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Veatch, Sarah Louise. "Liquid immiscibility in model bilayer lipid membranes /." Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/9772.
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Hartshorn, Christopher M. "Studies of the molecular effects of a solid support upon lipid membranes and membrane bound proteins." Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Dissertations/Fall2009/c_Hartshorn_101209.pdf.
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Wang, Chih-Ying. "Diffusion in hydrogel-supported lipid bilayer membranes." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=123227.
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Biomimetic membranes are powerful tools for fundamental studies of transmembrane proteins, and they can be used in sensing and separation technologies. This thesis presents theoretical models and experimental studies of diffusion in hydrogel-supported lipid bilayer membranes. Three hydrodynamic models are developed to assess tracer diffusion in (i) an hydrogel-supported single-leaflet membrane; (ii) a solid-supported dual-leaflet membrane; and (iii) an hydrogel-supported dual-leaflet membrane. The hydrogel-supported single-leaflet model describes transmembrane protein (tracer) diffusion in lipid bilayer membranes, and the hydrogel-supported dual-leaflet model generalizes this single-leaflet model, including inter-leaflet friction. The solid-supported dual-leaflet model allows tracers to span either one or both leaflets. The models quantify how the tracer diffusion is affected by hydrogel concentration, inter-leaflet friction, and a dimensionless parameter Λ. Thus, the models predict tracer diffusion coefficients based on key system parameters. In addition to theory, experiments were undertaken to measure lipid (PE-CF) and lipopolymer (DSPE-PEG2k-CF) self-diffusion coefficients in hydrogel-supported membranes, using fluorescence recovery after photo-bleaching (FRAP). The results show that polyacrylamide and agarose hydrogels can enhance tracer diffusion in DOPC bilayers, relative to their glass-supported counterparts. Moreover, the hydrogels impart size-exclusion and Brinkman screening effects, which may benefit membrane-based molecular-separation and sensing platforms.Les membranes biomimétiques sont des outils puissants pour des études fondamentales sur des protéines transmembranaires, et pourraient être utilisées par les technologies de détection et de séparation. Cette thèse présente trois modèles théoriques et les études expérimentales de diffusion avec les membranes bicouches lipidiques soutenus par hydrogels. Trois modèles hydrodynamiques adresse la diffusion du traceur dans: (i) une membrane à feuillet unique soutenus par hydrogel, (ii) une membrane à double feuillet soutenus par solide, et (iii) une membrane à double feuillet soutenus par hydrogels. Le modèle à feuillet unique hydrogel soutenu décrit la diffusion de protéine transmembranaire (traceur) dans les membranes bicouches lipidiques, et le modèle à double feuillet hydrogel soutenu généralise ce modèle avec feuillet unique, dont la friction se prèsente inter-feuillet. Le modèle à double feuillet solide soutenu permet les traceurs de durée une ou deux feuillets bicouches lipidiques. Ces trois modèles wxpliquent comment la diffusion traceur est affectée par la concentration de l'hydrogel, et quantifiet les frottements entre feuillet, et un paramètre sans dimension Λ. Ces modèles peuvent ê tre utilisés pour prédire les coefficients de diffusion de traceurs grâce à des paramètres clés du système. Les expériences comprennent la diffusion des lipides (PE-CF) et diffusion lipopolymère (DSPE-PEG2k-CF) dans des bicouches lipidiques hydrogel soutenus, mesurée par la récupération de fluorescence après photoblanchiment. Les résultats expérimentaux montrent que le hydrogels polyacrylamide et agarose peuvent améliorer la diffusion de traceur dans des bicouches DOPC, par rapport à leurs homologues verre soutenus. Les hydrogels présentent également d'exclusion de taille et les effets de dépistage Brinkman. Les applications peuvent bénéficier des séparations moléculaires.
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Danial, John Shokri Hanna. "Imaging lipid phase separation on droplet interface bilayers." Thesis, University of Oxford, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.711943.
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LADHA, PARAG. "POLYMERIC MEMBRANE SUPPORTED BILAYER LIPID MEMBRANES RECONSTITUTED WITH BIOLOGICAL TRANSPORT PROTEINS." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1145901880.
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Daulton, Emma. "Biomimetic floating lipid membranes." Thesis, University of Bath, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.675722.
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Sears, Randy Bryan. "Permeability of POPC bilayer by dirhodium complexes." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1194529853.
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Oldham, Alexis Jean. "Modulation of lipid domain formation in mixed model systems by proteins and peptides." View electronic thesis, 2008. http://dl.uncw.edu/etd/2008-1/r1/oldhama/alexisoldham.pdf.
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Zhang, Huaiying. "Lipopolymer diffusion and electrophoresis in supported lipid bilayer membranes." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=103712.
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Lipopolymer-containing phospholipid bilayers are important because of their potential as biological membrane models and biosensing platforms. This thesis presents systematic studies of lipopolymer self-diffusion, gradient diffusion, and electrophoresis in solid-supported lipid bilayers (SLBs). A reaction-diffusion fluorescence recovery after photobleaching (FRAP) model was developed to improve accuracy in furnishing the self-diffusion coefficient. Fourier transform post-electrophoresis relaxation (PER) was developed to ascertain the gradient diffusion coefficient, which had not been previously measured in two-dimensional membranes. Finally, a photobleaching technique was adopted to measure the electrophoretic mobility. Hindered self-diffusion and enhanced gradient diffusion with increasing lipopolymer concentration in SLBs were observed. The diffusion data at small but finite concentrations were successfully interpreted using existing theories for transmembrane protein diffusion with a soft lipopolymer interaction potential. Lipopolymer electrophoretic mobility qualitatively correlates with lipopolymer concentration in the same manner as the self-diffusion coefficient. However, the drag force during electrophoresis is larger than derived from the self-diffusion coefficient using the Stokes-Einstein relation. This is attributed to the oppositely directed electro-osmotic flow. A continuum model that calculates the hydrodynamic drag on the polymer chains according to a Brinkman model was developed to quantify lipopolymer electrophoresis. This model furnished excellent agreement with experiments, yielding the polymer segment Stokes radius, and a lipid-tail drag coefficient that increases slightly with lipopolymer concentration.Les bicouches de phospholipides contenant des lipopolymères sont importantes en raison de leur potentiel en tant que substituts de membranes biologiques et plate-formes de bio-détection. Cette thèse présente l'étude systématique de l'auto-diffusion, de la diffusion sous gradient et de l'électrophorèse des lipopolymères au travers de bicouches lipidiques soutenues au moyen de supports solides (SLBs). Un model de récupération de fluorescence sous forme de réaction-diffusion après photo-blanchiment (FRAP) a été développé afin d'améliorer la précision des résultats fournissant les coefficients d'autodiffusion. La transformée de Fourier de relaxation post-électrophorèse (PER) a été calculée afin de confirmer la valeur du coefficient de diffusion sous gradient qui n'avait pas encore été mesurée pour le cas de membranes bidimensionnelles. Enfin, une technique de photo-blanchiment a été adoptée en vue de mesurer la mobilité électrophorétique. Les résultats ont montré d'une part qu'une augmentation de la concentration en lipopolymères SLBs avait pour effets contraires de faciliter la diffusion sous gradient mais de contrarier l'auto-diffusion. D'autre part, les données relatives à la diffusion dans le cas de concentrations faibles mais mesurables ont pu être interprétées à l'aide de théories déjà existantes sur la diffusion de protéines transmembranaires ayant un potentiel d'interaction peu élevé avec les lipopolymères. La mobilité électrophorétique des lipopolymères est en corrélation avec leur concentration d'un point de vue qualitatif, de même que l'est le coefficient d'auto-diffusion. Toutefois, la force de traînée expérimentale obtenue pour l'électrophorèse est plus importante que la force théorique calculée par implémentation du coefficient d'auto-diffusion dans la relation de Stokes-Einstein. Cette hausse est attribuée à l'écoulement du flux électro-osmotique en sens inverse. Un modèle en continuum calculant la traînée hydrodynamique sur les chaînes polymériques à partir d'un modèle de Brinkman a été développé afin de quantifier l'électrophorèse des lipopolymères. Ce modèle a fourni des résultats en excellent accord avec les expériences, entre autres concernant le rayon de Stokes de segments polymériques et le coefficient de traînée de la terminaison lipidique qui augmente légèrement avec la concentration en lipopolymères.
