begs to question what, if any, byproducts could be contaminating the Cu3P NPs. Therefore, we develop and probe stoichiometric syntheses that isolate phase pure Cu3P NPs to avoid the original 30-fold excess of P. The transformation of hexadecylamine (reductant and ligand) and TPOP were characterized with 1H and 31P NMR to evaluate the role of each en route to forming Cu3P. As this is project is still developing, the necessary future directions are given to systematically approach this problem, with an emphasis on first-step experiments and essential characterization methods to completely grasp the decomposition mechanism of TPOP. Ultimately, this has implications when systematically applying TPOP to alternate transitional metal phosphide NP syntheses, as well as developing more precise Cu-P-Se syntheses. Finally, the work presented herein is summarized in Chapter 6 along with an outlook on the project as a whole. Specifically, future directions and preliminary insight into the underlying reaction pathways and mechanism of Cu3PSe4 formation are explored. Additionally, we explore preliminary data on an analogous material Ag-P-Se, which was plagued for years by the lack of a reproducible Ag-P precursor synthesis that limited our ability to extract the synthetic intuition from the Cu-P-Se system. However, recent literature findings on a potential Ag3P precursor provides promise on synthesizing Ag-P-Se phases in the future, which is critically analyzed to ensure that any bottlenecks in future syntheses are limited. Ultimately, the work provided in the following chapters is aimed at making strides to developing a more in depth understanding of precursor interactions between transition metals and main group elements, as well as properly monitoring such reactions to extract synthetic information to analogous systems. With the knowledge gained on the presented studies, we aspire to contribute to the NP field in order to continually improve NP synthesis and therefore nanomaterials. Finally, this work is supported by NSF Macromolecular, Supramolecular, and Nanochemistry (MSN #2109141).
Open Access
Enabling and understanding low-temperature kinetic pathways in solid-state metathesis reactions
(Colorado State University. Libraries, 2020) Todd, Paul Kendrick, author; Neilson, James, advisor; Finke, Richard, committee member; Prieto, Amy, committee member; Henry, Chuck, committee member; Ma, Kaka, committee member
For the kinetic pathway to influence the outcome of a solid-state reaction, diffusion barriers must be lowered or circumvented through low-temperature chemistry. Traditional ceramic synthesis use high temperatures to overcome diffusion, yet they result in the thermodynamically stable product. If the desired product lies higher in energy, they are unattainable at such temperatures. Extrinsic parameters, like pressure, can be used to change the stability of products (kinetic trapping), yet require extreme conditions. Another strategy involves kinetically controlling the energy barriers of the reaction to select for a given product. Here, we use solid-state metathesis reactions to understand and control kinetic pathways in the formation of complex oxides and binary metal sulfides. Through simple changes to precursor composition, three unique polymorphs of yttrium manganese oxide are synthesized, two of which are metastable phases. Using in situ diagnostics, the reaction pathways are characterized to identity intermediates and the temperature regimes at which they react. Using this information we identify why different polymorphs form using different precursors. Additionally, small functional organosilicon molecules are shown to catalyze the formation of iron(II) sulfide using metathesis reactions. Here we show that the Si-O functional group stabilizes intermediate species along the pathway to avoid forming more stable intermediates. The result is higher yields of FeS2 at lower temperatures and times. The included chapters will hopefully better inform future solid-state chemists when exploring new composition spaces and reaction pathways.
Open Access
Investigation of the growth mechanism of highly branched silica nanowires grown using in-situ Cu-catalyst loading, and the development of electrochemical anodization synthetic methods specifically targeting solid ionically conducting materials
(Colorado State University. Libraries, 2023) Boissiere, Jacob Daniel, author; Prieto, Amy, advisor; Finke, Richard, committee member; Rappe, Anthony, committee member; Dandy, David, committee member
Gaining a better understanding of the world around us is the fundamental objective of science, with chemistry looking to better understand the processes and applications that occur on a molecular and sub-molecular scale. Developing this better understanding has allowed us to create medicine and computers, begin exploring space and understanding the atom and is a never-ending process of asking questions and testing hypotheses as we work toward an increasingly objective answer. The best that I can hope for, not only in my time in graduate school, but as I move forward in life, is that I have moved this understanding, even in the slightest, in the correct direction. This may be a small impact, but much of the work presented in this dissertation will focus on small things. Two significant research directions will be presented along with work on device and process development for characterization. The first major system that will be discussed is the chemical vapor deposition of highly branched silica nanowires that were grown in a single synthetic step as a result of in-situ Cu-catalyst loading. The second research direction involves the investigation into using electrochemical anodization synthesis as a way to target the formation and discovery of ionically conducting materials. The overall link between these research topics involves the focus on solid inorganic materials, with a broad direction of understanding materials systems, process development and optimization, careful characterization, hypothesis generation, and considerations of potential applications and future directions of the materials and techniques being investigated. Systems of interest could loosely be classified as energy related materials. Both systems provided unique and challenging aspects to understanding the synthetic processes involved as products were formed under highly dynamic environments. Additionally, device and process developments were perused to address systematic variables such as instability of products and improve overall reaction design and therefore reproducibility and significance of results. The first system investigated involved the chemical vapor deposition of silicon-based nanowire products. The initial objective of the project was to investigate the unique structures of highly branched nanowires that were grown through in-situ doping of Cu, and investigate their properties and performance as a potential anode material for use in Li-ion battery devices. The synthetic method used, and the unique structures observed were previously reported by the Prieto research group. The hypothesis was that these products were grown as crystalline Si and being catalytically oxidized due to the presence of Cu and Cu3Si post synthesis. The work presented here disproves this hypothesis, instead proposing that the product is grown as the oxide. Due to this new conclusion, the battery application study was no longer pursued, and investigation instead focused on developing and proposing a new growth hypothesis. This new hypothesis involves the formation of a multi-wire backbone, which is believed to be the first report to directly investigate and explain this phenomenon. The second research direction outlines the motivation, theory, and initial outcomes of attempting to develop a new synthetic methodology for ionically conducting materials through electrochemical anodization. While anodization is itself far from a new synthetic method, it has never been used to synthesize the targeted material systems, nor has it been used to pursue the synthesis of ionically conducting materials generally. Much of the discussion will revolve around the background, motivation, and hypotheses relating to this project. This focus is partially due to the limited success of certain research objectives, but the intention is to hopefully highlight the intrinsic value of the synthetic concept and theory behind it, as well as direct future potential research based on what has been learned. The synthetic results and discussion focus on the anodization synthesis of AgI, the morphologies and crystallographic properties of the materials formed, and insights into the synthetic process. The related systems of CuI and CuxS will also be touched upon, as well as attempts to pursue the synthesis of Na3PS4. Throughout these investigations, a variety of side project and collaborations were worked on, but the one of significance that will be included in the final chapter relates to the development of an air-free sample transfer holder. This was developed to allow the air-free transfer of a surface sensitive material between a glove-box and an X-ray photoelectron spectroscopy instrument. This enables more accurate and meaning data to be collected on samples that could otherwise be modified or compromised through exposure to ambient air before analysis.
