O presente trabalho teve como objetivo principal estudar os processos de intercalação e esfoliação do niobato lamelar H2K2Nb6O17 em soluções aquosas de n-hexilamina, n-propilamina e hidróxido de tetrabutilamônio (TBAOH). Procurou-se avaliar a influência do agente esfoliante no processo de separação das lamelas do niobato. Para tanto, uma quantidade fixa de H2K2Nb6O17 foi suspensa em solução do agente esfoliante, nas razões molares amina/H+-niobato iguais a 0,25, 0,50, 0,75 e 1,0, e mantida sob agitação à temperatura ambiente por 2 semanas. O sólido depositado foi separado do sobrenadante opaco (isto é, do sólido esfoliado). Para a caracterização do sólido depositado, determinou-se a composição química e registrou-se o difratograma de raios-X, a curva termogravimétrica e os espectros vibracionais no IV e Raman. A dispersão de partículas esfoliadas foi caracterizada por espectroscopia eletrônica enquanto o sólido esfoliado, por DRX, medidas de área superficial, MEV e HRTEM. Nos sólidos depositados, as alquilaminas se encontram intercaladas em um arranjo de monocamada e praticamente orientadas perpendicularmente em relação às lamelas do niobato. As suspensões contendo as razões molares amina/H+-niobato = 0,5 para a n-hexilamina e 1,0 para a n-propilamina produziram a maior quantidade de sólido esfoliado (ca. 35%). As micrografias revelam que o sólido esfoliado é formado por partículas flexíveis em um arranjo desorganizado, muito diferente da morfologia do K4Nb6O17. Os difratogramas mostram perfil de material com organização somente no eixo de empilhamento das lamelas e, ainda, que nessas partículas as aminas mantêm o arranjo de monocamadas. As partículas esfoliadas contêm 50% e 70% de n-hexilamina e n-propilamina, respectivamente, neutralizando os íons H+ do niobato. Esses dados mostram que a insaturação das lamelas em relação às aminas favorecem a estabilização dos sistemas esfoliados, uma vez que diminuem as interações de van der Waals entre as cadeias carbônicas e promovem a hidratação da superfície das lamelas. Os sólidos depositados em suspensão de TBAOH não possuem espécie orgânica intercalada e as suspensões contendo as razões TBA+/H+-niobato ? 0,5 produziram maior quantidade de sólido disperso (ca. 65%). O sólido esfoliado isolado da suspensão com razão 0,75 contém 10% de TBA+ neutralizando os íons H+ do niobato. À medida que o pH das suspensões é diminuído, o TBA+ é substituído por H3O+ e as partículas planas começam a encaracolar. Observou-se a formação de nanotubos nas razões molares TBA+/H+-niobato = 0,5 e 1,0, que tiveram o pH alterado para 1 e 7 respectivamente. A amostra isolada em pH 1 apresenta área específica de 139 m²g?¹ enquanto o K4Nb6O17 possui apenas 2 m²g?¹ . Os sistemas contendo tanto partículas tabulares quanto tubulares possuem potencial aplicação na área de (foto)catálise e de sensores. / The main aim of this work was to study the intercalation and exfoliation processes of the layered niobate H2K2Nb6O17 in aqueous solutions of n-hexylamine, n-propylamine and tetra-n-butylammonium hydroxide (TBAOH). It was evaluated the influence of the exfoliation agent in the process of separation of the niobate layers. A fixed amount of H2K2Nb6O17 was suspended in solution of the exfoliation agent, in the molar ratios amine/H+-niobate 0.25, 0.50, 0.75 and 1.0, and maintained under stirring at room temperature for 2 weeks. The deposited solid was separated from the opaque suspension (i.e., the exfoliated solid). For the characterization of the deposited solid, it was determined the chemical composition and the X-ray diffractogram, the termogravimetric curve and the infrared and Raman vibrational spectra were recorded. The dispersion of exfoliated particles was characterized by electronic spectroscopy while the exfoliated solid, for XRD, surface area measurement, SEM and HRTEM. Considering the deposited solids, the alkylamines are intercalated in a monolayer arrangement and practically oriented perpendicularly in relation to the niobate layers. The suspensions containing the molar ratios amine/H+-niobate 0.5 for the n-hexylamine and 1.0 for the n-propylamine produced the highest amount of exfoliated solid (ca. 35%). SEM images reveal that exfoliated solid is formed by flexible particles in a disorganized arrangement, very different from the K4Nb6O17 morphology. The diffractograms profile show a solid with organization only in the axis of piling up of the layers and also that in these particles the amines maintain the monolayer arrangement. The exfoliated particles contain 50% and 70% of n-hexylamine and n-propylamine, respectively, neutralizing the H+ ions of the niobate. These data show that the layers insaturation in relation to the amines seems to favor the stabilization of the exfoliated systems, once it reduces the van der Waals interactions among the carbon chains and facilitate the hydration of the layer surfaces. The deposited solids in suspension of TBAOH do not possess organic species intercalated and the suspensions containing the ratio TBA+/H+-niobate ? 