Matching Items (18)
Description
The use of enzyme-catalyst interfaces is underexplored in the field of biocatalysis, particularly in studies on enabling novel reactivity of enzymes. For this thesis, the HaloTag® protein tagging platform was proposed as a bioconjugation method for a pinacol coupling reaction using lipases, as a model for novel reactivities proceeding via ketyl radical intermediates and hydrogen-bonding-facilitated redox attenuation. After an initial lipase screening of 9 lipases, one lipase (Candida rugosa) was found to perform the pinacol coupling of p-anisaldehyde under standard conditions (fluorescein and 530nm light, 3% yield). Based on a retrosynthetic analysis for the photocatalyst-incorporated HaloTag® linker, the intermediates haloamine 1 and aldehyde 6 were synthesized. Further experiments are underway or planned to complete linker synthesis and conduct pinacol coupling experiments with a bioconjugated system. This project underscores the promising biocatalytic promiscuity of lipases for performing reactions proceeding through ketyl radical intermediates, as well as the underdeveloped potential of incorporating bioengineering principles like bioconjugation into biocatalysis to overcome kinetic barriers to electron transfer and optimize biocatalytic reactions.
ContributorsMcrae, Kenna Christine (Author) / Biegasiewicz, Kyle (Thesis director) / Ghirlanda, Giovanna (Committee member) / Moore, Ana (Committee member) / Department of Physics (Contributor) / School of Human Evolution & Social Change (Contributor) / School of International Letters and Cultures (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
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
This dissertation describes the work on two projects which involves measuring molecular conductance and studying their properties on the nanoscale using various Scanning Tunneling Microscopy (STM) techniques. The first molecule studied was a porphyrin-fullerene moiety known as a molecular Dyad for photovoltaic applications. This project is further divided into two section, the first one involving the characterization of the Dyad monolayers and conductance measurement in the dark. The Dyads are designed to form charge separated states on illumination. The lifetime of the charged states have been measured efficiently but the single-molecule conductance through the molecules have yet to be characterized. The second part of the project describes the set-up of a novel sample stage which enables the study of molecular conductance under illumination. This part also describes the subsequent study of the molecule under illumination and the observation of a unique charge-separated state. It also contains the verification of the presence of this charge-separated using other characterization techniques like transient absorption spectroscopy. The second project described in the dissertation was studying and comparing the predicted rectifying nature of two molecules, identical in every way except for one stereocenter. This project describes the formation of monolayers of the molecule on gold and then studying and analyzing the current-voltage characteristics of the molecules and looking for rectification. Both the molecules proved to be rectifying, one more than the other as predicted by theoretical calculations.
ContributorsBhattacharyya, Shreya (Author) / Lindsay, Stuart (Thesis advisor) / Moore, Ana (Committee member) / Levitus, Marcia (Committee member) / Arizona State University (Publisher)
Created2011
Description
Combretastatin A-4 (CA-4) represents one of the most promising antineoplastic and cancer vascular targeting stilbenes that have been isolated from the South African bush willow, Combretum Caffrum Kuntze. In order to further explore the bioactivity of this molecule, a diiodo derivative of CA-4, as well as its phosphate prodrug, was synthesized and analyzed for its biological activity; although only a scale up synthesis of this compound was performed herein for ongoing analysis. In general, no increased specificity was noted for the human cancer cell lines. Antiangiogenic properties were similar to the untreated control. The diiodocombstatin was active against M. luteus, and its phosphate prodrugs were very active against N. gonorrhoeae. Combretastain A-2 is another biologically active stilbene isolated from Combretum Caffrum Kuntze. In an attempt to increase biological activity of this molecule both mono-iodo and diiodo derivatives have been partially synthesized. The initial step involving the iodination of piperonal utilizes a novel, cost effective and mild reaction. The iodo stilbenes were obtained via a Wittig reaction using phosphonium salts 25 and 27 along with 2,3-Bis-[tert-butyldimethylsiloxy]-4-methoxy benzaldehyde 29. Deprotection of the subsequent z-stilbenes, non-isolated mono-iodo stilbene and the diiodo 30 produced two synthetic objective z-stilbenes 16 and 17. Synthesis as well as biological analysis is ongoing.
