Дисертації з теми "Interface membrane"
Щоб переглянути інші типи публікацій з цієї теми, перейдіть за посиланням: Interface membrane.
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся з топ-50 дисертацій для дослідження на тему "Interface membrane".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Переглядайте дисертації для різних дисциплін та оформлюйте правильно вашу бібліографію.
1
Britt, Hannah Mary. "Reactivity at the membrane interface." Thesis, Durham University, 2018. http://etheses.dur.ac.uk/12787/.
Анотація:
Modulation of internal environment and maintenance of cellular structure and stability are basic requirements to ensure cell survival. These cellular functions are provided by the cell outer membrane, a phospholipid bilayer characterised by the fluid mosaic model. Chemical reactivity at the membrane interface has previously been identified between phospholipids and membrane binding species. Observed reactivity, termed intrinsic lipidation, involves non-enzymatic acyl transfer from phospholipids to a nucleophilic membrane bound molecule. Reactivity has been characterised for membrane active peptides and proteins, and been found influential to the structure and function of both the newly modified species, and the bulk membrane. Research presented within this thesis probes fundamental features of observed intrinsic lipidation reactivity at the membrane interface. This work has expanded upon previous intrinsic lipidation research, facilitated by the development of informative and robust analytical techniques for the study of reactivity. Optimised TLC has allowed improved routine high throughput reactivity screening, compared to alternative fluorescence and solution state NMR techniques. Informative analysis and mechanistic understanding of intrinsic lipidation has been achieved through LCMS and solid state NMR analysis. Synthetic protocols for preparation of isotopically labelled 15N small molecules, and 13C phospholipids, has facilitated solid state NMR in particular. Biological relevance of peptide intrinsic lipidation has also been probed to determine the role of reactivity in natural function, and disease induction. Biophysical techniques such as CD and tryptophan fluorescence revealed that solution phase intrinsically lipidated melittin adopts an α-helical structure with central proline kink, in contrast to the random coil of unmodified melittin. Furthermore, at μM concentrations, palmitoylated species were shown to undergo spontaneous micelle formation. Disease related behaviour linked to peptide intrinsic lipidation includes moderate antimicrobial activity, and possible induction of amyloid nucleation. Additionally, this study has identified novel intrinsic lipidation of small molecules in vitro utilising chromatographic and ionisation conditions optimised with synthetically prepared standards. Observed for multiple cationic amphiphilic small molecules, intrinsic lipidation was promoted by primary amines in a hydrophilic environment, due to increased proximity between reactive moieties. Small molecule intrinsic lipidation products were shown to exhibit biological relevance, including spontaneous micelle formation, membrane disruption, and phospholipidosis induction. Pharmaceutical propranolol displayed notable intrinsic lipidation in vitro, and in Hep G2 cell culture. Initial transesterification from membrane phospholipids produced O-acylated propranolol, followed by secondary N-acylated propranolol formation by intramolecular O to N migration. Study of propranolol reactivity has revealed preferential eukaryotic transfer from the sn-1 phospholipid backbone position, and reaction kinetics influenced by temperature, pH, and membrane composition.
2
Luo, Yuzhong. "Membrane extraction with a sorbent interface." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq38251.pdf.
3
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.
4
Ge, Changrong. "Property-controlling Enzymes at the Membrane Interface." Doctoral thesis, Stockholms universitet, Institutionen för biokemi och biofysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-61988.
Анотація:
Monotopic proteins represent a specialized group of membrane proteins in that they are engaged in biochemical events taking place at the membrane interface. In particular, the monotopic lipid-synthesizing enzymes are able to synthesize amphiphilic lipid products by catalyzing two biochemically distinct molecules (substrates) at the membrane interface. Thus, from an evolutionary point of view, anchoring into the membrane interface enables monotopic enzymes to confer sensitivity to a changing environment by regulating their activities in the lipid biosynthetic pathways in order to maintain a certain membrane homeostasis. We are focused on a plant lipid-synthesizing enzyme DGD2 involved in phosphate shortage stress, and analyzed the potentially important lipid anchoring segments of it, by a set of biochemical and biophysical approaches. A mechanism was proposed to explain how DGD2 adjusts its activity to maintain a proper membrane. In addition, a multivariate-based bioinformatics approach was used to predict the lipid-binding segments for GT-B fold monotopic enzymes. In contrast, a soluble protein Myr1 from yeast, implicated in vesicular traffic, was also proposed to be a membrane stress sensor as it is able to exert different binding properties to stressed membranes, which is probably due to the presence of strongly plus-charged clusters in the protein. Moreover, a bacterial monotopic enzyme MGS was found to be able to induce massive amounts of intracellular vesicles in Escherichia coli cells. The mechanisms involve several steps: binding, bilayer lateral expansion, stimulation of lipid synthesis, and membrane bending. Proteolytic and mutant studies indicate that plus-charged residues and the scaffold-like structure of MGS are crucial for the vesiculation process. Hence, a number of features are involved governing the behaviour of monotopic membrane proteins at the lipid bilayer interface.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 5: Manuscript.
5
Co, Carl. "N-WASP at the membrane-actin interface." Diss., Search in ProQuest Dissertations & Theses. UC Only, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3251943.
6
Lindahl, Erik. "Computational Modeling of Biological Membrane and Interface Dynamics." Doctoral thesis, Stockholm : Tekniska högsk, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3141.
7
Hwang, William. "Droplet interface bilayers for the study of membrane proteins." Thesis, University of Oxford, 2008. http://ora.ox.ac.uk/objects/uuid:0ba680ba-75f1-4cd9-9600-3e251b948a3d.
Анотація:
Aqueous droplets submerged in an oil-lipid mixture become enclosed by a lipid monolayer. The droplets can be connected to form robust networks of droplet interface bilayers (DIBs) with functions such as a biobattery and a light sensor. The discovery and characterization of an engineered nanopore with diode-like properties is enabling the construction of DIB networks capable of biochemical computing. Moreover, DIB networks might be used as model systems for the study of membrane-based biological phenomena. We develop and experimentally validate an electrical modeling approach for DIB networks. Electrical circuit simulations will be important in guiding the development of increasingly complex DIB networks. In cell membranes, the lipid compositions of the inner and outer leaflets differ. Therefore, a robust model system that enables single-channel electrical recording with asymmetric bilayers would be very useful. Towards this end, we incorporate lipid vesicles of different compositions into aqueous droplets and immerse them in an oil bath to form asymmetric DIBs (a-DIBs). Both α-helical and β-barrel membrane proteins insert readily into a-DIBs, and their activity can be measured by single-channel electrical recording. We show that the gating behavior of outer membrane protein G (OmpG) from Escherichia coli differs depending on the side of insertion in an asymmetric DIB with a positively charged leaflet opposing a negatively charged leaflet. The a-DIB system provides a general platform for studying the effects of bilayer leaflet composition on the behavior of ion channels and pores. Even with the small volumes (~100 nL) that can be used to form DIBs, the separation between two adjacent bilayers in a DIB network is typically still hundreds of microns. In contrast, dual-membrane spanning proteins require the bilayer separation to be much smaller; for example, the bilayer separation for gap junctions must be less than 5 nm. We designed a double bilayer system that consists of two monolayer-coated aqueous spheres brought into contact with each side of a water film submerged in an oil-lipid solution. The spheres could be brought close enough together such that they physically deflected without rupturing the double bilayer. Future work on quantifying the bilayer separation and studying dual-membrane spanning proteins with the double bilayer platform is planned.
8
Franz, João Paulo Vicentini. "Interface : a projeção como membrana semipermeável." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2018. http://hdl.handle.net/10183/184850.
Анотація:
A pesquisa "Interface: a projeção como membrana semipermeável" aborda um processo de criação artística que teve origem no início do ano de 2011. Os trabalhos, pensados inicialmente como vídeos, pelos quais foi experimentado romper com a estrutura narrativa do cinema tradicional, foram modificando-se no decorrer da pesquisa, desse modo, abrangendo o olhar sobre a instalação que continha o vídeo e a projeção. Passou-se, então, a explorar diferentes situações de apresentação espacial nas instalações propostas, muitas vezes, utilizando recursos computacionais de modelagem projetiva como suavização das áreas de projeção, delimitação da abrangência projetiva e inserção de múltiplos vídeos, bem como experimentou-se com interferências nas projeções. Para refletir sobre os trabalhos desenvolvidos, partiu-se de alguns artistas e autores que discutem o espaço de exposição e como o observador relaciona-se com ele, como Thommas Zummer, Andre Parente, Malcom Le Grice e Philippe Dubois. Mediante os conceitos de projeção, interface e membrana – abordados sob diferentes perspectivas do conhecimento – considerou-se o espaço de instalação em uma relação multidirecional entre o observador e o espaço de exposição.The research, "Interface: projection as semipermeable membrane", approaches a process of artistic creation that originated in the beginning of 2011. The works, initially thought as videos, by which it was tried to break with the narrative structure of traditional cinema, were modified in the course of the research, thus covering the view on the installation that contained the video and the projection. Then proceeded to explore different spatial presentation situations in the proposed installations, often using computational resources of projective modeling such as smoothing projection areas, delimiting the projective range and inserting multiple videos, as well as experimenting with interferences projections. In order to reflect on the work developed, it was used some artists and authors who discuss the exhibition space and how the observer relates to him, such as Thommas Zummer, Andre Parente, Malcolm Le Grice and Philippe Dubois. Through the concepts of projection, interface and membrane - approached from different perspectives of knowledge - the installation space was considered in a multidirectional relation between the observer and the exhibition space.
9
Danial, John Shokri Hanna. "Imaging lipid phase separation in droplet interface bilayers." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:34bb015f-2bc1-43bb-bc29-850e0b55edac.
Анотація:
The spatiotemporal organization of membrane proteins is implicated in cellular trafficking, signalling and reception. It was proposed that biological membranes partition into lipid rafts that can promote and control the organization of membrane proteins to localize the mentioned processes. Lipid rafts are thought to be transient (microseconds) and small (nanometers), rendering their detection a challenging task. To circumvent this problem, multi-component artificial membrane systems are deployed to study the segregation of lipids at longer time and length scales. In this thesis, multi-component Droplet Interface Bilayers (DIBs) were imaged using fluorescence and interferometric scattering microscopy. DIBs were used to examine and manipulate microscopic lipid domains and to observe, for the first time, transient nanoscopic lipid domains. The techniques and results described here will have important implications on future research in this field.
