Matching Items (33)
Description
Development of efficient and renewable electrocatalytic systems is foundational to creation of effective means to produce solar fuels. Many redox enzymes are functional electrocatalysts when immobilized on an electrode, but long-term stability of isolated proteins limits use in applications. Thus there is interest in developing bio-inspired functional catalysts or electrocatalytic systems based on living organisms. This dissertation describes efforts to create both synthetic and biological electrochemical systems for electrocatalytic hydrogen production.
The first part of this dissertation describes the preparation of three different types of proton reduction catalysts. First, four bioinspired diiron complexes of the form (μ-SRS)Fe(CO)3[Fe(CO)(N-N)] for SRS = 1,2-benzenedithiolate (bdt) and 1,3-propanedithiolate (pdt) and N-N = 2,2’-bipyridine (bpy) and 2,2’-bypyrimidine (bpym), are described. Electrocatatlytic experiments show that although the byprimidinal complexes are not catalysts, the bipyridyl complexes produce hydrogen from acetic acid under reducing conditions. Second, three new mononuclear FeII carbonyl complexes of the form [Fe(CO)(bdt)(PPh2)2] in which P2 = bis-phosphine: 4,5-Bis(diphenylphosphino)- 9,9-dimethylxanthene (Xantphos), 1,2-Bis(diphenylphosphino)benzene (dppb), or cis- 1,2-Bis(diphenylphosphino)ethylene (dppv) are described. All are functional bio-inspired models of the distal Fe site of [FeFe]-hydrogenases. Of these, the Xanthphos complex is the most stable to redox reactions and active as an electrocatalyst. Third, a molybdenum catalyst based on the redox non-innocent PDI ligand framework is also shown to produce hydrogen in the presence of acid.
The second part of this dissertation describes creating functional interfaces between chemical and biological models at electrode surfaces to create electroactive systems. First, covalent tethering of the redox probe ferrocene to thiol-functionalized reduced graphene oxide is demonstrated. I demonstrate that this attachment is via the thiol functional groups. Second, I demonstrate the ability to use electricity in combination with light to drive production of hydrogen by the anaerobic, phototrophic microorganism Heliobacterium modesticaldum.
The first part of this dissertation describes the preparation of three different types of proton reduction catalysts. First, four bioinspired diiron complexes of the form (μ-SRS)Fe(CO)3[Fe(CO)(N-N)] for SRS = 1,2-benzenedithiolate (bdt) and 1,3-propanedithiolate (pdt) and N-N = 2,2’-bipyridine (bpy) and 2,2’-bypyrimidine (bpym), are described. Electrocatatlytic experiments show that although the byprimidinal complexes are not catalysts, the bipyridyl complexes produce hydrogen from acetic acid under reducing conditions. Second, three new mononuclear FeII carbonyl complexes of the form [Fe(CO)(bdt)(PPh2)2] in which P2 = bis-phosphine: 4,5-Bis(diphenylphosphino)- 9,9-dimethylxanthene (Xantphos), 1,2-Bis(diphenylphosphino)benzene (dppb), or cis- 1,2-Bis(diphenylphosphino)ethylene (dppv) are described. All are functional bio-inspired models of the distal Fe site of [FeFe]-hydrogenases. Of these, the Xanthphos complex is the most stable to redox reactions and active as an electrocatalyst. Third, a molybdenum catalyst based on the redox non-innocent PDI ligand framework is also shown to produce hydrogen in the presence of acid.
The second part of this dissertation describes creating functional interfaces between chemical and biological models at electrode surfaces to create electroactive systems. First, covalent tethering of the redox probe ferrocene to thiol-functionalized reduced graphene oxide is demonstrated. I demonstrate that this attachment is via the thiol functional groups. Second, I demonstrate the ability to use electricity in combination with light to drive production of hydrogen by the anaerobic, phototrophic microorganism Heliobacterium modesticaldum.
ContributorsLaureanti, Joseph Anthony (Author) / Jones, Anne K. (Thesis advisor) / Moore, Thomas (Committee member) / Redding, Kevin E. (Committee member) / Arizona State University (Publisher)
Created2017
Description
This dissertation describes work on three projects concerning the design and implementation of instrumentation used to study potential organic electronic devices. The first section describes the conducting atomic force microscope (CAFM) in the study of the mechanical and electronic interactions between DNA bases and nucleosides. Previous STM data suggested that an STM tip could recognize single base pairs through an electronic interaction after a functionalized tip made contact with a self assembled monolayer then was retracted. The conducting AFM was employed in order to understand the mechanical interactions of such a system and how they were affecting electrical responses. The results from the conducting AFM showed that the scanning probe system was measuring multiple base-pair interactions, and thus did not have single base resolution. Further, results showed that the conductance between a single base-nucleoside pair is below the detection limit of a potential commercial sequencing device. The second section describes the modifications of a scanning probe microscope in order to study the conductance of single organic molecules under illumination. Modifications to the scanning probe microscope are described as are the control and data analysis software for an experiment testing the single molecule conductance of an organic molecule under illumination. This instrument was then tested using a novel charge-separation molecule, which is being considered for its potential photovoltaic properties. The experiments showed that the instrumentation is capable of detecting differences in conductance upon laser illumination of the molecule on a transparent conductive surface. The third section describes measurements using the illuminated CAFM, as well as the design and construction of an illuminated mercury drop electrode apparatus. Both instruments were tested by attempting to observe photovoltaic behavior in a novel self-organized film of the charge-separation molecules mentioned in the previous paragraph. Results and calculations show that the conducting AFM is not a useful tool in the examination of these organic photovoltaics, while the mercury drop apparatus measured photovoltaic effects in the film. Although photovoltaic effects were measurable with the mercury drop electrode, it was found that the film exhibited very low photon-to-electron conversion efficiency (IPCE).
