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Estudo espectroscopico e morfologico de filmes automontados de azocompostos; Spectroscopic and morphological study of self-assembly films of azocompounds

Davison Storai de Barros
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 17/11/2006 PT
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Neste trabalho são estudadas as propriedades fotoquímicas e morfológicas de filmes automontados compostos de um polieletrólito fraco e azocorantes em função das condições impostas nas soluções de origem, como o pH, a força iônica e tamponamento. Na automontagem, os filmes são fabricados pela deposição de camadas alternadas de dois materiais, de cargas elétricas opostas, a partir de suas soluções aquosas em um substrato de vidro. Os materiais usados foram o polieletrólito catiônico hidrocloreto de poli(alilamina) (PAH) e três azocorantes aniônicos: Vermelho do Congo (CR), Ponceau SS (PSS) e Alaranjado de Metila (MO). Foram fabricados filmes de PAH/CR, PAH/PSS e PAH/MO. Para avaliar somente o efeito do pH, foram usados três valores de pH (3, 7 e 10). Para verificar o efeito da força iônica, foram usadas soluções aquosas de cloreto de potássio em diferentes concentrações e, para verificar a influência de tampão, foram usados três sistemas tampão, um para cada valor de pH. Foram usadas as técnicas de espectroscopia UV-vis e turbidimetria para investigar as propriedades espectroscópicas das soluções, dos filmes e a solubilidade do PAH. Foi utilizada a técnica de microscopia de força atômica para verificar a morfologia do filme. Observa-se que a deposição dos corantes e do PAH no filme depende de suas densidades de carga...

USING THE SELF-ASSEMBLY TECHNIQUE FOR THE FABRICATION OF ULTRA-THIN FILMS OF A PROTEIN

Borato,C.E.; Herrmann,P.S.P.; Colnago,L.A.; Oliveira Jr.,O.N.; Mattoso,L. H. C.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/1997 EN
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The self-assembly technique is employed for producing alternating ultra-thin films of lysozyme and poly(styrene sulfonate) (PSS). The influence of important parameters in the self-assembly process, namely immersion time, drying method, solution pH and ionic strength, on adsorption kinetics is investigated by ultraviolet (UV) spectroscopy. The absorbance increases rapidly in the initial stages of adsorption for all pHs studied, before reaching a plateau indicative of complete adsorption. Adsorption is considerably more effective when the proton concentration in the solution increases, which is attributed to the increase in the positive charge density within the protein molecules. Furthermore, UV absorbance increases linearly with the number of bilayers (lysozyme/PSS), indicating that a constant amount of material is being adsorbed at each deposition process. These results are highly promising as the self-assembled films are of great interest for biotechnology and molecular electronic applications

Self-Assembly of Polyhedral Hybrid Colloidal Particles

Perro, Adeline; Duguet, Etienne; Ravaine, Serge; Manoharan, Vinothan N.
Fonte: Materials Research Society Publicador: Materials Research Society
Tipo: Artigo de Revista Científica
EN_US
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We have developed a new method to produce hybrid particles with polyhedral shapes in very high yield (liter quantities at up to 70% purity) using a combination of emulsion polymerization and inorganic surface chemistry. The procedure has been generalized to create complex geometries, including hybrid line segments, triangles, tetrahedra, octahedra, and more. The optical properties of these particles are tailored for studying their dynamics and self-assembly. For example, we produce systems that consist of index-matched spheres allowing us to define the position of each elementary particle in three-dimensional space. We present some preliminary studies on the self-assembly of these complex shaped systems based on electron and optical microscopy.; Engineering and Applied Sciences; Physics

Self-Assembly of Colloidal Spheres with Specific Interactions

Collins, Jesse Wronka
Fonte: Harvard University Publicador: Harvard University
Tipo: Thesis or Dissertation
EN_US
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In this thesis, I discuss engineering colloidal particles to have specific, isotropic interactions and studying their cluster geometries in equilibrium. I discuss light scattering experiments showing that a highly specific protein, Dscam, is unstable against thermal aggregation. This result lead me to use DNA instead to control interparticle specificity. I coated 1-micron diameter polystyrene particles uniformly with DNA. I used fluorescence microscopy with oxygen-scavenging enzymes to observe these particles self-assembling in clusters. These experiments show that a packing of 6 spheres that is rarely seen in a single-component system is observed very often in an optimized 3-species system. Then I show experiments using the same 3 species but 9 total particles, finding that the equilibrium yields of the most likely cluster relative to other stable clusters are lower than at 6 particles. I conclude from these experiments that optimizing the assembly of an otherwise unlikely configuration may require nearly as many species as particles. Finally, I investigate the scalability of self-assembly of particles with isotropic and specific interactions theoretically. I use both exact and approximate partition functions to show that spheres with specific interactions can have energy landscapes with thermodynamically large numbers of strictly local minima relative to the number of their ground states. Compared to single-component systems...

