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Supramolecular and heterosupramolecar chemistry in controlled release and molecular recognition processesAgostini, Alessandro 03 June 2013 (has links)
La presente tesis doctoral titulada ¿Supramolecular and heterosupramolecular chemistry in controlled release and molecular recognition
processes¿ está centrada en los dos aspectos principales de la química
supramolecular que han experimentado un gran auge en los últimos años:
el reconocimiento molecular y los procesos de liberación controlada.
En particular la primera parte de la tesis se focaliza en el diseño y
síntesis de moléculas orgánicas que pueden ser empleados cómo sensores
para especies aniónicas y neutras. El paradigma seleccionado para los
procesos de reconocimiento molecular fue la aproximación del dosimetro
químico. Esta aproximación presenta ventajas con respecto a los otros dos
métodos de determinación de aniones (desplazamiento y unidad coordinanteunidad indicadora), cómo, por ejemplo, la posibilidad de determinar los
analitos en disolución acuosa. Así se sintetizaron dos sensores selectivos,
uno para el anión fluoruro (F-) y el otro para glutatión (GSH). El sensor
selectivo para la determinación de F- está basado en un colorante azoico
funcionalizado, en su ¿OH fenólico, cómo silileter. Esta molécula presenta
una banda de absroción muy intensa centrada a 350 nm que, después de la
adición de F-
, sufre un efecto hipocrómico significativo y un
desplazamiento batocromico ligero (de ca. 10 nm), mientras aparece una
nueva banda a 470 nm, determinando un cambio de incoloro a amarillorojo. Para obtener un sensor selectivo para GSH se sintetizó una sonda
químico basado en una sal de 2,6-difenilpirilio. Sucesivamente se preparó
una disolución de este compuesto en agua/CTAB, que se caracterizaba por
un intenso color azul. En este caso, la adición de GSH produce una
disminución significativa de la banda del visible, acompañada por la
consecuente decoloración. Además la adicón de GSH induce la aparición de Resumen
vi
una intensa banda de emisión centrada a 485 nm (después de la irradiación
a 350 nm).
La segunda parte de esta tesis doctoral se basa en el diseño y síntesis de
nuevos sistemas híbridos orgánicos-inorgánicos para procesos de liberación
controlada en ambiente celular. Estos materiales híbridos se componen en
general, de dos unidades: una matriz inorgánica mesoporosa de base
silícea, capaz de almacenar moléculas orgánicas (colorantes, farmacos...) y
un compuesto orgánico anclado covalentemente a la superficie externa del
soporte inorgánico mesoporoso, que actúa cómo puerta molecular. La
aplicación de un estímulo externo puede modificar la conformación de la
puerta molecular permitiendo o bien impidiendo la difusión de la carga
almacenada en los mesoporos hacía el exterior (disolución o citoplasma). El
primer sistema sintetizado y estudiado se compone de una matriz
inorgánica mesoporosa (MCM-41), cargada con el colorante Ru(bipy)3
2+ y
funcionalizada en la superficie con un oligoetilen glicol mediante un grupo
ester. La adición de la enzima esterasa determinaba la hidrólisis del grupo
ester y la consecuente reducción del tamaño de la puerta molecular,
acompañada por la liberación del colorante previamente cargado. Otro
sistema de liberación preparado consiste en el uso de la misma matriz
MCM-41 nanoscópica y el mismo colorante Ru(bipy)3
2+, pero se
funcionalizó la superficie con una puerta molecular fotolabil. La irradiación
en el maximo de absorción de la puerta molecular inducía la
fotodegradación de la misma y la consecuente liberación del colorante. Un
tercer ejemplo de sistema de liberación consiste en una puerta molecular
caracterizada por la presencia de dos grupos funcionales hidrolizables con
enzimas diferentes: grupos urea y amida. vii
El material final, caracterizado por la presencia del mismo esqueleto
inorgánico, y cargado con Ru(bipy)3
2+, era capaz de liberar selectivamente
cantidades distintas de colorante, dependiendo del enzima empleado. Así
se podían conseguir dos tipos de perfiles de liberación: uno muy rápido y
