3.10 Tesis magíster

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Asirunaka: Generador de Potencia Pulsada de Doble Pulso Dedicado a Plasmas de Explosión de Alambres y Formación de Nanopartículas
(2017) Masoliver Aguirre, Pavel; Bhuyan, Heman; Pontificia Universidad Católica de Chile. Facultad de Física
Caracterización de propiedades clásicas y cuánticas de pulsos de femtosegundos
(2017) Rojas Aedo, Ricardo; Seifert, Birger; Pontificia Universidad Católica de Chile. Facultad de Física
Este informe de tesis versa sobre propuestas hacia la caracterización de las propiedades clásicas y cuánticas de pulsos de femtosegundos, que en principio pueden ser expandidas a pocos pico segundosy a atto segundos, al menos en su sentido conceptual. El texto principalmente analizará en detalle el método de caracterización de propiedades clásicas de pulsos, basado en la mezcla no lineal de diferentes trenes pulsados, llamado FROG, reinterpretando el campo mezcla, desde una perspectiva clásica, donde se desarrolla una nueva técnica de caracterización analítica y no interferométrica llamada “VAMPIRE analítico” , y otra perspectiva cuántica, donde surge una propuesta para el análisis de las propiedades cuánticas internas de pulsos haciendo uso de esquemas tipo FROG . Por completitud en la última línea, además se comentará como generar estados cuánticos interesantes (no-coherentes), y los resultados obtenidos experimentalmente en el laboratorio, con pulsos de femtosegundos utilizando fibras ópticas.
Caracterización eléctrica de juntura de arreglos nanotubos de carbono de baja cristalinidad con silicio dopado tipo N
(2022) Cerda Villaseca, Daniel Andrés; Hevia, Samuel; Pontificia Universidad Católica de Chile. Facultad de Física
En este trabajo se estudian las propiedades de transporte eléctrico de un set de 3 dispositivos basados en arreglos altamente ordenados de nanotubos de carbono de baja cristalinidad (LC-CNTs) crecidos directamente sobre un sustrato de silicio dopado tipo N, mediante la utilización de alúmina nanoporosa como molde. Los nanotubos de carbono (CNTs) fueron sintetizados mediante depósito químico en fase vapor (CVD) dentro de los poros de las membranas de alúmina. Estas membranas, que cumplen el rol de molde y de otorgar estabilidad al sistema se fabricaron mediante la anodización controlada de una película de aluminio depositada directamente sobre el sustrato de Si. Dado que este método de fabricación permite un alto grado de control en las dimensiones de los LC-CNTs (largo, diámetro externo y espesor de pared), se definió realizar un estudio en función del espesor de pared del nanotubo, ya que es en esta variable en la que el transporte eléctronico presenta una fuerte dependencia. Se fabricaron tres dispositivos conteniendo LC-CNTs con espesores de pared promedio de 0.4, 0.7 y 1.1 nm. Para llevar a cabo el estudio, se depositó un contacto de oro en la parte superior de los LC-CNTs, con la finalidad de tener un contacto eléctrico apropiado. Luego, se midió la curva de corriente eléctrica en función del voltaje aplicado a diferentes temperaturas, en el rango de 20 a 300 K y en condiciones de alto vacío y oscuridad. De acuerdo a lo observado en las mediciones, los dispositivos mostraron un comportamiento tipo rectificador, lo cual se atribuye principalmente a la existencia de una juntura tipo Schottky entre los LC-CNTs y el silicio. Los LC-CNTs no han sido estudiados exhaustivamente, a diferencia de los CNTs de pared simple o múltiple, por lo que uno de los objetivos de este trabajo es estudiar el comportamiento eléctrico de los LC-CNTs en este tipo de junturas. Una juntura tipo Schottky es un caso particular de una juntura entre un metal y un semiconductor, en la cual la corriente a través de esta es modelada usualmente mediante el modelo de emisión termoiónica, pero también se deben tener en cuenta el modelo de recombinación en la región espacial de carga y el mecanismo de tunneling. En este trabajo se utilizó el modelo de emisión termoiónica y adicionalmente se llevo a cabo un modelo circuital para ajustar teóricamente los datos experimentales. Si bien se observó un comportamiento rectificador en las mediciones, este no era puro, ya que para los regímenes de polarización directa e inversa el comportamiento de la curva de corriente versus voltaje era lineal. En base a esto, se requería parámetros adicionales al modelo que se justifican con el modelo circuital utilizado. Una vez agregados dichos parámetros, los resultados obtenidos reflejaron que los tres dispositivos ajustan al modelo de emisión termoiónica en un rango determinado de temperatura. Los parámetros del modelo permitieron estudiar los dispositivos en un amplio rango de temperatura y permitieron obtener información