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Zhu, Hong 1975. "Numerical studies of diffusion in lipid-sterol bilayer membranes." Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=30776.
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We examine tracer diffusion in lipid bilayer membranes containing either cholesterol or lanosterol, using a random lattice Ising model. Specifically the model is a two-state off lattice tethered network of hard disks which is dynamically triangulated and the interactions between the hard disks are only effective along the tethers linking the disks. The model was already applied to lipid-sterol systems and was successful in reproducing the phase diagrams and related physical properties. In this thesis we apply this model in conjunction with Monte Carlo simulation methods as follows. We calculate the diffusion constant for lipid-cholesterol and lipid-lanosterol bilayer membranes both as function of temperature and sterol concentration in all accessible regions of the relevant phase diagrams. Comparison with experiment and comments on sterol related evolution are included.
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Zhu, Hong. "Numerical studies of diffusion in lipid-sterol bilayer membranes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ64487.pdf.
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Patterson, Brian Clay. "Viologen-mediated electron transfer across dihexadecylphosphate bilayer membranes /." Full text open access at:, 1990. http://content.ohsu.edu/u?/etd,238.
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DHOKE, MANJIRI ARVIND. "POROUS POLYMER MEMBRANES AS SUPPORTING SCAFFOLDS FOR BILAYER UPID MEMBRANES (BLM)." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1123818311.
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Punnamaraju, Srikoundinya. "Voltage and Photo Induced Effects in Droplet-Interface-Bilayer Lipid Membranes." University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1321648604.
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Lee, Chongsoo. "Raman spectroscopy of supported lipid bilayers and membrane proteins." Thesis, University of Oxford, 2005. http://ora.ox.ac.uk/objects/uuid:76f4be6e-b7d3-46c5-a2a1-3dcc7a399410.
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Off-resonance unenhanced total internal reflection (TIR) Raman Spectroscopy was explored to investigate supported single lipid bilayers with incorporated membrane peptides/proteins at water/solid interface. A model membrane was formed on a planar supported lipid layer (pslb) by the fusion of the reconstituted small unilamellar vesicles (SUVs), and the intensity of bilayer was confirmed by a comparison of Raman spectral intensity in the C-H stretching modes with C16TAB. With prominent Raman sensitivity attained, we studied the 2-D phase transition of DMPC and DPPC pslbs and the temperature-dependent polarised spectra revealed a broad transition range of ca. 10 °C commencing at the calorimetric phase transition temperature. We applied polarised TIR-Raman Spectroscopy to pslbs formed by DMPC SUVs reconstituted with a model membrane-spanning peptide gramicidin D. A preferential channel structure formed by dissolution of trifluoroethanol could be probed by polarised Raman Spectroscopy qualitatively showing an antiparallel β-sheet conformation (different from "standard" one) and our Raman spectra by correlation with NMR and CD data confirmed single-stranded π6.3 β-helical channel structure in the single bilayer. We also studied the membrane-penetrating peptide indolicidin in the presence of DMPC pslb over the chain melting temperature and a β-turn structure was dominantly observed concomitant with membrane perturbation. Dynamic adsorption of DPPC to form pslb from a micellar solution of n-dodecyl-β- D-maltoside could be examined with high sensitivity of every 1-min acquisition. Finally we used polarised TIR-Raman scattering to porcine pancreatic phospholipase A2 hydrolytic activity on DPPC pslbs and revealed lipid-active conformation different from that of the enzyme alone.
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Connell, Karen Elizabeth. "Studies of transport through curved and planar lipid bilayers /." Title page, contents and summary only, 1990. http://web4.library.adelaide.edu.au/theses/09PH/09phc7522.pdf.
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Helmers, Michael. "Kinks in a model for two-phase lipid bilayer membranes." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:15343985-1b1c-4123-838d-8e157e837db1.
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In the spontaneous curvature model for two-phase lipid bilayer membranes the shape of vesicles is governed by a combination of an elastic bending energy and an interface energy that penalises the size of phase boundaries. Each lipid phase induces a preferred curvature to the membrane surface, and these curvatures as well as phase boundaries may lead to the development of kinks. In a rotationally symmetric setting we introduce a family of energies for smooth surfaces and phase fields for the lipid components and study convergence to a sharp-interface limit, which depends on the choice of the bending parameters of the phase field model. We prove that, if kinks are excluded, our energies $Gamma$-converge to the commonly used sharp-interface spontaneous curvature energy with the additional assumption of $C^1$-regularity across interfaces. For a choice of parameters such that kinks may appear, we obtain a limit that coincides with the $Gamma$-limit on all reasonable membranes and extends the classical model by assigning a bending energy also to kinks. We illustrate the theoretical result by some numerical examples.
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Bingham, Richard John. "A continuum model of the electroporation of bilayer lipid membranes." Thesis, University of Leeds, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.535113.
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Carpenter, M. L. "The interaction of pressure and anaesthetics with lipid bilayers." Thesis, University of Salford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376841.
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Towles, Kevin Bradley Dan Nily. "Modeling and experimental approaches for investigating lipid bilayer heterogeneity /." Philadelphia, Pa. : Drexel University, 2007. http://hdl.handle.net/1860/1798.
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Brown, Aidan. "A physical study of model biological membranes." Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609720.
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Clogston, Jeffrey. "Applications of the lipidic cubic phase from controlled release and uptake to in meso crystallization of membrane proteins /." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1117564268.
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Thesis (Ph.D.)--Ohio State University, 2005.Title from first page of PDF file. Document formatted into pages; contains xxii, 352 p.; also includes graphics. Includes bibliographical references (p. 346-352). Available online via OhioLINK's ETD Center
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Renner, Lars. "Polymer Supported Lipid Bilayer Membranes for the Integration of Transmembrane Proteins." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1241457489091-02157.
