Matching Items (16)
Description
The discovery of DNA helical structure opened the door of modern molecular biology. Ned Seeman utilized DNA as building block to construct different nanoscale materials, and introduced a new field, know as DNA nanotechnology. After several decades of development, different DNA structures had been created, with different dimension, different morphology and even with complex curvatures. In addition, after construction of enough amounts DNA structure candidates, DNA structure template, with excellent spatial addressability, had been used to direct the assembly of different nanomaterials, including nanoparticles and proteins, to produce different functional nanomaterials. However there are still many challenges to fabricate functional DNA nanostructures. The first difficulty is that the present finite sized template dimension is still very small, usually smaller than 100nm, which will limit the application for large amount of nanomaterials assembly or large sized nanomaterials assembly. Here we tried to solve this problem through developing a new method, superorigami, to construct finite sized DNA structure with much larger dimension, which can be as large as 500nm. The second problem will be explored the ability of DNA structure to assemble inorganic nanomaterials for novel photonic or electronic properties. Here we tried to utilize DNA Origami method to assemble AuNPs with controlled 3D spacial position for possible chiral photonic complex. We also tried to assemble SWNT with discrete length for possible field effect transistor device. In addition, we tried to mimic in vivo compartment with DNA structure to study internalized enzyme behavior. From our results, constructed DNA cage origami can protect encapsulated enzyme from degradation, and internalized enzyme activity can be boosted for up to 10 folds. In summary, DNA structure can serve as an ideal template for construction of functional nanomaterials with lots of possibilities to be explored.
ContributorsZhao, Zhao (Author) / Yan, Hao (Thesis advisor) / Liu, Yan (Thesis advisor) / Chen, Julian (Committee member) / Seo, Dong-Kyun (Committee member) / Arizona State University (Publisher)
Created2013
Description
Thiol functionalization is one potentially useful way to tailor physical and chemical properties of graphene oxides (GOs) and reduced graphene oxides (RGOs). Despite the ubiquitous presence of thiol functional groups in diverse chemical systems, efficient thiol functionalization has been challenging for GOs and RGOs, or for carbonaceous materials in general. In this work, thionation of GOs has been achieved in high yield through two new methods that also allow concomitant chemical reduction/thermal reduction of GOs; a solid-gas metathetical reaction method with boron sulfides (BxSy) gases and a solvothermal reaction method employing phosphorus decasulfide (P4S10). The thionation products, called "mercapto reduced graphene oxides (m-RGOs)", were characterized by employing X-ray photoelectron spectroscopy, powder X-ray diffraction, UV-Vis spectroscopy, FT-IR spectroscopy, Raman spectroscopy, electron probe analysis, scanning electron microscopy, (scanning) transmission electron microscopy, nano secondary ion mass spectrometry, Ellman assay and atomic force microscopy. The excellent dispersibility of m-RGOs in various solvents including alcohols has allowed fabrication of thin films of m-RGOs. Deposition of m-RGOs on gold substrates was achieved through solution deposition and the m-RGOs were homogeneously distributed on gold surface shown by atomic force microscopy. Langmuir-Blodgett (LB) films of m-RGOs were obtained by transferring their Langmuir films, formed by simple drop casting of m-RGOs dispersion on water surface, onto various substrates including gold, glass and indium tin oxide. The m-RGO LB films showed low sheet resistances down to about 500 kΩ/sq at 92% optical transparency. The successful results make m-RGOs promising for applications in transparent conductive coatings, biosensing, etc.