sustancial de los LC-CNTs. Al saber de un trabajo previo que el contacto entre el oro y los LC-CNTs es óhmico, se logró determinar que adicionalmente el contacto entre el silicio y los LC-CNTs también lo es. Adicionalmente se logró estudiar la conductividad de los LC-CNTs en función de la temperatura, en donde el dispositivo con menor espesor de pared ajustó con el transporte eléctrico por Hopping de rango variable, mientras que los de mayor espesor de pared no. Debido a lo anterior y tomando en cuenta un trabajo previo realizado en el laboratorio, se propuso la existencia de un mecanismo en paralelo que justificara el transporte eléctrico de los dispositivos de mayor espesor de pared. Dicho mecanismo estuvo dado por la teoría de Bloch-Grüneisen, en donde se logró determinar que el transporte eléctrico de dichos dispositivos posee una contribución metálica. Finalmente, al analizar los parámetros del modelo se concluyó que a medida que baja la temperatura, el modelo de emisión termoiónica tiende a desaparecer, es decir, que ya no ajusta correctamente a las mediciones. En particular se observa que el voltaje de barrera presente en la juntura entre los LC-CNTs y el silicio disminuye con la temperatura. Entonces, dado que el transporte de electrones mediante emisión termoiónica es un proceso de activación térmica, los electrones a baja temperatura sólo pueden superar barreras energéticas de menor valor. Esto, a través de tunneling o recombinación, ya que la energía que poseen los electrones no les permite estar en la banda de conducción que es donde se lleva a cabo la emisión termoiónica.
Characterization of the ionizing radiation emission of a plasma focus device
(2018) Díaz Contreras, Daniela Alejandra; Caprile Etchart, Paola F.; Moreno Martínez, José; Schwahofer, Andrea; Pontificia Universidad Católica de Chile. Facultad de Física
The PF2kJ plasma focus device was studied as a pulsed source of x-rays neutron radiation. X-rays are emitted during the focalization process of the plasma if the device is operated using hydrogen as the filling gas. Fusion reactions can be obtained if deuterium gas is used, with the consequent emission of fast neutrons. The x-ray emission is characterized by spatial distribution measurements by using TLD100 dosimeters and radiochromic films, the linearity of the output, as well as the effective energy of the x-ray radiation by measuring transmission through different aluminum thicknesses. A low effective energy of 7.5 keV is estimated. The variation of the intensity of the emission in distance and the assessment of the radiation levels which a device operator may be exposed are also included as part of the x-ray emission characterization study. Personal equivalent dose value of 2.8 mSv/year is estimated in a normal regime of the device operation. This level is not harmful based on ICRP recommendations. Fast neutron fluence of the order of 105n/cm2per shot in 4π sr is estimated by means of 3He proportional detector, and preliminary measurements are performed by using pairs of TLD 600 and TLD 700 dosimeters.
Design of microwave antennas for nitrogen-vacancy centers applications
(2018) Ortiz Moreno, Ari Rolando; Maze Ríos, Jerónimo; Gence, Loik; Pontificia Universidad Católica de Chile. Facultad de Física
Nitrogen-vacancy centers in diamond are promising candidates for a wide range of applications due to their quantum sensing capabilities at room temperature and easy optical readout and manipulation by means of confocal microscopy and the application of microwave radiation. Applying microwave radiation is not a trivial task depending on the application. If a single NV center is addressed, then a thin (20 —m diameter) copper wire is sufficient if the NV is within 50 —m from the wire. However in a large area with a lot of NV centers that must be addressed simultaneously with a homogeneous microwave intensity, then a more specialized microwave antenna is required. Towards this goal, a complete procedure for developing microstrip antennas for NV centers applications is presented. In order to drive all NV centers that point along a given direction with the same intensity, an antenna with a uniform intensity over this area is needed, which is not a trivial task. At a given power, there is a compromise between a uniform intensity and high intensity. This procedure includes the antenna design using optical lithography in order to achieve the desired spatial resolution, fabrication and testing using a vector network analyzer and different diamond samples. The fabricated antennas reached a maximum transmission of around 40% near the desired frequency (2.87 GHz), a 100 MHz bandwidth and are capable of resolving electronic spin resonance with a maximum contrast of 22%.