poco intenso y otro más lento pero mucho mas intenso. Finalmente se
sintetizó un material híbrido siempre basado en la misma matriz de MCM-
41, cargado con rodamina-B y funcionalizado en la superficie con
galactooligosacáridos. Con este material se podía conseguir una liberación
controlada del colorante selectivamente en células senescentes, debido a
que estas sobreexpresan el enzima ß-galactosidasa que es capaz de
hidrolizar los galactooligosacáridos. / Agostini, A. (2013). Supramolecular and heterosupramolecar chemistry in controlled release and molecular recognition processes [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/29397
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[pt] DESENVOLVIMENTO DE ELETRODOS DE POLÍMEROS DE BAIXO CUSTO PARA APLICAÇÕES GEOTÉCNICAS / [en] DEVELOPMENT OF LOW-COST POLYMER ELECTRODES FOR GEOTECHNICAL APPLICATIONSRONALD BEYNER MEJIA SANCHEZ 29 June 2023 (has links)
[pt] O presente trabalho de pesquisa buscou desenvolver eletrodos que
apresentem uma alta resistência à corrosão, baixa atividade eletroquímica, fáceis de
fabricar e economicamente viáveis. No decorrer do trabalho experimental
desenvolveram-se eletrodos poliméricos através de três procedimentos distintos. O
primeiro procedimento envolveu a sintetização de óxido de cobre em escala
nanométrica. O segundo procedimento envolveu a síntese do cobre puro em escala
nanométrica. E finalmente, o terceiro procedimento empregou filamentos de latão
que é uma mistura de cobre e zinco cujo filamentos foram incorporados a uma
matriz polimérica para a obtenção dos eletrodos. O eletrodo utilizando filamentos
de latão misturado com resina epóxi exibiu o melhor desempenho por apresentar
boa condutividade elétrica, menor custo e fácil fabricação. Os eletrodos de polímero
ofereceram boa resistência à corrosão em ambientes agressivos causados pela
variação do pH no decorrer do processo de eletro-drenagem. O programa
experimental buscou comparar o comportamento do eletrodo com filamentos de
latão imerso em uma matriz de resina epóxi com eletrodos de cobre. Verificou-se
que os eletrodos de cobre sofrem uma rápida corrosão que gera uma taxa de perda
de massa muito elevada, gerando óxidos que são depositados na superfície do
eletrodo, diminuindo sua capacidade de condução. Já os eletrodos desenvolvidos na
presente pesquisa apresentaram uma perda de massa inexpressiva. Em relação ao
consumo de energia no decorrer do processo de eletro-drenagem, observou-se que
os ensaios com eletrodos de cobre apresentam uma maior demanda energética. / [en] This research aimed to develop electrodes that have high resistance to
corrosion, low electrochemical activity, ease of manufacturing and economically
viable. The experimental work was focused on the development of polymeric
electrodes through three different procedures. The first procedure involved the
synthesis of copper oxide at the nanometric scale. The second one involved the
synthesis of pure copper at the nanometric scale. Finally, the last one used
commercial alloys obtained from a mixture of copper and zinc. Their filaments were
incorporated into a polymer matrix to obtain the electrodes. The brass wire
electrode mixed with epoxy resin presented the best performance due to its high
electrical conductivity, low cost, and ease of manufacturing. These polymer
electrodes presented good corrosion resistance in aggressive environments, which
are caused by pH variation during the electro-drainage process. The experimental
setup aimed the comparison of the behavior between the electrode with bass
filaments immersed in an epoxy resin matrix and copper electrodes. The
comparison has shown that copper electrodes undergo rapid corrosion with higher
rate of mass loss generating oxides. These oxides are deposited on the surface of
the electrode reducing its electrical conduction capacity. On the other hand, the
electrodes developed in the present study showed a low loss of mass. In relation to
energy consumption during the electro-drainage process, it was observed that the
tests with copper electrodes present higher energy demand than the developed
electrodes.