ContributorsTrickey-Platt, Brindi Brooks (Author) / Pettit, George R. (Thesis advisor) / Moore, Ana (Committee member) / Skibo, Edward (Committee member) / Arizona State University (Publisher)
Created2011
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
Mitochondria produce most of the ATP needed for the cell as an energy source. It is well known that cellular respiration results in oxidative damage to the cell due to the production of reactive oxygen species (ROS). Mitochondrial dysfunction is believed to contribute to a number of degenerative diseases; because of this the mitochondrial respiratory chain is considered as potential drug target. A few series of idebenone analogues with quinone, pyridinol and pyrimidinol redox cores have been synthesized and evaluated as antioxidants able to protect cellular integrity and, more specifically, mitochondrial function. The compounds exhibited a range of activities. The activities observed were used for the design of analogues with enhanced properties as antioxidants. Compounds were identified which provide better protection against oxidative stress than idebenone, and it is thought that they do so catalytically.
ContributorsArce Amezquita, Pablo M (Author) / Hecht, Sidney M. (Thesis advisor) / Moore, Ana (Committee member) / Rose, Seth (Committee member) / Arizona State University (Publisher)
Created2012
Description
Most of the sunlight powering natural photosynthesis is absorbed by antenna arrays that transfer, and regulate the delivery of excitation energy to reaction centers in the chloroplast where photosynthesis takes place. Under intense sunlight the plants and certain organisms cannot fully utilize all of the sunlight received by antennas and excess redox species are formed which could potentially harm them. To prevent this, excess energy is dissipated by antennas before it reaches to the reaction centers to initiate electron transfer needed in the next steps of photosynthesis. This phenomenon is called non-photochemical quenching (NPQ). The mechanism of NPQ is not fully understood, but the process is believed to be initiated by a drop in the pH in thylakoid lumen in cells. This causes changes in otherwise nonresponsive energy acceptors which accept the excess energy, preventing oversensitization of the reaction center. To mimic this phenomenon and get insight into the mechanism of NPQ, a novel pH sensitive dye 3'6'-indolinorhodamine was designed and synthesized which in a neutral solution stays in a closed (colorless) form and does not absorb light while at low pH it opens (colored) and absorbs light. The absorption of the dye overlaps porphyrin emission, thus making energy transfer from the porphyrin to the dye thermodynamically possible. Several self-regulating molecular model systems were designed and synthesized consisting of this dye and zinc porphyrins organized on a hexaphenylbenzene framework to functionally mimic the role of the antenna in NPQ. When a dye-zinc porphyrin dyad is dissolved in an organic solvent, the zinc porphyrin antenna absorbs and emits light by normal photophysical processes. Time resolved fluorescence experiments using the single-photon-timing method with excitation at 425 nm and emission at 600 nm yielded a lifetime of 2.09 ns for the porphyrin first excited singlet state. When acetic acid is added to the solution of the dyad, the pH sensitive dye opens and quenches the zinc porphyrin emission decreasing the lifetime of the porphyrin first excited singlet state to 23 ps, and converting the excitation energy to heat. Under similar experimental conditions in a neutral solution, a model hexad containing the dye and five zinc porphyrins organized on a hexaphenylbenzene core decays exponentially with a time constant of 2.1 ns, which is essentially the same lifetime as observed for related monomeric zinc porphyrins. When a solution of the hexad is acidified, the dye opens and quenches all porphyrin first excited singlet states to <40 ps. This converts the excitation energy to heat and renders the porphyrins kinetically incompetent to readily donate electrons by photoinduced electron transfer, thereby mimicking the role of the antenna in photosynthetic photoprotection.