Estudio de fotoconductividad de película delgada de CuFeO2 tipo delafossite mediante mediciones de resistencia eléctrica.
(2019) Vojkovic Lagno, Smiljan Andrej; Cabrera, Alejandro Leopoldo; Pontificia Universidad Católica de Chile. Facultad de Física
El trabajo realizado en esta tesis consiste en el estudio de la dependencia de la resistencia eléctrica en función de la longitud de onda incidente en una película delgada semiconductora de CuFeO2 de 75 nm de espesor obtenida por técnica de deposición por laser pulsado sobre zafiro y con ello, basándose en el efecto fotoconductivo, determinar las brechas semiconductoras del material y así conocer su viabilidad como electrodo para procesos de fotólisis de agua, permitiendo la producción sustentable de hidrógeno gaseoso como fuente de energía. Para ello se mide experimentalmente la resistencia eléctrica de la muestra usando método Van der Pauw, en ambiente de alto vacío, en función de longitud de onda incidente, obtenida con monocromador, en el rango de 450 a 1.080 nanómetros usando lámpara Thorlabs SLS201L. La resistencia en completa oscuridad es de 1,132 MΩ y ante luz de amplio espectro de 1,117 MΩ. El gráfico de cambio en resistencia en función de longitud de onda, corregida según la potencia incidente, muestra cambios de conductividad, asociables a brechas semiconductora, en 1,3 - 1,7 - 1,9 - 2,0 - 2,1 - 2,3 eV y un cambio notorio entre 2,5 - 2,6 eV que coinciden razonablemente con resultados obtenidos previamente mediante gráficos tipo Tauc en base a datos de espectroscopía de transmisión de la muestra y otras referencias.El trabajo realizado en esta tesis consiste en el estudio de la dependencia de la resistencia eléctrica en función de la longitud de onda incidente en una película delgada semiconductora de CuFeO2 de 75 nm de espesor obtenida por técnica de deposición por laser pulsado sobre zafiro y con ello, basándose en el efecto fotoconductivo, determinar las brechas semiconductoras del material y así conocer su viabilidad como electrodo para procesos de fotólisis de agua, permitiendo la producción sustentable de hidrógeno gaseoso como fuente de energía. Para ello se mide experimentalmente la resistencia eléctrica de la muestra usando método Van der Pauw, en ambiente de alto vacío, en función de longitud de onda incidente, obtenida con monocromador, en el rango de 450 a 1.080 nanómetros usando lámpara Thorlabs SLS201L. La resistencia en completa oscuridad es de 1,132 MΩ y ante luz de amplio espectro de 1,117 MΩ. El gráfico de cambio en resistencia en función de longitud de onda, corregida según la potencia incidente, muestra cambios de conductividad, asociables a brechas semiconductora, en 1,3 - 1,7 - 1,9 - 2,0 - 2,1 - 2,3 eV y un cambio notorio entre 2,5 - 2,6 eV que coinciden razonablemente con resultados obtenidos previamente mediante gráficos tipo Tauc en base a datos de espectroscopía de transmisión de la muestra y otras referencias.El trabajo realizado en esta tesis consiste en el estudio de la dependencia de la resistencia eléctrica en función de la longitud de onda incidente en una película delgada semiconductora de CuFeO2 de 75 nm de espesor obtenida por técnica de deposición por laser pulsado sobre zafiro y con ello, basándose en el efecto fotoconductivo, determinar las brechas semiconductoras del material y así conocer su viabilidad como electrodo para procesos de fotólisis de agua, permitiendo la producción sustentable de hidrógeno gaseoso como fuente de energía. Para ello se mide experimentalmente la resistencia eléctrica de la muestra usando método Van der Pauw, en ambiente de alto vacío, en función de longitud de onda incidente, obtenida con monocromador, en el rango de 450 a 1.080 nanómetros usando lámpara Thorlabs SLS201L. La resistencia en completa oscuridad es de 1,132 MΩ y ante luz de amplio espectro de 1,117 MΩ. El gráfico de cambio en resistencia en