10
Foster, Simon Edward. "Routes to interfacial deposition of platinum microparticles in solid polymer fuel cells." Thesis, Loughborough University, 1998. https://dspace.lboro.ac.uk/2134/28053.
11
Bansal, A. "The interferometric study of liquid transport across membranes." Thesis, University of Surrey, 1988. http://epubs.surrey.ac.uk/847237/.
Анотація:
A Twyman-Green interferometer was used to study the selective transport of ethanol-water mixtures of various concentration across a nonporous homogeneous silicone rubber membrane at 25°C. The instrument developed enabled the measurement of the transient concentration profiles within the boundary layers bathing the membrane. Measurements as close as 5um from the membrane surface were possible. The majority of the reported interferometric studies of liquid/membrane transport have been limited to the observation of the fringes and stop short of a full theoretical analysis. Such analysis is complicated by the optical effects of light deflection and the computational burden involved in the transient solution of the mathematical models required to describe membrane transport. A rigorous treatment of light deflection was developed on the basis of Fermat's principle of least time. The transient numerical solution of the model equations was accomplished by the application of the method of lines. To decouple the equilibrium and kinetic phenomena in membrane transport requires the independent measurement of the sorption isotherm. Traditional techniques for measuring the extent and composition of the imbibed phase involve removing the membrane from the liquid and are therefore limited by the inherent difficulties of obtaining a 'clean' separation. This was circumvented by measuring the excess (relative) sorption isotherm without removing the membrane from the liquid. The data was analysed in terms of Flory-Huggins thermodynamics which was fitted to the measured excess isotherm across the entire concentration range. For a binary mixture, transport across a homogeneous membrane involves two simultaneous fluxes which can be coupled through kinetic and/or equilibrium interactions. A measure of the extent of coupling was obtained by comparing the results from a simplified 'decoupled' flux model with those based on a 'coupled' flux model allowing for equilibrium interactions. Such interactions were found to have little effect on the flux of ethanol but strongly influenced the flux of water across silicone rubber. In particular, coupling through equilibrium interaction was found to be responsible for as much as 75% of the total flux of water. The diffusion coefficients of both ethanol and water in silicone rubber were shown to decrease strongly with alcohol concentration.
12
Wang, Fang. "Peptide channel redesign: mutations of gramicidin A at membrane-water interface." Thesis, Boston College, 2012. http://hdl.handle.net/2345/3411.
Анотація:
Thesis advisor: Jianmin GaoMy graduate research focuses on engineering and characterizing gramicidin A (gA), a natural fifteen-residue transmembrane channel peptide. It consists of D- and L- amino acids at alternate positions. gA is believed to fold into a β-helix in membranes, and two folded monomers at each leaflet of the lipid bilayer dimerize to form a transmembrane channel. gA shares the common features of other known membrane channels: a well defined structure that only allows the passage of specific ions, a gating mechanism, and a high abundance of aromatic residues. This dissertation includes two subprojects: I. Understanding Channel Formation: Aromatic Modifications of Gramicidin A Channel Ion channels are key elements in signaling and molecule transport, and therefore crucial for normal function of cells. Defective ion channels are known to be responsible for a number of diseases. Although hundreds of crystallographic structures of membrane proteins have been deposited into the PDB in the past few decades, our knowledge on this large family of proteins is still limited and mostly descriptive. Study of small peptides in model membranes is a good simplification of the more complex biological systems. In chapter 1, I will introduce my research using gA as a model system to understand the significant role of aromatic residues in membrane channel structure formation. Channel activities of these gA-Ar mutants were evaluated by ion leakage assays. The structure activity relationship of a library of gA mutants was discussed. The alternating chirality of amino acids was proven to be essential for gA channel activity. Several additional interesting observations are discussed. II. Towards Bacterium Specific Ion Channels: Solublized Gramicidin A as Potential Systemic Antibiotics The rapid development of multidrug resistance by pathogenic bacteria poses a serious threat to society and demands new antibiotics with different mechanisms. Often considered as a model transmembrane channel, gA also has proven antibiotic activities. The gA channel facilitates passive diffusion of water and monovalent cations (e.g. H+, Na+, K+) thus killing bacteria by disrupting the ion gradient across the cell membrane. However because of its poor solubility and high toxicity, its medicinal application as an antibiotic has been limited to topical reagents. A detailed understanding of gA allows rational optimization of the gA-WT to potential systemic antibiotics. Bacterial membranes are composed of a large fraction of anionic species, therefore, we hypothesize that strategic incorporation of cationic residues into gA will afford bacterium-specific toxicities. In addition, the charged residues will greatly improve the water solubility of gA. In chapter 2, I will introduce my research on developing soluble and bacterium specific gA as a potential systemic antibiotic. We firstly incorporated D-Lys at the C-terminus to obtain our first generation of gA based antibiotics. The best candidate (D-Leu10,12,14D-Lys gA) shows significantly increased water solubility (~ 1, 000 times) and therapeutic index (˃ 50 times). Modifications on the Lys side chain were then carried out to fine tune the antibiotic activities of these cationic gA. My research has pointed out a possible strategy to convert hydrophobic membrane channel peptides into potential systemic antibiotics. In addition to targeting the negative charges of bacterial membranes with cationic gA mutants, we proposed a novel strategy in which boronic acid is used to chase after the 1,2-diol substructure in the PG headgroup through boronate ester formation. Polyvalent display of boronic acids on a peptide scaffold results in enhanced binding with diols, showing promise of the boronate approach in the development of bacterium specific reagents
Thesis (PhD) — Boston College, 2012
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
13
Duckney, Patrick James. "Functional analysis of NET2A at the actin-membrane interface of plants." Thesis, Durham University, 2017. http://etheses.dur.ac.uk/12130/.
Анотація:
Recently, NET2A was characterised as a novel, plant-specific actin-binding protein that binds actin at the plasma membrane of growing pollen tubes (Deeks et al. 2012; Dixon. 2013). However, a function for NET2A has not yet been identified. Throughout the course of this investigation, several strategies were employed to elucidate the roles of NET2A in Arabidopsis, including reverse-genetic analysis, in situ localisation studies of NET2A in developing pollen grains and growing pollen tubes, as well as several protein-protein interaction screens. During this study, multiple NET2 subfamily members were shown to interact with plasma membrane integral proteins, demonstrating novel mechanisms by which the actin cytoskeleton is linked to the plasma membrane in plants. Through these interactions, NET2 proteins are implicated in the regulation of pollen tube growth in vivo during fertilisation, and regulation of the cytoskeleton in response to extracellular signals. A role for NET2A in pollen grain development was also studied during this investigation, in which NET2A was observed to associate with the actin cytoskeleton of developing pollen grains, and undergo dynamic reorganisations in subcellular localisation timed to specific developmental events in male gametogenesis. Reverse-genetic analysis of individual NET2 subfamily members has identified no phenotypic growth defects in pollen grain development or fertilisation. Several lines of evidence suggest functional redundancy and cooperation between individual NET2 proteins, including their involvement with common interacting partners at the plasma membrane, and interactions with one another in NET2 hetero-oligomers. Additionally, this project describes the discovery of a novel microtubule-associated protein in Arabidopsis. This protein, named herein as MAP7A, was demonstrated to associate with microtubules directly, and localise to the pollen tube plasma membrane and generative cell nucleus. Described in this thesis are the potential roles for NET2A and MAP7A in the regulation of the plant cytoskeleton during anisotropic cell growth.
14
Maltseva, Elena. "Model membrane interactions with ions and peptides at the air,water interface." Phd thesis, [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=976724537.
15
Gross, Linda C. M. "Applications of droplet interface bilayers : specific capacitance measurements and membrane protein corralling." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:0b7ffba6-b86d-499c-a93f-3b2fc46a427b.
Анотація:
Droplet Interface Bilayers (DIBs) have a number of attributes that distinguish them from conventional artificial lipid bilayers. In particular, the ability to manipulate bilayers mechanically is explored in this thesis. Directed bilayer area changes are used to make precise measurements of the specific capacitance of DIBs and to control the two dimensional concentration of a membrane protein reconstituted in the bilayer. Chapter 1 provides a general introduction to the role of the lipid membrane en- vironment in the function of biological membranes and their integral proteins. An overview of model lipid bilayer systems is given. Chapter 2 introduces work carried out in this laboratory previously and illustrates the experimental setup of DIBs. Some important bilayer biophysical concepts are covered to provide the theoretical background to experiments in this and in later chapters. Results from the characterisation of DIBs are reported, and an account of the development of methods to manipulate the bilayer by mechanical means is given. Chapter 3 describes experiments that apply bilayer area manipulation in DIBs to achieve precise measurement of specific capacitance in a range of lipid systems. Chapter 4 reports results from experiments investigating the response of bilayer specific capacitance to an applied potential. Chapter 5 covers the background and experimental setup for total internal fluo- rescence microscopy experiments in DIBs and describes the expression, purification and characterisation of the bacterial β-barrel membrane protein pore α-Hemolysin. Chapter 6 describes experiments that apply the mechanical manipulation of bilayer area in DIBs to the corralling and control of the surface density of α-Hemolysin.
16
Bhumbra, Rej-Paul. "Sealing the bone-implant interface around total hip replacements using guided bone regeneration." Thesis, University of London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313796.
17
Yuen, Christopher Tze Kiu. "Bacteriophage M13 major coat protein, roles of aromatic residues at the membrane-water interface." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0021/MQ45882.pdf.
18
Washo, Dawn Llewellyn. "Using membrane interface probe (MIP) to characterize chlorinated volatile organic compounds in glacial sediments." Diss., Online access via UMI:, 2009.
19
Schmidt, Piet O. "Origins of Effective Charge of Multivalent Ions at a Membrane/Water Interface and Distribution of 2,3,4,5-Tetrachlorophenol in a Membrane Model System." PDXScholar, 1995. https://pdxscholar.library.pdx.edu/open_access_etds/5049.