0.5 produce the highest amount of dispersed solid (ca. 65%). The exfoliated solid isolated from suspensions with ratio 0.75 contains 10% of TBA+ neutralizing the H+ ions of the niobate. As the pH of the suspensions is decreased, TBA+ ion is replaced by H3O+ and the tabular particles begin to scroll. The nanotubes formation was observed to molar ratios TBA+/H+-niobate = 0.5 and 1.0, which pH values were changed to 1 and 7 respectively. The sample isolated at pH 1 presents specific area of 139 m²g?¹ while K4Nb6O17 possesses only 2 m²g?¹ . The systems containing plate and tubular particles possesses potential application in (photo)catalysis and sensors areas.

In this dissertation, I report my thesis work on studying surface electron dynamics for intercalated graphene on a metal template using both experimental and theoretical methods. A general description of the research motivation is summarized in the first Chapter. The experimental and theoretical techniques involved in this thesis research are introduced in Chapter 2. In Chapter 3 and Chapter 4, the key findings of this thesis work are reported. These findings concern two novel surface electronic phenomena in oxygen intercalated-graphene on Ir(111) interface. The first phenomenon was the observation of strongly excited image potential states (IPS) in a well-defined quasi-free-standing graphene (QFG) at an oxygen-intercalated Gr/Ir interface. Specifically, the interfaces were synthesized to form Gr/Ir and QFG (Gr/O/Ir) by oxygen intercalation. The syntheses were monitored by low-energy-electron-diffraction (LEED). Our research succeeded in exciting and measuring IPSs on both interfaces by angle-resolved two-photon-photoemission (AR-2PPE) and then the increasing of the IPS binding energy of 0.17 eV following the oxygen intercalation. Finally, our work proposed a theoretical model based on density-functional-theory (DFT) calculations and effective potential models to simulate the surface potential variations in the presence of the intercalated oxygen and its influence on IPSs. The energy shift could be understood by an approximation considering only the out-of-plane chemical and structural modulations. In addition, the results of the model are in strong agreement with the measured IPS band structures. The agreement enables us to attribute the IPS binding energy shift to two potential modulations: a deepened and widened interfacial potential well due to the presence of oxygen intercalants and an increased graphene-Ir interlayer distance. The second phenomenon investigated was a non-dispersive unoccupied band at the Brillouin Zone (BZ) center, which was observed only for Gr/O/Ir but not for Gr/Ir interface. The unoccupied state is approximately 2.6 eV above Fermi energy and was discovered by AR-2PPE. The existence of the non-dispersive band inspired us to undertake a careful examination of the in-plane structural modulation induced by oxygen intercalants. LEED measurements confirm the presence of an in-plane 2$\times$2 periodicity of the intercalated oxygen in QFG. This periodicity can provide periodic perturbation to QFG and can generate the flat unoccupied state due to zone-folding effects from the BZ edge. Angle-resolved photoemission measurements and DFT-based calculations were used to compare the measured Gr/O/Ir states to that of Gr/Ir and O/Ir, providing solid evidence for this zone-folding interpretation. The realization of mixing bands between high symmetry points in BZ by zone-folding in Gr/O/Ir demonstrates a pathway for engineering the graphene electronic structure and its two-photon optical excitation via other ordered intercalants. In addition, a separate but related collaboration work on the phase-transition and electronic-structure evolution in W-doped \ce{MoTe2} is documented in Chapter 5. In this work, I contributed expertise in photoemission to study the critical dopant stoichiometry responsible for the phase transition.