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This work reports on the successful formation of supported multicomponent lipid bilayer membranes (sLBMs) from natural occurring lipids as well as synthetic lipids on a set of polymer cushions consisting of alternating maleic acid copolymers. Maleic acid copolymers provide a versatile platform to adjust the physico-chemical behaviour by the choice of the comonomer unit. The formation of sLBMs was triggered by a transient reduction of the electrostatic repulsion between the polymer cushions and the lipid vesicles by lowering the solutions pH to 4. Upon formation the stability of sLBMs was not affected by subsequent variations of the environmental pH to 7.2. Even drastic changes in the environmental pH (between pH 2 and pH 9) did not lead to delamination and proved the stability of the polymer sLBM. The degree of hydrophilicity and swelling of the anionic polymer cushions was found to determine both the kinetics of the membrane formation and the mobility of the lipid bilayer with lipid diffusion coefficients in the range from 0.26 to 2.6 µm2 s-1. An increase in cushion hydrophilicity correlated with a strong increase in the diffusion coefficient of the lipids. This trend was found to correlate with the kinetics of bilayer formation in the process of vesicle spreading. The observations strongly support the important role of the support’s polarity for the fluidity of the sLBM, which is probably related to the presence of a water layer between support and bilayer. The investigated polymer cushions are considered to open new options for the in situ modulation of lipid bilayer membranes characteristics to match the requirements for the successful integration of functional transmembrane proteins (TMPs). As each cushion exhibits different physico-chemical properties, the resulting behaviour of the sLBMs and TMPs could be exactly adjusted to the specific requirements of biological samples. This is exemplarily shown by the integration of the TMP beta amyloid precursor protein cleaving enzyme (BACE). Integrated BACE was observed to be mobile on all polymer cushions. On the contrary, no lateral mobility of BACE was found in solid sLBM. Furthermore, the activity of integrated BACE was analysed by the cleavage of an amyloid precursor protein analogue. Remarkably, the polymer cushions did not only enhance the mobility but were also found to increase the activity of BACE by a factor of 1.5 to 2.5 in comparison to solid sLBM. From the obtained results it is obvious that even small cytoplasmic domains of transmembrane proteins might not be preserved upon the integration in silica sLBM. The observed beneficial effects of the utilised polymer cushions on the mobility and activity of transmembrane proteins motivate further studies to clarify the general applicability of the polymer platform. Altogether, this polymer platform provides valuable options to form sLBM with varying characteristics to reconstitute transmembrane proteins for a wide range of possible future applications in biologyDie vorliegende Arbeit beschreibt die Bildung von polymer unterstützten Lipiddoppelschichten zur Integration von transmembranen Proteinen. Das Polymerkissensystem besteht aus alternierenden Maleinsäurecopolymeren. Lipiddoppelschichten wurden durch die Steuerung der elektrostatischen Repulsion erzeugt: die Verringerung des pH-Wertes auf 4 wurde eine Erhöhung der adsorbierten Vesikelmenge auf den Polymeroberflächen induziert. Nach der erfolgten Bildung der Lipiddoppelschichten kann der pH-Wert beliebig variiert werden, ohne dass die Stabilität der Lipiddoppelschichten beeinflusst wird. Auch drastische Veränderungen des pH-Milieus (pH 2 - pH 9) führten zu keinen Veränderungen in der Membranintegrität. Der Grad der Hydrophilie und der Quellung der anionischen Polymerschichten beeinflusst sowohl die Bildung der Modellmembranen als auch die Mobilität der integrierten Lipidmoleküle. Dabei reichen die erzielten Lipiddiffusionskoeffizienten von 0.26 bis 2.6 µm2 s-1. Dabei ist die Mobilität direkt von der Hydrophilie des Substrates abhängig. Die beobachteten Ergebnisse zeigen deutlich die entscheidende Rolle der Polarität der verwendeten Substratoberflächen auf die Lipidmobilität, die sehr wahrscheinlich mit der Präsenz einer variablen Wasserschicht zusammenhängt. Die untersuchten Polymerkissen eröffnen neue Möglichkeiten für die insitu Modulierung der Charakteristika von Lipidschichten, um funktionale transmembrane Proteine zu integrieren. Aufgrund der unterschiedlichen physiko-chemischen Eigenschaften kann das Verhalten der Lipidschichten und der transmembranen Proteine nach den spezifischen Anforderungen des Modellsystems angepasst werden. Die funktionale Integration wurde am Beispiel des transmembranen Proteins BACE nachempfunden. Die Mobilität des integrierten BACE wurde auf allen Polymerkissen beobachtet. Im Gegensatz dazu wurde auf harten Substraten keine BACE Mobilität gefunden. Die Aktivität des integrierten BACE wurde durch die enzymatische Spaltung eines APP-Analogons nachgewiesen. Bemerkenswerteweise wurde ein Anstieg der BACE Aktivität auf den Polymerkissen um den Faktor 1,5 bis 2,5 im Vergleich zu den auf harten Substraten integrierten BACE beobachtet. Zusammenfassend, die verwendeten Polymerkissen bieten vielfältige Möglichkeiten Lipidschichten mit variierenden Eigenschaften für die Integration von transmembranen Proteinen zu erzeugen
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Hopkinson, David P. "Measurements and Modeling of the Failure Pressure of Bilayer Lipid Membranes." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/30064.
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Bilayer lipid membranes (BLMs) are formed from phospholipid molecules which self-assemble into a lipid bilayer with 4 to 9 nm thickness when submerged in an aqueous solution. This is due to their amphiphilic nature, meaning that one part of the molecule is hydrophilic, or attracted to water, and one part is hydrophobic, or repelled by water. They are the primary structural component of cell membranes in living organisms and therefore are useful for modeling the properties of cell membranes since they share many of the same chemical and physical properties.
The objective of this dissertation is to investigate the maximum pressure that can be withstood by a BLM formed over a porous substrate, which will be referred to as the failure pressure. This work represents the first time that this quantity has been measured and reported. The failure pressure is investigated in several complementary ways, including mechanical, electrical, and optical measurements and modeling. The phospholipids that are tested include 1-Stearoyl-2-Oleoyl-sn-Glycero-3-Phosphatidylcholine (SOPC) and mixtures of SOPC and cholesterol (CHOL), which was chosen because cholesterol is known to increase the strength of SOPC BLMs.
A new test methodology was developed to measure the failure pressure of BLMs. A custom test fixture was used to pressurize BLMs while measuring the applied pressure with a high degree of precision and repeatability. The BLMs were tested in an electrolyte solution over substrates that contained a single pore and also substrates that contained an array of many pores. SOPC BLMs were tested over single pore substrates with pore sizes ranging from 5 to 20 microns, and this resulted in failure pressures from 67 to 19 kPa, respectively. For single pore tests, the addition of 50 mol% cholesterol to SOPC resulted in a 56% higher failure pressure on average than SOPC alone. For multi pore substrates, SOPC BLMs were tested using pore sizes between 0.05 and 10 microns, which yielded bulk failure pressures of 380 to 1.5 kPa, respectively. For multi pore tests, SOPC/CHOL-50 mol% resulted in a 47% higher bulk failure pressure on average.
A model was developed to predict the pressurization curve of BLMs and was applied to both the single and multi pore tests. It was found that the failure pressure of BLMs follows a distribution which was well modeled by a Weibull distribution with a positive skew. Parameters such as the Weibull shape parameter were determined by fitting the model to the experimental pressurization curves and it was found that the shape of the Weibull distribution was nearly the same for every pore size. Using the pressurization model it was estimated that the percentage of failed BLMs that were pressurized over a multi pore substrate ranged from 4% to 33%. The model also coupled the bulk failure pressure of BLMs formed over multiple pores to the failure pressure of a single BLM, showing that the bulk failure pressure of multiple BLMs is smaller than the failure pressure of a single BLM because it represents the failure of only the weakest BLMs in a group.
Electrical impedance was measured before and after pressurization of the BLMs, and these measurements were modeled by assuming that the BLMs act as a resistor and a capacitor configured in parallel. In general, the impedance magnitude dropped by two to three orders of magnitude after BLM pressurization, which was a result BLMs failing and opening conductive pathways through the subsequently empty pores. It was found that normalized conductance values for SOPC BLMs were between G / A = 4 x 10^-12 and 2 x 10^-8 S/cm^2, and normalized capacitance values varied between C / A = 3 x 10^-14 and 1 x 10^-10 F/cm^2. In the literature these values ranged from G / A = 10^-1 to 10^-9 S/cm^2 and C / A = 10^-6 to 10^-8 F/cm^2, having a wide range of values due to the many variations of experimental test procedures.
Visual images of BLMs were produced using fluorescence microscopy. Images were recorded before and after pressurization of SOPC BLMs formed over a multi pore substrate. As predicted by the pressurization model, it was found that some but not all BLMs fail after pressurization. It was also found that BLMs fail over the center of a pore, and leave remnants around the perimeter of the pore.Ph. D.
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Fournier, Luc. "A lattice model for the rupture kinetics of lipid bilayer membranes." Thesis, University of Ottawa (Canada), 2002. http://hdl.handle.net/10393/6293.
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We have constructed a model for the kinetics of rupture of membranes under tension, applying physical principles relevant to lipid bilayers held together by hydrophobic interactions. The membrane is characterized by the bulk compressibility (for expansion) K and the thickness 2ht of the hydrophobic part of the bilayer. The model is a lattice model which incorporates stress relaxation, and considers the nucleation of pores at constant area, constant temperature, and constant particle number. The particle number is conserved by allowing multiple occupancy of the sites. A value for the rigidity of the phopholipid tails in the Lalpha liquid phase are found for saturated and unsaturated lipids, and long diblock copolymers. An equilibrium "phase diagram" is constructed as a function of temperature and strain with the pores total surface and distribution as the order parameters. With parameters relevant to saturated phosphatidylcholine (PC) lipid membranes, well defined regions of "no pores", "protopores (non-critical pores)", "rupture" are found. The model also reproduces recent results on super-thick membranes, and on membranes in presence of peptides. Free energy curves as a function of total pore surface are presented for various values of tension and temperature, and the fractal dimension of the pore edge is evaluated.
