Mask-wearing emerged as the primary safety measure to prevent spreading COVID-19. During the COVID-19 pandemic, there was growing evidence that SARS-CoV-2 could spread by aerosol transmission. Thus, increased understanding of mask performance was important to help reduce viral transmission. In addition, the CDC recommended wearing double masks to provide better fit and additional protection when people could not access respirators. This thesis aims to investigate the performance of single mask and double mask combinations, and using a parallel resistance model to quantify leakage.
\r\n \r\nMultiple copies of different mask types were tested: N95 respirators, KN95 respirators, procedure masks, and cloth masks. For all of the single masks, the penetration increased with flow rate, while the most penetrating particle size (MPPS) generally decreased. The peak penetration is lowest for N95 respirators, and the peak penetration is highest for cloth masks at all flow rates. For double masking, we observe that wearing a combination of cloth and procedure masks has a higher amount of decreased penetration and a lower amount of increased pressure drop than a combination involving N95 and KN95 respirators. For quantifying leakage, a parallel resistance model was used to calculate the resistance for leaks. The procedure and cloth masks had lower resistance for leaks and leakage flow rates than N95 and KN95 respirators. The procedure and cloth masks are more susceptible to leaks than respirators and thus reducing the effectiveness of these masks.
" }, { "name": "Du, Yun Emily", "degree": "Senior Thesis", "year": "2022", "title": "Surveying Notions of Queer Asian American Community Through Literature: 1972\u20131998", "advisor": "Dykstra, Maura", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082022-220335559", "creators": [ { "name": { "family": "Du", "given": "Yun Emily" }, "id": "Du-Yun-Emily", "orcid": "0000-0003-0634-910X", "display_name": "Du, Yun Emily" } ], "advisors": [ { "name": { "family": "Dykstra", "given": "Maura" }, "id": "Dykstra-M", "orcid": "0000-0001-6036-6440", "role": "advisor", "display_name": "Dykstra, Maura" } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "chemistry", "history" ], "doi": "10.7907/43ya-7t94", "abstract": "The history of queer Asian America has, to date, largely been studied as a history of organizations. This has lent a particular tilt to both the preservation and the study of queer Asian America: the activism of the late 20th century has been archivally and academically preserved, while records of everyday queer Asian American experiences -- of the ways individuals discovered their identities, formed communities, found loves, and filled their days -- have been more rarely preserved and written of. This thesis seeks to fill that gap by analyzing the history of queer Asian American literature. Specifically, the thesis offers a broad survey of queer Asian American writing from the 1970s through the 90s. It then uses methods of literary and historical analysis to shed light on how individuals have grappled with the question of what it means to be queer and Asian American. Ultimately, the thesis turns to the queer Asian American community and asks, \"Who are 'we'?\"
" }, { "name": "Zhou, Andrew Z.", "degree": "Senior Thesis", "year": "2021", "title": "Biocatalytic Lactone Carbene C\u2013H, B\u2013H, and N\u2013H Insertion Reactions Enabled by Directed Evolution", "advisor": "Arnold, Frances Hamilton", "url": "https://resolver.caltech.edu/CaltechThesis:06232021-201833496", "creators": [ { "name": { "family": "Zhou", "given": "Andrew Z." }, "id": "Zhou-Andrew-Z", "orcid": "0000-0002-1763-7353", "display_name": "Zhou, Andrew Z." } ], "advisors": [ { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "advisor", "display_name": "Arnold, Frances Hamilton" } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "chemistry" ], "doi": "10.7907/zqcp-jt95", "abstract": "Enzymes are biological catalysts, and they accelerate reactions by lowering the activation barrier. In nature, enzymes have been optimized by natural selection and possess precise three-dimensional active sites. With these active sites, they can typically catalyze reactions with high efficiency and specificity. Compared to traditional catalysts, enzymes are generally more environmentally friendly, and they can catalyze reactions in water and at ambient temperature and pressure. However, native enzymes are usually only well suited for a restricted range of substrates and are limited in the types of reactions they perform. The Arnold lab has recently focused on endowing enzymes with the ability to catalyze new-to-nature reactions through directed evolution. Here, we present a set of enzymes engineered for the ability to insert a lactone carbene into B\u2013H, C\u2013H, and N\u2013H bonds with high yield and enantioselectivity. B\u2013H insertion is achieved by engineered cytochrome c enzymes, while N\u2013H