función de longitud de onda, corregida según la potencia incidente, muestra cambios de conductividad, asociables a brechas semiconductora, en 1,3 - 1,7 - 1,9 - 2,0 - 2,1 - 2,3 eV y un cambio notorio entre 2,5 - 2,6 eV que coinciden razonablemente con resultados obtenidos previamente mediante gráficos tipo Tauc en base a datos de espectroscopía de transmisión de la muestra y otras referencias.El trabajo realizado en esta tesis consiste en el estudio de la dependencia de la resistencia eléctrica en función de la longitud de onda incidente en una película delgada semiconductora de CuFeO2 de 75 nm de espesor obtenida por técnica de deposición por laser pulsado sobre zafiro y con ello, basándose en el efecto fotoconductivo, determinar las brechas semiconductoras del material y así conocer su viabilidad como electrodo para procesos de fotólisis de agua, permitiendo la producción sustentable de hidrógeno gaseoso como fuente de energía. Para ello se mide experimentalmente la resistencia eléctrica de la muestra usando método Van der Pauw, en ambiente de alto vacío, en función de longitud de onda incidente, obtenida con monocromador, en el rango de 450 a 1.080 nanómetros usando lámpara Thorlabs SLS201L. La resistencia en completa oscuridad es de 1,132 MΩ y ante luz de amplio espectro de 1,117 MΩ. El gráfico de cambio en resistencia en función de longitud de onda, corregida según la potencia incidente, muestra cambios de conductividad, asociables a brechas semiconductora, en 1,3 - 1,7 - 1,9 - 2,0 - 2,1 - 2,3 eV y un cambio notorio entre 2,5 - 2,6 eV que coinciden razonablemente con resultados obtenidos previamente mediante gráficos tipo Tauc en base a datos de espectroscopía de transmisión de la muestra y otras referencias.
Formación y transiciones de fase de bicapas lipídicas depositadas desde su fase de vapor sobre sustratos de silicio poroso.
(2020) Moraga Alarcón, Nicolás; Volkmann, Ulrich; Pontificia Universidad Católica de Chile. Instituto de Física
Implementación de un evaporador E-beam y su posterior uso en incorporación de nanopartículas de oro sobre fotocatalizadores de hematita.
(2019) Álvarez Vega, Pedro Felipe; Hevia, Samuel; Pontificia Universidad Católica de Chile. Instituto de Física
Uno de los candidatos a ser fuente de energía limpia, renovable y abundante es el hidrógeno producido por iluminación (Fotolisis). Este proceso consiste en un electrodo (fotocatalizador) que es capaz de absorber fotones y usar esa energía en separar la molécula de agua, que con ayuda de un electrodo auxiliar (contraelectrodo) se obtiene hidrógeno y oxígeno en estado gaseoso. En este trabajo se fabricaron mediante evaporación química de vapor (CVD) una serie de fotocatalizadores de hematita (F2O3) sobre vidrio con oxido de estaño dopado con flúor (FTO), con el fin de mejorar sus propiedades se le agregaron en la superficie nanopartículas de oro mediante evaporación de haz de electrones (0.2nm a 20.0nm de espesor depositado de oro), además se utilizó distintas técnicas de caracterización, como: microscopía electrónica de barrido (SEM) donde se pudo ver las nanopartículas de oro donde los tamaños van de los 5nm a 120nm según el espesor del depósito; espectroscopía UV-VIS, que permitió comparar como aumentan las absorbancias de las muestras con modificación respecto a su equivalente de control, las muestras con partículas tienen una mayor absorbancia; eficiencia fotocatalítica donde se los resultados indicaron valores del 1.5% donde además se comprobó que tiene un mejor comportamiento a baja irradiancia (4% de AMG 1.5); eficiencia de conversión de fotón a electrón (IPCE) lo cual se obtuvo que al agregar nanopartículas de oro agregó una mejora importante para longitudes de onda cercanas a 350nm y 620nm. Además, en este trabajo se detalló como se implementó un evaporador e-beam y equipamiento para realizar mediciones IPCE en los fotocatalizadores.
