Matching Items (16)
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
Industrial interest in electrocatalytic production of hydrogen has stimulated considerable research in understanding hydrogenases, the biological catalysts for proton reduction, and related synthetic mimics. Structurally closely related complexes are often synthesized to define structure-function relationships and optimize catalysis. However, this process can also lead to drastic and unpredictable changes in the catalytic behavior. In this paper, we use density functional theory calculations to identify changes in the electronic structure of [Ni(bdt)(dppf)] (bdt = 1,2-benzenedithiolate, dppf = 1,1ʹ-bis(diphenylphosphino)ferrocene) relative to [Ni(tdt)(dppf)] (tdt = toluene-3,4-dithiol) as a means to explain the substantially reduced electrocatalytic activity of the tdt complex. An increased likelihood of protonation at the sulfur sites of the tdt complex relative to the Ni is revealed. This decreased propensity of metal protonation may lead to less efficient metal-hydride production and subsequently catalysis.
ContributorsHerringer, Nicholas Stephen (Author) / Jones, Anne (Thesis director) / Mujica, Vladimiro (Committee member) / Pilarisetty, Tarakeshwar (Committee member) / School of Molecular Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
There is an ever-increasing need in the world to develop a source of fuel that is clean, renewable and feasible in terms of production and implementation. Hydrogen gas presents a possible solution to these energy needs, particularly if given a way to produce hydrogen gas efficiently. Biological hydrogen (biohydrogen) production presents a potential way to do just this. It is known that hydrogenases are active in wild-type algal photosynthesis pathways but are only active in anoxic environments, where they serve as electron sinks and compete poorly for electrons from photosystem I. To circumvent these issues, a psaC-hydA1 fusion gene was designed and incorporated into a plasmid that was then used to transform hydrogenase-free Chlamydomonas reinhardtii mutants. Results obtained suggest that the psaC-hydA1 gene completely replaced the wild-type psaC gene in the chloroplast genome and the fusion was expressed in the algal cells. Western blotting verified the presence of the HydA1-PsaC fusion proteins in the transformed cells, P700 photobleaching suggested the normal assembly of FA/FB clusters in PsaC-HydA1, and PSII fluorescence data suggested that HydA1 protein limited photosynthetic electron transport flow in the fusion. Hydrogen production was measured in dark, high light, and under maximal reducing conditions. In all conditions, the wild-type algal strain (with a normal PsaC protein) exhibited higher rates of hydrogen production in the light over 2 hours than the WT strain, though both strains produced similar rates in the dark.
ContributorsSmith, Alec (Author) / Redding, Kevin (Thesis director) / Jones, Anne (Committee member) / Vermaas, Willem (Committee member) / School of Molecular Sciences (Contributor) / Sanford School of Social and Family Dynamics (Contributor) / Barrett, The Honors College (Contributor)
Created2017-12
Description
Heliobacterium modesticaldum (H. modesticaldum) is an anaerobic photoheterotroph that can produce molecular hydrogen (H2) when it is fixing dinitrogen (N2). In addition, electrons can be injected into this organism via an electrode and redox mediator in a light-dependent fashion, as shown recently by the Redding and Jones research groups. These factors make H. modesticaldum an ideal organism for use in a microbial photoelectrosynthesis cell, in which electricity can be used to power specific metabolic processes that produce a desired compound (e.g. H2). However, the injection of electrons into this organism is not optimal, which may limit the H2 production rate. There is a gene (HM1_0653) in the genome encoding a multi-heme cytochrome c that is similar to the proteins known to be used for exit of electrons in the well- known electrode-respiring bacteria (e.g. Geobacteria). RNA-sequencing in the Redding lab has shown that the HM1_0653 gene is very poorly expressed in H. modesticaldum. Boosting expression of this cytochrome could lead to faster electron transfer into the cells and thereby more H2 production via photoelectrosynthesis. In order to gain a deeper understanding of this protein, it was expressed in E.coli by two different versions: (1) the entire gene and (2) a truncated gene with an additional hexahistidine tag (truncHM1_0653). Both cultures had a pink color, indicating the biosynthesis of cytochrome. It was discovered that the HM1_0653 protein was likely released into the medium and shows the most promise for ease of purification of HM1_0653. Furthermore, we explored protein expression in H. modesticaldum using the current transformation system in the Redding Lab, but the combination of gene toxicity and copy number of the vector resulted in cloning difficulties in E.coli. An alternative vector may prove more successful.
