Matching Items (76)
Description
There is a critical need for the development of clean and efficient energy sources. Hydrogen is being explored as a viable alternative to fuels in current use, many of which have limited availability and detrimental byproducts. Biological photo-production of H2 could provide a potential energy source directly manufactured from water and sunlight. As a part of the photosynthetic electron transport chain (PETC) of the green algae Chlamydomonas reinhardtii, water is split via Photosystem II (PSII) and the electrons flow through a series of electron transfer cofactors in cytochrome b6f, plastocyanin and Photosystem I (PSI). The terminal electron acceptor of PSI is ferredoxin, from which electrons may be used to reduce NADP+ for metabolic purposes. Concomitant production of a H+ gradient allows production of energy for the cell. Under certain conditions and using the endogenous hydrogenase, excess protons and electrons from ferredoxin may be converted to molecular hydrogen. In this work it is demonstrated both that certain mutations near the quinone electron transfer cofactor in PSI can speed up electron transfer through the PETC, and also that a native [FeFe]-hydrogenase can be expressed in the C. reinhardtii chloroplast. Taken together, these research findings form the foundation for the design of a PSI-hydrogenase fusion for the direct and continuous photo-production of hydrogen in vivo.
ContributorsReifschneider, Kiera (Author) / Redding, Kevin (Thesis advisor) / Fromme, Petra (Committee member) / Jones, Anne (Committee member) / Arizona State University (Publisher)
Created2013
Description
Gold-silver alloy nanoparticles (NPs) capped with adenosine 5'-triphosphate were synthesized by borohydride reduction of dilute aqueous metal precursors. High-resolution transmission electron microscopy showed the as-synthesized particles to be spherical with average diameters ~4 nm. Optical properties were measured by UV-Visible spectroscopy (UV-Vis), and the formation of alloy NPs was verified across all gold:silver ratios by a linear shift in the plasmon band maxima against alloy composition. The molar absorptivities of the NPs decreased non-linearly with increasing gold content from 2.0 x 108 M-1 cm-1 (fÉmax = 404 nm) for pure silver to 4.1 x 107 M-1 cm-1 (fÉmax = 511 nm) for pure gold. The NPs were immobilized onto transparent indium-tin oxide composite electrodes using layer-by-layer (LbL) deposition with poly(diallyldimethylammonium) acting as a cationic binder. The UV-Vis absorbance of the LbL film was used to calculate the surface coverage of alloy NPs on the electrode. Typical preparations had average NP surface coverages of 2.8 x 10-13 mol NPs/cm2 (~5% of cubic closest packing) with saturated films reaching ~20% of ccp for single-layer preparations (1.0 ~ 10-12 mol NPs/cm2). X-ray photoelectron spectroscopy confirmed the presence of alloy NPs in the LbL film and showed silver enrichment of the NP surfaces by ~9%. Irreversible oxidative dissolution (dealloying) of the less noble silver atoms from the NPs on LbL electrodes was performed by cyclic voltammetry (CV) in sulfuric acid. Alloy NPs with higher gold content required larger overpotentials for silver dealloying. Dealloying of the more-noble gold atoms from the alloy NPs was also achieved by CV in sodium chloride. The silver was oxidized first to cohesive silver chloride, and then gold dealloyed to soluble HAuCl4- at higher potentials. Silver oxidation was inhibited during the first oxidative scan, but subsequent cycles showed typical, reversible silver-to-silver chloride voltammetry. The potentials for both silver oxidation and gold dealloying also shifted to more oxidizing potentials with increasing gold content, and both processes converged for alloy NPs with >60% gold content. Charge-mediated electrochemistry of silver NPs immobilized in LbL films, using Fc(meOH) as the charge carrier, showed that 67% of the NPs were electrochemically inactive.