Open Access
Kinetic, mechanistic, and active site studies of copper metal-organic framework catalyzed nitric oxide generation from S-nitrosoglutathione in water and blood plasma
(Colorado State University. Libraries, 2021) Tuttle, Robert Reeves, author; Reynolds, Melissa M., advisor; Finke, Richard, committee member; Crans, Debbie, committee member; Popat, Ketul, committee member
Catalytic generation of nitric oxide (NO) from endogenous sources by copper-based materials at the surfaces of implanted medical devices improves device performance by promoting vasodilation and inhibiting bacterial adhesion. Oxidation of the endogenous tripeptide S-Nitrosoglutathione (GSNO) to release NO is catalyzed by the copper-based metal-organic framework (MOF) H3[(Cu4Cl)3(BTTri)8] (CuBTTri) in the presence of glutathione (GSH). MOFs are solid-state, crystalline, porous materials composed of metal cation nodes and organic linkers forming three-dimensional structures. MOFs have generated interest as catalysts because of their unparalleled tunability via synthesis (compared to other solids), well-defined structures, coordinatively unsaturated metal sites, and high surface areas. Mechanistic insight into MOF catalysts promises to allow for the directed design of next-generation catalysts via leveraging synthetic tunability. However, because necessary studies to propose reliable reaction mechanisms are rarely reported for MOF catalysts, mechanistic understanding is lacking in the field. This Dissertation works toward a reaction mechanism of CuBTTri catalyzed GSNO to NO conversion in water in the presence of GSH. The strategies used to better understand this mechanism can also generate mechanistic knowledge in other MOF catalysis systems. Chapter I provides a discussion of NO release catalyzed by soluble and insoluble Cu-based species focusing on CuBTTri. Chapter I also introduces MOFs as catalysts and explains the requirements to propose a reliable reaction mechanism. Chapters II and III focus on the development of monitoring methods to quantify [GSNO], [GSH], and [glutathione disulfide] (the other main reaction product, GSSG) in real time in H2O and blood plasma. 1H nuclear magnetic resonance (NMR) and ultraviolet-visible (UV-VIS) spectroscopies can together effectively monitor the NO release reaction. The observation of an inverse dependence on added GSH for CuBTTri versus solvated Cu ions for NO generation shows that the two catalysts operate via different reaction mechanisms. Chapter III shows how the monitoring method in H2O reported in Chapter II can be extended to track the reaction in blood plasma. The observed GSNO to NO reaction stoichiometry is effectively identical in H2O and blood plasma, which indicates that the mechanism does not change in vivo versus the model biological solvent H2O. Hence, mechanistic findings in this dissertation for NO generation in water are likely biologically applicable. Chapter IV establishes the catalytically active Cu sites in CuBTTri for GSNO to NO conversion. Studies comparing the reaction rate (-d[GSNO]/dt) to particle size revealed that ~100% of the observed catalysis is caused by Cu atoms on the external surfaces of CuBTTri particles. Kinetic poisoning studies of CuBTTri particles with potassium cyanide (KCN) and 3,3',3''-phosphanetriyltris (benzenesulfonic acid) trisodium salt (TPPTS) showed that the active sites are kinetically uniform. Fourier transform infrared spectroscopic analysis of CN-poisoned CuBTTri detected Cu(CN)3 and Cu(CN) sites, which correspond to the idealized metal-terminated CuBTTri crystal structure. Size-selective kinetic poisoning studies of CuBTTri using TPPTS measured the active site density to be (1.3 ± 0.4)% of total Cu atoms in 600 ± 400 nm CuBTTri particles. Active site density was used to calculate a normalized turnover frequency for CuBTTri to make informed inter-catalyst comparisons. Chapter V presents the rate law and proposed mechanism for CuBTTri catalyzed GSNO to NO conversion. Four other competing, minimalistic mechanistic hypotheses were considered and disproven. The mechanism proposed is a CuII to formally CuIII redox mechanism with two proton-coupled electron transfer elementary steps. The proposed mechanism exhibits a derived rate law which matches the experimental rate law, has elementary steps which sum to the observed reaction stoichiometry, and provides a reasonable driving force for S-N bond homolysis in GSNO. Future computational and laboratory experiments suggested by the proposed mechanism promise to yield a level of mechanistic understanding for CuBTTri which has traditionally not been achievable for solid-state catalysts.