Анотація:
Biological cells and subcellular organelles are surrounded by membranes to form compartments performing specialized functions. Adsorption or partitioning of biologically active compounds into the membrane is the first step in the process of modification of cell function. This work is concerned with the problem of distribution of charged molecules between water and electrically charged membrane surface and between water and octanol. Part I of this thesis is focused on the electrostatic interactions taking place between charges on the membrane and ions present in the aqueous region of the membrane/water interface. The objective was to explore theoretically the origin of anomalous behavior of Ruthenium Red (RuR), a positively charged hexavalent ion. It was discovered in studies of RuR adsorption to negatively charged membranes that within the framework of the Gouy-Chapman theory of the membrane/water interface, RuR behaves as an ion with effective charge less than its physical charge. Moreover, the effective charge was found to be dependent on the density of electric charge at the membrane surface. Two theoretical models of the interfacial region were examined: the Rod Model and the Maximum Density Model. The Rod Model takes into account steric constraints imposed on RuR at the vicinity of the membrane surface. The Maximum Density Model attempts to account for non-ideal behavior by including repulsive interactions. These theoretical studies illustrate the consequences of finite size and ion-ion interactions of adsorption of large molecular ions to electrically charged membrane surfaces. Part II is an experimental study whose objective was to determine the partition coefficient of the negatively charged 2,3,4,5-tetrachlorophenol (TeCP) between water and octanol. The study was based on spectrophotometric measurements of the equilibrium concentrations of TeCP in water and octanol as a function of pH. The octanol/water partition coefficient for both the non-ionized and ionized species of TeCP were determined. It was found that the partition coefficient of ionized TeCP to lipid membrane is about 400 times greater than that for octanol. This result supports the hypothesis that the octanol/water partition coefficient of ionized chlorophenols cannot be used for predicting their distribution between water and lipid-bilayercontaining elements of the environment.
20
Najem, Joseph Samih. "Droplet Interface Bilayers for Mechano-Electrical Transduction Featuring Bacterial MscL Channels." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/83399.
Анотація:
This dissertation investigates the behavior of the Escherichia Coli mechanosensitive (MS) channel MscL, when incorporated within a droplet interface bilayer (DIB). The activity of MscL channels in an artificial DIB system is demonstrated for the first time in this document. The DIB represents a building block whose repetition can form the basis to a new class of smart materials. The corresponding stimuli-responsive properties can be controlled by the type of biomolecule incorporated into the lipid bilayer, which is in the heart of this material. In the past decade, many research groups have proven the capability of the DIB to host a wide collection of natural and engineered functional biomolecules. However, very little is known about the mechano-electrical transduction capabilities of the DIB. The research present herein specifically seeks to achieve three direct goals: 1) exploring the capabilities of the DIB to serve as a platform for mechano-electrical transduction through the incorporation of bacterial MscL channels, 2) understanding the physics of mechano-electrical transduction in the DIB through the development of theoretical models, and 3) using the developed science to regulate the response of the DIB to a mechanical stimulus.
MscL channels, widely known as osmolyte release valves and fundamental elements of the bacterial cytoplasmic membrane, react to increased tension in the membrane. In the event of hypo-osmotic shocks, several channels residing in the membrane of a small cell can generate a massive permeability response to quickly release ions and small molecules, saving bacteria from lysis. Biophysically, MscL is well studied and characterized primarily through the prominent patch clamp technique. Reliable structural models explaining MscL's gating mechanism are proposed based on its homolog's crystal structure modeling, which lead to extensive experimentation. Under an applied tension of ~10 mN/m, the closed channel which consists of a tight bundle of transmembrane helices, transforms into a ring of greatly tilted helices forming an ~8 A water-filled conductive pore. It has also been established that the hydrophobicity of the tight gate, positioned at the intersection of the inner TM1 domains, determines the activation threshold of the channel. Correspondingly, it was found that by decreasing the hydrophobicity of the gate, the tension threshold could be lowered. This property of MscL made possible the design of various controllable valves, primarily for drug delivery purposes. For all the aforementioned properties and based on its fundamental role of translating cell membrane excessive tensions into electrophysiological activities, MscL makes a great fit as a mechanoelectrical transducer in DIBs.
The approach presented in this document consists of increasing the tension in the lipid bilayer interface through the application of a dynamic mechanical stimulus. Therefore, a novel and simple experimental apparatus is assembled on an inverted microscope, consisting of two micropipettes (filled with PEG-DMA hydrogel) containing Ag/AgCl wires, a cylindrical oil reservoir glued on top of a thin acrylic sheet, and a piezoelectric oscillator actuator. By using this technique, dynamic tension can be applied by oscillating one droplet, producing deformation of both droplets and area changes of the DIB interface. The tension in the artificial membrane will cause the MS channels to gate, resulting in an increase in the conductance levels of the membrane. The increase in bilayer tension is found to be equal to the sum of increase in tensions in both contributing monolayers. Tension increase in the monolayers occurs due to an increase in surface area of the constant volume aqueous droplets supporting the bilayer.
The results show that MS channels are able to gate under an applied dynamic tension. Interestingly, this work has demonstrated that both electrical potential and surface tension need to be controlled to initiate mechanoelectric coupling, a property previously not known for ion channels of this type. Gating events occur consistently at the peak compression, where the tension in the bilayer is maximal. In addition, the experiments show that no activity occurred at low amplitude oscillations (< 62.5um). These two findings basically present an initial proof that gating is occurring and is due to the mechanical excitation, not just a random artifact. The role of the applied potential is also highlighted in this study, where the results show that no gating happens at potentials lower that 80 mV. The third important observation is that the frequency of oscillation has an important impact of the gating probability, where no gating is seen at frequencies higher than 1 Hz or lower than 0.1 Hz.
Each of the previous observations is addressed separately in this research. It was found that the range of frequencies to which MscL would respond to in a DIB could be widened by using asymmetrical sinusoidal signals to stimulate the droplets. By increasing the relaxation time and shorting the compression time, a change in the monolayer's surface area is achieved, thus higher tension increase in the bilayer. It was also found that a high membrane potential assists in the opening of MscL as the droplets are stimulated. This is due to the sensitivity of MscL to the polarity of the signal. By using the right polarity the channel could be regulated to become more susceptible to opening, even at tensions lower than the threshold.
Finally, it was demonstrated, for the first time, that MscL would gate in asymmetric bilayers without the need to apply a high external potential. Asymmetric bilayers, which are usually composed from different lipids in each leaflet, generate an asymmetric potential at the membrane. This asymmetric potential is proven to be enough to cause MscL to gate in DIBs upon stimulation.Ph. D.
21
Fossati, M. "MECHANISMS OF PROTEIN TRANSPORT AT THE ER-GOLGI INTERFACE." Doctoral thesis, Università degli Studi di Milano, 2013. http://hdl.handle.net/2434/214981.
Анотація:
The Endoplasmic Reticulum represents the first station of the secretory path-way, where proteins destined to the cell surface or to some intracellular organelles are recruited in specific ER subdomains, the ER Exit Sites (ERES), and start to travel into transport carriers to reach the proper final destination. Even though cargoes are usual-ly recruited to ERES by a sequence-dependent mechanism, it is known that other fac-tors contribute to protein export from the ER. Using model fluorescent tail-anchored proteins our group previously demonstrated that the length/hydrophobicity of the transmembrane domain is an important factor determining recruitment to or exclusion from ERES: a protein with a short TMD (FP-17) is excluded from ERES and retained in the ER, while a longer TMD (FP-22) determines enrichment in ERES. In order to clarify the molecular mechanism underlying this TMD-dependent transport, we first compared the transport of an export signal-bearing (VSV-G DxE) membrane protein with our model protein FP22, which lacks an export signal. FP22 and VSV-G accu-mulate together at ERES, but VSVG reaches the plasma membrane more rapidly than FP22. To investigate the basis of this difference, we combined cDNA microinjection to temperature blocks and live-cell imaging approaches that allowed us to analyze the transport at early steps of the secretory pathway at the ER-Golgi interface. At 20°C, a temperature at which only the transport between the ER and the Golgi is allowed, all of the VSVG accumulates in the Golgi, while FP-22 remains distributed between the ER and the Golgi. After bleaching the Golgi fraction of FP22 we observed a rapid, energy-dependent, fluorescence recovery, indicating an efficient ER to Golgi transport even in the absence of the export signal and suggesting that FP22 may be re-cycled between the two compartments. In agreement, a rapid emptying of the Golgi was observed after ER bleaching (accompanied by a fluorescence recovery of the ER fraction). To investigate whether this phenomenon is restricted to our model protein only or it is more general event, we then tested the behavior of a signal-deleted form of VSV-G (VSV-G AxA). Similarly to FP22, VSVG AxA is distributed between the Golgi and the ER at 20°C and Golgi fluorescence rapidly decreases after ER bleach-ing, suggesting a new role of the ER export signal, which is important not only in re-cruiting cargoes at the ERES, but also in preventing their recruitment into futile cy-cles between the Golgi and the ER, which delay their arrival to the cell surface.
To further characterize the mechanism of TMD-dependent sorting, we then in-vestigated the role of membrane curvature; our group previously demonstrated that FP-22 is segregated from FP-17 in specific ER subdomains, which are characterized by membrane curvature (ERES and ER tubules). In collaboration with Bruno Goud and Jean-Baptiste Manneville (Institute Curie, Paris), we created highly curved do-mains using membranes composed of a uniform lipid composition (POPC, palmitoyl-oleyl-phosphatidylcholine) or ER lipids extracted from rat liver microsomes, and we analyzed the distribution of our two model proteins in flat and curved domains. Our results indicate that the two proteins are uniformly distributed in curved membranes and strongly suggest that the membrane curvature alone cannot drive the TMD-dependent partitioning of membrane proteins in ERES and ER tubules.
Taken together, our data contribute to clarify the role of two fundamental fac-tors influencing the transport of membrane proteins along the secretory pathway that were never investigated before.
22
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.
23
Segal, Alina. "Development of membrane extraction with a sorbent interface for the analysis of environmental and clinical samples." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ65260.pdf.
24
Barlow, Nathan. "Droplet interface bilayers : on the theory and application of the small molecule passive membrane permeability assay." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/57509.