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Lundquist, Anna. "Nanosized Bilayer Disks as Model Membranes for Interaction Studies." Doctoral thesis, Uppsala universitet, Fysikalisk kemi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8495.
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PEG-lipid stabilized bilayer disks have been found in lipid mixtures containing polyethylene glycol (PEG)-lipids where the combination of a high bending rigidity and low PEG-lipid/lipid miscibility favours disk formation. The disks are planar and circular in shape and their long-term stability is excellent. Theoretical calculations and experimental observations suggest that the micelle forming PEG-lipid are situated at the rim of the aggregate, protecting the hydrophobic lipid chains in the bulk of the aggregate from contact with water. This thesis deals with fundamental aspects concerning the lipid distribution in the disks, as well as with development, optimization, and initial evaluation of the disks as model membranes in partition and interaction studies. Small angle neutron scattering was used to study the partial segregation of components within the bilayer disk. The experiments verified that the PEG-lipids segregate and accumulate at the bilayer disk rim. The proof of component segregation is important from a fundamental point of view and useful, as exemplified in the below-mentioned study of melittin-lipid interaction, when interpreting partition or binding data obtained from studies based on bilayer disks. Today liposomes are often used as model membranes in partition and interaction studies. Using liposomes to predict, e.g., drug partitioning can however have certain drawbacks. In this thesis the disks were proven to be attractive alternatives to liposomes as model membranes in partition studies. The formation of bilayer disks by a technique based on detergent depletion enabled incorporation of a transmembrane protein in the bilayer disks and opened up for the use of disks as model membranes in membrane protein studies. Further, bilayer disks were used in a comparative study focused on the effect of aggregate curvature on the binding of the peptide melittin. Various techniques were used to perform initial evaluations of the bilayer disks as model membranes. Of these, capillary electrophoresis and biosensor-based technology had not been used before in combination with bilayer disks.
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Polozov, Ivan V. "Interactions of class A and class L amphipathic helical peptides with model membranes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape16/PQDD_0006/NQ30110.pdf.
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Elliott, Richard. "Phase separation in mixed bilayers containing saturated and mono-unsaturated lipids with cholesterol as determined from a microscopic model /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/9675.
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Davis, Joseph E. "Refinement, validation, and application of a charge equilibration force field for simulations of phospholipid bilayers." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 67 p, 2009. http://proquest.umi.com/pqdweb?did=1885474371&sid=2&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Rahmi, Mohammad. "Shape dynamics and lipid hydrodynamics of bilayer membranes: modeling, simulation and experiments." Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/117462.
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Biological membranes are continuously brought out of equilibrium, as they shape organelles, package and transport cargo, or respond to external actions. The dynamics of lipid membranes are very complex due to the tight interplay between the bilayer architecture, the shape dynamics, the rearrangement of the lipid molecules, and their interactions with adjacent structures. The main goal of the present work is to understand the dynamical shape deformations and reorganizations of lipid bilayers, including lipid hydrodynamics, and the mechanical shaping and stabilization of highly curved membrane structures. Towards this goal, we develop theory, simulation methods, and perform experiments.
We formulate and numerically implement a continuum model of the shape dynamics and lipid hydrodynamics, which describes the bilayer by its mid-surface and by a lipid density field for each monolayer. In this model, the viscoelastic response of bilayers is determined by the stretching and curvature elasticity, and by the intermonolayer friction and the membrane interfacial shear viscosity. In contrast with previous studies, our numerical approach incorporates the main physics, is fully nonlinear, does not assume predefined shapes, and can access a wide range of time and length scales. We apply our model to describe the dynamics of biologically relevant experimental observations, which are insufficiently understood through simpler models introducing geometrical and physical simplifications. We study the dynamical formation of membrane tubes, followed by pearling instabilities, as a consequence of a localized density asymmetry, the tubular lipid transport between cells, the dynamics of bud absorption, and the very recently observed protrusions out of planar confined bilayers. The passive formation of stable highly curved protrusions in confined bilayers suggests that mechanics plays a role in the morphogenesis and homeostasis of complex organelles (e.g., endoplasmic reticulum, or mitochondrial cristae), in addition to the widely accepted role of proteins and the regulation of lipid composition. We also study experimentally and theoretically the shape transformations and membrane reorganizations of model membranes upon the adsorption of cholesterol, a ubiquitous constituent of biomembranes, which regulates their structural and mechanical properties. Our observations offer new insights into the reorganizations of macrophages and the formation of foam cells as a consequence of the cholesterol elevation in vessel walls.
In this thesis, we have payed particular attention to the membrane fluidity and the influence of the membrane viscosity in the bilayer dynamics. The role of the membrane interfacial viscosity is often ignored due to its minor role in the linearized equations about planar states. We challenge this assumption, show theoretically that membrane viscosity plays an important role in the presence of high curvature, and show its effect on the membrane fluctuations of quasi-spherical vesicles and tubular membranes.
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Cheetham, Matthew Richard. "Electric field manipulation of charged components in patterned supported bilayer lipid membranes." Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.559369.
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A new method for manipulating charged components of a supported bilayer lipid membrane (sBLM) has been developed. The method makes use of AC electric fields applied in the plane of asymmetrically patterned sBLMs, to rectify diffusion and create net motion in a given direction. This motion has been controlled by tailoring the pattern geometry to perform different functions, and was initially investigated using finite element analysis (FEA), before being shown experimentally. A double-sawtooth pattern was demonstrated to move charges along a narrow channel through the use of an AC field. The operation of this pattern was based on the idea of a Brownian ratchet. Using this pattern, it was shown that a charged fluorescent lipid probe could be transferred in around 25 AC cycles. The double-sawtooth pattern formed the basis of a more advanced "pump" pattern, which was shown to transfer charges from one reservoir into another. This was demonstrated with a fluorescently labelled transmembrane protein. A charge concentrator pattern was also developed. This achieved a 3.5-fold concentration increase in 2 AC cycles. The probe remained in the "trap" region for many hours after removal of the AC field, with a relaxation half-life of around 3.5 h. This pattern was developed further by nesting three traps within one another. The nested trap was demonstrated with a fluorescently labelled transmembrane protein, and yielded a 3D-fold concentration increase after 8 AC cycles. After removal of the AC field, the concentrated protein diffused out from the trap with a half-life of around 2.2 h. Additionally, a computational study of sBLMs with incomplete coverage was done. The study showed that the long-range diffusivity increased linearly with the membrane area fraction, but that the "measured" mobile fraction was unaffected' unless the area fraction was close to the percolation threshold. These results are important for consideration of systems with high protein concentration, or phase-separating mixtures. It is believed that the new method presented here could be used for in- membrane separation and concentration of proteins, and possibly in lab-on- chip devices for bio-analytical techniques.
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Campos, Rui César de Almeida. "Studies of electron transfer in self-assembled monolayers and bilayer lipid membranes." Thesis, Durham University, 2012. http://etheses.dur.ac.uk/3899/.