ContributorsKibel, Ashley Ann (Author) / Lindsay, Stuart M (Thesis advisor) / Chamberlin, Ralph (Committee member) / Moore, Thomas (Committee member) / Ozkan, Sefika (Committee member) / Sankey, Otto (Committee member) / Arizona State University (Publisher)
Created2010
Description
This paper outlines the issue of end-of-life management in small scale solar systems deployed generally in Sub-Saharan Africa, known as PAYGos (Pay-as-you-go). Research and interviews were conducted in order to determine the current state of the industry and plans in terms of waste management. Considering the current capabilities and technology of PV recycling, the future of the industry was analyzed. It is important to provide the highest quality of service to the customer and minimize issues with environmental hazards. Therefore, it is recommended here that PAYGo companies create contracts with recycling companies before the issue of solar waste increases drastically.
ContributorsDiehl, Phoebe (Author) / Kelman, Jonathan (Thesis director) / Moore, Thomas (Committee member) / Barrett, The Honors College (Contributor) / School of Molecular Sciences (Contributor)
Created2023-05
Description
Exploration of long-range conductance in non-redox-active proteins at the single molecule scale is aided by the development of innovative, tailor-made quantitative data analysis techniques. This thesis details the rationale behind the proposed approaches, the steps taken to design and implement every method, and the validation of the methodologies using appropriate experiments, benchmarks, and rigorous statistical data analysis. The first chapter conducts a thorough literature review, sets the stage for the subsequent investigation, and underscores the importance of the research questions addressed in this thesis. The second chapter describes the solvent effects on the electronic conductance of a series of Consensus Tetratricopeptide Repeat proteins (CTPR) measured with Scanning Tunneling Microscopy (STM). The study reveals a reversible reduction in electronic conductance when water (H2O) is replaced with heavy water (D2O) due to a ~6-fold decrease in the carrier diffusion constant as proteins become solvated by D2O. Similar observations are made in a ~7 nm long tryptophan zipper protein, while a phenylalanine zipper protein of comparable length remains unchanged in D2O, highlighting the critical role of aromatic residues in proteins lacking redox cofactors. As an extension to this finding, the third chapter describes the development of a machine-learning model to detect the presence of a protein and identify essential features helping in the detection. For this purpose, a solid-state device was engineered to measure the conductance of CTPR-16 protein wires. This approach addresses the limitations in characterizing the STM gap, enables the collection of stable current vs. time data, and provides a statistical understanding of the electronic transport through a protein. The final chapter investigates real-time changes in conductance in response to protein conformation alterations. A deoxyribonucleic acid (DNA) polymerase Φ29 was chosen for its potential utility as a single-molecule DNA sequencing device. The modified enzyme was bound to electrodes functionalized with streptavidin. Φ29 connected by one biotinylated contact and a second nonspecific contact showed rapid small fluctuations in current when activated. Signals were greatly enhanced with two specific contacts. Features in the distributions of conductance increased by a factor of 2 or more over the open-to-closed conformational transition of the polymerase.
ContributorsMukherjee, Sohini (Author) / Lindsay, Stuart (Thesis advisor) / Moore, Thomas (Committee member) / Qing, Quan (Committee member) / Arizona State University (Publisher)
Created2023
Description
This thesis develops molecular models for electron transport in molecular junctions and intra-molecular electron transfer. The goal is to identify molecular descriptors that afford a substantial simplification of these electronic processes.
First, the connection between static molecular polarizability and the molecular conductance is examined. A correlation emerges whereby the measured conductance of a tunneling junction decreases as a function of the calculated molecular polarizability for several systems, a result consistent with the idea of a molecule as a polarizable dielectric. A model based on a macroscopic extension of the Clausius-Mossotti equation to the molecular domain and Simmon’s tunneling model is developed to explain this correlation. Despite the simplicity of the theory, it paves the way for further experimental, conceptual and theoretical developments in the use of molecular descriptors to describe both conductance and electron transfer.
Second, the conductance of several biologically relevant, weakly bonded, hydrogen-bonded systems is systematically investigated. While there is no correlation between hydrogen bond strength and conductance, the results indicate a relation between the conductance and atomic polarizability of the hydrogen bond acceptor atom. The relevance of these results to electron transfer in biological systems is discussed.
