• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 151
  • 88
  • 74
  • 10
  • 9
  • 8
  • 6
  • 5
  • 3
  • 1
  • 1
  • Tagged with
  • 406
  • 79
  • 60
  • 43
  • 36
  • 34
  • 33
  • 29
  • 29
  • 28
  • 27
  • 26
  • 24
  • 24
  • 24
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Engineering Stimuli-Responsive Protein Phase Separations for Protein Stabilization, Modulation of Protein Activity, and Intracellular Protein Delivery

Horn, Justin Michael January 2022 (has links)
Proteins and peptides represent a unique class of biological materials, capable of self-assembling into higher-order structures and participating in multiple types of phase separation. Recruitment of proteins into separate phases or small-scale self-assemblies has been leveraged to produce unique behaviors in peptides, with applications in intracellular protein delivery, increasing enzyme catalytic activity, and protein separation and purification. Proteins are chemically diverse and highly modifiable, both through post-translational modification of amino acid residues and through modification of the primary peptide sequence. Here, we use the unique chemical and genetic modifiability of proteins to control protein self-assembly, phase separation, and tertiary structure in several model systems. In the first of these systems the gene editing enzyme, cas9 is modified to facilitate encapsulation in protein-synthetic polymer polyelectrolyte complex (PEC) micelles. These micelles were designed for endosomal uptake and then subsequent disassembly at mildly acidic pH and in the presence of endosomal proteases to facilitate endosomal escape of the cas9 protein cargo. In the second system, we designed an intrinsically disordered peptide to form a stimuli-responsive, entirely peptide PEC micelle system, capable of encapsulating a supercationic protein. The phase behavior of the peptide PEC micelles was characterized with respect to salt concentration, positive charge fraction, and temperature. Finally, an enzymatic protein was conjugated to a temperature- and light-responsive polymer. The resulting bioconjugate was purified and shown to undergo light- and temperature-induced changes in the phase behavior.
42