Open Access
Mechanism-enabled population balances and the effects of anisotropies in the complex Ginzburg-Landau equation
(Colorado State University. Libraries, 2019) Handwerk, Derek, author; Shipman, Patrick, advisor; Dangelmayr, Gerhard, committee member; Oprea, Iuliana, committee member; Finke, Richard, committee member
This paper considers two problems. The first is a chemical modeling problem which makes use of ordinary differential equations to discover a minimum mechanism capable of matching experimental data in various metal nanoparticle nucleation and growth systems. This research has led to the concept of mechanism-enabled population balance modeling (ME-PBM). This is defined as the use of experimentally established nucleation mechanisms of particle formation to create more rigorous population balance models. ME-PBM achieves the goal of connecting reliable experimental mechanisms with the understanding and control of particle-size distributions. The ME-PBM approach uncovered a new and important 3-step mechanism that provides the best fits to experimentally measured particle-size distributions (PSDs). The three steps of this mechanism are slow, continuous nucleation and two surface growth steps. The importance of the two growth steps is that large particles are allowed to grow more slowly than small particles. This finding of large grow more slowly than small is a paradigm-shift away from the notion of needing nucleation to stop, such as in LaMer burst nucleation, in order to achieve narrow PSDs. The second is a study of the effects of anisotropy on the dynamics of spatially extended systems through the use of the anisotropic Ginzburg-Landau equation (ACGLE) and its associated phase diffusion equations. The anisotropy leads to different types of solutions not seen in the isotropic equation, due to the ability of waves to simultaneously be stable and unstable, including transient spiral defects together with phase chaotic ripples. We create a phase diagram for initial conditions representing both the longwave k = 0 case, and for wavevectors near the circle |k| = μ using the average L² energy.
Open Access
Microfluidics for environmental analysis
(Colorado State University. Libraries, 2018) Gerold, Chase T., author; Henry, Charles S., advisor; Krummel, Amber, committee member; Levinger, Nancy, committee member; Finke, Richard, committee member; Dandy, David, committee member
During my graduate dissertation work I designed and utilized microfluidic devices to study, model, and assess environmental systems. Investigation of environmental systems is important for areas of industry, agriculture, and human health. While effective and well-established, traditional methods to perform environmental assessment typically involve instrumentation that is expensive and has limited portability. Because of this, analysis of environmental systems can have considerable financial burden and be limited to laboratory settings. To overcome the limitations of traditional methods researchers have turned to microfluidic devices to perform environmental analyses. Microfluidics function as a versatile, inexpensive, and rapidly prototyped analytical tool that can achieve analysis in field setting with limited infrastructure; furthermore, microfluidic devices can also be used to study fundamental chemistry or model complex environmental systems. Given the advantages of microfluidic devices, the research presented herein was accomplished using this alternative to traditional instrumentation. The research projects described in this dissertation involve: 1) the study of fundamental chemistry associated with surfactant surface fouling facilitated by divalent metal cations; 2) the creation of a microfluidic device to study fluid interactions within an oil reservoir; and 3) the fabrication of a paper-based microfluidic to selectively quantify K+ in complex samples. The first research topic discussed involves observation of dynamic evidence that supports the hypothesized cation bridging phenomenon. Experimental results were acquired by pairing traditional microfluidics with the current monitoring method to observe relative changes to a charged surface's zeta potential. Divalent metal cations were found to increase surfactant adsorption, and cations of increasing charge density were found to have a greater effect on surface charge. Analysis of the experimental data further supports theoretical cation bridging models and expands on knowledge relating to the mechanism by which surfactant adsorption occurs. This work was published in the ACS journal Langmuir (2018, 34 (4), pp 1550–1556). The second project discussed herein focuses on the development of the microfluidic Flow On Rock Device (FORD) that was designed to study fluid interactions within complex media. The FORD was designed to be an alternative to existing fluid modeling methods and microfluidic devices that test oil recovery strategies. Fabrication of the FORD was accomplished by incorporating real reservoir rock core samples into the device. The novelty of this device is due to the simplicity and accuracy by which the physical and chemical characteristics are represented. This project has been accepted for publication pending minor revisions in Microfluidics and Nanofluidics. The final project discussed the creation of the first non-electrochemical microfluidic paper-based analytical device (µPAD) capable of quantitatively measuring alkali or alkaline earth metals using K+ as a model analyte. This device was fabricated by combining distance-based analytical quantification in µPADs with optode nanosensors. Experimental results were obtained using the naked eye without the requirement of a power source or external hardware. The resulting distance-based µPAD showed high selectivity and the capacity to quantify K+ in real undiluted human serum samples. This work has been published in the ACS journal Analytical Chemistry (2018, 90 (7), pp 4894–4900). The research projects briefly described above and thoroughly discussed later within this dissertation were made possible by the utilization of microfluidic devices. These projects investigated various aspects of environmental chemistry without the use of traditional instrumentation or methods. The experimental results that were obtained further the fundamental understanding of surfactant adsorption, provide an inexpensive and accurate model to observe fluid interactions within reservoir rock material, and allow for the selective quantification of K+ in a paper-based device without the use of a power source. The funding for each of these projects was supplied by BP plc and Global Good, as is mentioned accordingly within this dissertation.
Open Access
Molecular dynamics simulations of peptide and protein systems
(Colorado State University. Libraries, 2021) Weber, Ryan Nicholas, author; McCullagh, Martin, advisor; Szamel, Grzegorz, committee member; Finke, Richard, committee member; Wang, Qiang, committee member
Molecular systems composed of amino acids play an important role in biological systems and have numerous functions and applications due to their enormous chemical versatility. These systems are usually divided into peptides and proteins based on the number of amino acids that compose each molecule. Molecular dynamics simulations can provide molecular-level insights into the self-assembly of peptide systems and the function of protein systems where experimental methods fail. Peptides are utilized for their switchable and self-assembling properties for the engineering of novel biomaterials which are responsive to external stimuli. Often, peptides are paired with aromatic molecules to incorporate interesting optoelectronic properties into the material. Chapter 2 discusses a molecular dynamics simulation study on the self-assembling properties of the self-complimentary (RXDX)4 sequence paired with an unnatural coumarin amino acid for the design of a pH-switchable, optoelectronic, self-assembling biomaterial. Specifically, it is found that the hydrophobicity of the peptide sequence plays a significant role in the stability and pH-switchability of (RXDX)4 and coumarin-(RXDX)4 β-sheet fibers. Proteins are essential to all known life and participate in nearly every cellular process. There are many varieties of proteins with important diverse functions. Helicase proteins hydrolyze NTP to catalyze the translocation and unwinding of double-stranded nucleic acids such as RNA and DNA and play a critical and extensive role in viral replication. Nsp13 is a helicase protein that is an important component of the viral replication machinery of the severe acute respiratory syndrome coronavirus-2 and remains a promising target for antiviral drugs. Chapter 3 presents a molecular dynamics simulation study on the ATP-dependent translocation mechanism of the SARS-CoV-2 nsp13 helicase. Specifically, the results from the study suggest that nsp13 may translocate using an inchworm stepping mechanism and that the binding of ATP may cause the first step in the translocation cycle. Motifs Ia, IV, and V are identified as key motifs in the translocation mechanism of nsp13 and as potential targets for the development of antiviral drugs against SARS-CoV-2. Although molecular dynamics simulation is a powerful approach to investigate condensed phase molecular phenomenon such as protein folding, allostery, and self-assembly, molecular dynamics is limited in the size and length of simulations that can be performed. Implicit solvent simulation methods, such as Implicit Solvation using the Superposition Approximation (IS-SPA), were developed to address these issues in solvated systems. The goal of IS-SPA is to improve the efficiency of molecular dynamics simulations by removing the solvent from the system, but still include the effect of the solvent on the solute. Chapter 4 presents the development and optimization of an IS-SPA molecular dynamics code on a GPU using CUDA. Specifically, the performance of three different IS-SPA CUDA algorithms are compared. The future studies of the self-assembly of peptide systems for the design of biomaterials, the ATP-dependent translocation mechanism of the SARS-CoV-2 nsp13, and the optimization of the GPU-capable IS-SPA molecular dynamics code in CUDA are discussed in the final chapter.