O presente trabalho teve como objetivo principal estudar os processos de intercalação e esfoliação do niobato lamelar H2K2Nb6O17 em soluções aquosas de n-hexilamina, n-propilamina e hidróxido de tetrabutilamônio (TBAOH). Procurou-se avaliar a influência do agente esfoliante no processo de separação das lamelas do niobato. Para tanto, uma quantidade fixa de H2K2Nb6O17 foi suspensa em solução do agente esfoliante, nas razões molares amina/H+-niobato iguais a 0,25, 0,50, 0,75 e 1,0, e mantida sob agitação à temperatura ambiente por 2 semanas. O sólido depositado foi separado do sobrenadante opaco (isto é, do sólido esfoliado). Para a caracterização do sólido depositado, determinou-se a composição química e registrou-se o difratograma de raios-X, a curva termogravimétrica e os espectros vibracionais no IV e Raman. A dispersão de partículas esfoliadas foi caracterizada por espectroscopia eletrônica enquanto o sólido esfoliado, por DRX, medidas de área superficial, MEV e HRTEM. Nos sólidos depositados, as alquilaminas se encontram intercaladas em um arranjo de monocamada e praticamente orientadas perpendicularmente em relação às lamelas do niobato. As suspensões contendo as razões molares amina/H+-niobato = 0,5 para a n-hexilamina e 1,0 para a n-propilamina produziram a maior quantidade de sólido esfoliado (ca. 35%). As micrografias revelam que o sólido esfoliado é formado por partículas flexíveis em um arranjo desorganizado, muito diferente da morfologia do K4Nb6O17. Os difratogramas mostram perfil de material com organização somente no eixo de empilhamento das lamelas e, ainda, que nessas partículas as aminas mantêm o arranjo de monocamadas. As partículas esfoliadas contêm 50% e 70% de n-hexilamina e n-propilamina, respectivamente, neutralizando os íons H+ do niobato. Esses dados mostram que a insaturação das lamelas em relação às aminas favorecem a estabilização dos sistemas esfoliados, uma vez que diminuem as interações de van der Waals entre as cadeias carbônicas e promovem a hidratação da superfície das lamelas. Os sólidos depositados em suspensão de TBAOH não possuem espécie orgânica intercalada e as suspensões contendo as razões TBA+/H+-niobato ? 0,5 produziram maior quantidade de sólido disperso (ca. 65%). O sólido esfoliado isolado da suspensão com razão 0,75 contém 10% de TBA+ neutralizando os íons H+ do niobato. À medida que o pH das suspensões é diminuído, o TBA+ é substituído por H3O+ e as partículas planas começam a encaracolar. Observou-se a formação de nanotubos nas razões molares TBA+/H+-niobato = 0,5 e 1,0, que tiveram o pH alterado para 1 e 7 respectivamente. A amostra isolada em pH 1 apresenta área específica de 139 m²g?¹ enquanto o K4Nb6O17 possui apenas 2 m²g?¹ . Os sistemas contendo tanto partículas tabulares quanto tubulares possuem potencial aplicação na área de (foto)catálise e de sensores. / The main aim of this work was to study the intercalation and exfoliation processes of the layered niobate H2K2Nb6O17 in aqueous solutions of n-hexylamine, n-propylamine and tetra-n-butylammonium hydroxide (TBAOH). It was evaluated the influence of the exfoliation agent in the process of separation of the niobate layers. A fixed amount of H2K2Nb6O17 was suspended in solution of the exfoliation agent, in the molar ratios amine/H+-niobate 0.25, 0.50, 0.75 and 1.0, and maintained under stirring at room temperature for 2 weeks. The deposited solid was separated from the opaque suspension (i.e., the exfoliated solid). For the characterization of the deposited solid, it was determined the chemical composition and the X-ray diffractogram, the termogravimetric curve and the infrared and Raman vibrational spectra were recorded. The dispersion of exfoliated particles was characterized by electronic spectroscopy while the exfoliated solid, for XRD, surface area measurement, SEM and HRTEM. Considering the deposited solids, the alkylamines are intercalated in a monolayer arrangement and practically oriented perpendicularly in relation to the niobate layers. The suspensions containing the molar ratios amine/H+-niobate 0.5 for the n-hexylamine and 1.0 for the n-propylamine produced the highest amount of exfoliated solid (ca. 35%). SEM images reveal that exfoliated solid is formed by flexible particles in a disorganized arrangement, very different from the K4Nb6O17 morphology. The diffractograms profile show a solid with organization only in the axis of piling up of the layers and also that in these particles the amines maintain the monolayer arrangement. The exfoliated particles contain 50% and 70% of n-hexylamine and n-propylamine, respectively, neutralizing the H+ ions of the niobate. These data show that the layers insaturation in relation to the amines seems to favor the stabilization of the exfoliated systems, once it reduces the van der Waals interactions among the carbon chains and facilitate the hydration of the layer surfaces. The deposited solids in suspension of TBAOH do not possess organic species intercalated and the suspensions containing the ratio TBA+/H+-niobate ? 