ContributorsStarr, Christopher A (Author) / Buttry, Daniel A (Thesis advisor) / Petuskey, William (Committee member) / Jones, Anne (Committee member) / Arizona State University (Publisher)
Created2014
Description
Hydrogenases catalyze the interconversion of protons, electrons, and hydrogen according to the reaction: 2H+ + 2e- <-> H2 while using only earth abundant metals, namely nickel and iron for catalysis. The enzymatic turnover of Clostridium acetobutylicum [FeFe]-hydrogenase has been investigated through the use of electrochemical and scanning probe techniques. Scanning tunneling microscopy (STM) imaging revealed sub-monolayer surface coverage. Cyclic voltammetry yielded a catalytic, cathodic hydrogen production signal similar to that observed for a platinum electrode. From the direct observation of single enzymes and the macroscopic electrochemical measurements obtained from the same electrode, the apparent turnover frequency (TOF) per single enzyme molecule as a function of potential was determined. The TOF at 0.7 V vs. Ag/AgCl for the four SAMs yielded a decay constant for electronic coupling (β) through the SAM of ~ 0.82 Å -1, in excellent agreement with published values for similar SAMs. One mechanism used by plants to protect against damage is called nonphotochemical quenching (NPQ). Triggered by low pH in the thylakoid lumen, NPQ leads to conversion of excess excitation energy in the antenna system to heat before it can initiate production of harmful chemical species by photosynthetic reaction centers. Here a synthetic hexad molecule that functionally mimics the role of the antenna in NPQ is described. When the hexad is dissolved in an organic solvent, five zinc porphyrin antenna moieties absorb light, exchange excitation energy, and ultimately decay by normal photophysical processes. However, when acid is added, a pH-sensitive dye moiety is converted to a form that rapidly quenches the first excited singlet states of all five porphyrins, converting the excitation energy to heat and rendering the porphyrins kinetically incompetent to perform useful photochemistry. Charge transport was also studied in single-molecule junctions formed with a 1,7-pyrrolidine-substituted 3,4,9,10-Perylenetetracarboxylic diimide (PTCDI) molecule. A reduction in the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals energy gap due to the electronic properties of the substituents is seen when compared to an unsubstituted-PTCDI. The small HOMO-LUMO energy gap allows for switching between electron- and hole-dominated charge transport with a gate voltage, thus demonstrating a single-molecule ambipolar field effect transistor.
ContributorsMadden, Christopher (Author) / Moore, Thomas A. (Thesis advisor) / Jones, Anne (Committee member) / Tao, Nongjian (Committee member) / Arizona State University (Publisher)
Created2012
Description
The heliobacterial reaction center (HbRC) is widely considered the simplest and most primitive photosynthetic reaction center (RC) still in existence. Despite the simplicity of the HbRC, many aspects of the electron transfer mechanism remain unknown or under debate. Improving our understanding of the structure and function of the HbRC is important in determining its role in the evolution of photosynthetic RCs. In this work, the function and properties of the iron-sulfur cluster FX and quinones of the HbRC were investigated, as these are the characteristic terminal electron acceptors used by Type-I and Type-II RCs, respectively. In Chapter 3, I develop a system to directly detect quinone double reduction activity using reverse-phase high pressure liquid chromatography (RP-HPLC), showing that Photosystem I (PSI) can reduce PQ to PQH2. In Chapter 4, I use RP-HPLC to characterize the HbRC, showing a surprisingly small antenna size and confirming the presence of menaquinone (MQ) in the isolated HbRC. The terminal electron acceptor FX was characterized spectroscopically and electrochemically in Chapter 5. I used three new systems to reduce FX in the HbRC, using EPR to confirm a S=3/2 ground-state for the reduced cluster. The midpoint potential of FX determined through thin film voltammetry was -372 mV, showing the cluster is much less reducing than previously expected. In Chapter 7, I show light-driven reduction of menaquinone in heliobacterial membrane samples using only mild chemical reductants. Finally, I discuss the evolutionary implications of these findings in Chapter 7.
ContributorsCowgill, John (Author) / Redding, Kevin (Thesis advisor) / Jones, Anne (Committee member) / Fromme, Petra (Committee member) / Arizona State University (Publisher)
Created2012
Description
The addition of aminoalkyl-substituted α-diimine (DI) ligands to bis(1,5 cyclooctadiene) nickel (or (COD)2Ni) resulted in the formation of two new nickel complexes with the general formula of (Me2NPrDI)2Ni and (PyEtDI)2Ni. Investigation of these complexes by 1H NMR spectroscopy revealed diimine coordination but also the absence of amine arm coordination. Using the 1H NMR spectra in conjunction with structures determined through single crystal X-ray diffraction, the electronic structure of both complexes was described as having a Ni(II) metal center that is antiferromagnetically coupled to 2 DI radical monoanions. A greater ligand field was sought by replacing the pendant amines with phosphine groups on the DI ligands. This yielded ligands with the general formula (Ph2PPrDI) and (Ph2PEtDI). Upon addition to (COD)2Ni, each ligand immediately displaced both COD ligands from the Ni0 center to produce new κ4 N,N,P,P complexes, (Ph2PPrDI)Ni and (Ph2PEtDI)Ni, as observed via single crystal X-ray diffraction and NMR spectroscopy. Reduction of the DI backbone was observed in both complexes, with both complexes being described as having a Ni(I) metal center that is antiferromagnetically coupled to a DI radical monoanion. In addition to alkylphosphine substituted DI ligands, the coordination of a pyridine diimine (PDI) ligand featuring pendant alkylphosphines was also investigated. The addition of (Ph2PPrPDI) to (COD)2Ni produced a new paramagnetic (μeff = 1.21 μB), κ4-N,N,N,P complex identified as (Ph2PPrPDI)Ni. Reduction of the PDI chelate was observed through single crystal X-ray diffraction with the electronic structure described as having a low-spin Ni(I) metal center that is weakly coupled to a PDI radical monoanion (SNi = 1/2). The ability of the three Ni complexes to mediate the hydrosilylation of several unsaturated organic substrates was subsequently investigated. Using a range of catalyst loadings, the hydrosilylation of various substituted ketones afforded a mixture of both the mono- and di-hydrosilylated products within 24 hours, while the hydrosilylation of various substituted aldehydes afforded the mono-hydrosilylated product almost exclusively within hours. (Ph2PEtDI)Ni and (Ph2PPrPDI)Ni were identified as the most effective catalysts for the hydrosilylation of aldehydes at ambient temperature using catalyst loadings of 1 mol%.