Developmental Self-Assembly of a DNA Tetrahedron

Sadowski, John P.; Calvert, Colby R.; Zhang, David Yu; Pierce, Niles A.; Yin, Peng
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
EN_US
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Kinetically controlled isothermal growth is fundamental to biological development, yet it remains challenging to rationally design molecular systems that self-assemble isothermally into complex geometries via prescribed assembly and disassembly pathways. By exploiting the programmable chemistry of base pairing, sophisticated spatial and temporal control have been demonstrated in DNA self-assembly, but largely as separate pursuits. By integrating temporal with spatial control, here we demonstrate the “developmental” self-assembly of a DNA tetrahedron, where a prescriptive molecular program orchestrates the kinetic pathways by which DNA molecules isothermally self-assemble into a well-defined three-dimensional wireframe geometry. In this reaction, nine DNA reactants initially coexist metastably, but upon catalysis by a DNA initiator molecule, navigate 24 individually characterizable intermediate states via prescribed assembly pathways, organized both in series and in parallel, to arrive at the tetrahedral final product. In contrast to previous work on dynamic DNA nanotechnology, this developmental program coordinates growth of ringed substructures into a three-dimensional wireframe superstructure, taking a step toward the goal of kinetically controlled isothermal growth of complex three-dimensional geometries.

Monitoring Defect Formation in Colloidal Self Assembly using Photonic Bandgap Variations

Koh, Yaw Koon; Wong, Chee Cheong
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Artigo de Revista Científica Formato: 549266 bytes; application/pdf
EN
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Defect control in colloidal crystals is essential for these nanostructures to be effective as photonic bandgap (PBG) materials. We have used in-situ monitoring of the PBG of a colloidal crystal to study the structural changes during colloidal self assembly, with a focus on the formation of macroscopic defects such as cracks. These findings allow us to model the final stages of colloidal self assembly and explain the formation of growth defects in colloidal crystal. Our model suggests that cracks are intrinsic to self assembly growth methods. . However, by tuning the interaction potential between the colloids, it is possible to minimize the cracks in colloidal crystals.; Singapore-MIT Alliance (SMA)

Clarifying the determinants of self-assembly in the amyloid-β 16–22 peptide; Clarifying the determinants of self-assembly in the amyloid-[beta] 16–22 peptide

Senguen, Fehmi Timur (1980 - ); Nilsson, Bradley L.
Fonte: University of Rochester Publicador: University of Rochester
Tipo: Tese de Doutorado Formato: Number of Pages:xvi, 288 leaves; Illustrations:ill. (some col.)
ENG
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Thesis (Ph. D.)--University of Rochester. Dept. of Chemistry, 2011.; Amyloidogenic peptides and proteins have been of great interest recently, not only due to their presence in pathogenic plaques in humans but also as novel biopolymer materials. While much is known about the physico-kinetic forces and amino acid properties that are involved in the formation of amyloid peptides, two issues remain to be resolved. The role of aromatic π-π interactions during the formation and stabilization of amyloid fibers have been intensely debated for the better part of two decades and still no consensus has been reached. Another question arose with the advent of novel methods for the prediction of amyloidogenic sequences which are suggesting that our understanding of underlying forces involved in the formation of amyloid fibers is not complete. Predictive algorithms that consider only the steric profiles of peptide sequences have achieved similar levels of success to those algorithms that consider all other known factors, which implies that the steric interactions may be of great importance, although they have been generally overlooked in experimental studies. This thesis aims to answer both questions with the use of a the model amyloid fragment peptide Aβ(16–22) and rational mutational analysis. To elucidate the role of aromatic π-π interactions during amyloidogenesis the aromatic Phe residues at positions 19 and 20 were mutated to the non-natural amino acids pentafluorophenylalanine (F5-Phe) and cyclohexylalanine (Cha). These mutations allow for the selective tuning of aromaticity while only minimally perturbing the carbon skeleton. The results of this study clearly indicate that aromatic π-π interactions are not required for the formation or stabilization of amyloid fibers...