0.5 produce the highest amount of dispersed solid (ca. 65%). The exfoliated solid isolated from suspensions with ratio 0.75 contains 10% of TBA+ neutralizing the H+ ions of the niobate. As the pH of the suspensions is decreased, TBA+ ion is replaced by H3O+ and the tabular particles begin to scroll. The nanotubes formation was observed to molar ratios TBA+/H+-niobate = 0.5 and 1.0, which pH values were changed to 1 and 7 respectively. The sample isolated at pH 1 presents specific area of 139 m²g?¹ while K4Nb6O17 possesses only 2 m²g?¹ . The systems containing plate and tubular particles possesses potential application in (photo)catalysis and sensors areas.

Compostos de vanádio são extensivamente estudados, devido suas propriedades redox, eletroquímicas, catalíticas, magnéticas e biológicas. Nesta dissertação tivemos como foco de nosso trabalho o composto VOPO4.2H2O que apresenta uma forma lamelar com suas lamelas unidas por interações de Van der Waals. Essas fracas interações interlamelares fazem do fosfato de vanadila e de seus componentes análogos excelentes matrizes para a síntese de compostos de intercalação. A morfologia do VOPO4.2H2O mostrou-se sensível a alterações de temperatura e tempo durante síntese. Através da alteração destes parâmetros obtivemos um sólido lamelar com um grau de organização inferior a matriz sintetizada à 130oC e 16 horas, devido a existência da fase II-VOPO4 que foi constatada por difração de raios-X. A quantidade de dois mols de água por mol de VOPO4 manteve-se constante segundo as análises termogravimétricas. As imagens de microscopia eletrônica de varredura confirmaram a estrutura lamelar dos produtos, no entanto uma forma rosácea foi constatada em VOPO4/160oC, sugerindo a presença da fase VOHPO4.0,5H2O, precursora da fase (VO)2P2O7 que atua como catalisador seletivo na reação de oxidação do n-butano à anidrido malêico. A intercalação de íons lantanídeos na matriz VOPO4.2H2O produziu sólidos lamelares com cristalinidade inferior a matriz hospedeira, devido a distorção dos octaedros ocasionado pela redução dos íons vanádio (V) à (IV) apresentando uma diminuição na distância interlamelar com concomitante inserção de íons lantanídeos visando o balanceamento de carga na matriz. A reação de intercalação da matriz VOPO4.2H2O utilizando os tensoativos CTAB e CPC apresentaram resultados satisfatórios confirmados por difração de raios-X e espectrofotometria na região infravermelho. A intercalação de poli(óxido de etileno) assistida com brometo de cetiltrimetilamônio mostrou-se mais adequada apresentando sólidos organizados devido as moléculas de CTAB atuarem como agente diretivo. / Vanadium compounds are intensively studied due to their electrochemical, catalytic, magnetic and biological properties. In this work, our goal was to investigate the VOPO4.2H2O (vanadyl phosphate), which has a lamellar structure formed by VOPO4 sheets interconnected by weak interactions. Taking advantage of this structure, it is possible to synthesize several different intercalation compounds in which the guest species can vary from simple ions to polymeric species. The morphology of VOPO4.2H2O is very sensitive to temperature and time of reaction changes. By varying both parameters, several lamellar matrices have been synthesized. X-ray diffraction, thermal analysis and scanning electronic microscopy showed that depending on the synthetic conditions the arrangements VOPO4.2H2O can change the shape. For instance, in one of the experiments, a rose-like structure was produced, suggesting the presence of VOHPO40.5H2O phase, precursor of (VO)2P2O7 phase, which acts as oxidation catalyst of the n-butane to maleic anhydride. Intercalation of lanthanide ions leads to lamellar solids with low crystallinity in relation to the matrix due to octahedric distortion caused by reduction of vanadium ions (VV to VIV). Besides, it was observed a decrease of the interlamellar distance in function of the electroneutrality balance between the lamellar sheets. Intercalation compounds were produced by reacting surfactants molecules directly with the matrix under hydrothermal conditions. Surfactant-assisted intercalation of poly(ethylene oxide) into VOPO4.2H2O was conducted under soft conditions with the surfactant/matrix compound as a suspension in an aqueous polymer solution.