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High temperature phase behavior of 2D transition metal carbidesBrian Cecil Wyatt Jr (19179565) 03 September 2024 (has links)
<p dir="ltr">The technological drive of humanity to explore the cosmos, travel at hypersonic speeds, and pursue clean energy solutions requires ceramic scientists and engineers to constantly push materials to their functional, behavioral, and chemical extremes. Ultra-high temperature ceramics, and particularly transition metal carbides, are promising materials to meet the demands of extreme environment materials with their >4000 °C melting temperature and impressive thermomechanical behaviors in extreme conditions. The advent of the 2D version of these transition metal carbides, known as MXenes, added a new direction to design transition metal carbides for energy, catalysis, flexible electronics, and other applications. Toward extreme conditions, although MXenes remain yet unexplored, we believe that the ~1 nm flakes of MXenes gives ceramics scientists and engineers the ability to truly engineer transition metal carbides layer-by-layer at the nanoscale to endure the extreme conditions required by future harsh environment technology. Although MXenes have this inherent promise, fundamental study of their behavior in high-temperature environments is necessary to understand how their chemistry and 2D nature affects the high-temperature stability and phase behavior of MXenes toward application in extreme environments.</p><p dir="ltr">In this dissertation, we investigate the high-temperature phase behavior of 2D MXenes in high temperature inert environments to understand the stability and phase transition behavior of MXenes. In this work, we demonstrate that 1) MXenes’ transition at high-temperatures is to highly textured transition metal carbides is due to the homoepitaxial growth of these phases onto ~1-nm-thick MXenes’ highly exposed basal plane, 2) the MXene to MXene interface plays a major role in the phase behavior of MXenes, particularly toward building layered transition metal carbides using MXenes as ~1-nm-thick building blocks, and 3) Defects are the primary site at which atomic migration begins during phase transition of MXenes into these highly textured transition metal carbides, and these defects can be engineered for different phase stability of MXenes. To do so, we investigate the phase behavior of Ti<sub>3</sub>C<sub>2</sub>T<sub><em>x</em></sub>, Ta<sub>4</sub>C<sub>3</sub>T<sub><em>x</em></sub>, Mo<sub>2</sub>TiC<sub>2</sub>T<sub><em>x</em></sub>, and other MXenes using a combination of <i>in situ</i> x-ray diffraction and scanning transmission electron microscopy and other <i>ex situ</i> methods, such as secondary ion mass spectrometry and x-ray photoelectron spectroscopy, with other methods. By investigating the fundamentals of the high-temperature phase behavior of MXenes, we hope to establish the basic principles behind use of MXenes as the ideal material for application in future extreme environments.</p>
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Investigation of Electron Irradiation Induced Amorphous to Crystalline Phase Transformations in Nanostructured CeramicsNathaniel John Keninger (20383413) 05 December 2024 (has links)
<p dir="ltr">The effects of electron irradiation induced amorphous-to-crystalline (a-to-c) phase transformations were investigated for 5 different nanostructured ceramic materials. Nanoporous Al<sub>2</sub>O<sub>3</sub>, TiO<sub>2</sub> nanotubes, ZrO<sub>2</sub> nanotubes, nanoporous Nb<sub>2</sub>O<sub>5</sub>, and nanoporous Ta<sub>2</sub>O<sub>5</sub> were analyzed <i>in situ </i>using transmission electron microscopy (TEM) techniques, where the imaging 200kV electron beam was used also as an electron irradiation source. TEM techniques for analysis include high-resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED), and electron energy-loss spectroscopy (EELS). Each material was examined starting from an as-grown amorphous state, with experiments using diffuse, intermediate, and concentrated beam conditions and various durations of irradiation. Flux of irradiating electrons, as controlled by the spread of the electron beam, showed to have considerable and consistent impact on a-to-c phase transformations for all materials. Diffuse beam experiments, where the electron beam was spread to an area of 30-80μm<sup>2</sup>, with low electron flux consistently observed little to no a-to-c phase transformations, even over longer time scales. Intermediate beam experiments, where the electron beam was spread to an area of .08-.03μm<sup>2</sup>, observed consistent a-to-c phase transformation across all materials, though at varying rates and producing crystallites of various sizes between materials. Concentrated beam experiments, where the electron beam was spread to an area of .003μm<sup>2</sup>, consistently observed rapid a-to-c phase transformation, and also consistently produced larger crystallites compared to intermediate beam experiment counterparts. Comparison between materials showed a trend in susceptibility of crystallization under electron irradiation, with Nb<sub>2</sub>O<sub>5</sub> as the least susceptible to electron irradiation induced crystallization, followed by Ta<sub>2</sub>O<sub>5</sub>, then TiO<sub>2</sub>, then ZrO<sub>2</sub>, and Al<sub>2</sub>O<sub>3</sub> as the most susceptible to electron irradiation induced crystallization. The area of observed crystalline phases was fairly consistent with some outliers within each experiment, though varied both with material and beam concentration. Both production and dissipation of crystalline phases were observed. Dissipation of crystalline phases into amorphous phases appeared to be loosely correlated to the size of the grain within the material. Multiple material properties from literature were compared against the trend observed between materials, though no individual material property showed clear or consistent alignment with the experimental trend observed.</p>
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Factors influencing the uptake and fate of metallic nanoparticles in filter-feeding bivalvesHull, Matthew S. 22 September 2011 (has links)
Metallic nanoparticles (MetNPs) with unique nanoscale properties, including novel optical behavior and superparamagnetism, are continually being developed for biomedical and industrial applications. In certain biomedical applications where extended blood half-lives are required, MetNPs are surface-functionalized using polymers, proteins, and other stabilizing agents to facilitate their resistance to salt-induced aggregation. Given their colloidal stability in high ionic-strength matrices, functionalized MetNPs are anticipated to be persistent aquatic contaminants. Despite their potential environmental significance, the persistence of surface- functionalized MetNPs as individually-stabilized nanoparticles in aquatic environments is largely unknown. Further, few studies have investigated the fundamental factors that influence MetNP uptake and fate/transport processes in ecologically susceptible aquatic biota, such as filter- feeding bivalves, which ingest and accumulate a broad range of dissolved- and particulate-phase contaminants.