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The work presented on this thesis is focused on studies of the kinetics of electron transfer in bilayer lipid membranes (BLMs). Three different types of BLM were studied: i) tethered, ii) pore suspended (commonly known as ‘black’) and iii) based on the avidin – biotin interaction (these are part of the wider group of polymer cushioned BLMs). In order to produce tethered BLMs (tBLMs) of the best quality possible, self – assembled monolayers (SAMs) of a thiolipid (1,2 dipalmitoyl-sn-glycero-phosphothioethanol (DPPTE)) and of the same thiolipid mixed with L α phosphatidylcholine (EggPC) were characterised and their behaviour compared to that of SAMs of two alkanethiols (1 – heptanethiol and 1 – dodecanethiol). The SAMs that were formed by a mixture of lipids (DPPTE+EggPC) presented better kinetic parameters and were the chosen to produce tBLMs. Tethered BLMs were made by using the SAM described above as the lower leaflet; the second leaflet was deposited by vesicle fusion, the vesicles were made of EggPC. tBLMs are commonly used as model membranes, however in biophysical studies free-standing membranes or ‘black’ lipid membranes are more realistic models of cellular processes. The rates of electron transfer in both types of bilayer lipid membranes are compared. These BLMs were modified using two very important mitochondrial membrane associated molecules – ubiquinone-10 (UQ10) and α-tocopherol (VitE). The studies involved the use three redox couples, Fe(CN)_6^(3-/4-), Ru(NH_3 )_6^(3+/2+) and NAD+/NADH using cyclic voltammetry and electrochemical impedance spectroscopy. The NAD+/NADH couple is of particular interest as it is the key to several important biochemical processes. The last type of BLM that was studied was the BLMs based on the avidin – biotin interaction. Avidin was deposited on a platinum surface by electrodeposition and then vesicles composed of EggPC and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(biotinyl) (sodium salt) (DOPE(B)) are burst by applying +0.7V (vs. Ag/AgCl, KCl 3.5M), leading to the formation of a supported BLM. The vesicles used had methylene blue (MB) inside; its release, when the vesicles burst, was monitored by cyclic voltammetry and UV-Vis. The kinetic parameters were determined based on the EIS measurements using Fe(CN)_6^(3-/4-) and Ru(NH_3 )_6^(3+/2+) as redox couples.
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Teeters-Kennedy, Shannon Marie. "Infrared surface plasmons in double stacked nickel microarrays lipid bilayer systems /." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1180531191.
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Horton, Margaret R. (Margaret Ruth). "Influence of protein and lipid domains on the structure, fluidity and phase behavior of lipid bilayer membranes." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/38982.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, February 2007.Includes bibliographical references (p. 136-148).
The lipid bilayer forms the basic structure of the cell membrane, which is a heterogeneous matrix of proteins and lipids that provides a barrier between the interior of a cell and its outside environment. Protein and lipid domains in cell membranes can facilitate receptor localization, stabilize membranes, and influence membrane fluidity. In this thesis, we study how ordered protein and lipid domains influence the physical properties of lipid bilayers to better understand the roles of membrane domains in biological mechanisms. Model cellular membranes that mimic the behavior of biological membranes offer a controllable environment for systematically studying the isolated effects of protein and lipid ordering on membrane organization. Using fluid and solid-supported lipid bilayers, we study ordered peripheral membrane proteins and lateral lipid phase separation with fluorescence microscopy and X-ray reflectivity. To model cellular protein coatings and peripheral proteins, we prepare biotin-functionalized membranes that bind the proteins streptavidin and avidin. Fluorescence microscopy studies demonstrate that proteins crystallized in a single layer on lipid bilayer surfaces can change the lipid curvature and stabilize lipid vesicles against osmotic collapse.
(cont.) At solid interfaces, we characterize the electron density profiles of protein-coated bilayers to determine how a water layer separates an immobile protein layer from the fluid lipid bilayer. Liquid-ordered lipid phases enriched in cholesterol and sphingomyelin can localize molecules in cell membranes and this lipid phase separation behavior may be influenced by proteins and molecules in the membrane. Caveolae are specialized liquid-ordered domains in the plasma membrane that are enriched in the protein caveolin-1. We demonstrate that caveolin-1 peptides influence the onset of lipid phase separation and bind phase-separated lipid bilayers in solution. On solid surfaces, the formation of liquid-ordered lipid phases is influenced by surface roughness; with reflectivity, we determine that lipid bilayers containing cholesterol and sphingomyelin thicken with increasing cholesterol content. The membrane receptor GM1 also thickens the lipid bilayer when it is incorporated into the bilayer upper leaflet. The diverse experimental platforms that we present are applicable to studying additional and more complex biological systems to elucidate the influence of lipid and protein domains on cell membrane structure, organization and fluidity.
by Margaret R. Horton.
Ph.D.
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Gardam, Michael A. "Mixing of sphingolipids with phospholipids in lipid bilayer membranes : calorimetric and fluorescence studies." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=55671.
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Vockenroth, Inga Kerstin. "Investigations of tethered bilayer lipid membranes for their potential use in biosensing devices." Thesis, University of Bath, 2007. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486480.
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Tethered bilayer lipid membranes (tBLMs) provide a model platform for the investigation ofvarious membrane related processes. They are especially suited to study the incorporation and function of ion channel proteins, where a high background resistance ofthe membrane is essential. In this study, the electrochemical sealing properties ofnew tBLMs are characterised and improved. Membranes of different compositions have been studied for their ability to host ion channels using Surface Plasmon Resonance Spectroscopy (SPR) and Electrochemical Impedance Spectroscopy (EIS). Several membrane proteins such as carriers, channels and pores were functionally incorporated. and investigated in different tBLM architectures. As a first test of the functionality of the membrane assembly the carrier valinomycin and the channel gramicidin were incorporated and their ion selectivity demonstrated with EIS. The transmembrane fragment M2 of the nicotinic acetylcholine receptor (nAChR) was embedded into a tBLM by fusion of proteoliposomes with different monolayers. The pore was selective for small monovalent cations, while bulky ions could not pass the membrane. The tBLMs provide a platfonn for the study of ion transport phenomena and ligand interactions of channels such as the nAChR, as the presented method should be generally applicable to other membrane proteins. Incorporation of a-haemolysin, a toxin that leads to lysis of cells by formation of large pores in the cell m,e. mbrane, was achieved. The tBLM provides a fluidity that allows incorporating the pores, while at the same time providing a submembrane space between the solid support and the bilayer. This offers the ability to measure ion currents through the incorporated channels. A membrane architecture specially suited for an enhanced functionality ofthe pores was designed and characterised. Downsizing the membrane area on Jl-electrodes gave gigaohmic membrane resistances, showing sealing properties comparable to BLMs. This gigaseal allowed for highly f sensitive measurements ofcurrents through incorporated a-haemolysin pores. With this system, a biosensor with modified biological receptors as actual sensing units is feasible, whereas the high stability opens the perspective of long-term experiments and continuous monitoring. Thus, a major step towards the use of proteins as stochastic sensing elements in prospective biosensor applications has been accomplished.
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Flippin, Stefanie Lee. "Synthesis of phospholipid analogs /." Electronic version (PDF), 2003. http://dl.uncw.edu/etd/2003/flippins/stefanieflippin.pdf.
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Mulligan, Kirk M. "Development of New Supported Bilayer Platforms for Membrane Protein Incorporation." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24022.
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Membranes are essential components of all living organisms forming the borders of cells and their organelles. Planar lipid membranes deposited on solid substrates (solid supported membranes) provide models to study the functions of membrane proteins and are used as biosensing platforms. However, despite remarkable progress, solid supported membranes are not stable to harsh conditions such as dehydration, high temperature and pressure, and mechanical stress. In addition, the direct deposition of membranes onto a solid substrate often causes restricted mobility and denaturation of reconstituted membrane proteins.
Membrane stability can be addressed by altering the structure of the component lipids. Bolalipids are an interesting class of bipolar lipids that have been proposed for biosensing applications. Membranes formed from mixtures of a bolalipid, C20BAS, and dioleoylphosphaphatidylcholine, POPC, were characterized by atomic force spectroscopy (AFM). The lipid mixtures produced a phase separated membrane consisting of thinner bolalipid-rich and thicker monopolar-rich POPC regions, with a height difference of approximately 1-2 nm. This confirmed an earlier prediction that some bolalipid/PC membranes would phase separate due to the hydrophobic mismatch between the two lipids. Interestingly, the surface coverage of the two phases was inconsistent with what one would expect from the initial starting lipid ratios. The complex membrane morphologies observed were accredited to the interplay of several factors, including a compositionally heterogeneous vesicle population, exchange of lipid between the vesicle solution and solid substrate during formation of the supported membrane, and slow equilibration of domains due to pinning of the lipids to the solid support.