and C\u2013H insertions are achieved by engineered cytochrome P450 enzymes. With this work, we expand nature\u2019s toolbox for lactone insertion chemistry. Since lactones are highly bioactive, these engineered enzymes could be powerful tools in the synthesis of a range of pharmaceuticals and natural product targets." }, { "name": "Aksenfeld, Rita Beth", "degree": "Senior Thesis", "year": "2020", "title": "Investigating the Functional Significance of O-GlcNAc Substrate/Interactor Networks", "advisor": "Hsieh-Wilson, Linda C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06092020-142540694", "creators": [ { "name": { "family": "Aksenfeld", "given": "Rita Beth" }, "id": "Aksenfeld-Rita-Beth", "orcid": "0000-0002-2911-9211", "display_name": "Aksenfeld, Rita Beth" } ], "advisors": [ { "name": { "family": "Hsieh-Wilson", "given": "Linda C." }, "id": "Hsieh-Wilson-L-C", "role": "advisor", "display_name": "Hsieh-Wilson, Linda C." } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "chemistry" ], "doi": "10.7907/gvhh-xf87", "abstract": "O-linked \u03b2-N-acetylglucosamine glycosylation (O-GlcNAcylation) is a dynamic, inducible post-translational modification (PTM) of thousands of intracellular proteins. There are only two enzymes responsible for O-GlcNAc cycling in higher eukaryotes, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), which catalyze addition and removal, respectively. We hypothesized that constructing OGT substrate/interactor networks could serve as a useful foundation for understanding the functions of O-GlcNAcylation. Moreover, this approach might reveal novel insights into how OGT is able to coordinate the specific modification of thousands of proteins in response to individual stimuli.
\r\n\r\nHere, we first sought to validate interactor-substrate relationships suggested by these networks. Specifically, we found that knockdown (KD) of OGT interacting proteins was sufficient to disrupt O-GlcNAcylation of non-interacting OGT substrates. KD of the OGT interacting protein BAP1 changed the O-GlcNAcylation of several of its interactor proteins, many of which do not themselves interact with OGT. This KD strategy was attempted with other potential adaptor proteins such as WDR5 and CDK9, but KD was unsuccessful. KD of the OGT interacting protein GIT1 lead to intriguing changes in the O-GlcNAcylation of liprin-\u03b11. Both of these proteins are vital for synaptic function in excitatory neurons. This result appears significant to the latter protein\u2019s function as it changes with neuronal activity. The aforementioned two findings suggest that association between OGT and its interactors may allow OGT to engage different sets of substrates in different contexts.
\r\n\r\nFurther, we investigated whether modulating global O-GlcNAcylation can affect peroxisome and lipid droplet biogenesis and function, a potentially novel role for O-GlcNAcylation revealed by our network. Together, these studies demonstrate that our networking approach highlights functional connections between OGT interactors and substrates.
" }, { "name": "Johnstone, Christopher Patrick", "degree": "Senior Thesis", "year": "2019", "title": "Control of Aggregated Bacterial Communities through Engineered Surface Displayed Proteins", "advisor": "Tirrell, David A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06102019-011804885", "creators": [ { "name": { "family": "Johnstone", "given": "Christopher Patrick" }, "id": "Johnstone-Christopher-Patrick", "orcid": "0000-0002-7255-0218", "display_name": "Johnstone, Christopher Patrick" } ], "advisors": [ { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "role": "advisor", "display_name": "Tirrell, David A." } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "chemeng" ], "doi": "10.7907/827E-J857", "abstract": "Bacterial aggregation through surface display of cross-associating proteins has previously been demonstrated, but the formation of these aggregates is only controllable and reversible through the addition of chemical inducers or soluble proteins. Here, we present a design for a photoswitchable surface-display system that causes bacterial aggregation. This system should reversibly disaggregate under exposure to blue light. We created our mutant by modifying Photoactive Yellow Protein (PYP), a fluorescent protein that undergoes a large reversible conformational change when exposed to blue light. We computationally designed this mutant to drive photoswitchable sequestration of a cap domain that is designed to selectively aggregate with SynZip18. Characterization of this designed protein's photoactivity was inconclusive due to its limited solubility though the synthesized chormophore, a p-coumaric acid derivative, was capable of reconstituting native photoactive PYP. While we did not show that the designed mutant could cause disaggregation under exposure to blue light, it was capable of selectively aggregating with surface displayed SynZip18 as desired.