Transport and Adsorption in Nanoscale Confinement

Zhang, Zechen 27 September 2022 (has links)
Nanoscale confinement can be defined as a space confined by interfaces with at least one nanometer-scale dimension. Objects under nanoscale confinement have a large ratio of interfacial area to volume that makes interfacial properties have significant impact. This dissertation examines three cases in which liquids are confined between solids. The main focus (two papers) describes how electrostatic interactions between two interfaces affect ions confined within the liquid. Commonly, the charge distribution near an interface is described by electrical double layer model, where the characteristic decay length of the potential is the Debye length κ^(-1), which is typically 1–100 nm. In a nanoscale confinement, the electrostatic potential from both confining surfaces overlaps, and there is no bulk solution in the confined liquid. If the two surfaces have the same potential in isolation, the potential will increase throughout the liquid phase. I examine two hypotheses for ions under confinement in aqueous solution: (1) diffusion of ions will be hindered by the electrostatic potential; (2) surfactants will form surface aggregates (a form of micelles) that would not occur without the modified potential. To test the first hypothesis, I studied diffusion of fluorescein sodium salt in the nanoscale water confined between glass surfaces. The confining glass surfaces were fabricated by thermally bonding Borofloat glass wafers. Fluorescence microscopy was used to monitor the amount of fluorescein throughout the confined water, and thereby to understand the diffusion Measurements with done for a variety of different Debye lengths and water film thicknesses. I found that the time for fluorescein to reach equilibrium distribution in the nano-scale confinement could be 10× longer when there was no salt initially present compared to when salt was present. However, even a small amount of salt initially in the confined liquid led to a very weak effect of Debye length on diffusion. Thus, provided that the surface potential inside a thin film is initially screened by even a low concentration of electrolyte inside the confinement, diffusion is unhindered. A practical application of this result is delivery of dissolved species should not be preceded by infusion of pure water into pores if speedy delivery is desired. For the second hypothesis, I studied adsorption and aggregation of dodecyltrimethylammonium bromide (DTAB), a cationic surfactant, within the same type of nanoscale confinement by Borofloat glass. A fluorescent dye, Nile red, whose fluorescence depends on its solvent environment was used to indicate formation of surface aggregates by the surfactant. We found that surface aggregation of DTAB occurred at a very low surfactant concentration (<1 % of the critical micelle concentration) when the confinement was less than 30 nm, which was about one Debye length of the solution. This finding overturns a major assumption of many surface forces measurements and ideas of colloidal stability. It has been customary to assume that the state of surfactant aggregation is constant when two particles approach, whereas we find that aggregation changes with the solution is confined. The change in aggregation can lead to a change in electrical potential, which affects the surface forces and colloidal stability. Past work that used this assumption will need to be re-interpreted. The third topic was the study of the displacement of oil trapped in dead-end nanopores by water. This is a model of the process of tertiary oil recovery. Surfactants are used to assist with oil recovery, but the mechanism is not well studied. Three hypotheses were considered for the effect of surfactant on oil displacement: (1) Lowering of the oil–water interfacial tension; (2) Adsorption to the water–solid interface; and (3) Effects on transport rather than thermodynamics. Measurements of three different types of surfactants: sodium dodecyl sulfate (SDS), an anionic surfactant; Aerosol OT (AOT), an anionic surfactant; dodecyltrimethylammonium bromide (DTAB), a cationic surfactant; and no surfactant. Results show that AOT was the only surfactant that led to substantial spontaneous displacement of oil within 12 hours. The effect was attributed to AOT's ability for form reverse micelles in the oil phase that could deliver water to the hydrophilic solid walls, thereby displacing oil. No prior literature describing this mechanism has been found. / Doctor of Philosophy / Nanoscale confinement are domains contained by interfaces with at least one dimension on the nanometer scale level. This dissertation describes very thin (1–100 nm) layers of water between solids. Such thin layers of water are important in oil recovery, cellular processes, delivery of sham-poo to hair, drug delivery, etc. I studied the transport and adsorption of ions in these thin layers, particularly when the solid walls were charged. Results show that (1) Diffusion of ions could be se-verely hindered by unscreened electrostatic potential within the thin film of water. Diffusion times were increased by up to 10 times; (2) Surfactant aggregation occurred in the thin film, even when it did not occur in bulk solution at the same concentration; (3) Water could not displace oil in a thin film, even when assisted by a variety of surfactants. One particular surfactant, Aerosol OT could displace the oil, which I attribute to its ability to transport water through the oil and onto the solid.
43

Dual effect of thiol addition on fluorescent polymeric micelles: ON-to-OFF emissive switch and morphology transition

Mabire, A.B., Robin, M.P., Willcock, H., Pitto-Barry, Anaïs, Kirby, N., O'Reilly, R.K. 07 August 2014 (has links)
Yes / The morphology transition from micelles to vesicles of a solution-state self-assembled block copolymer, containing a fluorescent dye at the core–shell interface, has been induced by an addition–elimination reaction using a thiol, and has been shown to be coupled to a simultaneous ON-to-OFF switch in particle fluorescence. / EPSRC and the IAS at the University of Warwick
44

Troca iônica em micelas: teoria e aplicações / Ion exchange in micelles: theory and applications