The present study describes a comprehensive approach to prepare and rigorously characterize MetNP test suspensions to facilitate fundamental examinations of nanoparticle uptake and fate/transport processes in freshwater and marine bivalves. We demonstrate the importance of accurately characterizing test suspensions in order to better understand MetNP persistence as individually-stabilized nanoparticles within aquatic test media, and define an optical-activity metric suitable for quantifying and comparing the persistence of variable MetNP formulations as National Nanotechnology Initiative (NNI) definable nanoscale materials. We also show that individually-stabilized MetNPs of variable elemental composition, particle diameter, and surface coating are accessible to bivalves in both freshwater and marine environments. Clearance rates for MetNPs are positively related to the diameter and initial concentration of MetNP suspensions. The observed size-dependence of particle filtration rates facilitates ‘size-selective biopurification' of particle suspensions with nanoscale resolution, and may have applicability in future sustainable nanomanufacturing processes. Filtered MetNPs are retained for extended periods post-exposure primarily within the bivalve digestive tract and digestive gland, but migration to other organ systems was not observed. Clusters of MetNPs were recovered in concentrated form from excreted feces, suggesting that biotransformation and biodeposition processes will play an important role in transferring MetNPs from the water column to benthic environments. / Ph. D.
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Characterization of Fluorescent Nanodiamonds containing Nitrogen-Vacancy and Silicon-Vacancy Color Centers as Produced by Pulsed Laser Ablation in Liquid ConfinementPiccoli, Alessandro 27 February 2024 (has links)
Nanodiamonds are a promising platform for quantum technologies due to the combinations of their inherent properties and the properties of the fluorescent color centers hosted in diamond. They can be employed as quantum sensing devices with spatial resolution in the range of the nanometer and capable of withstanding harsh conditions while also being biocompatible, allowing applications with sensitive biological systems; but they also find application in quantum computing and photonics fields. For all these applications the central features are the properties of the photoluminescent
color centers employed, the color centers on which this thesis is focused are the Nitrogen-Vacancy (NV) and Silicon-Vacancy (SiV) centers of diamond. Both centers are of high interest due to spin dependent properties of their
fluorescent emission which can be accessed at room temperature. The development of quantum technologies based on such fluorescent nanodiamonds is stifled by the the lack of production techniques that can be easily scaled to industrial levels. In fact most of the more prominent techniques found in literature exhibit drawbacks both in terms of control of particle properties and of scalability. This thesis focuses on the synthesis of nanodiamonds by Pulsed Laser Ablation in Liquid, with particular interest in the possibility of producing continuously nanodiamonds containing NV and SiV centers. For the NV center the technique of choice have been Pulsed Laser Ablation in liquid nitrogen focusing on the yield of the process as the technique has already been experimentally validated. For the SiV centers the ablation process was performed in water and the graphite precursor have been substituted for a composite graphite and silicon carbide precursor.