Анотація:
Investigations into characterising and measuring bio-membrane permeability have been ongoing for over a century. Driven by both industry and academia, a variety of in vivo, in vitro, and in silico techniques have been developed and employed to understand the mechanisms and thermodynamics of drug and agrochemical transport in living systems. Unfortunately, many of the techniques suffer from a lack of high-throughput implementation or suffer physical restrictions such as bulk diffusion limitations. Moreover, it is apparent that membrane permeability data is lacking, particularly with respect to the agricultural industry and non-mammalian biological sciences. With the invention of the droplet interface bilayer (DIB) a decade ago, there have been several breakthroughs in membrane technologies for electro-physiology, membrane protein reconstitution, and membrane permeability assay methods. In this thesis, I have studied DIBs as a possible candidate for a rapid and high-throughput membrane permeability assay that can be used to measure rates for speci c agrochemicals in varying lipid systems in situ. The rst output of this research includes device engineering, design and fabrication techniques of novel micro uidic chips for improved DIB formation, droplet rendering, and manipulation. More speci cally, on demand and high through-put DIB manufacture has been achieved for the rst time, the results of which has been published in the peer reviewed journal, Lab on a Chip. Furthermore, to prove that the application of DIBs are not categorically limited to a small subset of lipid types, it has been proven that DIBs can be formed with a variety of lipids, including some plant lipid extracts. For the rst time, DIB model membranes have been formed to mimic soy, Arabidopsis, tobacco, and oat plasma membranes. A successful permeability assay was performed with these DIBs, and the results were published in the peer reviewed journal, Biomicro uidics. A serious challenge of measuring membrane permeability in DIBs is the limitation of bulk diffusion, which often leads to underestimates in intrinsic membrane permeability rates. To further the understanding of this limitation, the uid dynamics of coupled advection-diffusion in stirred droplets has been investigated experimentally and computationally. As a result, a novel micro uidic device has been developed to induce shear stress along the membrane to disrupt the effects of the bulk uid stagnation in the permeability assay, which allows for more accurate measurements of the intrinsic membrane permeability. To the best of my knowledge, this is the most accurate technique available, and is a breakthrough tool for future applications, such as supplying permeability data to systems transport models. The results of the intrinsic membrane permeability of various lipid types have been published in the journal, Nature Scienti c Reports. Furthermore, the physical properties of DIBs have been investigated including surface energy driven morphology, formation dynamics, and bilayer surface tension measurements. For the rst time, the effect of membrane curvature in DIBs has been thoroughly scrutinized, and new insights into DIB behaviour have been established.
25
Mrad, Christine. "Caractérisation ex-situ par RMN et IRM des transferts d'eau à l'interface membrane/électrode dans les piles à combustible PEMFC." Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0358.
Анотація:
Dans le cadre de la transition énergétique durable, les piles à combustible à membrane échangeuse de protons (PEMFC) sont considérées comme des alternatives prometteuses aux moteurs conventionnels. Elles offrent une conversion efficace de l'hydrogène en électricité sans émettre de polluant. Néanmoins, pour espérer un large déploiement de ces systèmes il est indispensable de réduire leur coût et améliorer leur durabilité. C'est pourquoi le projet européen « ALPE : Advanced Low-Platinum hierarchical Electrocatalysts for low-T fuel cells », dans lequel s'inscrit cette thèse, vise à réduire le coût des PEMFC en diminuant la quantité du catalyseur de platine (Pt) utilisée dans leurs électrodes, ciblant une réduction de 1.5 à 2 fois par rapport à l'état de l'art de 2019. Le fonctionnement des PEMFC repose essentiellement sur les réactions électrochimiques se produisant sur les sites catalytiques de Pt, et le transport protonique est étroitement lié à l'état d'hydratation de la membrane électrolyte (l'eau servant de vecteur pour les protons). Ce travail de thèse a donc pour objectif d'étudier l'impact de la réduction de la quantité de Pt sur les phénomènes de transport de l'eau à travers les interfaces membrane-électrode/air. Afin d'atteindre cet objectif, des dispositifs et des méthodologies expérimentaux permettant l'analyse de l'interface membrane/électrode par spectroscopie et imagerie de résonance magnétique (RMN/IRM) ont été développés. Dans un premier temps, l'étude se focalise sur l'étude d'une membrane seule de type Nafion® (N1110). Une analyse in-situ permettant de visualiser l'impact de l'histoire hygrothermale de la membrane sur les propriétés de l'eau est présentée. De plus, des expérimentations sous différentes conditions d'humidité relative, d'un côté et de l'autre de cette membrane, démontrent la capacité de notre approche à quantifier les résistances au transport de l'eau à interface de la membrane en les découplant des effets diffusifs. En complément, une modélisation 1D en régime permanent de la diffusion de l'eau à travers l'épaisseur de la membrane permet de déterminer l'évolution du coefficient de diffusion mutuelle de l'eau. Pour compléter notre analyse, une séquence de mesure en acquisition partielle a été conçue pour minimiser le temps d'acquisition des profils d'eau dans la membrane, ouvrant la voie à une étude en régime transitoire. Enfin, une comparaison des résistances d'interfaces entre une membrane seule et une membrane avec électrode(s) permet d'évaluer l'impact de l'ajout d'un dépôt d'une électrode et celui d'une variation de quantité de platine, sur les phénomènes de transport de l'eau. Les résultats mettent en lumière qu'en régime transitoire, il n'y a pas de différences significatives entre une membrane seule et un assemblage membrane/électrode (avec une seule ou deux électrodes). Toutefois, il apparaît que la présence de l'électrode et la quantité de platine semblent avoir un impact sur l'évolution des résistances d'interfaces en fonction de l'humidité relative de l'air alimentant la membraneIn the context of sustainable energy transition, Proton Exchange Membrane Fuel Cells (PEMFC) are considered promising alternatives to conventional engines. They offer efficient conversion of hydrogen into electricity without emitting pollutants. However, for the widespread deployment of these systems, it is essential to reduce their cost and improve their durability. This is the focus of the European project « ALPE: Advanced Low-Platinum hierarchical Electrocatalysts for low-T fuel cells », in which this thesis is situated. The project aims to reduce the cost of PEMFCs by decreasing the amount of platinum (Pt), catalyst used in their electrodes, targeting a reduction of 1.5 to 2 times compared to the state of the art in 2019. The operation of PEMFCs relies essentially on the electrochemical reactions occurring on the Pt catalytic sites, and proton transport is closely linked to the hydration state of the electrolyte membrane (water serving as a vector for protons). Therefore, the objective of this thesis is to study the impact of reducing the amount of Pt on the water transport phenomena across the membrane-electrode/air interfaces. In order to achieve this goal, experimental devices and methodologies for analyzing the membrane/electrode interface through spectroscopy and magnetic resonance imaging (NMR/MRI) have been developed. Initially, the study focuses on the examination of a single Nafion® membrane (N1110). An in-situ analysis that allows visualization of the impact of the membrane's hygrothermal history on the properties of water is presented. Furthermore, experiments under different relative humidity conditions on each side of the membrane demonstrate the capability of our approach to quantify interfacial resistances of water transfer while decoupling them from diffusive effects within the membrane. Additionally, a 1D steady-state model of the diffusion of water across the thickness of the membrane allows to determine the evolution of the mutual water diffusion coefficient. To complement our analysis, a partial acquisition measurement sequence has been designed to minimize the acquisition time of water profiles within the membrane, paving the way for a transient study. Finally, a comparison of interfacial resistances between a single membrane and a membrane with electrode(s) provides insights into the impact of adding an electrode deposit and varying the platinum loading on water transport phenomena. The results highlight that in transient conditions, there are no significant differences between a single Nafion® membrane and a membrane/electrode assembly (with one or two electrodes). However, it appears that the presence of the electrode and the amount of platinum seem to influence the evolution of interfacial resistances depending on the relative humidity (RH) of the air supplied to the sample
26
Fujita, Katsuhiko. "Supramolecular Assembly Containing α-Helical Peptide Molecules in Lipid Bilayer Membrane and at the Air/Water Interface". Kyoto University, 1995. http://hdl.handle.net/2433/160763.
Анотація:
本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものであるKyoto University (京都大学)
0048
新制・課程博士
博士(工学)
甲第6024号
工博第1421号
新制||工||985(附属図書館)
UT51-95-D343
京都大学大学院工学研究科高分子化学専攻
(主査)教授 今西 幸男, 教授 砂本 順三, 教授 田中 渥夫
学位規則第4条第1項該当
27
He, Tao. "I. Exploration of Amphitropic Protein Interactions at the Membrane Interface; II. DNF2—A Plant Protein with Homology to Bacterial PI-PLC Enzymes." Thesis, Boston College, 2015. http://hdl.handle.net/2345/bc-ir:104815.
Анотація:
Thesis advisor: Mary F. RobertsAmphitropic proteins, such as the virulence factor phosphatidylinositol-specific phospholipase C (PI-PLC) from Bacillus thuringiensis, often depend on lipid-specific recognition of target membranes. However, the recognition mechanisms for zwitterionic lipids such as phosphatidylcholine (PC), which is enriched in the outer leaflet of eukaryotic cell membranes, are not well understood. Molecular dynamics (MD) simulation and mutagenesis results strongly indicate that PI-PLC interacts with PC head groups via cation-π interactions with aromatic tyrosine residues, and suggest that cation-π interactions at the interface may be a mechanism for specific lipid recognition by amphitropic and membrane proteins. Aromatic amino acids can not only form cation-π interactions at the interface but also insert into membranes and have hydrophobic interactions with lipid tails. Heretofore there has been no facile way to differentiate these two types of interactions. We show that specific incorporation of fluorinated amino acids into proteins can experimentally distinguish cation-π interactions from membrane insertion of the aromatic side-chains. Fluorinated aromatic amino acids destabilize the cation-π interactions by altering electrostatics of the aromatic ring while their enhanced hydrophobicity enhances membrane insertion. Incorporation of pentafluorophenylalanine or difluorotyrosine into a Staphylococcus aureus phosphatidylinositol-specific phospholipase C (PI-PLC) variant engineered to contain a specific PC-binding site demonstrates the effectiveness of this methodology. Applying this methodology to the plethora of tyrosine residues in Bacillus thuringiensis PI-PLC identifies those involved in cation-π interactions with PC. Cation-π interactions provide a likely molecular mechanism for BtPI-PLC PC specificity but do not account for its preference for bilayers containing a small fraction of anionic lipids. MD simulations and fluorescence correlation spectroscopy (FCS) vesicle binding measurements of positively charged amino acids as well as surface tyrosine residues are used to formulate a complete model of BtPI-PLC specific binding to mixed anionic phospholipid/PC membrane. DNF2, a new plant protein with homology to bacterial PI-PLC, is confirmed to be the first plant small PI-PLC enzyme that can cleave both PI and glycosylphosphatidylinositol (GPI) anchored proteins. GPI-anchored protein cleavage also confirms that DNF2 plays an important role in symbiosome, the intracellular compartment formed by the plant that contains nitrogen fixing bacteria
Thesis (PhD) — Boston College, 2015
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
28
Agel, Eric. "Electrode à air électrolyte solide polymère alcalin pour piles à combustible et générateur métal-air." Paris 7, 2002. http://www.theses.fr/2002PA077002.