ContributorsJeon, Kiwan (Author) / Seo, Dong-Kyun (Thesis advisor) / Jones, Anne K (Committee member) / Yarger, Jeffery (Committee member) / Arizona State University (Publisher)
Created2013
Description
Deoxyribonucleic acid (DNA) has been treated as excellent building material for nanoscale construction because of its unique structural features. Its ability to self-assemble into predictable and addressable nanostructures distinguishes it from other materials. A large variety of DNA nanostructures have been constructed, providing scaffolds with nanometer precision to organize functional molecules. This dissertation focuses on developing biologically replicating DNA nanostructures to explore their biocompatibility for potential functions in cells, as well as studying the molecular behaviors of DNA origami tiles in higher-order self-assembly for constructing DNA nanostructures with large size and complexity. Presented here are a series of studies towards this goal. First, a single-stranded DNA tetrahedron was constructed and replicated in vivo with high efficiency and fidelity. This study indicated the compatibility between DNA nanostructures and biological systems, and suggested a feasible low-coast method to scale up the preparation of synthetic DNA. Next, the higher-order self-assembly of DNA origami tiles was systematically studied. It was demonstrated that the dimensional aspect ratio of origami tiles as well as the intertile connection design were essential in determining the assembled superstructures. Finally, the effects of DNA hairpin loops on the conformations of origami tiles as well as the higher-order assembled structures were demonstrated. The results would benefit the design and construction of large complex nanostructures.
ContributorsLi, Zhe (Author) / Yan, Hao (Thesis advisor) / Liu, Yan (Thesis advisor) / Seo, Dong-Kyun (Committee member) / Wachter, Rebekka (Committee member) / Arizona State University (Publisher)
Created2012
Description
Nanoporous electrically conducting materials can be prepared with high specific pore volumes and surface areas which make them well-suited for a wide variety of technologies including separation, catalysis and owing to their conductivity, energy related applications like solar cells, batteries and capacitors. General synthetic methods for nanoporous conducting materials that exhibit fine property control as well as facility and efficiency in their implementation continue to be highly sought after. Here, general methods for the synthesis of nanoporous conducting materials and their characterization are presented. Antimony-doped tin oxide (ATO), a transparent conducting oxide (TCO), and nanoporous conducting carbon can be prepared through the step-wise synthesis of interpenetrating inorganic/organic networks using well-established sol-gel methodology. The one-pot method produces an inorganic gel first that encompasses a solution of organic precursors. The surface of the inorganic gel subsequently catalyzes the formation of an organic gel network that interpenetrates throughout the inorganic gel network. These mutually supporting gel networks strengthen one another and allow for the use of evaporative drying methods and heat treatments that would usually destroy the porosity of an unsupported gel network. The composite gel is then selectively treated to either remove the organic network to provide a porous inorganic network, as is the case for antimony-doped tin oxide, or the inorganic network can be removed to generate a porous carbon material. The method exhibits flexibility in that the pore structure of the final porous material can be modified through the variation of the synthetic conditions. Additionally, porous carbons of hierarchical pore size distributions can be prepared by using wet alumina gel as a template dispersion medium and as a template itself. Alumina gels exhibit thixotropy, which is the ability of a solid to be sheared to a liquid state and upon removal of the shear force, return to a solid gel state. Alumina gels were prepared and blended with monomer solutions and sacrificial template particles to produce wet gel composites. These composites could then be treated to remove the alumina and template particles to generate hierarchically porous carbon.
ContributorsVolosin, Alex (Author) / Seo, Dong-Kyun (Thesis advisor) / Buttry, Daniel (Committee member) / Gust, John D (Committee member) / Arizona State University (Publisher)
Created2012
Description
The movement of energy within a material is at the heart of numerous fundamental properties of chemistry and physics. Studying the process of photo-absorption in real time provides key insights into how energy is captured, stabilized, and dissipated within a material. The work presented in this thesis uses ultrafast time-of-flight mass spectrometry and computational modeling to observe and understand the properties of photo-excited states within molecules and clusters. Experimental results provide direct measurement of excited state lifetimes, while computational modeling provides a more thorough understanding of the movement of energy within an excited state. Excited state dynamics in covalent molecules such as n-butyl bromide (C4H9Br), presented in Chapter 4, demonstrate the significance of IVR of photo-excited states. Exciting to the high energy Rydberg manifold leads to predissociation into fragments of various lengths and degrees of saturation but the predissociation process is disrupted by energy redistribution into hot vibrational states. Experimental lifetimes show that IVR occurs over rapidly (~ 600 fs) leaving less energy for bond dissociation. Additionally, a long-lived feature in the dynamics of C4H9+ shows evidence of ion-pair formation – a known phenomenon which creates a stable A+/B- pair separated by several angstroms and occurring at energies lower than direct ionization. The results of this research show the dynamics of energy transfer into bond fragmentation, kinetic energy, and vibrational motion.