" }, { "name": "Cai, Sarah Wang", "degree": "Senior Thesis", "year": "2018", "title": "Elucidating the Mechanism of mRNA Export Regulation by the Nuclear Pore Complex", "advisor": "Hoelz, Andre", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042018-212155038", "creators": [ { "name": { "family": "Cai", "given": "Sarah Wang" }, "id": "Cai-Sarah-Wang", "display_name": "Cai, Sarah Wang" } ], "advisors": [ { "name": { "family": "Hoelz", "given": "Andre" }, "id": "Hoelz-A", "role": "advisor", "display_name": "Hoelz, Andre" } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "chemistry" ], "doi": "10.7907/dca1-n844", "abstract": "The nuclear pore complex (NPC) is one of the largest and most complex protein assemblies in eukaryotic cells, and it facilitates and regulates the bidirectional transfer of molecules between the nucleus and cytoplasm. One of the essential functions of the NPC is to directly regulate the export of mature mRNAs, but the mechanism is not well understood, especially in humans. Export of mRNA is completed at the cytoplasmic side of the NPC, where ATPase activity of the DEAD-box helicase DDX19 is specifically activated by the NPC components Gle1, Nup42, and Nup214. The mRNA export factor Gle1 is an essential nucleoporin, and Gle1 dysfunction has been linked to human diseases. We show that the Gle1-Nup42 interaction is highly conserved with X-ray crystal structures and that the thermostability of Gle1 is highly dependent on Nup42. We also find that disease-linked mutants of Gle1 show strongly altered thermostability. Analysis of DDX19 steady-state ATPase activity reveals a novel mode of activation by Gle1 in humans. Structural studies of DDX19 complement the biochemical characterization of DDX19, and we have proposed a working model for the DDX19 catalytic cycle. An outstanding question remains in this model, as the details of DDX19-mediated removal of the export factor NXF1-NXT1 from mRNA are unknown. We describe a method for large-scale purification of retroviral constitutive transport element (CTE) RNA, which hijacks NXF1-NXT1 to be exported through the NPC, for X-ray crystallographic studies of a NXF1-NXT1-CTE complex. Together, these results provide a detailed structural and functional description of mRNA export regulation by the NPC and a framework for understanding the molecular basis of human disease linked to Gle1 and viral proliferation. " }, { "name": "Ordner, Ciara Mary", "degree": "Senior Thesis", "year": "2018", "title": "Synthesis of Enantioenriched Heterocycles by Tandem Sakurai Allylation/Intramolecular Cyclization Processes", "advisor": "Reisman, Sarah E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10192018-145939043", "creators": [ { "name": { "family": "Ordner", "given": "Ciara Mary" }, "id": "Ordner-Ciara-Mary", "orcid": "0000-0002-6644-7863", "display_name": "Ordner, Ciara Mary" } ], "advisors": [ { "name": { "family": "Reisman", "given": "Sarah E." }, "id": "Reisman-S-E", "role": "advisor", "display_name": "Reisman, Sarah E." } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "chemistry" ], "doi": "10.7907/FHRD-3724", "abstract": "Organosilanes are advantageous in organic synthesis due to their ability to act as both stable products and reactive intermediates. A stereospecific one-pot cascade reaction that converts chiral allylic silanes into chiral heterocycles was developed using Lewis acid catalysis. We report on the development of this cascade reaction, optimization to benchtop- scale chemistry, and preliminary investigation into the synthetic scope. In our studies, we were successful in varying the cyclization ring size, investigating cyclization preference in the presence of multiple electrophilic leaving groups, and altering the functional groups present on the aldehyde starting material. Ultimately, we envision this method will be useful in the synthesis of a variety of enantioenriched heterocycles found in bioactive natural products, many of which have may find use as potential drug targets." }, { "name": "Gupta, Ayush", "degree": "Senior Thesis", "year": "2016", "title": "Noncovalent Immobilization of Electrocatalysts on Carbon Electrodes via a Pyrenyl Ligand", "advisor": "Gray, Harry B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032016-120223836", "creators": [ { "name": { "family": "Gupta", "given": "Ayush" }, "id": "Gupta-Ayush", "display_name": "Gupta, Ayush" } ], "advisors": [ { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "advisor", "display_name": "Gray, Harry B." } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "chemistry" ], "doi": "10.7907/Z9G15XTQ", "abstract": "There are many problems that need to be overcome if solar energy is to be viable on a global scale. Photons must be harvested and stored in a usable to allow efficient use of energy throughout the day. The functionalization of electrode surfaces with molecular catalysts is an attractive route for assembling (photo)electrochemical devices that convert renewable energy into chemical fuels. This work focuses on one method of noncovalently attaching molecular catalysts to graphitic surfaces.