Self-assembly and hydrogelation of Fmoc-phenylalanine derivatives

Ryan, Derek M. (1985 - ); Nilsson, Bradley L.
Fonte: University of Rochester Publicador: University of Rochester
Tipo: Tese de Doutorado Formato: Number of Pages:xvii, 347 leaves; Illustrations:ill. (some col.)
ENG
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Thesis (Ph. D.)--University of Rochester. Dept. of Chemistry, 2011.; The ability of peptides and small molecules to spontaneously self-assemble into amyloid-like fibrils has been exploited in the development of noncovalent hydrogels. Noncovalent hydrogels have been utilized for numerous biomedical applications such as cell culture, drug delivery, and tissue scaffolding. To date a large number of the reported small molecule based hydrogels have been discovered serendipitously, making customization of the bulk material properties a largely trial and error process. Fluorenylmethoxycarbonyl (Fmoc) protected amino acids have been shown to be a potent low molecular weight hydrogelators. There is a growing need for further understanding of the molecular recognition events that drive the self-assembly and hydrogelation processes. Insights into the molecular origins of the self-assembly will facilitate the de novo development of amino acid based noncovalent hydrogelators. This thesis investigates the influence of side chain [pi]-[pi] interactions on the self-assembly and hydrogelation of Fmoc-Phenylalanine derivatives. Halogenation of the phenyl side chain was shown to promote the assembly of a previously unassembled amino acid derivative. It was also demonstrated that the rate of self-assembly could be effectively tuned through substitution of the phenyl side chain of Fmoc-Phenylalanine...

Dimension Controlled Self-Assembly of Perylene Based Molecules

Sayyad, Arshad S.
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
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Recent advances in the self-assembly of highly organized structures of organic semiconducting molecules by controlled non-covalent interactions has opened avenues for creating materials with unique optical and electrical properties. The main focus of this thesis lies in the synthesis and self-assembly of n-type perylene based organic semiconducting molecules into highly organized materials. Perylene based molecules used in this study are perylene diimide (PTCDI, two side-chains), perylene mono imide (m-PTCI, one side-chain), perylene tetracarboxylic acid (PTCA, no side-chain) and tetra-alkali metal salts of PTCA (M 4 -PTCA, no side-chain), which are synthesized from the parent perylene tetracarboxylic dianhydride (PTCDA). The self-assembly of these molecules have been performed using solution processing methods (dispersion, phase-transfer, and phase-transfer at high temperature) by taking advantage of the changes in solubility of the molecules, wherein the molecular interactions are maximized to favorably allow for the formation of highly organized structures. Dimension control (1D, 2D and 3D structures) of self-assembly has been obtained for different perylene based molecules by appropriate design of the molecule followed by controlling the conditions of assembly. In case of PTCDI...

Multi-Hierarchical Self-Assembly of Collagen Mimetic Peptides into AAB Type Heterotrimers, Nanofibers and Hydrogels Driven by Charged Pair Interactions

O'Leary, Lesley Russell
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Thesis; Text Formato: 258 p.; application/pdf
ENG
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Replicating the multi-hierarchical self-assembly of collagen (peptide chain to triple helix to nanofiber and, finally, to a hydrogel) has long attracted scientists, both from the fundamental science perspective of supramolecular chemistry and for the potential biomedical applications perceived in tissue engineering. In terms of triple helical formation, collagen is the most abundant protein in the human body with at least 28 types, yet research involving collagen mimetic systems has only recently began to consider the innate ability of collagen to control helix composition and register. Collagen triple helices can be homotrimeric or heterotrimeric and while some types of natural collagen form only one specific composition of helix, others can form multiple. It is critical to fully understand and, if possible, reproduce the control that native collagen has on helix composition and register. In terms of nanofiber formation, many approaches to drive the self-assembly of synthetic systems through the same steps as natural collagen have been partially successful, but none have simultaneously demonstrated all levels of structural assembly. In this work, advancements in the ability to control helix composition and replicate the multi-hierarchical assembly of collagen are described. Both positive and negative design for the assembly of AAB type collagen heterotrimers were utilized by promoting heterotrimer formation though the use of charged amino acids to form intra-helix electrostatic interactions...