Hydrogen production and oxidation using catalysts inspired by hydrogenases provides a more sustainable alternative to the use of precious metals. To understand electrochemical and spectroscopic properties of a collection of Fe and Ni mimics of hydrogenases, high-level density functional theory calculations are described. The results, based on a detailed analysis of the energies, charges and molecular orbitals of these metal complexes, indicate the importance of geometric constraints imposed by the ligand on molecular properties such as acidity and electrocatalytic activity. Based on model calculations of several intermediates in the catalytic cycle of a model NiFe complex, a hypothetical reaction mechanism, which very well agrees with the observed experimental results, is proffered.
Future work related to this thesis may involve the systematic analysis of chemical reactivity in constrained geometries, a subject of importance if the context of enzymatic activity. Another, more intriguing direction is related to the fundamental issue of reformulating Marcus theory in terms of the molecular dielectric response function.
First, the connection between static molecular polarizability and the molecular conductance is examined. A correlation emerges whereby the measured conductance of a tunneling junction decreases as a function of the calculated molecular polarizability for several systems, a result consistent with the idea of a molecule as a polarizable dielectric. A model based on a macroscopic extension of the Clausius-Mossotti equation to the molecular domain and Simmon’s tunneling model is developed to explain this correlation. Despite the simplicity of the theory, it paves the way for further experimental, conceptual and theoretical developments in the use of molecular descriptors to describe both conductance and electron transfer.
Second, the conductance of several biologically relevant, weakly bonded, hydrogen-bonded systems is systematically investigated. While there is no correlation between hydrogen bond strength and conductance, the results indicate a relation between the conductance and atomic polarizability of the hydrogen bond acceptor atom. The relevance of these results to electron transfer in biological systems is discussed.
Hydrogen production and oxidation using catalysts inspired by hydrogenases provides a more sustainable alternative to the use of precious metals. To understand electrochemical and spectroscopic properties of a collection of Fe and Ni mimics of hydrogenases, high-level density functional theory calculations are described. The results, based on a detailed analysis of the energies, charges and molecular orbitals of these metal complexes, indicate the importance of geometric constraints imposed by the ligand on molecular properties such as acidity and electrocatalytic activity. Based on model calculations of several intermediates in the catalytic cycle of a model NiFe complex, a hypothetical reaction mechanism, which very well agrees with the observed experimental results, is proffered.
Future work related to this thesis may involve the systematic analysis of chemical reactivity in constrained geometries, a subject of importance if the context of enzymatic activity. Another, more intriguing direction is related to the fundamental issue of reformulating Marcus theory in terms of the molecular dielectric response function.
ContributorsKhezr Seddigh Mazinani, Shobeir (Author) / Mujica, Vladimiro (Thesis advisor) / Pilarisetty, Tarakeshwar (Committee member) / Angell, Charles A (Committee member) / Jones, Anne K (Committee member) / Arizona State University (Publisher)
Created2015
ContributorsMoore, Thomas (Arranger)
ContributorsMoore, Thomas (Performer) / ASU Library. Music Library (Publisher)
Created2000-10-13
ContributorsMoore, Thomas (Composer)
ContributorsMoore, Thomas (Composer) / Chavez, Jesse (Arranger)
Description
Two pentacoordinate mononuclear iron carbonyls of the form (bdt)Fe(CO)P2 [bdt = benzene-1,2-dithiolate; P2 = 1,1′-diphenylphosphinoferrocene (1) or methyl-2-{bis(diphenylphosphinomethyl)amino}acetate (2)] were prepared as functional, biomimetic models for the distal iron (Fed) of the active site of [FeFe]-hydrogenase. X-ray crystal structures of the complexes reveal that, despite similar ν(CO) stretching band frequencies, the two complexes have different coordination geometries. In X-ray crystal structures, the iron center of 1 is in a distorted trigonal bipyramidal arrangement, and that of 2 is in a distorted square pyramidal geometry. Electrochemical investigation shows that both complexes catalyze electrochemical proton reduction from acetic acid at mild overpotential, 0.17 and 0.38 V for 1 and 2, respectively. Although coordinatively unsaturated, the complexes display only weak, reversible binding affinity toward CO (1 bar). However, ligand centered protonation by the strong acid, HBF4·OEt2, triggers quantitative CO uptake by 1 to form a dicarbonyl analogue [1(H)-CO]+ that can be reversibly converted back to 1 by deprotonation using NEt3. Both crystallographically determined distances within the bdt ligand and density functional theory calculations suggest that the iron centers in both 1 and 2 are partially reduced at the expense of partial oxidation of the bdt ligand. Ligand protonation interrupts this extensive electronic delocalization between the Fe and bdt making 1(H)+ susceptible to external CO binding.
ContributorsRoy, Souvik (Author) / Mazinani, Shobeir Khezr Seddigh (Author) / Groy, Thomas (Author) / Gan, Lu (Author) / Pilarisetty, Tarakeshwar (Author) / Mujica, Vladimiro (Author) / Jones, Anne (Author) / Department of Chemistry and Biochemistry (Contributor)
Created2014-09-01