\r\nThe first part describes the synthesis of a pyrene-appended bipyridine ligand that serves as the linker between the catalysts and the surface. Using this ligand, a rhodium proton-reduction catalyst and a rhenium CO2-reduction catalyst were synthesized in order to study the electrochemistry of the surface-attached species. Electrochemical and spectroscopic analysis confirm catalyst immobilization and electrocatalytically active assemblies. Bulk electrolysis of the surface-attached complexes confirm catalytic turnover formation of H2 for the rhodium complex and CO for the rhenium complex.\r\nThe second part describes three new complexes utilizing the same pyrene-appended bipyridine ligand. These are [Ru(P)(4,4\u2019-dimethyl-2,2\u2019-bipyridine)2]Cl2, [Cp*Ir(P)Cl]Cl, and [Mn(P)(CO)3Br]. Once again, spectroscopic and electrochemical analyses confirmed successful immobilization of these complexes on high surface area carbon electrodes. The iridium complex was found to be unstable with respect to redox cycling due to ligand exchange. The ruthenium complex exhibited very high stability over long periods of redox cycling. The manganese complex was found to catalytically produce CO during bulk electrolysis.\r\n" }, { "name": "Betz, Kerry Nicole", "degree": "Senior Thesis", "year": "2015", "title": "A Novel, General Method for the Construction of C-Si Bonds by an Earth-Abundant Metal Catalyst", "advisor": "Grubbs, Robert H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12162015-163246183", "creators": [ { "name": { "family": "Betz", "given": "Kerry Nicole" }, "id": "Betz-Kerry-Nicole", "orcid": "0000-0001-9118-5909", "display_name": "Betz, Kerry Nicole" } ], "advisors": [ { "name": { "family": "Grubbs", "given": "Robert H." }, "id": "Grubbs-R-H", "role": "advisor", "display_name": "Grubbs, Robert H." } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "chemistry" ], "doi": "10.7907/Z9FT8HZ9", "abstract": "Compounds containing carbon-silicon (C-Si) bonds are of great interest in numerous fields, including but not limited to synthetic chemistry, organic electronics, pharmaceutical chemistry, nuclear medicine, and complex molecule synthesis. Compounds that contain C-Si bonds display useful physicochemical properties, and the C-Si bond can readily be converted into other desirable functional groups. Current methods for the creation of C-Si bonds are somewhat limited, requiring either stoichiometric pyrophoric organometallic species or highly expensive, fine-tuned precious-metal catalysts; both methods have significant limitations in terms of applicability and scope. A novel and general catalytic approach to C-Si bond construction avoiding such limitations has been developed. Herein is disclosed a new method of cross-dehydrogenative heteroaromatic C-H functionalization catalyzed by certain Earth-abundant alkali metal species that is able to access all hybridizations of carbon: sp3, sp2, and sp -hybridized carbons are all silylated in good yield under different conditions; prior to the discovery of this method, no known chemistry for C-Si bond construction was capable of accessing all hybridizations of carbon. Aromatic compounds, including heterocycles and oxygen-substituted arenes; benzylic sp3-hybridized carbons; and terminal alkynes, are directly silylated by potassium and sodium bases using hydrosilanes as the Si source, furnishing the silylated product in a single step. The overall catalysis is highly efficient: it proceeds under mild conditions, in the absence of hydrogen acceptors or other additives, and liberates dihydrogen as the sole byproduct; no competing hydrosilylation is observed. The scope of the method is broad, enabling the direct silylation of aromatic and aliphatic substrates in the presence of a wide array of valuable functional groups. Substrate classes such as nitrogen heterocycles that are challenging to activate with known transition metal catalysis strategies are functionalized in good yields by this Earth-abundant metal catalysis. Facile scalability, low cost, and excellent scope make this an attractive method for either large scale synthesis of versatile building blocks or late-stage functionalization of advanced intermediates and lead compounds. Turn-over numbers (TONs) of nearly 100 are achieved, demonstrating the remarkably high, albeit unanticipated efficiency and activity of the catalysis. The derived products readily engage in versatile transformations enabling new synthetic strategies for molecular diversification, and are