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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Electrostatics of the Binding and Bending of Lipid Bilayers: Charge-Correlation Forces and Preferred Curvatures

Li, Yang January 2004 (has links)
Lipid bilayers are key components of biomembranes; they are self-assembled two-dimensional structures, primarily serving as barriers to the leakage of cell's contents. Lipid bilayers are typically charged in aqueous solution and may electrostatically interact with each other and with their environment. In this work, we investigate electrostatics of charged lipid bilayers with the main focus on the binding and bending of the bilayers. We first present a theoretical approach to charge-correlation attractions between like-charged lipid bilayers with neutralizing counterions assumed to be localized to the bilayer surface. In particular, we study the effect of nonzero ionic sizes on the attraction by treating the bilayer charges (both backbone charges and localized counterions) as forming a two-dimensional ionic fluid of hard spheres of the same diameter <i>D</i>. Using a two-dimensional Debye-H??ckel approach to this system, we examine how ion sizes influence the attraction. We find that the attraction gets stronger as surface charge densities or counterion valency increase, consistent with long-standing observations. Our results also indicate non-trivial dependence of the attraction on separations <i>h</i>: The attraction is enhanced by ion sizes for <i>h</i> ranges of physical interest, while it crosses over to the known <i>D</i>-independent universal behavior as <i>h</i> &rarr; &infin;; it remains finite as <i>h</i> &rarr; 0, as expected for a system of finite-sized ions. We also study the preferred curvature of an asymmetrically charged bilayer, in which the inner leaflet is negatively charged, while the outer one is neutral. In particular, we calculate the relaxed area difference &Delta; <i>A</i><sub>0</sub> and the spontaneous curvature <i>C</i><sub>0</sub> of the bilayer. We find &Delta; <i>A</i><sub>0</sub> and <i>C</i><sub>0</sub> are determined by the balance of a few distinct contributions: net charge repulsions, charge correlations, and the entropy associated with counterion release from the bilayer. The entropic effect is dominant for weakly charged surfaces in the presence of monovalent counterions only and tends to expand the inner leaflet, leading to negative &Delta; <i>A</i><sub>0</sub> and <i>C</i><sub>0</sub>. In the presence of even a small concentration of divalent counterions, however, charge correlations counterbalance the entropic effect and shrink the inner leaflet, leading to positive &Delta; <i>A</i><sub>0</sub> and <i>C</i><sub>0</sub>. We outline biological implications of our results.
2

Electrostatics of the Binding and Bending of Lipid Bilayers: Charge-Correlation Forces and Preferred Curvatures

Li, Yang January 2004 (has links)
Lipid bilayers are key components of biomembranes; they are self-assembled two-dimensional structures, primarily serving as barriers to the leakage of cell's contents. Lipid bilayers are typically charged in aqueous solution and may electrostatically interact with each other and with their environment. In this work, we investigate electrostatics of charged lipid bilayers with the main focus on the binding and bending of the bilayers. We first present a theoretical approach to charge-correlation attractions between like-charged lipid bilayers with neutralizing counterions assumed to be localized to the bilayer surface. In particular, we study the effect of nonzero ionic sizes on the attraction by treating the bilayer charges (both backbone charges and localized counterions) as forming a two-dimensional ionic fluid of hard spheres of the same diameter <i>D</i>. Using a two-dimensional Debye-Hückel approach to this system, we examine how ion sizes influence the attraction. We find that the attraction gets stronger as surface charge densities or counterion valency increase, consistent with long-standing observations. Our results also indicate non-trivial dependence of the attraction on separations <i>h</i>: The attraction is enhanced by ion sizes for <i>h</i> ranges of physical interest, while it crosses over to the known <i>D</i>-independent universal behavior as <i>h</i> &rarr; &infin;; it remains finite as <i>h</i> &rarr; 0, as expected for a system of finite-sized ions. We also study the preferred curvature of an asymmetrically charged bilayer, in which the inner leaflet is negatively charged, while the outer one is neutral. In particular, we calculate the relaxed area difference &Delta; <i>A</i><sub>0</sub> and the spontaneous curvature <i>C</i><sub>0</sub> of the bilayer. We find &Delta; <i>A</i><sub>0</sub> and <i>C</i><sub>0</sub> are determined by the balance of a few distinct contributions: net charge repulsions, charge correlations, and the entropy associated with counterion release from the bilayer. The entropic effect is dominant for weakly charged surfaces in the presence of monovalent counterions only and tends to expand the inner leaflet, leading to negative &Delta; <i>A</i><sub>0</sub> and <i>C</i><sub>0</sub>. In the presence of even a small concentration of divalent counterions, however, charge correlations counterbalance the entropic effect and shrink the inner leaflet, leading to positive &Delta; <i>A</i><sub>0</sub> and <i>C</i><sub>0</sub>. We outline biological implications of our results.
3

Estudo por simulação computacional em larga escala da complexação de proteínas do leite / Computational simulation study in large scale of milk proteins complexation