ContributorsHerrera-Theut, Kathryn Ann (Author) / Redding, Kevin (Thesis director) / Jones, Anne (Committee member) / Torres, Cesar (Committee member) / School of Molecular Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
Targeting Tumors: Inclusion of Functional Groups on Ion-Containing Block Copolymers to Combat Cancer
Description
This research attempts to determine the most effective method of synthesizing a peptide such that it can be utilized as a targeting moiety for polymeric micelles. Two melanoma-associated peptides with high in vitro and in vivo binding affinity for TNF receptors have been identified and synthesized. Matrix Assisted Laser Desorption/Ionization-Time of Flight Mass Spectrometry (MALDI-ToF) was used to help verify the structure of both peptides, which were purified using Reversed-Phase High Performance Liquid Chromatography (RP-HPLC). The next steps in the research are to attach the peptides to a micelle and determine their impact on micelle stability.
ContributorsMoe, Anna Marguerite (Author) / Green, Matthew (Thesis director) / Jones, Anne (Committee member) / Sullivan, Millicent (Committee member) / Chemical Engineering Program (Contributor) / School of International Letters and Cultures (Contributor) / Sandra Day O'Connor College of Law (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
The development of sustainable catalysts that exhibit exceptional activity has become a major goal of organometallic chemists. Considering their low cost and environmentally benign nature, the use of base metals in catalysis has recently been explored. This dissertation is focused on the development of manganese catalysts for organic transformations and inorganic polymerizations. Previous advances in Mn-based hydrosilylation and hydroboration catalysis are reviewed in Chapter 1 and set the stage for the experimental work described herein.In Chapter 2, the electronic structure of [(2,6-iPr2PhBDI)Mn(μ-H)]2 is explored. This compound was evaluated by density functional theory calculations, SQUID magnetometry and EPR spectroscopy at low temperature. Single crystal X-ray diffraction data was collected for related compounds that feature bridging X-type ligands. The data revealed how bridging ligands impact the Mayer bond order between the two Mn atoms and explained why [(2,6-iPr2PhBDI)Mn(μ-H)]2 is an active catalyst for organic transformations.
Chapter 3 spotlights the first study to systematically demonstrate commercial aminosilane CVD precursor synthesis by way of SiH4 and amine dehydrocoupling using [(2,6-iPr2PhBDI)Mn(μ-H)]2. In addition, the study provided an efficient and halogen-free preparation of highly cross-linked polycarbosilazanes under ambient conditions. Furthermore, exceptionally pure perhydropolysilazane was directly prepared from ammonia and silane at room temperature through dehydrogenative coupling. These are also the first reported examples of Mn-catalyzed Si–N dehydrocoupling.
This research was then extended to the Mn-catalyzed dehydrogenative coupling of NH3 and diamines to organic silanes. Organic polysilazanes and polycarbosilazanes were synthesized and the structures were characterized by NMR, FT-IR, and MALDI-TOF spectroscopy. The thermal properties and coating applications of the products were evaluated by TGA, DSC, X-ray powder diffraction, SEM and EDX. A turnover frequency (TOF) experiment using 0.01 mol% of [(2,6-iPr2PhBDI)Mn(μ-H)]2 revealed a maximum TOF of 300 s-1, which is the highest activity ever reported for this transformation.
The last chapter highlights the first examples of nitrile dihydroboration mediated by a manganese catalyst. Using 0.5 mol% of [(2,6-iPr2PhBDI)Mn(μ-H)]2, 14 nitriles were reduced with HBPin at 80 ℃ to afford N,N-diborylamines after 24 h. A mechanism was proposed based on the isolation of [(2,6-iPr2PhBDI)Mn(NCHPh)]2 as an intermediate and further substantiated by DFT.
ContributorsNguyen, Thu Thao (Author) / Trovitch, Ryan (Thesis advisor) / Jones, Anne (Committee member) / Ackerman, Laura (Committee member) / Arizona State University (Publisher)
Created2022