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Master's Dissertation
DOI
https://doi.org/10.11606/D.43.2019.tde-22042019-095222
Document
Author
Full name
Matheus Jean Lazarotto
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2019
Supervisor
Committee
Coutinho, Kaline Rabelo (President)
Cuccovia, Iolanda Midea
Silva, Thereza Amélia Soares da
Title in Portuguese
Estudo teórico da interação entre líquido iônico e bicamadas fosfolipídicas
Keywords in Portuguese
Anisotropia de Fluorescência
Bicamadas
Dinâmica Molecular
Líquido Iônico
Abstract in Portuguese
Experimentalmente, a transição entre as fases gel e gel-líquida de bicamadas fosfolipídicas pode ser mensurada por técnicas de anisotropia de fluorescência. A partir de uma sonda interna à membrana, a diferença entre as radiações absorvida e emitida, causada pela rotação da sonda no intervalo de fluorescência, relaciona-se com a fluidez da membrana. Com esta técnica aplicada à sondas DPH, foi encontrada influência do líquido iônico (LI) C14MImCl na temperatura de transição de fase de fosfolipídios carregados (DPPG), mas não nos casos neutros (DPPC e DMPC). A temperatura de transição para DPPG apresenta queda de 45oC, em estado puro, para 26oC com concentração de 30%mol de LI. Neste estudo, simulações de dinâmica molecular foram conduzidas de forma a descrever as interações de LI com os fosfolipídios de bicamadas em dois casos, DPPC e DPPG, e de analisar o comportamento dinâmico da sonda. Diferentes condições iniciais de mistura entre lipídios e LI foram consideradas nas simulações. Os resultados indicam que, quando misturadas aleatoriamente, ambos os lipídios apresentam agregação espontânea, evoluindo para forma lamelar com LI distribuído uniformemente. Quando uniformemente distribuído, o LI diminuí a interação entre lipídios e outras moléculas do sistema nos dois casos, porém com maior intensidade em DPPG devido à repulsão dos contra íons catiônicos (Na+) do lipídio, enquanto que em DPPC os contra íons aniônicos provenientes do LI (Cl-) mantém-se perto da interface. O comportamento da sonda foi qualitativamente reproduzido e visto ser altamente correlacionado com a fluidez das caudas, medida por meio do parâmetro de ordem deutérica. Por conta da equivalência das caudas entre DPPC e DPPG, encontrou-se omportamento similar nos dois sistemas.
Title in English
Theoretical Study of the Interaction Between Ionic Liquid and Phospholipid Bilayers
Keywords in English
Bilayers
Fluorescent Anisotropy
Ionic Liquid
Molecular Dynamics
Abstract in English
The gel-liquid phase transition of phospholipid bilayers can be experimentally measured via fluorescence anisotropy techniques. Using a fluorescent probe within the membrane, the difference between absorbed and emitted radiation due to rotational movement can be related to the bilayer fluidity. The use of the fluorescent probe DPH shows the influence of the ionic liquid (IL) C14MImCl on the phase transition temperature of charged lipids (DPPG) but not neutral ones (DPPC and DMPC). The phase transition temperature for DPPG bilayers dropped from 45oC, in pure state, to 26oC, with 30%mol concentration of IL. In this study, molecular dynamics (MD) simulations were performed in order to describe the IL interactions with the phospholipids in the membranes for two cases, DPPG and DPPC, and to analyze the dynamical behavior of the probe. Different initial conditions of the mixture between IL and lipids were considered in the simulations. The results indicate that in random initial conditions, both lipids spontaneously aggregates with the IL into a bilayer shape with IL uniformly distributed across it. The uniform distribution of IL in the membranes decreased the total interaction of the lipids and the other molecules in the system for both cases, but with higher influence in DPPG due to repulsion of cationic counter ions from the lipids (Na+), whereas in DPPC the anionic counter ions from IL (Cl-) remained closer to the bilayer interface. The probe behavior was qualitatively verified and found to be highly correlated with the lipid tails fluidity, through the calculated Deuter order parameter. Because of tails equivalence between the DPPG and DPPC, it was found a similar behavior of the probe in both systems.
 
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Dissertacao_final.pdf (23.62 Mbytes)
Publishing Date
2019-04-22
 
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