Implementación experimental de un reactor químico de vapor CVD y pruebas de funcionamiento
(2019) Spring Flores, Pablo Andrés; Ramos Moore, Esteban; Pontificia Universidad Católica de Chile. Facultad de Física
Este trabajo presenta dos objetivos generales. Primero, la implementación de un reactor químico de vapor (CVD), y segundo, la generación de protocolos de operación óptimos del sistema. Para lograr los objetivos descritos se trabajó en la etapa de diseño, implementación y pruebas de funcionamiento, logrando el funcionamiento individual e interconectado de las distintas fases del experimento, mejorando los diseños preliminares y optimizando la elección de materiales para la construcción de las distintas etapas de un CVD. Finalmente, se consiguieron los objetivos principales, quedando como trabajo futuro la realización de pruebas de crecimiento de películas delgadas de TiC/TiN sobre sustratos de WC.
Nernst-Planck equation for electrolytes in the context of copper electro-refinement.
(2019) Escobar Blanc, Agustín Tomás; Muñoz Tavera, Enrique; Pontificia Universidad Católica de Chile. Instituto de Física
Non-equilibrium thermoelectric transport through a hybrid nano-junction
(2018) Álamo Ulloa, Manuel Lautaro; Muñoz Tavera, Enrique; Pontificia Universidad Católica de Chile. Facultad de Física
This thesis is focused in the study of transport phenomena in strongly correlated systems. Particularly we have evaluated the non-equilibrium thermoelectric transport current and thermoelectric transport coefficients of a hybrid system, composed by a quantum dot connected to a normal s-wave superconductor and a topological superconductor leads, using the Keldysh formalism and Floquet theory. Due the non-conventional terminals, these system presents interesting correlations between different kind of quasi-particles, in particular, Cooper pairs and Majorana Fermions. The later are characterized by a non-abelian statistics and its discover in strongly correlated systems has opened new research horizons for the condensed matter community. Our results show a non-linear electrical current for different magnetic fields, whose peaks are signatures of Majorana Bound States. We also show that the transport processes are highly mediated by Andreev reflections and Andreev bound states, which are the principal mechanism present in the superconducting proximity effect of these kind of systems. Starting from the electrical current, we have evaluated the thermoelectric performance of the system for different magnetic fields, characterized by the Seebeck coefficient S, electrical and thermal conductivities σ, κ, Lorenz number L and the figure of merit ZT,which reaches its maximum value ZT = 0.02∆/kB at a finite magnetic field H = 0.3∆ at an applied bias voltage 0.7eV/∆. We also found that this system has a Lorenz number which achieves a maximum and minimum values far apart to those reported for Fermi liquids, violating the Wiedemann-Franz law.
Studies of P2X4 receptor dynamics upon agonist activation by High-Speed Atomic Force Microscopy and Molecular Dynamics simulations
(2019) Fuentes Cassorla, Christian; Barrera Rojas, Nelson Patricio; Pontificia Universidad Católica de Chile. Instituto de Física
Membrane proteins are surrounded by a myriad of other biomolecules and hence most of the experiments conducted in native conditions are highly complex to interpret at the single molecule level. P2X membrane receptors, an ATP-triggered channel family, are involved in calcium signaling and inflammation. However, to date, there is limited information about its dynamical biophysical behavior in a well-known lipid environment. In particular, receptor diffusion and pore size should depend on agonist activation, lipid bilayer composition and vary throughout time. Suitable experimental methodologies to tackle them have just recently emerged, such as HSAFM where topographic features of the membrane proteins can be recorded at second resolution. In addition, combining this with all-atom MD simulations, it would be possible to provide mechanistic understanding. Therefore, the goal of this thesis is to characterize the P2X4 receptor diffusion and pore dilation on reconstituted liposomes via HS-AFM imaging and MD simulations. Our HS-AFM results indicate that HOLO state of the P2X4 receptor decreased their mean displacements by 22% compared to the APO state and our MD results shows that interaction of protein-water and protein-lipid interaction fluctuate 9% and 43% higher in the APO state respectively. Also, the HOLO state showed a dilation of its extracellular domain compared to the APO state via HS-AFM imaging; however, MD showed us only a dilation of the internal profile of the P2X4 receptor but not an external broadening. This discrepancy may arise due to lipidic composition in MD which only had neutral lipids and experiments were carried with a proportion of 3:1 of neutral:negatively charged lipids. Moreover, each ATP molecule was calculated to have a high interaction with the two adjacent subunits that is in contact and therefore it may force the subunits to stay close at that point, working as a hinge. Taken together, combining HS-AFM and MD