useful in their own right in pharmaceutical and materials science applications." }, { "name": "Jiang, Siduo (Stone)", "degree": "Senior Thesis", "year": "2014", "title": "Structure-Guided Design and Biophysical Characterization of Novel Anti-HIV Reagents", "advisor": "Bjorkman, Pamela J.; Galimidi, Rachel P.; West, Anthony P.; Sievers, Stuart A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06172014-114402762", "creators": [ { "name": { "family": "Jiang", "given": "Siduo (Stone)" }, "id": "Jiang-Siduo-Stone", "orcid": "0000-0002-2143-4030", "display_name": "Jiang, Siduo (Stone)" } ], "advisors": [ { "name": { "family": "Bjorkman", "given": "Pamela J." }, "id": "Bjorkman-P-J", "orcid": "0000-0002-2277-3990", "role": "advisor", "display_name": "Bjorkman, Pamela J." }, { "name": { "family": "Galimidi", "given": "Rachel P." }, "id": "Galimidi-R-P", "role": "co-advisor", "display_name": "Galimidi, Rachel P." }, { "name": { "family": "West", "given": "Anthony P." }, "id": "West-A-P", "role": "co-advisor", "display_name": "West, Anthony P." }, { "name": { "family": "Sievers", "given": "Stuart A." }, "id": "Sievers-S-A", "role": "co-advisor", "display_name": "Sievers, Stuart A." } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "biology", "chemistry" ], "doi": "10.7907/SP19-9R34", "abstract": "Despite over 30 years of effort, an HIV-1 vaccine that elicits protective antibodies still does not exist. Recent clinical studies have identified that during natural infection about 20% of the population is capable of mounting a potent and protective antibody response. Closer inspection of these individuals reveal that a subset of these antibodies, recently termed potent VRC01-like (PVL), derive exclusively from a single human germline heavy chain gene. Induced clonal expansion of the B cell encoding this gene is the first step through which PVL antibodies may be elicited. Unfortunately, naturally occurring HIV gp120s fail to bind to this germline, and as a result cannot be used as the initial prime for a vaccine regimen. We have determined the crystal structure of an important germline antibody that is a promising target for vaccine design efforts, and have set out to engineer a more likely candidate using computationally-guided rational design.
\r\n\r\nIn addition to prevention efforts on the side of vaccine design, recently characterized broadly neutralizing anti-HIV antibodies have excellent potential for use in gene therapy and passive immunotherapy. The separation distance between functional Fabs on an antibody is important due to the sparse distribution of envelop spikes on HIV compared to other viruses. We set out to build and characterize novel antibody architectures by incorporating structured linkers into the hinge region of an anti-HIV antibody b12. The goal was to observe whether these linkers increased the arm-span of the IgG dimer. When incorporated, flexible Gly4Ser repeats did not result in detectable extensions of the IgG antigen binding domains, by contrast to linkers including more rigid domains such as \u03b22-microglobulin, Zn-\u03b12-glycoprotein, and tetratricopeptide repeats (TPRs). This study adds an additional set of linkers with varying lengths and rigidities to the available linker repertoire, which may be useful for the modification and construction of antibodies and other fusion proteins.
\r\n" }, { "name": "Laga, Stephanie Midori", "degree": "Senior Thesis", "year": "2014", "title": "A Tale of Two Cobalts", "advisor": "Gray, Harry B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05192014-150810287", "creators": [ { "name": { "family": "Laga", "given": "Stephanie Midori" }, "id": "Laga-Stephanie-Midori", "display_name": "Laga, Stephanie Midori" } ], "advisors": [ { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "advisor", "display_name": "Gray, Harry B." } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "chemistry" ], "doi": "10.7907/1B9V-AW18", "abstract": "There are important problems to overcome if solar energy or other renewable energy sources are to be used effectively on a global scale. Solar photons must not only be harvested and converted into a usable form, but they must also be efficiently stored so that energy is available for use on cloudy days and at night. In this work, both the energy conversion and energy storage problems are addressed. Specifically, two cobalt complexes were designed and their reactivity probed for applications in energy conversion and storage. The first chapter describes a cobalt complex that is the first example of a dimeric cobalt compound with two singly proton-bridged cobaloxime units linked by a central BO4--bridge. Using electrochemical methods, the redox properties of the dimer were evaluated and it was found to be an electrocatalyst for proton reduction in acetonitrile.