ContributorsPorter, Tyler Mathew (Author) / Trovitch, Ryan (Thesis director) / Jones, Anne (Committee member) / Mujica, Vladimiro (Committee member) / Barrett, The Honors College (Contributor) / Department of Chemistry and Biochemistry (Contributor)
Created2014-05
Description
The process of cooking a turkey is a yearly task that families undertake in order to deliver a delicious centerpiece to a Thanksgiving meal. While other dishes accompany and comprise the traditional Thanksgiving supper, focusing on creating a turkey that satisfies the tastes of all guests is difficult, as preferences vary. Over the years, many cooking methods and preparation variations have come to light. This thesis studies these cooking methods and preparation variations, as well as the effects on the crispiness of the skin, the juiciness of the meat, the tenderness of the meat, and the overall taste, to simplify the choices that home cooks have to prepare a turkey that best fits their tastes. Testing and evaluation reveal that among deep-frying, grilling, and oven roasting turkey, a number of preparation variations show statistically significant changes relative to a lack of these preparation variations. For crispiness, fried turkeys are statistically superior, scoring about 1.5 points higher than other cooking methods on a 5 point scale. For juiciness, the best preparation variation was using an oven bag, with the oven roasted turkey scoring about 4.5 points on a 5 point scale. For tenderness, multiple methods are excellent, with the best three preparation variations in order being spatchcocking, brining, and using an oven bag, each of these preparation variations are just under a 4 out of 5. Finally, testing reaffirms that judges tend to have different subjective tastes, with some having different perceptions and opinions on some criteria, while statistically agreeing on others: there was 67% agreement among judges on crispiness and tenderness, while there was only 17% agreement on juiciness. Evaluation of these cooking methods, as well as their respective preparation variations, addresses the question of which methods are worthwhile endeavors for cooks.
ContributorsVance, Jarod (Co-author) / Lacsa, Jeremy (Co-author) / Green, Matthew (Thesis director) / Taylor, David (Committee member) / Chemical Engineering Program (Contributor) / Computer Science and Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2020-05
Description
Hydrocephalus is a chronic neurological condition affecting an estimated 1 in every 500 infants born. The most common treatment method involves surgical implantation of a shunt system; however these systems have a high failure rate resulting in repeat invasive surgeries. A promising approach being researched to treat hydrocephalus is a miniaturized valve composed of silicon and a hydrogel material. The current chemical cross-linker used in the hydrogel, EGDMA, however is susceptible to hydrolytic cleavage due to the ester groups.
This thesis proposed a novel hydrogel composed of a HEMA backbone and methacrylated Jeffamines as the chemical cross-linker as a possible replacement for the HEMA and EGDMA hydrogel used currently in the hydrocephalus valve. Jeffamine EDR-148 was methacrylated through reaction with methacryloyl chloride and characterized using 1H NMR spectroscopy. Subsequently, hydrogels were synthesized, using both EGDMA and EDR-MA, and the properties were compared through swelling and rotational rheology. Finally, degradation tests were performed to compare the hydrolytic stability of the two cross-linkers.
Results of this work demonstrated that Jeffamine EDR-148 was able to be successfully methacrylated and used to synthesize a hydrogel. The new hydrogel was shown to have comparable mechanical behavior and robustness to the EGDMA hydrogel, with slightly increased swelling capabilities. Degradation tests did not confirm the theory that the EDR-MA gels would exhibit greater hydrolytic stability however. Future work includes perfecting the purification of the EDR-MA, conducting a longer-term degradation study at physiologically relevant conditions, and demonstrating the tunability of the Jeffamine hydrogels.
This thesis proposed a novel hydrogel composed of a HEMA backbone and methacrylated Jeffamines as the chemical cross-linker as a possible replacement for the HEMA and EGDMA hydrogel used currently in the hydrocephalus valve. Jeffamine EDR-148 was methacrylated through reaction with methacryloyl chloride and characterized using 1H NMR spectroscopy. Subsequently, hydrogels were synthesized, using both EGDMA and EDR-MA, and the properties were compared through swelling and rotational rheology. Finally, degradation tests were performed to compare the hydrolytic stability of the two cross-linkers.