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Evaluación del comportamiento de las propiedades físico-mecánicas de concreto de alta resistencia F’c = 500 kg/cm2, incorporando nanoplaquetas de grafeno con aplicación de ondas ultrasónicasGuevara Rimarachin, Kevin Paul January 2024 (has links)
El crecimiento poblacional ha generado necesidades en infraestructura, como vivienda y transporte. Para satisfacer la demanda y requerimientos técnicos, se necesita colocar concreto de alta resistencia y a edades menores. La calidad del concreto depende de varias variables que están en función de los materiales que lo componen. En el mercado existen opciones como aditivos, fibras y materiales con actividad puzolánica para mejorar sus propiedades. No obstante, su uso puede tener consecuencias negativas como pérdidas económicas, controles de calidad exhaustivos y explotación de recursos naturales.
Esta investigación busca determinar si la adición de nanoplaquetas de grafeno en porcentajes de 0.27% y 0.33% mejora las propiedades físico-mecánicas y facilita la elaboración del concreto de alta resistencia mediante la aplicación de ondas ultrasónicas. Con ello, se busca aportar al campo de los nanomateriales y la innovación de los materiales de construcción, abriendo nuevas puertas para los investigadores interesados en este ámbito.
La dosificación más efectiva obtenida fue la adición del 0.27% de nanoplaquetas de grafeno, tanto para las propiedades físicas como mecánicas. Además, se llevó a cabo un ensayo de durabilidad que permitió terminar de concluir que la adición de nanoplaquetas de grafeno al concreto F'c=500 kg/cm2, con la aplicación de ondas ultrasónicas, no produce cambios significativos en sus propiedades. Por lo tanto, esta solución no es viable debido a los altos costos de importación de la máquina de ultrasonidos y las nanoplaquetas de grafeno. / The population growth has generated infrastructure needs such as housing and transportation.
To meet the demand and technical requirements, high-strength concrete needs to be placed at younger ages. The quality of concrete depends on various variables that are influenced by its constituent materials. In the market, there are options such as additives, fibers, and materials with pozzolanic activity to improve its properties. However, their use can have negative consequences such as economic losses, rigorous quality controls, and exploitation of natural resources.
This research aims to determine whether the addition of graphene nanoplatelets at percentages f 0.27% and 0.33% enhances the physico-mechanical properties and facilitates the production of high-strength concrete using ultrasonic waves. It seeks to contribute to the field of nanomaterials and innovation in construction materials, opening new avenues for researchers interested in this area.
The most effective dosage obtained was the addition of 0.27% of graphene nanoplatelets for both physical and mechanical properties. Furthermore, a durability test was conducted, which concluded that the addition of graphene nanoplatelets to concrete with a strength of F'c=500 kg/cm2, using ultrasonic waves, does not produce significant changes in its properties.
Therefore, this solution is not viable due to the high costs of importing the ultrasound machine and graphene nanoplatelets.
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Design Principle on Carbon Nanomaterials Electrocatalysts for Energy Storage and ConversionZhao, Zhenghang 05 1900 (has links)
We are facing an energy crisis because of the limitation of the fossil fuel and the pollution caused by burning it. Clean energy technologies, such as fuel cells and metal-air batteries, are studied extensively because of this high efficiency and less pollution. Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential in the process of energy storage and conversion, and noble metals (e.g. Pt) are needed to catalyze the critical chemical reactions in these devices. Functionalized carbon nanomaterials such as heteroatom-doped and molecule-adsorbed graphene can be used as metal-free catalysts to replace the expensive and scarce platinum-based catalysts for the energy storage and conversion. Traditionally, experimental studies on the catalytic performance of carbon nanomaterials have been conducted extensively, however, there is a lack of computational studies to guide the experiments for rapid search for the best catalysts. In addition, theoretical mechanism and the rational design principle towards ORR and OER also need to be fully understood.
In this dissertation, density functional theory calculations are performed to calculate the thermodynamic and electrochemical properties of heteroatom-doped graphene and molecule-adsorbed graphene for ORR and OER. Gibb's free energy, overpotential, charge transfer and edge effect are evaluated. The charge transfer analysis show the positive charges on the graphene surface caused by the heteroatom, hetero-edges and the adsorbed organic molecules play an essential role in improving the electrochemical properties of the carbon nanomaterials. Based on the calculations, design principles are introduced to rationally design and predict the electrochemical properties of doped graphene and molecule-adsorbed graphene as metal-free catalysts for ORR and OER. An intrinsic descriptor is discovered for the first time, which can be used as a materials parameter for rational design of the metal-free catalysts with carbon nanomaterials for energy storage and conversion. The success of the design principle provides a better understanding of the mechanism behind ORR and OER and a screening approach for the best catalyst for energy storage and conversion.