\r\n\r\nBecause hydrogen gas is difficult to handle and store, the hydrogenation of CO2 and later dehydrogenation of the liquid product, formic acid, has been proposed as a hydrogen storage system. Thus, a second complex, described in chapter two, supported by a triphosphine ligand framework was used as a catalyst precursor for this key dehydrogenation step. The studies here demonstrate the efficacy of the complex as a precatalyst for the desired reaction, with good conversion of starting formic acid to CO2 and H2. In order to better understand the properties of the triphosphine cobalt complex, a synthetic procedure for substituting electron donating groups (e.g., methoxy groups) onto the ligand was investigated, yielding a novel diphosphine cobalt(II) complex.
" }, { "name": "Rreza, Iva", "degree": "Senior Thesis", "year": "2014", "title": "Development of Tantalum Phenoxy-Imine Compounds for Selective Ethylene Oligomerization", "advisor": "Bercaw, John E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052014-141223337", "creators": [ { "name": { "family": "Rreza", "given": "Iva" }, "id": "Rreza-Iva", "display_name": "Rreza, Iva" } ], "advisors": [ { "name": { "family": "Bercaw", "given": "John E." }, "id": "Bercaw-J-E", "role": "advisor", "display_name": "Bercaw, John E." } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "chemistry" ], "doi": "10.7907/YDBK-V594", "abstract": "The development of catalysts that selectively oligomerize light olefins for uses in polymers and fuels remains of interest to the petrochemical and materials industry. For this purpose, two tantalum compounds, (FI)TaMe2Cl2 and (FI)TaMe4, implementing a previously reported phenoxy-imine (FI) ligand framework, have been synthesized and characterized with NMR spectroscopy and X-ray crystallography. When tested for ethylene oligomerization catalysis, (FI)TaMe2Cl2 was found to dimerize ethylene when activated with Et2Zn or EtMgCl, and (FI)TaMe4 dimerized ethylene when activated with B(C6F5)3, both at room temperature." }, { "name": "Kalbarczyk, Karolina Zbigniew", "degree": "Senior Thesis", "year": "2013", "title": "Directed Evolution of Terpene Synthases for Non-Natural Substrates", "advisor": "Arnold, Frances Hamilton; Lauchli, Ryan", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302013-204117395", "creators": [ { "name": { "family": "Kalbarczyk", "given": "Karolina Zbigniew" }, "id": "Kalbarczyk-Karolina-Zbigniew", "display_name": "Kalbarczyk, Karolina Zbigniew" } ], "advisors": [ { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "advisor", "display_name": "Arnold, Frances Hamilton" }, { "name": { "family": "Lauchli", "given": "Ryan" }, "id": "Lauchli-R", "role": "co-advisor", "display_name": "Lauchli, Ryan" } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "chemeng" ], "doi": "10.7907/N4T5-FP16", "abstract": "Terpenes represent about half of known natural products, with terpene synthases catalyzing reactions to increase the complexity of substrates and generate cyclizations of the linear diphosphate substrates, therefore forming rings and stereocenters. With their diverse functionality, terpene synthases may be highly evolvable, with the ability to accept a wide range of non-natural compounds and with high product selectivity. Our hypothesis is that directed evolution of terpene synthases can be used to increase selectivity of the synthase on a specific substrate. In the first part of the work presented herein, three natural terpene synthases, Cop2, BcBOT2, and SSCG_02150, were tested for activity against the natural substrate and a non-natural substrate, called Surrogate 1, and the relative activities on both the natural and non-natural substrates were compared. In the second part of this work, a terpene synthase variant of BcBOT2 that has been evolved for thermostability, was used for directed evolution for increased activity and selectivity on the non-natural substrate referred to as Surrogate 2. Mutations for this evolution were introduced using random mutagenesis, with error prone polymerase chain reactions, and using site-specific saturation mutagenesis, in which an NNK library is designed with a specific active site amino acid targeted for mutation. The mutant enzymes were then screened and selected for enhancement of the desired functionality. Two neutral mutants, 19B7 W367F and 19B7 W118Q, were found to maintain activity on Surrogate 2, as measured by the screen." }, { "name": "Morris, Melody Ann", "degree": "Senior