ContributorsBhushan, Kul (Author) / Gust, Devens (Thesis advisor) / Moore, Ana (Committee member) / Hayes, Mark (Committee member) / Arizona State University (Publisher)
Created2012
Description
Titanium dioxide (TiO2) is widely used for photocatalysis and solar cell applications, and the electronic structure of bulk TiO2 is well understood. However, the surface structure of nanoparticulate TiO2, which has a key role in properties such as solubility and catalytic activity, still remains controversial. Detailed understanding of surface defect structures may help explain reactivity and overall materials performance in a wide range of applications. In this work we address the solubility problem and surface defects control on TiO2 nanoparticles. We report the synthesis and characterization of ∼4 nm TiO2 anatase spherical nanoparticles that are soluble and stable in a wide range of organic solvents and water. By controlling the temperature during the synthesis, we are able to tailor the density of defect states on the surface of the TiO2 nanoparticles without affecting parameters such as size, shape, core crystallinity, and solubility. The morphology of both kinds of nanoparticles was determined by TEM. EPR experiments were used to characterize the surface defects, and transient absorption measurements demonstrate the influence of the TiO2 defect states on photoinduced electron transfer dynamics.
ContributorsLlansola Portoles, Manuel (Author) / Bergkamp, Jesse (Author) / Finkelstein Shapiro, Daniel (Author) / Sherman, Benjamin (Author) / Kodis, Gerdenis (Author) / Dimitrijevic, Nada M. (Author) / Gust, Devens (Author) / Moore, Thomas (Author) / Moore, Ana (Author) / Department of Chemistry and Biochemistry (Contributor) / College of Liberal Arts and Sciences (Contributor) / School of Molecular Sciences (Contributor) / Center for Bioenergy and Photosynthesis (Contributor)
Created2014-11-13
Description
The ability to accurately predict the oxidation and reduction potentials of molecules is very useful in various fields and applications. Quantum mechanical calculations can be used to access this information, yet sometimes the usefulness of these calculations can be limited because of the computational requirements for large systems. Methodologies that yield strong linear correlations between calculations and experimental data have been reported, however the balance between accuracy and computational cost is always a major issue. In this work, linear correlations (with an R-2 value of up to 0.9990) between DFT-calculated HOMO/LUMO energies and 70 redox potentials from a series of 51 polycyclic aromatic hydrocarbons (obtained from the literature) are presented. The results are compared to previously reported linear correlations that were obtained with a more expensive computational methodology based on a Born-Haber thermodynamic cycle. It is shown in this article that similar or better correlations can be obtained with a simple and cheaper calculation.
ContributorsMendez-Hernandez, Dalvin (Author) / Pilarisetty, Tarakeshwar (Author) / Gust, Devens (Author) / Moore, Thomas (Author) / Moore, Ana (Author) / Mujica, Vladimiro (Author) / Department of Chemistry and Biochemistry (Contributor) / College of Liberal Arts and Sciences (Contributor) / School of Molecular Sciences (Contributor)
Created2013-10-28
Description
ABSTRACT
Transition metals have been extensively employed to address various challenges
related to catalytic organic transformations, small molecule activation, and energy storage
over the last few decades. Inspired by recent catalytic advances mediated by redox noninnocent
pyridine diimine (PDI) and α-diimine (DI) ligand supported transition metals,
our group has designed new PDI and DI ligands by modifying the imine substituents to
feature donor atoms. My doctoral research is focused on the development of PDI and DI
ligand supported low valent first row metal complexes (Mn, Fe, Co) and their application
in bond activation reactions and the hydrofunctionalization of unsaturated bonds.
First two chapters of this dissertation are centered on the synthesis and
application of redox non-innocent ligand supported low valent iron complexes. Notably,
reduction of a DI-based iron dibromide led to the formation of a low valent iron
dinitrogen compound. This compound was found to undergo a sequential C-H and C-P
bond activation processes upon heating to form a dimeric compound. The plausible
mechanism for dimer formation is also described here.