The desmosome is one of the major cell adhesion junctions found in the epithelia, heart, and hair follicle. Described as a “rivet” that hold cells together, it provides these tissues with the integrity to withstand the tremendous forces they face in everyday life. Defects in this junction can lead to devastating diseases where patients are susceptible to skin infections and cardiovascular defects. Limited treatments exist for diseases of the desmosome, and strategies do not target all symptoms. Therefore, delineating the function and regulation of desmosomes is of paramount importance for the development of prevention and treatment strategies. The Xenopus laevis has been utilized for the study of embryonic development and tissue movements. This study takes advantage of the frog model to study a key desmosomal protein, desmoplakin (Dsp), in the epidermal development of the embryo. First, Xenopus embryonic epidermis has junctional desmosomes as early as the blastula stages. Desmosomes numbers per junction increase as the embryo develops. Dsp is present in many epidermally-derived structures in the embryo at varying levels. Xenopus embryos deficient in desmoplakin have phenotypic defects in epidermal structures and the heart, mimicking mammalian models. Embryos with reduced Dsp exhibit an increased susceptibility to epidermal damage under applied mechanical forces. Assays also reveal a potential role for desmosomes in radial intercalation, a process through which cells move from the inner to the outer epidermal layers. Embryos with reduced Dsp exhibit a slight reduction in intercalation and defects in intercalating cell types, including multiciliated cells and small secretory cells. Finally, c-Jun N-terminal kinase (JNK) may have a potential role in the regulation of desmosome assembly and adhesion. Embryos with deficient Dsp display a partial recovery of mechanical integrity when treated with a JNK inhibitor.

Graduation date: 1996

Atomic force microscopy (AFM) is a particularly useful tool, for obtaining structural information about drug-nucleic acid interactions. The mode of drug binding intercalation versus groove binding can be determined from images acquired on individual DNA molecules as the length of a DNA molecule increases in direct proportion to the number of intercalators bound to it. The efforts of this research were directed toward elucidating the mode of binding of a series of drugs based on polymers of naphthalenetetracarboxyl diimide (NDI) interacting with a linearized DNA plasmid. During the course of the investigation of these drugs, DNA intercalation was confirmed as the mode of binding and the binding affinity estimated. Unexpectedly, concentration-dependent formation of secondary DNA structures including condensates was observed. DNA toroids, spheres, and rods were imaged and measured. Conformations that are believed to be intermediate condensate forms were also identified at lower poly-NDI concentrations. Models for the DNA condensation process have been proposed. Ultimately, this research furthers the understanding of DNA condensation which can be applied to gene delivery systems and anti-viral agents. It may also help direct the development of better drugs based on the insight of poly-intercalators interactions with DNA.