Delboni, Lariani Aparecida 24 January 2017 (has links)
A estrutura e o comportamento de proteínas são de grande interesse a uma infinidade de áreas de conhecimento, com especial destaque para alimentação e saúde. As proteínas compõem uma fundamental classe de moléculas biológicas, com capacidade para interagir com diversas outras estruturas e formar complexos. Dois tópicos principais são abordados neste trabalho: (a) avaliação da formação de complexos entre três proteínas do soro do leite (-lactoalbumina, -lactoglobulina e lactoferrina) em diferentes condições experimentais de força iônica e pH da solução através de derivadas da energia livre e (b) avaliação de aspectos relacionados com a fundamentação teórica dos modelos moleculares com granularidade grossa e uso do dielétrico contínuo empregados para estudo do fenômeno da complexação molecular, através da análise, em larga escala, da correlação de cargas em proteínas disponíveis no banco de dados de proteínas. Os estudos teóricos de complexação foram realizados através do emprego de simulações Monte Carlo Metropolis, com o modelo do solvente contínuo, constante dielétrica homogênea e sal implicitamente descrito. Os estudos de complexação permitem compreender os mecanismos moleculares envolvidos, elucidando, inclusive, controvérsias experimentais e oferecendo orientação para aplicações. Já os resultados do estudo de correlação de cargas em estruturas experimentais de proteínas permitem justificar as aproximações do modelo. / The structure and behavior of proteins are of great interest for a number of science fields, with special emphasis to food industry and health. Proteins comprise a fundamental group of biological molecules, with the capacity of interacting with several other structures and creating complexes. Two major topics are covered in this study: (a) evaluation of complex formation among three whey proteins (-lactalbumin, -lactoglobulin and lactoferrin) under different experimental conditions of ionic strength and pH of solution through free energy derivatives and (b) evaluation of features related to the theoretical basis of the coarse-grained molecular models and the use of continuous dielectric which are employed to investigate the molecular complexation phenomenon, through analysis, on a large scale, of charge correlation in proteins available in the protein data bank. The theoretical studies of complexation were performed through the use of Monte Carlo Metropolis simulations, with continuous solvent model, homogeneous dielectric constant and salt implicitly described. The complexation studies allow to understand the molecular mechanisms involved, also elucidating experimental controversies and offering orientation to applications; whereas the results of the charge correlation study in experimental structure of proteins allow justify the approximations of the model.
4

Estudo por simulação computacional em larga escala da complexação de proteínas do leite / Computational simulation study in large scale of milk proteins complexation

Lariani Aparecida Delboni 24 January 2017 (has links)
A estrutura e o comportamento de proteínas são de grande interesse a uma infinidade de áreas de conhecimento, com especial destaque para alimentação e saúde. As proteínas compõem uma fundamental classe de moléculas biológicas, com capacidade para interagir com diversas outras estruturas e formar complexos. Dois tópicos principais são abordados neste trabalho: (a) avaliação da formação de complexos entre três proteínas do soro do leite (-lactoalbumina, -lactoglobulina e lactoferrina) em diferentes condições experimentais de força iônica e pH da solução através de derivadas da energia livre e (b) avaliação de aspectos relacionados com a fundamentação teórica dos modelos moleculares com granularidade grossa e uso do dielétrico contínuo empregados para estudo do fenômeno da complexação molecular, através da análise, em larga escala, da correlação de cargas em proteínas disponíveis no banco de dados de proteínas. Os estudos teóricos de complexação foram realizados através do emprego de simulações Monte Carlo Metropolis, com o modelo do solvente contínuo, constante dielétrica homogênea e sal implicitamente descrito. Os estudos de complexação permitem compreender os mecanismos moleculares envolvidos, elucidando, inclusive, controvérsias experimentais e oferecendo orientação para aplicações. Já os resultados do estudo de correlação de cargas em estruturas experimentais de proteínas permitem justificar as aproximações do modelo. / The structure and behavior of proteins are of great interest for a number of science fields, with special emphasis to food industry and health. Proteins comprise a fundamental group of biological molecules, with the capacity of interacting with several other structures and creating complexes. Two major topics are covered in this study: (a) evaluation of complex formation among three whey proteins (-lactalbumin, -lactoglobulin and lactoferrin) under different experimental conditions of ionic strength and pH of solution through free energy derivatives and (b) evaluation of features related to the theoretical basis of the coarse-grained molecular models and the use of continuous dielectric which are employed to investigate the molecular complexation phenomenon, through analysis, on a large scale, of charge correlation in proteins available in the protein data bank. The theoretical studies of complexation were performed through the use of Monte Carlo Metropolis simulations, with continuous solvent model, homogeneous dielectric constant and salt implicitly described. The complexation studies allow to understand the molecular mechanisms involved, also elucidating experimental controversies and offering orientation to applications; whereas the results of the charge correlation study in experimental structure of proteins allow justify the approximations of the model.

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