Decoupling the membrane from its underlying surface is one strategy to maintain the structure and mobility of membrane proteins. This decoupling can be achieved by depositing the membrane on a soft cushion composed of a water swelling hydrophilic polymer. A polyelectrolyte multilayer (PEM) and a tethered poly(ethylene) glycol (PEG) polymer are the two types of polymer cushions used in this study. The PEMs consist of the charged polysaccharides, chitosan (CHI) and hyaluronic acid (HA) which offer the advantage of biocompatibility over synthetic PEMs. DOPC lipid bilayers were formed at pH 4 and 6.5 on (CHI/HA)5 films. At higher pH adsorbed lipids had low mobility and large immobile lipid fractions; fluorescence and AFM showed that this was accredited to the formation of poor quality membranes with defects and pinned lipids rather than to a layer of surface-adsorbed vesicles. However, more uniform bilayers with mobile lipids were produced at pH 4. Measured diffusion coefficients were similar to those for bilayers on PEG cushions and considerably higher than those measured on other polyelectrolyte films. The results suggest that the polymer surface charge is more important than the surface roughness in controlling formation of mobile supported bilayers.
The suitability of polymer supported membranes for the incorporation of integral membrane proteins was also assessed. The integral membrane protein Ste14p, a 26 kDa methyltransferase enzyme, was reconstituted into POPC membranes on PEM and PEG supports. A combination of fluorescence microscopy, FRAP, AFM and an in situ methyltransferase activity assay were utilized to characterize the protein incorporated polymer supported membranes. Fluorescence measurements showed that more protein was incorporated in model membranes formed on the PEG support, compared to either glass or PEM cushions. However, the protein activity on a PEG support was comparable to that of the protein in a membrane on glass. FRAP measurements showed that the lipid mobilities of the POPC:Ste14p bilayers on the various supports were also comparable.
Lastly, as a new platform for manipulating and handling membrane proteins, nanodiscs containing reconstituted Ste14p were studied. Nanodiscs are small, soluble and stable bilayer discs that permit the study of membrane proteins in a uniform phospholipid bilayer environment. Empty and protein containing nanodiscs were deposited on a mica surface and imaged by AFM. AFM showed that protein containing samples possessed two subpopulations of nanodiscs with a height difference of ~1 nm. The taller discs, ~20% of the population, contained protein. Other experiments showed that the packing of the nanodisc samples was influenced by their initial stock concentration and that both imaging force and the addition of Mg2+ caused formation of larger bilayer patches.
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Kuhlmann, Jan Wilhelm. "Modulation of lateral membrane tension and SNARE-mediated single vesicle fusion on pore spanning membranes." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2017. http://hdl.handle.net/11858/00-1735-0000-0023-3F13-E.
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Galla, Lukas [Verfasser]. "Nanopore modifications with lipid bilayer membranes for optical tweezers DNA force measurements / Lukas Galla." Bielefeld : Universitätsbibliothek Bielefeld, 2015. http://d-nb.info/1072224674/34.
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Mitrakos, Peter. "Polyelectrolyte induced domains in cationic lipid bilayer membranes, a deuterium nuclear magnetic resonance perspective." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq53678.pdf.
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Tejwani, Ravindra Wadhumal. "EXPERIMENTAL AND MOLECULAR DYNAMICS SIMULATION STUDIES OF PARTITIONING AND TRANSPORT ACROSS LIPID BILAYER MEMBRANES." UKnowledge, 2009. http://uknowledge.uky.edu/gradschool_diss/738.
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Most drugs undergo passive transport during absorption and distribution in the body. It is desirable to predict passive permeation of future drug candidates in order to increase the productivity of the drug discovery process. Unlike drug-receptor interactions, there is no receptor map for passive permeability because the process of transport across the lipid bilayer involves multiple mechanisms. This work intends to increase the understanding of permeation of drug-like molecules through lipid bilayers.
Drug molecules in solution typically form various species due to ionization, complexation, etc. Therefore, species specific properties must be obtained to bridge the experiment and simulations. Due to the volume contrast between intra- and extravesicular compartments of liposomes, minor perturbations in ionic and binding equilibria become significant contributors to transport rates. Using tyramine as a model amine, quantitative numerical models were developed to determine intrinsic permeability coefficients. The microscopic ionization and binding constants needed for this were independently measured. The partition coefficient in 1,9-decadiene was measured for a series of compounds as a quantitative surrogate for the partitioning into the hydrocarbon region of the bilayer. These studies uncovered an apparent long-range interaction between the two polar substituents that caused deviations in the microscopic pKa values and partition coefficient of tyramine from the expected values. Additionally the partition coefficients in the preferred binding region of the bilayer were also measured by equilibrium uptake into liposomes.
All-atom molecular dynamics simulations of lipid bilayers containing tyramine, 4- ethylphenol, or phenylethylamine provided free energies of transfer of these solutes from water to various locations on the transport path. The experimentally measured partition coefficients were consistent with the free energy profiles in showing the barrier in the hydrocarbon region and preferred binding region near the interface. The substituent contributions to these free energies were also quantitatively consistent between the experiments and simulations. Specific interactions between solutes and the bilayer suggest that amphiphiles are likely to show preferred binding in the head group region and that the most of hydrogen bonds involving solutes located inside the bilayer are with water molecules. Solute re-orientation inside the bilayer lowers the partitioning barrier by allowing favorable interactions.
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Wang, Kathleen F. "Characterizing molecular-scale interactions between antimicrobial peptides and model cell membranes." Digital WPI, 2014. https://digitalcommons.wpi.edu/etd-dissertations/153.
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Due to the escalating challenge of antibiotic resistance in bacteria over the past several decades, interest in the identification and development of antibiotic alternatives has intensified. Antimicrobial peptides (AMPs), which serve as part of the innate immune systems of most eukaryotic organisms, are being researched extensively as potential alternatives. However, the mechanism behind their bactericidal capabilities is not well understood. Previous studies have suggested that AMPs may first attach to the cell membranes, leading to pore formation caused by peptide insertion, lipid removal in the form of peptide-lipid aggregates, or a combination of both mechanisms. In addition to the lack of mechanistic knowledge, a significant hurdle in AMP-based drug development is their potential cytotoxicity to mammalian cells. Understanding AMP interactions with eukaryotic model membranes would allow therapeutics to be tailored for preferential action toward specific classes of bacterial membranes. In this study, we developed novel methods of quartz crystal microbalance with dissipation monitoring (QCM-D) data analysis to determine the fundamental mechanism of action between eukaryotic and bacterial membrane mimics and select membrane-active AMPs. A new technique for creating supported membranes composed entirely of anionic lipids was developed to model Gram-positive bacterial membranes. Atomic force microscopy (AFM) imaging was also used to capture the progression of AMP-induced changes in supported lipid membranes over time and to validate our method of QCM-D analysis. QCM-D and AFM were used to investigate the molecular-scale interactions of four peptides, alamethicin, chrysophsin-3, sheep myeloid antimicrobial peptide (SMAP-29) and indolicidin, with a supported zwitterionic membrane, which served as a model for eukaryotic cell membranes. Since established methods of QCM-D analysis were not sufficient to provide information about these interaction mechanisms, we developed a novel method of using QCM-D overtones to probe molecular events occurring within supported lipid membranes. Also, most previous studies that have used AFM imaging to investigate AMP-membrane interactions have been inconclusive due to AFM limitations and poor image quality. We were able to capture high-resolution AFM images that clearly show the progression of AMP-induced defects in the membrane. Each AMP produced a unique QCM-D signature that clearly distinguished their mechanism of action and provided information on peptide addition to and lipid removal from the membrane. Alamethicin, an alpha-helical peptide, predominantly demonstrated a pore formation mechanism. Chrysophsin-3 and SMAP-29, which are also alpha-helical peptides of varied lengths, inserted into the membrane and adsorbed to the membrane surface. Indolicidin, a shorter peptide that forms a folded, boat-shaped structure, was shown to adsorb and partially insert into the membrane. An investigation of rates at which the peptide actions were initiated revealed that the highest initial interaction rate was demonstrated by SMAP-29, the most cationic peptide in this study. The mechanistic variations in peptide action were related to their fundamental structural properties including length, net charge, hydrophobicity, hydrophobic moment, accessible surface area and the probability of alpha-helical secondary structures. Due to the charges associated with anionic lipids, previous studies have not been successful in forming consistent anionic supported lipid membranes, which were required to mimic Gram-positive bacterial membranes. We developed a new protocol for forming anionic supported lipid membranes and supported vesicle films using a vesicle fusion process. Chrysophsin-3 was shown to favor insertion into the anionic lipid bilayer and did not adsorb to the surface as it did with zwitterionic membranes. When introduced to supported anionic vesicle films, chrysophsin-3 caused some vesicles to rupture, likely through lipid membrane disruption. This study demonstrated that molecular-level interactions between antimicrobial peptides and model cell membranes are largely determined by peptide structure, peptide concentration, and membrane lipid composition. Novel techniques for analyzing QCM-D overtone data were also developed, which could enable the extraction of more molecular orientation and interaction dynamics information from other QCM-D studies. A new method of forming supported anionic membranes was also designed, which may be used to further investigate the behavior of bacterial membranes in future studies. Insight into AMP-membrane interactions and development of AMP structure-activity relationships will facilitate the selection and design of more efficient AMPs for use in therapeutics that could impact the lives of millions of people per year who are threatened by antibiotic-resistant organisms.