can lead to novel insights into the dynamical behavior of individual receptors. Since our experiments were performed on receptors supported on mica, future work could be to suspend lipid bilayers on porous alumina membranes to emulate the conditions observed in cell membranes where extra and intracellular sides are present.Membrane proteins are surrounded by a myriad of other biomolecules and hence most of the experiments conducted in native conditions are highly complex to interpret at the single molecule level. P2X membrane receptors, an ATP-triggered channel family, are involved in calcium signaling and inflammation. However, to date, there is limited information about its dynamical biophysical behavior in a well-known lipid environment. In particular, receptor diffusion and pore size should depend on agonist activation, lipid bilayer composition and vary throughout time. Suitable experimental methodologies to tackle them have just recently emerged, such as HSAFM where topographic features of the membrane proteins can be recorded at second resolution. In addition, combining this with all-atom MD simulations, it would be possible to provide mechanistic understanding. Therefore, the goal of this thesis is to characterize the P2X4 receptor diffusion and pore dilation on reconstituted liposomes via HS-AFM imaging and MD simulations. Our HS-AFM results indicate that HOLO state of the P2X4 receptor decreased their mean displacements by 22% compared to the APO state and our MD results shows that interaction of protein-water and protein-lipid interaction fluctuate 9% and 43% higher in the APO state respectively. Also, the HOLO state showed a dilation of its extracellular domain compared to the APO state via HS-AFM imaging; however, MD showed us only a dilation of the internal profile of the P2X4 receptor but not an external broadening. This discrepancy may arise due to lipidic composition in MD which only had neutral lipids and experiments were carried with a proportion of 3:1 of neutral:negatively charged lipids. Moreover, each ATP molecule was calculated to have a high interaction with the two adjacent subunits that is in contact and therefore it may force the subunits to stay close at that point, working as a hinge. Taken together, combining HS-AFM and MD can lead to novel insights into the dynamical behavior of individual receptors. Since our experiments were performed on receptors supported on mica, future work could be to suspend lipid bilayers on porous alumina membranes to emulate the conditions observed in cell membranes where extra and intracellular sides are present.Membrane proteins are surrounded by a myriad of other biomolecules and hence most of the experiments conducted in native conditions are highly complex to interpret at the single molecule level. P2X membrane receptors, an ATP-triggered channel family, are involved in calcium signaling and inflammation. However, to date, there is limited information about its dynamical biophysical behavior in a well-known lipid environment. In particular, receptor diffusion and pore size should depend on agonist activation, lipid bilayer composition and vary throughout time. Suitable experimental methodologies to tackle them have just recently emerged, such as HSAFM where topographic features of the membrane proteins can be recorded at second resolution. In addition, combining this with all-atom MD simulations, it would be possible to provide mechanistic understanding. Therefore, the goal of this thesis is to characterize the P2X4 receptor diffusion and pore dilation on reconstituted liposomes via HS-AFM imaging and MD simulations. Our HS-AFM results indicate that HOLO state of the P2X4 receptor decreased their mean displacements by 22% compared to the APO state and our MD results shows that interaction of protein-water and protein-lipid interaction fluctuate 9% and 43% higher in the APO state respectively. Also, the HOLO state showed a dilation of its extracellular domain compared to the APO state via HS-AFM imaging; however, MD showed us only a dilation of the internal profile of the P2X4 receptor but not an external broadening. This discrepancy may arise due to lipidic composition in MD which only had neutral lipids and experiments were carried with a proportion of 3:1 of neutral:negatively charged lipids. Moreover, each ATP molecule was calculated to have a high interaction with the two adjacent subunits that is in contact and therefore it may force the subunits to stay close at that point, working as a hinge. Taken together, combining HS-AFM and MD can lead to novel insights into the dynamical behavior of individual receptors. Since our experiments were performed on receptors supported on mica, future work could be to suspend lipid bilayers on porous alumina membranes to emulate the conditions observed in cell membranes where extra and intracellular sides are present.Membrane proteins are surrounded by a myriad of other biomolecules and hence most of the experiments conducted in native conditions are highly complex to interpret at the single molecule level. P2X membrane receptors, an ATP-triggered channel family, are involved in calcium signaling and