Thesis", "year": "2013", "title": "Three-Dimensional Self-Assembly of Brush Block Copolymers to Photonic Crystals", "advisor": "Grubbs, Robert H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06182013-115805695", "creators": [ { "name": { "family": "Morris", "given": "Melody Ann" }, "id": "Morris-Melody-Ann", "display_name": "Morris, Melody Ann" } ], "advisors": [ { "name": { "family": "Grubbs", "given": "Robert H." }, "id": "Grubbs-R-H", "role": "advisor", "display_name": "Grubbs, Robert H." } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "chemeng" ], "doi": "10.7907/D77G-4K14", "abstract": "The development of Ring Opening Metathesis Polymerization has allowed the world of block copolymers to expand into brush block copolymers. Brush block copolymers consist of a polymer backbone with polymeric side chains, forcing the backbone to hold a stretched conformation and giving it a worm-like shape. These brush block copolymers have a number of advantages over tradition block copolymers, including faster self-assembly behavior, larger domain sizes, and much less entanglement. This makes them an ideal candidate in the development of a bottom-up approach to forming photonic crystals. Photonic crystals are periodic nanostructures that transmit and reflect only certain wavelengths of light, forming a band gap. These are used in a number of coatings and other optical uses. One and two dimensional photonic crystals are commercially available, though are often expensive and difficult to manufacture. Previous work has focused on the creation of one dimensional photonic crystals from brush block copolymers. In this thesis, I will focus on the synthesis and characterization of asymmetric brush block copolymers for self-assembly into two and three dimensional photonic crystals. Three series of brush block copolymers were made and characterized by Gel Permeation Chromatography and Nuclear Magnetic Resonance spectroscopy. They were then made into films through compressive thermal annealing and characterized by UV-Vis Spectroscopy and Scanning Electron Microscopy. Evidence of non-lamellar structures were seen, indicating the first reported creation of two or three dimensional photonic crystals from brush block copolymers." }, { "name": "Nichols, Eva Megan", "degree": "Senior Thesis", "year": "2012", "title": "Structure and Reactivity of Copper Dipyridyl Carbinol- and Rhenium Diphosphine Complexes", "advisor": "Agapie, Theodor", "url": "https://resolver.caltech.edu/CaltechTHESIS:06142012-152459600", "creators": [ { "name": { "family": "Nichols", "given": "Eva Megan" }, "id": "Nichols-Eva-Megan", "display_name": "Nichols, Eva Megan" } ], "advisors": [ { "name": { "family": "Agapie", "given": "Theodor" }, "id": "Agapie-T", "role": "advisor", "display_name": "Agapie, Theodor" } ], "committee": [ { "name": { "family": "None", "given": "None" }, "display_name": "None, None" } ], "option_major": [ "chemistry" ], "doi": "10.7907/0P52-4M77", "abstract": "Two series of terphenyl-based ligands were designed and synthesized, and the reactivity of their transition metal complexes was examined in the context of small molecule activation.
\r\n\r\nLigands bearing pyridyl donors and pendant hydroxyl groups were synthesized in order to accommodate multiple copper centers with varying steric environments. Copper(I) complexes of these ligands were prepared and characterized, in which copper is coordinated only via the pyridyl nitrogen donors. Treatment of the Cu(I) species with O2 or deprotonation of the ligand followed by metallation with Cu(II) generates multinuclear copper cores supported by bridging alkoxides. Mono-, di-, tetra-, and hexanuclear copper complexes have been synthesized by changing the protonation state and backbone geometry of the ligand. The resulting copper complexes have been characterized by a variety of techniques including single-crystal X-ray diffraction and 1H NMR spectroscopy.
\r\n\r\nRhenium(I) carbonyl coordination chemistry was explored using a series of terphenyl diphosphine ligands with varying steric properties and substituents. Structural differences between complexes of the meta and para ligand variants have been characterized by single crystal X-ray diffraction and 31P-NMR spectroscopy. Cyclic voltammetry studies reveal differences in redox properties, though neither complex appears to exhibit catalytic activity under CO2. Subsequently, we investigate the chemistry of rhenium complexes of 2-methoxy-5-tert-butyl- or 2-methoxy-5- dimethylamino modified ligands.
