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Description
Developing a system capable of using solar energy to drive the conversion of an abundant and available precursor to fuel would profoundly impact humanity's energy use and thereby the condition of the global ecosystem. Such is the goal of artificial photosynthesis: to convert water to hydrogen using solar radiation as the sole energy input and ideally do so with the use of low cost, abundant materials. Constructing photoelectrochemical cells incorporating photoanodes structurally reminiscent of those used in dye sensitized photovoltaic solar cells presents one approach to establishing an artificial photosynthetic system. The work presented herein describes the production, integration, and study of water oxidation catalysts, molecular dyes, and metal oxide based photoelectrodes carried out in the pursuit of developing solar water splitting systems.
ContributorsSherman, Benjamin D (Author) / Moore, Thomas (Thesis advisor) / Moore, Ana (Committee member) / Buttry, Daniel (Committee member) / Arizona State University (Publisher)
Created2013
Description
[FeFe]-hydrogenases are enzymes for the reduction of protons to hydrogen. They rely on only the earth abundant first-row transition metal iron at their active site (H cluster). In recent years, a multitude of diiron mimics of hydrogenases have been synthesized, but none of them catalyzes hydrogen production with the same exquisite combination of high turnover frequency and low activation energy as the enzymes. Generally, model complexes fail to include one or both of two features essential to the natural enzyme: an intricate array of outer coordination sphere contacts that constrain the coordination geometry to attain a catalytically optimal conformation, and the redox non-innocence of accessory [FeS] clusters found at or near the hydrogen-activating site. The work presented herein describes the synthesis and electrocatalytic characterization of iron-dithiolate models designed to incorporate these features. First, synthetic strategies are developed for constructing peptides with artificial metal-binding motifs, such as 1,3-dithiolate and phosphines, which are utilized to append diiron-polycarbonyl clusters onto a peptide. The phosphine-functionalized peptides are shown to be better electrocatalysts for proton reduction in water/acetonitrile mixtures than in neat acetonitrile. Second, we report the impact of redox non-innocent ligands on the electrocatalytic properties of two types of [FeFe]-hydrogenase models: dinuclear and mononuclear iron complexes. The bidentate, redox non-innocent α-diimine ligands (N-N), 2,2'-bipyridine and 2,2' bipyrimidine, are used to create complexes with the general formula (μ-SRS)Fe2(CO)4(N-N), new members of the well known family of asymmetric diiron carbonyls. While the 2,2'-bipyridine derivatives can act as electrocatalysts for proton reduction, surprisingly, the 2,2'-bipyrimidine analogues are found to be inactive towards catalysis. Electrochemical investigation of two related Fe(II) complexes, (bdt)Fe(CO)P2 for bdt = benzene-1,2-dithiolate and P2 = 1,1'-diphenylphosphinoferrocene or methyl-2-{bis(diphenylphosphinomethylamino}acetate, related to the distal iron in [FeFe]-hydrogenase show that these complexes catalyze the reduction of protons under mild conditions. However, their reactivities toward the external ligand CO are distinguished by gross geometrical differences.
ContributorsRoy, Souvik (Author) / Jones, Anne K (Thesis advisor) / Moore, Thomas (Committee member) / Trovitch, Ryan (Committee member) / Arizona State University (Publisher)
Created2013
Description
A vast amount of energy emanates from the sun, and at the distance of Earth, approximately 172,500 TW reaches the atmosphere. Of that, 80,600 TW reaches the surface with 15,600 TW falling on land. Photosynthesis converts 156 TW in the form of biomass, which represents all food/fuel for the biosphere with about 20 TW of the total product used by humans. Additionally, our society uses approximately 20 more TW of energy from ancient photosynthetic products i.e. fossil fuels. In order to mitigate climate problems, the carbon dioxide must be removed from the human energy usage by replacement or recycling as an energy carrier. Proposals have been made to process biomass into biofuels; this work demonstrates that current efficiencies of natural photosynthesis are inadequate for this purpose, the effects of fossil fuel replacement with biofuels is ecologically irresponsible, and new technologies are required to operate at sufficient efficiencies to utilize artificial solar-to-fuels systems. Herein a hybrid bioderived self-assembling hydrogen-evolving nanoparticle consisting of photosystem I (PSI) and platinum nanoclusters is demonstrated to operate with an overall efficiency of 6%, which exceeds that of land plants by more than an order of magnitude. The system was limited by the rate of electron donation to photooxidized PSI. Further work investigated the interactions of natural donor acceptor pairs of cytochrome c6 and PSI for the thermophilic cyanobacteria Thermosynechococcus elogantus BP1 and the red alga Galderia sulphuraria. The cyanobacterial system is typified by collisional control while the algal system demonstrates a population of prebound PSI-cytochrome c6 complexes with faster electron transfer rates. Combining the stability of cyanobacterial PSI and kinetics of the algal PSI:cytochrome would result in more efficient solar-to-fuel conversion. A second priority is the replacement of platinum with chemically abundant catalysts. In this work, protein scaffolds are employed using host-guest strategies to increase the stability of proton reduction catalysts and enhance the turnover number without the oxygen sensitivity of hydrogenases. Finally, design of unnatural electron transfer proteins are explored and may introduce a bioorthogonal method of introducing alternative electron transfer pathways in vitro or in vivo in the case of engineered photosynthetic organisms.