Metal-oxide clusters are unique materials which are representative of bulk materials but with quantized excited states instead of bands and as such can be used as atomically precise analogs to semiconducting materials. Excited state lifetimes and theoretical descriptors of electron-hole interactions of titanium oxide clusters, presented in Chapter 5, shows the significance of structure and oxidation of charge-transfer materials. Modeling the excited states of the photo-generated electrons and holes provides a window into the dynamics of charge-transfer and electron-hole separation and recombination in bulk materials. Furthermore, changes in the oxidation of the cluster have a dramatic impact on the nature of excited states and overall cluster properties. Such changes are analogous to oxygen defects in bulk materials and are critical for understanding reaction chemistry at defect sites.
ContributorsHeald, Lauren (Author) / Sayres, Scott G (Thesis advisor) / Seo, Dong-Kyun (Committee member) / Mujica, Vladimiro (Committee member) / Arizona State University (Publisher)
Created2022
Description
Due to the potential synergistic properties from combining inorganic and organic moieties, inorganic/organic hybrids materials have recently attracted great attention. These hybrids are critical components in coating and nanocomposite additive technologies and have potential for future application in catalysis, energy production or storage, environmental remediation, electronic, and sensing technologies. Most of these hybrids utilize low dimensional metal oxides as a key ingredient for the inorganic part. Generally, clay materials are used as inorganic components, however, the use of low dimensional transition metal oxides may provide additional properties not possible with clays. Despite their potential, few methods are known for the use of low dimensional transition metal oxides in the construction of inorganic/organic hybrid materials.Herein, new synthetic routes to produce hybrid materials from low dimensional early transition metal oxides are presented. Included in this thesis is a report on a destructive, chemical exfoliation method designed specifically to exploit the Brønsted acidity of hydrated early transition metal oxides. The method takes advantage of (1) the simple acid-base reaction principle applied to strong two-dimensional Brønsted solid acids and mildly basic, high-polarity organic solvents, (2) the electrostatic repulsion among exfoliated nanosheets, and (3) the high polarity of the organic solvent to stabilize the macroanionic metal oxide nanosheets in the solvent medium. This exfoliation route was applied to tungstite (WO3∙H2O) and vanadium phosphate hydrate (VOPO4∙H2O) to produce stable dispersions of metal oxide nanosheets. The nanosheets were then functionalized by adduct formation or silane surface modification. Both functionalization methods resulted in materials with unique properties, which demonstrates the versatility of the new exfoliation methods in preparing novel hybrid materials.
Further extension of the method to aqueous systems allowed discovery of a new synthetic method for electrically-conducting polyaniline-polyoxometalate hybrid materials. Namely, destructive dissolution of MoO2(HPO4)(H2O) in water produces protons and Strandberg-type phosphomolybdate clusters, and in the presence of aniline and an oxidizing agent, the clusters self-assemble with protonated anilines and selectively form polyaniline-phosphomolybdate hybrids on various types of surfaces through in situ oxidative chemical polymerization. New conductive nanocomposite materials were produced by selectively coating the surface of silica nanoparticles.
ContributorsCiota, David (Author) / Seo, Dong-Kyun (Thesis advisor) / Trovitch, Ryan (Committee member) / Birkel, Christina (Committee member) / Arizona State University (Publisher)
Created2022
Description
Surface modification of (semi)conducting materials with polymers provides a strategy for interfacing electrodes with electrocatalysts for reactions of industrial importance. The resulting constructs create opportunities to capture, convert and store solar energy in the form of chemical bonds, generating solar fuels. This thesis describes III-V semiconductors, modified with molecular catalysts embedded in thin-film polymeric coatings. Overarching goals of this work include building protein-like, soft-material environments on solid-state electrode surfaces. This approach enables coordination of earth-abundant metal centers within the three-dimensional molecular coatings to modulate the electronic and catalytic properties of the overall assembly and provide assemblies for studying the effects of polymeric-encapsulation on electrocatalytic as well as photoelectrosynthetic performance. In summary, this work provides 1) new approaches to designing, interfacing, and characterizing (semi)conducting and catalytic materials to effectively power chemical transformations (including hydrogen evolution and carbon dioxide reduction), and 2) kinetic models for better understanding the structure-function relationships governing the performance of these assemblies.