Inspired by the excellent carbonyl hydrosilylation activity of our previously
reported Mn catalyst, (Ph2PPrPDI)Mn, attempts were made to synthesize second generation
Mn catalyst, which is described in the third chapter. Reduction of (PyEtPDI)MnCl2
furnished a deprotonated backbone methyl group containing Mn compound
[(PyEtPDEA)Mn] whereas reduction of (Ph2PEtPDI)MnCl2 produced a dimeric compound,
[(Ph2PEtPDI)Mn]2. Both compounds were characterized by NMR spectroscopy and XRD
analysis. Hydrosilylation of aldehydes and ketones have been studied using
[(PyEtPDEA)Mn] as a pre-catalyst. Similarly, 14 different aldehydes and 6 different
ii
formates were successfully hydrosilylated using [(Ph2PEtPDI)Mn]2 as a pre-catalyst.
Encouraged by the limited number of cobalt catalysts for nitrile hydroboration, we
sought to develop a cobalt catalyst that is active for hydroboration under mild conditions,
which is discussed in the last chapter. Treatment of (PyEtPDI)CoCl2 with excess NaEt3BH
furnished a diamagnetic Co(I) complex [(PyEtPDIH)Co], which exhibits a reduced imine
functionality. Having this compound characterized, a broad substrate scope for both
nitriles and imines have been investigated. The operative mechanism for nitrile
dihydroboration has been investigated based on the outcomes of a series of stoichiometric
reactions using NMR spectroscopy.
Transition metals have been extensively employed to address various challenges
related to catalytic organic transformations, small molecule activation, and energy storage
over the last few decades. Inspired by recent catalytic advances mediated by redox noninnocent
pyridine diimine (PDI) and α-diimine (DI) ligand supported transition metals,
our group has designed new PDI and DI ligands by modifying the imine substituents to
feature donor atoms. My doctoral research is focused on the development of PDI and DI
ligand supported low valent first row metal complexes (Mn, Fe, Co) and their application
in bond activation reactions and the hydrofunctionalization of unsaturated bonds.
First two chapters of this dissertation are centered on the synthesis and
application of redox non-innocent ligand supported low valent iron complexes. Notably,
reduction of a DI-based iron dibromide led to the formation of a low valent iron
dinitrogen compound. This compound was found to undergo a sequential C-H and C-P
bond activation processes upon heating to form a dimeric compound. The plausible
mechanism for dimer formation is also described here.
Inspired by the excellent carbonyl hydrosilylation activity of our previously
reported Mn catalyst, (Ph2PPrPDI)Mn, attempts were made to synthesize second generation
Mn catalyst, which is described in the third chapter. Reduction of (PyEtPDI)MnCl2
furnished a deprotonated backbone methyl group containing Mn compound
[(PyEtPDEA)Mn] whereas reduction of (Ph2PEtPDI)MnCl2 produced a dimeric compound,
[(Ph2PEtPDI)Mn]2. Both compounds were characterized by NMR spectroscopy and XRD
analysis. Hydrosilylation of aldehydes and ketones have been studied using
[(PyEtPDEA)Mn] as a pre-catalyst. Similarly, 14 different aldehydes and 6 different
ii
formates were successfully hydrosilylated using [(Ph2PEtPDI)Mn]2 as a pre-catalyst.
Encouraged by the limited number of cobalt catalysts for nitrile hydroboration, we
sought to develop a cobalt catalyst that is active for hydroboration under mild conditions,
which is discussed in the last chapter. Treatment of (PyEtPDI)CoCl2 with excess NaEt3BH
furnished a diamagnetic Co(I) complex [(PyEtPDIH)Co], which exhibits a reduced imine
functionality. Having this compound characterized, a broad substrate scope for both
nitriles and imines have been investigated. The operative mechanism for nitrile
dihydroboration has been investigated based on the outcomes of a series of stoichiometric
reactions using NMR spectroscopy.
ContributorsGhosh, Chandrani (Author) / Trovitch, Ryan J. (Thesis advisor) / Seo, Don (Committee member) / Moore, Ana (Committee member) / Arizona State University (Publisher)
Created2018