Open Access
Nitric oxide generation from S-nitrosothiols via interactivity with polymer-supported metal-organic frameworks
(Colorado State University. Libraries, 2018) Neufeld, Megan J., author; Reynolds, Melissa, advisor; Chen, Eugene, committee member; Finke, Richard, committee member; Kipper, Matthew, committee member; Ravishankara, A. R., committee member
Catheters, extracorporeal systems, stents, and artificial heart valves are all common blood-contacting medical devices. Due to the differences in the chemical and physical properties of the polymeric materials used to construct medical devices and biological tissues in the cardiovascular system, complications such as thrombus formation arise from the resulting incompatibilities. Introduction of foreign materials that lack critical biological cues can result in disruption of the delicate balance maintained within the circulatory system. This disruption of homeostasis initiates a complex cascade of events such as platelet adhesion and protein deposition that ultimately result in thrombus formation. As such, the propensity of blood to clot upon contact with a foreign surface represents a challenge unique to devices intended for vascular applications. The current clinical use of devices such as vascular catheters includes the administration of anticoagulants, however their associated complications such as internal hemorrhaging renders this practice undesirable as a long-lasting solution. A general limitation of existing devices made from synthetic polymers is their inability to integrate with their environment through biological cues (natural regulators). Materials that lack this behavior are often described as passive towards their environment. In comparison, active materials that can simulate natural molecules used to maintain biological responses may result in enhanced integration of medical devices. In the natural, healthy endothelium, the prevention of thrombus formation occurs through the release of anticoagulants and platelet inhibitors such as gaseous nitric oxide (NO). While the use of NO for medicinal purposes began indirectly in the late 1800s, the significance of its endogenous production was not known until the 1970s. In particular, NO is a key factor in the prevention of thrombus formation. While its remedial potential has led to its use as an exogenous therapeutic agent, its high reactivity limits its applicability as a localized therapeutic. This limitation is addressed by mimicking the natural endothelium and using small molecules in the bloodstream known as S-nitrosothiols (RSNOs) to produce NO directly from this physiological source. Biological RSNOs are theorized to aid in the stabilization and transport of NO and undergo an NO-forming decomposition in the presence of heat, light, and certain metals such as copper. Prior strategies have evaluated exploiting the physiological supply of RSNOs through the incorporation of copper complexes into polymeric materials. While these copper-based materials demonstrate the production of NO from RSNO decomposition, limitations arise due to the gradual loss of the catalytic material and toxicity from copper leaching. In order for this type of approach to be feasible, the active metal species must remain immobilized within the structural framework. Metal–organic frameworks (MOFs) are a class of crystalline materials that consist of organic ligands coordinated to metal centers. Certain copper-based MOFs have demonstrated the ability to enhance the generation of NO from RSNOs without the gradual loss of the active species. Through integration of certain copper-based MOFs with medically relevant polymers, materials can be prepared that promote the localized generation of NO at their surfaces. However, the feasibility of utilizing copper-based MOFs for such applications depends on effective incorporation within a supporting polymeric matrix and the retention of useful activity thereafter. As such, it is necessary to assess different MOF/polymer composites for their ability to promote NO generation from RSNOs prior to use in medical applications. This dissertation investigates the incorporation of two distinct copper-based MOFs into a selection of medically-relevant polymeric materials including cotton, poly(vinyl chloride), chitosan, and poly(vinyl alcohol). These MOF/polymer materials were subsequently tested for their ability to promote NO generation from RSNOs in an effort to assess the impact of incorporation within a polymer matrix. Overall, this work demonstrates the potential for blood-contacting MOF-containing materials in biomedical settings by identifying ideal characteristics that MOF/polymer composites should exhibit for optimization and translation to a clinical setting.
Open Access
Nonlinear dynamics of plant pigmentation
(Colorado State University. Libraries, 2022) Hsu, Wei-Yu, author; Shipman, Patrick, advisor; Mueller, Jennifer, committee member; Bradley, Richard, committee member; Finke, Richard, committee member
Red, blue, and purple colors in plants are primarily due to plant pigments called anthocyanins. In a plant cell, an equilibrium is established between anionic and cationic forms of anthocyanins as well electrically neutral colorless forms called hemiketals. In typical cellular pH ranges, the colorless hemiketal would be expected to be the dominant form. Why then, do plants, in fact, display colors? We propose that this is part due to self association and intermolecular association of the colored forms of anthocyanins. We develop a series of models for the interconversion of the colorless and colored forms of anthocyanins, including zwitterionic species and extend these models to include association of the colored species. Analysis of these models leads us to suggest and implement experiments in which the total concentration changes over time, either slowly or quickly compared to the kinetics. Coupling these models to a system of partial differential equations for in vivo anthocyanin synthesis (a modification of the Gierer-Meinhardt activator-inhibitor model), we simulate and analyze a variety of colorful spotted patterns in plant flowers. These studies are aided by a linear stability analysis and nonlinear analysis of the modified Gierer-Meinhardt model. The extended model that we propose is a first model to analyze the effects of association in pattern formation. Association may occur with various geometries which have an effect on the absorbance spectrum. Based on the Beer–Lambert law and our evaporative experiments, we develop methods of deconvoluting absorbance spectra of anthocyanin solutions into absorbance spectra of monomers, dimers and trimers, thus providing clues into the geometry of the smallest associated particles. Finally, we propose a novel geometric method of probing association by observing the changing shape of evaporating solution droplets. The associated mathematical model involves solving the highly nonlinear mean-curvature equation with nonconstant mean curvature (surface tension), and we present new solutions making use of the hodograph transform.