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Design, Synthesis and Characterization of Novel NanomaterialsThirupathi, Ravula January 2014 (has links) (PDF)
The present thesis entitled “Design, Synthesis and Characterization of Novel Nanomaterials” is divided into five chapters, staring with a general introduction. The remaining chapters focus on four different areas/projects that I have worked on.
Chapter 1: Introduction to nanomaterials
This chapter reviews the basic concepts of nanomaterials and their fabrication methods. Nanomaterials are defined as materials whose dimensions (at least one) are below 100 nm. One of the most exciting aspects of nanomaterials is that their properties may differ significantly from those of the corresponding bulk materials. Nanomaterials fabrication methods can be broadly classified according to whether the assembly follows either i) the bottom-up approach or ii) the top-down approach. These methods have been discussed with various examples including the self-assembly of proteins, peptides and small molecules. In the top-down approach synthetic procedures for Graphene Oxide and its application are discussed. All characterization techniques that are used for characterizing the nanomaterials are also described briefly.
Chapter 2 Section A: Self-assembly of 1-Hydroxy benzotriazole (HOBT) in water
The studies presented in Chapter 2 identifies HOBT as the smallest non-peptide building block that spontaneously self-assembles into hollow micro tubular structures upon evaporation of water. The tubes form under ambient conditions by rolling over of crystalline sheets of HOBT. The packing of HOBT in the tubes seem to be predominantly driven by intermolecular π-stacking interactions between the aromatic rings of HOBT. These structural and packing patterns are similar to those found in nanotubes formed by the self-assembly of peptides and other larger molecules. The cavities of these thermolabile microtubes act as molds for casting gold nanoparticles for the synthesis of gold microrods with monodisperse dimensions. The non-reacting inner surfaces of the cavities have been used to uniquely synthesize R6G-functionalized gold microrods. With these features, HOBT is an important novel non-peptide building block for accessing micro and nanometric materials for their applications in medicine, biology and molecular biotechnology.
Section B: Controlling the orientation of self-assembly of HOBT microtubes
The studies presented in this chapter address the self-assembly of HOBT into microtubular structures in different solvents of varying polarities (H2O and DCM:MeOH) to understand the role of solvent volatility and its direction on the orientation of the HOBT microtubes. HOBT self-assembles from DCM:MeOH mixtures in its bipolar canonical form and is coordinated with its water of hydration, similar to its crystals obtained from water. FTIR and TGA data shows that MeOH is also integrated with the microtubes. We observe for the first time that the orientation of microtubular self-assembly is controlled in the direction of evaporation of the solvent. We demonstrate further this feature by controlling the orientation of HOBT self-assembly in exclusively vertical direction through controlled vertical evaporation of the solvent mixture DCM:MeOH (9:1). Additionally, the unique transition between vertical and horizontal orientations for self-assembled HOBT microtubes is achieved by simple change of solvation between aqueous and organic solvents. These results reveal a dynamic relationship between the rate of evaporation of solvent and the rates of formation of different self-assembled morphologies. The rate of evaporation of the solvent primarily governs the rate of formation of the tubes, rather than their orientations in three dimensions.
Chapter 3: Chemical origins of debris in Graphene Oxide (GO)
This chapter is focused on the investigation of the carbonyl rich fragments arising from GO and provides an understanding of its formation. The fragments are expelled from GO due to an uncontrolled nucleophile driven reaction in aqueous medium leaving the holes on the sheet. These fragments are carbonyl rich small (5 ± 2 nm) nonaromatic molecules that form as by-products of oxidative chemical reactions that occur at the sp3 clusters on the basal surface of GO sheets when they are treated with nucleophilic bases under aqueous conditions. The structure and size of the debris, and hence that of the hole, depend on the size of the sp3 cluster on the sheet. These debris fall out of the GO sheet surface, leading to formation of nanometer sized holes. Formation of debris and hence the holes can be avoided by using anhydrous polar solvents. This work sheds new light on the fundamental structure of GO and the prevention of debris from it during redox reactions enabling better control over functionalization of the GO surface.