inflammation. However, to date, there is limited information about its dynamical biophysical behavior in a well-known lipid environment. In particular, receptor diffusion and pore size should depend on agonist activation, lipid bilayer composition and vary throughout time. Suitable experimental methodologies to tackle them have just recently emerged, such as HSAFM where topographic features of the membrane proteins can be recorded at second resolution. In addition, combining this with all-atom MD simulations, it would be possible to provide mechanistic understanding. Therefore, the goal of this thesis is to characterize the P2X4 receptor diffusion and pore dilation on reconstituted liposomes via HS-AFM imaging and MD simulations. Our HS-AFM results indicate that HOLO state of the P2X4 receptor decreased their mean displacements by 22% compared to the APO state and our MD results shows that interaction of protein-water and protein-lipid interaction fluctuate 9% and 43% higher in the APO state respectively. Also, the HOLO state showed a dilation of its extracellular domain compared to the APO state via HS-AFM imaging; however, MD showed us only a dilation of the internal profile of the P2X4 receptor but not an external broadening. This discrepancy may arise due to lipidic composition in MD which only had neutral lipids and experiments were carried with a proportion of 3:1 of neutral:negatively charged lipids. Moreover, each ATP molecule was calculated to have a high interaction with the two adjacent subunits that is in contact and therefore it may force the subunits to stay close at that point, working as a hinge. Taken together, combining HS-AFM and MD can lead to novel insights into the dynamical behavior of individual receptors. Since our experiments were performed on receptors supported on mica, future work could be to suspend lipid bilayers on porous alumina membranes to emulate the conditions observed in cell membranes where extra and intracellular sides are present.Membrane proteins are surrounded by a myriad of other biomolecules and hence most of the experiments conducted in native conditions are highly complex to interpret at the single molecule level. P2X membrane receptors, an ATP-triggered channel family, are involved in calcium signaling and inflammation. However, to date, there is limited information about its dynamical biophysical behavior in a well-known lipid environment. In particular, receptor diffusion and pore size should depend on agonist activation, lipid bilayer composition and vary throughout time. Suitable experimental methodologies to tackle them have just recently emerged, such as HSAFM where topographic features of the membrane proteins can be recorded at second resolution. In addition, combining this with all-atom MD simulations, it would be possible to provide mechanistic understanding. Therefore, the goal of this thesis is to characterize the P2X4 receptor diffusion and pore dilation on reconstituted liposomes via HS-AFM imaging and MD simulations. Our HS-AFM results indicate that HOLO state of the P2X4 receptor decreased their mean displacements by 22% compared to the APO state and our MD results shows that interaction of protein-water and protein-lipid interaction fluctuate 9% and 43% higher in the APO state respectively. Also, the HOLO state showed a dilation of its extracellular domain compared to the APO state via HS-AFM imaging; however, MD showed us only a dilation of the internal profile of the P2X4 receptor but not an external broadening. This discrepancy may arise due to lipidic composition in MD which only had neutral lipids and experiments were carried with a proportion of 3:1 of neutral:negatively charged lipids. Moreover, each ATP molecule was calculated to have a high interaction with the two adjacent subunits that is in contact and therefore it may force the subunits to stay close at that point, working as a hinge. Taken together, combining HS-AFM and MD can lead to novel insights into the dynamical behavior of individual receptors. Since our experiments were performed on receptors supported on mica, future work could be to suspend lipid bilayers on porous alumina membranes to emulate the conditions observed in cell membranes where extra and intracellular sides are present.Membrane proteins are surrounded by a myriad of other biomolecules and hence most of the experiments conducted in native conditions are highly complex to interpret at the single molecule level. P2X membrane receptors, an ATP-triggered channel family, are involved in calcium signaling and inflammation. However, to date, there is limited information about its dynamical biophysical behavior in a well-known lipid environment. In particular, receptor diffusion and pore size should depend on agonist activation, lipid bilayer composition and vary throughout time. Suitable experimental methodologies to tackle them have just recently emerged, such as HSAFM where topographic features of the membrane proteins can be recorded at second resolution. In addition, combining this with all-atom MD simulations, it would be possible to provide mechanistic understanding. Therefore, the goal of this thesis is to