Self-Assembly of Dinuclear Complexes Featuring Aromatic and Aliphatic Walls

Stevenson, Kristina
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
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The objective of my MSc thesis is to study the self-assembly process of macrocyclic complexes, as well as the properties that affect the obtained supramolecular architectures. The possibility of substrate recognition within the cavity of these complexes is also of interest. Preparation of three new ligands based on the triazole-pyridine chelating units connected through variable spacer groups, as well as the complexes formed with octahedral metal ions, are described herein. The first ligand contained a naphthalene spacer region, which was longer than the previously examined xylene spacer. This extension increases the distance between metal ions in the complex, as well as the size of the cavity. More work is required to obtain the unsaturated double-stranded complex, which could potentially bind substrate molecules within its cavity. The triple-stranded saturated complexes with [Fe(H2O)6](BF4)2 and [Ni(H2O)6](BF4)2 both gave insight into the process of self-assembly. The next two ligands were designed to probe the effect that increasing the length of an aliphatic spacer had on complex self-assembly. Both ethyl and propyl spacer units had been previously studied, so butyl and pentyl spacer groups were the natural next step to analyze. The length of the alkyl spacer was found to be very important in the nature of the obtained complex. As the length of the alkyl chain...

Autoensamblaje del caseinomacropéptido (CMP) y su impacto en la gelificación y espumado; Casinmacropeptide (CMP) self-assembly and its impact on gelation and foam

Farías, María Edith
Fonte: Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires Publicador: Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires
Tipo: info:eu-repo/semantics/doctoralThesis; tesis doctoral; info:eu-repo/semantics/publishedVersion Formato: application/pdf
Publicado em //2012 SPA
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El objetivo de este trabajo fue estudiar mediante dispersión dinámica de luz (DLS) el autoensamblaje del caseinomacropéptido (CMP) en relación al pH, tipo de ácido y presencia de sales y su impacto en la gelificación y el espumado. A pH 7,0, las soluciones de CMP son estables con el tiempo y no gelifican aún bajo calentamiento. La forma predominante del CMP en estas condiciones es la monomérica. A pH < 4,5 ya sea a temperatura ambiente o por calentamiento, el CMP genera en el tiempo una estructura ordenada gelificada de características viscoelásticas, baja dureza y cohesividad. Dicha estructura es reversible a un cambio ulterior de pH pero no a la forma monomérica original. Se propuso un modelo de autoensamblaje y gelificación del CMP. El autoensamblaje del CMP y su gelificación están modulados por diferentes condiciones del medio: pH, temperatura, tipo de ácido y presencia de sales. El tipo de ácido y la presencia de sales impactan en la asociación del CMP por vía hidrofóbica, la cual constituye la primera etapa del autoensamblaje, conduciendo a dímeros (HCl), tetrámeros (ácido cítrico, ácido láctico, NaCl, CaCl2) o hexámeros (ácido acético). Estas formas asociadas del CMP son las que posteriormente interactúan a pH < 4...

Expanding the Solvent Chemical Space for Self-Assembly of Dipeptide Nanostructures

Mason, Thomas O.; Chirgadze, Dimitri Y.; Levin, Aviad; Adler-Abramovich, Lihi; Gazit, Ehud; Knowles, Tuomas P. J.; Buell, Alexander K.
Fonte: ACS Publicador: ACS
Tipo: Article; accepted version
EN
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This is the accepted manuscript for a paper published in ACS Nano, 2014, 8 (2), pp 1243?1253 DOI: 10.1021/nn404237f , Publication Date (Web): January 14, 2014; Nanostructures composed of short, noncyclic peptides represent a growing field of research in nanotechnology due to their ease of production, often remarkable material properties, and biocompatibility. Such structures have so far been almost exclusively obtained through self-assembly from aqueous solution, and their morphologies are determined by the interactions between building blocks as well as interactions between building blocks and water. Using the diphenylalanine system, we demonstrate here that, in order to achieve structural and morphological control, a change in the solvent environment represents a simple and convenient alternative strategy to the chemical modification of the building blocks. Diphenylalanine (FF) is a dipeptide capable of self-assembly in aqueous solution into needle-like hollow micro- and nanocrystals with continuous nanoscale channels that possess advantageous properties such as high stiffness and piezoelectricity and have so emerged as attractive candidates for functional nanomaterials. We investigate systematically the solubility of diphenylalanine in a range of organic solvents and probe the role of the solvent in the kinetics of self-assembly and the structures of the final materials. Finally...