Lifes origin is, in many ways, coupled to understanding the evolution of nucleic acids. In contemporary life, proteins and nucleic acids are intricately dependent upon each other for a host of functions including, but not limited to, replication and chemical ligation. Protein enzymes are necessary for the synthesis of DNA and RNA, while nucleic acids are necessary for both the coding and synthesis of proteins. According to the RNA World hypothesis, early life used nucleic acids for both information storage and chemical catalysis before the emergence of protein enzymes. However, it still remains a mystery how nucleic acids were able to assemble and replicate before the advent of protein enzymes. We have utilized the ability of small molecule intercalation to assemble nucleic acids into stable secondary structures. Our motivation in this pursuit comes from the recently proposed Molecular Midwife hypothesis where small molecules may have acted as nanoscale structural scaffolds upon which the nucleic acid bases were able to stack into stable structures and undergo assembly into polymers. We have also found that the kinetics and thermodynamics of small molecule-mediated assembly and secondary structure formation are strongly dependent upon oligonucleotide length. Small molecules bind to nucleic acids by multiple modes of binding and this phenomenon must be properly understood in order to achieve robust and versatile assembly of nucleic acid structures.

Non-covalent interactions are of great interest to chemists and biologists who study the molecular structure and function of biological systems, as well as those who seek to control, undo, or improve upon the efficiency of these systems with man-made chemical tools. The Iverson group has specifically applied noncovalent aromatic donor-acceptor interactions to biotic and abiotic aqueous systems through the use of the electron-rich 1,5-dialkoxynaphthalene (DAN) and electron-deficient 1,4,5,8-naphthalenetetracarboxylic diimide (NDI) moieties. Chapter 1 introduces and reviews the current state of self-assembly research, especially work conducted in aqueous media. Chapter 2 delineates the design and synthesis of a molecule that can self-assemble and form disulfide bonds, with the goal of creating higher-order structure. Chapter 3 comprises the design and synthesis of a series of pendant-NDI bisintercalators of DNA that are distinct from the backbone-incorporated intercalators previously employed in our laboratory. Chapter 4 contextualizes the term of art “pi-stacking,” reviewing the current state of knowledge of specific contributions to this effect and commenting on the putative uniqueness of the interaction. Theoretical and experimental work in the field is summarized. The work discussed in this dissertation serves to expand the scope of programmability of our DNA intercalators, to probe the higher-order assembly behavior of our donor-acceptor pair, and to clarify the term “pi-stacking,” lately overused, that imperfectly describes the interaction that gives both these systems their compelling binding properties. / text

A series of studies from our lab have investigated the threading polyintercalator approach to sequence specific DNA binding using a 1,4,5,8-naphthalene tetracarboxylic diimide (NDI) intercalating unit connected by flexible peptide linkers. Herein is a report of the sequence specificity, as well as a detailed kinetic analysis, of a threading NDI tetraintercalator. DNase I footprinting using two ~500 base pair DNA fragments containing one designed binding site for the tetraintercalator confirmed highly sequence specific binding. Kinetic analyses include 1H NMR, gel mobility-shift assays, and stopped-flow UV measurements to reveal a polyintercalation binding mode that demonstrates significant similarities between association rate profiles and rate constants for the tetraintercalator binding to its preferred versus a random oligonucleotide sequence. Sequence specificity was found to derive almost entirely from large differences in dissociation rates from the preferred versus random oligonucleotide sequences. Interestingly, the dissociation rate constant of the tetraintercalator complex dissociating from its preferred binding site was extremely slow, corresponding to a 16 day half-life at a benchmark 100 mM [Na+]. This dissociation result for the tetraintercalator is one of the longest bound half-lives yet measured, and to the best of our knowledge, the longest for a DNA binding small molecule. Such a long-lived complex raises the possibility of using threading polyintercalators to disrupt biological processes for extended periods. Current focus is given to deciphering a mechanism for the molecular recognition of the tetraintercalator preferred binding site within a long sequence of DNA. Initial DNase I footprinting results on an approximate 500mer DNA sequence containing three sequential preferred binding sites reveal that the tetraintercalator likely locates its designed binding site by a macro- or microscopic dissociation/re-association type of mechanism. Cooperativity is a possible ally to binding, leaving future studies to distinguish the mechanism for molecular recognition in a manner that is capable of circumventing cooperative binding. Taken together, the threading polyintercalation binding mode presents an interesting topology to sequence specific DNA binding. Extraordinarily long dissociation rates from preferred binding sites offers many future possibilities to disrupt biological processes in vivo. / text