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Strömstedt, Adam A. "Antimicrobial Peptide Interactions with Phospholipid Membranes : Effects of Peptide and Lipid Composition on Membrane Adsorption and Disruption." Doctoral thesis, Uppsala universitet, Institutionen för farmaci, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-100966.
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The interactions between antimicrobial peptides and phospholipid membranes were investigated, in terms of lipid headgroup variations and the role of cholesterol, as well as peptide composition and structure. Also strategies for increasing proteolytic stability were evaluated. The interactions were studied on model membranes in the form of liposomes and supported bilayers, through a combination of ellipsometry, fluorescence spectroscopy, circular dichroism, dynamic light scattering, electrophoresis, electron cryomicroscopy, and bacterial/cell culture experiments. The findings showed that membrane tolerance against the lytic activity of melittin, was increased on anionic membranes by electrostatic arrest in the headgroup region, and was reduced by hydration repulsion. The presence of cholesterol caused a reduction in melittin adsorption, while at the same time reducing membrane tolerance per adsorbed peptide. Differences in membrane leakage mechanisms were also attributed to cholesterol, where large scale structural effects contributed to the leakage, while other membranes followed the pore formation model. Substituting specific amino acids for tryptophan on an LL-37 derivative, was shown to increase stability against bacterial proteases, while at the same time significantly increasing antibacterial properties. These substitutions, as well as terminal modifications, increased adsorption and membrane lytic properties in a way that was less dependent on electrostatics. Furthermore, by comparing short cationic peptides with oligotryptophan end-tagged versions, the lytic mechanism of end-tagged peptides, and the different contributions of arginine and lysine to membrane adsorption and disruption were demonstrated. This thesis is a contribution to the development of antimicrobial peptides as therapeutic alternatives to conventional antibiotics.
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Barrett, Matthew. "Structure and dynamics of model lipid membranes." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://dx.doi.org/10.18452/17540.
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Das Peptid Amyloid-beta wird seit vielen Jahren mit der Alzheimer''schen Demenz in Verbindung gebracht, aber die Verbindung zwischen dem Peptid und der Herkunft der Symptome bleibt unklar. Eine neue Hypothese besagt, dass Wechselwirkungen von Mono- oder Oligomeren des Amyloid-beta mit neuronalen Zellmembranen zu Veränderungen der Membran-Doppelschichtsruktur führen und Störungen dynamischer Prozesse in den Membranen verursachen können. Mit Methoden der Röntgen- und Neutronenstreuung wurden die Struktur und Dynamik von Modellmembranen und Änderungen durch den Einfluss des Peptids Amyloid-beta auf die Modellmembranen untersucht. Es konnte gezeigt werden, dass Monomere des Peptidfragments Amyloid-beta 22-40 in anionische Lipidmembranen eingebaut werden. Mittels quasielastischer-inkohärenter Neutronenstreuung wurde die Dynamik von Lipidmembran untersucht. Ein Anteil von 1,5 mol % Amyloid-beta 22-40 in einer Lipidmembran bei 30°C verursacht eine Verringerung der Diffusionskoeffizienten sowohl der Schwerpunktbewegung der Lipide im ns-Bereich als auch der Dynamik der Fettsäurereste im ps-Bereich. Andererseits wird in der Gelphase der Lipidmembran bei 15°C ein Anstieg der Diffusionskoeffizienten beider Prozesse beobachtet. Eine Serie von Lipidproben mit unterschiedlichem Cholesteringehalt und eingelagerten Peptiden Amyloid-beta 1-42 und Amyloid-beta 22-40 wurde Mittels Röntgendiffraktion charakterisiert. Für das Peptid Amyloid-beta 22-40 wurden zwei Positionen gefunden, eine auf der Oberfläche der Membran, eine zweite in der Membran eingelagert. Das Peptid Amyloid-beta 1-42 ist teilweise in die Membran eingelagert und ist in einer 40 mol % Cholesteringehaltige Membrane durch eine einzelne Position modelliert. Zusätzlich wird der Entwurf und die Inbetriebnahme der BerILL Feuchtekammer beschrieben.The peptide amyloid-beta has long been associated with Alzheimer’s disease; however the link between the peptide and the origin of symptoms is poorly understood. An emerging hypothesis is that monomeric and oligomeric forms of the peptide interact with neuronal membranes, resulting in perturbations in the bilayer structure and in the dynamic processes which take place in the bilayer. Using X-ray and neutron scattering techniques, the structure and dynamics of model lipid membranes and the changes which arise in the presence of amyloid-beta peptide fragments have been studied. Monomers of the peptide fragment amyloid-beta 22-40 were found to intercalate into an anionic lipid bilayer. Through quasi-elastic neutron scattering, dynamics of bilayer lipids were observed. The presence of 1.5 mol % of the peptide results in a decrease in the diffusion coefficients for lipid centre of mass motion on the nanosecond time-scale, as well as for the lipid tail dynamics on the picosecond scale at 30°C. On the other hand, in the gel-phase of the lipid, at 15°C, an increase in the diffusion coefficients for both of these processes was observed. A series of samples with various cholesterol content and either the amyloid-beta 22-40 peptide fragment or the amyloid-beta 1-42 full length peptide was characterized using X-ray diffraction. The amyloid-beta 22-40 peptide was found to populate two positions, on the surface and embedded in the bilayer. The amyloid-beta 1-42 peptide embeds itself into the membrane, and is modelled by a single population for high cholesterol levels (40 mol % cholesterol). In addition, the design and commissioning of the BerILL humidity chamber, a sample environment with precise temperature and humidity control compatible with neutron scattering experiments is presented.
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Korfhagen, Scott. "Stabilization of Scaffold-Supported, Photopolymerized Bilayer Lipid Membranes with Gramicidin-D for Novel Fuel Cells." University of Cincinnati / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1212085821.
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Khadka, Nawal Kishore. "Modulations of Lipid Membranes Caused by Antimicrobial Agents and Helix 0 of Endophilin." Scholar Commons, 2019. https://scholarcommons.usf.edu/etd/7829.
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Understanding the cellular membrane interaction with membrane active biomolecules and antimicrobial agents provides an insight in their working mechanism. Here, we studied the effect of antimicrobial agents; a recently developed peptidomimetics E107-3 and colistin as well as the N-terminal helix H0, of Endophilin A1 on the lipid bilayer.