29
Baxani, Kamal Divesh. "Hydrogel encapsulated droplet interface bilayer networks as a chassis for artificial cells and a platform for membrane studies." Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/112707/.
Анотація:
There has been increasing interest in droplet interface bilayers (DIBs) as novel devices for the study of lipid membranes and the development of artificial cell systems. Although DIBs have demonstrated to be useful in a number of laboratory applications, their wider use is hampered by a limited ability to exist untethered and remain mechanically stable beyond controlled laboratory environments. In this thesis, a microfluidic system is developed which enables the facile generation of hydrogel-encapsulated DIB networks which are freestanding and can exist in air, water and oil environments, without compromise to their ability to interface with the surrounding environment. Electrophysiology is employed in order to demonstrate the formation of bilayers between the encapsulated DIBs (eDIBs) and their external environment, achieved via the incorporation of the transmembrane pore α-Hemolysin. The eDIBs produced here are able to form higher-order structures akin to tissues via their assembly and adherence to one another, further demonstrating their potential to act as a chassis for artificial cells. Furthermore, the potential of eDIBs to be used as a platform for membrane studies is demonstrated via their use as a high-throughput array for membrane disruption fluorescence measurements using a plate reader, which makes use of the ability of eDIBs to be generated in large numbers as well as to be mechanically handled and placed in the wells of a 96-well plate. Fluorescence measurements were taken on up to 47 eDIBs simultaneously, and were able to detect bilayer leakage through pores as well as bilayer failure. The above experiments comprise the design, manufacture and use of a novel kind of DIB construct as a chassis for artificial cells and a platform for high-throughput membrane studies. It is proposed that eDIBs may help in realising the unfulfilled potential of DIB networks in applications in healthcare and beyond.
30
JAYASINGHE, MANORI I. "HEAVY-METAL-ION TRANSPORT IN NANOPOROUS SELECTIVE-MEMBRANES: THEORY AND EXPERIMENT." University of Cincinnati / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1186764159.
31
Aland, Sebastian, Sabine Egerer, John Lowengrub, and Axel Voigt. "Diffuse interface models of locally inextensible vesicles in a viscous fluid." Elsevier, 2014. https://htw-dresden.qucosa.de/id/qucosa%3A32307.
Анотація:
We present a new diffuse interface model for the dynamics of inextensible vesicles in a viscous fluid with inertial forces. A new feature of this work is the implementation of the local inextensibility condition in the diffuse interface context. Local inextensibility is enforced by using a local Lagrange multiplier, which provides the necessary tension force at the interface. We introduce a new equation for the local Lagrange multiplier whose solution essentially provides a harmonic extension of the multiplier off the interface while maintaining the local inextensibility constraint near the interface. We also develop a local relaxation scheme that dynamically corrects local stretching/compression errors thereby preventing their accumulation. Asymptotic analysis is presented that shows that our new system converges to a relaxed version of the inextensible sharp interface model. This is also verified numerically. To solve the equations, we use an adaptive finite element method with implicit coupling between the Navier-Stokes and the diffuse interface inextensibility equations. Numerical simulations of a single vesicle in a shear flow at different Reynolds numbers demonstrate that errors in enforcing local inextensibility may accumulate and lead to large differences in the dynamics in the tumbling regime and smaller differences in the inclination angle of vesicles in the tank-treading regime. The local relaxation algorithm is shown to prevent the accumulation of stretching and compression errors very effectively. Simulations of two vesicles in an extensional flow show that local inextensibility plays an important role when vesicles are in close proximity by inhibiting fluid drainage in the near contact region.
32
Villar, Gabriel. "Aqueous droplet networks for functional tissue-like materials." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:602f9161-368c-48c0-9619-7974f743f2f2.
Анотація:
An aqueous droplet in a solution of lipids in oil acquires a lipid monolayer coat, and two such droplets adhere to form a bilayer at their interface. Networks of droplets have been constructed in this way that function as light sensors, batteries and electrical circuits by using membrane proteins incorporated into the bilayers. However, the droplets have been confined to a bulk oil phase, which precludes direct communication with physiological environments. Further, the networks typically have been assembled manually, which limits their scale and complexity. This thesis addresses these limitations, and thereby enables prospective medical and technological applications for droplet networks. In the first part of the work, defined droplet networks are encapsulated within mm-scale drops of oil in water to form structures called multisomes. The encapsulated droplets adhere to one another and to the surface of the oil drop to form interface bilayers that allow them to communicate with each other and with the surrounding aqueous environment through membrane pores. The contents of the droplets can be released by changing the pH or temperature of the surrounding solution. Multisomes have potential applications in synthetic biology and medicine. In the second part of the work, a three-dimensional printing technique is developed that allows the construction of complex networks of tens of thousands of heterologous droplets ~50 µm in diameter. The droplets form a self-supporting material in bulk oil or water analogous to biological tissue. The mechanical properties of the material are calculated to be similar to those of soft tissues. Membrane proteins can be printed in specific droplets, for example to establish a conductive pathway through an otherwise insulating network. Further, the networks can be programmed by osmolarity gradients to fold into designed shapes. Printed droplet networks can serve as platforms for soft devices, and might be interfaced with living tissues for medical applications.
33
Czarske, Jürgen, C. Leithold, Hannes Radner, Lars Büttner, Moritz Stürmer, and U. Wallrabe. "Undisturbed interferometric sensing through a fluid interface by electrically-tunable lenses and micro mirrors." SPIE, 2015. https://tud.qucosa.de/id/qucosa%3A34996.
Анотація:
We have harnessed the power of various programmable photonics devices for an interferometric measurement technique. Distortion-free laser-based velocity measurements through a dynamic gas-liquid interface are enabled by a closed-loop optoelectronic system. We are employing electrically tunable lenses and micro mirrors to correct low-order wavefront distortions effectively. Our work represents a paradigm shift in interferometric velocity measurement techniques from using static to dynamic optical elements.
34
Colliat-Dangus, Perrine. "Complexation interfaciale de polymères : propriétés et stabilité d'émulsions millimétriques." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066134/document.
Анотація:
Ce travail de thèse porte sur l’étude d’une interface eau-huile où a lieu une complexation de deux polymères. La phase aqueuse est une solution de microgels de polyacide acrylique réticulé (carbomer) et la phase organique comprend un polyélectrolyte possédant des fonctions amines (amodiméthicone). Cette interface polymérique permet la stabilisation d’émulsions directes dont la taille des gouttes atteint le millimètre. Les gouttes sont ici fabriquées une à une via une technique millifluidique, ce qui permet d’obtenir une émulsion calibrée. Ce procédé a été mis au point par la société Capsum afin d’encapsuler des parfums ou bien des principes actifs pour la cosmétique. L’adsorption et la complexation des polyélectrolytes à l’interface eau-huile sont tout d’abord caractérisées à l’aide de méthodes de tensiométrie, en statique et en dynamique. Les propriétés mécaniques de la membrane polymérique ainsi que son potentiel stabilisateur d’émulsions sont ensuite étudiés à l’échelle d’une collection de gouttes, en compression par gravité ou bien par centrifugation, ainsi que pour des gouttes uniques en écoulement dans un tube. Ces diverses approches expérimentales permettent de mettre en lumière différents régimes de stabilisation des émulsions en fonction des conditions physico-chimiques. Une observation majeure est que la quantité d’amodiméthicone contrôle l’ancrage du carbomer à l’interface ainsi que l’état fluide ou bien solide de l’interface et donc la stabilité de l’émulsion correspondante. De plus, lorsque la membrane est solide, c’est-à-dire lorsqu’il y a réticulation des microgels via l’amodiméthicone, un phénomène remarquable de propagation de la rupture de la membrane au sein d’une émulsion sous compression est révéléThis work focuses on the study of an oil-water interface where the complexation of two polymers takes place. The aqueous phase is a solution of cross-linked polyacrylic acid microgels (carbomer) and the oil phase contains a polyelectrolyte possessing amine groups (amodimethicone). The stabilization of an emulsion of millimeter-sized droplets is achieved with this polymeric interface. Designed by millifluidic, the droplets are made one by one and a calibrated emulsion of oil in water is obtained. The process was developed by the company Capsum, with the objective to encapsulate perfumes or active ingredients for cosmetics. First, we characterize the adsorption and complexation of the polyelectrolytes at the oil-water interface with both static and dynamic tensiometry methods. Then, we study the mechanical properties of the polymeric membrane along with its capacity to stabilize emulsions, at the level of a collection of droplets undergoing compression which is applied either by gravity or by centrifugation, and also at the level of single droplets flowing through a glass capillary. Thanks to those various experimental methods, and depending on the physico-chemical conditions, the different emulsion stabilization regimes are highlighted. A major observation is that the amount of amodimethicone controls the anchoring of the carbomer at the interface, setting the interface state from fluid to solid, and therefore the corresponding emulsion stability. Moreover, when the membrane is solid, that is to say when the microgels are electrostatically cross-linked with the amodimethicone, a remarkable propagation of membrane rupture within an emulsion undergoing compression is revealed
35
Peker, Mevlut Fatih. "INVESTIGATIONS ON THE MICRO-SCALE SURFACE INTERACTIONS AT THE TOOL AND WORKPIECE INTERFACE IN MICRO-MANUFACTURING OF BIPOLAR PLATES FOR PROTON EXCHANGE MEMBRANE FUEL CELLS." VCU Scholars Compass, 2011. http://scholarscompass.vcu.edu/etd/2760.