Chaimovich Guralnik, Hernan 11 October 1979 (has links)
A consideração explicita de troca iônica em soluções micelas conduz a expressões gerais que contém somente termos experimentalmente acessíveis. Estas expressões servem como marco de referência geral para a análise do efeito de micelas em reações que envolvem íons. As expressões incluem: a ligação de um íon reativo a micela na presença ou ausência de sal, a reação monomolecular de um substrato iônico na fase micelar, a reação bimolecular de um nucleófilo iônico na fase micelar e o efeito de micelas na dissociação de ácidos fracos e as suas consequências cinéticas. Estas expressões foram utilizadas para analisar quantitativamente a hidrólise alcalina de acetato de p-nitrofenila em tampão. Uma das predições do modelo, um mínimo no pK aparente de um ácido fraco na presença de micelas foi confirmado estudando o efeito de brometo de hexadeciltrimetilamônio na dissociação de n-heptilmercaptana e fenol. O efeito de sais no pK do fenol na presença de micelas, também predito pelo modelo, foi analisado quantitativamente. / The explicit consideration of specific ion exchange leads to general expressions which contain experirmentally accessible terms. These expressions serve as an unified conceptual framework for the quantitative dissection and analysis of the influence of charged interfaces on reactions which involve such specifically-bound ionic species. These include the binding of a reactive ion to the micelle in the presence ar absence of salt, the first order reaction of an ionic substrate in the micelle. a second order reaction of an ionic nucleophile solubilized in the micellar phase and the effect of micelles on the dissociation of weak acids and the reactions of the corresponding conjugate base. These expressions were used to analyze quantitatively the micellar modified hydrolysis of p-nitrophenyl acetate in the presence of buffer. One of the predictions of the model, a minimum in the pK apparent of a weak acid, was confirmed in a study of the effect of hexadecyltrimethylamonium bromide on the apparent pK's of phenol and n-heptylmercaptan. The effect of salts on the pK of weak acids in the presence af micelles, also predicted by the model, was analysed quantitatively.
45

Troca iônica em micelas: teoria e aplicações / Ion exchange in micelles: theory and applications

Hernan Chaimovich Guralnik 11 October 1979 (has links)
A consideração explicita de troca iônica em soluções micelas conduz a expressões gerais que contém somente termos experimentalmente acessíveis. Estas expressões servem como marco de referência geral para a análise do efeito de micelas em reações que envolvem íons. As expressões incluem: a ligação de um íon reativo a micela na presença ou ausência de sal, a reação monomolecular de um substrato iônico na fase micelar, a reação bimolecular de um nucleófilo iônico na fase micelar e o efeito de micelas na dissociação de ácidos fracos e as suas consequências cinéticas. Estas expressões foram utilizadas para analisar quantitativamente a hidrólise alcalina de acetato de p-nitrofenila em tampão. Uma das predições do modelo, um mínimo no pK aparente de um ácido fraco na presença de micelas foi confirmado estudando o efeito de brometo de hexadeciltrimetilamônio na dissociação de n-heptilmercaptana e fenol. O efeito de sais no pK do fenol na presença de micelas, também predito pelo modelo, foi analisado quantitativamente. / The explicit consideration of specific ion exchange leads to general expressions which contain experirmentally accessible terms. These expressions serve as an unified conceptual framework for the quantitative dissection and analysis of the influence of charged interfaces on reactions which involve such specifically-bound ionic species. These include the binding of a reactive ion to the micelle in the presence ar absence of salt, the first order reaction of an ionic substrate in the micelle. a second order reaction of an ionic nucleophile solubilized in the micellar phase and the effect of micelles on the dissociation of weak acids and the reactions of the corresponding conjugate base. These expressions were used to analyze quantitatively the micellar modified hydrolysis of p-nitrophenyl acetate in the presence of buffer. One of the predictions of the model, a minimum in the pK apparent of a weak acid, was confirmed in a study of the effect of hexadecyltrimethylamonium bromide on the apparent pK's of phenol and n-heptylmercaptan. The effect of salts on the pK of weak acids in the presence af micelles, also predicted by the model, was analysed quantitatively.
46

Micelles polymères unimoléculaires ou inverses pour l'administration orale d'agent thérapeutiques

Jones, Marie-Christine January 2007 (has links)
Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.
47

Micelles polymères unimoléculaires ou inverses pour l'administration orale d'agent thérapeutiques

Jones, Marie-Christine January 2007 (has links)
Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal
48