Chapter 4: Measurement of mechanical properties of polypeptide fragment from Insulin like growth factor binding protein nanotubes by the Peak Force QNM method
This chapter describes the discovery of Polypeptide fragment from an IGFBP-2. This fragment self-assembles spontaneously and reversibly into nanotubular structures under oxidizing conditions. These nanotubes were characterized by using Transmission electron microscopy. Notably as compared to the monomer, an increase in intrinsic fluorescence upon self-assembly. The thermal stability of these nanotubes is realized form the fluorescence studies. Peak Force Quantitative Nanomechanical Mapping method of AFM was used to measure the Young’s modulus of the nanotubes. These nanotubes were found to have Young’s modulus value of ~10 Gpa, which is comparable to those of bones presumably due to intermolecular disulphide bonds. These nanotubes will have potential applications in tissue engineering.
Chapter 5: Probing the pathways of n→π* interaction in peptides
This chapter deals with the theoretical study of n→π* interaction in designed peptidomimetics. The n→π* interaction involves the delocalization of the lone pair of the donor group into the antibonding orbital (π*) of a carbonyl group. However despite beeing extensively studied there exists a debate over the validation of these n→π* interaction which is reminiscent to Bürgi and Dunitz trajectory. This chapter present our findings that peptidomimetics containing the 5,6-dihydro-4H-1,3-oxazine (Oxa) and 5,6-dihydro-4H-1,3-thiazine (Thi) functional groups at the C-terminus of Pro selectively stabilizes the cis conformer by reverse n→πi-1* interaction. These systems have been used to study the n→πi1* interaction using Natural Bond Orbital (NBO) method. Our study reveals that the energetically most favorable trajectory of a nucleophile for a favorable n→π* interaction presumably to facilitate the overlap between the lonepair of the nucleophile and the antibonding orbital of the carbonyl group. The geometrical requirements for the optimum n→π* interaction depends on the relative orientations of the orbitals that are involved. This study has implications for more accurately identifying long distant n→π* interaction.
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Surface Engineering and Synthesis of Graphene and Fullerene Based NanostructuresGnanaprakasa, Tony Jefferson January 2016 (has links)
Graphene is a two-dimensional carbon structure that exhibits remarkable structure-property relations. Consequently, there has been immense effort undertaken towards developing methods for graphene synthesis. Chemical vapor deposition (CVD) and chemical exfoliation from colloidal suspensions are two common methods used for obtaining graphene films. However, the underlying experimental conditions have to be carefully optimized in order to obtain graphene films of controllable thickness and morphology. In this context, a significant part of this dissertation was devoted towards developing and improving current CVD-based and chemical exfoliation based methods for synthesizing high quality graphene films. Specifically, in the CVD based procedure for growing graphene on copper, the effect of surface pretreatment of copper was investigated and the quality of graphene grown using two different pretreatment procedures was compared and analyzed. In particular, graphene grown on electropolished copper (EP-Cu) was analyzed with respect to its surface morphology, surface roughness and thickness, and compared with graphene grown on as cold-rolled acetic acid cleaned copper (AA-Cu). It was shown that electropolishing of the Cu substrates prior to graphene growth greatly enhanced the ability to obtain flat, uniform, predominantly single layer graphene surface coverage on copper. The reported surface roughness of the graphene on EP-Cu was found to be much lower than for previously reported systems, suggesting that the electropolishing procedure adopted in this work has great promise as a pretreatment step for Cu substrates used in CVD growth of graphene. Obtaining graphene from colloidal suspensions of graphitic systems was also examined. In this work, an acid (H₂SO₄ + HNO₃) treatment process for intercalating natural graphite flakes was examined and the ability to reversibly intercalate and deintercalate acid ions within graphitic galleries was investigated. More importantly, a rapid-thermal expansion (RTP) processing was developed to thermally expand the acid-treated graphite, followed by exfoliation of predominantly bilayer graphene as well as few layer graphene flakes in an organic solvent (N, N-Dimethylformamide - DMF). The developed method was shown to provide bilayer and few layer graphene flakes in a reliable fashion. Fullerene is another carbon nanostructure that has garnered attention due to unique structure and chemical properties. Recently, there has been increased focus towards harnessing the properties of fullerenes by synthesizing fullerene self-assemblies in the form of extended rods, tubes and more complex shapes. Current methods to synthesize these self-assemblies are either cumbersome, time consuming or expensive. In this context, an alternate, straightforward dip-coating procedure technique to self-assemble equal-sized, faceted, polymerized fullerene nanorods on graphene-based substrates in a rapid fashion was developed. By suitably modifying the kinetics of self-assembly, the ability to reliably control the spatial distribution, size, shape, morphology and chemistry of fullerene nanorods was achieved.
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