Анотація:
Micro-forming studies have been more attractive in recent years because of miniaturization trend. One of the promising metal forming processes, micro-stamping, provides durability, strength, surface finish, and low cost for metal products. Hence, it is considered a prominent method for fabricating bipolar plates (BPP) with micro-channel arrays on large metallic surfaces to be used in Proton Exchange Membrane Fuel Cells (PEMFC). Major concerns in micro-stamping of high volume BPPs are surface interactions between micro-stamping dies and blank metal plates, and tribological changes. These concerns play a critical role in determining the surface quality, channel formation, and dimensional precision of bipolar plates. The surface quality of BPP is highly dependent on the micro-stamping die surface, and process conditions due to large ratios of surface area to volume (size effect) that cause an increased level of friction and wear issues at the contact interface. Due to the high volume and fast production rates, BPP surface characteristics such as surface roughness, hardness, and stiffness may change because of repeated interactions between tool (micro-forming die) and workpiece (sheet blank of interest). Since the surface characteristics of BPPs have a strong effect on corrosion and contact resistance of bipolar plates, and consequently overall fuel cell performance, evolution of surface characteristics at the tool and workpiece should be monitored, controlled, and kept in acceptable ranges throughout the long production cycles to maintain the surface quality. Compared to macro-forming operations, tribological changes in micro-forming process are bigger challenges due to their dominance and criticality. Therefore, tribological size effect should be considered for better understanding of tribological changes in micro-scale. The integrity of process simulation to the experiments, on the other hand, is essential. This study describes an approach that aims to investigate the surface topography changes during long-run micro-stamping of BPPs, and establish relationships between surface roughness–corrosion resistance and surface roughness–contact resistance characteristics of BPPs. Formability levels of formed BPPs and repeatability characteristics of the process were investigated. In addition, blank thickness changes, von-Mises stress, plastic strain levels and distributions of micro-stamping process were determined via finite element analysis (FEA). Test results revealed that the surface roughness change for the stamping dies and BPPs was unsteady (no trend) due to the continuous change of surface topography (i.e. asperity deformation). Sub-micron range local plastic deformations on stamping dies led to surface topography changes on BPP in long-run manufacturing case. As surface defects trigger corrosion, the correlation between surface roughness and corrosion resistance of BPPs was found to be direct. Increasing number of surface irregularities (asperities) lowered contact surface area that resulted in increased contact resistance. ZrN coated BPPs, on the other hand, did not change surface roughness, however; it improved the protection of BPPs against corrosion significantly. In addition, ZrN coating increased the conductivity of BPPs and reduced the contact resistance between BPP and gas diffusion layer (GDL), at certain extent. As dimensional stability and repeatability was confirmed in forming of both uncoated and coated BPPs during the long run manufacturing, different formability levels were achieved for coated and uncoated samples. Lower channel height values were obtained for coated plates because of the different surface hardness of uncoated and coated plates. In tribological size effect part of study, micro stamping experiments using three different dies with distinct channel height values at different stamping force levels were performed. It was concluded that decrease in forming die dimensions led to increase in coefficient of friction as previously reported by other researchers as one of the consequences of tribological size effect. On the other hand, coefficient of friction values were not affected by the force levels used in the experiments and simulations, whereas plastic strain, equivalent stress, and formability levels were increased with increasing stamping force, as expected. In essence, this study proposed a methodology to investigate the long-run manufacturing effects on dimensional stability and surface characteristics of micro-stamped sheets. It also correlates these parameters to fuel cell performance measures such as interfacial contact and corrosion resistance.
36
Thoreson, Erik J. "Apparatus to deliver light to the tip-sample interface of an atomic force microscope (AFM)." Link to electronic thesis, 2002. http://www.wpi.edu/Pubs/ETD/Available/etd-1003102-092130.
Анотація:
Thesis (M.S.)--Worcester Polytechnic Institute.Keywords: purple membrane; photomechanics; photoinduced conformation change; photocycle; photoactive; photoinduced; bimetallic bending; bacteriorhodopsin; atomic force microscope; tip-sample interface; molecular conformation; PLDS; photoreactive; AFM. Includes bibliographical references (p. E-1-E-4).
37
Touze-Foltz, Nathalie. "Modélisation des transferts advectifs dans les étanchéités composites de centres de stockage de déchets." Paris, ENMP, 2001. http://www.theses.fr/2001ENMPA001.
Анотація:
Les géomembranes des étanchéités composites présentent fréquemment des défauts qui constituent des passages préférentiels d'écoulement pour les lixiviats. Plusieurs auteurs ont développe des modèles mathématiques et des équations empiriques pour interpréter les débits de fuite, générés par les transferts advectifs obtenus au laboratoire et les étendre aux conditions de terrain en régime permanent, pour une transmissivité d'interface uniforme, un sol et une interface saturés en eau. La synthèse bibliographique réalisée permet de déterminer les limites de validité des modèles mathématiques et des équations empiriques existantes, pour une transmissivité d'interface uniforme. Il s'avère que la transmissivité d'interface dans les étanchéités composites est non uniforme. Le travail de thèse a donc consiste à étudier l'influence a travers différents outils de cette non-uniformité. Le développement de solutions analytiques basées sur les modèles mathématiques existants tout comme des expérimentations de laboratoire et de terrain ont permis de montrer l'influence de la prise en compte des non-uniformités de l'interface et du positionnement des défauts dans la géomembrane par rapport à celle-ci. Toutes les observations réalisées montrent la nécessité pour progresser dans la connaissance de transferts advectifs de pouvoir disposer d'une cartographie précise de la transmissivité d'interface et des défauts dans la géomembrane, à l'échelle d'un site. Deux méthodes ont d'ailleurs été testées au cours de la thèse pour décrire les états de surface de géomembranes et d'un limon compacté.
38
COLLAZOS, STEPHANIE ORTIZ. "PHYSICAL-CHEMICAL STUDIES OF THE EFFECT OF ANTIBIOTIC INCORPORATION IN THE STRUCTURE AND MOLECULAR ORGANIZATION OF CLINICAL-GRADE LUNG SURFACTANT MONOLAYERS AND MEMBRANE MODELS AT THE AIR-WATER INTERFACE." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2018. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=36895@1.
Анотація:
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
PROGRAMA DE DOUTORADO SANDUÍCHE NO EXTERIOR
O surfactante pulmonar é um sistema lipo-proteico que atua na interface alveolar com vital importância para manter funcional a mecânica respiratória. Os comprometimentos na sua função estão associados a diversas infecções pulmonares. Os sistemas de administração de fármacos baseados em surfactantes pulmonares derivados de animais são complexos, dificultando a compreensão do papel individual das moléculas hóspedes nas suas interações com a membrana. Aqui apresentamos uma caracterização de um extrato surfactante de pulmão porcino de grau clínico misturado com os antibióticos Levofloxacina e Claritromicina, usando uma abordagem multi-técnica – em conjunto com a metodologia de monocamadas de Langmuir– consistindo de isotermas de pressão de superfície-area, microscopia de ângulo de Brewster (BAM), espectroscopia de reflexão-absorção do infravermelho com modulação da polarização (PM-IRRAS), reflectometria de nêutrons (NR), ensaios in vitro e simulações de dinâmica molecular. Avaliou-se o efeito de ambos os antibióticos na estrutura das monocamadas de surfactantes de origem porcino bem como em monocamadas de DPPC. Foi revelado que a estabilidade / integridade das monocamadas é preservada na presença de ambas as drogas. Os sistemas mistos de antibiótico / surfactante pulmonar aumentam a atividade antibacteriana contra bactérias Gram-positivas (Bacillus cereus) e Gram-negativas (Escherichia coli). Essas descobertas fornecem novas percepções sobre a otimização de sistemas eficientes de administração de medicamentos para o tratamento de condições patológicas no nível respiratório.
The lipo-proteic surfactant system acting at the alveolar interface is of vital importance for keeping functional the respiratory mechanics. Its impairments are associated with several pulmonary infections. Drug delivery systems based on animal-derived lung surfactants are complex making it difficult to understand the individual role of guest molecules in membrane interactions. Here we present a characterization of a clinical-grade porcine lung surfactant extract mixed with the antibiotics Levofloxacin and Clarithromycin, using a multi-technique approach –in conjunction with the Langmuir-monolayer methodology– consisting of surface pressure-area isotherms, Brewster angle microscopy (BAM), polarization modulation-infrared reflection-adsorption spectroscopy (PM-IRRAS), neutron reflectometry (NR), in vitro assays, and molecular dynamics simulations. The effect of both antibiotics in the structure of porcine lung surfactant monolayers as well as in DPPC monolayers was examined. It was revealed that the stability/integrity of the monolayers is preserved in the presence of both drugs. The mixed antibiotic/lung surfactant systems enhance the antibacterial activity against Gram-positive (Bacillus cereus) and Gram-negative (Escherichia coli) bacteria. These findings provide new insights into the optimization of efficient drug delivery systems for the treatment of pathological conditions at the respiratory level.
39
Haelssig, Jan B. "Improving the Energy Efficiency of Ethanol Separation through Process Synthesis and Simulation." Thèse, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/20100.
Анотація:
Worldwide demand for energy is increasing rapidly, partly driven by dramatic economic growth in developing countries. This growth has sparked concerns over the finite availability of fossil fuels and the impact of their combustion on climate change. Consequently, many recent research efforts have been devoted to the development of renewable fuels and sustainable energy systems. Interest in liquid biofuels, such as ethanol, has been particularly high because these fuels fit into the conventional infrastructure for the transportation sector.
Ethanol is a renewable fuel produced through the anaerobic fermentation of sugars obtained from biomass. However, the relatively high energy demand of its production process is a major factor limiting the usefulness of ethanol as a fuel. Due to the dilute nature of the fermentation product stream and the presence of the ethanol-water azeotrope, the separation processes currently used to recover anhydrous ethanol are particularly inefficient. In fact, the ethanol separation processes account for a large fraction of the total process energy demand.
In the conventional ethanol separation process, ethanol is recovered using several distillation steps combined with a dehydration process. In this dissertation, a new hybrid pervaporation-distillation system, named Membrane Dephlegmation, was proposed and investigated for use in ethanol recovery. In this process, countercurrent vapour-liquid contacting is carried out on the surface of a pervaporation membrane, leading to a combination of distillation and pervaporation effects. It was intended that this new process would lead to improved economics and energy efficiency for the entire ethanol production process.