Results of this work demonstrated that Jeffamine EDR-148 was able to be successfully methacrylated and used to synthesize a hydrogel. The new hydrogel was shown to have comparable mechanical behavior and robustness to the EGDMA hydrogel, with slightly increased swelling capabilities. Degradation tests did not confirm the theory that the EDR-MA gels would exhibit greater hydrolytic stability however. Future work includes perfecting the purification of the EDR-MA, conducting a longer-term degradation study at physiologically relevant conditions, and demonstrating the tunability of the Jeffamine hydrogels.
ContributorsTrimble, Kari Leigh (Author) / Green, Matthew (Thesis director) / Chae, Junseok (Committee member) / Chemical Engineering Program (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2019-05
Description
Obtaining access to clean water is a global problem that is becoming more important with increasing population and advancing technology. Desalination through reverse osmosis (RO) is a promising technology takes advantage of the global supply of saline water to augment its limited freshwater reservoirs. To increase RO membrane performance, the feedwater is pretreated to take any excess pollutants out before the desalination. These pretreatment membranes are susceptible to fouling, which reduces efficiency and drives up costs of the overall process. Increasing the hydrophilicity of these membranes would reduce fouling, and electrospinning is a production method of pretreatment membranes with the capability to control hydrophilicity. This work explores how the composition of electrospun fibrous membranes containing blends of hydrophilic and hydrophobic polymers affects membrane characteristics such as wettability as well as filtration performance. Nonwoven, nanoscale membranes were prepared using electrospinning with a targeted application of pretreatment in water filtration. Using a rotating collector, electrospun mats of hydrophobic poly(vinyl chloride) (PVC) and hydrophilic poly(vinyl alcohol) (PVA) were simultaneously deposited from separate polymer solutions, and their polymer compositions were then characterized using Fourier Transform Infrared (FTIR) spectra. The data did not reveal a reliable correlation established between experimental control variables like flow rate and membrane composition. However, when the membranes' hydrophilicity was analyzed using static water contact angle measurements, a trend between PVA content and hydrophilicity was seen. This shows that the hypothesis of increasing PVA content to increase hydrophilicity is reliable, but with the current experimental design the PVA content is not controllable. Therefore, the primary future work is making a new experimental setup that will be able to better control membrane composition. Filtration studies to test for fouling and size exclusion will be performed once this control is obtained.
ContributorsTronstad, Zachary (Author) / Green, Matthew (Thesis director) / Holloway, Julianne (Committee member) / Epps, Thomas (Committee member) / Chemical Engineering Program (Contributor) / Materials Science and Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2018-12
Description
Gold nanoparticles are valuable for their distinct properties and nanotechnology applications. Because their properties are controlled in part by nanoparticle size, manipulation of synthesis method is vital, since the chosen synthesis method has a significant effect on nanoparticle size. By aiding mediating synthesis with proteins, unique nanoparticle structures can form, which open new possibilities for potential applications. Furthermore, protein-mediated synthesis favors conditions that are more environmentally and biologically friendly than traditional synthesis methods. Thus far, gold particles have been synthesized through mediation with jack bean urease (JBU) and para mercaptobenzoic acid (p-MBA). Nanoparticles synthesized with JBU were 80-90nm diameter in size, while those mediated by p-MBA were revealed by TEM to have a size between 1-3 nm, which was consistent with the expectation based on the black-red color of solution. Future trials will feature replacement of p-MBA by amino acids of similar structure, followed by peptides containing similarly structured amino acids.
ContributorsHathorn, Gregory Michael (Author) / Nannenga, Brent (Thesis director) / Green, Matthew (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
Membrane proteins (MPs) are an important aspect of cell survival that ensure structural integrity, signaling, and transportation of molecules. Since 2015, over 450 MPs have been studied to find their functionalities and structure. Sufficient amounts of correctly folded MPs are needed to accurately study them through crystallography and other structural study methods. Use of recombinant technology is needed to overexpress MPs as natural abundance of MP is often too slow to provide the necessary amounts. However, an increase in toxicity and decrease in generation time deter the overexpression of MPs. The following report discusses two methods of enhancing overexpression in Escherchia coli, the use of T7 RNA polymerase (T7RNAP) and the reprogramming of chaperon pathways, that combats toxicity and promotes cell growth. Overall, both methods are proven to work effectively to overexpress MPs by regulating transcription rate of mRNA (T7RNAP) or folding and transporting of polypeptides to inner membrane (chaperon pathway). To further study the effectiveness of the two methods, they will need to be compared at the same conditions. In addition, a combination of two methods should also be studied to find out if the combination would have a great impact on the overexpression of the MPs.
ContributorsHan, Sue Jisue (Author) / Nannenga, Brent (Thesis director) / Green, Matthew (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05