ContributorsVaughn, Michael David (Author) / Moore, Thomas (Thesis advisor) / Fromme, Petra (Thesis advisor) / Ghirlanda, Giovanna (Committee member) / Redding, Kevin (Committee member) / Arizona State University (Publisher)
Created2014
Description
Redox reactions are crucial to energy transduction in biology. Protein film electrochemistry (PFE) is a technique for studying redox proteins in which the protein is immobilized at an electrode surface so as to allow direct exchange of electrons. Establishing a direct electronic connection eliminates the need for redoxactive mediators, thus allowing for interrogation of the redox protein of interest. PFE has proven a versatile tool that has been used to elucidate the properties of many technologically relevant redox proteins including hydrogenases, laccases, and glucose oxidase.
This dissertation is comprised of two parts: extension of PFE to a novel electrode material and application of PFE to the investigation of a new type of hydrogenase. In the first part, mesoporous antimony-doped tin oxide (ATO) is employed for the first time as an electrode material for protein film electrochemistry. Taking advantage of the excellent optical transparency of ATO, spectroelectrochemistry of cytochrome c is demonstrated. The electrochemical and spectroscopic properties of the protein are analogous to those measured for the native protein in solution, and the immobilized protein is stable for weeks at high loadings. In the second part, PFE is used to characterize the catalytic properties of the soluble hydrogenase I from Pyrococcus furiosus (PfSHI). Since this protein is highly thermostable, the temperature dependence of catalytic properties was investigated. I show that the preference of the enzyme for reduction of protons (as opposed to oxidation of hydrogen) and the reactions with oxygen are highly dependent on temperature, and the enzyme is tolerant to oxygen during both oxidative and reductive catalysis.
This dissertation is comprised of two parts: extension of PFE to a novel electrode material and application of PFE to the investigation of a new type of hydrogenase. In the first part, mesoporous antimony-doped tin oxide (ATO) is employed for the first time as an electrode material for protein film electrochemistry. Taking advantage of the excellent optical transparency of ATO, spectroelectrochemistry of cytochrome c is demonstrated. The electrochemical and spectroscopic properties of the protein are analogous to those measured for the native protein in solution, and the immobilized protein is stable for weeks at high loadings. In the second part, PFE is used to characterize the catalytic properties of the soluble hydrogenase I from Pyrococcus furiosus (PfSHI). Since this protein is highly thermostable, the temperature dependence of catalytic properties was investigated. I show that the preference of the enzyme for reduction of protons (as opposed to oxidation of hydrogen) and the reactions with oxygen are highly dependent on temperature, and the enzyme is tolerant to oxygen during both oxidative and reductive catalysis.
ContributorsKwan, Patrick Karchung (Author) / Jones, Anne K (Thesis advisor) / Francisco, Wilson (Committee member) / Moore, Thomas (Committee member) / Arizona State University (Publisher)
Created2014
Description
Natural photosynthesis features a complex biophysical/chemical process that requires sunlight to produce energy rich products. It is one of the most important processes responsible for the appearance and sustainability of life on earth. The first part of the thesis focuses on understanding the mechanisms involved in regulation of light harvesting, which is necessary to balance the absorption and utilization of light energy and in that way reduce the effect caused by photooxidative damage. In photosynthesis, carotenoids are responsible not only for collection of light, but also play a major role in protecting the photosynthetic system. To investigate the role of carotenoids in the quenching of the excited state of cyclic tetrapyrroles, two sets of dyads were studied. Both sets of dyads contain zinc phthalocyanine (Pc) covalently attached to carotenoids of varying conjugation lengths. In the first set of dyads, carotenoids were attached to the phthalocyanine via amide linkage. This set of dyads serves as a good model for understanding the molecular "gear-shift" mechanism, where the addition of one double bond can turn the carotenoid from a nonquencher to a very strong quencher of the excited state of a tetrapyrrole. In the second set of dyads, carotenoids were attached to phthalocyanine via a phenyl amino group. Two independent studies were performed on these dyads: femtosecond transient absorption and steady state fluorescence induced by two-photon excitation. In the transient absorption study it was observed that there is an instantaneous population of the carotenoid S1 state after Pc excitation, while two-photon excitation of the optically forbidden carotenoid S1 state shows 1Pc population. Both observations provide a strong indication of the existence of a shared excitonic state between carotenoid and Pc. Similar results were observed in LHC II complexes in plants, supporting the role of such interactions in photosynthetic down regulation. In the second chapter we describe the synthesis of porphyrin dyes functionalized with carboxylate and phosphonate anchoring groups to be used in the construction of photoelectrochemical cells containing a porphyrin-IrO2·nH2O complex immobilized on a TiO2 electrode. The research presented here is a step in the development of high potential porphyrin-metal oxide complexes to be used in the photooxidation of water. The last chapter focuses on developing synthetic strategies for the construction of an artificial antenna system consisting of porphyrin-silver nanoparticle conjugates, linked by DNA of varied length to study the distance dependence of the interaction between nanoparticles and the porphyrin chromophore. Preliminary studies indicate that at the distance of about 7-10 nm between porphyrin and silver nanoparticle is where the porphyrin absorption leading to fluorescence shows maximum enhancement. These new hybrid constructs will be helpful for designing efficient light harvesting systems.