characterize the P2X4 receptor diffusion and pore dilation on reconstituted liposomes via HS-AFM imaging and MD simulations. Our HS-AFM results indicate that HOLO state of the P2X4 receptor decreased their mean displacements by 22% compared to the APO state and our MD results shows that interaction of protein-water and protein-lipid interaction fluctuate 9% and 43% higher in the APO state respectively. Also, the HOLO state showed a dilation of its extracellular domain compared to the APO state via HS-AFM imaging; however, MD showed us only a dilation of the internal profile of the P2X4 receptor but not an external broadening. This discrepancy may arise due to lipidic composition in MD which only had neutral lipids and experiments were carried with a proportion of 3:1 of neutral:negatively charged lipids. Moreover, each ATP molecule was calculated to have a high interaction with the two adjacent subunits that is in contact and therefore it may force the subunits to stay close at that point, working as a hinge. Taken together, combining HS-AFM and MD can lead to novel insights into the dynamical behavior of individual receptors. Since our experiments were performed on receptors supported on mica, future work could be to suspend lipid bilayers on porous alumina membranes to emulate the conditions observed in cell membranes where extra and intracellular sides are present.Membrane proteins are surrounded by a myriad of other biomolecules and hence most of the experiments conducted in native conditions are highly complex to interpret at the single molecule level. P2X membrane receptors, an ATP-triggered channel family, are involved in calcium signaling and inflammation. However, to date, there is limited information about its dynamical biophysical behavior in a well-known lipid environment. In particular, receptor diffusion and pore size should depend on agonist activation, lipid bilayer composition and vary throughout time. Suitable experimental methodologies to tackle them have just recently emerged, such as HSAFM where topographic features of the membrane proteins can be recorded at second resolution. In addition, combining this with all-atom MD simulations, it would be possible to provide mechanistic understanding. Therefore, the goal of this thesis is to characterize the P2X4 receptor diffusion and pore dilation on reconstituted liposomes via HS-AFM imaging and MD simulations. Our HS-AFM results indicate that HOLO state of the P2X4 receptor decreased their mean displacements by 22% compared to the APO state and our MD results shows that interaction of protein-water and protein-lipid interaction fluctuate 9% and 43% higher in the APO state respectively. Also, the HOLO state showed a dilation of its extracellular domain compared to the APO state via HS-AFM imaging; however, MD showed us only a dilation of the internal profile of the P2X4 receptor but not an external broadening. This discrepancy may arise due to lipidic composition in MD which only had neutral lipids and experiments were carried with a proportion of 3:1 of neutral:negatively charged lipids. Moreover, each ATP molecule was calculated to have a high interaction with the two adjacent subunits that is in contact and therefore it may force the subunits to stay close at that point, working as a hinge. Taken together, combining HS-AFM and MD can lead to novel insights into the dynamical behavior of individual receptors. Since our experiments were performed on receptors supported on mica, future work could be to suspend lipid bilayers on porous alumina membranes to emulate the conditions observed in cell membranes where extra and intracellular sides are present.
Wetting properties of n-alkane thin films to understand the adherence mechanism of artificial membranes on silicon substrates
(2017) Díaz Díaz, Diego Ignacio; Volkmann, Ulrich; Pontificia Universidad Católica de Chile. Facultad de Física
In this work we present a study of the wetting properties of silicon samples coated with a single layer of n-alkane molecules that self-assemble perpendicular to the surface.The types of molecules studied here are n-alkane chains, mainly n-dotriacontane (n-C32 H66), that were deposited on silicon substrates with a thin native silicon oxidelayer (15˚A). The thin films were prepared by Dip-Coating technique in a C32 H66/n-heptane solution. The techniques used to characterize these films are Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). In this research a contact angle setup was developed to measure wettability of submonolayer films. An influence of morphology and coverage on the contact angle was found. Moreover, alkane molecules migrate much like a reverse coffee-ring effect after drop evaporation, forming complex tail-like morphologies.This research is relevant to understand alkane adhesion on silicon substrates, which is related with artificial membrane fabrication, which are used for biosensors applications. Micro-structured pattern like stripes could be applied as templates for other materials, especially considering the possibility of creating homogeneous surfaces with nanometer thick films.

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