" }, { "name": "Deem, Michael William", "degree": "Senior Thesis", "year": "1991", "title": "Numerical Investigation of Some Aspects of Fourier Transform Ion Cyclotron Resonance Spectroscopy", "advisor": "Beauchamp, Jesse L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02112026-221909043", "creators": [ { "name": { "family": "Deem", "given": "Michael William" }, "id": "Deem-Michael-William", "orcid": "0000-0002-4298-3450", "display_name": "Deem, Michael William" } ], "advisors": [ { "name": { "family": "Beauchamp", "given": "Jesse L." }, "id": "Beauchamp-J-L", "orcid": "0000-0001-8839-4822", "role": "advisor", "display_name": "Beauchamp, Jesse L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "chemeng" ], "doi": "10.7907/8ccb-sv98", "abstract": "Chapter 1
\r\n\r\nA detailed kinematic analysis is presented comparing the use of quadrupole and\r\noctopole ion guides in conjunction with external ion source Fourier transform ion\r\ncyclotron resonance spectrometers. Methods to determine simply the electric fields\r\nfor ideal and real quadrupoles and octopoles are presented, with emphasis on the\r\nimportance of the effective potential in analyzing the design of an ion guide.\r\nTrajectory calculations are presented for a wide range of ion guide operating\r\nparameters and initial ion energies, along with an evaluation of the range of injected\r\nmasses. Radial and axial ion energies together with a projection of the off-axis\r\nexcursions of the ion motion on the plane perpendicular to the axis of the ICR cell are\r\ngraphically illustrated. The real octopole exhibits more nearly ideal behavior than does\r\na real quadrupole. It does not suffer from the anti-magnetic mirror effect, has uniform\r\nmass cutoffs, and has a four times greater maximum mass cutoff for given operating\r\nparameters than does a quadrupole.
\r\n\r\nChapter 2
\r\n\r\nA detailed analysis of ion motion in a cubic FT-ICR cell reveals dephasing effects of\r\nthe z-axis (magnetic field direction) oscillations that limit the maximum resolution that\r\ncan be achieved. With typical ranges of operating conditions using a 1 inch cubic cell\r\nin a 7 Tesla field, unit mass resolution is lost in the range between 103 and 104 amu,\r\nand peaks may be up to 20 amu in width at the upper end of this range. The finite\r\ntransient length is due to the coupling between the effective radial force on the ion\r\nand the z-axis motion and to a lesser extent, on the instantaneous center of the\r\ncyclotron orbit. Operating conditions that minimize the amplitude of the z-axis\r\noscillations and cell designs that incorporate more homogeneous electric fields serve\r\nto increase the coherence time and provide higher ultimate resolution\"
\r\n\r\nChapter 3
\r\n\r\nWe report here a detailed numerical study of space charge effects on ion trajectories\r\nin a typical FT-ICR experiment. In particular, we focus on ions with high mass to\r\ncharge ratios, 3000 amu/|e-| \u2264 m/z \u2264 10000 amu/|e-|, which are particularly relevant\r\nto experimental studies of clusters, polymers, or biomolecules. We assume excitation\r\nand trapping voltages of 1 V in the one inch cubic cell and a magnetic field of 7 T.\r\nWe find essentially no discernable effect on the dephasing time, mass resolution, or\r\nmass shifts for ion densities below about 7 x 104 |e-|/cm3. That is, the natural\r\ninhomogeneous broadening due to the excitation fields[1] is far more deleterious to\r\nFT-ICR performance than are space charge effects.
\r\n\r\nChapter 4
\r\n\r\nA numerical study of the application of magnetic excitation to FT-ICR is presented. It\r\nis concluded that magnetic excitation, which would permit nonstandard cell designs,\r\nmight be practical for excitation to small final cyclotron radii. For greater degrees of\r\nexcitation, this technique results in excessive magnetron motion and consequent loss\r\nof phase coherence and loss of signal. Unlike conventional rf excitation, the time\r\nrequired for magnetic excitation to a given final radius scales linearly with the mass to\r\ncharge ratio. The technique is thus most applicable to low mass to charge ratio\r\nspecies.
\r\n\r\nChapter 5
\r\n\r\nWe present here computational results for the collision cross section and rate constant\r\nfor proton transfer reactions of a multiply-charged, linear, gas-phase protein. The\r\nprotein is intended to resemble cytochrome c, with a length of 400 \u00c5, a mass of\r\n12 400 amu. The model protein is studied with proton charges of between 9 and 15\r\n|e-|. The computational reactant is intended to model dimethyl amine, with a mass of\r\n45 amu, a polarizability of 5.0 \u00c53 (dimethyl amine has a polarizability estimated by the\r\nLe Fevre method of 5.86 \u00c53[1]), and a dipole moment of 1.03 Debye[2]. Results\r\nfor low linear charge densities on the protein are interpretable in terms of a geometric\r\nmodel that accounts for the overlap of adjacent spheres of capture of each charge on\r\nthe protein.
" } ]