Open Access
Part I: Structural characterization of doped nanostructured magnesium: understanding disorder for enhanced hydrogen absorption kinetics. Part II: Synthesis, film deposition, and characterization of quaternary metal chalcogenide nanocrystals for photovoltaic applications
(Colorado State University. Libraries, 2017) Braun, Max B., author; Prieto, Amy, advisor; Finke, Richard, committee member; Rappe, Anthony, committee member; Neilson, James, committee member; de la Venta, Jose, committee member
The production, storage, and subsequent consumption of energy are at the foundation of all human activity and livelihood. The theme of this dissertation is the pursuit of fundamentalunderstanding of the chemistry of materials that are used for energy production and storage. A strong emphasis is placed on a synthetic foundation that allows for systematic investigation into the fundamental chemistry that controls the applicable properties of the materials of interest. This dissertation is written in the "journals format" style—which is accepted by the Graduate School at Colorado State University—and is based on one peer-reviewed publication that has appeared in Chemistry of Materials as well as two manuscripts to be submitted, one to The Journal of Physical Chemistry C, and one to ACS Applied Materials and Interfaces. In order to create a context forthese publications, Chapters 1 and 3 provide an overview of the motivations for the projects, and then continue to detail the initial synthetic investigations and considerations for the two projects. In addition to recounting Mg nanocrystals synthetic refinement that was necessary for reproducible hydride kinetic analysis, Chapter 1 also briefly introduces some of the conventional models used for fitting of the hydriding kinetics data. Furthermore, initial investigations into the use of these models for our system are presented. Chapter 2 is a paper to be submitted to The Journal of Physical Chemistry C that describes the local and extended structure characterization of Mg nanocrystals (NCs) with a small amount of nickel added during synthesis. Ni has a dramatic effect on the de/hydriding kinetics of Mg NCs, and this chapter describes the use of a combination of multiple state-of-the-art characterization techniques to gain insight into the structural perturbations due to Ni inclusion in the Mg NCs. This insight is then used to establish the characteristics of Ni inclusion that results in the enhanced hydrogen absorption processes. Chapter 3 introduces the many considerations needed to be taken into account during the development of a novel synthesis for copper zinc tin chalcogenide colloidal nanocrystals. In addition to introducing synthetic approaches to achieve this goal, Chapter 3 also describes essential characteristics that need to be considered for further investigation into the properties of films made from the nanocrystals. Chapter 4 is a publication that appeared in Chemistry of Materials, that describes an approach to tuning the surface and ligand chemistry of Cu2ZnSnS4 nanocrystals for use as an absorber layer in next generation photovoltaic devices. The publication describes ligand exchange chemistry achieved via layer-by-layer dip-casting of nanocrystal thin films, and the effects that this exchange chemistry has on the resulting films. It also details the fabrication of full photovoltaic (PV) devices to characterize the benefits of controlling the surface chemistry can have on PV performance. Chapter 5 is a paper—to be submitted to ACS Applied Materials and Interfaces—that describes the investigations into how varying the chalcogen ratio (i.e., S:Se) leads to changes in the physical and electrical properties of thin films made from Cu2ZnSn(S1-xSex)4 (where 0 < x < 1) NCs. It highlights the novel synthetic procedure (detailed in chapter 3) that was required for a systematic, deconvoluted evaluation of S:Se composition on the materials optical and electronic properties. Moreover, the characteristics of full PV devices based on thin films of each stoichiometry (x=0 to x=1) are assessed to establish a relationship between composition and the materials performance.
Open Access
Quantification and application of uncertainty in the formation of nanoparticles
(Colorado State University. Libraries, 2023) Long, Danny, author; Bangerth, Wolfgang, advisor; Shipman, Patrick, committee member; Liu, Jiangguo, committee member; Finke, Richard, committee member
Nanoparticles are essential across many scientific applications, but their properties are size-dependent. Despite the usefulness of producing monodisperse particle size distributions, it still remains a challenge to fully understand – and hence be able to control – nanoparticle formation reactions due to limitations in what can be observed experimentally. This thesis transfers mathematical, statistical, and computational techniques to this area of nanoparticle chemistry to substantially bolster the sophistication of the quantitative analysis used to better understand nanoparticle systems. First, more efficient software is developed to simulate the reactions. Then, parameter estimation is performed in a robust manner through Bayesian inference, where I demonstrate the ability to parameterize nonlinear ordinary differential equations in such a way that I can fit the observed data and quantify the uncertainty in the parameter estimates. From Bayesian inference, I build three additional analysis frameworks. (1) Model selection through a Bayesian framework; (2) optimizing the yield of the nanoparticle-forming reactions while accounting for uncertainty; and (3) optimizing future measurements to collect data providing the most new information. The culmination of this thesis provides a quantitative framework to analyze arbitrary nanoparticle systems to complement and fill in the gaps of the current experimental techniques.