Self-assembly of synthetic and biological components in water using cucurbit[8]uril

Zayed, Jameel Majed
Fonte: University of Cambridge; Department of Chemistry Publicador: University of Cambridge; Department of Chemistry
Tipo: Thesis; not applicable; doctoral; PhD Formato: Digital copy of the submitted hard-bound thesis
EN
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This thesis discusses progress made towards assembling molecular building blocks in the presence of our molecular host of choice, cucurbit[8]uril (CB[8]). Our studies on the self-assembly of synthetic and biological components in water bridge overlapping concepts and techniques drawn from the fields of synthetic organic chemistry, supramolecular self-assembly, and applied NMR techniques. Chapter 1 introduces the reader to chemical complexity, and how supramolecular chemists have advanced in their capability of assembling more complex molecular architectures. The discussion focusses particularly on self-assembly carried out in the aqueous phase, and how, like in biology, molecular design of the building blocks become critical in enabling non-covalent assembly to occur in this dynamic, and relatively competitive environment. The cucurbit[n]uril family of molecular hosts are then introduced with an overview of their modes of binding, and affinities towards typical guests. Finally, a practical introduction to NMR methods gaining prominence in supramolecular chemistry is presented. In particular, the use of diffusion NMR, a key tool for probing the solution dynamics of molecular assemblies, is highlighted. Chapter 2 details work carried out on the CB[8]-mediated self-assembly of supramolecular block copolymers from polymeric...

Rational design of self-assembly pathways for complex multicomponent structures

Jacobs, William M.; Reinhardt, Aleks; Frenkel, Daan
Fonte: PNAS Publicador: PNAS
Tipo: Article; accepted version
EN
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This is the author accepted manuscript. The final version is available from PNAS at http://www.pnas.org/content/112/20/6313.abstract.; The field of complex self-assembly is moving toward the design of multiparticle structures consisting of thousands of distinct building blocks. To exploit the potential benefits of structures with such ?addressable complexity,? we need to understand the factors that optimize the yield and the kinetics of self-assembly. Here we use a simple theoretical method to explain the key features responsible for the unexpected success of DNA-brick experiments, which are currently the only demonstration of reliable self-assembly with such a large number of components. Simulations confirm that our theory accurately predicts the narrow temperature window in which error-free assembly can occur. Even more strikingly, our theory predicts that correct assembly of the complete structure may require a time-dependent experimental protocol. Furthermore, we predict that low coordination numbers result in nonclassical nucleation behavior, which we find to be essential for achieving optimal nucleation kinetics under mild growth conditions. We also show that, rather surprisingly, the use of heterogeneous bond energies improves the nucleation kinetics and in fact appears to be necessary for assembling certain intricate 3D structures. This observation makes it possible to sculpt nucleation pathways by tuning the distribution of interaction strengths. These insights not only suggest how to improve the design of structures based on DNA bricks...

Theoretical prediction of free-energy landscapes for complex self-assembly

Jacobs, William M.; Reinhardt, Aleks; Frenkel, Daan
Fonte: AIP Publicador: AIP
Tipo: Article; accepted version
EN
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This is the accepted manuscript. Copyright (2015) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in The Journal of Chemical Physics 142, 021101 (2015) and may be found at http://doi.org/10.1063/1.4905670; We present a technique for calculating free-energy profiles for the nucleation of multicomponent structures that contain as many species as building blocks. We find that a key factor is the topology of the graph describing the connectivity of the target assembly. By considering the designed interactions separately from weaker, incidental interactions, our approach yields predictions for the equilibrium yield and nucleation barriers. These predictions are in good agreement with corresponding Monte Carlo simulations. We show that a few fundamental properties of the connectivity graph determine the most prominent features of the assembly thermodynamics. Surprisingly, we find that polydispersity in the strengths of the designed interactions stabilizes intermediate structures and can be used to sculpt the free-energy landscape for self-assembly. Finally, we demonstrate that weak incidental interactions can preclude assembly at equilibrium due to the combinatorial possibilities for incorrect association.; W.M.J. acknowledges support from the Gates Cambridge Trust and the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1143678. D.F. acknowledges European Research Council Advanced Grant No. 227758 and Engineering and Physical Sciences Research Council Programme Grant No. EP/I001352/1. Research carried out in part at the Center for Functional Nanomaterials...