ContributorsNguyen, Nghi Do Phuong (Author) / Moore, Gary F. (Thesis advisor) / Seo, Dong-Kyun (Committee member) / Sayres, Scott G. (Committee member) / Arizona State University (Publisher)
Created2023
Description
Despite comprising a variety of bioactive compounds that can be utilized as effective synthetic precursors, the construction of halogenated arenes often relies on hazardous reagents and conditions that pose regioselectivity issues in complex systems. Halodecarboxylation using vanadium-dependent haloperoxidases (VHPOs) has emerged as a sustainable alternative for the synthesis of halogenated arenes. In the Biegasiewicz group, we recently discovered that VHPOs can furnish 3-bromooxindoles from 3-carboxyindoles through a decarboxylation event, followed by oxidation. While this tandem process was exciting, the intermediates of this process, 3- bromoindoles are independently valuable reagents, which necessitated further investigation. Herein we examine the biocatalytic access to bromoindoles for which we addressed the major challenge of undesired oxidation event. The first preventative approach acylated the indole nitrogen, resulting in 1-acetylindole-3-CO2H. This could then be subjected to optimized enzymatic bromination conditions to produce 1-acetyl-3-bromoindole in 98% yield with CiVCPO. The second preventative approach was to modify the reaction conditions, furnishing 1-methyl-3-bromoindole in 73% yield from 1-methylindole-3- CO2H with AmVBPO.
ContributorsLee, Hyung Ji (Author) / Biegasiewicz, Kyle (Thesis director) / Ackerman-Biegasiewicz, Laura (Committee member) / Seo, Dong-Kyun (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor) / School of Molecular Sciences (Contributor)
Created2023-05
Description
Late first row transitional metals have attracted attention for the development of sustainable catalysts due to their low cost and natural abundance. This dissertation discusses the utilization of redox-active ligands to overcome one electron redox processes exhibited by these base metals. Previous advances in carbonyl and carboxylate hydrosilylation using redox active ligand-supported complexes such as (Ph2PPrPDI)Mn and (Ph2PPrDI)Ni have been reviewed in this thesis to set the stage for the experimental work described herein.The synthesis and electronic structure of late first row transition metal complexes featuring the Ph2PPrPDI chelate was pursued. Utilizing these complexes as catalysts for a variety of reactions gave a recurring trend in catalytic activity. DFT calculations suggest that the trend in activity observed for these complexes is associated with the ease of phosphine arm dissociation.
Furthermore, the synthesis and characterization of a phosphine-substituted aryl diimine ligand, Ph2PPrADI-H was explored. Addition of Ph2PPrADI-H to CoCl2 resulted in C-H activation of the ligand backbone and formation of [(Ph2PPrADI)CoCl][Co2Cl6]0.5. Reduction of [(Ph2PPrADI)CoCl][Co2Cl6]0.5 afforded the precatalyst, (Ph2PPrADI)Co, that was found to effectively catalyze carbonyl hydrosilylation. At low catalyst loading, TOFs of up to 330 s-1 could be achieved, the highest ever reported for metal-catalyzed carbonyl hydrosilylation.
This dissertation also reports the first cobalt catalyzed pathway for dehydrocoupling diamines or polyamines with polymethylhydrosiloxanes to form crosslinked copolymers. At low catalyst loading, (Ph2PPrADI)Co was found to catalyze the dehydrocoupling of 1,3-diaminopropane and TMS-terminated PMHS with TOFs of up to 157 s-1, the highest TOF ever reported for a Si-N dehydrocoupling reaction. Dehydrocoupling of diamines with hydride-terminated polydimethylsiloxane yielded linear diamine siloxane copolymers as oils.