Open Access
Residency of rhenium and osmium in a heavy crude oil
(Colorado State University. Libraries, 2017) DiMarzio, Jenna, author; Stein, Holly, advisor; Hannah, Judith, advisor; Georgiev, Svetoslav, committee member; Finke, Richard, committee member
The Re-Os geochronometer is an emerging tool for the study of oil formation and migration processes, and a new technology for petroleum exploration. Very little is known, however, about the residency of Re and Os within asphaltene and maltene sub-fractions of crude oil. This information is crucial for better understanding of petroleum systems in general, and especially for successful geochronology of key processes such as oil formation, migration, or biodegradation. In this work, a heavy crude oil was separated into soluble (maltene) and insoluble (asphaltene) fractions using n-heptane as the asphaltene-precipitating agent. The asphaltenes were separated sequentially into sub-fractions using two different solvent pairs (heptane-DCM and acetone-toluene), and the bulk maltene was separated into saturate, aromatic, and resin (SAR) fractions using open column chromatography. Each asphaltene and maltene sub-fraction was analyzed for Re and Os. The asphaltene sub-fractions and bulk samples were analyzed for a suite of trace metals by ICP-MS. Our results show that Re and Os concentrations co-vary between the asphaltene sub-fractions, and that both elements are found mostly in the highly polar, highly aromatic sub-fractions; significant Re and Os are also present in the aromatic and resin fractions of the maltenes. However, each asphaltene and maltene sub-fraction has a distinct isotopic composition, and these sub-fractions are not isochronous. This may suggest that asphaltene sub-fractionation separates Re-Os complexes to the point that the isotopic integrity of the geochronometer is undercut. The decoupling possibilities of radiogenically produced 187Os from Re remain elusive, and more work is needed to determine the mobility of radiogenically produced 187Os. Re-Os and Ni-V budgets track each other, suggesting that some Re and Os may form metalloporphyrins. On the other hand, Re correlates strongly with Mo and Cd in the asphaltene sub-fractions; as Re and Os track each other, this suggests that Re-Os, Mo, and Cd occupy similar sites. Finally, we suggest that progressive asphaltene precipitation during migration and mixing of oils can change the resultant oil's isotopic ratios. This is key to interpretation of Re-Os data for tar mats and live oils, whether the data form an isochron or scatter. By combining data from source rocks, oils, and asphaltenes generated along the migration pathway, we are constructing temporal histories for whole petroleum systems.
Open Access
Synthesis and characterization of multidentate iminopyridine and polypyridine transition metal complexes
(Colorado State University. Libraries, 2013) McDaniel, Ashley M., author; Shores, Matthew, advisor; Anderson, Oren, committee member; Borch, Thomas, committee member; Finke, Richard, committee member; Rickey, Dawn, committee member
The work described in this dissertation details the syntheses and characterization of transition metal complexes featuring polypyridyl and iminopyridine ligands. The primary focus has been the synthesis of 3d metal complexes of multidentate iminopyridine ligands bearing functionalizations relevant to spin crossover and photochemistry. These seemingly disparate areas of research are linked by the facts that subtle metal-ligand interactions play enormous roles in determining complex properties and that understanding these types of interactions is crucial for eventual property control. In Chapter 1, the underpinnings of spin crossover in transition metals with d4-d7 configurations are discussed along with progress toward linking spin-switching events with host-guest interactions in solution. My research on Fe(II) hexadentate iminopyridine complexes is placed into context with extending anion sensing to biologically and environmentally relevant media. Also in Chapter 1, my work on hexadentate iminopyridine and polypyridine Cr complexes is related to the current understanding of the excited state behavior of 3d iminopyridine complexes, specifically, and 3d aromatic diimines in general. Additionally, the redox non-innocence of iminopyridine and polypyridine ligands is discussed. In Chapter 2, the preparation and characterization of a series of divalent 3d transition metal complexes (Cr to Zn), featuring an ester functionalized multidentate, tripodal iminopyridine Schiff-base L5-OOMe is reported. X-ray structural studies reveal complex geometries ranging from local octahedral coordination to significant distortion towards trigonal prismatic geometry to heptacoordinate environments. Regardless of coordination mode, magnetic and spectroscopic studies show the ligand to provide moderately strong ligand fields: the Fe complex is low-spin, while the Co and Mn complexes are high-spin at all temperatures proved. Cyclic voltammograms exhibit multiple reversible ligand-based reductions, which are relatively consistent throughout the series; however, the electrochemical behavior of the Cr complex is fundamentally different from those of the other complexes. Time-dependent (TD) DFT and natural transition orbital (NTO) computational analyses for the ligand, its anion, and complexes were provided by Prof. Anthony Rappé: the computed spectra reproduce the major differential features of the observed visible absorption spectra, and NTOs provide viable interpretations for the observed features. The combined studies indicate that for Mn-Zn complexes, neutral ligands are bound to M(II) ions, but Cr is best described as a Cr(III) species bound to a radical anionic ligand. In Chapter 3, the syntheses and characterizations of Fe(II) complexes of hexadentate ligands poised for anion-triggered spin-state switching in polar solution media are reported. The tripodal iminopyridine ligands L5-OH, L6-OH and L5-ONHtBu, L6-ONHtBu contain methanolic or t-butylamide functional groups, respectively. Solid-state evidence for anion-cation hydrogen bonding interactions are observed for halide complexes of [Fe(L6-OH)]2+ and [Fe(L5-ONHtBu)]2+; [Fe(L5-ONHtBu)]2+ forms a preorganized pocket which strongly binds Cl-. Strong anion binding events in the 5-position complexes are also observed in solution via 1H NMR monitored chloride titrations in acetonitrile. And while no temperature dependence or anion dependence on spin-state is apparent for 6-position complexes in solution, a small but significant increase in magnetic susceptibility is observed for [Fe(L5-ONHtBu)]2+ as up to one equivalent of tetrabutylammonium chloride is added; suggesting that spin-state control by anion-cation interactions may be accessible for this class of compounds. In Chapter 4, the preparation and characterization of homo- and heteroleptic Cr(III) coordination complexes featuring the dimethyl 2,2'-bipyridine-4,4'-dicarboxylate (4-dmcbpy) ligand are discussed. Static and nanosecond time-resolved absorption and emission properties of these complexes dissolved in