ContributorsPillai, Smitha (Author) / Moore, Ana (Thesis advisor) / Moore, Thomas (Committee member) / Gould, Ian (Committee member) / Arizona State University (Publisher)
Created2011
Description
Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is widely accepted as the world's most abundant enzyme and represents the primary entry point for inorganic carbon into the biosphere. Rubisco's slow carboxylation rate of ribulose-1,5-bisphosphate (RuBP) and its susceptibility to inhibition has led some to term it the "bottle neck" of photosynthesis. In order to ensure that Rubisco remains uninhibited, plants require the catalytic chaperone Rubisco activase. Activase is a member of the AAA+ superfamily, ATPases associated with various cellular activities, and uses ATP hydrolysis as the driving force behind a conformational movement that returns activity to inhibited Rubisco active sites. A high resolution activase structure will be an essential tool for examining Rubisco/activase interactions as well as understanding the activase self-association phenomenon. Rubisco activase has long eluded crystallization, likely due to its infamous self-association (polydispersity). Therefore, a limited proteolysis approach was taken to identify soluble activase subdomains as potential crystallization targets. This process involves using proteolytic enzymes to cleave a protein into a few pieces and has previously proven successful in identifying crystallizable protein fragments. Limited proteolysis, utilizing two different proteolytic enzymes (alpha-chymotrypsin and trypsin), identified two tobacco activase products. The fragments that were identified appear to represent most of what is considered to be the AAA+ C-terminal all alpha-domain and some of the AAA+ N-terminal alpha beta alpha-domain. Identified fragments were cloned using the pET151/dTOPO. The project then moved towards cloning and recombinant protein expression in E. coli. NtAbeta(248-383) and NtAbeta(253-354) were successfully cloned, expressed, purified, and characterized through various biophysical techniques. A thermofluor assay of NtAbeta(248-383) revealed a melting temperature of about 30°C, indicating lower thermal stability compared with full-length activase at 43°C. Size exclusion chromatography suggested that NtAbeta(248-383) is monomeric. Circular dichroism was used to identify the secondary structure; a plurality of alpha-helices. NtAbeta(248-383) and NtAbeta(253-354) were subjected to crystallization trials.
ContributorsConrad, Alan (Author) / Wachter, Rebekka (Thesis advisor) / Moore, Thomas (Committee member) / Redding, Kevin (Committee member) / Arizona State University (Publisher)
Created2012
Description
The purpose of this paper is to understand how companies are finding high potential employees and if they are leaving top talent behind in their approach. Eugene Burke stated in 2014 that 55% of employees that are labeled as a High Potential Employee will turn over and move companies. Burke (2014) also states that the average high potential employee tenure is five years. The Corporate Leadership Council says that on average, 27% of a company's development budget is spent on its high potential program (CEB 2017). For a midsize company, the high potential development budget is almost a million dollars for only a handful of employees, only to see half of the investment walking out the door to another company . Furthermore, the Corporate Leadership Council said that a study done in 2005 revealed that 50% of high potential employees had significant problems within their job (Kotlyar and Karkowsky 2014). Are time and resources are being given to the wrong employees and the right employees are being overlooked? This paper exams how companies traditionally select high potential employees and where companies are potentially omitting employees who would be better suited for the program. This paper proposes that how a company discovers their top talent will correlate to the number of turnovers or struggles that a high potential employee has on their job. Future research direction and practical considerations are also presented in this paper.