Finally, dehydrocoupling between diamines and organosilanes catalyzed by a manganese dimer complex, [(2,6-iPr2PhBDI)Mn(μ-H)]2, has allowed for the preparation of silane diamine copolymers. Exceptional solvent absorption capacity was demonstrated by the solid networks, which were found to absorb up to 7 times their own weight. Furthermore, degradation of these networks revealed that their Si-N backbones are easily hydrolysable when exposed to air. The use of lightly crosslinked copolymers as coatings was also studied using SEM analysis.
ContributorsSharma, Anuja (Author) / Trovitch, Ryan J. (Thesis advisor) / Seo, Dong-Kyun (Committee member) / Moore, Gary F. (Committee member) / Arizona State University (Publisher)
Created2024
Description
New sol-gel routes were developed to fabricate transparent conducting oxide coatings for energy applications. Sol-gel synthesis was chosen because the metal oxide products have high surface area and porosity. Titanium sol-gel chemistry was the main focus of the studies, and the synthesis of macroporous antimony-doped tin oxide was also explored. The surface chemistry and band characteristics of anatase TiO2 show promise for solar energy purposes as photoelectrodes in DSSCs and as photocatalysts to degrade organic dyes and to split water. Modifying the band structure by increasing the conduction band edge energy is specifically of interest for reducing protons in water. To this end, a new sol-gel method was developed for incorporating Zr-dopant in nanoporous anatase TiO2. The products follow Vegard’s law up to 20 atom%, exhibiting surface area of 79 m2/g and pore volume of 0.20 cm3/g with average pore diameter of 10.3 nm; the conduction band edge energy increased by 0.22 eV and the band gap increased by 0.1 eV.
In pursuit of a greener sol-gel route for TiO2 materials, a solution of TiOSO4 in water was explored. Success in obtaining a gel came by utilizing hydrogen peroxide as a ligand that suppressed precipitation reactions. Through modifying this sol-gel chemistry to obtain a solid acid, the new material hydrogen titanium phosphate sulfate, H1-xTi2(PO4)3-x(SO4)x, (0 < x < 0.5) was synthesized and characterized for the first time. From the reported synthetic route, this compound took the form of macroscopic agglomerates of nanoporous aggregates of nanoparticles around 20 nm and the product calcined at 600 °C exhibited surface area of 78 m2/g, pore volume of 0.22 cm3/g and an average pore width of 11 nm. This solid acid exhibits complete selectivity for the non-oxidative dehydrogenation of methanol to formaldehyde and hydrogen gas, with >50% conversion at 300 °C.
Finally, hierarchically meso-macroporous antimony doped tin oxide was synthesized with regular macropore size around 210 nm, determined by statistical dye trajectory tracking, and also with larger pores up to micrometers in size. The structure consisted of nanoparticles around 4 nm in size, with textural mesopores around 20 nm in diameter.
In pursuit of a greener sol-gel route for TiO2 materials, a solution of TiOSO4 in water was explored. Success in obtaining a gel came by utilizing hydrogen peroxide as a ligand that suppressed precipitation reactions. Through modifying this sol-gel chemistry to obtain a solid acid, the new material hydrogen titanium phosphate sulfate, H1-xTi2(PO4)3-x(SO4)x, (0 < x < 0.5) was synthesized and characterized for the first time. From the reported synthetic route, this compound took the form of macroscopic agglomerates of nanoporous aggregates of nanoparticles around 20 nm and the product calcined at 600 °C exhibited surface area of 78 m2/g, pore volume of 0.22 cm3/g and an average pore width of 11 nm. This solid acid exhibits complete selectivity for the non-oxidative dehydrogenation of methanol to formaldehyde and hydrogen gas, with >50% conversion at 300 °C.
Finally, hierarchically meso-macroporous antimony doped tin oxide was synthesized with regular macropore size around 210 nm, determined by statistical dye trajectory tracking, and also with larger pores up to micrometers in size. The structure consisted of nanoparticles around 4 nm in size, with textural mesopores around 20 nm in diameter.
ContributorsMieritz, Daniel (Author) / Seo, Dong-Kyun (Thesis advisor) / Petuskey, William (Committee member) / Herckes, Pierre (Committee member) / Arizona State University (Publisher)
Created2016