acidic aqueous (1 M HCl(aq)) solutions were investigated by Huan-Wei Tseng and Prof. Niels Damrauer. The photophysical data suggest that in these acidic aqueous environments these complexes store ~1.7 eV for multiple microseconds at room temperature. The electrochemical properties of these polypyridyl complexes were investigated by cyclic voltammetry. It is found that inclusion of 4-dmcbpy shifts the 'CrIII/II' E1/2 by +0.22 V compared to those of homoleptic parent complexes. The electrochemical and photophysical data allow for excited state potentials to be determined: for [Cr(4-dmcbpy)3]3+, CrIII*/II lies at +1.44 V versus Fc+/0 (~+2 V vs NHE), suggesting it would act as one of the most powerful photooxidants reported. In Chapter 5, the preparation, photophysical characterization, and computed excited state energies for Cr(III) complexes of a family of tripodal hexadentate and tris(bidentate) iminopyridine ligands are reported. Cyclic voltammograms reveal that the hexadentate and tris(bidentate) analogues have almost identical reduction potentials, and overall electrochemical behavior similar to the polypyridyl complexes described in Chapter 3. The absorption spectra of the hexadentate complexes show improved absorption of visible light compared to the tris(bidentate) analogues. Photophysical characterization provided by Huan-Wei Tesng and Prof. Niels Damrauer show a doublet excited state with 17 to 19 μs lifetime at room temperature for the ester functionalized tris(bidentate) complex, while no doublet states are observed for the ester functionalized hexadentate analogue under the same conditions. The electronic structure contributions to the differences in observed photophysical properties are compared by extensive computational analyses provided by Prof. Anthony Rappé. These studies indicate that the presence of non-ligated bridgehead nitrogen atoms in the complexes of tripodal hexadentate iminopyridines significantly reduce excited state doublet, quartet, and sextet energies and change the character of the low lying doublet states in compared to species that show population of doublet excited states. In Chapter 6 the syntheses and characterization of reduced forms of Cr complexes of 4-dmcbpy (described in Chapter 4), [Cr(4-dmcbpy)3]n+ (n = 2, 1), and tren(py)3 (L1, described in Chapter 5) [Cr(tren(py)3)]n+ (n = 2) are reported. Comparison of electrochemical data for the series (n = 3, 2, 1) and solid state structures of the divalent complexes are consistent with consecutive reducing equivalents added to Cr polypyridine or iminopyridine complexes not residing on the metal, and that these complexes are best described as Cr(III) ions ligated to anionic radical ligands. Final remarks about the work in Chapters 2-6 and suggested directions for future work are presented in Chapter 7.
Open Access
Synthesis, postsynthetic modification, and investigation of metal-organic frameworks for environmental and biological applications
(Colorado State University. Libraries, 2018) Rubin, Heather N., author; Reynolds, Melissa, advisor; Chen, Eugene, committee member; Finke, Richard, committee member; Van Orden, Alan, committee member; James, Susan, committee member
Metal-organic frameworks (MOFs) are unique porous coordination polymers having record-high surface areas, and tunability at both the organic linkers and metal ions. As such, MOFs are advantageous for various applications including electronics, gas adsorption, and separations amongst others. Despite the advantages associated with MOFs, there are several key challenges that must be addressed in order to broadly expand the practicality of these materials. Such challenges include synthetic pitfalls, structural instability, selectivity, and inefficient heterogeneous catalysis. For instance, most MOFs are not stable in moisture-rich environments, which leads to structural collapse even in the open atmosphere. This instability poses a serious limitation for useful applications. In addition, the synthesis of MOF-related ligands is underdeveloped, which can lead to costly or inaccessible materials. To overcome these challenges, one goal of this research is to develop a solution to enhance the kinetic stability of MOFs to water and another is to execute an efficient and cost-effective synthetic strategy to generate the MOFs used herein. CuBTC (copper benzene-1,3,5-tricarboxylate), a commercially available MOF that has been well-studied and designated as having great potential for many applications, undergoes rapid degradation in humid atmospheres. Therefore, a novel synthetic approach was developed to efficiently access NH2BTC on gram-scale. Postsynthetic modification to the amine of the MOF powder material enhances the kinetic stability of the MOF to water. A distinct linear relationship between the number of carbons in the modification and observed water contact angle is described for the first time. This facilitates the first report of reliable access to mixed-ligand frameworks with predictable, calculated wettability and tunable kinetic stability to water. This work is also the first report of functionalizing copper MOFs as well as MOFs containing a benzene-1,3,5-tricarboxylate ligand to alter hydrophobic characteristics. That initial work inspired further exploration of CuNH2BTC as an antibacterial surface when synthetically grown on the surface of carboxymethylated cotton. The resultant material is capable of tunable Cu2+ ion release (via postsynthetic modification) and exceeds current industry standards for antibacterial agents, exhibiting a log-3 or greater reduction in bacteria both on the surface and in solution. As the scientific community continues to explore and understand MOFs, the implementation of these materials for various applications is dramatically increasing. As such, the second part of this research was devoted to applying and manipulating MOFs to better understand the interactions of MOFs with small molecules and ions. The photophysical properties of CuNH2BTC were investigated and specific interactions between anions and metal ions with MOFs were identified, encouraging the strategic design of MOFs to detect target-analytes via changing fluorescence emission properties in dimethylformamide (quenching or enhancing emission intensity or changing emission wavelength). This work provides a prerequisite study towards the development of improved next-generation MOF chemosensors. In addition, the open coordination site of thermodynamically stable porphyrin-based MOFs was exploited for simultaneous heavy metal detection and metal ion removal from aqueous solutions. Lastly, to better understand heterogenous catalysis with MOFs in biologically relevant media water, a 1HNMR method with solvent suppression was implemented and allows for kinetic and mechanistic studies of biologically relevant MOF-catalyzed decomposition of GSNO with thermodynamically stable MOF CuBTTri in H2O and eventually in blood. As a whole this research provides valuable insights as to how MOFs may be strategically designed, manipulated, and utilized for sensing, catalysis, and antibacterial applications.