Studies of drug-surfactant interactions

Patel, Rajesh January 2000 (has links)
No description available.
49

Synthesis and characterisation of methacrylate-based water-soluble diblock and triblock copolymers for drug dispersion in aqueous media

Unali, Giovanni Francesco January 2000 (has links)
No description available.
50

Micelles complexes de polyions à base de copolymères à blocs double hydrophiles et d’homopolyélectrolytes : Etudes physico-chimiques et applications à la synthèse de matériaux nanostructurés / Polyion complex micelles based on double hydrophilic block copolymers and homopolyelectrolytes : Physico-chemical studies and applications for the synthesis of nanosructured materials

Houssein, Dania 31 January 2013 (has links)
Les micelles complexes de polyions, ou « micelles PIC », formées par interaction électrostatique entre un copolymère à blocs double hydrophile neutre-ionique (DHBC) et un homopolyélectrolyte de charge opposée au DHBC possèdent des propriétés particulièrement intéressantes : solubilité des polyélectrolytes dans l'eau, stabilité des micelles, contrôle de l'association/dissociation micellaire par divers stimuli (pH, force ionique, irradiation lumineuse…). Dans cette thèse, les propriétés physico-chimiques des micelles PIC de type DHBC neutre-cationique/homopolymère anionique et DHBC neutre-anionique/homopolyélectrolyte cationique ont été étudiées en solution aqueuse en vue de leur utilisation comme agent structurant des matériaux siliciques organisés à l'échelle nanométrique. La gamme de pH de formation des micelles PIC, la concentration micellaire critique et le nombre d'agrégation des micelles ont été déterminés pour chacun des systèmes étudiés. Nous avons montré que la formation des micelles suit un mécanisme coopératif qui dépend de la taille de l'homopolymère. Par ailleurs, nous avons proposé une voie originale de formation des micelles PIC photoinduite, basée sur une modification du pH suite à l'irradiation d'une molécule photochrome. Les études concernant l'utilisation des micelles PIC comme agent structurant des matériaux nous ont permis de montrer que la morphologie (nanoparticulaire, massif) et la structure des matériaux (lamellaire, vermiculaire) peuvent être contrôlés par divers paramètres, tels que la concentration en masse du système DHBC/homopolyélectrolyte/précurseur de silice, la teneur en précurseur de silice et le rapport entre les fonctions cationique et anionique des polyélectrolytes. Le lavage des matériaux sous des conditions douces (à l'eau) permet de récupérer l'agent structurant. / Polyion complex micelles, or "PIC micelles", formed by electrostatic interaction between a neutral-ionic double hydrophilic block copolymer (DHBC) and an oppositely charged homopolyelectrolyte possess interesting properties: solubility of the polyelectrolytes in water, stability of micelles, control of the micellar association / dissociation by various stimuli (pH, ionic strength, light irradiation ...). In this thesis, the physico-chemical properties of PIC micelles of neutral-cationic DHBC/ anionic homopolymer and neutral-anionic DHBC/cationic homopolymer were studied in aqueous solution for use as structuring agents of silica-based organized nanomaterials. The pH range of PIC micelle formation, the critical micelle concentration and aggregation number of micelles were determined for each studied system. We have shown that the formation of micelles follows a cooperative mechanism which depends on the size of the homopolymer. Furthermore, we proposed an original way of photoinduced PIC micelle formation, based on a pH change after irradiation of a photochromic molecule. The studies on the PIC micelles as structuring agents of materials have shown that the morphology (nanoparticular, bulk) and the material structure (lamellar, vermicular) can be controlled by various parameters, such as the mass concentration of the DHBC / homopolyelectrolyte / silica precursor system, the content of the silica precursor and the ratio between the functions of the cationic and anionic polyelectrolytes. Finally, the template was removed by washing the hybrid materials under soft conditions in water.

Page generated in 0.0604 seconds