ContributorsHarrison, Carrie (Author) / Mizzi, Philip (Thesis director) / Ruediger, Stefan (Committee member) / Department of Management and Entrepreneurship (Contributor) / School of Sustainability (Contributor) / Department of Supply Chain Management (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
In which industry that has ever been profit generating, does a firm profit from their failure? The United States has a mass incarceration problem. With 25% of the world prison population residing in the US, spending on detention costs the US government $80 billion annually. Over 50% of the individuals incarcerated in America are of black or Latino descent. This massive growth in the incarcerated population of America began in the 1970s and with the passive support of American citizens has created an industry whose players profit from the detention of people. Currently, the privately run detention facilities in the United States hold 7% of state prisoners, 18% of federal prisoners, and nearly 75% of ICE's undocumented detainee population. The detention of people for profit is an idea rooted in the same profit motive that allowed the institution of slavery to flourish. However even after the 13th Amendment abolished slavery in the U.S., the oppressive forces behind slave-era economics have been perpetuated through legislation and policies that continued the stratification of society and reinforcement of the social order. With the help of corporate lobbyists, political action committees, and organizations such as the American Legislative Exchange Council, the corporate shareholders of private prisons, such as CoreCivic and The GEO Group, are able to directly align their profit-driven interests with those of federal and state legislators. By the incorporation of legislation and policy into state and federal law, the shareholders of private prisons are able to directly affect legislation as well as their own potential for profit. The justification for the usage of private prisons is thought to be seen in the price savings and flexibility that it provides for federal and state governments. However, due to the law enforcement contractor's exemption from public record laws, there is no clear evidence of where the cost savings occur, or even if there are cost savings at all. Is it ethical for a for-profit-prison corporation to be responsible for the care, security, and rehabilitation of an individual, when if they fail to rehabilitate the individual, it will add to the number of inmates under their control? The measure of a prison's failure to rehabilitate an inmate is considered the recidivism rate, and is affected when an inmate leaves a detention facility, commits another crime, then is arrested. This profit motive is causing our society to incarcerate increasing numbers of people in private prisons. For-profit prisons financially benefit from long-term incarceration and recidivism. The passive investments from public and private employees and institutions through investment corporations are the legs that allow the private prison industry to stand. Twenty-nine investment firms, such as The Vanguard Group and Fidelity Investments, own nearly two-thirds of the two largest players in the private prison industry. This includes the passive investments by public institutions such as the Arizona State University Foundation's $600 million endowment fund as well as the $500 million directly invested into CoreCivic and GEO Group from the University of Texas/ Texas A&M Investment Management Company. The goal of abolishing private prisons will require years of litigation against the giants of the industry as well as the governmental entities supporting them. However, we can start today by demanding divestiture by our school and similar institutions as well continuing to share the knowledge of the oppressive forces associated with the detention of individuals for profit.
ContributorsBayham, Michael (Author) / Gomez, Alan (Thesis director) / Dacey, John (Committee member) / W.P. Carey School of Business (Contributor) / Department of Supply Chain Management (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
The purpose of this thesis is to explore how Blockchain technology can help solve problems large corporations commonly face. For example, it is a common problem for large businesses and organizations to manage sales contracts with thousands of items on them. Likewise, it can be difficult to accurately monitor complex payment histories with thousands of items on them. Another issue is the difficulty that is introduced when making periodic reconciliations based on separate recording systems. At a broader level, some organizations may hesitate to do business with new strange companies or oversea companies for the first time because they do not trust that the other organization can deliver what they promise. Such problems cost organizations a lot of money, effort, and time to solve. However, Blockchain technology, first developed in 2009, could revolutionize how the business community deals with these common problems. The shared and immutable ledger on Blockchain can help organizations to keep track on transactions, manage the contracts in a smarter way, ensure correct purchase history records, eliminate the periodically reconciliation processes, and provide visibility for real-time transactions.
ContributorsHuynh, Phu Thanh (Author) / Popova, Laura (Thesis director) / Pankaj, Sneha (Committee member) / Department of Supply Chain Management (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
As climate change and air pollution continue to plague the world today, committed citizens are doing their part to minimize their environmental impact. However, financial limitations have hindered a majority of individuals from adopting clean, renewable energy such as rooftop photovoltaic solar systems. England Sustainability Consulting plans to reverse this limitation and increase affordability for residents across Northern California to install solar panel systems for their energy needs. The purpose of this proposal is to showcase a new approach to procuring solar panel system components while offering the same products needed by each customer. We will examine market data to further prove the feasibility of this business approach while remaining profitable and spread our company's vision across all of Northern California.
ContributorsEngland, Kaysey (Author) / Dooley, Kevin (Thesis director) / Keahey, Jennifer (Committee member) / Department of Supply Chain Management (Contributor) / School of Social and Behavioral Sciences (Contributor) / W.P. Carey School of Business (Contributor) / School of Sustainability (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05