Open Access
The progress towards the total synthesis of (ent)-MPC1001
(Colorado State University. Libraries, 2011) Schuber, Paul, author; Williams, Robert M., advisor; Crans, Debbie, committee member; Finke, Richard, committee member; McNaughton, Brian, committee member; Slayden, Richard, committee member
Herein are my efforts toward the total synthesis of (ent)-MPC1001, beginning with the development of a novel asymmetric [1-3]-dipolar cycloaddition utilizing a vinyl silane and a chiral lactone template. The mechanism of the cycloaddition was investigated and the cyclized product can be elaborated in 6 steps to the A-B-C ring system of the MPC family of natural products. However, the key ring-closing metathesis reaction provided irreproducible results. Therefore, a macrolactonization was utilized to synthesize an advanced lactone derivative. Current research is focused on the elaboration of the lactone to the oxepin ring. Efforts were also focused on the development of a novel β-hydroxy-α-amino acid derivative to be used in the preparation of analogues of the natural product (ent)-MPC1001. The amino acid was efficiently prepared in six steps via a Mukaiyama aldol reaction by a chiral oxazinone and 3-bromo-4-methoxybenzaldehyde. With the dipole product and the β-hydroxyl-α-amino acid derivative in hand, efforts were focused on the coupling of the two components to afford the DKP. Research was also focused on the installation of the diaryl ether portion of (ent)-MPC1001 as well as an interesting dimerization reaction. The dimerization reaction can serve as a point of divergence to the aronotin family of natural products.
Open Access
The total synthesis of the baulamycins
(Colorado State University. Libraries, 2019) Thielman, Jonathan Rhines, author; Williams, Robert M., advisor; Bandar, Jeffrey, committee member; Finke, Richard, committee member; Slayden, Richard, committee member
Described herein are the total syntheses of the antibiotic polyketides baulamycin A and baulamycin B. A synthesis giving rise to much of the baulamycins' initially-proposed structures is also described.
Open Access
The use of coordinating solvents in gold cluster synthesis
(Colorado State University. Libraries, 2016) Compel, W. Scott, author; Ackerson, Christopher J., advisor; Finke, Richard, committee member; Krapf, Diego, committee member; Prieto, Amy, committee member; Reynolds, Melissa, committee member
Monolayer-protected clusters (MPCs) are nanoparticles ca. 1-3 nm in diameter composed of a metal core and an organic monolayer shell. In this size range MPCs are larger than metal-ligand complexes but too small to exhibit a surface plasmon resonance. The electronic structures of particles in this size regime resemble discrete molecular orbital energy levels as opposed to the band-like behavior observed in larger, plasmonic nanoparticles. MPCs are composed of ten to a few hundred atoms and can be characterized as simple chemical compounds with discrete molecular formulae as opposed to average particle diameters. In these systems, addition or removal of a single metal atom profoundly affects stability and observed properties. This phenomenon gives rise to an exceptionally diverse class of materials with seemingly endless potential evolving from minute compositional changes. Thiolate-protected gold clusters are exemplary MPCs due to their intrinsic high stability that allows for long-term studies and post-synthetic modification. These clusters exhibit unique physiochemical properties that allow for potential applications in electronics, catalysis, biomedicine, and sensing. The past two decades since their discovery brought about a significant body of research regarding the origin of Au cluster properties and total structure elucidation. However, modern approaches for Au cluster synthesis produce polydisperse mixtures of clusters that must undergo extensive postreaction ripening or fractionalization to obtain a pure, single product. New synthetic approaches for monodisperse Au clusters in high yield must be developed before their applications may be realized. The motivation behind this work was to explore the issue of polydispersity in Au cluster synthesis. Through combinatorial screening of synthetic co-solvent systems we find that synthesis in coordinating solvents (i.e., glymes) greatly enhances the monodispersity of Au cluster products. During synthesis, glyme chelates the metal in the metallopolymer precursor and modifies the surface of the resulting particle, resulting in a new series of metastable Au clusters. The synthetic methods presented herein result in pure, single products in high yield. The surface modification brought about by diglyme potentially renders the clusters available for single-ligand functionalization to tailor cluster properties for desired functionality. The products are evaluated for biomedical and sensing applications.
Open Access
Towards elucidating photochemical reaction pathways in nickel catalyzed cross coupling and organocatalyzed Birch reduction
(Colorado State University. Libraries, 2021) Kudisch, Max, author; Miyake, Garret, advisor; Finke, Richard, committee member; Chung, Jean, committee member; Reisfeld, Brad, committee member
Carbon-nitrogen (C─N) bond forming reactions to couple aryl halides with amines are essential for the discovery and production of medicinal compounds. The state-of-the-art method uses a precious metal palladium catalyst at high temperatures which poses sustainability concerns. Recently, a method was reported in which an iridium photocatalyst (PC) works in tandem with a nickel catalyst under blue light irradiation to achieve C─N bond formation at room temperature. Herein, it was discovered that the iridium PC could be omitted if 365 nm light is used, constituting a precious metal-free approach. This discovery suggests that a nickel-centered excited state can mediate C─N bond formation, raising the possibility of an energy transfer type pathway in dual catalytic systems. The nickel complexes formed were identified for the first time and mechanistic evidence was found that is consistent with energy transfer with both [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) and a phenoxazine PC. A series of [NiBr2(amine)n] complexes were isolated, characterized, and detected in C─N coupling reaction mixtures. A theoretical framework for predicting energy transfer rate constant ratios based on Förster theory and UV-visible spectroscopy was developed. The phenoxazine PC was both predicted and found to exhibit faster energy transfer and enhanced reaction performance when compared with [Ru(bpy)3]2+. In addition, a light-driven, organocatalyzed system for Birch reduction was developed. Historically, Birch reduction to reduce an arene to a 1,4-cyclohexadiene has been limited by the required use of alkali metals which are pyrophoric and can be explosive. Under violet light, a benzo[ghi]perylene imide PC was found to reduce challenging arenes such as benzene, constituting the first visible light driven approach capable of this reactivity. Mechanistic studies were performed that are consistent with a catalytic cycle involving addition of OH─ to the PC to form an adduct, [PC─OH]─. Photolysis of the adduct forms OH• and the PC radical anion which subsequently undergoes photoionization, ejecting a solvated electron that reduces the substrate.