The Membrane Dephlegmation process was investigated using both numerical and experimental techniques. Multiphase Computational Fluid Dynamics (CFD) was used to study vapour-liquid contacting behaviour in narrow channels and to estimate heat and mass transfer rates. Results from the CFD studies were incorporated into a simplified design model and the Membrane Dephlegmation process was studied numerically. The results indicated that the Membrane Dephlegmation process was more efficient than simple distillation and that the ethanol-water azeotrope could be broken. Subsequently, a pilot-scale experimental system was constructed using commercially available, hydrophilic NaA zeolite membranes. Results obtained from the experimental system confirmed the accuracy of the simulations.
40
Bories, Florent. "Interaction entre inclusions transmembranaires transmise par la membrane cellulaire." Sorbonne Paris Cité, 2015. http://www.theses.fr/2015USPCC224.
Анотація:
L'objet de cette thèse est d'étudier les interactions entre inclusions transmembranaires imposant un excès d'épaisseur en utilisant un modèle élastique décrivant les membranes au niveau de leur épaisseur. Dans un premier temps, je montre que ce modèle généralise bien les précédents en prenant en compte toutes les constantes physiques possibles. J'ajoute ensuite une condition d'ancrage au bord de l'inclusion qui peut induire ou non une pente préférentielle. Je m'assure que les résultats trouvés dans le cadre de mon modèle rejoignent le précédent pour une seule inclusion dans deux cas limites. Dans un deuxième temps, je développe une méthode de calcul multipolaire me permettant d'envisager des calculs de la forme d'une membrane où plusieurs inclusions sont présentes. Je donne les solutions générales de ce modèle et donne une manière de déterminer la solution dans le cas où deux inclusions sont présentes dans une membrane de taille infinie. Enfin, je donne pour une bicouche lipidique typique certaines courbes de profil et d'énergie d'interaction attendues. Je compare mes résultats à des expériences de Constantin à l'aide d'un algorithme de traitement reposant sur l'équation d'Ornstein-Zernike et une relation de fermeture. Le premier système "C12E5 + gramicidine", dont la membrane est constituée de surfactants, me permet de faire concorder le modèle théorique avec les expériences et je donne ainsi pour celui-ci les premières mesures de paramètres physiques nouveaux. Le deuxième système "DLPC + gramicidine" donne un moins bon accord entre la théorie et les expériences mais je donne une nouvelle piste de traitement afin de donner des estimations pour ce systèmeThe present thesis is a study of interactions between transmembrane proteins inducing a hydrophobic mismatch with an elastic model describing the membranes at the scale of their thickness. I begin by showing that this model generalizes the precedent ones found in litterature by taking in account every possible physical constants. I add also an anchoring term at the edge of the inclusion that can induce a preferential slope. I verify that the results found with this addition is what was found previously with one inclusion in a membrane in two différent cases. Next, I develop a multipolar computation method that allows me to compute the shape of a membrane where several inclusions are presents. I give the general solutions of this model and gives an algorithm in the case where two inclusions are present in an infinite membrane. Then, I give the expected profile and the interaction energies for a typical lipidic bilayer. I compare my results to experiments performed by Constantin with an algorithm using Omstein-Zernike equation and closure relations. The first system "C12E5 + gramicidin", where the membrane is made of surfactant, gives good agreement between the theory and the experiments and allows me to give a first measurement for new physical parameters. The second system "DLPC + gramicidin" does not allow such an agreement between the theory and the experiments but I give a new lead which may give a measurement for this system
41
Sitte, Astrid [Verfasser], Kai [Akademischer Betreuer] Tittmann, and Ulf [Akademischer Betreuer] Diederichsen. "Catalysis at the Interface- Elucidation of the Activation Process and Coupling of Catalysis and Compartmentalization of the Peripheral Membrane Protein Pyruvate Oxidase from Escherichia coli / Astrid Sitte. Gutachter: Kai Tittmann ; Ulf Diederichsen. Betreuer: Kai Tittmann." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2014. http://d-nb.info/1047237008/34.
42
Zhao, Hang. "Synthetic membranes in microfluidic interfaces." Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8632/.
Анотація:
This thesis explores the development of microfluidic technology for generating and manipulating micro-sized vesicles with the incorporation of specific membrane proteins as artificial cellular systems to mimic natural existing cells. Synthetic biology (SynBio) is an emerging area of research concerned with the application of engineering methods to the creation of new biological processes and constructs. Understanding the working principle of living cellular system is one of significant issue for scientists working in this field. Cells are known as the basic unit of life: creating model synthetic analogues offers opportunities for us to deepen our insights of complex interaction and to understand features and functions of the living cells. Microfluidic technologies have provided the capabilities of compartmentalisation, monodispersity and high-throughput generation for engineering architectures resembling cell-like structures. In vitro transcription and translation (IVTT) enables the expression of specific proteins of interest within synthetic cells via encapsulation of cell-free protein expression solution has demonstrated artificial cells with the capability of containing the process of central dogma of molecular biology. The thesis investigates the building of synthetic cell-like constructs by microfluidics. The first area of investigation focusses on the fabrication of lipid/polymer vesicles transformed from ultra-thin shell double emulsions, which were prepared using microfluidics. To bring the biological function into both vesicle-based synthetic chassis, a fluorescent protein and a pore-forming membrane protein were in vitro expressed in the artificial cell chassis. The second area of study centres on the viscosity analysis of artificial cell membranes using a combination of molecular rotors and the fluorescence lifetime imaging microscopy. The membrane viscosity plays a crucial role in membrane proteins insertion that influences the cell function regulation through functional biomembranes. The alteration of lifetime of the molecular rotors trapped in the artificial membranes reports the viscosity changes in the membrane environment induced by the dewetting process. Comparisons of viscosity values over time between lipid vesicle templated by thin-shell double emulsions with GUVs produced by an oil-free method (electroformation) offers the ability of measuring the amount of oil phase (organic solvent mixture) in artificial cell membranes. In the final chapter, the research detailed the construction of lipid bilayers with asymmetric arrangement used as more complex artificial cell models compared with most of synthetic cells with symmetric composition in their bilayers. A vesicle with hybrid asymmetric bilayer is also fabricated in same microfluidic fashion where phospholipid deposits on the inner-leaflet and block copolymer coats the outer monolayer. Taken together, the work presented in this thesis shows the potential to exploit the microfluidic construction of a functioning synthetic cell from individual molecular components, which could advance new application areas in biotechnology and health. Further developments in this research will aim to develop microfluidic technologies for: (i) physically investigating cell division process using lipid vesicles as cell models; and (ii) producing complex multicompartmental systems for the use of mimicking natural cells. The asymmetric bilayers will be studied for their influences on the integration of transmembrane proteins.
43
Mulligan, J. L. "Studies of membrane transport and liquid interfaces." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47196.
44
Mosadegh, Sedghi Sanaz. "Fabrication and characterization of new and highly hydrophobic hollow fiber membranes for CO₂ capture in membrane contactors." Doctoral thesis, Université Laval, 2013. http://hdl.handle.net/20.500.11794/24658.
Анотація:
Dans ce projet de doctorat, des membranes microporeuses (fibres creuses) et hautement hydrophobes à base de polyéthylène basse densité (LDPE) pour utilisation dans la capture du CO2 dans des contacteurs gaz-liquide à membrane (GLMC), ont été fabriquées en utilisant une nouvelle méthode simple, sans solvant ou diluants, autant écologique qu’économique, et qui ne nécessite aucun post-traitement mécanique ou thermique. Pour produire des fibres creuses et contrôler leur porosité, on combine deux techniques, l’extrusion et le lavage de sel. Un mélange de LDPE et de particules de NaCl de différentes concentrations en sel conduit à la production des fibres (par extrusion) qui sont ensuite immergées dans l’eau pour éliminer le sel emprisonné dans le polymère et obtenir autant une structure microporeuse qu’une surface rugueuse hautement hydrophobe. La nouvelle méthode constitue une alternative très prometteuse aux méthodes actuellement utilisées pour la fabrication des membranes hydrophobes, principalement basées sur un processus d'inversion de phase qui implique des solvants toxiques et coûteux. Les membranes fabriquées ont été caractérisées en termes de morphologie, densité, porosité et distribution de taille des pores, hydrophobicité, pression de percée et propriétés mécaniques. Comme le phénomène de mouillage des membranes en contact avec les solutions absorbantes est la cause principale de la réduction de l’efficacité des GLMC à long terme, une étude approfondie sur la compatibilité membrane/liquide absorbant a été réalisée. La stabilité morphologique, chimique et thermique des membranes en contact avec différentes solutions aqueuses d'alcanolamines à base de monoéthanolamine (MEA) et 2-amino-2-hydroxyméthyl-1,3-propanediol (AHPD), ainsi que des mélanges MEA/PZ (pipérazine) et AHPD/PZ, a été investiguée en détail.In this work, highly hydrophobic low density polyethylene (LDPE) hollow fiber membranes aiming to be used for CO2 capture in gas-liquid membrane contactors (GLMC) were fabricated using a simple, novel method, without solvent or diluents, economic and environmentally friendly, which does not require any mechanical or thermal post-treatments. In order to produce hollow fibers and control their porosity, the process combines melt extrusion and template-leaching techniques. A mixture of LDPE and NaCl particles first produce blends with different salt contents. A microporous structure and a rough highly hydrophobic surface can then be produced by leaching the salt particles from the hollow fiber matrix via immersion in water. The new method represents a very promising alternative to conventional membrane fabrication approaches which are mainly based on phase inversion process that involves toxic and expensive solvents. The fabricated membranes were characterized in terms of morphology, density, porosity and pore size distribution, hydrophobicity, breakthrough pressure and mechanical properties. Since the phenomenon of membrane wetting by liquid absorbents is the major cause of the reduction of long-term efficiency of GLMC, a comprehensive study on the compatibility between membrane and absorbent liquid was performed. Morphological, chemical and thermal stability of LDPE membranes in contact with different aqueous alkanolamine solutions including monoethanolamine (MEA) and 2-amino-2-hydroxymethyl-1,3-propanediol (AHPD), as well as blends of MEA/PZ (piperazine) and AHPD/PZ, was investigated in detail.
45
Velicky, Matej. "Transfer of small molecules across membrane-mimetic interfaces." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/transfer-of-small-molecules-across-membranemimetic-interfaces(a6abfe3c-9e0f-4fc6-bd6b-d2f8ec017c4e).html.