Understanding Elastin-Like Polypeptide Block Copolymer Self-assembly Behavior

Hassouneh, Wafa Saadat
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2013
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Elastin-like polypeptides (ELPs) are thermally responsive polymers composed of the pentapeptide repeat Valine-Proline-Glycine-X-Glycine where X is any amino acid except proline. ELP diblocks have been engineered by creating two ELP blocks with hydrophilic and hydrophobic guest residues. The hydrophobic block desolvates at a lower temperature and forms the core of a micelle while the still hydrated hydrophilic block forms the corona. ELP micelles are promising drug delivery vehicles for cancer therapeutics. ELP diblocks offer a unique method to display targeting proteins multivalently on micelles to improve tumor cell uptake. As ELPs are genetically encoded, proteins can be seamlessly fused at the genetic level to the ELP diblock. The protein ELP diblock fusions can be synthesized as one polypeptide chain that is of precise molecular weight and highly monodisperse, and no post-synthesis modification is necessary. Self-assembly behavior of ELP diblocks is known to tolerate fusion to small peptides (< 10 amino acids) but their self-assembly behavior has not be examined when fused to proteins that are 100-200 amino acids. Here, we hypothesize that molecular weight of the protein and the surface properties of the protein will be factors in determining its effect on ELP diblock self-assembly. In addition...

A Theoretical and Experimental Study of DNA Self-assembly

Chandran, Harish
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2012
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The control of matter and phenomena at the nanoscale is fast becoming one of the most important challenges of the 21st century with wide-ranging applications from energy and health care to computing and material science. Conventional top-down approaches to nanotechnology, having served us well for long, are reaching their inherent limitations. Meanwhile, bottom-up methods such as self-assembly are emerging as viable alternatives for nanoscale fabrication and manipulation.

A particularly successful bottom up technique is DNA self-assembly where a set of carefully designed DNA strands form a nanoscale object as a consequence of specific, local interactions among the different components, without external direction. The final product of the self-assembly process might be a static nanostructure or a dynamic nanodevice that performs a specific function. Over the past two decades, DNA self-assembly has produced stunning nanoscale objects such as 2D and 3D lattices, polyhedra and addressable arbitrary shaped substrates, and a myriad of nanoscale devices such as molecular tweezers, computational circuits, biosensors and molecular assembly lines. In this dissertation we study multiple problems in the theory, simulations and experiments of DNA self-assembly.

We extend the Turing-universal mathematical framework of self-assembly known as the Tile Assembly Model by incorporating randomization during the assembly process. This allows us to reduce the tile complexity of linear assemblies. We develop multiple techniques to build linear assemblies of expected length N using far fewer tile types than previously possible.

We abstract the fundamental properties of DNA and develop a biochemical system...

Self-assembly of magnetic nanoparticles into complex superstructures: Spokes and spirals

Neto, Chiara; Bonini, Massimo; Baglioni, Piero
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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Dipole-dipole interactions in the most commonly used ferrofluids are relatively weak and there are only a few reports of chain formation in zero magnetic field. Here we report on the pronounced aggregation of a ferrofluid formed by maghemite nanoparticles (10 nm in diameter), investigated by atomic force microscopy (AFM), small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS). The ferrofluid forms chain-like filaments independently of particle concentration. Furthermore, the ferrofluid forms self-assembled patterns, namely ordered superstructures, such as spirals, concentric rings and spokes (radially directed lines), when deposited on a substrate under a magnetic field. Our results reveal an unprecedented level of complexity in the self-assembly of magnetic nanoparticles. Further optimization of the working conditions could eventually enable the reproducible creation of three-dimensional magnetic structures with chosen architecture on submicron length scales.

Critical self-assembly concentration of bolaamphiphilic peptides and peptide hybrids determined by fluorescence measurements

Martari,Marco; Sanderson,Ronald D.
Fonte: South African Journal of Chemistry Publicador: South African Journal of Chemistry
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2008 EN
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The study of the self-assembly properties of peptides and proteins is important for the understanding of molecular recognition processes and for the rational design of functionalbiomaterials. Novel bolaamphiphilic peptides and peptide hybrids incorporating non-natural aminoacids were designed around a model lysine/leucine-rich peptide with the intention to study their self-assembly behaviour. Steady-state fluorescence measurements using pyrene as fluorescent probe were adapted to the determination of the critical self-assembly concentrations (CSACs) of these amphiphilic peptides and peptide hybrids. Different experimental conditions were studied. The morphology of the peptide aggregates was evaluated by scanning electron microscopy (SEM). Concentration and pH have been revealed to play a key role in the control of the process. Peptides presented different three-dimensional supramolecular arrangements that were correlated with their aminoacid compositions (specifically considering the presence of tyrosine and proline) and CSAC values.