It is important to discern the interaction mechanism of antimicrobial peptides with lipid membranes in battling multidrug resistant bacterial pathogens. We study the modification of structural and mechanical properties with a recently reported peptidomimetic on lipid bilayer. The compound referred to as E107-3 is synthesized based on the acylated reduced amide scaffold and has been shown to exhibit good antimicrobial potency. This compound increases lipid bilayer permeability as indicated by our vesicle leakage essay. Micropipette aspiration experiment shows that exposure of GUV to the compound causes the protrusion length Lp to spontaneously increase and then decrease, followed by GUV rupture. Solution atomic force microscopy (AFM) is used to visualize lipid bilayer structural modulation within a nanoscopic regime. This compound induces nanoscopic heterogeneous structures rather than pore like structures as produced by melittin. Finally, we use AFM-based force spectroscopy to study the impact of the compound on lipid bilayer’s mechanical properties. With the incremental addition of this compound, we found the bilayer puncture force decreases moderately and a 39% decrease of the bilayer area compressibility modulus KA. To explain our experimental data, we propose a membrane interaction model encompassing disruption of lipid chain packing and extraction of lipid molecules. The later action mode is supported by our observation of a double-bilayer structure in the presence of fusogenic calcium ions.
Polyanionic Lipopolysaccharides LPS are important in regulating the permeability of outer membrane (OM) of gram-negative bacteria. To initiate the bactericidal activity of polymyxins, it is essential to impair the LPS-enriched OM. Here, we study the mechanism of membrane permeability caused by colistin (Polymyxin E) of LPS/phospholipid bilayers. Our vesicle leakage experiment showed that colistin binding enhanced bilayer permeability; the maximum increase in the bilayer permeability was positively correlated with the LPS fraction. Addition of magnesium ions abolished the effect of LPS in enhancing bilayer permeabilization. Solution atomic force microscopy (AFM) measurements on planar lipid bilayers shows the formation of nano- and macro clusters which protruded from the bilayer by ~2nm. Moreover, increasing the fraction of LPS or colistin enhances the formation of clusters but inhibits by magnesium ions addition. To explain our experimental data, we proposed a lipid-clustering model where colistin binds to LPS to form large-scale complexes segregated from zwitterionic phospholipids. The discontinuity (and thickness mismatch) at the edge of LPS-colistin clusters will create a passage that allows solutes to permeate through. The proposed model is consistent with all data obtained from our leakage and AFM experiments. Our results of LPS-dependent membrane restructuring provided useful insights into the mechanism that could be used by polymyxins in impairing the permeability barrier of the OM of Gram-negative bacteria.
Also, we studied the effect of helix H0 of a membrane modification inducing protein endophilin, on planar bilayer. We obtained transmembrane defects on the bilayer when scanned.with AFM.
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Ayoub, Pierre. "Molecular dynamics study of pyrene excimer formation and oxidation in lipid bilayer models." Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAE038/document.
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Nous proposons une nouvelle approche pour déterminer le coefficient de diffusion dans des membranes lipidiques se basant sur la formation d'excimères. Alors que les autres modèles statistiques considèrent le système comme un ensemble de points sur un réseau, nous utilisons un modèle à gros grain afin d'étudier des bicouches lipidiques simulées à l'aide du champs de force Martini. Nous déterminons le taux de réaction dépendant du temps à partir des probabilités de survie obtenues a posteriori à l'aide des trajectoires numeriques des bicouches symétriques de DOPC (1,2-Dioleoyl-sn-glycero-3-phosphocholine) et POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) simulées à 283 K et 293 K respectivement. Les dynamiques de collision sont obtenues en distinguant virtuellement les molécules simulées. Les sondes fluorescentes sont supposées semblables aux lipides, et par conséquent, ne modifient pas la dynamique. Nous obtenons une expression générale pour la probabilité de survie en combinant approximation des paires indépendantes et propriétés d'échelle, mais aucune hypothèse n'est faite pour le taux de formation d'excimère. En superposant les intensités d'émission de fluorescence normalisées, déterminées numériquement, aux courbes de titrations expérimentales, nous obtenons deux ensembles de résultats pour le coefficient de diffusion latéral, selon que l'association entre feuillets est autorisée ou pas. Nous utilisons un rayon de capture de 0.5 nm, la distance à partir de laquelle les deux sondes réagissent pour former un excimère. En comparant la dynamique Martini aux expériences de fluorescence, il est possible d'estimer le facteur d'accélérationWe propose a novel approach to extract the lateral diffusion coefficient in lipid bilayers using excimer formation. In contrast to previous statistical models that modeled the system as points undergoing jumps from site to site on a lattice, we use coarse-grained molecular dynamics to study lipid bilayers simulated using the Martini force field. We derive time dependent reaction rates from survival probabilities obtained a posteriori from numerically generated trajectories of symmetric DOPC (1,2-Dioleoyl-sn-glycero-3-phosphocholine) and POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) bilayers at 283K and 293K respectively. Collision dynamics are determined by virtually relabeling the simulated molecules. The fluorescent probes are assumed to behave like ordinary membrane lipids and therefore the dynamics remain unaffected. We derive a generalized expression for the survival probability combining independent pairs and size scaling assumptions, but no assumption is made regarding the kinetic rate of the excimer formation process. By fitting the numerically determined normalized fluorescence emission intensities to experimental titration curves, we obtain two sets of results for the lateral diffusion coefficients depending whether interleaflet excimer association is allowed or not. We use a capture radius of 0.5 nm, the distance at which the probes react to form excimers. By relating Martini dynamics to real fluorescence experiments, we estimate the numerical Martini acceleration factor. We also study mixtures of oxidized-non oxidized DOPC and POPC bilayers using a hydroperoxidized model of these lipids for different concentrations of the oxidized component (3.1%, 25% and 50%). Using pair correlation functions, we extract structural information on the systems and determine whether the two components are prone to mixing or not. Finally, we calculate the thermodynamic mixing parameters within the framework of the virial expansion
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Villazana-Kretzer, Diana L. "Giardia lamblia genomic and molecular analyses of flippase /." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2008. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Thet, Naing Tun. "Modified tethered bilayer lipid membranes for detection of pathogenic bacterial toxins and characterization of ion channels." Thesis, University of Bath, 2010. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.530158.
Full textAbstract:
Pathogenic bacteria secrete various virulence factors as their biochemical weapons to gain access to and destroy the target cells. They can directly interact with the outer lipid bilayer membrane of eukaryotic cells, inducing the premature cell death by either apoptosis or necrosis. Such virulence factors account for much of the toxic actions associated with bacterial infection; therefore the detection of such proteins could provide a methodology for sensing/detection of pathogenic bacteria in, for example, food or human tissue. Detection and identification of pathogenic bacteria by conventional methods such as plating and counting in laboratory is expensive and time consuming. With growing concerns over emergence and re-emergence of pathogenic bacteria with high resistant to current antibiotics, there is a potential need for effective detection of pathogenic toxins invitro. On the other hand, artificially prepared lipid bilayer membrane on planar metallic surfaces provides the cell membrane mimics which are extremely useful in exploring the cellular functions and processes at the molecular level. Therefore in this work, an application of planar tethered bilayer lipid membrane (pTBLM) as a biomimetic sensing platform for the detection of clinically important pathogens, Staphylococcus aureus and Pseudomonas aeruginosa via their secreted virulence factors was presented. Planar TBLM was modified by incorporation of cholesterol and detection of bacterial toxins at human body temperature was examined by impedance and surface plasmon resonance methods. The results of pathogenic bacterial toxin detection were compared with those of Escherichia coli (DH5α), the human gut normal flora with non-pathogenic strain, as a control. Additionally pTBLM was transferred onto single nanoporous Si3N4 membrane to enhance the toxin sensitivity and extend the lifetime for the possible realization of future membrane chips for ion channel characterizations and drug screenings. Then the single ion channel measurement was demonstrated with nanopore-suspended TBLM (Nano-psTBLM) using α-toxin of S. aureus. The results presented in this work therefore, may pave the more effective and efficient ways for future pathogenic bacterial detection in which the sensing mechanism was solely based on the nature of interactions as well as modes of action between bacterial toxins and artificial lipid bilayer membranes.