Анотація:
The presented thesis investigates the transfer of drug molecules across interfaces that mimic biological membrane barriers. The permeability of drug molecules across biological membrane mimics has been investigated in a novel artificial membrane permeation assay configuration using an in situ time-dependent approach and reproducible rotation of the membrane. A method to determine the membrane permeability from the knowledge of measured permeability and the applied stirring rate is presented. The initial transient of the permeation response, previously not observed in situ, is investigated and its importance in data evaluation is discussed. The permeability coefficients of 31 drugs are optimised for the conditions found in vivo and a correlation with the fraction absorbed in humans is presented. The evidence for ionic and/or ion-pair flux across the artificial membrane obtained from measurement of permeability at different pH is supported by the investigation of the permeation assay with external membrane polarisation. The permeability coefficient of the solute's anionic form is determined. Liquid/liquid electrochemistry has been used to study the transfer of ionized species across the interface between water and 1,2-dichloroethane. An alternative method to study the transfer of partially ionised drug molecules employing a rotating liquid/liquid interface is presented. In addition, a bipolar electrochemical cell with a rotating-disc electrode is developed and its properties investigated in order to verify the hydrodynamics of the rotating artificial membrane configuration. Finally, in support of the electrochemical techniques used is this thesis, a detailed preparation and evaluation of the silver/silver sulphate reference electrode is presented.
46
Pascutti, Pedro Geraldo. "Dinâmica Molecular de Peptídeos na Interface Membrana-Água." Universidade de São Paulo, 1996. http://www.teses.usp.br/teses/disponiveis/43/43133/tde-09122013-161044/.
Анотація:
Um programa computacional foi desenvolvido para otimização de geometria e simulação de dinâmica molecular baseado em um campo de forças clássicas parametrizado. O solvente foi considerado como um contínuo eletrostático e a interface entre o meio aquoso e o interior de uma membrana biológica como uma superfície de descontinuidade dielétrica, tratada pelo \"método das imagens eletrostáticas\". Nesse método, o campo de polarização produzido na superfície de descontinuidade por uma carga pontual é representado por uma carga fictícia, colocada na fase oposta, cuja distância e sinal é definida pelas condições de contorno na superfície. Diversos sistemas foram estudados, tanto em solventes contínuos como na presença de superfícies de descontinuidade: a) Foram estudadas as distribuições populacionais dos rotâmeros do triptofano na forma zwitteriônica e no peptídeo Ala-Trp- Ala, em solvente polar e apolar. Foi demonstrado que a dinâmica do triptofano e as populações de rotâmeros são compatíveis com as observações experimentais de fluorescência resolvida no tempo e NMR; b) Em um estudo das conformações em polialanina, verificou-se que a estabilidade da estrutura secundária hélice- é um efeito cooperativo entre pontes de hidrogênio em solvente de baixa constante dielétrica. Na presença da interface água-membrana, a hélice- anfifílica de um modelo para a -endorfina estabiliza-se sobre a interface. Um comportamento anfifílico foi também observado na seqüência sinal para o receptor- da e. coli, a qual estabilizou-se perpendicularmente à interface, na conformação parcial hélice- proposta na literatura; c) Em um estudo sobre o hormônio -MSH observou-se que, em solvente polar, de uma conformação helicoidal ele passa para uma conformação estendida. Porém, ao atravessar para o interior hidrofóbico de uma membrana, o peptídeo estabiliza-se em dobra-. Observou-se ainda que a estabilidade dessa conformação no interior da membrana é reforçada por pontes salinas entre os resíduos carregados do peptídeo, os quais formam um \"caroço\" hidrofílico circundado por resíduos hidrofóbicos. Esse arranjo estrutural está em concordância com o proposto para a conformação biologicamente ativa. De um modo geral, o modelo para biomembrana proposto no presente trabalho reproduziu o comportamento hidrofóbico, hidrofílico ou anfifílico dos peptídeos estudados.A software was developed for optimisation of geometry and molecular dynamics simulation, based on a parameterized classical force field. Solvent was assumed as an electrostatic continuum. The interface between the aqueous medium and the hydrophobic core of biological membranes was described by a surface of dielectric discontinuity, treated by the \"method of images\". In this method, the polarization field produced at the surface of discontinuity by a point charge was represented by a fictitious charge, placed in the opposite phase. The position and signal of this charge-image were defined by boundary conditions at the surface. Several systems were studied, either in continuous solvent, as in the presence of discontinuity surfaces: a) the population distribution of tryptophan rotamers was studied in the zwytterion and in the peptide Ala-Trp-Ala, in polar and apolar solvents; the results for the tryptophan dynamics and the rotamers populations agree with experimental observations using time resolved fluorescence and NMR spectroscopies. b) analysis of polyalanin conformations showed that the stabililty of the -helix is a cooperative effect between hydrogen bonds in low dielectric constant solvent; in the presence of the water-membrane interface, the amphyphilic -helix of a -endorphin model stabilizes on the interface; a similar behavior was observed in the signal sequence for the E. Coli -receptor, that stabilized perpendicular to the interface in a partial -helix conformation, as proposed in the literature. c) calculations on melanotropic hormone a.-MSH showed that in polar solvent it goes from helycoidal conformation to an extended one; in the presence of the interface water-membrane, the peptide goes into the interior of the membrane and stabilizes in a -turn; the stability ofthis conformation was reinforced by salt bridges between charged residues, forming a hydrophilic core surrounded by hydrophobic residues; this structural arrangement agrees with the one proposed for the biologically active conformation of the hormone. In general terms, the model proposed here for the biomembrane was able to mimic the hydrophobic, hydrophihlic or amphyphilic behavior of the peptides studied.
47
Norman, Robert Ellis. "Statistical mechanics of vesicles, membranes and interfaces." Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358818.
48
Lindström, Fredrick. "Biological membrane interfaces involved in diseases : a biophysical study." Doctoral thesis, Umeå universitet, Kemi, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-806.
Анотація:
Interactions between peptides and biological lipid membranes play a crucial role in many cellular processes such as in the mechanism behind Alzheimer’s disease where amyloid-beta peptide (Abeta)is thought to be a key component. The initial step of binding between a surface active peptide and its target membrane or membrane receptor can involve a non specific electrostatic association where positively charged amino acid residues and a negatively charged membrane surface interact. Here, the use of high resolution MAS NMR provides a highly sensitive and non perturbing way of studying the electrostatic potential present at lipid membrane surfaces and the changes resulting from the association of peptides. The interaction between pharmacologically relevant peptides and lipid membranes can also involve incorporation of the peptide into the membrane core and by complementing the NMR approach with differential scanning calorimetry (DSC) the hydrophobic incorporation can be studied in a non invasive way. By using 14N MAS NMR on biological lipid systems for the first time, in addition to 31P, 2H NMR and differential scanning calorimetry (DSC), gives a full picture of the changes all along the phospholipid following interactions at the membrane interface region. Being able to monitor the full length of the phospholipid enables us to differentiate between interactions related to either membrane surface association or hydrophobic core incorporation. This approach was used to establish that the interaction between nociceptin and negatively charged lipid membranes is electrostatic and hence that nociceptin can initially associate with a membrane surface before binding to its receptor. Also, it was found that Abeta can interact with phospholipid membranes via two types of interactions with fundamentally adverse effects. The results reveal that Abeta can associate with the surface of a neuronal membrane promoting accelerated aggregation of the peptide leading to neuronal apoptotic cell death. Furthermore it is also shown that Abeta can anchor itself into the membrane and suppress the neurotoxic aggregation of Abeta.
49
Lindström, Fredrick. "Biological membrane interfaces involved in diseases : a biophysical study /." Umeå : Universitetet, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-806.
50
Ngo, Thi Hong Giang. "Interfaces bleu de Prusse, bicouches lipidiques : vers un nouveau vecteur biomimétique." Thesis, Montpellier, 2020. http://www.biu-montpellier.fr/florabium/jsp/nnt.jsp?nnt=2020MONTT011.
Анотація:
L'objectif de cette étude était de démontrer la faisabilité d’une préparation de vecteurs hybrides biomimétiques, combinant des liposomes avec une couche externe de Bleu de Prusse pour des applications théranostiques. Les liposomes permettraient l’encapsulation de substances actives, quand la couche de Bleu de Prusse assurerait une activité photothermique et un rôle d’agent contrastant. Le dépôt de Bleu de Prusse a d’abord été optimisé sur une surface plane d’or fonctionnalisée par des amines, en y déposant dans un premier temps des nanoparticules d’Analogue de Bleu de Prusse préformées. Puis une nouvelle méthode de préparation du Bleu de Prusse a été développée, par addition simultanée de précurseurs, conduisant à la croissance de nanostructures directement sur le modèle planaire. Ce modèle a ensuite été amélioré en y déposant une bicouche lipidique. Cela rendit possible la croissance de structures de Bleu de Prusse sur une bicouche lipidique plane, toujours en utilisant notre méthode rapide d’addition simultanée. Puis l’influence de la composition de la bicouche lipidique a été étudiée, de même que le temps d’interaction entre les précurseurs de Bleu de Prusse et les lipides. Finalement, il fut démontré que le dépôt de nanostructures de Bleu de Prusse pouvait être réalisé sur un modèle sphérique de bicouche lipidique, ouvrant la voie au recouvrement de liposomes chargés d’actifs par du Bleu de PrusseIn this study, we aimed to show the feasibility of the preparation of biomimetic hybrid vectors combining liposomes with a Prussian blue coating for theranostic application. The liposomes would allow us to encapsulate drugs, while the Prussian blue outer layer would provide photothermal and contrasting features to the vector. The Prussian blue deposition has first been optimized on a simple amino-gold flat surface, on which we deposited Prussian blue Analog preformed particles. Then, a new method of Prussian blue preparation has been developed, by simultaneous addition of Prussian blue precursors, to grow nanostructures directly on the flat surface model. This model was then improved by depositing a supported lipid bilayer on top of it. It made possible the growth of Prussian blue structures on a flat lipid bilayer, still by our rapid method of simultaneous addition. Then, the influence of the lipid bilayer composition was studied, as well as the interaction time between the Prussian blue precursors and the lipids. Finally, it has been showed that the deposition of Prussian blue nanostructures could also be performed on a spherical model of supported lipid bilayer, paving the way to the coating of liposomes encapsulating drugs